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Acute Osseous Injury to the Hip and Proximal Femur
Radiologic Anatomy of the Proximal Femur
A thorough knowledge of radiologic anatomy and anatomic variations of the proximal femur is required for interpreting hip studies. Although excellent descriptions of femoral anatomy are readily available in classic textbooks, volume-rendered multidetector computed tomography (MDCT) images provide an optimal opportunity for reviewing the topic.
The proximal femur is formed by the head, the neck, the greater and lesser trochanters, the intertrochanteric region, and the proximal shaft ( Fig. 22-1 ). The femoral head is globular in shape and reaches two thirds of a sphere. It shows a smooth contour, outlined by two or three curved lines. The femoral head is partially covered by the acetabulum on its most anterior aspect. The subcapital physeal scar lies near the head-neck junction. The anterior aspect of the femoral neck is almost flat, except for the so-called reaction area. An extension of the articular cartilage into the anterior femoral neck is common and has been termed Poirier's facet. The anterior trochanteric line shows a variable degree of development and is more prominent in the elderly. The tubercle for the iliofemoral ligament is seen on top of the anterior intertrochanteric line.
The posteromedial view of the proximal femur shows the posterior aspect of the femoral head and neck, but also the greater and lesser trochanters, the trochanteric fossa, the linea aspera, the quadrate tubercle, and the posterior intertrochanteric crest ( Fig. 22-2 ). The greater trochanter is quadrilateral, broad, rough, and convex. The lesser trochanter is a conical eminence with rough surface that projects from the lower and back part of the base of the neck. The quadrate tubercle of the femur lies at the junction of the upper and middle thirds of the intertrochanteric crest.
A basic radiographic survey of the hip joints includes anteroposterior (AP) and oblique-axial (frog-leg) views. An AP radiograph of the hip ( Fig. 22-3 ), performed in slight internal rotation of the limb, offers the best representation of the proximal femur. However, external rotation of the lower limb may occur, particularly in an emergency setting, limiting the evaluation of the femoral neck. The anterior head-neck junction, the reaction area, and the anterior intertrochanteric line, easy to identify on a coronal volume-rendered MDCT image, are poorly represented on the AP plain film. Conversely, the posterior intertrochanteric crest cannot be appreciated on the anterior coronal MDCT reconstruction. On the greater trochanter, the lateral facet and the ridge for insertion of the gluteus minimus muscle are seen. The anterior aspect of the free margin of the greater trochanter lies lateral to the posterior aspect. The trochanteric fossa is seen as a small depression at the base of the greater trochanter.
On the oblique-axial (frog-leg) view ( Fig. 22-4 ), anterior structures such as the iliofemoral ligament tubercle, the anterior intertrochanteric line, and the ridge for the insertion of the vastus lateralis lie laterally. Conversely, posterior structures such as the posterior head-neck junction, the quadratus femoris tubercle, the internal calcar septum, and the lesser trochanter lie medially.
Alternative projections such as Lauenstein, Hickey, and Dunn may be attempted. On both frog-leg and Lauenstein views, the free margin of the greater trochanter may project on the head-neck junction, depending on degree of hip flexion, obliquity of central beam incidence, and other factors (see eFig. 22-1 ).
In an emergency setting, projections requiring hip flexion should be systematically avoided and substituted by a true lateral (cross-table) view. On the lateral (cross-table) view ( eFig. 22-2 ), which is performed with horizontal beam and contralateral hip flexion, the anterior structures of the proximal femur tend to alineate. On the posterior aspect, the quadratus femoris tubercle is more prominent than the lesser trochanter.
In spite of efficient radiographic technique, emergency radiographs of the hip are often difficult to interpret. The radiographic appearance of the hip joint is highly dependent on technical and anatomic factors. Complex superimposition of bony contours in occasionally suboptimal radiographic projections may cause diagnostic dilemmas. Several anatomic features and variations may be particularly challenging.
On AP radiographs, the anterior and posterior acetabular rims project on the femoral head ( eFig. 22-3 ). The acetabular notch, at the caudal aspect of the acetabulum, is continuous with a circular nonarticular depression, the acetabular fossa. The margins of the notch serve for the attachment of the ligamentum teres. On AP radiographs, the posterior rim of the acetabular notch, more prominent and caudal than the anterior rim, commonly projects on the inferior aspect of the femoral head. In severe acetabular anteversion, the anterior acetabular rim projects on the upper aspect of the femoral head, which may mimic subchondral fracture or avascular necrosis. In coxa profunda, protrusio acetabuli, or hip osteoarthritis, the posterior rim may project on the head-neck junction, which should not be misinterpreted as a subcapital fracture ( eFig. 22-4 ).
The physeal interface of the head-neck junction and greater trochanter is commonly identified during late adolescence. However, a physeal scar may persist into adult life as a thin sclerotic line ( eFig. 22-5 ). Although physeal scars rarely cause diagnostic difficulties, they may superimpose with other radiographic lines (acetabular rims, fovea capitis, head-neck junction), leading to confusing images.
The configuration of the head-neck junction is highly variable. On a small proportion of individuals the anterior border of the femoral head shows a gently convex contour. More commonly, an extension of the articular surface of the femoral head into the anterior aspect of the femoral neck is present, which is generally known as the Poirier's facet. This is sometimes confused with the so-called reaction area. Special consideration should be given to the capsular ridge. It is transverse to the long axis of the neck, parallel to the anterior intertrochanteric line, and distant from that line about 1.5 cm. When present, it may mimic an incomplete stress fracture ( Fig. 22-5 ).
The anterior intertrochanteric line is hard to appreciate on AP radiographs of the hip but is usually seen on axial and lateral projections. In the elderly, the anterior intertrochanteric line is particularly prominent and occasionally shows a cortical spread-out that should not be misinterpreted as pathologic ( Fig. 22-6 ).
The internal calcar septum or femoral thigh spur is a cortical septum in the region of the lesser trochanter of the human femur ( Fig. 22-7 ). Within the cancellous bone, the femoral spur starts at the point where the neck joins the shaft, just external to the lesser trochanter, and extends in the direction of the digital fossa. The internal calcar septum reinforces the medial arc of the proximal femur. Intertrochanteric fractures involving the calcar avis may cause instability. Also, osteoporotic resorption of the thigh spur may contribute to the high incidence of proximal femoral fractures in the elderly.
The spatial orientation of the bony trabeculae within the proximal femur influences the distribution of fracture lines. The Ward triangle is an anatomic area of decreased density in the trabecular pattern of the femoral neck ( eFig. 22-6 ). The Ward triangle is radiographically evident and is commonly affected by fracture lines in the elderly. The orientation of the trabecular pattern may be significantly disturbed in the diseased or dysplastic hip ( eFig. 22-7 ). For example, the increase of femoral neck angle (coxa valga) leads to formation of more compression trabeculae following a longitudinal axis. These distortions may help radiographic examination, but also cause interpretation dilemmas.
Identification of soft-tissue folds around the head-neck junction, femoral neck, and trochanteric region is usually straightforward ( eFig. 22-8 ). However, these inguinal folds may occasionally be misinterpreted as fracture lines. Conversely, and more importantly, inguinal and other soft-tissue folds may occult or distract from true fractures. Consequently, a close scrutiny of bone structures underlying soft-tissue folds around the hip is mandatory in an emergency setting.
The gluteal, iliopsoas, and obturator fat pads, which delineate the respective muscles surrounding the hip, should be seen as distinct and straight lines. Convexity of a fat pad implies distention of the hip joint with fluid. Routine identification of normal fat pads may help exclude hip fractures. However, the fat pads are inconsistently seen on plain films ( eFig. 22-9 ).
Subcapital collar osteophytes may mimic fracture lines around the head-neck junction. This is particularly true on scintigraphy, where linear increased uptake around the femoral neck can simulate a femoral neck fracture. This false positive may have potentially serious consequences, as it may precipitate urgent hip surgery ( eFig. 22-10 ).
General Considerations
Fractures of the proximal femur, loosely referred to as hip fractures, are particularly common in the elderly population and are associated with high mortality rates and great socioeconomic impact. In this age group, more than 90% of hip fractures result from low-energy trauma or minor falls. Osteoporosis remains the single most relevant predisposing factor, although other bone and systemic disorders also increase the risk of hip fracture.
Hip fractures are less frequent in young or middle-aged patients. In this age group, hip fractures and dislocations are generally caused by high-energy trauma and frequently associated with coexistent orthopedic, neurologic, or visceral complications. In these patients, true avulsion fractures of the greater and lesser trochanter may also occur as the result of forceful muscle contraction.
Stress fractures, which are classified as fatigue and insufficiency fractures, can also involve the proximal femur. Fatigue fractures occur in young athletic individuals who undergo unaccustomed strenuous activities. Insufficiency fractures involve obese or overweight patients, frequently osteoporotic females. The term pathologic fracture is usually reserved for fractures involving bone weakened by tumor.
Conventional radiographs allow efficient detection of most hip fractures and dislocations. Occasionally, MDCT, MR imaging, and bone scintigraphy may be required for further evaluation. Advanced imaging is particularly useful for confirming a suspected injury, excluding associated lesions (such as pelvic fractures), or assessing treatment options. Diagnostic imaging strongly influences prognosis and treatment of hip fractures and dislocations by providing precise assessment of injury patterns.
We review acute osseous injuries to the hip and proximal femur, including hip dislocations and fractures of the femoral head, femoral neck, greater and lesser trochanters, intertrochanteric region, and subtrochanteric area. We also discuss pathologic fractures of the proximal femur. Emphasis is put on the widely accepted role of conventional radiographs for routine work-up of hip fractures and dislocations, but also on the complementary aid provided by classic bone scintigraphy and modern cross-sectional imaging.
Traumatic Hip Dislocations and Femoral Head Fractures
Prevalence, Epidemiology, and Definitions
Traumatic hip dislocations are uncommon injuries, accounting for 2% to 5% of all joint dislocations. Failure to promptly recognize them may delay reduction, which increases the risk of osteonecrosis of the femoral head. Hip dislocations typically derive from high-energy trauma. However, in children and young adults, hip dislocations may occasionally arise from minor trauma, due to ligamentous laxity. Traumatic hip dislocations are classified as posterior and anterior. Central hip dislocations may also occur but are usually considered a modality of acetabular fracture.
Anatomy (Including Gross Anatomy and Normal Variants)
The hip joint is a large ball-and-socket synovial joint. The round head of the femur articulates with the cuplike acetabulum. The depth of the acetabulum is increased by the fibrocartilaginous labrum. The joint capsule is reinforced by strong ligaments, which extend from the acetabular rim to the anterior intertrochanteric line and posterior femoral neck. The sciatic nerve is in close relationship with the posterior capsule. The femoral head is irrigated by arterial branches originating at the anterior and posterior circumflex arteries, but also by a branch of the obturator artery coursing through the ligamentum teres, the foveal artery. Most hip dislocations lead to disruption of ligamentum teres and joint capsule, although labral tears, muscle injuries, fractures, and neural damage may also occur.
Biomechanics
The degree of hip flexion, the direction of the applied forces, and the individual's anatomy influence the injury pattern, leading to posterior, anterior-superior, and anterior-inferior dislocations (see Fig. 22-8 ). Most hip dislocations occur in a posterior direction, which typically derive from dashboard trauma. In this injury pattern, violent longitudinal forces act on a flexed knee and hip. With very slight degrees of hip flexion and adduction, there is increased probability of posterior acetabular fracture. An iliofemoral ligament disruption may also occur. Anterior hip dislocations represent only 11% of all hip dislocations and may occur in a superior or inferior direction. In inferior-anterior dislocation, which occurs with forced abduction, external rotation, and flexion of the hip, the femoral head extrudes beneath the pubofemoral ligament. In superior-anterior hip dislocation, which occurs following forced abduction, external rotation, and extension of the femur, the femoral head extrudes between the iliofemoral and the pubofemoral ligaments. However, pubofemoral ligament disruption may also occur.
Manifestations of the Disease
Most patients with hip dislocation present in severe distress after a high-energy trauma. Associated neurologic and visceral injuries are common. Coexistent fractures of the spine, pelvis, and extremities are also possible and should always be ruled out. Direct vascular compromise or major sciatic nerve dysfunction may occur.
Radiographic
Imaging Techniques
In the acute setting, AP radiographs of the pelvis may show the hip dislocation and suggest the injury pattern in most patients. Occasionally, lateral and oblique views of the hip may be required to confirm the diagnosis, suggest the direction, or depict associated injuries. Conventional radiographs may be occasionally supplemented by CT when reduction becomes difficult or associated injuries are not clearly shown. After reduction, conventional radiographs are used to confirm the adequacy of reduction. These should always be supplemented by CT for assessing loose body entrapment, acetabular fracture, joint instability, or surgical indications.
Imaging Findings
In AP views of posterior hip dislocations, the femoral head typically lies superior to the acetabulum (iliac), the femur is found in adduction and internal rotation, and the lesser trochanter is less visible than usual ( Fig. 22-9 ). If the femoral head lies immediately behind the acetabulum, hip dislocation may be more difficult to detect in AP views. However, the femoral head will appear smaller than usual, and dislocation may be confirmed with a groin-lateral view. More rarely, purely inferior hip dislocations (luxatio erecta) may occur.
An acetabular fracture is found in up to 60% of posterior hip dislocations ( Fig. 22-10 ). Posterior acetabular fractures are best evaluated with oblique or lateral views, may radiographically mask hip dislocation, and may interfere with closed reduction. When acetabular fracture is radiographically detected, a CT scan should be obtained before closed reduction.
Osteochondral impaction fractures of the femoral head commonly occur in posterior hip dislocations (see Fig. 22-9 ). They appear as subtle areas of focal flattening at the lateral aspect of the femoral head, may be easily overlooked on plain films, and significantly increase the risk of posttraumatic osteoarthritis.
After closed reduction, special attention should be paid to subtle widening of the joint space, caused by interposition of bony or soft-tissue fragments. At this stage, plain films should always be supplemented by cross-sectional imaging (see eFig. 22-11 ).
Femoral head fractures may also occur in posterior hip dislocation, with a simple or comminuted appearance. Although several classifications have been suggested, the most commonly used is the scheme proposed by Pipkin ( Table 22-1 ; Figs. 22-11 and 22-12 ). Associated fractures of the femoral neck and shaft may also occur and should be systematically ruled out before closed reduction, in order to avoid further displacement.
TABLE 22–1
Pipkin Classification of Posterior Hip Dislocations Associated with Femoral Head Fracture
| Type I | Posterior hip dislocation with associated femoral head fracture below the fovea |
| Type II | Posterior hip dislocation with associated femoral head fracture above the fovea |
| Type III | Posterior hip dislocation with associated femoral head and neck fractures |
| Type IV | Types I, II, or III with associated posterior acetabular fracture |
During follow-up, conventional and cross-sectional imaging may also be used to detect potential complications, such as osteonecrosis of the femoral head, degenerative osteoarthritis, joint instability, or heterotopic ossification, which may cause up to 50% of unfavorable outcomes.
Other associated musculoskeletal injuries include vertebral fractures and posterior cruciate ligament injuries ( Box 22–1 ).
Box 22–1
Associated Injuries in Posterior Hip Dislocation
-
Vertebral fracture
-
Pelvic fracture
-
Posterior acetabular fracture
-
Osteochondral impaction fracture of the femoral head
-
Femoral head fracture
-
Femoral neck fracture
-
Femoral diaphysis fracture
-
Cruciate ligament injury
-
Sciatic nerve dysfunction
In anterior-inferior hip dislocation, the femoral head overlies the ischium and obturator foramen ( Fig. 22-13 ), and an avulsion of the anterior inferior iliac spine may occur. In anterior-superior hip dislocation, which represents barely 1% of all hip dislocations, the femoral head overlies the medial or lateral aspect of the acetabulum, leading to pubic or iliac dislocations, respectively. A superior-anterior dislocation may be occasionally misinterpreted as a posterior dislocation. However, in superior-anterior hip dislocation, the lesser trochanter appears particularly prominent, owing to the external rotation of the femur, and the femoral head may become slightly magnified on AP radiographs. In addition, anterior hip dislocations may present with chondral and osteochondral impaction fractures of the posterolateral aspect of the femoral head ( Fig. 22-14 ; Table 22-2 ).
TABLE 22–2
Topographic Classification of Anterior Hip Dislocations
| Obturator | Inferior-anterior dislocation with the femoral head overlying the obturator foramen |
| Pubic | Superior-anterior dislocation with the femoral head overlying the medial acetabulum |
| Iliac | Superior-anterior dislocation with the femoral head overlying the lateral acetabulum |
| Inferior | Luxatio erecta |
Classifications of anterior and posterior hip dislocations have been condensed in a more global scheme, such as that suggested by Levine ( Table 22-3 ).
TABLE 22–3
Levine Classification of Hip Dislocations
| Type I | Hip dislocation without associated fracture or instability |
| Type II | Unreductible hip dislocation without associated fracture |
| Type III | Hip dislocation with limited congruence, instability, or loose bodies after closed reduction |
| Type IV | Hip dislocation associated with acetabular fracture that requires surgical treatment |
| Type V | Hip dislocation associated with femoral head or neck fracture |
Computed Tomography
After closed reduction, intraarticular entrapment of bony fragments is more easily identified on CT scans. In addition, CT scans allow an accurate assessment of the extent and significance of posterior acetabular fractures. CT scans are also accurate for detecting osteochondral impaction fractures of the femoral head, which increase the risk of posttraumatic osteoarthritis. Complex, displaced fractures of the femoral head are also better evaluated with CT.
Magnetic Resonance Imaging
Although CT has traditionally been used to supplement conventional radiographs in the diagnostic work-up of hip dislocations, MR imaging may also be valuable in various regards. MR imaging is very accurate in detecting osteochondral impaction fractures of the femoral head (see eFig. 22-12 ) and associated soft-tissue injuries (see eFig. 22-13 ). It is also valuable in detecting intraarticular labral entrapment. In children, MR imaging may help discriminate the real extent of posterior acetabular fracture, which is of prognostic significance. In addition, MR imaging is far superior to other imaging techniques in detecting secondary osteonecrosis of the femoral head. Consequently, either CT or MR scans should be performed on a routine basis following closed reduction of hip dislocations for assessing congruence, stability, and related injuries ( Table 22-4 ).
TABLE 22–4
Cross-Sectional Imaging in Hip Dislocation
| CT | MR | |
|---|---|---|
| Joint congruency | +++ | +++ |
| Soft-tissue injury | + | +++ |
| Chondral loose bodies | + | +++ |
| Bony loose bodies | +++ | + |
| Acetabular fracture assessment | +++ | ++ |
| Contusion of the femoral head | + | +++ |
| Osteochondral impaction fracture of the femoral head | ++ | +++ |
| Fracture of the femoral head | +++ | ++ |
| Avascular necrosis of the femoral head | + | +++ |
Nuclear Medicine
Bone scintigraphy has traditionally been used to assess the vascularity of the femoral head after hip dislocations or proximal femoral fractures. However, previous investigations have shown the inability of isotopic bone scan for diagnosing or predicting osteonecrosis of the femoral head in the early stages. The emerging role of MR imaging has dramatically decreased the use of bone scintigraphy in this regard.
Classic Signs of Hip Dislocation
Posterior dislocation
-
Femoral head small and superiorly displaced
-
Adduction and internal rotation
-
Decreased prominence of lesser trochanter
-
Anterior-lateral osteochondral impaction fracture of the femoral head
-
Common posterior acetabular fracture
-
Possible avascular necrosis
Anterior dislocation
-
Femoral head enlarged and superiorly or inferiorly displaced
-
Abduction and external rotation
-
Increased prominence of lesser trochanter
-
Posterior-lateral osteochondral impaction fracture of the femoral head
-
Common avulsion fracture of the anterior inferior iliac spine
-
Rare avascular necrosis
Differential Diagnosis
Clinical Diagnosis
From a clinical standpoint, traumatic hip dislocations are hard to distinguish from fractures of the hip and proximal femur. In addition, it should be kept in mind that many of these fractures may coexist with hip dislocation and should be systematically ruled out.
Radiologic Diagnosis
The radiographic detection of hip dislocation is usually straightforward, although posterior hip dislocations without cranial displacement of the femoral head may be occasionally overlooked. The true diagnostic dilemma in hip dislocations is distinguishing anterior from posterior dislocations and detecting associated injuries that may alter management and prognosis. In this regard, the complementary role of cross-sectional imaging may be crucial.
Treatment Options
Medical
Closed reduction of traumatic hip dislocations should be performed within 6 hours of injury, in order to decrease the risk of osteonecrosis and posttraumatic osteoarthritis. Nonsurgical management is preferred for joints that demonstrate adequate congruence and stability after closed reduction.
Surgical
Blocking of concentric reduction after traumatic hip dislocation may be caused by associated acetabular fracture or by interposition of labrum, capsule, ligamentum teres, or intraarticular hematoma. In these patients, open reduction is required in the acute setting, in order to avoid complications. After reduction, congruency and stability of the hip joint are important factors determining the need for operative stabilization. In particular, fractures involving more than 40% of the posterior acetabulum may cause joint instability, thus requiring internal fixation in order to prevent osteoarthritis. Large femoral head fractures also require internal fixation.
Subchondral Insufficiency Fractures of the Femoral Head
Prevalence, Epidemiology, and Definitions
Traumatic femoral head fractures typically associate with hip dislocations. Isolated femoral head fractures are rare and commonly occur in young patients. Femoral head fractures that occur in the absence of major trauma have been termed subchondral insufficiency fractures. These injuries, which represent a rare type of stress fracture, are found in osteoporotic, overweight patients and renal transplant recipients. They may also occur in competitive or recreational athletes and be termed fatigue fractures.
Anatomy (Including Gross Anatomy and Normal Variants)
The subchondral bone of the weight-bearing portion of the femoral head is mainly supplied by the lateral epiphyseal arteries and is particularly prone to avascular necrosis. A major compressive group of reinforcing trabeculae is found at the subchondral region of the femoral head, whereas the weakest point is located within the femoral neck, also termed the Ward triangle. This explains why the femoral neck is much more prone to stress fractures than the subchondral region of the femoral head.
Biomechanics
Subchondral insufficiency fractures of the femoral head vary with different body constitutions and levels of physical activity. Progressive imbalance between bone resorption and bone repair following mechanical overload may lead to weakening of cortical bone, further propagation of cracks through cement lines, and eventual microfractures, which may subsequently lead to insufficiency fractures.
Pathology
Insufficiency fractures usually involve the weight-bearing portion of the femoral head and may or may not extend through the articular cartilage. Microscopic examination of subchondral insufficiency fractures of the femoral head has revealed a small area of necrosis between the fracture and the articular surface, with a fracture callus along the fracture line. However, a well-defined area of wedge-shaped osteonecrosis is typically absent. Consequently, this band of subchondral osteonecrosis has been considered a secondary phenomenon, resulting from subchondral fracture.
Manifestations of the Disease
Symptoms of insufficiency fracture of the femoral head are characterized by sudden onset of pain, which progressively worsens. Some cases of femoral head fracture may resolve spontaneously. However, in some other patients the disease progresses, associating with increasing pain and motility restriction of the hip joint.
Radiographic
Imaging Findings
Osteoporosis may be apparent on plain films of patients suffering insufficiency fractures of the femoral head. However, the radiographic appearance of the involved femoral head may be unremarkable. Three to 4 months after the onset of pain, some collapse of the superolateral portion of the femoral head may occur. Narrowing of the joint space and areas of mixed increased and decreased bone density in the collapsed subchondral portion are present. Occasionally, an insufficiency fracture of the femoral head may be followed by rapid destruction of the hip joint, once the subchondral collapse has occurred.
Magnetic Resonance Imaging
On T1-weighted MR images, a subchondral low-intensity band is usually seen, which lies parallel to the articular surface and may have a serpentine or undulated contour. This finding is believed to represent the fracture line and associated repair tissue. On T2-weighted or fat-suppressed sequences, a pattern of bone marrow edema is usually observed, with diffuse high signal intensity that extends from the superolateral part of the femoral head to the femoral neck or intertrochanteric region ( Fig. 22-15 ). As the disease progresses, subchondral collapse of the femoral head may occur, but subsequent resolution of the low-intensity band with complete preservation of the femoral head may also be observed.
Nuclear Medicine
Bone scintigraphy may demonstrate global increased uptake of the affected femoral head, commonly extending into the femoral neck. This nonspecific appearance may be difficult to interpret and is also possible in other traumatic, inflammatory, or degenerative disorders of the hip region.
Classic Signs of Subchondral Insufficiency Fractures of the Femoral Head
Conventional radiographs
-
Normal during the first 3 months
-
Mixed altered radiodensity
-
Superolateral collapse of the femoral head
-
Occasional rapid destruction of the hip joint
Bone scintigraphy
-
Increased uptake of the femoral head
MR imaging
-
Subchondral low-intensity band of undulated contour on T1-weighted MRI
-
Bone marrow edema of the femoral head and neck on T2-weighted MRI
-
May simulate avascular necrosis of the femoral head
Differential Diagnosis
From Clinical Data
Insufficiency fractures of the femoral head should be differentiated from other conditions, including degenerative osteoarthritis as the leading cause of hip pain and disability in the elderly population. From a clinical standpoint, insufficiency fractures of the femoral head cannot be distinguished from other more usual stress fractures of the pelvic region, including those involving the sacral wing, the pubic bones, and the femoral neck. Avascular necrosis of the femoral head may also cause hip pain and disability but usually occurs in a younger age-group, usually in patients with history of corticosteroid intake or alcohol abuse. Transient osteoporosis of the hip may also present similar clinical manifestations but is more frequent in pregnant or puerperal young women.
From Diagnostic Techniques
Imaging plays a major role in the differential diagnosis of subchondral insufficiency fractures of the femoral head ( Table 22-5 ).
TABLE 22–5
Differential Diagnosis of Subchondral Insufficiency Fractures of the Femoral Head
| Degenerative hip osteoarthritis | Asymmetric joint space narrowing and subchondral bone sclerosis Osteophytic proliferation Subchondral geodes may collapse |
| Other regional stress fractures | More common than femoral head fractures in osteoporotic patients Commonly occult on conventional radiographs Clear indication for bone scintigraphy or MRI |
| Avascular necrosis | No or minimal radiographic signs in early stages Subchondral hypointensity contour concave to the articular surface Spontaneous progression to femoral head collapse and osteoarthritis |
| Rapidly destructive coxarthrosis | Rapid progression to femoral head collapse and osteoarthritis Simulates avascular necrosis stage IV Potential relationship with insufficiency fractures |
| Transient osteoporosis | Osteoporosis selectively involving the proximal femur Bone marrow edema without subchondral hypointensity Spontaneous resolution without femoral head collapse |
The radiographic manifestations of degenerative osteoarthritis include asymmetric joint space narrowing, subchondral bone sclerosis, osteophytic proliferation, and subchondral geodes. Large geodes may undergo collapse, rarely simulating avascular necrosis or insufficiency fracture.
Stress fractures of the sacrum, pubic bones, and femoral neck are much more common than insufficiency fractures of the femoral head and may be hard to detect on plain films. At present, MR imaging is the technique of choice when occult fractures of the pelvis and hip are suspected.
In early stages, avascular necrosis and insufficiency fracture show no radiographic findings or minimal osteoarthritic changes. Both conditions also show similar MR findings. However, in classical osteonecrosis, the shape of the low-intensity band is usually concave to the articular surface, whereas it is typically bandlike, or slightly undulating, in insufficiency fracture. In addition, the subchondral low-intensity band may resolve in insufficiency fracture, which rarely occurs in avascular necrosis.
In advanced stages, insufficiency fractures of the femoral head may lead to femoral head collapse and secondary osteoarthritis, which is also possible in avascular necrosis stages III to IV and also in rapidly destructive osteoarthritis of the hip joint. Occasional case reports have suggested that there may be some causal or conceptual relationship between these conditions. In practical terms, an accurate distinction is crucial before femoral head collapse. After the onset of bone collapse, the etiologic diagnosis will fail to influence treatment.
Transient osteoporosis of the hip may also simulate insufficiency fracture of the femoral head on MR images. However, in typical transient osteoporosis, a pattern of bone marrow edema of the proximal femur will rarely be associated with a subchondral low-intensity band. Radiographic follow-up of transient osteoporosis usually reveals recovery of bone density within months, but femoral head collapse is not expected to occur.
Treatment Options
Medical
Insufficiency fractures of the femoral head are initially treated by conservative measures, including nonsteroidal anti-inflammatory drugs. A crutch or walker may be sometimes recommended and help to decrease mechanical loads on the femoral head.
Surgical
Although conservative treatment is initially undertaken, subchondral insufficiency fracture of the femoral head may also be as devastating as avascular necrosis or rapidly progressive osteoarthritis of the hip joint, leading to femoral head collapse and severe loss of articular congruence. In these severe cases, total hip replacement is usually required.
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