Predicting Outcome after total hip and knee replacement Study (POSt) – a prospective observational pilot study

Osteoarthritis causes joint pain over 8.5 million people in the UK and was the primary reason (>95%) for performing over 150,000 hip and knee replacements annually in the NHS. Up to 20% of patients continue to be dissatisfied following surgery. The reasons for this are multi-factorial and remain unclear. The Predicting Outcome Study after total hip and knee replacement (POSt) was designed to predict which patients are likely to have a poor outcome after surgery by assessing psychological factors, patient expectations and using accelerometers to provide an objective measurement of physical activity. The POSt Pilot study was conducted to help determine the general feasibility of the study, evaluate the study protocol, identify any problems with study conduct, assess the use of questionnaires and accelerometers and finally to determine the level of missing data and propose a method for mitigating and managing this in the data analysis plan. The first 100 patients recruited to POSt were included in the pilot with 95 patients having data available for analysis at 6 months postoperatively. The pilot study had a recruitment rate of 30%, consent rate of over 70% and retention rates of 99%. An error with the use of one of the questionnaires (TSK-11) was identified and a plan of action explored to manage this error. Missing data in terms of body mass index (BMI), Oxford hip and knee scores was examined and an analysis plan for managing this issue proposed. Finally, the use of accelerometers in the study was assessed and found to be a valuable method of providing objective measurements of physical activity. In summary, the results of the pilot study showed that the study protocol was appropriate, the study was feasible, the use of the questionnaires and accelerometers acceptable by patients and a missing data analysis plan was developed.