Abstract
INTRODUCTION: No study has identified predictors of improvement and decrease in postoperative range of motion (ROM) after medial pivot (MP) total knee arthroplasty (TKA) compared to preoperative ROM. This multicenter study aimed to identify predictors of improved postoperative range of motion (ROM) after MP-TKA. METHODS: The study included 107 consecutive patients who underwent MP-TKA for knee osteoarthritis at six different centers. Data on patient age, gender, hip knee angle, and pre- and postoperative ROM in extension and flexion were collected. A 9° improvement or decrease in postoperative knee flexion was considered positive. Patients were divided into three groups according to whether knee flexion improved by more than 9° (group I; 35 patients), changed within the minimal clinically important difference (MCID) (group M; 54 patients), or decreased by more than 9° (group D; 18 patients) one year after surgery. RESULTS: Significant differences in preoperative ROM for flexion were observed between the groups (P < 0.001). Multivariate and receiver operating characteristic (ROC) curve analyses revealed that preoperative flexion less than 118.0° (area under the curve (AUC): 0.957, 95 % confidence interval (CI): 0.924-0.990) was a significant positive prognostic factor for improved postoperative ROM one year postoperatively (odds ratio (OR): 0.75, 95 % CI: 0.66-0.85, P < 0.001) and that preoperative flexion greater than 128.0° (AUC: 0.899, 95 % CI: 0.836-0.961) was a significant positive prognostic factor for decreased postoperative ROM one year postoperatively (OR: 1.14, 95 % CI: 1.07-1.22, P < 0.001). DISCUSSION: The results showed that a preoperative knee flexion ROM of less than 118° was a significant positive predictor of an improvement in knee flexion ROM of MCID or greater after MP-TKA, and a knee flexion ROM of 128° or greater was a significant positive predictor of a decrease in knee flexion ROM of MCID or greater one year after surgery.