Strain pattern following surface replacement of the hip.

Area of Science:

• Orthopedic biomechanics
• Biomaterials science
• Surgical outcomes research

Background:

• Hip resurfacing arthroplasty is an alternative to total hip replacement.
• Understanding the biomechanical effects of hip resurfacing on the femur is critical for long-term implant survival and patient outcomes.
• Previous studies have indicated potential risks associated with hip resurfacing, including femoral neck fracture.

Purpose of the Study:

• To compare the strain distribution in intact versus resurfaced composite femurs under various loading conditions.
• To investigate the influence of abductor load on femoral strain patterns after hip resurfacing.
• To identify potential biomechanical factors contributing to adverse outcomes after hip resurfacing.

Main Methods:

• Utilized validated third-generation composite femurs for biomechanical testing.
• Applied rosette strain gauges at critical anatomical locations: lateral and medial femoral neck, and lesser trochanter.
• Measured maximum and minimum principal strains under axial loads (600-1000 N) and with simulated abductor forces.

Main Results:

• Resurfaced femurs exhibited approximately 50% higher maximum principal strains at the lateral femoral neck compared to intact femurs.
• A ~25% increase in strain was observed in the lesser trochanteric region of resurfaced femurs.
• Incorporating abductor load reduced strain in both intact and resurfaced femurs, most notably at the lateral femoral neck.

Conclusions:

• Elevated strain at the lateral femoral neck post-hip resurfacing may increase the risk of neck fracture, especially with pre-existing factors like notching or abductor dysfunction.
• Optimal repair of abductor muscles is essential, particularly following a lateral surgical approach.
• These findings underscore the importance of biomechanical considerations in hip resurfacing implant design and surgical technique.