Evaluation of soft-tissue balance during total knee arthroplasty.

PURPOSE To evaluate soft-tissue balance during versus after total knee arthroplasty (TKA). METHODS 18 men and 75 women aged 52 to 85 (mean, 68) years who had moderate-to-severe varus deformity underwent TKAs using the Scorpio non-restrictive geometry posterior-stabilised system (Stryker Howmedica Osteonics; Allendale, [NJ], USA). All surgeries were performed by a single surgeon using the medial parapatellar approach. After the bony and soft-tissue procedures, soft-tissue balance was measured intra-operatively using a tensor/balancer device. The coronal laxity--angles between the cut surfaces of the femur and tibia--were measured at 0 degree (in extension) and 90 degrees (in flexion). The central gap was also measured. Immediate postoperative soft-tissue balance was measured using an arthrometer, while anteroposterior stress radiographs were being taken. A valgus or varus force was applied just above the knee on the lateral or medial side, with the knee counter-supported and at 15 degrees flexion. RESULTS Intra-operatively, the mean coronal laxity at 0 degree (in extension) and 90 degrees (in flexion) was 2.1 degrees and -1.6 degrees, and the mean central gaps were 21.2 and 23.5 mm, respectively. Immediate postoperative mean coronal laxity was 2.9 degrees, indicating that lateral laxity was greater than medial laxity. The postoperative coronal laxity was positively corrected to the intra-operative coronal laxity at 0 degree (r=0.304, p=0.003), but not to the intra-operative coronal laxity at 90 degrees (r= -0.07, p=0.47). CONCLUSION Slightly greater lateral laxity was observed after TKA, although equal medial-lateral balance was achieved intra-operatively.