NAVIGATION PREDICTORS IN DETERMINING THE FREQUENCY OF SOFT TISSUE RELEASE IN KNEE ARTHROPLASTY

Abstract

The necessity of soft tissue release to achieve a stable, balanced knee in previous publications has a high rate and a wide range of 50–100% of total knee arthroplasties (TKA). This reflects disagreement regarding the determinants for soft tissue release which is partly due to lack of standardized quantitative measures. Recent advances in navigation may standardize and replace conventional methods regarding soft tissue balancing. We propose two navigation predictors that quantitatively determine the least amount of collateral ligament release necessary to achieve a stable neutral knee, thus reducing the frequency of release.

100 patients underwent navigated TKA. Data of 93 were eligible. Preoperative deformity ranged 18°varus −13° valgus. Ratio of Varus/Valgus= 66/27. Ages were 46–85 yrs. Mean BMI= 36Kg/m²

First navigation predictor determines collateral release when varus/valgus deformity is uncorrectable by stress deflection test before tibia resection. Second predictor determines release when delta mediolateral gap > 4mm before femoral resection using a Tensioner with two independent pads.

10 out of 93 cases (10.75 %), required collateral ligament release to achieve a postoperative mechanical axis of 0° (SE±0.11) with a mean mediolateral deflection in extension of 1.43°, and a mean range of motion of −3° to 127° of flexion. First predictor has 98% accuracy. Second predictor has 96% accuracy but their combination had 100% accuracy with no false negative predictions.

Balanced neutral TKA is achieved by soft tissue release, bone resection or as in this study, by adjusted navigated femoral resection (through rotation, size and level of resection) which balanced knees that otherwise should have soft tissue release. Navigation predictors are reliably accurate to quantitatively determine the necessity of soft tissue release to achieve a neutral stable knee with a significantly lower release rate in comparison to non navigated TKA series rate of 50–100%. (p< 0.001) (95% confidence interval).