Predicting Functional Coronal Knee Laxity in Pre-Operative TKA Patients Using Morphological Measurements

Abstract

Currently, pre-operative analysis of soft-tissue balance is limited to measures of passive laxity rather than active laxity. By including active laxity data, a more comprehensive surgical plan can be delivered, however there are no measures for active laxity currently in routine use. Therefore, the validation of a proxy measure based on routine collected imaging is valuable. This study aimed to determine whether coronal knee laxity can be predicted from pre-operative alignment and bony morphology of the knee. Fifty-eight patients with pre-operative CT and stressed x-ray imaging for activity laxity were analysed to identify anatomical landmarks and determine varus-valgus laxity ranges for a range of flexion angles with the joint subjected to lateral forces. Correlations between anatomical and alignment parameters, vs laxity ranges and midpoints were determined using pairwise complete Pearson linear correlation analyses. Of the 17 anatomical/alignment measurements studied, 8 correlated significantly with the knee laxity range’s midpoint at 20 ̊ flexion, with the strongest correlation being with supine coronal alignment (r = 0.95, p < 0.001); the findings were similar at 45-90 ̊. Compared to knee laxity midpoint, knee laxity range was not as strongly correlated with anatomical and alignment parameters, with only 3 anatomical parameters correlated significantly with laxity range at 20 ̊ flexion and none at 45-90 ̊ flexion. These results suggest morphological measurements and anatomical characteristics may help define functional coronal laxity range of the knee.