Hip Dislocation and Femoral Component Disassembly After Bipolar Hemiarthroplasty

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Hip Dislocation and Femoral Component Disassembly After Bipolar Hemiarthroplasty: A Report of Four Cases and Introduction of New Reduction Maneuvers

Bipolar hemiarthroplasty is a widely utilized surgical intervention for managing unstable femoral neck fractures in elderly patients. While effective for early mobilization and functional recovery, this procedure is not without complications. Hip dislocation remains a recognized postoperative challenge, but a rarer and more severe complication—disassembly of the bipolar prosthesis components—poses unique diagnostic and therapeutic dilemmas. This article details four cases of femoral component disassembly following primary bipolar hemiarthroplasty, analyzes the underlying mechanisms, and introduces novel reduction techniques to address this complication.

Case Presentations

Case 1
A 79-year-old female underwent left bipolar hemiarthroplasty (Smith & Nephew, Switzerland) for a subcapital femoral fracture. Two days postoperatively, she experienced sudden pain and immobility while repositioning in bed. Clinical examination revealed limb shortening and internal rotation. Radiographs confirmed posterior-superior hip dislocation (Figure 1A). During closed reduction under general anesthesia, the polyethylene cup dislodged from the inner femoral head. The cup extruded from the acetabulum, while the inner head remained lodged within (Figure 1B). Open reduction was required to reassemble the components and stabilize the hip.

Case 2
A 92-year-old female sustained a posterior dislocation nine days after right bipolar hemiarthroplasty (Smith & Nephew) for a subcapital fracture. Closed reduction under anesthesia inadvertently caused dissociation: the cup displaced superiorly, and the inner head migrated into the acetabulum. Intraoperative inspection revealed an intact locking mechanism, suggesting soft tissue insufficiency as the primary failure cause. The components were reassembled, and postoperative immobilization with an orthopedic cast was implemented for four weeks.

Case 3
An 85-year-old female underwent right bipolar hemiarthroplasty (Smith & Nephew) for a transcervical fracture. Six days post-surgery, dislocation occurred during bed repositioning. Closed reduction succeeded initially, but a second dislocation happened four weeks later while rising from a chair. Repeat reduction attempts led to cup-head dissociation. Intraoperative findings included torn external rotators and component extrusion through the repaired capsule. The femoral head was replaced with a longer-neck prosthesis (0 mm to 8 mm offset) to enhance soft tissue tension. Stability was restored post-revision.

Case 4
A 76-year-old male developed left hip dislocation four weeks after bipolar hemiarthroplasty (Smith & Nephew) for a transcervical fracture. Radiographs showed the outer bipolar shell entrapped behind the acetabular rim (Figure 1D). A novel “push-turnover-pull” maneuver was employed under fluoroscopy: proximal limb translation with internal rotation and adduction leveraged the outer cup over the acetabular rim (Figure 1G–H). Subsequent standard reduction successfully relocated the hip (Figure 1E).

Mechanisms of Component Disassembly

Disassembly typically occurs during closed reduction maneuvers, often due to excessive traction forces acting on the bipolar components. The “bottle-opener mechanism” (Figure 1F) describes how the outer cup’s edge catches the acetabular rim, creating a fulcrum that separates the polyethylene liner from the inner head. This results in the cup displacing externally while the inner head migrates into the acetabulum. Contributing factors include:

  1. Inadequate soft tissue tension: Insufficient offset or femoral neck length reduces capsuloligamentous stability.
  2. Locking mechanism failure: Although rare, wear or intraoperative malpositioning of the polyethylene cup’s locking ring may predispose to dissociation.
  3. Trauma: Falls or abrupt movements generate shear forces exceeding the prosthesis’s mechanical integrity.

Innovative Reduction Techniques

Traditional closed reduction maneuvers risk exacerbating component dissociation. The push-turnover-pull technique (Figure 1G–I) addresses this by:

  1. Proximal limb translation: Axial pressure directs the femoral head toward the acetabulum.
  2. Internal rotation and adduction: These movements pivot the outer cup over the acetabular rim via leverage, reorienting the convex head surface against the acetabulum.
  3. Standard traction-countertraction: Finalizes reduction once the components are realigned.

Fluoroscopic guidance is critical to monitor component positioning and avoid iatrogenic dissociation.

Preventive and Intraoperative Considerations

  1. Component Selection:

    • Neck length adjustment: Increasing offset (e.g., 8 mm in Case 3) enhances soft tissue tension.
    • Locking mechanism integrity: Intraoperative verification of the polyethylene cup’s engagement with the inner head is essential.

  2. Soft Tissue Management:

    • Repair of external rotators and capsule during initial surgery reduces dislocation risk.
    • Postoperative bracing (e.g., orthopedic casts) may stabilize vulnerable patients.

  3. Surgical Technique:

    • Avoid excessive force during closed reduction.
    • Early recognition of dissociation signs (e.g., abrupt resistance during maneuvers) necessitates conversion to open reduction.

Clinical Implications

Component disassembly complicates 0.5–2% of bipolar hemiarthroplasties, often necessitating revision surgery. Key takeaways include:

  • Preoperative planning: Optimize femoral neck length and offset to balance stability and mobility.
  • Intraoperative vigilance: Ensure proper locking ring engagement and soft tissue repair.
  • Reduction strategy: Employ fluoroscopy-guided techniques like push-turnover-pull to minimize dissociation risk.

doi:10.1097/cm9.0000000000000057

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