For patients with hip joint disease, total hip replacement (THR) is often the only option available to alleviate pain and restore normal function. Mechanical failure (i.e. loosening) has emerged as a major long-term complication and previous research has suggested that torsional loading may play a role in implant loosening. This retrospective study was undertaken in an effort to evaluate the kinematic and kinetic characteristics of the hip and knee joints in patients with unilateral THR and in normal elderly adults during the performance of daily activities. It was hypothesized that:​ (1) hip abductor strength of the affected limb in THR patients would be significantly less than that of normal elderly;​ (2) THR patients would have reduced torsional loading at their affected hip joint when compared to normal elderly;​ and (3) joint moments at both of the knee joints and the contralateral hip joint in THR patients would be significantly different from that ofnormal elderly.

The motions, forces and moments of the knee and hip joints were examined on 23 unilateral THR patients (average age 63.7), two to six years post-operatively, and 20 normal elderly adults (average age 65.3). The subjects were studied during the performance of repeated trials of level walking, stair ascent, stair descent, and arising from a seated position. Isometric abductor strength was also measured.

Results proved that affected limb abductor strength was reduced in THR patients as compared to normal elderly and that this strength reduction may have implications for joint loading. No significant differences were observed between the THR patients and normal controls during level walking but during the more demanding tasks ofstair ascent, stair descent, and arising from a seated position, a significantly reduced internal rotation moment was seen in the affected hip ofthe THR patients. The loading at both ofthe knee joints and the contralateral hip joint in THR patients was, in general, not significantly different from that ofthe normal elderly. An unexpected but important finding was the occurrence of an asymmetric loading pattern during both the stair and chair rising activities in the normal elderly