Design optimization of skeletal hip implant cross-sections using finite-element analysis.

The major causes for revision surgery after total hip arthroplasty are aseptic loosening, dislocation, wear, design factors, stress shielding on the bone, and mechanical and biological factors. A material with toughness and high wear properties is essential for a good hip implant because these implants fail due to design. Stress shielding is found to be the major cause for the failure of hip implants, and can lead to the implant needing to be replaced or revised, which is painful for the patient and costly for the health care industry. The hip stem designs developed by various manufacturers are solid stems with indentations; stems with collars; collarless, tapered stems; and teardrop-shaped, polished stems without indentations. They are found to have a greater rigidity, and therefore they transfer less load proximally, which results in high proximal stress shielding of the proximal femur. A stem of low stiffness alone would not suffice in achieving a reduced or optimal stress shielding. The existing design proposals to minimize the effect of stress shielding are focused on the use of lightweight materials, composite materials, circular and longitudinal hole patterns, and different hollow-bore depths. A skeletal hip implant with varying cross-sections was designed and finite-element analysis was performed. The skeletal hip implant with a hexagonal cross-section was optimized based on the mass of the implant and the load-bearing capacity. This lightweight, novel design ameliorates implant fixation, minimizes stress shielding, enhances the longevity of the implant, and offers better mobility to the patient.