Range of motion studies for total hip replacements. A comparative study with a new experimental apparatus.

Significant differences in ROM exist between different THR prosthesis designs: several of the prosthesis designs tested are marginal in flexion; several millimeters of socket wear will decrease the ROM. The results also emphasize the importance of proper component orientation at surgery. The surgeon has less latitude in orienting the components of a THR with limited ROM. Subluxation and dislocation due to rim contact can be minimized with most prosthetic units by instructing the patients to abduct and/or externally rotate their hips during acute flexion. Analyses suggest that impingement of prosthesis neck and socket rim may lead to increased risk of dislocation and increased rim wear. Prostheses with adequate ROM for everyday activities should provide stability, less frequent neck and socket contact with decreased rim wear, less force transmission to acrylic-bone interface, and less diminution of ROM with wear of the socket wall.