Custom and modular components in primary total hip replacement.

Cementless custom implants attempted to enhance fit and fill of variable hip geometry. Fabrication of custom implants in referenced from a computed tomography scan, thus allowing three dimensional specifications of femoral anatomy. However, the aggregate charge of manufacturing the implant and obtaining the computed tomography scan is prohibitive in today's healthcare climate. Clinical studies have not shown that customized implants incrementally improve clinical success or implant longevity. Modular prostheses allow the surgeon intraoperative versatility, allowing adjustment of leg length, offset, neck length, anteversion, and fixation. This is particularly helpful in developmental dysplasia of the hip and posttraumatic arthritis. Other advantages of modularity include decreased implant inventory and the ability to remove the femoral head at revision surgery to improve exposure or change head size without component removal. Subsequent clinical experience has witnessed significant drawbacks associated with modularity. These include corrosion, especially with mixed metals, fretting, dissociation, implant fracture below the head and neck taper joint, and reduced range of motion. In addition, thin acetabular polyethylene contributes to higher were rates, earlier failure, local or distal debris particles, and osteolysis. Finally, the cost of modular implants is generally higher than a comparable monolithic prosthesis. In primary hip arthroplasty, use of custom or modular implants should be judicious. Modularity beyond the head and neck junction should be reserved for those cases where a comparable monolithic implant would not suffice.