Modelling Knee Range of Motion Post Arthroplasty: Clinical Applications

Purpose: To model change in knee range of motion (ROM) post total knee arthroplasty (TKA) and to show how this information can be incorporated into clinical decision making. Method: We applied a variable-occasion repeated-measures study design. Patients' knee flexion and extension ROM were assessed pre- and post arthroplasty over the ensuing 60 weeks. We examined change in ROM post TKA using linear and nonlinear mixed-effects modelling, and examined whether age, body mass index, prearthroplasty ROM, and gender were determinants of recovery in post-arthroplasty ROM. Results: Of 93 eligible patients, 74 provided pre- and post-arthroplasty data. A random intercept nonlinear model fit the flexion data best, and a random intercept linear model fit the extension data best. Pre-arthroplasty ROM was found to be a determinant of recovery in ROM post arthroplasty. This finding was common to both flexion and extension models. Conclusions: Our study showed that the greatest improvement for knee ROM took place during the first 12 weeks post arthroplasty. Of the variables examined, only pre-arthroplasty ROM was a determinant of outcome (p < 0.05). The study results provide clinicians with data to determine expected rates of improvement for patients as well as the projected maximum ROM, facilitating improved clinical decision making.