Retrospective studies demonstrated inadequate soft tissue balance is associated with the long-term outcome of total knee arthroplasty (TKA). However, most of these studies have evaluated the joint laxity only postoperatively without anesthesia. Therefore information about the effect of anesthesia on knee laxity is important for soft tissue balancing at the time of surgery. This study was conducted to determine how anesthesia affects the varus and valgus stress tests after TKA.
A consecutive series of 26 patients undergoing staged bilateral TKA was evaluated. Varus and valgus laxity of the knee with the TKA implant was measured a few days before the contralateral TKA without anesthesia and again immediately after the contralateral TKA under spinal anesthesia.
The laxity was significantly increased from 3.0° to 3.6° (p = 0.005) and from 4.7° to 5.7° (p = 0.007) in medial and lateral side, respectively, when the stress tests were performed under anesthesia in comparison to the laxity measured without anesthesia. The major change in laxity (≥3°) was measured in 6 (23%) patients tested without anesthesia.
Anesthesia significantly influenced knee joint laxity after TKA. The findings of this study suggest that muscular forces impart a stabilizing force across the joint.