Patient-reported outcome measures versus inertial performance-based outcome measures: A prospective study in patients undergoing primary total knee arthroplasty

Background: Outcome assessment of total knee arthroplasty (TKA) by subjective patient reported outcome measures (PROMs) may not fully capture the functional (dis-)abilities of relevance. Objective performance-based outcome measures could provide distinct information. An ambulant inertial measurement unit (IMU) allows kinematic assessment of physical performance and could potentially be used for routine follow-up. Aim: To investigate the responsiveness of IMU measures in patients following TKA and compare outcomes with conventional PROMs. Methods: Patients with end stage knee OA (n = 20, m/f = 7/13; age = 67.4 standard deviation 7.7 years) were measured preoperatively and one year postoperatively. IMU measures were derived during gait, sit-stand transfers and block step-up transfers. PROMs were assessed by using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Knee Society Score (KSS). Responsiveness was calculated by the effect size, correlations were calculated with Spearman's rho correlation coefficient. Results: One year after TKA, patients performed significantly better at gait, sit-to-stand transfers and block step-up transfers. Measures of time and kinematic IMU measures demonstrated significant improvements postoperatively for each performance-based test. The largest improvement was found in block step-up transfers (effect size = 0.56-1.20). WOMAC function score and KSS function score demonstrated moderate correlations (Spearman's rho = 0.45-0.74) with some of the physical performance-based measures pre- and postoperatively. Conclusion: To characterize the changes in physical function after TKA, PROMs could be supplemented by performance-based measures, assessing function during different activities and allowing kinematic characterization with an ambulant IMU.