1. HIP DISLOCATIONS

    

    

    

    

   EPIDEMIOLOGY

2. Up to 50% of patients sustain concomitant fractures elsewhere at the time of hip dislocation.

3. The majority of hip dislocations occur in 16- to 40-year-old males involved in motor vehicle accidents.

4. Almost all posterior hip dislocations result from motor vehicle accidents.

5. Unrestrained motor vehicle accident occupants are at a significantly higher risk for sustaining a hip dislocation than passengers wearing a restraining device.

6. Anterior dislocations constitute 10% to 15% of traumatic dislocations of the hip, with posterior dislocations accounting for the remaining majority.

7. The incidence of femoral head osteonecrosis is between 2% and 17% of patients, whereas 16% of patients develop posttraumatic arthritis.

8. Sciatic nerve injury is present in 10% to 20% of posterior dislocations (Fig. 27.1).

    

    

    

   ANATOMY

9. The hip articulation has a ball-and-socket configuration with stability conferred by bony and ligamentous restraints, as well as the congruity of the femoral head with the acetabulum.

10. The acetabulum is formed from the confluence of the ischium, ilium, and pubis at the triradiate cartilage.

11. Forty percent of the femoral head is covered by the bony acetabulum at any position of hip motion. The effect of the labrum is to deepen the acetabulum and increase the stability of the joint.

12. The hip joint capsule is formed by thick longitudinal fibers supplemented by much stronger ligamentous condensations (iliofemoral, pubofemoral, and ischiofemoral ligaments) that run in a spiral fashion, preventing excessive hip extension (Fig. 27.2).

     

     

     

13. The main vascular supply to the femoral head originates from the medial and lateral femoral circumflex arteries, branches of the profunda femoral artery. An extracapsular vascular ring is formed at the base of the femoral neck with ascending cervical branches that pierce the hip joint at the level of the capsular insertion. These branches ascend along the femoral neck and enter the bone just inferior to the cartilage of the femoral head. The artery of the ligamentum teres, a branch of the obturator artery, may contribute blood supply to the epiphyseal region of the femoral head (Fig. 27.3).

     

     

     

14. The sciatic nerve exits the pelvis at the greater sciatic notch. A certain degree of variability exists in the relationship of the nerve with the piriformis muscle and short external rotators of the hip. Most frequently, the sciatic nerve exits the pelvis deep to the muscle belly of the piriformis.

    MECHANISM OF INJURY

15. Hip dislocations almost always result from high-energy trauma, such as a motor vehicle accident, fall from a height, or an industrial accident. Force transmission to the hip joint results from one of three common sources:

    • The anterior surface of the flexed knee striking an object

    • The sole of the foot, with the ipsilateral knee extended

    • The greater trochanter

16. Less frequently, the dislocating force may be applied to the posterior pelvis with the ipsilateral

    foot or knee acting as the counterforce.

17. Direction of dislocation—anterior versus posterior—is determined by the direction of the pathologic force and the position of the lower extremity at the time of injury.

    Anterior Dislocations

18. These injuries result from external rotation and abduction of the hip.

19. The degree of hip flexion determines whether a superior or inferior type of anterior hip dislocation results.

    • Inferior (obturator) dislocation is the result of simultaneous abduction, external rotation, and hip flexion.

    • Superior (iliac or pubic) dislocation is the result of simultaneous abduction, external rotation,

      and hip extension.

      Posterior Dislocations

20. These comprise 85% to 90% of traumatic hip dislocations.

21. They result from trauma to the flexed knee (e.g., dashboard injury), with the hip in varying degrees of flexion.

    • If the hip is in the neutral or slightly adducted position at the time of impact, a dislocation without acetabular fracture will likely occur.

    • If the hip is in slight abduction, an associated fracture of the posterior–superior rim of the

      acetabulum usually occurs.

      CLINICAL EVALUATION

22. A full trauma survey is essential because of the high-energy nature of these injuries. Many patients are obtunded or unconscious when they arrive in the emergency room as a result of associated injuries. Concomitant intra-abdominal, chest, and other musculoskeletal injuries, such as acetabular, pelvic, or spine fractures, are common.

23. Patients presenting with dislocations of the hip typically are unable to move the lower extremity and are in severe discomfort.

24. The classic appearance of an individual with a posterior hip dislocation is a patient in severe pain with the hip in a position of flexion, internal rotation, and adduction. Patients with an anterior dislocation hold the hip in marked external rotation with mild flexion and abduction. The appearance and alignment of the extremity, however, can be dramatically altered by ipsilateral extremity injuries.

25. A careful neurovascular examination is essential because injury to the sciatic nerve or femoral neurovascular structures may occur at time of dislocation. Sciatic nerve injury may occur with stretching of the nerve over the posteriorly dislocated femoral head. Posterior wall fragments from the acetabulum have the potential to injure the nerve. Usually, the peroneal portion of the nerve is affected, with little, if any, dysfunction of the tibial nerve. Rarely, injury to the femoral artery, vein, or nerve may occur as a result of an anterior dislocation. Ipsilateral knee, patella, and femur

    fractures are common. Pelvic fractures and spine injuries may also be seen.

    RADIOGRAPHIC EVALUATION

26. An anteroposterior (AP) radiograph of the pelvis is essential, as well as a cross-table lateral view of the affected hip.

27. On the AP view of the pelvis:

    • The femoral heads should appear similar in size, and the joint spaces should be symmetric throughout. In posterior dislocations, the affected femoral head will appear smaller than the normal femoral head (closer to plate = less magnification). In anterior dislocation, the femoral head will appear slightly larger.

    • The Shenton line should be smooth and continuous.

    • The relative appearance of the greater and lesser trochanters may indicate pathologic internal or external rotation of the hip. The adducted or abducted position of the femoral shaft should also be noted.

    • One must evaluate the femoral neck to rule out the presence of a femoral neck fracture before any manipulative reduction.

28. A cross-table lateral view of the affected hip may help distinguish a posterior from an anterior

    dislocation.

29. Use of 45-degree oblique (Judet) views of the hip may be helpful to ascertain the presence of osteochondral fragments, the integrity of the acetabulum, and the congruence of the joint spaces. Femoral head depressions and fractures may also be seen.

30. Computed tomography (CT) scans may be obtained following closed reduction of a dislocated hip. If closed reduction is not possible and an open reduction is planned, a CT scan should be obtained to detect the presence of intra-articular fragments and to rule out associated femoral head and acetabular fractures.

31. The role of magnetic resonance imaging in the evaluation of hip dislocations has not been established; it may prove useful in the evaluation of the integrity of the labrum and the vascularity of the femoral head.

    CLASSIFICATION

    Hip dislocations are classified based on (1) the relationship of the femoral head to the acetabulum and (2) whether or not associated fractures are present.

    Thompson and Epstein Classification of Posterior Hip Dislocations (Fig. 27.4)

    Type I: Simple dislocation with or without an insignificant posterior wall fragment

    Type II: Dislocation associated with a single large posterior wall fragment

    Type III: Dislocation with a comminuted posterior wall fragment

    Type IV: Dislocation with fracture of the acetabular floor

    Type V: Dislocation with fracture of the femoral head (Pipkin classification)

     

     

     

    Epstein Classification of Anterior Hip Dislocations (Fig. 27.5)

    Type I: Superior dislocations, including pubic and subspinous

    IA: No associated fractures

    IB: Associated fracture or impaction of the femoral head

    IC: Associated fracture of the acetabulum

    Type II: Inferior dislocations, including obturator, and perineal

    IIA: No associated fractures

    IIB: Associated fracture or impaction of the femoral head

    IIC: Associated fracture of the acetabulum

     

     

     

    Orthopaedic Trauma Association Classification of Hip Dislocations See Fracture and Dislocation Classification Compendium at http://www.ota.org/compendium/compendium.html.

    TREATMENT

32. One should reduce the hip on an urgent basis to minimize the risk of osteonecrosis of the femoral head; it remains controversial whether this should be accomplished by closed or open methods. Most authors recommend an immediate attempt at a closed reduction, although some believe that all fracture-dislocations should have immediate open surgery to remove fragments from the joint and to reconstruct fractures.

33. The long-term prognosis worsens if reduction (closed or open) is delayed more than 12 hours. Associated acetabular or femoral head fractures can be treated in the subacute phase.

Closed Reduction

Regardless of the direction of the dislocation, the reduction can be attempted with in-line traction with the patient lying supine. The preferred method is to perform a closed reduction using general anesthesia, but if this is not feasible, reduction under conscious sedation is possible. There are three

popular methods of achieving closed reduction of the hip:

1. Allis Method. This consists of traction applied in line with the deformity. The patient is placed supine with the surgeon standing above the patient on the stretcher or table. Initially, the surgeon applies in-line traction while the assistant applies countertraction by stabilizing the patient’s pelvis. While increasing the traction force, the surgeon should slowly increase the degree of flexion to approximately 70 degrees. Gentle rotational motions of the hip as well as slight adduction will often help the femoral head to clear the lip of the acetabulum. A lateral force to the proximal thigh may assist in reduction. An audible “clunk” is a sign of a successful closed reduction (Fig. 27.6).

    

    

    

2. Stimson Gravity Technique. The patient is placed prone on the stretcher with the affected leg hanging off the side of the stretcher. This brings the extremity into a position of hip flexion and knee flexion of 90 degrees each. In this position, the assistant immobilizes the pelvis, and the surgeon applies an anteriorly directed force on the proximal calf. Gentle rotation of the limb may assist in reduction (Fig. 27.7). This technique is difficult to perform in the emergency department.

    

    

    

3. Bigelow and Reverse Bigelow Maneuvers. These have been associated with iatrogenic femoral neck fractures and are not as frequently used as reduction techniques. In the Bigelow maneuver, the patient is supine, and the surgeon applies longitudinal traction on the limb. The adducted and internally rotated thigh is then flexed at least 90 degrees. The femoral head is then levered into the acetabulum by abduction, external rotation, and extension of the hip. In the reverse Bigelow maneuver, used for anterior dislocations, traction is again applied in the line of the deformity. The hip is then adducted, sharply internally rotated, and extended.

   • Following closed reduction, AP pelvis radiographs should be obtained to confirm the adequacy of reduction. The hip should be examined for stability while the patient is still sedated or under anesthesia. If there is an obvious large displaced acetabular fracture, the stability examination need not be performed.

     • If possible, stability is checked by flexing the hip to 90 degrees in neutral position under fluoroscopy. A posteriorly directed force is then applied. If any sensation of subluxation is detected, the patient will require additional diagnostic studies and possibly surgical exploration or traction.

     • Following successful closed reduction and completion of the stability examination, the patient should undergo CT evaluation.

Open Reduction

• Indications for open reduction of a dislocated hip include:

  • Dislocation irreducible by closed means

  • Nonconcentric reduction

  • Fracture of the acetabulum or femoral head requiring excision or open reduction and internal fixation

  • Ipsilateral femoral neck fracture

• A standard posterior approach (Kocher–Langenbeck) will allow exploration of the sciatic nerve, removal of posteriorly incarcerated fragments, treatment of major posterior labral disruptions or instability, and repair of posterior acetabular fractures.

• An anterior (Smith–Peterson) approach is recommended for isolated femoral head fractures. A concern when using an anterior approach for a posterior dislocation is the possibility of complete vascular disruption. By avoiding removal of the capsule from the femoral neck and trochanters (i.e., taking down the capsule from the acetabular side), the lateral circumflex artery is preserved.

• An anterolateral (Watson–Jones) approach is useful for most anterior dislocations and combined fracture of both femoral head and neck.

• A direct lateral (Hardinge) approach will allow exposure anteriorly and posteriorly through the same incision.

• In the case of an ipsilateral displaced or nondisplaced femoral neck fracture, closed reduction of the hip should not be attempted. The hip fracture should be provisionally stabilized through a lateral approach. A gentle reduction is then performed, followed by definitive fixation of the femoral neck.

• Management after closed or open reduction ranges from short periods of bed rest to various durations of skeletal traction. No correlation exists between early weight bearing and osteonecrosis. Therefore, partial weight bearing is advised.

  • If reduction is concentric and stable: A short period of bed rest is followed by protected weight bearing for 4 to 6 weeks.

  • If reduction is concentric but unstable: Operative intervention should be considered, followed

    by protective weight bearing.

    PROGNOSIS

• The outcome following hip dislocation ranges from an essentially normal hip to a severely painful and degenerated joint.

• Most authors report a 70% to 80% good or excellent outcome in simple posterior dislocations. When posterior dislocations are associated with a femoral head or acetabular fracture, however, the associated fractures generally dictate the outcome.

• Anterior dislocations of the hip are noted to have a higher incidence of associated femoral head injuries (transchondral or indentation types). The only patients with excellent results in most authors’ series are those without an associated femoral head injury.

  COMPLICATIONS

• Osteonecrosis (AVN): This is observed in 5% to 40% of injuries, with increased risk associated with increased time until reduction (>6 to 24 hours); however, some authors suggest that osteonecrosis may result from the initial injury and not from prolonged dislocation. Osteonecrosis may become clinically apparent several years after injury. Repeated reduction attempts may also increase its incidence.

• Posttraumatic osteoarthritis: This is the most frequent long-term complication of hip

  dislocations; the incidence is dramatically higher when dislocations are associated with acetabular fractures or transchondral fractures of the femoral head.

• Recurrent dislocation: This is rare (<2%), although patients with decreased femoral anteversion may sustain a recurrent posterior dislocation, whereas those with increased femoral anteversion may be prone to recurrent anterior dislocations.

• Neurovascular injury: Sciatic nerve injury occurs in 10% to 20% of hip dislocations. It is usually caused by a stretching of the nerve from a posteriorly dislocated head or from a displaced fracture fragment. Prognosis is unpredictable, but most authors report 40% to 50% full recovery. Electromyographic studies are indicated at 3 to 4 weeks for baseline information and prognostic guidance. If no clinical or electrical improvement is seen by 1 year, surgical intervention may be considered. If a sciatic nerve injury occurs after closed reduction is performed, then entrapment of the nerve is likely and surgical exploration is indicated. Injury to the femoral nerve and femoral vascular structures has been reported with anterior dislocations.

• Femoral head fractures: These occur in 10% of posterior dislocations (shear fractures) and in 25% to 75% of anterior dislocations (indentation fractures).

• Heterotopic ossification: This occurs in 2% of patients and is related to the initial muscular damage and hematoma formation. Surgery increases its incidence. Prophylaxis choices include indomethacin for 6 weeks or use of radiation.

• Thromboembolism: This may occur after hip dislocation owing to traction-induced intimal injury to the vasculature. Patients should be given adequate prophylaxis consisting of compression stockings, sequential compression devices, and chemoprophylaxis, particularly if they are placed in traction.