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Hip dislocations

Introduction

Traumatic hip dislocations (not including those after hip arthroplasty) are almost always due to high energy trauma.  Unrestrained MVA passengers are more likely to have a hip dislocation that restrained passengers.  The classic mechanism for posterior dislocation is during a dashboard injury (hip and knee are in flexion and an axial load transmitted posteriorly through the femur).  Anterior dislocations result from external rotation and abduction of the hip. Posterior dislocations account for approximately 90%; anterior dislocations account for approximately 10%. Concomitant injuries should be expected.  Sciatic nerve injury is present 10-20% of the time, and up to half of patients sustain another fracture. 

Anatomy

The hip joint capsule consists of thick longitudinal fibers in addition to much stronger ligamentous condensations (iliofemoral, ischiofemoral, and pubofemoral).  Forty percent of the femoral head is covered by the bony acetabulum, and the labrum increases the coverage and the stability of the joint.  The sciatic nerve passes directly posterior to the hip joint and is therefore susceptible to injury in posterior dislocations.

Classification

Hip dislocations are classified based on the head / acetabulum relationship and by the presence of associated fractures. 

Posterior hip dislocations are described by the Thompson and Epstein Classification:

  • Type I - Simple dislocation with or without an insignificant posterior wall fragment
  • Type II - Dislocation 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

Anterior hip dislocations are described by the Epstein Classification:

  • Type I - Superior dislocations (pubic and subspinous locations)

            A - No associated fractures

            B - Associated fracture or impaction of the femoral head

            C - Associated fracture of the acetabulum

  • Type II - Inferior dislocations (obturator and perineal locations)

            A - No associated fractures

            B - Associated fracture or impaction of the femoral head

            C - Associated fracture of the acetabulum

The AO/OTA classification for hip dislocations (JOT supplement, November/December 2007) is presented below.  Associated fractures are coded separately.

30A - dislocation of the hip

            1 - Anterior

            2 - Posterior

            3 - Medial or central (fracture through acetabulum)

            4 - Obturator

            5 - Other

Presentation

The classic deformity in a posterior hip dislocation is hip flexion, internal rotation, and adduction.  The patient is typically is severe pain and cannot move the involved lower extremity.  Many are obtunded or unconscious.  Other common injuries include chest and abdominal injuries, acetabular, pelvic, spine, and ipsilateral lower extremity fractures. 

Diagnosis

A full trauma survey is essential.  A neurovascular examination should include evaluation of the sciatic nerve (tibial portion most often affected) and femoral nerve/artery.

An AP radiograph of the pelvis and a cross-table lateral of the affected hip are necessary.  Both femoral heads should appear the same size.  On an AP, if the femoral head on the suspected side appears larger, it is likely anterior.  Shenton's line should be continuous.  Once the diagnosis of hip dislocation has been verified by x-ray, one should evaluate the rest of the limb and pelvis to make sure that reduction maneuvers will not cause greater harm.  For instance, in an unstable pelvis, large traction forces may increase the disruption in the pelvis and can lead to higher mortality secondary to bleeding.  Also, a non-displaced femoral neck fracture that is discovered on x-ray can be stabilized with cannulated screws prior to hip reduction under general anesthesia. 

CT scans are typically obtained after reduction, unless open reduction is required.  This is to detect the presence of intra-articular fragments and rule out femoral head, neck, and acetabular fractures. 

Treatment

Closed reduction, if possible, should be achieved on an emergent basis due to the risk of osteonecrosis.  Regardless of the direction of the dislocation, the reduction can be attempted with the patient in supine position and by applying in-line traction.  General anesthesia is preferred; however, more often closed reduction under sedation is performed in the emergency room.  There are several methods described.  In the Allis method, the surgeon stands on the stretcher.  By pulling just below the knee, he/she applies traction in line with the femur.  The assistant applies counter traction by pushing downward on both ASIS's.  With steady increasing traction, the hip is flexed to ~70 degrees.  Adduction and gentle internal and external rotation of the hip help the hip pass across the lip of the acetabulum. A lateral directed force may also help.  This can be applied with an assistant's hands on the upper thigh, or with a sheet wrapped around the ipsilateral groin and pulled in a lateral and superior direction.  Stability should be checked 

Indications for open reduction:

  • Unable to obtain closed reduction
  • Noncencentric reduction
  • Fracture of acetabulum or femoral head requiring excision or ORIF
  • Ipsilateral femoral neck fracture

The Kocher-Langebeck approach is best for posterior work.   An anterior Smith-Peterson approach is often best for femoral head fractures.  The anterolateral Watson-Jones approach is useful for anterior dislocations with fractures of the femoral head and neck.  A direct lateral Hardinge approach allows for posterior and anterior exposure.

Complications

Complications of hip dislocations include:

  • Post-traumatic arthritis   most common - incidence is increased with acetabular or femoral head fractures
  • Osteonecrosis                 (5-40%) risk is increased with increasing duration of dislocation
  • Sciatic nerve injury         (10-20%) usually caused by stretch; recovery unpredictable, but most report ~50% full recovery
  • Femoral head fractures    (10% in posterior dislocations; 25-75% in anterior dislocations)
  • Recurrent dislocation       (2%)
  • Heterotopic ossification    (2%)
  • Deep vein thrombosis

Outcomes

The outcome is variable from normal function without pain to severely painful and debilitating.  For simple posterior dislocations, ~75% good or excellent outcomes have been reported.  In both anterior and posterior dislocations, expect worse outcomes when concomitant acetabular or femoral head fractures exist.

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