Hip Dislocation and Femoral Component Disassembly After Bipolar Hemiarthroplasty: A Report of Four Cases and Introduction of New Reduction Maneuvers
Femoral neck fractures are a leading cause of disability in older adults, with over 90% of cases occurring in people aged 65 and above. For unstable fractures, bipolar hemiarthroplasty is a go-to treatment—it’s less invasive than total hip replacement, reduces surgical trauma, and helps patients recover faster. But while dislocation after this procedure is uncommon, a rare and dangerous complication can arise: the disassembly of the bipolar prosthesis’s components. A 2019 study from Peking Union Medical College Hospital details four such cases and shares a new technique to safely fix these dislocations without open surgery.
What Is Bipolar Hemiarthroplasty?
Bipolar hemiarthroplasty replaces the broken femoral head (the “ball” of the hip) with a two-part prosthetic: an inner metal head and an outer polyethylene cup. The cup moves within the patient’s natural acetabulum (hip socket), which lowers wear and improves mobility compared to single-piece (unipolar) devices. It’s widely used for elderly patients with femoral neck fractures because of its balance of effectiveness and simplicity.
A Rare but Serious Complication
Dislocation after hemiarthroplasty affects just 1–3% of patients, and rates are similar between unipolar and bipolar designs. But disassembly—when the polyethylene cup separates from the inner metal head—is even rarer. This almost always happens during attempted closed reduction (non-surgical realignment) under anesthesia: as surgeons pull to fix a dislocated hip, the outer cup gets stuck on the acetabular rim, and continued traction tears the components apart. The result? The cup pops out of the socket, while the inner head falls in—forcing surgeons to switch to open surgery.
Four Cases: What Happened
The study, led by Yan-Yan Bian and colleagues from the Department of Orthopaedic Surgery at Peking Union Medical College Hospital, describes four elderly patients (ages 76–92) who experienced disassembly after bipolar hemiarthroplasty. Here’s a breakdown of their stories:
- Case 1: A 79-year-old woman with a left subcapital fracture had surgery and dislocated 2 days later while moving in bed. During closed reduction, the cup and inner head separated. She needed open surgery to reassemble the prosthesis.
- Case 2: A 92-year-old woman with a right subcapital fracture dislocated 9 days post-op after falling out of bed. Closed reduction caused disassembly; open surgery fixed it, and she wore a cast for 4 weeks.
- Case 3: An 85-year-old woman with a right transcervical fracture dislocated twice—first 6 days post-op, then 4 weeks later while sitting up. Closed reduction caused disassembly. Surgeons found torn external rotators and used a longer-neck prosthesis to improve soft tissue tension (preventing re-dislocation).
- Case 4: A 76-year-old man with a left transcervical fracture dislocated 4 weeks post-op after a fall. The outer cup was locked behind the acetabular rim. Instead of forceful traction, surgeons used a new “push-turnover-pull” technique: they pushed the leg toward the hip, adducted it (brought it toward the body) to flip the cup over, then did routine reduction. It worked—no open surgery needed.
The “Bottle-Opener” Mechanism
The authors call the cause of disassembly the “bottle-opener mechanism.” Imagine trying to open a bottle: if the opener (outer cup) gets stuck on the bottle’s rim (acetabular edge), pulling the screw (inner head) will pop the opener off. The same happens with a dislocated bipolar prosthesis—traction on the inner head while the outer cup is stuck tears the components apart.
A New Technique to Avoid Disassembly
To fix this, the team developed a three-step maneuver for locked outer cups:
- Push: Move the affected leg toward the hip (proximal translation) to relieve pressure on the rim.
- Turnover: Adduct the leg (bring it toward the body) to use leverage and flip the outer cup—so the rounded part of the cup touches the acetabulum instead of the edge.
- Pull: Perform the routine closed reduction once the cup is properly aligned.
This worked in Case 4, avoiding open surgery. The authors stress using fluoroscopy (real-time X-ray) to guide the process and ensure safety.
Key Takeaways for Surgeons
The study offers critical lessons for anyone treating elderly patients with bipolar hemiarthroplasty:
- Caution during closed reduction: If the outer cup is locked on the acetabular rim, avoid forceful traction—use the push-turnover-pull technique instead.
- Inspect and repair: If disassembly occurs, open surgery is needed to check the locking mechanism and repair torn muscles (like external rotators).
- Soft tissue tension matters: Using a longer-neck prosthesis (as in Case 3) can improve stability and prevent re-dislocation.
About the Study
The research was published in the Chinese Medical Journal in 2019 by a team from Peking Union Medical College Hospital, a leading institution in orthopedic surgery. All patients provided informed consent for their cases to be shared.
doi.org/10.1097/CM9.0000000000000057
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