Total Hip Replacement Complication, ABOS Oral Boards Preparation

This is a 58-year-old female nurse, three weeks out from a right total hip arthroplasty that I performed through a posterior approach for end-stage osteoarthritis. She was doing well, walking with a cane, progressing with therapy. Today she bent forward to pick up her grandchild and felt a pop in her right hip, followed by immediate severe pain and inability to bear weight. She said her leg felt short.

On exam, the right lower extremity was shortened, internally rotated, and adducted, that is the classic presentation of a posterior dislocation. Distal neurovascular function was intact. No wound drainage or signs of infection.

AP pelvis radiograph confirmed a posterior dislocation. The acetabular component appeared well-positioned on the AP film, cup abduction around 42 degrees. The femoral component was in good position. No periprosthetic fracture.

I performed closed reduction under procedural sedation with fluoroscopic guidance. The hip was stable through a functional range of motion after reduction. Post-reduction films confirmed concentric reduction with no fracture.

I obtained a CT scan to accurately assess component position, because plain films are unreliable for measuring anteversion. The CT showed cup anteversion of 10 degrees, that is the low end of the Lewinnek safe zone. Combined anteversion was 28 degrees. While these are technically within acceptable ranges, the low cup anteversion in a patient who dislocated with a flexion mechanism suggests the combined anteversion may be insufficient for her daily activities.

I discussed this with her openly. A first-time dislocation after a posterior approach, with a provocative mechanism and components that are close to but not clearly outside acceptable position, is best managed conservatively first. I placed her in a hip abduction brace and reinforced posterior hip precautions, no flexion past 90 degrees, no internal rotation, no adduction past midline. I also emphasized that as a nurse, she needs to be especially careful with bending mechanics at work.

At two weeks, she was comfortable and compliant with precautions. At six weeks, she was out of the brace and the hip remained stable. At three months, she was walking without assistive devices and back to work with modified duties. At six months, the hip remained stable through a full range of motion and she had returned to full nursing duties. I did counsel her that if she had a recurrent dislocation, we would need to discuss revision options, either correcting the cup anteversion, using a dual-mobility bearing, or a constrained liner.

She was satisfied and the hip remained stable. In retrospect, I would have used a dual-mobility bearing at the index procedure. Her combined anteversion was on the low end, and as a nurse she needs deep flexion for her work, bending, lifting, and transitioning patients. A dual-mobility construct would have provided a wider arc of motion before impingement and likely prevented this dislocation altogether. I have since lowered my threshold for dual-mobility bearings in patients with occupational demands that involve repetitive deep flexion. I followed her closely for two years with no further instability episodes.