Range of motion in total knee arthroplasty: a prospective comparison of high-flexion and standard cruciate-retaining designs.

BACKGROUND: Range of motion after a total knee arthroplasty is an important indicator of clinical outcome. Recently, a high-flexion posterior cruciate ligament-retaining knee prosthesis was designed to allow greater flexion after total knee arthroplasty. The purpose of this study was to compare range of motion and functional outcomes in patients who received either a high-flexion cruciate-retaining or a standard cruciate-retaining knee replacement.

METHODS: Fifty knees that had a total knee arthroplasty with a high-flexion design and fifty that had a total knee arthroplasty with a standard design were included in this study and were followed prospectively for a minimum of two years. The arcs of maximal non-weight-bearing passive flexion and weight-bearing flexion were measured, and the number of knees that allowed the patients to kneel and sit cross-legged in comfort was determined. In addition, the functional outcomes in these two groups were assessed with use of the Hospital for Special Surgery and Western Ontario and McMaster Universities Osteoarthritis Index scores.

RESULTS: At the time of the final follow-up, the average maximal non-weight-bearing flexion was 135.3 degrees for the knees in the high-flexion group and 134.3 degrees for the knees in the standard group; the difference was not significant. Moreover, no significant difference was found between the groups in terms of weight-bearing flexion (124.8 degrees in the high-flexion group and 123.7 degrees in the standard group) and the number of knees that allowed kneeling and sitting cross-legged. The average Hospital for Special Surgery knee score was 94.4 points in the high-flexion group and 92.4 points in the standard group; the difference was not significant. The Western Ontario and McMaster Universities Osteoarthritis Index scores also showed no significant difference between the groups.

CONCLUSIONS: For knees managed with a cruciate-retaining total knee arthroplasty, those that had the high-flexion design and those that had the standard design were found to have a similar range of motion under both non-weight-bearing and weight-bearing conditions. Moreover, no significant difference was found in terms of the other functional outcomes examined.