Design optimization of a prosthesis stem reinforcing shell in total hip arthroplasty

Area of Science:

• Biomedical Engineering
• Orthopedic Surgery
• Materials Science

Background:

• Total hip arthroplasty (THA) aims to restore function and alleviate pain in patients with hip joint degeneration.
• Proximal femoral support is critical for THA implant stability and longevity.
• The efficacy of novel support structures like perforated titanium funicular shells requires rigorous evaluation.

Purpose of the Study:

• To evaluate the biomechanical performance of a perforated titanium funicular shell for supporting the proximal femoral cortex in THA.
• To determine optimal dimensions for the implant stem and reinforcing shell using analytical and numerical methods.
• To compare outcomes with and without collar contact between the prosthesis and the calcar femorale.

Main Methods:

• Analytical and numerical techniques, including beam on elastic foundations and two-dimensional elasticity theory, were employed.
• A nonlinear design optimization problem was formulated to minimize a material failure criterion.
• Two cases were analyzed: Case A (rigid collar contact) and Case B (no collar contact).

Main Results:

• In Case A (collar contact), optimal solutions were found with specific stem and shell dimensions, indicating collar support influences fixation requirements.
• In Case B (no collar contact), optimal solutions favored larger stem diameters and did not recommend the use of a shell.
• The study highlights the importance of collar-to-calcar femorale contact in THA biomechanics.

Conclusions:

• The perforated titanium funicular shell is not recommended for collarless prostheses or in scenarios with potential post-operative loosening (Case B).
• Optimal implant and shell designs are highly dependent on the presence or absence of collar support.
• Further research may explore alternative fixation strategies for THA in the absence of collar engagement.