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

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. 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 patient-reported outcome measure scores.

Methods: Data were 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 1-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 to 89) and a mean body mass index 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 1-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).

Conclusions: 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.

Level Of Evidence: Level II, Prospective cohort study.