Review Question - QID 219125

The patient has sustained a right hip dislocation and an associated posterior wall fracture of the acetabulum, with a post-reduction incarcerated fragment. Given his hemodynamic instability, incomplete resuscitation, and suspected multi-ligamentous injury to the ipsilateral knee, the next best step would be to place a distal femoral traction pin.

Traumatic hip dislocations are high-energy injuries, with 90% occurring secondary to an axial loading mechanism on a flexed and adducted hip resulting in a posterior dislocation (dashboard injury). These may be classified as simple (pure dislocation without fracture) or complex (associated fracture of the acetabulum or proximal femur). Associated injuries and complications are very common, including acetabular or femoral head fractures, avascular necrosis, ipsilateral knee injuries, and sciatic nerve injuries. Dislocations should be reduced within 6 hours to minimize the risk of avascular necrosis and to optimize outcomes, and post-reduction CT is required to evaluate for incarcerated fragments. Incarcerated intra-articular fragments are an indication for operative intervention; however, this may occur in a delayed fashion in the setting of hemodynamic instability. Therefore, longitudinal skeletal traction via either the proximal tibia or distal femur may be applied to minimize pressure injury to the articular surface until the patient is adequately stabilized and resuscitated.

Foulk and Mullis published a 2010 review on the evaluation and management of hip dislocations. The authors state that CT is the preferred modality for evaluating post-reduction concentricity and preoperatively detecting intra-articular bony fragments. Additionally, a non-concentric reduction in the absence of discrete bony fragments on CT may suggest the presence of a displaced chondral fragment. The presence of intra-articular loose bodies mandates operative removal, save for select cases involving small fragments within the fovea centralis. Larger bony fragments contacting the articular surface may be treated with either urgent open reduction and internal fixation, or interval placement of skeletal traction and definitive fixation as soon as the patient is stable enough for operative intervention.

Firoozabadi and colleagues published a 2015 retrospective review on the utility of radiographic parameters in determining hip stability in patients with a history of posterior wall acetabular fractures. The degree of posterior wall involvement was measured using the Calkins, Keith, Moed, and the authors’ “percent femoral head coverage” methods. The traditional thought of fractures involving 20% or less of the posterior wall as stable and those involving 50% or more as unstable is inaccurate, as many fractures do not fulfill these criteria and the stability of the hip joint can be difficult to determine. The authors found that radiographic parameters using the Calkins, Keith, and Moed techniques had limited utility in determining hip stability, where the smallest unstable wall size was 15% and the largest stable wall size was 65%. A subgroup analysis performed on wall sizes less than 20% by the Moed technique demonstrated that 4/5 unstable fractures had a cranial exit point of the posterior wall fracture within 5 mm of the dome. Of the 21 patients who had a stable hip on EUA and a wall size of less than 20%, 90% had a cranial exit point more than 5 mm from the acetabular dome.

Figure A is a radiograph demonstrating a posterior dislocation of the right hip with an associated acetabular fracture. Figure B is an axial CT demonstrating a large incarcerated bony fragment within the hip joint.

Incorrect Answers:
Answer 1: While the presence of an intra-articular fragment is an indication for fragment removal and ORIF, the patient is currently in hypovolemic shock and is not yet stabilized enough for a large operation such as a posterior wall ORIF.
Answer 3: The presence of laxity to the ipsilateral knee on physical exam is suspicious for a multiligamentous knee injury. Therefore skeletal traction should be applied through the distal femur, not the proximal tibia.
Answer 4: A pelvic binder is indicated in the setting of a volume-expanding pelvic ring injury, not a hip dislocation.
Answer 5: An examination under anesthesia is not indicated in the setting of an intra-articular fragment, which can potentially cause more damage to the articular surface.