Age and waiting time as predictors of outcome after total hip replacement for osteoarthritis

Objective. To investigate in a prospective study the relationship between age, pre-operative status, waiting time and post-operative outcome in patients assigned for unilateral total hip replacement (THR) due to osteoarthritis (OA). Method. One hundred and forty-eight patients (mean age 71 yr) with primary OA of the hip were investigated pre-operatively and 3, 6 and 12 months post-operatively with the Medical Outcomes Study 36-Item Short Form Health Survey (SF-36) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). For 56 of the patients an additional evaluation was made when they were placed on the waiting list. Results. One hundred and twenty-four patients fulfilled the study criteria (age 50 yr or over and unilateral THR for OA during the study period). Before surgery there were no differences in the WOMAC or SF-36 subscales (except mental health) between patients aged over and under 72 yr. Post-operatively, the younger patients reached a better score than the older patients. There were no differences in pre-operative status or post-operative outcome between the patients who had been on the waiting list more than and less than 3 months. Most pain relief after hip replacement was obtained by 3 months, while it took at least 1 yr to reach the full benefit in improved function. Ninety per cent of the patients had improved by at least 10 points on a 100-point scale for pain and function at 12 months. Conclusion. The age of the patients assigned for THR did not determine their pre-operative status. However, younger patients gained more function post-operatively than older patients and reached higher absolute mean SF-36 values, except for pain. An average difference in time on the waiting list of 3 months did not result in a difference in post-operative outcome. At least 1 yr is required for the average OA patient to gain the full benefit of the THR.