A NOVEL ALGORITHM TO ACHIEVE EFFECTIVE SOFT TISSUE MANAGEMENT IN TKR USING NAVIGATION

Abstract

Introduction: A successful total knee replacement (TKR) relies upon effective soft tissue management. Historically, soft tissue balancing has been difficult to assess and quantify intraoperatively. Computer navigation permits us to accurately assess kinematics during surgery. In a previous study we performed a series of varus and valgus stress measurements in extension to devise an algorithm for soft tissue management. In this study we evaluate the effectiveness of this algorithm.

Methods: This prospective study used the Orthopilot® CT-free navigation system during TKR for 57 patients with end-stage arthritis. We collected intraoperative kinematic data for 42 varus knees. Pre- and post-operatively, a varus and valgus stress was applied at maximum extension, recording the mechanical femorotibial (MFT) angle. There were no patellar resurfacings. The following medial releases were performed based upon the kinematics and the algorithm below:

1. No release–MFT angle not less than −12° with varus stress, greater than 2° with valgus stress, and/or if extension deficit was not greater than 5°.

2. Moderate release–MFT angle less than −12° with varus stress, between −5° and 2° with valgus stress, and/or extension deficit not greater than 5°.

3. Proximal release–MFT angle less than −12° with varus stress, less than −5° with valgus stress, and/or extension deficit greater than 5°.

Results: Pre-operatively, the mean MFT angle was −9.6°varus (−3° to −22°) with varus stress and −0.8°varus (4° to −11°) with valgus stress. Post-operatively, the mean MFT angle was −3.5° varus (0° to −5°) with varus stress, and 2.1° valgus (4° to −1°) with valgus stress.

Using regressional analysis, there was a strong linear correlation between both varus (r=0.871, p< 0.0001) and valgus (r=0.894, p< 0.0001) stresses and the MFT angle.

Post-operatively, the mean MFT angle was maintained within a narrow range (0° to −5° with varus stress, 4° to −1° with valgus stress), with no outliers. There were no extension deficits.

Conclusions: Using computer navigation a quantifiable soft tissue management system was introduced. We evaluated this algorithm, and obtained reproducible results within a narrow range and no outliers. This algorithm may provide an effective soft tissue management plan in TKR.