Surgical Treatment of Acetabular Fractures

Radiographs

Pelvic radiology is even more complex than pelvic osteology, but is the essential key to understanding acetabular fractures. Acetabular fracture diagnosis and classification schemes are based on the radiographic findings and Letournel's two-column acetabular concept, which, however, is based on conventional radiographs, not computed tomography (CT) scans, which are currently preferred. An anterior-posterior (AP) radiograph taken early in the workup of a trauma patient often alerts the treating physician to an acetabulum fracture. For this reason, certain radiographic osseous landmarks were introduced by Letournel and still serve as the foundation of acetabular imaging. Many clinicians evaluate the uninjured side initially to review the relevant landmarks and then compare them and their asymmetry with the injured side.

The normal radiographic markers represent bony cortical edges revealed by tangential radiograph beams. These cortical lines include the peripheral edges of both the anterior and posterior walls; the dense line representing the pelvic brim and superior pubic ramus's posterior-cranial edge (iliopectineal line); the dense line representing the pelvic brim and quadrilateral surface (ilioischial line); the dome region's subchondral arc (sourcil); and the acetabular “teardrop” representing the fossa acetabuli, obturator sulcus, and a portion of the quadrilateral surface. These six radiographic markers help clinicians to better understand and mark the two walls, the two supporting columns, the weight-bearing dome, and the caudal joint ( Fig. 39.4 ).

Clinicians should learn about normal acetabular radiology first while holding and handling a pelvic model. The osseous model helps correlate osteology and radiology. Three-dimensional radiographic modeling and volume rendered images capable of on-screen manipulation should also facilitate pelvic and acetabular radiographic correlations and learning. Normal radiology should be mastered first, then the clinician moves on to trying to comprehend displaced fracture imaging:

• Normally, the anterior wall is medially located relative to the more peripheral posterior wall on the AP pelvic film. This is due to the acetabular anteversion. The anterior wall has an undulating edge anatomy attributed to the iliopsoas gutter, iliopectineal eminence, and pectineal cortical sulcus. Imaging of the anterior wall area reveals it to appear more radiodense than the posterior wall because of the superimposed (stacked) osseous anatomy.

• The posterior wall edge anatomy is usually convex and located peripherally relative to the anterior wall.

• The anterior acetabular supporting column is represented on the AP pelvic film by the iliopectineal (iliopubic) line. This radiodense line is formed from tangential imaging of the pelvic brim cortical bone as it extends from the sacroiliac (SI) area to the pubis. The superior and posterior cortical edge of the superior pubic ramus in continuity with the pelvic brim cortical bone form the iliopectineal line. The iliopectineal line representing the supporting acetabular anterior column is only imaged on the AP plain pelvic radiograph.

• The posterior acetabular supporting column is represented on the AP pelvic film by the ilioischial line. This radiodense line is formed from the tangential imaging of the pelvic brim, quadrilateral surface, and medial ischial cortical bone. As with the iliopectineal line, the ilioischial line is only seen on the AP plain pelvic radiograph. When learning Letournel's inverted Y model of the structural anterior and posterior acetabular columns, most students view the hemipelvis and acetabulum from a direct lateral side view. Learning the acetabular structural columnar osteology and its imaging on an AP view is more difficult because now the inverted Y and two supporting osseous columns and their representative radiographic landmarks are viewed obliquely. With a pelvic model in hand and a high-quality AP pelvic image to study, the learning is enhanced. Understanding that the AP pelvic image reveals the structural acetabular columns obliquely and that they are superimposed on one another is the second step to learning the osteology, related radiography, and fracture patterns.

• Normally, the acetabular dome's subchondral arc is seen cranial to and congruent with the femoral head. It represents the weight-bearing area of the articular acetabulum and is vital to assessing hip joint congruity. A variety of acetabular fracture patterns will divide the dome area. In most patterns, the medial portion of the dome will be the displaced fracture fragment and the lateral dome will be the stable or intact part. In other fracture patterns, the medial dome will be stable on the intact pelvis and the lateral dome will be the displaced and unstable fracture fragment. The dome area is also affected by impaction, almost always located on the intact side of the fracture just at the fracture's edge. This crushed articular area along the fracture line is termed marginal impaction. Fracture displacement through the acetabular dome region is very important because accurate operative restoration of the dome articular surfaces and congruity with the femoral head correlate with improved long-term function and durability of the injured hip joint.

• The acetabular “ teardrop ” is probably the most difficult radiographic landmark of the six to understand, but its value is relevant, especially when assessing the accuracy of surgical repair. The medial cortical portion of the teardrop is formed by the obturator neurovascular sulcus and a portion of the quadrilateral surface. The lateral cortical boundary represents the cortical surface of the fossa acetabuli. For certain displaced fracture patterns, the teardrop is no longer recognizable on the AP pelvic film. After operative acetabular fracture repair, the teardrop landmark should be symmetrical to the contralateral normal hip joint. If not, the reduction is not accurate.

These six AP pelvic radiographic acetabular markers represent acetabular supporting columns, walls, and the dome area. On the injured side, depending on the specific fracture details, the walls, columns, and the dome arc may be divided by fracture lines, impacted or displaced along with certain fracture fragments.

Imaging Technique

Once an acetabular fracture is identified, further radiographic assessments are indicated after any dislocations have been reduced. Biplanar imaging is obtained by placing the radiographic cassette beneath the patient's pelvis as for an AP image but then logrolling the patient approximately 45 degrees onto the uninjured side for the film, and then rolling similarly onto the injured side using the same imaging technique. Rolling the patient onto the injured acetabular side usually causes pain and should be performed last. These two biplanar images identify the columns and walls more specifically and are named according to the injured side. When the injured side is rolled up, the obturator foramen is relatively perpendicular to the radiograph beam so the image is termed an “obturator oblique.” The obturator oblique (OO) image demonstrates the structural anterior column and the posterior wall area. Similarly when the injured side is rolled down, the iliac fossa is essentially perpendicular to the radiograph beam, and the image is named an “iliac oblique” view. The iliac oblique (IO) film reveals the anterior wall area and the structural posterior column ( Fig. 39.5 ). These two images are often collectively referred to as Judet views.

Rolling the patient for the oblique images not only causes pain, but also often reveals fracture instability sites that may not have been apparent on the AP plain pelvic film. The oblique acetabular images should not be obtained with the hip dislocated. The displaced fracture fragments and femoral head will obstruct important anatomic landmarks. Whenever the clinical situation allows it, routine reduction maneuvers should be performed before obtaining the oblique films.

Other plain pelvic radiographs, such as inlet and outlet images, are indicated for those patients with pelvic ring injuries coupled with acetabular fractures. Combination pelvic ring–acetabular injuries are common with high-energy injury mechanisms, and inlet and outlet plain pelvic views should be obtained if a concurrent injury is suspected. Certain acetabular fracture patterns, most commonly transverse fractures, may represent the anterior portion of a pelvic ring disruption with combined injuries.

Computed Tomography

Pelvic CT imaging further delineates acetabular injuries and replaces extensive conventional radiograph imaging. Two-dimensional (2D) pelvic CT scans are usually obtained in 5-mm axial slices from the iliac crest to the acetabular dome. From the dome region through the caudal articular areas, 2-mm images are recommended, and then 5-mm axial slices through the ischium. Two-dimensional pelvic CT imaging including axial, coronal, and sagittal reformations provides information regarding bone quality, body habitus, surrounding soft tissue injury, occult posterior pelvic injury, and other acetabular details. Related local osseous findings may include acetabular or femoral head impaction injuries, intraarticular debris, and subtle incongruity, among other findings. If the patient has received an intravenous contrast agent before the scan, the fracture fragments’ displacemen ts and their relationship with the pelvic vascular structures will be highlighted as well as related bleeding sites and accumulations. Displaced anterior column fracture fragments often deform the iliac artery and vein ( Fig. 39.6 ). Medial displacement of quadrilateral surface fracture fragments will usually affect the course of the obturator vessels and nerve. Fractures displaced through the cranial portion of the greater sciatic notch may injure the superior gluteal neurovascular complex. Vascular contrast on the pelvic CT scan also may reveal other relevant vascular anatomy such as the corona mortis vascular conduits and their relationship to the fracture fragments or anticipated surgical exposure. Numerous studies have demonstrated the need for CT when evaluating acetabular fractures.

Recent computer imaging software allows the operator to produce “plain films” from the data acquired during pelvic CT. These surface-rendered pelvic images can then be rotated and manipulated on the monitor to provide the necessary oblique images. The treating physicians must remember that such computer-generated and rotated oblique films are processed data acquired with the injured patient positioned supine in the CT scanner and are not obtained by rolling the patient as the routine oblique films are performed ( Fig. 39.7 ). Because of this, subtle or occult fracture instability will not be identified as it is with the traditional oblique films that apply positional body-weight clinical loading of the acetabular fracture.

Three-dimensional (3D) pelvic CT techniques have been refined, thus improving the model quality and decreasing the radiographic exposure needed. The 3D volume rendered acetabular images provide the treating physician with a more realistic understanding of the overall acetabular pattern and fragment relationships. The displacements and fracture line specifics are revealed on a radiographic model. Such modeling should facilitate understanding and treatment planning. Volume-rendered images allow the surgeon to plan for fracture site access and extent, clamp site application and vectoring, and implant locations. Many surgeons are lured by and may prefer the 3D images solely for obvious reasons but must be aware that certain 3D imaging software packages may smooth some fracture lines. The 2D pelvic CT remains the radiographic standard for acetabular fracture imaging and planning ( Fig. 39.8 ).

Angiography

Pelvic angiography is indicated in hemodynamically unstable patients with acetabular fractures (with or without associated pelvic ring disruption) who have not responded to routine resuscitation techniques and evaluations. The angiographer should access the pelvic arterial tree using the contralateral side from the acetabular injury since fracture displacements may alter the groin vascular anatomy. Similarly, contrast agent leakage or hematoma in the ipsilateral groin area can cause significant dermatitis. These conditions in turn can adversely affect acetabular fracture treatment. Strategic embolizations can be lifesaving but also influence treatment decisions such as surgical exposure choice and have been associated with increased rates of postoperative infection. The embolization procedure and its details should be documented in the permanent medical record. Radiodense metallic coils are commonly used to treat the injured artery, are visible on plain pelvic and CT imaging, and alert the surgeon to the prior embolization procedure. Conversely, other embolic substances are radiolucent and therefore not obvious on routine imaging. The treating surgeon should always consider the injured artery site as well as the level of embolization when planning for surgery. The treating surgeon should also remember that angiographic images are usually multiplanar and of the highest quality. These images should be reviewed whenever possible.

The angiography suite is often an ideal location for closed manipulative reduction of acetabular fracture–dislocations. Typically the patients are amply sedated, and the reductions can be performed under real-time imaging if desired. Using the angiographic imaging equipment, the biplanar oblique plain radiographs can be obtained without moving the patient since the radiographic beam rotates around the patient. Coordinating the closed reduction in the angiography suite requires consent of the patient before anesthesia and consent of the angiography team.

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) has thus far had limited indications in patients with acetabular fractures due to acute trauma. Insufficiency fractures of the peripheral pubic ramus and related acetabular stress fractures have been identified using MRI. Skeletally immature patients in whom cartilaginous portions of the acetabulum have not yet ossified may benefit from MRI, especially after closed reduction of a hip dislocation. Treatment of acetabular injuries with fragments that have not ossified in children should follow the same principles used to treat the injuries in their skeletally mature counterparts. For patients with an open triradiate cartilage, the surgeon should remove any implants that bridge growth plates to allow continued maturation of the acetabulum. We usually remove implants 6 months after the index procedure ( Fig. 39.9 ).

Posterior Wall Acetabular Fractures

The most common fracture pattern occurs in the posterior wall. These injuries tend to occur when the flexed hip loads the posterior wall and a portion of the posterior wall is displaced away from its base. These injuries are often seen after automobile accidents when the seated motorist rapidly decelerates and the flexed knee contacts the dashboard causing the flexed hip to load the posterior acetabular wall to failure. Because of this mechanism, knee-related injuries such as patellar fractures, traumatic arthrotomy, and posterior cruciate ligament injuries are associated with posterior wall acetabular fractures, which sometimes occur in combination with hip dislocations. In drivers contacting the steering mechanism with or without airbag protection, thoracic aortic injuries were previously identified and therefore must be ruled out.

Like all acetabular fractures, posterior wall patterns have a variety of appearances, depending on the limb's position at load, the local bone quality, and the normal anatomy of the acetabulum. Posterior wall acetabular injuries range from superior dome area wall displacements, to more common posterior wall displacements, to more caudal wall displacements, to “barn door” comminuted wall injuries, among other configurations. In some patients, the posterior wall fragment fractures incompletely, and the femoral head crushes several chondrocancellous articular fragments into the intact posterior column cancellous bone, thereby producing an “intraarticular” posterior wall variant fracture–dislocation. Experienced clinicians recognize the variety of posterior wall injuries due to impact loading as well as those seen with the more complex associated acetabular fracture patterns in which the posterior wall fracture fragment is caused by capsular avulsion ( Fig. 39.11 ).

Posterior wall fractures can be comminuted or associated with osteochondral impaction injuries along the fracture margin of the stable posterior column fragment, or they can involve both. Marginal impaction is not the only local chondro-osseous problem related to these fractures. Displaced posterior wall fractures imply that the patient experienced an associated dislocation. For this reason, the femoral head should be evaluated for resultant impaction or cleavage injuries and the hip joint inspected for related bone or chondral debris. Common sites for debris include the fossa acetabuli, between the femoral head and acetabular dome, and between the anterior femoral head and capsule. Debris can be fragments of cartilage, cancellous bone, cortical bone, or any combination of the three. Capsular and labral tissues may also be mislocated within the hip joint and cause joint incongruity.

Routine posterior wall fractures are best identified on the OO image, especially when displaced ( Fig. 39.12 ). Usually, the displaced wall fragment yields in tension caudally along with tearing of the local capsule and labral tissues while the superoanterior labrum and capsule remain intact. The superior cortical aspect of the fracture is often comminuted since it yields in compression as the wall displaces. The displaced posterior wall fracture fragment damages the superior gemellus muscle and the lower portions of the gluteus minimus muscle caudal to the superior gluteal neurovascular bundle as well. With more extensively displaced and dramatic injuries, the piriformis muscle belly can be transected by the displaced wall fragment's sharp cortical edge. In some instances, inspection of the buttock skin will reveal a circular ecchymotic area representative of the femoral head contusion ( Fig. 39.13 ). Not surprisingly, the sciatic nerve may be damaged by direct injury from the displaced wall fragment, the extruded femoral head at the time of dislocation, or by other direct or indirect factors. The piriformis anatomy is variable and its relationship with the sciatic nerve bundles may be responsible for nerve injury also. The sciatic nerve can also escape injury by the fracture–dislocation only to be injured by the reduction maneuver. In these unusual instances, the displaced wall fracture fragment follows the hip reduction and the sciatic nerve becomes compressed between the posterior wall fragment and its base.

Posterior Column Acetabular Fractures

Posterior column fractures occur infrequently but are relatively predictable in their appearance. As an elementary pattern, the fracture plane is singular, descending from the greater sciatic notch, with the lateral cortical disruption splitting the posterior column and posterior wall anatomic areas while the medial cortical line divides the quadrilateral surface. The fracture plane progresses through the dome area, exits the caudal posterior wall and fossa acetabuli, and terminates through the ischium–inferior ramus junction. It is not unusual for dome chondrocancellous pyramidal-shaped fragments to be displaced and associated with this pattern. Similarly, portions of the torn posterior labrum may be mislocated between the femoral head and weight-bearing dome with this fracture pattern. The displaced posterior column fracture fragment may injure the superior gluteal neurovascular bundle, especially when the fracture line is located high in the greater sciatic notch. This is important to remember both before and during surgery because arterial injury may cause ongoing bleeding and require embolization. At surgery, the superior gluteal neurovascular bundle should be visually identified to ensure that it is not displaced between the fracture fragments. If it is displaced, it should be carefully retracted as the fracture is reduced and clamped. Commonly, displaced posterior column fractures obstruct venous flow of the superior gluteal vein, causing its tributaries locally to engorge and dilate throughout the gluteal muscle bellies. These enlarged veins are fragile and often require ligation individually to control bleeding if they tear. It is important to spare the superior gluteal nerve during these ligations. The surgeon must resist the urge to simply apply a large vascular clip that could inadvertently damage the artery, vein, and nerve. Retraction of the proximal vascular bundle into the true pelvis due to either a traumatic or iatrogenic injury usually obviates ligation, so packing is then recommended attempting to control such bleeding. Venous bleeding and often arterial bleeding will respond to packing. The packing material should be applied so that the superior gluteal and sciatic nerves are not inadvertently injured by overly aggressive packing. If the packing fails to control superior gluteal arterial bleeding, prompt wound closure is performed and urgent angiographic evaluation and embolization if possible are advised.

Similar to the superior gluteal neurovascular structures, the sciatic nerve can also be injured by displaced posterior column acetabular fractures. These are usually traction or contusion injuries noted at patient presentation. Some may be related to direct contusion or stretch, and some may be related to piriformis muscle anatomic abnormalities that divide and tether the nerve, making it less able to displace along with the fracture fragment. Sciatic nerve injury can also result from the closed reduction. This occurs because the sciatic nerve course parallels certain displaced posterior column fracture planes and can become trapped within the fracture line as the displaced fracture–dislocation is reduced. This happens rarely but must be remembered and not missed or justified as an injury-related occurrence. For this reason, the prereduction and postreduction nerve assessments are carefully detailed and documented. If the sciatic nerve examination changes after closed reduction of any acetabular fracture, urgent exploration, neuroplasty, and fracture fixation are recommended.

Posterior column acetabular fractures are best seen on the IO and AP plain pelvic radiographs. The pelvic CT scan reveals detailed displacement information and identifies comminution, dome fragmentation, and loose bodies within the joint, as well as impaction injuries that may occur along the fracture line.

Anterior Wall Acetabular Fractures

Anterior wall acetabular fractures are the least common of all types. The unnatural limb position needed to load the anterior wall coupled with the tiny surface area of the anterior wall make this pattern the most unlikely. Simply because of their anatomy, these fractures are quite small and associated with anterior dislocations. The iliac vasculature, femoral nerve, and lateral femoral cutaneous nerve (LFCN) can be injured in association with anterior wall fracture–dislocations.

The anatomic area of the anterior wall is often involved in pelvic ring fractures when the fracture lines of the peripheral superior pubic ramus extend into the anterior wall area. This pelvic ring injury, however, should not be misclassified as an anterior acetabular wall fracture.

Anterior wall acetabular fractures may involve a small portion of the iliopectineal line on the AP film. The OO image may show subluxation of the femoral head, whereas the IO demonstrates the anterior wall fragment displacement.

Anterior Column Acetabular Fractures

Anterior column acetabular fractures disrupt the iliopectineal line on the AP film and have a variety of appearances depending on their peripheral exit points and displacement extents. As an elementary pattern, the fracture plane is singular but may have three distinct surface orientations. These fractures were subclassified according to their iliac exit site. “High” anterior column fractures include those in which the iliac crest is the peripheral exit point. “Intermediate” patterns have their exit points in the region of the anterior superior iliac crest, and “low” patterns exit adjacent to the anterior inferior iliac spine (AIIS). “Very low” patterns only involve the region medial to the IPE. The fracture displacement depends on the subclassification type. The high types have the tensor, abdominal obliques, gluteus medius, and sartorius muscle forces to cause displacement. Because of this displacement, the LFCN may be injured in association with this particular fracture type. On its other end, the fracture exits through the superior ramus. Displacement at the ramus region can injure or deform the iliac vessels and femoral nerve, as well as the obturator neurovascular bundle. It is not difficult to understand why femoral deep venous thrombosis (DVT) occurs for these fractures; however, the risk is increased in all pelvic fracture types. The other patterns have variable deformities depending on the fracture specifics and related deforming forces. Displaced intermediate and low types risk associated femoral and obturator neurovascular injuries. In some patients, the anterior column fracture's exit at the iliac crest is incomplete and demonstrates plastic deformation. The incomplete fracture at the iliac exit site allows deformity but usually lends some degree of fracture stability. This incomplete fracture may need to be osteotomized at surgery to reduce the fracture accurately.

The IO image usually best demonstrates displaced anterior column acetabular fractures. These fractures are often missed on the screening AP film. The IO film reveals the peripheral exit points well, especially for the high patterns. The radiolucent fracture gap along the pelvic brim is also apparent. The femoral head typically remains congruent with the displaced anterior column fracture fragment, which usually indicates a disrupted ligamentum teres ( Fig. 39.14 ). High anterior column acetabular fractures usually have three different planes: the portion that splits the anterior wall area, the portion paralleling the pelvic brim, and the iliac crest exit site. These three planar surfaces allow for strategic reduction clamp and implant applications.

Transverse Acetabular Fractures

Transverse acetabular fractures often confuse clinicians because of their inclusion in the elementary fracture group despite involving the two supporting columns and wall areas. Transverse fracture patterns occur in a variety of orientations and obliquities but remain a singular yet often complex and multiplanar fracture surface. Because of their singular fracture plane “purity,” transverse fractures were included in the elementary group.

A common transverse fracture pattern begins at the anterior wall anatomic area, extends through the iliopsoas gutter and anterior wall articular surface, progresses across the pelvic brim and anterior column, through the quadrilateral surface dividing the upper and lower halves of the fossa acetabuli, and exits the posterior column and posterior wall's edge. The labrum is also usually injured at both the anterior and posterior exit sites, especially in displaced transverse patterns. The torn labrum or portions of it can intrude into the joint, causing further incongruity between the femoral head and intact dome region.

Transverse fractures are the only elementary pattern to extend through both wall areas and both acetabular supporting column zones. The terminology can be confusing because the fracture involves “both of the acetabular columns” but is not an “associated both-column” fracture pattern. As previously stated, fracture patterns and anatomic areas share terminology but should not be confused with each other nor the terms used synonymously.

The transverse pattern splits the acetabulum into two halves. The upper or cephalad half is almost always the stable portion of the fracture, whereas the caudal segment is mobile and displaced. The caudal fragment mobility is due to the fracture plane and the fact that the symphysis pubis ligaments function as a hinge for it ( Fig. 39.15 ).

The acetabular dome is involved to some extent by the transverse fracture plane. Letournel subclassified transverse fractures depending on their dome involvement:

• Transtectal transverse fractures involve the weight-bearing dome.

• Juxtatectal transverse fractures preserve the dome and exit at the junction of the dome and fossa acetabuli.

• Infratectal transverse patterns divide the fossa acetabuli.

Typically, more intact dome before fracture involvement correlates with improved hip stability, congruity, and outcome. In cadaveric mechanical evaluations, step malreductions of transverse acetabular fractures in the superior articular surface resulted in abnormally high contact forces that in clinical practice should predispose to the development of posttraumatic arthritis.

Certain transverse acetabular fractures are associated with intrapelvic displacement of the femoral head along with the caudal fracture fragment. As the fracture displacement occurs, the femoral head can sustain a superolateral impaction fracture and/or the intact upper portion of the acetabular fracture line can be crushed.

In these fractures, the femoral head may remain beneath the weight-bearing dome or follow the caudal segment's displacement depending on several factors. For transtectal patterns, there may be insufficient intact dome laterally for the femoral head to remain stable. Muscular spasm, especially from the iliopsoas muscle, causes further displacement of the femoral head medially and superiorly through the fracture. As the intact dome coverage expands medially with juxtatectal and infratectal transverse patterns, femoral head stability improves.

Transverse acetabular fracture patterns or other associated fracture patterns with a transverse fracture component should alert the treating physician to potential associated pelvic ring injuries, especially ipsilateral SI joint (SIJ) injuries. Careful study of all preoperative imaging is imperative. In these situations, both the upper and lower portions of the transverse fracture are unstable. The upper fracture fragment of such a transverse acetabular fracture pattern is displaced and unstable because the ipsilateral SIJ is disrupted or an unstable ipsilateral sacral fracture is present. In this unusual scenario, the transverse acetabular fracture behaves as an associated both-column acetabular pattern since there is no articular component in continuity with the intact hemipelvis.

Similar to certain posterior column acetabular fractures and their relationship with the sciatic nerve, transverse fractures can also be associated with sciatic nerve injury if the posterior column portion of the transverse fracture plane parallels the nerve pathway ( Fig. 39.16 ).

Transverse Fractures With Associated Posterior Wall Involvement

Transverse with associated posterior wall acetabular fractures are common patterns combining the elementary transverse fracture plane with an additional displaced posterior wall component. The AP film demonstrates both iliopectineal and ilioschial line disruptions, along with the loss of the posterior wall convex edge due to its displacement. Often the displaced wall is noted superimposed on the dome area on this film. If the film is examined carefully, the transverse fracture plane's displacement through the anterior wall area is seen as a lucent gap. On the AP film, the femoral head has several location options with these injuries. The simplest occurs when the femoral head is noted to be congruent with the dome. Another displacement pattern occurs when the femoral head follows the posterior wall displacement. Another pattern occurs when the femoral head follows the transverse caudal segment and is displaced medially. The oblique images are obtained after closed reduction of the femoral head beneath the dome. The IO image shows the exit points of the transverse fracture line in the areas of the posterior column and anterior wall. The OO image demonstrates the anterior column exit point of the transverse fracture as well as the displaced posterior wall fracture fragment and the defect left due to its displacement. It is not unusual in unstable patterns for the femoral head to redislocate as the patient is turned for each image and the body weight or limb weight is applied onto the injury. After closed reduction, an AP film in traction may reveal a previously missed superolateral femoral head impaction fracture. Just as for any fracture that includes a transverse fracture component, the ipsilateral SIJ and sacral areas should be carefully assessed on the radiographs for injuries and displacements.

The pelvic CT scan reveals the transverse fracture orientation, dome area involvement, and specific exit sites, as well as any loose bodies within the joint or marginal impaction associated injuries. Posterior wall comminution is not always obvious on the plain images and is best seen on the CT scan. The CT scan may also confirm femoral head impaction lesions ( Fig. 39.17 ).

Posterior Column Fracture With Associated Posterior Wall Involvement

In these uncommon injuries the ilioischial line is disrupted and the posterior wall defect and displacement are seen on the AP film. The IO image shows the posterior column component's exit through the greater sciatic notch, whereas the OO view identifies the displaced posterior wall fracture fragment. The pelvic CT scan should be examined not only for the specific fracture-related details but also for the local soft tissues. An injury to the superior gluteal artery or vein may cause deep buttock asymmetry or accumulated vascular contrast agent on the scan due to local bleeding. The details cited earlier regarding both posterior column and posterior wall fracture elementary patterns are also relevant here.

Anterior Column Fracture With Associated Posterior Hemitransverse Injury

Acetabular fracture patterns that involve the anterior column as well as associated posterior hemitransverse injuries combine any variety of anterior column fracture with an additional fracture line that splits the posterior column, usually through the greater sciatic notch. Both the iliopectineal and ilioischial lines are disrupted on the plain AP film. The IO pelvic film reveals the anterior column fracture component's exits both along the iliac crest and through the anterior wall area, as well as the posterior hemitransverse fracture component's exit point, usually through the greater sciatic notch. These injuries can be unstable although each fracture component and the oblique radiograph films demonstrate the instability and displacement sites. Just as for anterior column elementary patterns, the anterior column component of the fracture is variable. The posterior hemitransverse component predictably divides the greater sciatic notch. These fractures are common in elderly patients ( Fig. 39.18 ).

T-Type Acetabular Fracture

The T-type acetabular fracture is simply a transverse fracture plane but with the unstable caudal segment split into two individual unstable segments. When viewed laterally, this acetabular fracture pattern is T-shaped. For example, the anterior column portion of the fracture line begins at the anterior wall area and extends along the iliopsoas gutter across the pelvic brim and descends the quadrilateral surface. The posterior column portion of the fracture line begins at the greater sciatic notch and descends to split the posterior wall area and meets the anterior column fracture line at the quadrilateral surface. The fracture line that divides the quadrilateral surface is a common fracture line. It is the vertical fracture line that descends from the transverse component to make this a T-type fracture pattern.

The low anterior column component is unstable due to the symphyseal hinge. The posterior column component is tethered by the sacrospinous and sacrotuberous ligaments. These injuries often have central displacement of the femoral head between the fracture fragments, or the femoral head can remain attached to the posterior column fragment if the ligamentum teres is intact.

On the AP film, both iliopectineal and ilioischial lines are disrupted, and the femoral head may be dislocated away from the intact dome. The ischial fracture may be minimally displaced and not always obvious. The IO image reveals the posterior column exits at the greater sciatic notch and ischial ramus. The OO image identifies the anterior column exit site and displacements. CT details each components location ( Fig. 39.19 ).

Both-Column Acetabular Fracture

The associated both-column acetabular fracture pattern is thought by many surgeons to be the most difficult of all 10 acetabular fracture types. In these injuries, the articular dome and all other articular fracture fragments are without connection to the intact hemipelvis. In all nine other patterns, at least some portion of the articular acetabulum remains attached to the intact hemipelvis. Because of this traumatic fracture-separation of the articular fragments from the stable ilium, some use the term “floating acetabulum” for these patterns. Because this term is misleading and not descriptive, most surgeons do not use it.

Associated both-column acetabular fractures have several consistent fracture fragments. The intact iliac piece is the stable component. Its caudal extent represents the “spur sign,” so named because it resembles a cockspur on the OO image, as the unstable articular fragments displace from it medially. Such medial articular fragment displacements cause the intact ilium's caudal extent (the “spur”) to appear prominent as it remains in its normal site. When seen on the OO film, this spur sign is indicative of an associated both-column acetabular fracture. Inexperienced surgeons may confuse a displaced posterior wall acetabular fracture with the spur sign of an associated both-column fracture since both are seen on the OO image ( Fig. 39.20 ).

When articular fragment displacement is minimal yet there is still no articular connection to the intact iliac segment, no spur sign is obvious, but an associated both-column acetabular fracture pattern is the correct diagnosis. In some patients, the intact iliac caudal extent is obvious even on the AP and IO films, so it is possible to see the spur on these other images. It is easy for the clinician to see that which he or she knows to look for ( Fig. 39.21 ).

Besides the intact iliac component, associated both-column fractures have several other consistent components. The upper anterior column fracture fragment usually contains the majority of the dome and may be incomplete at its iliac crest exit point. If so, the anterior column fragment may be displaced and relatively stable because of the deformed yet incomplete fracture along the crest. The lower anterior column fracture fragment typically includes the articular anterior wall and pubic ramus limbs. The posterior column component typically exits the greater sciatic notch and ischial areas. It is not unusual for the pelvic brim to have some degree of cortical comminution. In some patterns as detailed in the earlier section on posterior wall fracture, the posterior wall fracture component is an avulsion injury due to medial displacement of the proximal femur.

Variant Patterns

Certain acetabular fractures do not fit Letournel's classification system ( Fig. 39.22 ). These variant patterns exist and must be recognized after routine patterns have been ruled out. For example, a T-type fracture pattern may have an associated displaced posterior wall fracture. The “T-type with associated posterior wall” fracture pattern is not an option in the Letournel classification scheme, but this and other variant patterns do occur, and the treating physician needs to be aware of and able to plan treatment for such variant and hybrid fracture patterns. Unusual position of the lower extremity at injury, poor bone quality, or extreme loading conditions are often the causes for these injuries. Variant patterns are assessed and managed routinely. Their fracture specifics may necessitate more detailed planning, more extensile exposure, or special fixation tools. Dramatic impaction injuries for example may demand allograft bone or other suitable material to fill the defects.

Acetabular fractures in association with unstable pelvic ring injuries are included as variant patterns as well ( Fig. 39.23 ). When acetabular fractures are encountered in combination with injury to the pelvic ring, the surgeon must assess the injuries in a detailed fashion as planning and sequencing are important. An early malreduction of the posterior or anterior pelvic ring may prevent accurate articular reduction of the acetabular fracture; open approaches to ipsilateral sacral fractures or SIJ disruptions may be chosen to ensure the posterior ilium is anatomically positioned before acetabular reduction and fixation.