Contralateral knee flexion predicts postoperative knee flexion in unilateral total knee arthroplasty: A retrospective study

Abstract

Background: Postoperative flexion angle is associated with preoperative flexion in the same knee after total knee arthroplasty (TKA). However, whether the preoperative contralateral knee flexion angle could influence postoperative flexion remains unknown. This study aimed to test the effect of contralateral knee flexion on final flexion in the postoperative knee after unilateral TKA. We hypothesized that the preoperative contralateral knee flexion angle affects postoperative knee flexion, as does preoperative flexion, in the operated knee.

Patients and methods: Ninety-five patients with knee osteoarthritis (OA) who underwent cruciate-retaining TKA were included in this study, and their maximum passive knee flexion angle was evaluated preoperatively and at final follow-up on the operative and contralateral sides. Patients were divided according to their preoperative flexion angles: Group C, those whose contralateral knee flexion angle was greater than the operative knee flexion angle; and Group O, those whose contralateral knee flexion angle was equal to or smaller than the operative knee flexion angle. We performed multiple regression analysis, with postoperative flexion and improvement in the flexion angle as objective variables and preoperative predictors (age, sex, body mass index, preoperative flexion, and contralateral knee flexion) as explanatory variables. The results of the flexion angles were compared between the two groups using unpaired t-tests.

Results: Postoperative flexion angle was significantly affected by the preoperative contralateral knee flexion angle (β=0.35, p=0.002), and an improvement in flexion was negatively affected by preoperative flexion of the operated knee (β=-0.83, p<0.001) and positively affected by contralateral knee flexion (β=0.35, p=0.001). Group O achieved poorer postoperative flexion than Group C (110.4±16.6° vs 119.6±16.5°, p=0.0017).

Conclusion: Patients with less flexion of the contralateral knee are less likely to obtain a greater degree of knee flexion after TKA.

Level of evidence: III; retrospective comparative study.

Keywords: Contralateral knee; Flexion angle; Range of motion; Total knee arthroplasty.