AAOS Comprehensive Orthopaedic Review

Section 6 - Trauma

Chapter 54. Hip Dislocations and Femoral Head Fractures

I. Hip Dislocations

A. Epidemiology


1. 90% of dislocations of the hip are posterior, most often secondary to motor vehicle accidents (MVAs) and knee-to-dashboard trauma with a posterior directed force.


2. Right hip involved much more often than left in MVAs


B. Anatomy/surgical approaches


1. Anatomy


a. Strong capsular ligaments—The anterior iliofemoral and posterior ischiofemoral ligament run from the acetabulum to the femoral neck (

Figure 1).


b. The ligamentum teres runs from the acetabulum (cotyloid fossa) to the femoral head (fovea centralis).


c. The main arterial blood supply is from the superior and posterior cervical arteries, which are primarily derived from the medial circumflex artery (posterior); the lesser blood supply (10% to 15%) is through the artery of the ligamentum teres (

Figure 2).


2. Surgical approaches—For irreducible dislocations, "go where the money is."


a. Posterior approach (Kocher-Langenbeck)—Allows access to posterior dislocations.


b. Anterior approach (Smith-Petersen)—Allows access to anterior dislocations and also better visualization of the anterior joint.


c. Anterolateral approach (Watson-Jones)—Allows access to the posterior hip through the same incision.


   *Robert F. Ostrum, MD, is a consultant for or an employee of DePuy and Biomet.


C. Mechanism of injury


1. Anterior dislocations


a. Result from an abduction and external rotation force


b. A flexed hip leads to an inferior (obturator) dislocation; an extended hip results in a superior (pubic) dislocation.


[Figure 1. The hip capsule and its thickenings (ligaments) as visualized from anteriorly (A) and posteriorly (B).]

[Figure 2. The vascular supply to the femoral head arises from the medial and lateral circumflex vessels, which create a ring giving rise to the cervical vessels. A minor contribution comes from the obturator artery via the ligamentum teres.]

c. Femoral head impaction or osteochondral fractures are commonly seen.


2. Posterior dislocations


a. Most commonly seen after dashboard injuries, where the knee hits the dashboard, resulting in a posteriorly directed force through the femur


b. The presence of an associated fracture as well as the location and extent of the fracture are dictated by the flexion, abduction, and rotation of the hip joint at the time of the impact. Increased flexion and adduction favor a pure dislocation without fracture of the posterior wall.


D. Clinical evaluation


1. High incidence of associated injuries (up to 95%) in patients with a hip dislocation secondary to MVA


2. Anterior dislocations present with the leg in a flexed (inferior) or extended (superior), abducted, and externally rotated attitude.


3. Posterior hip dislocations present with the limb in an adducted and internally rotated position.


4. Common associated injuries include those around the ipsilateral knee secondary to direct trauma.


a. Patella fractures


b. Ligamentous tears and dislocations (posterior)


c. Bone bruises


d. Meniscal tears


5. Sciatic nerve injury may be seen in up to 8% to 20% of patients; a thorough neurologic examination should precede any attempts at reduction. Prereduction and postreduction neurologic examinations should be documented.


E. Imaging evaluation


1. Standard AP radiograph shows dislocation of the femoral head.


a. The attitude of the limb and appearance of the femoral head can distinguish an anterior from a posterior dislocation.


b. In posterior dislocations, the femoral head appears small and is located superiorly, whereas with anterior dislocations the femoral head appears larger and overlaps the medial acetabulum or the obturator foramen.


2. Judet views (iliac and obturator oblique)


a. Can help with diagnosing the location of the dislocation but also assist in identifying associated transverse or posterior wall fractures


b. The obturator oblique view gives the best picture of the posterior dislocation and the posterior wall.


3. CT scans are necessary following all reductions of hip dislocations.


a. Important information gained from this study includes:


i. Concentric reduction


ii. Bony or cartilaginous fragments in the joint


iii. Associated fractures


iv. Marginal impaction of the posterior wall


v. Avulsion fractures


vi. Femoral head or neck fractures


b. The percentage of posterior wall fracture can also be calculated. Assess need for internal fixation on postreduction CT scan. Identify size of posterior wall fragment and dome involvement. More than 25% involvement of the posterior wall is an indication for fixation.


4. Prereduction CT scans


a. Reserved for irreducible dislocations in an attempt to determine the block to reduction


b. Obtaining these CT scans before reduction in simple dislocations or fracture-dislocations provides little information and may lead to prolonged dislocation and concomitant osteonecrosis or sciatic nerve or cartilage injury.


F. Classification


1. Hip dislocations are classified as anterior or posterior.


2. Further clarification that also helps with prognosis is gained by using the Thompson-Epstein classification (

Table 1).


G. Treatment


1. Preoperative—Abduction pillows are usually sufficient for postreduction stability while awaiting surgery. Skeletal traction is reserved for patients with instability or dome involvement.


2. Closed reduction


a. Prompt closed reduction as an emergent procedure should be the initial treatment.


b. Adequate pharmacologic muscle relaxation is necessary.


c. Reduction is performed by using traction in line with the thigh, with the extremity in an adducted attitude, and with countertraction exerted on the pelvis. Avoid forceful reduction, which can lead to femoral head or neck fractures.


d. Once reduction is successful, abduction with external rotation and extension should maintain reduction for posterior dislocations. For anterior dislocations, the limb is maintained in extension, abduction, and either neutral or internal rotation. Traction is indicated for unstable injuries or for those with dome involvement.


e. Irreducible dislocations are seen in 2% to 15% of patients with these injuries.


i. Irreducible anterior dislocations are due to buttonholing through the capsule or soft-tissue interposition.


ii. In posterior dislocations, the piriformis, gluteus maximus, capsule, labrum, or a bony fragment can prevent reduction.


[Table 1. Thompson-Epstein Classification of Hip Dislocations]

f. If one or two attempts at closed reduction with sedation are unsuccessful, then an emergent open reduction is necessary.


g. A CT scan should be done before open reduction to determine pathology.


h. Nonconcentric reductions can be missed even with careful scrutiny of postreduction radiographs of the hip. Postreduction CT is mandatory to assess the hip joint following reduction.


3. Surgical treatment


a. Indications


i. Irreducible dislocations


ii. Nonconcentric reductions


iii. Unstable hip joints


iv. Associated femoral or acetabular fractures


b. Stability determination


i. Stress testing under anesthesia is controversial.


ii. Do not assess hip stability after reduction with range of motion. No real parameters have been established for stability, and further damage to cartilage or nerves may occur.


c. Open reduction or internal fixation should be performed through an approach from the direction of the dislocation.


i. Posterior dislocations: Kocher-Langenbeck approach is used.


ii. Anterior dislocations: An anterior (Smith-Petersen) or anterolateral (Watson-Jones) approach is used.


H. Rehabilitation


1. Early mobilization


2. Avoid hyperflexion with posterior dislocations for 4 to 6 weeks.


3. Immediate weight bearing for simple dislocations


4. Delayed weight bearing with large posterior wall or dome fracture fixation


I. Complications


1. Posttraumatic arthritis develops in 15% to 20% of patients due to cellular cartilage injury, non-concentric reduction of hip, articular displacement, marginal impaction. Posttraumatic arthritis can develop years after the initial injury.


2. Osteonecrosis develops in approximately 2% to 10% of patients reduced within 6 hours.


a. The rate of osteonecrosis increases with a delay in reduction.


b. Osteonecrosis usually appears within 2 years after the injury but is evident at 1 year in most patients.


3. Sciatic nerve injury affects the peroneal division.


a. Seen in 8% to 19% of posterior dislocations


b. More common with fracture-dislocations than simple dislocations


4. Redislocation reported in 1% of dislocations


5. Myositis around the hip is uncommon after posterior dislocation.

II. Femoral Head Fractures

A. Epidemiology


1. Femoral head fractures occur in 6% to 16% of patients with posterior hip dislocations.


2. May be the result of impaction, avulsions, or shear fractures


3. Anterior dislocations are more commonly associated with impaction of the femoral head.


4. Produced by contact of the femoral head on the posterior rim of the acetabulum at the time of dislocation


5. The location and size of the fracture and degree of comminution are a result of the position of the hip at the time of dislocation impact.


B. Anatomy/surgical approaches—Same as for hip dislocations, described in section I. B.


C. Mechanism of injury/clinical evaluation—Same as for hip dislocations, described in section I. C.



Figure 3. Pipkin classification of femoral head fractures. A, Infrafoveal fracture, Pipkin type 1. B, Suprafoveal fracture, Pipkin type II. C and D, Intrafoveal fracture or suprafoveal fracture associated with femoral neck fracture, Pipkin type III. E, Any femoral head fracture configuration associated with an acetabular fracture, Pipkin type IV.]

D. Imaging evaluation


1. Radiographs—AP and Judet views of the acetabulum, both prereduction and postreduction.


2. CT scan—2-mm sections through the acetabulum. CT scans should be obtained postreduction only because delay in reduction caused by waiting for a CT scan can lead to further damage to the femoral head blood supply or possible sciatic nerve injury.


E. Classification—The Pipkin classification system is used for femoral head fractures (Figure 3)


F. Treatment—Based on fragment location, size, displacement, and hip stability (

Table 2)


[Table 2. Treatment of Femoral Head Fractures Based on the Pipkin Classification]

G. Rehabilitation


1. Immediate early range of motion of the hip with weight bearing delayed for 6 to 8 weeks is recommended.


2. Stress strengthening of the abductors and quadriceps


3. Radiographs after 6 months to evaluate for osteonecrosis and arthritis


H. Complications


1. Anterior approach associated with decreased surgical time, better visualization, improved fracture reduction, and no osteonecrosis but an increase in heterotopic ossification compared with posterior approach. Heterotopic ossification is extra-articular and rarely clinically significant.


2. Osteonecrosis related to a delay in hip dislocation reduction


a. Impact of anterior surgical incision on osteonecrosis is unknown.


b. Occurs in 0% to 23% of patients


c. Patients should be counseled about this complication preoperatively.


3. Fixation failure associated with osteonecrosis or nonunion


4. Posttraumatic arthritis seen as a result of joint incongruity or initial cartilage damage


5. Decreased internal rotation is commonly seen after these femoral head fractures, but it may not be a clinical problem or cause disability.


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Top Testing Facts

Hip Dislocations

1. Assess hip stability, intra-articular fragments, and concentric reduction on postreduction CT scan of the hip.


2. Check postreduction CT scan for marginal impaction of the posterior wall.


3. Assess need for internal fixation on postreduction CT scan. Identify size of posterior wall fragment and dome involvement. Anything over 25% involvement of the posterior wall is an indication for fixation.


4. Good relaxation is required with attempted closed reduction of posterior hip dislocations. Avoid forceful reduction, which can lead to femoral head or neck fractures.


5. Document the neurologic examination before and after reduction.


6. In most patients, osteonecrosis is evidenced at 1 year following injury. Arthritis can develop later.


7. Check the ipsilateral knee in posterior dislocations to assess for ligamentous or other injury.


Femoral Head Fractures

1. Assess good quality radiographs with Judet views preand postreduction for femoral head fractures. Diagnosis can be made on postreduction CT scan.


2. There is no need for prereduction CT scan, and leaving the hip dislocated for a longer period can lead to further damage to the femoral head blood supply or possible sciatic nerve injury.


3. It is important to identify whether the femoral head fracture is suprafoveal (weight bearing) or intrafoveal.


4. Usually a Smith-Petersen approach to the hip is used for fixation, with a periacetabular capsulotomy to preserve blood supply.


5. Femoral head fracture is easier to see and fix through an anterior approach with countersunk or headless screws.


6. With a large posterior wall fracture (Pipkin type 4), a Kocher-Langenbeck approach can be used with subluxation or dislocation of the femoral head. This will allow access to the femoral head for fracture reduction and fixation.


7. Small fragments or foveal avulsion fractures can be excised through a posterior approach when associated with a posterior wall fracture.


8. Decreased internal rotation is commonly seen after femoral head fractures, but this may not be a clinical problem or cause disability.