The effect of locomotion on the outcome following total hip arthroplasty.

The relationship between contralateral hip arthritis and co-morbid medical conditions that affect a patient's ability to walk, and outcome following total hip arthroplasty (THA) is not fully understood. We investigated this relationship in a prospective, multi-centre study. 1497 hips (1428 patients) were recruited. At five years follow-up there was complete data for 1053 hips. We recorded Oxford Hip Score (OHS) and Charnley Class (CC) both preoperatively and at one and five years after surgery. Preoperatively there was a significant difference in OHS between CC categories and OHS deteriorated from CC-A to CC-C (p<0.001). The absolute OHS was significantly worse in CC-C compared to CC-A. Patients who remained in CC-A at five year follow-up had a larger change in OHS (mean 24) compared to those who had changed from CC-A to CC-C at five years (mean 21) p<0.001. The OHS an outcome measure frequently used for THA is influenced by several extraneous factors which may be present preoperatively but also change over time. These factors include the condition of the opposite hip as well as other disease processes that affect a patient's locomotion and therefore interpretation of OHS in isolation without additional information may not be appropriate.