Uncommon injury usually requiring high-energy mechanism.

1. 
   

   Ninety to 95% of patients have concomitant injuries.

Four types of dislocations—posterior, anterior, obturator, and medial.

1. 
   

   Ninety percent are posterior, 10% are anterior, and < 1% are obturator dislocations.

   
   
2. 
   

   Medial dislocations through the fossa acetabulum are seen with complex acetabular fractures or with severe rheumatoid arthritis.

Timely reduction is critical to limit the risk of avascular necrosis (AVN) and for preservation of hip function.

The primary goal in treatment is obtaining urgent concentric reduction and maintaining stability.

Dislocations of the hip are often associated with fractures of the femoral head, acetabulum, and femoral neck. Partial or full-thickness delamination of cartilage with or without femoral head impaction are expected with any injury (▶Video 32.1).

History and physical examination

1. 
   

   The alert patient will be in significant discomfort, will typically refuse to move the injured extremity, and may complain of numbness in the affected extremity.

   
   
2. 
   

   Patients can have “distracting injuries” and may be repeat offenders.

   
   
3. 
   

   Patients with a traumatic hip dislocation warrant a trauma surgery evaluation. Advanced Trauma Life Support (ATLS) protocol ensures a full and complete workup for these patients.

   
   
4. 
   

   Observe the position of the affected leg.

   
   
   
   
   1. 
      

      Posterior dislocations—the hip will be held in flexion, internal rotation, and adduction. It may also be shorter than the other leg (▶ Fig. 32.1 , left hip).

      

      
      
   2. 
      

      “Irreducible” posterior fracture-dislocations—the hip will be held in flexion, adduction, and neutral rotation.

      
      
   3. 
      

      Obturator dislocations—the hip will be held in extension, external rotation, and significant abduction (▶ Fig. 32.1 , right hip). It is a variant of an anterior dislocation where the femoral head is inferior as opposed to superior in a pubic ramus dislocation.

      
      
   4. 
      

      Anterior dislocations—the hip will be held in mild flexion, external rotation, and abduction (▶ Fig. 32.2 ).

      

      
      
   5. 
      

      Medial fracture dislocation (protrusion)—the limb will be shortened and with some abduction.

   
   
5. 
   

   The physical exam must include the entire affected lower extremity from the pelvis and hip joint to the foot.

   
   
6. 
   

   It is very important to document a detailed neurovascular exam, if possible, prior to any reduction attempt.

   
   
   
   
   1. 
      

      The sciatic nerve is most commonly affected. Peroneal division is affected more often than the tibial division.

      
      
   2. 
      

      Lower extremity nerve function should be documented pre and post reduction.

   
   
7. 
   

   Ligamentous knee injuries, distal femur fractures, and patella fractures are associated with dashboard injuries and posterior hip dislocations.

Anatomy

1. 
   

   The hip joint is made up of the pelvic acetabulum and the femoral head.

   
   
   
   
   1. 
      

      The acetabulum is an articular surface formed by the convergence of the ilium, ischium, and pubis.

      
      
   2. 
      

      The femoral head articulates with the acetabulum and is attached to the cotyloid fossa by the ligamentum teres.

   
   
2. 
   

   The hip joint is inherently stable due to the depth of the bony acetabulum and labrum, diameter of the femoral head relative to the femoral neck, the capsule, and strong surrounding soft tissue. The capsule is thick and formed by a confluence of ligaments that extend from the pelvis to the femur including the iliofemoral, ischiofemoral, and pubofemoral ligaments (▶ Fig. 32.3 ).

   

   
   
3. 
   

   Blood supply is predominantly derived from the ascending branch of the medial femoral circumflex artery. The lateral epiphyseal vessels enter in the cranial and posterior portion of the femoral neck. (See Chapter 33, Femoral Neck and Head Fractures, ▶ Fig. 33.1 ).

   
   
4. 
   

   Approximately 50% of the femoral head is covered by the bony acetabulum and labrum.

   
   
   
   
   1. 
      

      Femoral head anteversion averages 10 to 15 degrees relative to the femoral condyles.

      
      
   2. 
      

      Decreased anteversion predisposes to posterior dislocation—acetabular dysplasia, femoral retroversion, crossover sign.

   
   
5. 
   

   Soft tissues, including the piriformis tendon, iliopsoas tendon, or displaced fracture fragments may obstruct closed reduction.

Imaging

1. 
   

   Plain film analysis

   
   
   
   
   1. 
      

      The anteroposterior pelvis is key for diagnosing dislocations and confirming reduction.

      
      
   2. 
      

      Systematic evaluation is paramount every time—joint space and femoral heads should be symmetric, Shenton’s line intact, and rotation assessed by the greater and lesser trochanters.

   
   
2. 
   

   Computed tomography (CT)

   
   
   
   
   1. 
      

      Obtain the CT after successful reduction unless reduction cannot be achieved.

      
      
   2. 
      

      2-mm cuts through the pelvis allow for enhanced assessment of the bony anatomy.

      
      
   3. 
      

      CT scans can identify intra-articular fragments, osteochondral lesions on the femoral head, fracture displacement, and details about an acetabular injury.

      
      
   4. 
      

      Three-dimensional CT scans serve as a useful adjunct in preoperative planning for acetabular fracture-dislocations.

Classification

1. 
   

   Anatomic classification using the location of the distal segment relative to the acetabulum (See ‘Introduction’ of this chapter). Other previously described systems are not commonly used.