EARLY POST-OPERATIVE MEDIAL KNEE STABILITY HAS AN IMPORTANT ROLE ON ONE-YEAR POST-OPERATIVE AMBULATORY FUNCTIONAL RECOVERY IN TKA

Objective As the aging society progresses rapidly in Japan, the number of elderly patients underwent TKA is increasing. These elderly patients do not expect to do sports, but regain independency in the activity of daily living. Therefore, we measured basic ambulatory function quantitatively using 3m timed up and go (TUG) test. We clinically experienced patient with medially unstable knee after TKA was more likely to result in the unsatisfactory outcome. We hypothesized that post-operative knee stability influenced ambulatory function recovery after TKA. In this study, we evaluated ambulatory function and knee stability quantitatively, and analyzed the effect of knee stability on the ambulatory function recovery after TKA. Materials & Methods Seventy nine patients with varus type osteoarthritic knees underwent TKA were subjected to this study. The mean age of surgery was 72.4 years old. Preoperative standing coronal deformity was 9.6 degrees in varus. TUG test results in less duration with faster ambulatory function. TUG (seconds) was measured at 3 time periods; pre-operatively, at hospital discharge and 1year after surgery. To standardize TUG recovery time during 1 year after TKA, we defined TUG recovery rate as the percentage of recovery time to the pre-operative TUG as shown in the following equation. TUG recovery rate (%) = (TUG pre-op –TUG 1y po) / TUG pre-op ×100 We also evaluated the knee stability at hospital discharge and 1year after surgery. The knee stability at extension and flexion were assessed by varus and valgus stress radiography using Telos (10kg) and stress epicondylar view with 1.5kg weight at the ankle respectively. Image analyzing software was used to measure joint separation distance (mm) at medial as medial joint opening (MJO) and at lateral as lateral joint opening (LJO) at both knee extension and flexion. (Fig.1) The sequential change of TUG was analyzed using repeated measures ANOVA (p Results The mean TUGs were 13.4, 13.7 and 10.8 seconds pre-operatively, at hospital discharge and 1 year after TKA respectively. Significant decrease was found at 1 year after surgery. TUG pre-op did not show significant correlation to any joint openings. TUG 1y po was positively correlated with both flexion and extension MJO at hospital discharge. (Fig.2) TUG recovery rate negatively correlated to flexion-MJO at hospital discharge. (Fig.3) Discussions The most interesting findings in the present study were that both flexion and extension MJO at hospital discharge were positively correlated with TUG 1y po and negatively correlated with TUG recovery rate. This indicated that early post-operative medial stability played an important role in the recovery of ambulatory function. The early post-operative medial instability would cause pain and deteriorate functional recovery after surgery. There is some disagreement regarding the importance of pursuing the perfect ligament balance, which would be more likely to result in medial instability. Consequently, surgeons should prioritize medial stability for better ambulatory functional recovery after TKA.