What is the diagnosis?

Posterior superior dislocation of right hip arthroplasty 

• Pearl: Prosthetic hips typically require less energy to achieve dislocation in comparison to native dislocation. Rate of dislocation after total hip arthroplasty is reported at 1%- 10% [1]. 

• Pearl: The most common occurrence of prosthetic hip dislocation occurs within 3 months of total hip replacement [2]. Total hip arthroplasties typically dislocate in the direction of surgical approach taken. Most commonly it is the posterior direction. 

What is the mechanism of injury?

Generally prosthetic hip dislocation results from a low energy mechanism in comparison to native hip dislocations. Posterior dislocations of prosthetic hips typically result from flexion, internal rotation, and adduction (i.e. rising from seated to standing position) [1]. 

What physical exam findings are expected?

On examination, you expect the involved extremity to be visibly shortened, adducted and internally rotated. There can be a palpable deformity of the involved hip. 

What is the management in the ED?

These patients should undergo immediate closed reduction. Typically this will require procedural sedation. Procedural sedation does confer some risk especially in the elderly patient or patients with multiple medical comorbidities. There are reports in the literature about successful reduction using US guided femoral nerve blocks for adequate analgesia to attempt closed reduction without the risk associated with sedation [3]. 

There are several reported maneuvers to achieve reduction in posterior dislocation (i.e. Allis, Captain Morgan). These techniques focus on traction of the ipsilateral limb with accompanying pelvic stabilization, hip flexion, and adduction.

• Pearl: Complications include bony, neurovascular injuries, and avascular necrosis (AVN). 

• Femur and acetabular fractures are examples of common bony injuries. Bony injuries are more common in native hip dislocations owing to larger forces associated with native hip dislocations [5]. 

• Vascular injuries are additional complications that should be evaluated with thorough neurovascular exams before and after reduction. 

• Avascular necrosis is a feared complication in native hip dislocations. AVN in prosthetic hips is not possible given altered anatomy. 

• Sciatic nerve injury can also occur due to traction on the nerve during posterior dislocation. Look for weakness in ankle dorsiflexion/plantar flexion or decreased sensation over L4-S dermatomes. Click here for a more detailed discussion of reduction techniques [5]. 

Image 2. Post-reduction plain radiograph of the right hip. Author’s own images.

When do you consult Orthopedics?

While consultation practices are case and institution dependent orthopedics ideally should be consulted prior to any reduction given the range of implants and surgical approaches which may complicate care.  Consider deferring reduction to orthopedic specialists in the case of reductions that are in close proximity to initial surgery (i.e. 4-6 weeks post procedure). Prompt consultation will also expedite follow-up.