Impact of Range of Motion Trajectory on Patient-Reported Outcomes Following Total Knee Arthroplasty.

Abstract

Background: Postoperative knee range of motion (ROM) is among the most frequently reported functional metrics following total knee arthroplasty (TKA). Despite the major use of ROM as a metric, minimal literature exists assessing the progression of motion postoperatively over time or its implications on patient-reported outcome measures (PROMs). As such, this study aimed to (1) determine the recovery trajectory in knee ROM during the first year following primary TKA and (2) determine if a correlation existed between patients' ROM recovery trajectory and PROM scores.

Methods: Data was collected prospectively on all patients undergoing a unilateral primary TKA between 2017 and 2019. Standardized goniometric measurements were used to measure knee flexion and extension at five time points: preoperatively, intraoperatively, and postoperatively at two weeks, six weeks, and one year. In addition, the Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS-JR) was collected preoperatively and at the one-year postoperative visit. A total of 306 TKA procedures were performed on 269 patients, and of those patients, 63.9% (N = 172) were women and 36.1% (N = 97) were men who had a mean age of 67 years (range, 29.0 to 89.4) and a mean body mass index (BMI) of 30.8 (range, 18.2 to 49.0).

Results: Mean knee flexion significantly increased from 112.8 (range, 63.0 to 140.0) degrees preoperatively to 119.0 (range, 95.0 to 140.0) degrees at one year postoperatively (mean difference = 4.61, P < 0.001). More specifically, 97.4% of flexion was restored by six weeks (111.2; range, 58.0 to 132.0) postoperatively. Knee extension also significantly improved from 5.9 (range, -5.0 to 32.0) degrees to 0.9 (range, 0 to 8.0) degrees at one-year follow-up (mean difference = 5.03, P < 0.001). A weak positive correlation existed between preoperative ROM and KOOS JR scores (r = 0.24, P < 0.01).

Conclusion: Knee flexion ROM is restored in a nonlinear trajectory following a primary TKA, with over 90% of the progress occurring within the first six weeks postoperatively. In contrast, knee extension ROM is restored in a more linear manner. At one year postoperatively, target ROM fell between preoperative and intraoperative measurements. Neither ROM nor the recovery trajectory of motion correlates with KOOS-JR scores. As such, this information can be valuable when attempting to set expectations for patient recovery.