Current Trends in Hemi Arthroplasty

Courtesy: Dr Suryanaraya, Ashok Shyam TV, Ortho

Hemiarthroplasty vs Total Hip Arthroplasty in the Elderly

• Ongoing debate in displaced femoral neck fractures:

  • Internal fixation vs hemiarthroplasty vs THA.

• Considerations:

  • Functional outcome

  • Morbidity and mortality

  • Revision risk

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Historical Failures of Early Hemiarthroplasty

Primary Causes of Early Failure

1. Metallurgical failure

2. Fixation failure

3. Cartilage degeneration over time

Design-Related Issues

• Monoblock prostheses:

  • Poor restoration of hip biomechanics

  • Suboptimal offset and kinematics

• Cemented stems:

  • Sharp corners ? cement mantle breakdown

• Early uncemented stems:

  • Non-porous or poorly integrating surfaces

  • Inconsistent bone ingrowth

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Cartilage Failure: A Major Limitation

• Progressive acetabular cartilage erosion over 5–10 years.

• Leads to:

  • Pain

  • Protrusio acetabuli

  • Progressive migration

  • Need for revision

Histological Findings at Revision

• Near-complete loss of acetabular cartilage

• Replacement with fibrous tissue

Revision Rates

• Approximately 37–40% revision at 5–8 years in symptomatic cases.

• Strong correlation with:

  • Younger age

  • Higher activity levels

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Unipolar Hemiarthroplasty

Characteristics

• Single articulation: metal head against native cartilage.

• Simpler design.

Limitations

• High cartilage wear rate.

• Increased acetabular erosion in active patients.

• ~40% revision risk in symptomatic patients within 5–8 years.

• Faster cartilage loss compared to non-implanted matched groups.

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Bipolar Hemiarthroplasty

Design Concept

• Dual articulation:

  • Inner bearing (between head and polyethylene liner)

  • Outer bearing (between metal shell and acetabulum)

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Early Bipolar Designs

• Concentric centers of rotation.

• Problems included:

  • Varus migration

  • Impingement

  • Polyethylene wear

  • Dislocation

  • Component dissociation

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Modern Bipolar Designs

• Eccentric center of rotation.

• Improved containment of the head.

• Promotes self-centering mechanism.

• Better stress distribution across acetabulum.

• Reduced point loading.

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Mechanics of Bipolar Motion

In Vitro Observations

• At low loads:

  • Both articulations function.

• At higher loads:

  • Outer articulation predominates.

Influence of Cartilage Condition

• Normal cartilage:

  • Bipolar motion tends to be preserved.

• Degenerated cartilage:

  • Motion becomes predominantly unipolar.

• Dual motion decreases over time.

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Head Size Considerations

• No strong evidence that head size (22, 28, 32 mm) significantly alters long-term bipolar function.

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Complications of Bipolar Prostheses

• Component dissociation

• Impingement

• Polyethylene wear

• Gradual loss of bipolar function

• Potential mode of failure due to polyethylene debris

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Long-Term Results

• 10-year survival approximately 80–85% in modern series.

• Bipolar prostheses generally show:

  • Lower failure rates

  • Slightly better functional scores compared to unipolar designs

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Key Principles for Successful Hemiarthroplasty

Patient Selection

• Best suited for:

  • Low-demand

  • Very elderly patients

• Younger or active individuals:

  • Consider THA due to better long-term outcomes.

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Surgical Technique

• Treat hemiarthroplasty like a total hip replacement:

  • Proper femoral preparation

  • Accurate sizing

  • Correct offset restoration

• Cemented or uncemented choice:

  • Based on bone quality and patient condition

• Emphasize:

  • Proper cementation technique (if cemented)

  • Secure fixation

  • Modular stem use

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Soft Tissue Considerations

• Smaller surgical approaches when appropriate

• Meticulous capsular repair

• Preserve acetabular labrum if possible

• Reduce dislocation risk

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Current Perspective

• Fixation-related failures are largely addressed with modern implants.

• Cartilage erosion remains the main long-term limitation.

• Bipolar designs appear to offer advantages over unipolar designs.

• Outcomes around 80% at 5–8 years in appropriate patients.

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Final Take-Home Messages

• Hemiarthroplasty remains primarily a fracture solution.

• Optimal in low-demand elderly patients.

• Modern modular and bipolar designs improve outcomes.

• Proper surgical technique and patient selection are critical.

• In higher-demand patients, total hip arthroplasty often provides superior long-term results.