LIGAMENT BALANCE FOR TOTAL KNEE ARTHROPLASTY

Abstract

Purpose: The purpose of this work was to validate the most reliable technique for obtaining ligament isometry of the knee in flexion.

Material and methods: This prospective series of non-cemented non-posterior stabilised Interax knee prostheses (Howmedica) implanted by the same surgeon included 57 genu varum knees with degenerative disease. Mean preoperative femorotibial varus was 8.23°. Landmarks used intraoperatively included the posterior condylar line (PCL), the biepicondylar line (BECL) and the Whiteside line (WL). Ligament balance was measured with the Derby tensor.

Results: The first part of the assessment concerned ligament balance in extension. Mean initial medial retraction, measured with the tensor, was 3.6°. Release of the concavity was performed in 62% of the knees with mean residual retraction of 1°. The second time was to evaluate balance at 90°. Using the anatomic landmarks, the PCL was parallel to the BECL in 22% of the knees and perpendicular to the WL in 26%. There was a weak angulation in 28% and 30% of the knees and in 50% and 44% respectively. There was thus a strong correlation intra-operatively between these two landmarks and the initial radiographic varus. Evaluation with the tensor showed mean 2.96° medial retraction. The correlation between the anatomic measures and the tensor ligament measures was very significant. When the BECL was parallel to the PCL, medial retraction with the tensor was 1.12°. The angulation was small, 2.25°. When the angle was wide, the mean measure was 4.4°. We found the same results with the WL. External rotation of the anteroposterior femoral cut was then guided by these different measures. It was 2.6° on average (0–6°). Residual medial retraction, measured with the tensor, was thus significantly improved, only 0.4° on average (−2 to +2).

Discussion: After ligament rebalancing in extension, there persisted frequently an imbalance in flexion (62%). This was independent of the preoperative varus. It was corrected by external rotation of the femoral implant, the value assess approximately from the landmarks. It was measured in our hands reliably with the Derby ligament tensor.