Pelvic Ring Injuries - Clinical Tree

Introduction

The pelvis is a key component of the axial skeleton that links the lower extremities with the rest of the body through the lumbosacral spine. Its ringlike structure allows it to surround and protect important inner organs, such as the urinary bladder, the lower intestines, and the reproductive organs, as well as major nerves and blood vessels. In patients with healthy bone, high-energy injuries are required to disrupt the integrity of the pelvic ring. However, because of age-related demographic changes in Western populations, injuries of the pelvic ring are increasingly being seen in elderly patients after minor trauma due to decreased bone mineral density, primarily caused by osteoporosis. However, the incidence of pelvic ring fractures under these circumstances (3% to 8%) is relatively low compared with other fractures.

Because of the high-energy injury mechanisms required to sustain these injuries in the younger population, patients with pelvic fractures have a high likelihood of associated injury to the abdominopelvic structures, including neurologic and vascular injuries, which can result in permanent neurologic deficits as well as severe, life-threatening hemorrhage. Compared with other injuries, death after pelvic ring fractures is high, particularly because these injuries often occur in polytraumatized patients. In the long term, fractures of the pelvis may result in considerable morbidity due to different reasons ( Fig. 38.1 ).

$Fig. 38.1, Morbidity after pelvic fractures can be caused by different sequelae.$

The treatment of pelvic ring injuries can be challenging and requires an in-depth understanding of the complex pelvic anatomy as well as a high degree of surgical experience and skills. Because of the polytraumatized nature of these patients, a coordinated multidisciplinary approach to treatment is essential. Treatment of pelvic ring injuries is often done in stages, which include a “damage control” phase that must be performed urgently to address concerns such as acute, life-threatening hemorrhage due to significant instability and internal bleeding, followed by the final reconstruction of the pelvis and associated injuries after the patient has been appropriately resuscitated and physiologically stabilized. Proper identification of the specific injury patterns and their associated injuries can help guide both emergent treatment and definitive reconstruction. The principles behind damage control surgery should be familiar to every surgeon who deals with trauma patients. However, the definitive reconstruction of pelvic ring injuries should be reserved for appropriately experienced surgeons whenever possible. Ideally, there should be a low threshold to transfer these patients to specialized centers once these patients have been stabilized. Final reconstruction of the pelvis is a potentially high-risk and sophisticated task requiring intensive preoperative planning combined with experience and skills to optimize reduction and minimize complications.

Anatomy

The pelvis has a ring-shaped structure that is formed by two innominate bones and the sacrum. The innominate bones are formed by the fusion of three ossification centers between the ilium, the ischium, and the pubis. These are linked through cartilaginous growth plates during childhood but coalesce with each other during adolescence at the triradiate cartilage of the acetabulum ( Fig. 38.2 ).

Key Points: Anatomy

Treatment of pelvic fractures requires experienced surgeons.
Surgeons must pay attention to organs placed in the pelvis.
Always keep in mind the nerves and vessels. They might be bruised as part of the injury. Moreover, uncontrolled damage can lead to major complications.
The pelvis has a ring structure. Integrity is achieved by both bony structures as well as ligaments.

Fig. 38.2, The sacroiliac (SI) joint. (A) Iliac side of the SI joint, as well as the remainder of the innominate bone and the important bony landmarks. (B) Sacral side. The two portions of the SI joint can best be appreciated on this view. The articular surface of the SI joint on the sacrum has a ridge and is covered by articular cartilage. The posterior portion is filled with ligamentous structures. (C and D) Ligamentous complexes of the pelvis. (C) Posteriorly, the major ligaments noted in the region of the SI joint are the posterior SI ligaments, both long and short. The long blend with the sacrospinous and the sacrotuberous ligaments. (D) In cross section, the orientation of the very thick posterior interosseous SI ligaments is noted.

Familiarity with the anatomy of the ilium is important, especially for accurate iliac screw placement in spinopelvic fixation techniques. The ilium provides a continuous bony channel, the sciatic buttress, that extends between the posterior superior iliac spine (PSIS) and the anterior inferior iliac spine (AIIS), with dimensions that readily accommodate iliac screws. The osseous sacral anatomy is composed of five kyphotically aligned, fused vertebral segments, with significant variability in upper sacral anatomy in the form of transitional vertebrae and sacral dysplasia. Because upper sacral variability results in a significant alteration in the relationships between the sacrum, pelvis, and spinal column relative to their adjacent neurovascular structures, these variations must be recognized, particularly if surgical treatment of sacral fractures is being considered.

The upper sacral body has the densest sacral cancellous bone, particularly adjacent to the superior S1 endplate. The ventral aspect of the upper S1 body that projects anteriorly and superiorly into the pelvis is termed the sacral promontory. The sacral ala, the lateral portion of the sacrum that articulates with the ilium through the sacroiliac (SI) joints, is largely cancellous and is formed by the coalescence of the sacral transverse processes. The cancellous alar bone is hypodense, particularly in older individuals, and an alar void is a consistent finding in middle-aged and older adults. The relative difference in bone density between the upper and lower sacral body predisposes this area to fracture. The hypodense ala is predisposed, particularly in older and osteopenic patients. This problem is accentuated by the relative strength of the SI joint ligaments. The suboptimal alar bone density must be taken into consideration when planning reconstructive procedures, particularly in the elderly or osteoporotic.

The posterior surface of the sacrum is convex and is formed by the coalescence of posterior elements. The middle sacral crest corresponds to the spinous processes, the intermediate sacral crests to the zygapophyseal joints, and the area in between to the lamina. The lowest one or two sacral segments have incompletely formed bony posterior elements, resulting in an aperture into the sacral spinal canal known as the sacral hiatus. Enlargement of the sacral hiatus may weaken the sacrum and predispose it to fracture, and it must also be recognized as a potential source of intraoperative iatrogenic sacral root injury.

The sacrum and the two innominate bones are linked by tenacious ligamentous structures that are the most essential in providing pelvic stability. Minimal mobility within the pelvic ring occurs between the innominate bones and the sacrum at three joints: two SI joints and the pubic symphysis. Rupture of the pubic symphysis as well as the ligaments forming the SI joint results in pelvic instability. The SI joint has two parts. The caudal portion consists primarily of the articular surface, and the upper, more dorsal portion, between the posterior tuberosity of the ilium and the sacrum, contains the fibrous or ligamentous parts of the joint. The anterior portion of this synovial joint is covered with articular cartilage on the sacral side and fibrocartilage on the iliac side. The joint itself has a small ridge on the sacral side that provides minimal intrinsic stability. In general, SI joint stability is contingent on the integrity of a complex of anterior and posterior SI ligaments.

The pubic symphysis consists of two opposed surfaces of hyaline cartilage covered with intervening fibrocartilage surrounded by a thick band of fibrous tissue. The joint is further strengthened by the superior pubic ligament above and the arcuate pubic ligament below. Moreover, adjacent pelvic floor muscle insertions, such as that of the levator ani muscle, provide a minor amount of additional stability. The pubic symphysis is usually widest superiorly and anteriorly.

The pelvis is designed to ideally provide the necessary rigidity for upright gait and the transmission of forces between the lower extremities and the spine while allowing mobility, such as during parturition. Because the forces that are transmitted from the lower extremities to the spine affect mainly the posterior pelvic ring, the integrity of the SI ligamentous complex is essential to pelvic stability. The posterior SI ligaments are divided into two components, short and long. The short posterior ligaments are oblique and run from the posterior ridge of the sacrum to the posterior superior and posterior inferior spines of the ilium. The long posterior ligaments are longitudinal fibers that course from the lateral aspect of the sacrum to the PSIS and then merge with the sacrotuberous ligament. The long ligaments lie posterior and superficial to the short ligaments. Anterior SI ligaments, which provide less stability than their posterior counterparts, also connect the ilium to the sacrum. The most important ligaments for pelvic ring stability are the posterior interosseous SI ligaments that join the sacrum and the tuberosities of the ilium in the transverse plane.

The aforementioned ligaments are the most important for maintaining the stability of the pelvic ring. Additional ligaments that do not directly span the joints but connect various portions of the pelvic ring also have important stabilizing roles. The sacrotuberous ligament is a strong band that runs from the posterolateral aspect of the sacrum and the dorsal aspect of the posterior iliac spine to the ischial tuberosity. Its medial border thickens to form a falciform tendon, which blends with the obturator membrane at the ischial tuberosity. It also merges into the posterior origin of the gluteus maximus. This ligament, in association with its ipsilateral posterior SI ligaments, is especially important in maintaining the vertical stability of the pelvis. The sacrospinous ligament is triangular and runs from the lateral margins of the sacrum and coccyx and the sacrotuberous ligament to insert onto the ischial spine. It serves as the border between the greater and lesser sciatic notches. The sacrospinous ligament may be important in maintaining rotational control of the pelvis if the posterior SI ligaments are intact.

Several ligaments extend from the spine to the pelvis and are important in providing spinopelvic stability. The iliolumbar ligaments originate from the L4 and L5 transverse processes and insert onto the posterior iliac crest, securing the pelvis to the lumbar spine. The lumbosacral ligaments run from the transverse process of L5 to the ala of the sacrum. They form a strong ridge anteriorly and abut the L5 root.

If its ligamentous structures and bony elements are intact, the pelvis constitutes a stable ring. The sacrum forms the posterior aspect of the pelvic ring and serves as its keystone because it maintains stability while transmitting forces from the lumbosacral articulation across the SI joints to the pelvis. This keystone function is particularly true in the pelvic outlet plane, in which the orientation of the sacrum relative to the ilium is such that axial forces lock the sacrum into the pelvic ring and further stabilize the SI articulation. In the pelvic inlet plane, the sacrum is shaped like a “reverse keystone,” which is more inherently unstable and therefore requires substantial intrinsic and extrinsic ligamentous stabilization of the SI joints while permitting required pelvic ring motion. The posterior SI ligaments create a posterior tension band for the pelvis. The transversely oriented ligaments, including the short posterior SI and the anterior SI ligaments, along with the iliolumbar and sacrospinous ligaments, resist rotational forces. The vertically placed ligaments, including the long posterior SI, sacrotuberous, and lateral lumbosacral ligaments, help resist vertical shear and vertical migration.

The pelvis contains two major anatomic regions: the true pelvis and false pelvis. The false pelvis and the true pelvis are divided by the pelvic brim, which extends from the sacral promontory along the junction between the ilium and the ischium onto the pubic ramus. No major muscular structures cross the pelvic brim. Above the brim, the false pelvis (greater pelvis) is contained by the sacral ala and the iliac wings. The false pelvis is lined laterally by the iliopsoas muscle. It forms part of the abdominal cavity. The true pelvis (lesser pelvis) lies below the pelvic brim, and its lateral wall consists of portions of the pubis, ischium, and a small triangular portion of the ilium.

The obturator foramen, which is covered by muscles and a membrane, also defines the boundary of the true pelvis. The foramen opens superiorly and laterally for passage of the obturator nerve and vessels. An aberrant obturator artery is one of the many known vascular variants in the pelvis that is located near the pubic ramus to supply the musculature of the obturator foramen. Because of its location, it is often injured in pelvic ring disruptions. Pelvic surgeons should have a thorough understanding of the pelvic vasculature because major bleeding is one of the most important complications after pelvic ring fractures.

The obturator internus muscle originates from the obturator membrane and courses through the lesser sciatic notch to insert onto the proximal end of the femur. The obturator internus tendon is an important structure because it serves as an intraoperative guide to identify the posterior column. The piriformis originates from the lateral aspect of the sacrum and is key to identifying the sciatic nerve. A schematic illustration of the pelvic musculature is presented in Fig. 38.3 .

Fig. 38.3, Internal aspect of the pelvis. (A) The inner aspect of the pelvis consists of the true pelvis, which is below the pelvic brim, and the false pelvis above it. The sacrotuberous and sacrospinous ligaments are attached to their appropriate structures and form the basis of the pelvic floor. (B) The major structures in the inner aspect of the pelvis are the lumbosacral plexus, which originates from the L5 and the sacral roots and leaves the pelvis through the greater sciatic notch as the sciatic nerve and the superior gluteal artery. The obturator internus originates from the obturator membrane and loops out through the lesser sciatic notch. Note that no muscles cross the pelvic brim. (C) Internal aspect of the pelvis showing the great vessels and the lumbosacral plexus, as well as the pelvic floor, bladder, and rectum.

Usually, the sciatic nerve exits the pelvis anterior to the piriformis muscle and enters the greater sciatic notch. Occasionally, the peroneal division exits either through or posterior to the piriformis. It is important to be familiar with the anatomical variants when performing reconstructive procedures. The floor of the true pelvis consists of the coccyx; the coccygeal and levator ani muscles; and the urethra, rectum, and vagina in females.

The dural sac typically ends at the S2 level, and the filum terminale attaches at its caudal end to the coccyx. Four paired ventral and dorsal neuroforamina are formed at the junction of the sacral body and ala, through which pass the ventral and dorsal rami of the sacral nerve roots. The relative space available to the sacral nerve roots in the ventral foramina is lowest at the S1 and S2 levels, where the nerve roots occupy one-third to one-fourth of the foraminal space compared with the S3 and S4 levels, where the nerve roots occupy one-sixth of the available foraminal space. The lower sacral roots are therefore less likely to be impinged upon in injuries involving displacement of the neuroforamina.

The dorsal nerve roots exit through their respective posterior neuroforamina to supply motor branches to the paraspinal muscles and cutaneous sensory branches that form the cluneal nerves. Anteriorly, the L5 nerve root passes underneath the inferior edge of the sacrolumbar ligament and drapes over the anterosuperior aspect of the sacral ala. It anastomoses with the L4 ventral ramus to form the lumbosacral plexus at the level of the sacral promontory, approximately 12 mm lateral to the SI joint. The sacral roots join the lumbosacral plexus along the sacral ala as they exit through their respective ventral sacral foramina. The lumbosacral coccygeal plexus is made up of the anterior rami of T12 through S4. The L4 through S1 roots are most at risk of compromise due to pelvic injury or surgical intervention. Whereas the L4 and L5 roots enter the true pelvis from the false pelvis, the sacral roots originate in the true pelvis. The L4 and L5 roots course, on average, 17.9 and 18.4 mm lateral to the SI joint, respectively. The dual innervation of the perineal structures from both the left and right sacral plexus is somewhat protective of bowel, bladder, and sexual function. These functions are largely preserved in the event of unilateral transection of the sacral nerve roots, but bilateral transection causes complete loss of function. Numerous nerve branches extend to the major muscles within the pelvis. The superior gluteal and inferior gluteal nerves exit the pelvis ventral to the piriformis and through the greater sciatic notch.

The major pelvic blood vessels lie along the inner wall of the pelvis. The bilateral common iliac arteries arise from the aorta at the level of L4 to L5 and give rise to the internal iliac arteries, which lie anterior to the SI joints and course beyond the pelvic brim into the true pelvis, giving off both superior and inferior lateral sacral arteries in the process. A branch of the internal iliac artery, the superior gluteal artery, crosses over the anterior and caudal portion of the SI joint to exit the greater sciatic notch. As it sweeps around the notch, it lies directly on bone. The external iliac artery runs cranially to the pelvic brim at the level of the pubic ramus, exiting the pelvis posterior to the inguinal ligament, where it becomes the common femoral artery. The presacral area has an extensive and highly variable vascular network. The middle sacral artery typically courses ventrally along the midline of the L5 vertebral body and the sacrum after branching from the aorta at the common iliac bifurcation. The superior lateral sacral artery arises from the internal iliac artery and courses caudally just lateral to the sacral foramina and supplies the spinal canal through the S1 and S2 ventral foramina, and the inferior lateral sacral artery traverses the inferior aspect of the SI joint before anastomosing with the middle sacral artery and giving off spinal arteries that pass through the S3 and S4 ventral foramina. The superior rectal artery, which is a continuation of the inferior mesenteric artery, lies posteriorly along the midline. Arteries are illustrated in Fig. 38.4 .

Fig. 38.4, Schematic illustration of arteries passing the pelvis.

All arteries are accompanied by correspondingly named veins. The internal iliac veins are located posteromedially to the internal iliac arteries and course caudally. They are located medial to the SI joint directly adjacent to the sacral ala. The internal iliac veins give rise to an extensive presacral venous plexus, formed by anastomoses between the lateral and middle sacral veins that communicate transforaminally with epidural veins in the spinal canal. This extensive vascular network renders anterior exposures to the sacrum impractical and perilous. The major arteries and veins are both at significant risk of injury during pelvic ring fractures and are a potential source of lethal hemorrhage. Data about the exact source of bleeding have been difficult to obtain. Nevertheless, only a minority of cases of lethal bleeding that result from pelvic ring fractures can be attributed to major arterial damage. Huittinen and colleagues reported only 11.1% of hemorrhage to be of arterial origin, with the rest being of venous origin. The pre-sacral venous plexus is at particularly high risk of rupture, leading to subsequent bleeding into the lesser and greater pelvis. The distribution of the bleeding source also is the reason for ongoing debate regarding how to treat hemodynamical unstable patients with pelvic ring fractures (i.e., pelvic packing, angiography; see later discussion).

Because of the substantial risk of injury to intrapelvic organs, which can occur from either the trauma itself or from surgical treatment, detailed anatomic knowledge of intrapelvic anatomy is crucial to the safety of patients. The bladder is situated immediately posterior to the symphysis pubis and cranial to the pelvic floor, which is formed by several different muscles, including the levator ani, transversus peroneus profundus, and coccygeal muscles. Similarly, the uterus in females is located behind the bladder and is connected to the ovaries through the fallopian tubes. The muscles of the pelvic floor arise in continuity from the ischial spines, obturator membranes, and pubis and insert into the coccyx and anal coccygeal raphe. They form a muscular diaphragm with a gap anteriorly, through which pass the urethra, vagina, rectum, and supporting ligaments. In contrast, the ureters course along the retroperitoneum from the kidneys into the pelvis and join the bladder after crossing over the external iliac arteries and veins. The fascia of the pelvic floor is loose and mobile. In males, the prostate lies between the bladder and the pelvic floor and is invested by a dense fascial membrane. The urethra passes through the prostate before exiting the pelvic floor. It is divided into five sections; the preprostatic urethra is the most cranial segment and is generally within the wall of the urinary bladder, depending on bladder fullness. The prostatic urethra courses through the prostate, transitioning to the membranous urethra, which passes through the external urethral sphincter. The part of the urethra that extends beyond the pelvic floor is divided into the bulbous and pendulous urethra. The junction between the prostate and the pelvic floor is strong, as is the membranous urethra. The weak link is the segment of urethra just below the pelvic diaphragm in its bulbous portion. Colapinto has shown that when the bladder is pulled forcefully, the urethra ruptures in its bulbous portion, which is the most common site of urethral rupture below the pelvic floor and a common associated injury in pelvic ring disruption. In contrast, the urethral injury in females occurs most commonly near the neck of the bladder. Urinary continence depends on the external (striated muscle) sphincter at the level of the membranous urethra (midurethra in females) and the bladder neck (smooth muscle) in both males and females. Other structures that pass through the urogenital diaphragm include the pudendal arteries and veins, the pudendal nerve (S2 to S4), and the autonomic nerves of the pelvis (S2 to S4). These are all responsible for normal sexual function and are at risk of injury in pelvic trauma.

A considerable part of the intestine is located within the confines of the pelvis. The descending colon transitions into the sigmoid colon, which transitions to the rectum and finally the anus, formed by internal and external sphincter muscle layers. The rectum and anus are located behind the uterus in women and behind the bladder in men. The diversity of anatomic structures within such a confined space lends itself to a high potential for injury to a multitude of organ systems, either from the trauma itself or from surgical treatment.

Pelvic Stability and Biomechanics

Therapeutic management of pelvic ring fractures largely depends on pelvic stability. Stable fractures can typically be managed nonoperatively, but unstable fractures generally require surgery. Unfortunately, a clear distinction between stable and unstable has yet to be defined. One should instead conceptualize a given injury as lying along a spectrum between the two extremes that are designated as stable and unstable.

Key Points: Biomechanics

Different forces strain the various parts of the pelvis during an injury. This results in typical variations of pelvic ring fractures.
Except in the elderly, where osteoporotic and fatigue fractures can be observed, high-energy trauma is required to cause pelvic ring fractures.
Depending on how the pelvic ring is stressed, different fracture types can be found.

For practical purposes, it is necessary to simplify the biomechanics of the pelvic ring into its basic elements. The articulations between the three bony elements (sacrum and two innominate bones) provide little in the way of inherent stability. As mentioned previously, the keystone function of the sacrum does provide some intrinsic stability in the outlet plane, but the reverse is true of the inlet plane. However, because of the aforementioned ligamentous structures that stabilize the pelvic ring at the SI joints and pubic symphysis, under physiologic conditions the pelvis is stable, meaning that it can withstand physiologic loads without displacement. The unstable pelvis will therefore displace under minimal load. However, because slight motion does occur at its three primary articulations under physiologic loads, the pelvic ring cannot be considered a completely rigid construct. In the upright position, loading of the sacrum between the iliac wings causes approximately 5 degrees of dorsoventral rotation of the sacrum. The innominate bones translate posteriorly, and flexion occurs as the pubic rami rotate cranially relative to the posterior ring. The physiologic motion at the symphysis pubis includes transverse and vertical translation of approximately 1 and 2 mm, respectively. Tile and Hearn also demonstrated that with sitting or double-leg standing, whereas the symphysis pubis is loaded in tension, the posterior ring is loaded in compression ( Fig. 38.5 ).

Fig. 38.5, Biomechanical load affecting the different parts of the pelvic ring.

In single-leg stance, the symphysis is compressed, and the posterior complex is loaded under tension. The ligaments, which maintain the integrity of the posterior ring, are among the strongest ligaments in the body. When Miller and colleagues tested isolated SI joints, some specimens withstood loads of 1440 N without failing. In addition, a normal pelvis can withstand vertical loads from 3630 to 5837 N without failing.

To better understand the relative contribution of individual components of the pelvic ring to the spectrum of pelvic stability, Tile and Hearn, based on work by Pennal, studied the consequences of sequential sectioning of the pelvic ligaments. Sectioning of the symphyseal ligaments alone resulted in symphyseal diastasis of no greater than 2.5 cm ( Fig. 38.6A ), but the relationship of this value to the integrity of the anterior SI, sacrotuberous, and sacrospinous ligaments is weak. The sacrospinous and anterior SI ligaments are thought to restrain further widening of the anterior pelvis. Additional sectioning of the sacrospinous and anterior SI ligaments results in increased diastasis (see Fig. 38.6B ), but intact posterior longitudinal and sacrotuberous ligaments prevent vertical translation. In this situation, the pelvis is only rotationally unstable and can therefore be restored to its anatomic integrity by reduction and stabilization of the anterior ring only using the intact posterior ligamentous hinge as a fulcrum. Sectioning of the posterior ligaments only with an intact symphysis results in relatively little posterior instability because the posterior bony complex is loaded primarily in compression. With sectioning of the symphyseal, sacrospinous, sacrotuberous, and posterior SI ligaments, the pelvis becomes globally unstable and is free to translate or rotate in any direction (see Fig. 38.6C ).

Fig. 38.6, (A) Division of the symphysis pubis allows the pelvis to open to approximately 2.5 cm with no damage to any posterior ligamentous structures. (B) Division of the anterior sacroiliac (SI) and sacrospinous ligaments, either by direct division of their fibers (right) or by avulsion of the tip of the ischial spine (left), allows the pelvis to rotate externally until the posterior superior iliac spines abut the sacrum. Note, however, that the posterior ligamentous structures (e.g., the posterior SI and iliolumbar ligaments) remain intact. Therefore no displacement in the vertical plane is possible. (C) Division of the posterior band ligaments, that is, the posterior SI, as well as the iliolumbar ligaments, causes complete instability of the hemipelvis. Note that global displacement is now possible.

However, this description represents a simplification of the complex interaction between the ligaments and soft tissues investing the pelvis, and the functional interaction of all components of the pelvic ring has yet to be fully understood. For example, although the sacrospinous and sacrotuberous ligaments were previously considered to have no effect on patterns of pelvic deformity, studies have suggested that they provide vertical load transfer, with resulting translation of the sacrum. In general, decreased ligament stiffness increases SI joint stress and angular motion, with maximum strains occurring at the interosseous SI ligament. However, increased sacrospinous and sacrotuberous ligament stiffness has been found to paradoxically increase SI motion.

In addition to the instability induced by ligamentous insufficiency, bony injuries can produce equivalent degrees of pelvic instability. Fractures through the iliac wing, fracture-dislocations of the SI joint, or some complete fractures of the sacrum bypass the ligamentous structures and may therefore constitute globally unstable posterior injuries.

Trauma Mechanism and Pathomechanics of Pelvic Injuries

Pelvic ring injuries usually occur because of high-energy trauma; however, because the older population in Western countries is growing, more and more geriatric insufficiency fractures can be seen due to minor trauma. Two different approaches allow for a better understanding of the relationship between the mechanism of injury and the pelvic fracture pattern. The more clinical way is to extrapolate from the trauma mechanism to fracture pattern or severity because the mechanism usually is known from third-party history. On the other hand, a biomechanical approach to injury patterns allows one to deduce the mechanism of injury based on the fracture configuration.

Trauma Mechanism

The medical history provides essential information about the mechanism of injury. Depending on the patient's age, it is possible to draw inferences about the severity of the pelvic injury from the trauma mechanism. In adult patients, high-energy trauma is usually necessary for pelvic ring disruption. Motor vehicle accidents and falls from a substantial height and industrial accidents are therefore the most common causes of severe pelvic fractures.

Motor Vehicle Accident

Motor vehicle accidents are the most common cause of complex pelvic trauma. One can distinguish among different accident mechanisms. Vehicle–pedestrian accidents are usually associated with low or moderate speed. There is a correlation between the speed of the automobile and the incidence and severity of pelvic fractures. A collision velocity of 30 mph (50 km/h) and above should raise the index of suspicion for pelvic ring injury. The collision type can also provide relevant clues in the suspicion of pelvic injuries. The risk of a pelvic injury is highest in side-impact collisions on the same side as the victim, followed by head-on collisions. Pedestrians, bicyclists, and motorcyclists have twice the risk of sustaining a pelvic fracture.

Fall From a Height

A fall from a height (>4 m) is considered a high-energy trauma because the injury severity and pattern are directly correlated with the height of the fall. If the height is relatively low (<7 m), fractures of the pelvis, upper limbs, lower limbs, and blunt thoracic trauma are the most common injuries. Above 7 m, traumatic brain injuries and spinal fractures are the most frequent causes of mortality.

Osteoporotic Pelvic Fractures of the Elderly

Demographic changes have been leading to an aging society and an increased number of elderly patients. With increasing age, the risk for osteoporosis increases, especially in postmenopausal females. Conditions contributing to osteoporosis are often present, such as chronic corticosteroid use or a history of radiation therapy to the pelvis ( Fig. 38.7 ).

$Fig. 38.7, U-type insufficiency fracture. Anterior-posterior (AP) radiograph (A), technetium bone scan (B), axial computed tomography (CT) image (C), and sagittal CT image (D) of the pelvis of a 72-year-old woman with a history of radiotherapy to the pelvic region for treatment of endometrial carcinoma. She had begun experiencing severe low back and gluteal pain and symptoms of cauda equina dysfunction without any inciting trauma and could neither sit nor stand because of pain. Postoperative AP radiograph of the pelvis (E) after spinopelvic fixation. The patient was able to tolerate sitting and standing immediately after surgery and had gradual resolution of her preoperative symptoms.$

In contrast to the pelvic ring of the adolescent and young adult, the compromised bone density in an elderly patient may result in pelvic fracture from minimal trauma, such as stumbling or falling from a low height from a standing or seating position. The precipitating event in insufficiency fractures is often not even identifiable. Usually, clinical signs of sacral and pelvic ring insufficiency fractures are rather vague and consist of poorly localized groin and low back pain in the region of the sacrum or SI joints that may be exacerbated by sitting and standing. Occasionally, radicular pain may be reported. The sacral component of these fractures is typically oriented vertically and occurs through the ala adjacent to the SI joint. There may also be a transverse component extending between bilateral vertical fractures, resulting in more complex U-fracture variants (see Fig. 38.7 ). Although neurologic deficits are uncommon under these circumstances, cauda equina dysfunction has been reported, and neurologic status must be carefully evaluated.

Magnetic resonance imaging (MRI)–based studies report a 25% incidence of occult pelvic ring fractures in elderly patients, of which two-thirds comprise injury of the posterior ring. One must therefore maintain a high index of suspicion to avoid overlooking these injuries.

Stress fractures of the pelvis, unlike insufficiency fractures, occur in bone that is not weakened by a pathologic process. They usually occur in individuals whose activity level causes repetitive stress that exceeds the bone's reparative ability. High-demand individuals such as endurance athletes and military recruits are particularly susceptible.

Pathomechanics of Pelvic Injuries

From a biomechanical point of view, fracture patterns can be construed from the primary-force vector because each applied force can result in characteristic deformities of the pelvic ring. Pennal postulated that three basic forces were responsible for traumatic pelvic deformities:

anterior-posterior (AP) compression,
lateral compression, and
vertical shear,

which, respectively, tend to open the pelvis like a book, collapse it toward the midline, or cause vertical translation.

Anterior-Posterior Force Pattern

AP force patterns typically cause external rotation of one hemipelvis. Two different application points are possible:

The most common is a direct posterior blow through the PSIS that leads to diastasis and disruption of the symphysis and, with increasing force, of the anterior SI ligaments as well.
Direct forces applied to the anterior superior iliac spine (ASIS) also cause disruption of symphyseal and anterior SI ligaments and can tear the posterior SI ligament or cause correspondingly unstable fractures through the sacrum.

In general, this force pattern leads to rotational instability (open book), with the posterior SI ligament remaining intact (see Fig. 38.6B ). If the force overcomes the integrity of the posterior ligamentous complex, the result is vertical instability.

Lateral Compression Force Pattern

The most common force pattern causing pelvic fractures is lateral compression. Depending on the point of application and the magnitude of this force, different lateral compression (LC) injuries are seen, as follows:

Posterior SI complex: If a force is applied to the posterior SI complex, it is typically parallel to the trabeculae of the sacrum, creating compression or impaction of the cancellous bone of the sacrum. It causes minimal soft tissue disruption because the posterior ligamentous structures relax as the hemipelvis is driven inward. Because the force of injury is essentially parallel to the ligament fibers and trabeculae of the bone, it produces a very stable fracture configuration.
Anterior part of iliac wing: If a force is applied to the anterior half of the iliac wing, it tends to rotate the hemipelvis internally, with the pivot point being the anterior SI joint or anterior ala. Consequently, the anterolateral portion of the sacrum adjacent to the SI joint sustains an impaction fracture, and injuries of the posterior SI ligament complex may follow. Rather than involving the sacrum, the fracture may involve the posterior ilium adjacent to the SI joint, producing relatively common patterns such as the “crescent” fracture. This injury becomes more unstable as disruptions of the posterior osseous or ligamentous structures become more severe. However, the sacrospinous and sacrotuberous ligaments remain intact along with the pelvic floor, thereby limiting translational instability. This force can continue to displace the hemipelvis across toward the opposite side, producing an LC injury on the side of force application and an external rotation injury on the contralateral side. The resulting anterior pelvic lesions may be any combination of ramus fractures or fracture-dislocations through the symphysis. The pubic ramus fractures are typically horizontal in orientation ( Fig. 38.8 ).

$Fig. 38.8, Lateral compression—unstable. In this mechanism, the force (arrow) is directed over the anterior aspect of the hemipelvis. The hemipelvis pivots around the anterior portion of the sacroiliac joint, thus compressing the sacrum or fracturing through the ilium (or both). Posteriorly, the posterior interosseous hinge is now disrupted, and the pelvis is unstable in internal rotation. It may exhibit some degree of vertical instability. Vertical instability is limited by the intact sacrotuberous ligaments.$
Greater trochanter: Finally, if force is applied to the greater trochanteric region, this leads to an LC injury, usually associated with an acetabular fracture.

External Rotation-Abduction Force Pattern

Because of its characteristic mechanism and direction, an external rotation-abduction force pattern is an independent force type. Nevertheless, there are several similarities with the AP force pattern. This force is common in motorcycle accidents and usually applied indirectly through the femoral shafts and hips. The leg is caught and externally rotated and abducted, a mechanism that tends to tear the hemipelvis from the sacrum. Coincident femoral neck and shaft fractures are common.

Shear Force Pattern

Shear fractures are the result of high-energy forces, usually applied perpendicular to the bony trabeculae. These forces quite commonly lead to unstable fractures or dislocations or both. The exact fracture pattern depends on both the amount of force applied and the bone strength in relation to the ligamentous structures. In general, if bone strength is less than ligamentous strength, a shear force will result in vertically oriented sacral and rami fractures, as opposed to the horizontal pattern seen in lateral compression. Conversely, if the bone strength is relatively high, ligamentous injuries usually occur and manifest as symphysis and SI joint dislocations but often with some degree of bony avulsion.

Traumatic hemipelvectomy, a rare injury, occurs most commonly because of an external rotation-abduction force followed by direct blow (e.g., ship's propeller). However, extreme shear forces can also lead to hemipelvectomy.

In conclusion, trauma mechanism can be obtained from personal or third-party history and may often be inferred from the pelvic fracture pattern. The fracture pattern, displacement, deformity, and the clinical examination provide clues to pelvic stability. Subsequent diagnostic tests and classifications are aimed at the categorization of the stability to enable appropriate treatment decisions.

Radiologic Diagnostics in Pelvic Injuries

Radiologic imaging is mandatory if the physician suspects that a patient has sustained a pelvic ring fracture and is generally dictated by standard trauma protocols in situations involving high-energy trauma. Pelvic imaging in the form of an AP radiograph of the pelvis is recommended in all polytrauma patients by the Acute Trauma Life Support (ATLS) guidelines published by the American College of Surgeons, highlighting the importance of excluding pelvic ring disruptions with potential lethal hemorrhage so that immediate damage control surgery can be initiated, if necessary. A more conservative approach to imaging can be considered under specific circumstances, such as in the case of pregnancy, particularly in the case of a relatively minor trauma with a low risk of a pelvic ring injury. However, in the case of a high-energy injury with potentially unstable isolated pelvic ring injury or multiple trauma patients, even in pregnancy, the mother's safety should take priority over radiation exposure to the fetus. Unfortunately, there are few data on pelvic ring injuries in pregnancy.

In general, a pelvic ring fracture has to be excluded after sufficient trauma has been sustained or if corresponding symptoms are suspicious of a fracture. Moreover, preoperative planning requires proper radiographic evaluation to minimize the rate of complications and to guarantee an optimal reduction during surgery. During the past decades, different planning tools and software have been established. These programs are mostly based on computed tomography (CT) imaging. Whereas plain radiographs constituted the gold standard in former decades, trauma centers routinely use abdominopelvic CT scans with reconstruction of the bony anatomy to establish the diagnosis of pelvic ring disruption while also being able to assess for visceral or vascular injuries. The different radiologic techniques are described in the following text.

Key Points: Diagnosis and Classification

Whereas radiography is a standard tool routinely used in trauma patients, assessment of patients with suspicion of pelvic fractures nowadays requires CT imaging.
Knowledge of different radiographic projections is required for intraoperative fluoroscopy.
MRI and scintigraphy are not used for the routine assessment of pelvic injuries. However, they may be important in cases with fragility fractures or other specific medical questions.
The Arbeitsgemeinschaft für Osteosynthesefragen (AO) classification and Young and Burgess classification are most commonly used.
Understanding of these classification systems helps evaluate fractures and to triage the need for treatment. Moreover, reduction and fixation can partially be derived.
Fractures of the posterior pelvic ring with external rotation force of the hemipelvis (AO B-type injury) and perhaps additional vertical shear (AO C-type injury) are most severe and can cause significant hemorrhage.

Plain Radiographs

Three standard plain radiographic images are used to evaluate the pelvic ring: AP, inlet, and outlet views ( Table 38.1 ). In former decades, all of them had to be obtained for thorough radiographic evaluation. However, CT evaluation with multiple reformations has become the gold standard, with the possible use of three-dimensional (3-D) CT, which allows for deep analysis of fracture patterns. Nevertheless, inlet and outlet views are still routinely used, both in the operating room during surgery to evaluate pelvic reduction and the placement of implants as well as during follow-up visits to evaluate pelvic alignment. The paradigm shift toward the use of CT imaging with 3-D reformations, especially during the initial radiographic assessment of a trauma patient, is illustrated by the ATLS guidelines, which recommend an AP view followed by CT of the pelvis. However, in hemodynamically and mechanically stable polytraumatized patients suspicious of pelvic ring fractures, there is evidence that the AP radiograph can be omitted in lieu of a CT scan. Because both the Young and Burgess classification and the AO classification modified by Tile refer to plain radiographs, this algorithm change has also had an impact on the classification of pelvic injuries.

Table 38.1

Three Standard Radiographs of the Pelvis Allowing Analysis of the Different Anatomic Regions

	AP Radiograph	Inlet Radiograph	Outlet Radiograph
Best assessment of anatomical structures	Overview of complete pelvis Pubic rami Symphysis	Pelvic brim Pubic rami SI joints Sacral ala Iliac ala Body of the sacrum Posterior iliac spine	Vertebral bodies S1 and S2 SI joints Symphysis

SI, Sacroiliac.

Anterior-Posterior Radiograph

The AP radiograph ( Fig. 38.9 ) gives an overview of the complete pelvis.

Fractures of the superior and inferior pubic ramus can be visualized, as can disruption of the pubic symphysis. Although injuries of the posterior pelvic ring might be identified, further imaging is often required to properly evaluate for injuries to the iliac wing as well as the sacrum. Useful indicators of sacral injuries include abnormalities in the contour of the sacral foramina and sacral arcuate lines and the presence of a “paradoxical inlet” view of the sacrum caused by an increase in sacral inclination that is so great as to give the appearance of an inlet view of the S1 vertebral body on the AP pelvic view. Their presence warrants CT evaluation of the sacrum. It is important to remember that in the supine position, the pelvis is anteverted 45 to 60 degrees relative to the long axis of the skeleton. This angulation pertains to pelvic tilt, the degree of which has considerable implications in the treatment of spine deformities and sacral fractures with spinopelvic dissociations. The pelvic tilt is, however, a flexible parameter that changes based on positioning. Consequently, an AP radiograph is essentially an oblique radiograph of the pelvis. The acquisition technique is as follows: The patient is placed supine with symmetrical positioning of the legs and subtle abduction and internal rotation of the hips. The beam is directed perpendicular to the midpelvis, about 2 fingerbreadths above the pubic symphysis and the radiologic plate.

Inlet Radiograph (Pennal I)

The inlet view ( Fig. 38.10 ) allows for evaluation of the pelvic brim, the pubic rami, the SI joints, the sacral ala, and the body of the sacrum as well as the posterior iliac spine.

$Fig. 38.10, Inlet radiograph of the pelvis: direction of radiograph beam angulation (A; arrow ) and resulting radiographic view (B). The radiographic view (B) demonstrates an Arbeitsgemeinschaft für Osteosynthesefragen (AO) type C fracture; the dislocation of the anterior pelvic ring is especially visible.$

Displacement of the hemipelvis in the transverse (axial) plane can be identified on this view. Fractures of the iliac wings and of the ala can be identified. The patient is positioned as described for the AP radiograph. The craniocaudal beam is directed at the level of the ASIS and the middle of the radiographic plate at an angle of approximately 40 degrees relative to the horizontal plane.

Outlet Radiograph (Pennal II)

The outlet view ( Fig. 38.11 ) is essentially the true “anterior” view of the pelvis and is orthogonal to the inlet view.

Fig. 38.11, Outlet radiograph of the pelvis: direction of radiograph beam angulation (A; arrow ) and resulting radiographic view (B). The radiographic view (B) demonstrates the same patient as in Fig. 38.10 .

The vertebral bodies of S1 and S2 can usually be clearly visualized. This view allows for the evaluation of the symmetry of the SI joints and the pubic symphysis. Vertical displacement of the hemipelvis can be identified. Because the obturator foramen is brought into profile, fractures extending into the obturator foramen can be detected more easily than on the AP view. However, the inferior aspect of the SI joint may not be visualized clearly because it is superimposed on the superior pubic rami. The acquisition technique involves positioning as described for the AP and inlet radiographs. The caudocranial beam is focused 2 to 3 fingerbreadths below the pubic symphysis.

Computed Tomography

Computed tomography is currently the accepted gold standard for the evaluation of pelvic fractures and is considered to be mandatory for the evaluation of patients who have sustained high-energy injuries or in whom a posterior pelvic injury is suspected for any reason. The use of CT has especially revolutionized the assessment of posterior osseoligamentous pelvic structures and may detect up to 50% of occult fractures. In fact, in a study that predates the routine use of abdominopelvic CT for the evaluation of trauma patients, Denis and colleagues found that in neurologically intact patients, the diagnosis of sacral fractures was made during the initial hospitalization only 51% of the time when using plain radiography. The presence of a neurologic deficit increased the diagnostic accuracy to only 70%. The etiology of missed sacral fractures is multifactorial and includes difficulty in identifying these fractures on screening AP pelvic radiographs because of the complex anatomy of the sacrum and pelvis; the presence of distracting injuries in the trauma patient; and low clinical suspicion in general, particularly in patients with insufficiency fractures. CT is mandatory for determining the exact nature of a posterior injury and can help determine whether an injury through the sacrum is a potentially stable impaction injury or a more unstable shear fracture with displacement. Establishing the extent of SI joint displacement is valuable in determining the stability of this posterior injury. Many pubic rami fractures that occur near the base of the anterior column involve the acetabulum, and CT imaging allows for appropriate assessment of these injuries.

It is currently recommended that polytraumatized patients should receive a CT scan of the pelvis. Moreover, the implementation of a similar diagnostic process after low-energy trauma has become increasingly common because osteoporotic fractures are happening with increasing frequency. These insufficiency or pathologic fractures are often difficult to diagnose without CT. CT imaging of the pelvis is therefore recommended if a patient presents with symptoms in the posterior pelvic region and a history that suggests a potential pelvic insufficiency fracture. If any fracture is identified on plain radiographs, the threshold to perform a pelvic CT should be low to properly delineate the fracture pattern for therapeutic purposes. High-energy pelvic ring fractures are often associated with life-threatening hemorrhage, which can be evaluated with contrast CT scan and computed tomography angiography (CTA). Contrast agent extravasations establish the presence of vessel injury and allow for subsequent therapeutic steps such as embolization or surgical intervention. However, potential sources of bleeding can be identified even without the use of contrast. CT evaluation can also be used to predict the risk of death after pelvic fracture. Two- and three-dimensional CT reconstructions may provide a more useful evaluation of fracture morphology and of the overall extent of pelvic fracture displacement than plain radiography. An important indicator of severe pelvic instability is a pelvic ring fracture associated with a fracture of the transverse process of L5, the attachment site of the iliolumbar ligament. Because this robust ligament serves as an important stabilizer of the spinopelvic junction, loss of its integrity caused by a transverse process fracture of L5 in the presence of a pelvic ring injury suggests severe instability of the posterior pelvic ring. Indications to perform a CT of the pelvis are summarized in Table 38.2 .

Table 38.2

Indications to Initiate a CT Scan in Trauma Patients

Indications for Pelvic CT

Multiply injured patients
Traumatic pain in the posterior pelvic region with history of osteoporosis or pelvic insufficiency fracture
Pelvic fracture on plain radiographs with suspicion of additional pelvic ring injury (posterior pelvic pain, high-energy trauma, etc.)

CT, Computed tomography.

An algorithm for radiologic assessment of the acute trauma patient is shown in Fig. 38.12 .

$Fig. 38.12, Algorithm for emergency assessment of pelvic ring fractures. AP, Anterior-posterior; CT, computed tomography.$

Magnetic Resonance Imaging

Despite the high sensitivity of CT scans for diagnosing pelvic ring fractures, delayed diagnosis may occur, particularly in minimally or nondisplaced insufficiency fractures. Potential reasons include the presence of overlying intact cortical bone or microfractures that involve minimal compromise of trabecular bone only. In these cases, MRI may successfully diagnose occult fractures. Cabarrus and colleagues were able to detect 100% of sacral fractures using MRI versus 74.6% with CT. The sensitivity has been shown to be much higher with MRI compared with CT. In another study, MRI detected 96.3% of all pelvic ring fractures compared with 77% with CT. Sacral fractures in particular were more consistently detected using MRI (98.6%) compared with CT (66.1%). MRI also has the advantage of allowing for the evaluation of ligamentous integrity, which can be helpful in cases of persistent joint instability. However, MRI is not the imaging modality of choice in the acute trauma setting because, for example, CT is much faster compared with MRI; moreover, the evaluation of fractures is limited in MRIs compared with CT scans. The clinical relevance of pelvic ring fractures that are only verifiable using MRI is not clear. A relevant proportion of asymptomatic fractures is more likely. Therefore it should be used primarily in cases with persistent posterior pelvic pain after trauma despite the absence of an obvious fracture on CT scan.

Scintigraphy

Scintigraphy also offers a means for identifying occult pelvic ring fractures that cannot be seen on CT, with a sensitivity that approaches 100% (see Fig. 38.7 ) and a positive predictive value of approximately 92%. However, most reports deal with isolated sacral fractures only. If CT findings are negative after trauma but pain persists, scintigraphy may be an alternative to MRI, especially if MRI is contraindicated or unavailable.

Special Imaging of the Symphysis

Bauman and colleagues published a study as to the ultrasonographic determination of pubic symphyseal disruption during focused assessment with sonography for trauma (FAST). All four of their patients who were diagnosed with pelvic fractures with widening of the symphysis pubis on subsequent AP radiographs had been previously identified using ultrasound during the FAST. All were detected by the ultrasound examination. However, because a standard AP radiograph is routinely obtained per standard ATLS recommendations anyway, ultrasound diagnosis of symphysis pubis disruption saves little in the way of time and provides no additional information. This technique may, however, be of potential benefit in specific circumstances, such as during pregnancy.

Classification of Pelvic Injuries

Various classification systems have been proposed for pelvic ring fractures. They can be divided into subgroups according to the mechanism of injury or based on an anatomic classification system that focuses primarily on the location and orientation of the fracture. Moreover, the AO published a classification that combined elements of both mechanism of injury and pelvic stability, the latter being specifically dependent on the anatomic location of the fracture. Because pelvic ring fractures are associated with a high risk of death, some authors have also tried to incorporate the presence of associated injuries or hemorrhage into their classification schemes. Furthermore, age-dependent differences in fracture morphology and adapted treatment strategies find expression in classifications of pelvic fragility fractures. In daily practice, surgeons should strive to describe the fracture according to both mechanism of injury as well as anatomic location to facilitate communication and rapid decision making in the acute damage control environment. Definitive surgical treatment requires a thorough comprehension of the injury and intensive preoperative planning. A potential limitation of most of the classification systems is that they were developed based on plain radiographic evaluation rather than the CT imaging with reformatting that is now more commonplace as a preliminary imaging study.

Anatomical Classification

Several different anatomic classifications have been proposed. Bucholz published a pathologic classification based on 47 autopsy studies. Five sites of injury were characterized:

1.
Anterior vertical fractures dividing the obturator ring or adjacent bodies of the pubis
2.
Transiliac fractures extending from the crest of the greater sciatic notch
3.
Transsacral fractures either outside or inside the foramina
4.
Pure separation of the symphysis
5.
Pure disruption of the SI joint

Judet et al. suggested a more comprehensive classification system based on the site of injury. These included injuries to the posterior ring (i.e., sacral fractures, SI joint fracture-dislocations, SI joint dislocations, and iliac wing fractures), acetabulum, and anterior ring (rami fractures, pubic body fractures, and symphyseal disruptions; Fig. 38.13 ).

$Fig. 38.13, The Letournel and Judet classification of pelvic fractures is anatomic. A, Iliac wing fractures. B, Ilium fractures with extension to the sacroiliac (SI) joint. C, Transsacral fractures. D, Unilateral sacral fractures. E, SI joint fracture-dislocation. F, Acetabular fractures. G, Pubic ramus fractures. H, Ischial fractures. I, Pubic symphysis separation. Combinations of all of these injuries can occur.$

Regardless of which classification scheme a surgeon subsequently uses, identifying the fracture site and pattern is an integral but not necessarily independently sufficient component of the evaluation. Although the classification by Judet et al. still serves as the most descriptive system, it is best used in conjunction with current mechanism-based classification schemes to define a specific patient's injury in a more sophisticated manner.

Mechanical Classification

Young and Burgess Classification

The classification by Young and Burgess is based on the mechanism of injury, which also suggests the most likely potential associated injuries and resuscitation requirements. It is among the most favored classifications of pelvic ring fractures. It should be noted that Pennal and colleagues had previously published a classification of pelvic ring disruptions that was primarily contingent on the force applied at the time of injury. The Young and Burgess classification has three major components (A to C; Fig. 38.14 ).

$Fig. 38.14, Young and Burgess classification. (A) Lateral compression force. Type I, a posteriorly directed force causing a sacral crushing injury and horizontal pubic ramus fractures ipsilaterally. This injury is stable. Type II, a more anteriorly directed force causing horizontal pubic ramus fractures with an anterior sacral crushing injury and either disruption of the posterior sacroiliac (SI) joints or fractures through the iliac wing. This injury is ipsilateral. Type III, an anteriorly directed force that is continued and leads to a type I or type II ipsilateral fracture with an external rotation component to the contralateral side; the SI joint is opened posteriorly, and the sacrotuberous and spinous ligaments are disrupted. (B) Anterior-posterior (AP) compression fractures. Type I, an AP-directed force opening the pelvis but with the posterior ligamentous structures intact. This injury is stable. Type II, continuation of a type I fracture with disruption of the sacrospinous and potentially the sacrotuberous ligaments and an anterior SI joint opening. This fracture is rotationally unstable. Type III, a completely unstable or a vertical instability pattern with complete disruption of all ligamentous supporting structures. (C) A vertically directed force or forces at right angles to the supporting structures of the pelvis, leading to vertical fractures in the rami and disruption of all the ligamentous structures. This injury is equivalent to an AP type III or a completely unstable and rotationally unstable fracture.$

The mechanism of injury is divided into

lateral compression (LC) (type A),
AP compression (APC) (type B), and
vertical shear stress and combined force injuries (type C).

The first component of the Young and Burgess classification is the LC injury. An LC type I injury results from a posteriorly applied force that causes a stable sacral impaction fracture. However, the possibility of mechanical instability has been reported by Tosounidis and colleagues, who have therefore recommended surgical stabilization of these fractures. Patients with these injuries usually have minimal problems with resuscitation. An LC type II injury is caused by a more anteriorly directed force with resultant injury to the posterior osseous–ligamentous structures, typically in the form of juxtaarticular fractures of the posterior ilium. Because of the preservation of pelvic floor integrity, these injuries are generally rotationally unstable only. LC type II injuries may be associated with an anterior sacral impaction injury and are often associated with head injuries and intra-abdominal trauma. An LC type III injury results from a laterally directed force that has continued to cross the pelvis to produce an external rotation injury to the contralateral hemipelvis. This is usually the result of an isolated direct impact (crush) to the pelvis. A common example is being run over by a car. The injury is usually isolated to the pelvis and has few significant associated injuries.

The second component is the APC injury, which is also divided into three types. Type I is characterized by less than 2.5 cm of anterior ring diastasis and consists of vertical fractures of the pubic rami or disruption of the symphysis. Because there is no significant associated posterior injury, relatively few patients tend to require resuscitation. An APC type II injury has greater than 2.5 cm of anterior ring diastasis with widening of the anterior SI joints, resulting in rotational instability. An APC type III injury is a complete fracture of the anterior and posterior pelvic ring. APC type II and type III injuries have a significant potential need for resuscitation because severe hemorrhage can occur. The APC type III fracture is globally unstable and should be interpreted as a vertically unstable or shear injury. A combined mechanism of injury is likely required to achieve this injury pattern, and the potential for retroperitoneal hemorrhage and major associated injuries is high. Table 38.3 outlines the Young and Burgess classification.

Table 38.3

Young and Burgess Classification

Type		Morphology	Stability
LC—lateral compression	I	Anterior sacral impression fracture and transverse pubic rami fracture, unimpaired ligaments	Stable
	II	Posterior iliac wing fracture (possibly crescent fracture) and transverse pubic rami fracture	Rotationally unstable, vertically stable
	III	Unilateral LC I or II and contralateral APC injury	Globally unstable
APC—anterior-posterior compression	I	<2.5-cm diastasis of symphysis or vertical pubic rami fractures with stretched anterior sacroiliac ligaments	Stable
	II	>2.5-cm diastasis of symphysis or vertical pubic rami fractures with ruptured anterior sacroiliac, interosseous, sacrotuberous, and sacrospinous ligaments (widening of anterior sacroiliac joint = “open book”)	Rotationally unstable, vertically stable
	III	>5-cm diastasis of symphysis with ruptured ligaments comparable to APC injury including posterior sacroiliac ligaments (widening of anterior and posterior sacroiliac joint)	Globally unstable
VC—vertical shear		Vertical dislocation of hemipelvis, pubic rami and sacroiliac fractures	Unstable
CM—combined		Complex fracture with combination of APC, LC, or VC injury	Variable

AO Classification (Modified Pennal and Tile Classification)

Similar to the classification by Young and Burgess, the classification by Müller as modified by Tile and published by the AO is widely used to classify pelvic ring fractures. It combines the mechanism of injury and the degree of pelvic stability as well as the site of injury. It can also help to assess the prognosis as well as treatment options. Determination of pelvic stability is based on the degree of rotational or global displacement and the mechanism of injury. The classification is completed with an assessment of associated injuries, especially soft tissue injuries such as the Morel-Lavallée lesion, and designation of the fracture as either open or closed.

The AO classification is partitioned into three groups (A to C), similar to the Young and Burgess classification, with greater attention given to the anatomic site of the fracture. Type A injuries are stable because the bony and ligamentous integrity of the posterior pelvic ring, as well as the pelvic floor, remains intact.

Subtype A1 injuries ( Fig. 38.15A ) consist of avulsions of the pelvic apophyses by a sudden muscular pull; these injuries usually require only symptomatic care. However, muscular dysfunction can be an indication for surgery, especially in young people.

$Fig. 38.15, Type A injuries. (A) Avulsion fracture of the ischial spine occurring in a skeletally immature athlete. (B) High-energy direct blow to the iliac wing resulting in an open fracture of the iliac wing.$
Subtype A2 injuries (see Fig. 38.15B ) represent isolated iliac wing fractures without violation of the posterior osseous ligamentous hinge. This group includes a spectrum of injuries resulting from direct blows. They constitute isolated fractures of the anterior pelvic ring. Whereas nondisplaced low-energy injuries are usually seen in osteoporotic bone, high-energy direct blows are usually responsible in younger individuals. Isolated wing fractures do not require surgery unless they are open.
Subtype A3 fractures involve the sacrum or coccyx below the SI joints (below S2), meaning that the integrity of the posterior pelvic ring and the spinopelvic junction are both preserved. Chronic pain is the main indication for surgery. In rare cases of sacral root symptoms, decompression of the sacral spinal canal is indicated, possibly with fracture stabilization. Assessment of neurologic deficits therefore is of great importance in the evaluation of type A3 pelvic ring fractures.

Type A pelvic ring fractures are illustrated in Fig. 38.16 . Type A fractures should generally be treated conservatively.

$Fig. 38.16, Modified Tile Arbeitsgemeinschaft für Osteosynthesefragen (AO) Müller classification. Type A, stable posterior arch with intact pelvic ring injuries. Group 1 represents avulsion fractures of the iliac spine (A1.1), iliac crest (A1.2), and ischial tuberosity (A1.3). Group 2 represents fractures of the innominate bone or injuries from direct blows: iliac wing (A2.1), unilateral anterior arch (A2.2), and bifocal anterior arch (A2.3). Group 3 represents transverse fractures of the sacrum caudal to S2: sacrococcygeal dislocation (A3.1), sacrum undisplaced (A3.2), and sacrum displaced (A3.3).$

Type B fractures are complete disruptions of the anterior pelvic ring combined with incomplete disruptions of the posterior arch that allow rotation of the hemipelvis. This fracture pattern therefore presents with rotational instability in the absence of vertical instability. Type B fractures, especially type B1, are at high risk for severe hemorrhage. Surgery is usually required to prevent exsanguination and to reestablish pelvic ring stability.

Subtype B1 injury is a unilateral external rotation or tension failure fracture through the sacrum (B1.2). A variable degree of rotational instability may be present with these injuries ( Fig. 38.17 ).

$Fig. 38.17, B-type injuries. (A) Type B1.1 with injury to the anterior sacroiliac (SI) joint. Note air density within the joint, which may indicate rotational injury through the joint. Physical examination may confirm the instability. (B) Type B1.1, injury with obvious instability. Computed tomography confirms unilateral injury through the SI joint with concomitant tensile sacral fracture. (C) Type B1.2, posterior injury noted through the sacrum. The anterior border of the sacrum is typically a location for simple fracture caused by the tensile force creating the posterior injury.$
Subtype B2 injuries are produced by LC or internal rotation. A type B2.1 injury is caused by a force directed over the posterior iliac wing. This results in a sacral impaction injury and most commonly with horizontally oriented rami fractures ( Fig. 38.18A ). As noted earlier, this does not result in injury to the posterior pelvic or pelvic floor ligaments. A B2.2 injury is produced by an LC force and involves a partial fracture-subluxation of the SI joint, associated with anterior ring fractures or fracture-dislocations of the pubic symphysis. The typical posterior fracture pattern extends from the iliac wing into the SI joint, with ligamentous disruption of the caudal SI joint. A portion of the cranial iliac wing and SI joint remains attached to the sacrum (see Fig. 38.18B ). These rotationally unstable injuries are the equivalent of the Young and Burgess LC type II injuries. Because the force of injury is applied in an oblique fashion across the pelvis, the involved portion of the pelvis is flexed, adducted, and internally rotated, positioning the femoral head cranially; these can be associated with a leg length discrepancy. This clinical finding, however, is usually sufficiently subtle as to not be easily identifiable in the emergency setting unlike in the case of femoral neck fractures or inner hemipelvectomies (type C pelvic ring fracture). Less common anterior arch injuries associated with B2 injuries can be a locked symphysis or a tilt fracture ( Fig. 38.19 ). A locked symphysis injury disrupts the symphysis rather than fracturing the rami as it drives one side of the symphysis behind the other. A tilt fracture is an unusual anterior variant associated with an LC mechanism in which the superior pubic ramus is fractured at the pubic root near the acetabulum and through the ischial ramus; continued medial displacement of the hemipelvis causes dislocation of the symphysis or fracture of the pubic body, allowing the fragment to tilt caudally and anteriorly into the perineum. Tilt fractures are at high risk of harming the perineum.

$Fig. 38.18, Clinical example of lateral compression-type injuries. (A) Type B2.1, anterior sacral compression fracture associated with contralateral segmental parasymphyseal fracture. (B) Crescent fracture. Note the fracture entering the caudal portion of the sacroiliac joint with dislocation.$

$Fig. 38.19, (A) A locked symphysis with one pubic body displaced behind the other. (B) A tilt fracture occurs when the superior pubic body has dislocated from the symphysis and rotates into the perineum around a fracture of the ipsilateral pubic root.$
Subtype B3 injuries are bilateral posterior ring injuries with each side possibly having a different mechanism of injury, but in which neither side is vertically unstable. A type B3.1 injury is a bilateral external rotation injury with greater than 2.5 cm of symphyseal displacement ( Fig. 38.20A ). Type B3.2 (see Fig. 38.20B ) and B3.3 injuries are secondary to an LC mechanism, respectively, causing either external rotation of the contralateral hemipelvis or an LC mechanism bilaterally. Type B fractures are summarized in Figs. 38.21 and 38.22 . Rotational instability generally requires either external or internal fixation.

$Fig. 38.21, Examples of B-type injuries, all with anterior symphyseal disruptions. Anterior injuries can also include unilateral or bilateral rami fractures.$

$Fig. 38.22, Modified Tile Arbeitsgemeinschaft für Osteosynthesefragen (AO) Müller classification. Type B, incomplete disruptions (internal rotation). Internally directed or lateral compression forces cause anterior sacral compression injuries (B2.1), partial fracture-subluxations of the sacroiliac joint (B2.2), and incomplete posterior iliac wing fractures (B2.3).$

Type A fractures are considered stable, and type B fractures are partially stable with only rotatory instability. Fractures that present with rotatory as well as vertical instability are classified as type C injuries. These injuries are generally caused by high-energy trauma. Subdivision of type C fractures depends on the characteristics of the posterior fracture ( Fig. 38.23 ).

C1.1 is an iliac fracture, C1.2 is an SI joint dislocation or fracture-dislocation, and C1.3 is a fracture through the sacrum.
C2 injuries are bilateral disruptions in which one hemipelvis is rotationally unstable (B types) and the other side is globally unstable (C types; Fig. 38.24 ).

$Fig. 38.24, Bilateral injuries. (A) Type C2, complete disruption of the left sacroiliac (SI) joint and subtle rotational displacement of the right SI joint, confirmed on computed tomography. (B) Left transsacral fracture and obvious complete dislocation of the right SI joint; both injuries are globally unstable posteriorly.$
C3 injuries represent bilateral, globally unstable hemipelves.
Type C fractures are summarized in Fig. 38.25 .

Fig. 38.23, Examples of C1 injuries. (A) Posterior injury occurring through the sacroiliac joint. (B) Sacrum. (C) Ilium.

Key characteristics of the AO classification of fracture types and their implications regarding treatment are summarized in Table 38.4 .

Table 38.4

AO Classification (Modified Pennal and Tile Classification)

Type	Subtypes			Indication for Surgery
Type A stable—intact posterior pelvic ring	A1	Fracture does not involve pelvic ring	A1.1 Iliac spine	Rarely
			A1.2 Iliac crest
			A1.3 Ischial tuberosity
	A2	Stable or minimal displaced fracture of pelvic ring	A2.1 Iliac wing fractures (ala ossis ilii)
			A2.2 Unilateral fracture of anterior pelvic ring
			A2.3 Bifocal fracture of anterior pelvic ring
	A3	Transverse sacral fractures	A3.1 Sacrococcygeal dislocation
			A3.2 Undisplaced sacral fracture
			A3.3 Displaced sacral fracture
Type B rotationally unstable, vertically stable—incomplete rupture of the posterior pelvic ring	B1	Open-book injuries (external rotation)	B1.1 Sacroiliac joint, anterior rupture	Yes
	B1	Open-book injuries (external rotation)	B1.2 Sacral fracture	Yes
	B2	Lateral compression injuries (internal rotation)	B2.1 Anterior compression fracture, sacrum	Often
			B2.2 Partial sacroiliac fracture, subluxation
			B2.3 Incomplete posterior iliac fracture
	B3	Bilateral type B injury	B3.1 Bilateral open book injury
			B3.2 Open-book injury and lateral compression injury
			B3.3 Bilateral lateral compression injury
Type C rotationally and vertically unstable—complete rupture of the posterior pelvic ring	C1	Unilateral fracture	C1.1 Iliac fracture	Yes
			C1.2 Sacroiliac dislocation and/or displaced fracture
			C1.3 Sacral fracture
	C2	Bilateral fracture with unilateral type B and unilateral type C injury
	C3	Bilateral fracture with bilateral type C injury

A good review of indications for surgery and the impact of classification was given by Tscherne and colleagues. This classification has been reported to have high interobserver reliability and is predictive of injury severity and prognosis. However, some authors have also stated that even though both the Young and Burgess and the Tile classifications are widely used, interobserver and intraobserver variability is low and might limit their validity.

Fractures With Proper Names

A handful of fractures are often designated by proper names.

Open-Book Fracture: The open-book fracture can be classified as type B1.1 and B1.2 according to the AO classification modified by Tile and APC type II in the Young and Burgess classification. The unilateral external rotation increases the volume of the true pelvis and often leads to severe hemorrhage.
Malgaigne Fracture: The Malgaigne fracture was first characterized in 1847 and describes an injury with multiple ipsilateral vertically oriented anterior and posterior pelvic ring fractures, resulting in a type C pattern of rotatory and vertical instability. The original fracture description, however, specifically included a vertical fracture of the sacrum as well as a unilateral fracture of the superior and inferior pubic ramus.
Hemipelvectomy: This is a very rare injury, which comprises less than 1% of all pelvic fractures. The osseous hemipelvis is completely disarticulated, with resulting disruption of nerves and vessels ( Fig. 38.26 ).
Duverney Fracture: This is a comminuted fracture of the iliac wing.

Osteoporotic Pelvic Ring Fracture Classification

Due to the relative aging of Western populations, fragility fractures appear to be progressively increasing. These osteoporotic fractures generally occur secondary to low-energy mechanisms or even in the absence of any known injury. They are most often located in the pubic and ischial rami but can also occur in the sacrum. In the posterior pelvic ring, the sacral ala are especially at risk for an osteoporotic fracture. Because fragility fractures of the pelvis are low-energy injuries that occur in the absence of ligamentous instability, fracture displacement is generally minimal compared with higher-energy injuries in younger patients. Classifying these injuries according to the AO and Young and Burgess classifications is therefore of limited value and results in misinterpretation of the biomechanical stability of these fractures. Rommens and Hofmann developed a classification system for fragility fractures of the pelvis, based on both plain radiographs as well as 3-D imaging using CT and MRI. A total of 245 patients were included, who were only operated on after having failed nonoperative therapy. Fractures with significant displacement and complete bilateral fractures required surgical treatment. They proposed a new classification based on the degree of instability. Fracture patterns of this classification are summarized in Table 38.5 .

Table 38.5

Classification of Fragility Fractures of the Pelvis According to Rommens and Hofmann

Type	Degree of Instability	Fracture Pattern	Posterior Displacement	Indication for Surgery
Ia	Stable	Isolated unilateral anterior fracture	None	No
Ib	Stable	Isolated bilateral anterior fracture	None	No
IIa	Moderate	Isolated sacral fracture	None	No
IIb	Moderate	Sacral crush with anterior fracture	None	Should be considered
IIc	Moderate	Sacral, iliosacral, or ilium fracture with anterior disruption	None	Should be considered
IIIa	High	Unilateral iliac fracture	Yes	Yes
IIIb	High	Unilateral iliosacral fracture	Yes	Yes
IIIc	High	Unilateral sacral fracture	Yes	Yes
IVa	Highest	Bilateral iliac or iliosacral fracture	Yes	Yes
IVb	Highest	Bilateral sacral fracture	Yes	Yes
IVc	Highest	Combination of posterior instabilities	Yes	Yes

Sacral Fracture Classification

Denis Classification

Sacral fractures play an integral role in pelvic ring stability and are thus generally incorporated into the pelvic ring injury classifications described previously. However, there is considerable value to looking at the sacral fracture location and configuration in a more isolated fashion for two reasons:

1.
Specific fracture patterns and location can have prognostic and treatment significance independent of the associated ring injury.
2.
Some sacral fractures have little effect on overall pelvic ring stability.

Although several sacral fracture classification systems were proposed earlier, none was widely adopted until 1988 when Denis and colleagues described an anatomic classification that correlated fracture location with the presence of neurologic injury. This classification divides the sacrum into three zones ( Fig. 38.27 ):

Zone I (alar zone) fractures remain lateral to the neuroforamina.
Zone II (foraminal zone) fractures involve one or more neuroforamina while remaining lateral to the spinal canal.
Zone III (central zone) fractures involve the spinal canal.

$Fig. 38.27, Denis and associates classified 236 fractures of the sacrum into zones. Zone I was the region of the ala, and fractures in this area occurred in 118 patients, 5.9% of whom had neurologic deficits. Zone II was the foraminal region, where the fracture line involved one or more foramina and exited without involvement of the central neural canal. This group consisted of 81 patients, 28.4% of whom had neurologic findings. The final group of patients had zone III injuries, or central canal involvement. This pattern was seen in only 21 patients, but they had an extremely high rate of neurologic deficit (56.7%).$

The likelihood of neurologic injury increases as fractures occur in more medial zones. In their series, zone I fractures had a 5.9% incidence of neurologic injury, primarily to the L5 nerve root as it courses over the ala. Zone II fractures had a 28.4% incidence of neurologic injury caused by either foraminal displacement with resulting impingement on the exiting nerve root or the “traumatic far-out syndrome,” in which the L5 nerve root is caught between the L5 transverse process and the displaced sacral ala. Zone III fractures had a 56.7% incidence of neurologic deficits resulting from injury within the spinal canal, with 76.1% of these individuals having bowel, bladder, and sexual dysfunction. It is important to note that more recent studies have demonstrated much lower rates of neurologic injury than those originally reported by Denis et al. Khan and coauthors recently reported an overall neurologic injury rate of 3.5%, compared with 21.6% in the series by Denis et al. They categorized their neurologic injury according to the Denis et al. zone of injury as follows: zone 1, 1.9% versus 5.9% in the series by Denis et al.; zone II, 5.8% versus 28.4%; and zone III, 8.6% versus 56.7%.

Denis and colleagues identified a broad spectrum of zone III sacral fracture-dislocations, which included the presence of both transverse and longitudinal fracture orientations. Because of their neurologic and biomechanical implications, zone III sacral fractures have been more formally characterized by several other investigators. Review of various series and case reports reveals a high likelihood of neurologic deficit characterized as cauda equina injury affecting the lower extremity as well as bowel and bladder function.

Early case reports often characterized the zone III injury pattern as solely a transverse fracture, possibly because of imaging limitations. CT demonstrates that most transverse fractures of the upper sacrum have complex, 3-D fracture patterns. The majority of these injuries are now understood to consist of a transverse fracture of the sacrum with associated “longitudinal” or “vertical” transforaminal or alar fractures that extend rostrally to the lumbosacral junction to form the so-called “U” fracture and its variations (e.g., H, Y, and lambda fracture patterns) ( Fig. 38.28 ).

$Fig. 38.28, Colloquial classification of zone III sacral fractures. Clockwise from top left, sacral H, U, Y, and lambda fractures.$

These fractures are also characterized by a high incidence of L5 transverse process fractures, indicating disruption of the iliolumbar ligament.

Roy-Camille Classification

Roy-Camille and coworkers reported a series of 13 patients with transverse sacral fractures, which they classified as type 1, flexion deformity of the upper sacrum (angulation alone); type 2, flexion deformity with posterior displacement of the upper sacrum (angulation and posterior translation); and type 3, anterior displacement of the upper sacrum without angulation (anterior translation alone). They hypothesized that whereas types 1 and 2 were caused by impact with the lumbar spine in flexion, type 3 fractures were caused by impact with the lumbar spine and hips in extension. Strange-Vognsen and Lebech added the type 4 injury, theorizing that comminution of the upper sacrum without significant angulation or translation was caused by impact with the lumbar spine in the neutral position ( Fig. 38.29 ). A type 5 direct impalement type injury has been proposed by Schildhauer and coworkers.

$Fig. 38.29, Roy-Camille et al. 92 classification of Denis zone III injuries. Type 1, nondisplaced; type 2, flexion injury; type 3, extension injury; and type 4, comminuted upper sacral fracture.$

Other patterns of zone III sacral fractures have been identified as resulting from specific mechanisms or having predictable patterns of associated injuries. In contrast to transverse Denis zone III sacral fractures, midline longitudinal Denis zone III sacral fractures, in which the sacrum is disrupted through the sagittal plane, have a low incidence of neurologic injury compared with transverse fractures, presumably because the nerve roots are subjected to a relatively less traumatic lateral displacement force rather than a shear force ( Fig. 38.30 ).

$Fig. 38.30, Midline longitudinal zone III sacral fracture. Unusual variant of zone III sacral fractures, which is the result of anterior-posterior (AP) compression mechanism with midline fracture of the sacrum, as seen on AP (A) and axial computed tomography (CT; B) images of the pelvis. Postoperative axial CT (C) and outlet (D) views of the pelvis demonstrate treatment with plating of the symphysis pubis and percutaneous iliosacral screw fixation.$

This injury appears to be a variant of the APC pelvic ring injury in which the tension failure of the posterior ring occurs through the middle of the sacrum rather than at the SI joints or their juxtaarticular bone. Neurologic deficits are not usually seen, in contrast to the high incidence of neurologic injury reported in patients with predominantly transverse sacral fractures involving the spinal canal.

Isler Classification

Isler demonstrated that even in the absence of a transverse fracture line, sacral fractures can be associated with spinal column instability. He described variations of longitudinal sacral fractures through the S1 and S2 neuroforamina that result in L5-S1 instability because of facet joint disruption ( Fig. 38.31 ).

$Fig. 38.31, Classification of injuries involving the lumbosacral junction as proposed by Isler. 96 (A) The fracture line goes lateral to the L5-S1 facet and does not destabilize it. The L5-S1 facet is destabilized when the fracture line either goes on both sides (B) or just medial to it (C).$

Injuries with the fracture line lateral to the S1 articular process are not associated with instability of the lumbosacral articulation because the L5-S1 articulation remains continuous with the stable component of the sacrum. Fractures that extend into or medial to the S1 articular process, however, may disrupt the associated facet joint and potentially destabilize the lumbosacral junction. Complete displacement of the facet joint can cause a locked facet joint, making sacral fracture reduction difficult with closed methods alone ( Fig. 38.32 ). Facet disruption may also cause posttraumatic arthrosis and late lumbosacral pain.

$Fig. 38.32, Axial computed tomography images of the pelvis show sacral fracture displacement (A) associated with dislocation of the ipsilateral L5-S1 facet joint (B). This injury pattern is generally not amenable to closed reduction and percutaneous iliosacral screw fixation because, without open reduction of the dislocated facet joint, realignment of the sacral fracture cannot be achieved (C).$

Lumbosacral Injury Classification

The importance of factors other than fracture pattern in guiding the treatment of sacral fractures was first introduced as part of a new classification system in 2012 called the lumbosacral injury classification system (LSICS), which was based on three injury characteristics:

1.
Injury morphology
2.
Posterior ligamentous complex integrity
3.
Neurologic status

An overall injury severity score was calculated by adding a weighted score from each category, allowing patients to be stratified into surgical and nonsurgical treatment groups. Modifiers to determining appropriate selection for operative treatment include the systemic injury load and the physiologic status of the polytraumatized patient, the status of the soft tissues, and the expected time to mobility. An algorithm was also developed to determine the recommended operative technique based on the previously outlined injury characteristics.

Based on the collaboration of an international group of spine and pelvis trauma surgeons, a recently revised AO sacral fracture classification has focused on categorizing sacral fractures based on issues pertaining to treatment and prognosis. The morphologic aspect of the classification primarily focuses on the extent and pattern of instability. It is a hierarchical system progressing from least to most unstable:

Type A, lower sacrococcygeal injuries: No impact on posterior pelvic or spinopelvic instability
Type B, posterior pelvic injuries: Minimal to no impact on spinopelvic stability
Type C, spinopelvic injuries: Spinopelvic instability

Type A fractures are either inconsequential injuries or occur below the SI joint and therefore result in neither posterior pelvic nor spinopelvic instability. Type B fractures are vertical fracture patterns that result in posterior pelvic instability only. Type C injuries either involve the S1 superior facet or are complex sacral U fracture variants or bilateral vertical fractures that result in posterior pelvic and spinopelvic instability. Within each type there are three to four subtypes, categorized based on worsening potential prognosis or greater likelihood of operative intervention due to greater risk of neurologic deficit or of instability ( Tables 38.6 and 38.7 ; Fig. 38.33 ).

Table 38.6

Type B: Posterior Pelvic Injuries

Definition
Unilateral longitudinal sacral fractures Primary impact is on posterior pelvic stability Minimal to no impact on spinopelvic stability (except B4 injuries extending in facet) Framework is variation of Denis zones I–III injuries Usually treated with SI screw fixation
Type	Description
B1	Central fracture that involves spinal canal but with primarily longitudinal fracture pattern Longitudinal injuries only; rare type of Denis zone III injuries Does not have the same impact on spinopelvic stability nor same propensity for cauda equina injury as transverse fractures involving canal
B2	Transalar fracture: does not involve foramina or spinal canal Denis zone I injury ≈5% chance of neurologic injury
B3	Transforaminal fracture: involves foramina but not spinal canal Denis zone II injury ≈25% chance of neurologic injury
B4	Any unilateral B subtype that involves fracture of ipsilateral L5–S1 facet joint May impact spinopelvic stability (Isler), thus potentially most unstable of B subtypes

SI, Sacroiliac.

Table 38.7

Type C: Spinopelvic Injuries

Definition
Injuries resulting in spinopelvic instability
Type	Description
C1	Nondisplaced sacral U-type fracture Commonly seen as low-energy insufficiency fracture
C2	Bilateral type B injuries without transverse fracture More unstable and higher likelihood of neurologic injury than C1 but lower than C3
C3	Displaced sacral U-type sacral fracture Worst comminution on instability and likelihood of neurologic injury Displaced transverse sacral fracture = canal compromise

Fig. 38.33, AOSpine Sacral Classification System.

Importantly, the type B category, which classifies the vertical sacral fractures in increasing order of severity, departs from the convention used by Denis and coauthors by classifying vertical fractures medial to the foramina (central sacral fractures) as the least severe (B1), followed by alar fractures entirely lateral to the foramina (B2), followed by fractures which involve the foramina (B3). This was based on both objective data and expert opinion that when considering vertical fracture patterns only, and not complex multiplanar sacral fractures that do not constitute type B fractures in the AO classification, fractures medial to the foramina have the lowest likelihood of neurologic injury and are likely the most stable.

In addition to its morphologic component, the AO classification also has two additional features: neurologic grading and identification of patient modifiers that may affect treatment or prognosis. Classification of the neurologic examination is the same as for all fractures of the spine classified according to the AO system: NX, neurologic examination cannot be obtained; N0, normal neurologic examination; N1, transient neurologic injury; N2, nerve root injury; N3, cauda equina syndrome or incomplete spinal cord injury; N4, complete spinal cord injury. It should be noted that because the spinal cord does not extend caudally to the level of the sacrum, N3 is the most severe possible grade of neurologic injury secondary to sacral fracture. Four patient modifiers have been included in the AO Sacral Fracture Classification, based on their potential to influence treatment and prognosis, as follows: M1 severe (open or closed) soft tissue injury; M2, metabolic bone disease; M3, anterior pelvic ring or acetabular injury; M4, SI joint injury.

By convention, the injury classification is listed, sequentially, according to morphologic grade, neurologic grade, and the presence of any modifiers. As an example, a patient with a high-energy, open sacral U fracture pattern with displaced anterior pelvic ring fracture and incomplete cauda equina syndrome, without metabolic bone disease or SI joint injury, would be classified as having a C3;N3;M1;M3 sacral fracture or, alternatively, a C3;N3 sacral fracture with M1 and M3 modifiers.

Acute Management

The acute management of pelvic ring injuries is inextricably linked with the management of multiple trauma because associated injuries are common due to its high-energy mechanism.

Prehospital Management

The initial evaluation and primary interventions follow ATLS protocols. Preclinical diagnosis of pelvic injury is based on personal or third-party history and clinical findings. Death in unstable pelvic fractures during the first 24 hours is caused by either associated injuries or by hemorrhage, and survival of multiply injured patients is negatively influenced by concomitant pelvic fracture. Therefore fast and reliable diagnosis and appropriate, timely therapy are crucial to the patient's outcome. The emergency physician or paramedic should gather all available information about circumstances and the mechanism of injury.

Diagnostics

During the initial evaluation of the patient, the emergency physician should get an idea of the injury pattern. An awake patient usually reports severe pain in the groin or lower back. Lower limb deformity or shortening without obvious associated lower extremity fracture or dislocation and pelvic motion on stress testing may be present. However, the lower extremity findings may only consist of subtle rotational asymmetry. Additional clinical signs are listed in Table 38.8 .

Table 38.8

Clinical Findings in Patients Suffering From Pelvic Ring Fractures

Pain

Abrasions

Bruises

Effusions

Discolorations

Swelling

Deformity

Shortening of leg

Pelvic asymmetry

Blocking of hip joint

Pulselessness

The clinical examination should include:

evaluation of peripheral perfusion,
evaluation of lower extremity motor function and sensation,
rectal examination to evaluate for sacral root injury and the presence of an open fracture, and
stability testing of the pelvic ring.

Rectal examination: Early detection of neurologic deficits is of paramount importance in patients with sacral fractures. It is particularly important to perform the rectal examination early in the evaluation of all multiply injured patients, even in the absence of obvious sensorimotor deficits in the extremities, to evaluate:

perianal sensation,
anal sphincter tone,
voluntary perianal contraction,
the presence of anal wink, and
the bulbocavernosus reflex.

A straight-leg raise test may detect lumbosacral entrapment in cognitively unimpaired patients.

Extremity motor function and sensation: Extremity motor function is graded on a scale of 0 to 5 according to the American Spinal Injury Association (ASIA) scoring system, and a sensory level is obtained.

Stability testing: For stability testing, the examiner applies lateral, medial, and anterior pressure to the iliac crests and palpates the pubic symphysis and sacral area. As a rule of thumb, an unstable pelvic ring fracture can be expected if a fingerbreadth gap of the pubic symphysis can be palpated and if the iliac wings can be shifted with manual compression. Diagnostic sensitivity is low, though, with a published sensitivity of only 55.9%. However, some authors published both sensitivity and specificity rates of 90%.

Depending on the mechanism of injury, one must be aware of serial injuries (e.g., dashboard injury). Typical serial injuries concomitant with pelvic fractures include calcaneal, ankle, tibial shaft, proximal tibia, femoral shaft and neck, acetabular, and spinal fractures (lumbar and thoracolumbar spine).

Treatment

In accordance with ATLS protocols, immediate lifesaving measures (e.g., release of tension pneumothorax) should be undertaken as needed. Because the most common cause of death in patients with unstable pelvic ring injuries is hemorrhagic shock due to uncontrolled bleeding, an early focus on restoring hemodynamic stability is essential.

Hemorrhagic shock: Trauma-induced hemorrhagic shock is a result of both obvious or occult bleeding and coincident extensive tissue damage, with the release of various inflammatory mediators. However, the initial injury itself usually does not lead to life-threatening bleeding, which appears to be more the result of injury-related coagulopathy, which triggers persistent, uncontrolled bleeding that maintains and intensifies shock. Compared with the established concept that characterizes hemorrhage as a combination of blood loss with dilution and disseminated intravascular coagulation, which is amplified by acidosis and hypothermia (lethal triad), trauma-induced coagulopathy is an independent disorder. Tissue damage and hypoperfusion (shock) endogenously lead to anticoagulant and fibrinolytic processes. Approximately one-quarter of all multiply injured patients have a coagulopathy at the time of admission. Injury severity positively correlates with the risk of early coagulopathy, which likely accounts for more than 40% of patients with an Injury Severity Score (ISS) greater than 30 manifesting symptoms of shock. Early coagulopathy is an independent predictor of morbidity and mortality and is associated with a fourfold increase in overall mortality and an eightfold increase in early mortality (<24 hours) in the presence of multiple injuries. The basic cause of trauma-induced coagulopathy is a function of the injury itself. Therefore therapy and prevention of amplifying factors have to begin as soon as possible, ideally even before hospitalization.

Resuscitation: If a pelvic ring injury is suspected and hemorrhagic shock is manifested, crucial therapeutic actions should be initiated at the scene of injury. Assessment of shock according to ATLS criteria can be challenging and often impossible in this environment, as suggested by data from the German trauma registry (TR-DGU). The use of the shock index, the ratio of heart rate to systolic blood pressure, seems to be more suitable to adequately estimate hypovolemic shock. Besides prevention of hypothermia and hypotension, hemorrhage control is the major concern. Open wounds should be covered with sterile and compressive dressings whenever possible. An alternative, if compression is impossible (e.g., in the groin), is the use of topical hemostatics such as chitosan, a polysaccharide polymer based on chitin. If pelvic ring injury is suspected, pelvic stabilization or even compression is reasonable. Different measures and devices are available.

Internal rotation: Internal rotation of the lower extremities can transmit an internal rotation force to the pelvis and therefore partially reduce the pelvic ring and diminish pelvic volume. Taping the knees and ankles with the limbs in this internally rotated position is therefore one option for temporary pelvic “stabilization.” The tape should be neither applied for excessive periods nor circumferentially to protect the soft tissues and lower extremity perfusion.
Vacuum body splint: Vacuum body splints are easy-to-use, time-saving devices. Their use is not limited to pelvic fractures because they can also be used with lower extremity and spine injuries, and they are usually available at the scene. They can be applied to the patient's flanks to maintain access to the abdomen and groin.
Pelvic circumferential compression device (PCCD): Noninvasive PCCDs are targeted more specifically to the site of injury, and their use has increased over the past decade. A concern with the application of PCCDs has been the potential for soft tissue or visceral injury to pelvic structures such as the bladder, urethra, and vagina because of accentuation of LC injury deformity. However, Bottlang and colleagues demonstrated that such injuries are not likely to occur. Skin lesions have been reported after tight compression and a longer duration of PCCD application. Application of any PCCD is time saving and can be done relatively effortlessly by two people. The device should be ideally positioned at the level of the greater trochanters. A PCCD results in only a slight diminution in the accessibility of the groin and lower abdomen. Furthermore, the position can be changed if access to the groin is necessary. An expeditiously accomplished, improvised alternative is the use of a sheet, which is longitudinally folded and wrapped circumferentially around the pelvis, placed between the iliac crests and greater trochanters. It can be secured either by anterior clamping or by creating a knot with a stick used to twirl and thereby compress the pelvis. Recent literature analysis suggests that PCCDs are effective in the early stabilization of unstable pelvic fractures, although the reasons for their effectiveness have not been fully explained. Although PCCDs may decrease the pelvic volume of open-book injuries, it is debatable whether they are actually able to exert a tamponade effect because the retroperitoneum is disrupted, and reduction in the volume of the true pelvis is much less than expected. For example, a wide pubic diastasis of 10 cm only corresponds to a 35% increase in pelvic volume, or approximately half a liter ( Fig. 38.34 ). Splinting of pathologic pelvic motion is more likely to be the mechanism that aids in hemostasis. However, because nearly all studies are retrospective, prospective data concerning mortality rates and complications are lacking.

$Fig. 38.34, (A and B) A pelvic ring fracture with symphyseal diastasis is treated with a pelvic circumferential compression device (PCCD). The effect of reducing the pelvic volume after application of the PCCD can be anticipated by narrowing of the anterior pelvic ring.$
Pneumatic antishock garment (PASG): The oldest form of emergency pelvic stabilization is the pneumatic antishock garment. This inflatable garment is placed over the lower extremities and around the abdomen and inflated until blood pressure is stabilized. Major concerns pertain to lower extremity compartment syndrome caused by prolonged inflation times. Research done over the years has shown contradictory results, so no recommendation can be made regarding its use as a first-line therapy. Because simpler and lower-priced alternatives are available, PASGs are used only rarely today and are mainly of historical interest.

Prehospital infusion therapy should be done with a balanced, crystalloid, isotonic electrolyte solution with acetate or malate. In the case of exsanguinating hemorrhage, the use of hypertonic 7.5% saline solution should be considered. The target systolic blood pressure should be around 90 mm Hg (permissive hypotension) to avoid potential clot disruption.

After noninvasive temporary pelvic stabilization has been performed and resuscitation is in progress, efficient transfer of the patient to a qualified trauma center is crucial. Appropriate interdisciplinary care, diagnostic evaluation of fracture pattern and associated injuries, and specialized surgical or interventional treatment options are generally available only at specialized hospitals. Whenever possible, direct transfer from the accident scene to a trauma center is preferred. However, if a hemodynamically unstable patient is at risk of not surviving a longer transport, the patient should be transported to the closest medical center and transferred as soon as possible to a trauma center after appropriate resuscitation and temporary hemodynamic stabilization.

Emergency Management

A defined protocol for the treatment of multiply injured patients is useful and helps facilitate and fast-track therapy. The trauma team is interdisciplinary and includes, depending on the healthcare system, a general or trauma or critical care surgeon, an emergency department physician, an anesthesiologist, and an orthopaedic surgeon. Clinicians from other disciplines join the team depending on the specific associated injuries.

Key Points: Acute and Emergency Management

Pelvic ring injuries can cause severe and potentially lethal hemorrhage. Prehospital hemodynamic and biomechanical stabilization of pelvic injuries should be followed by immediate patient transfer to an adequate trauma center.
Stability testing in the case of doubt should not be performed repeatedly but once by an experienced surgeon.
Biomechanical stabilization of the pelvis is of most importance in the case of pelvis-related hemorrhage.
Different expedients are available, which all intend to reduce an externally rotated hemipelvis, which increases the intrapelvic space for hemorrhage. Closing the pelvic ring, however, decreases the intrapelvic space and helps tamponade potential bleeding.
The most popular device used nowadays is the PCCD.
Initial assessment should be standardized by algorithms that everybody on the team is familiar with.
Assessment includes a body check, laboratory tests, and radiographic imaging.
Always be aware of signs of biomechanical and hemodynamic instability. These predetermine further treatment as well as timing.
Although pelvic ring fractures indicate severe trauma, we recommend that if a pelvic ring fracture is suspected or the patient underwent a high-energy injury with potential for pelvic ring fractures, an experienced orthopaedic trauma surgeon should be present.
With the exception of geriatric trauma, pelvic ring fractures require high-energy trauma. Consequently, most patients present with associated injuries. These must not be overlooked.
Associated injuries may require different medical specialists who should be involved early.

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Introduction

Anatomy

Pelvic Stability and Biomechanics

Trauma Mechanism and Pathomechanics of Pelvic Injuries

Trauma Mechanism

Motor Vehicle Accident

Fall From a Height

Osteoporotic Pelvic Fractures of the Elderly

Pathomechanics of Pelvic Injuries

Anterior-Posterior Force Pattern

Lateral Compression Force Pattern

External Rotation-Abduction Force Pattern

Shear Force Pattern

Radiologic Diagnostics in Pelvic Injuries

Plain Radiographs

Anterior-Posterior Radiograph

Inlet Radiograph (Pennal I)

Outlet Radiograph (Pennal II)

Computed Tomography

Magnetic Resonance Imaging

Scintigraphy

Special Imaging of the Symphysis

Classification of Pelvic Injuries

Anatomical Classification

Mechanical Classification

Young and Burgess Classification

AO Classification (Modified Pennal and Tile Classification)

Fractures With Proper Names

Osteoporotic Pelvic Ring Fracture Classification

Sacral Fracture Classification

Denis Classification

Roy-Camille Classification

Isler Classification

Lumbosacral Injury Classification

Acute Management

Prehospital Management

Diagnostics

Treatment

Emergency Management

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