Mediolateral coronal laxity does not correlate with knee range of motion after total knee arthroplasty

IntroductionIt remains controversial whether coronal laxity after total knee arthroplasty (TKA) is a critical factor in determining clinical outcomes such as knee range of motion (ROM). The purpose of this study was to evaluate the correlation between postoperative ROM and coronal laxity, which was defined as the angular motion from the neutral, unloaded position to the loaded position, in patients with medial knee osteoarthritis undergoing TKA.Materials and methodsPreoperative and 1-year postoperative coronal laxity were assessed using radiographs by applying a force of 150N with an arthrometer. A consecutive series of 204 knees was examined. A knee was defined as clinically balanced when the difference between medial and lateral laxity was 3 degrees or less. Active ROM was measured using a goniometer. Values were expressed as median values.ResultsThe ROM was 105 degrees preoperatively and 110 degrees postoperatively, with the correlation being weak (r=0.372, p<0.001) between the periods. The total laxity also revealed a weak correlation (r=0.270, p<0.001) between the periods. Preoperative laxity was significantly larger (4 degrees vs. 3 degrees) on the medial side (p<0.001) and postoperative laxity was larger (4 degrees vs. 3 degrees) laterally (p=0.001). There was no significant correlation between postoperative ROM and laxity pre- and postoperatively. Additionally, there were no differences in ROM between the balanced and unbalanced groups in the pre- and postoperative periods.ConclusionsThis study indicated that mediolateral coronal laxity in patients with an osteoarthritic knee did not correlate with knee ROM after TKA when 3 degrees-4 degrees of laxity in the medial and lateral orientations was maintained.