Range of motion in contemporary total hip arthroplasty. The impact of modular head-neck components.

The prosthetic range of motion (PROM) of two modular total hip arthroplasty (THA) systems and one older nonmodular comparison system was evaluated. The head-neck geometry of the modular systems resulted in a smaller PROM than the nonmodular system. Longer head-neck components commonly had flanges, which caused the greatest reduction in PROM. This effect became more pronounced as head size decreased. Modular head-neck components offer recognized benefits but can be associated with notably smaller ROM and increased risk of prosthetic impingement. The surgeon should be aware that in modern systems PROM decreases when neck width is increased. Moreover, in cases of prosthetic instability the potential role of the flange of a modular head should be evaluated. Methods are suggested for maximizing PROM clinically through preoperative planning, optimal femoral neck resection, and implant utilization.