Knee OA: Which patients are unlikely to benefit from manual PT and exercise?

Background The combination of manual physical therapy and exercise provides important benefit for more than 80% of patients with knee osteoarthritis (OA). Our objective was to determine predictor variables for patients unlikely to respond to these interventions. Methods We used a retrospective combined cohort study design to develop a preliminary clinical prediction rule (CPR). To determine useful predictors of nonsuccess, we used an extensive set of 167 baseline variables. These variables were extracted from standardized examination forms used with 101 patients (64 women and 37 men with a mean age of 60.5 +/- 11.8 and 63.6 +/- 9.3 years, respectively) in 2 previously published clinical trials. We classified patients based on whether they achieved a clinically meaningful benefit of at least 12% improvement in Western Ontario MacMaster (WOMAC) scores after 4 weeks of treatment using the smallest and most efficient subset of predictors. Results The variables of patellofemoral pain, anterior cruciate ligament laxity, and height >1.71 m (5'7 '') comprise the CPR. Patients with at least 2 positive tests yielded a posttest probability of 88% for nonsuccess with this treatment (positive likelihood ratio=36.7). The overall prognostic accuracy of the CPR was 96%. Conclusion Most patients with knee OA will benefit from a low-risk, cost-effective program of manual physical therapy and supporting exercise.(1,2) The few patients who may not benefit from such a program are identifiable by a simple (preliminary) CPR. After validation, this rule could improve primary patient management, allowing more appropriate referrals and choices in intervention.