Which procedure better restores intact hip range of motion: total hip arthroplasty or resurfacing? A combined cadaveric and computer simulation study.

Previous comparisons of hip range of motion (ROM) after THA and surface replacement arthroplasty (SRA) are inconclusive due to the lack of soft tissue considerations and dissimilar control groups. The normal ROMs of 8 intact cadaveric hips were determined by placing specimens in 6 discrete, predefined positions of rotation at a standard torque. In each position, the limiting factor of ROM, either bony impingement or soft tissue restriction, could be determined. Total hip arthroplasty and SRA components were virtually implanted, and ROM until impingement was determined. With a THA, the ROM was comparable to that of the intact hip. With an SRA, flexion (111° ± 13°) was less than for the intact hip (131° ± 6°). Surface replacement arthroplasty, but not THA, significantly decreases the ROM compared to intact hips.