Association between anteroposterior laxity in mid-range flexion and subjective healing ofinstability after total knee arthroplasty.

Abstract

Flexion instability following total knee arthroplasty (TKA) is a common indication of early revision. The association between the objective anteroposterior (AP) laxity direction in mid-range flexion and the subjective healing of instability remains unclear; thus, this study aimed to clarify this association. In this study, 110 knees (74 females, 92 knees; 16 males, 18 knees) with medial pivot implants were examined with a median age of 79 (range 60-92) years for a median follow-up duration of 22 (range 6-125) months. AP laxity was measured using a KT-1000 arthrometer. Self-reported knee instability score was used for the subjective healing of instability. Eighty-seven knees did not feel unstable (Group 0), whereas 23 knees felt unstable (Group 1). There was a significant difference in AP displacement [Group 0: median 6mm; range 2-15mm and Group 1: median 8mm; range 4-14; p<0.0001]. The threshold value of 7mm was determined using the area under receiver operating characteristic curve of 0.79 [95% confidence interval (CI) 0.69-0.88, p<0.0001]. In multivariate analysis, AP displacement of ≥7mm was an independent risk factor for feelings of instability (odds ratio 7.695; 95% CI 2.306-25.674; p=0.001). AP laxity of ≥7mm represents a known cause of feelings of instability. By controlling AP laxity in TKAs, without stiffness in the knee, it is possible to prevent feelings of instability. The clinical relevance is that AP laxity of <7mm is one of the target areas in TKA. IV.