Postoperative lateral ligamentous laxity diminishes with time after TKA in the varus knee

For successful TKA, good soft tissue balance is one of the most important factors; however, it is unknown whether the coronal balance immediately after surgery is maintained with time. We hypothesized, if neutral mechanical alignment was achieved at the time of TKA, some degree of lateral ligamentous laxity could be accepted and the laxity would diminish with time. To confirm this hypothesis, we posed two scientific questions: (1) Does the coronal ligament balance measured immediately after TKA change with time? (2) Does the degree of preoperative varus alignment correlate with the lateral or medial ligamentous laxity observed after TKA? We measured coronal lateral or medial ligamentous laxity in 71 knees with varus deformities immediately after surgery and at 3, 6, and 12 months thereafter. The mean mechanical axis was 15.9 degrees varus preoperatively and 0.4 degrees varus postoperatively. The mean medial ligamentous laxity was relatively constant postoperatively from immediately after surgery to 12 months. However, the mean lateral ligamentous laxity was as much as 8.6 degrees immediately after surgery and decreased to 5.1 degrees at 3 months. The lateral ligamentous laxity immediately after surgery correlated with the preoperative varus mechanical axis. Our data show residual lateral ligamentous laxity observed in preoperative varus deformity may be corrected spontaneously after TKA.