Partial release of the superficial medial collateral ligament for open-wedge high tibial osteotomy. A human cadaver study evaluating medial joint opening by stress radiography

To perform an open-wedge high-tibial osteotomy (HTO), the medial proximal tibia is frequently exposed by partial distal release of the overlying insertion of the medial collateral ligament (MCL). Biomechanically, any release of the MCL can increase knee laxity when valgus stress is applied. Clinically however, post-surgical valgus instability following HTO with partial MCL release is an uncommon complication. It is known that the open-wedge procedure can re-tention an intact MCL by the width of the base of the wedge. However, this re-tentioning effect is uncertain in small wedge sizes, preexisting medial compartment laxity and in the presence of a partially detached MCL. Considering the good clinical results after HTO, we hypothesized that a partial release of the superficial MCL for HTO does not play a crucial role in stabilizing valgus forces in the human knee. We therefore measured the effect of partial versus complete release of the superficial MCL to determine medial knee laxity represented by the amount of medial joint opening (MJO) under valgus stress in this human cadaver study. In ten knee pairs, the superficial and deep MCL were sectioned in sequence with a standardized abduction force of 15 kp with a Scheuba apparatus applied. In group 1 (5 knee pairs), the superficial MCL was completely sectioned whereas in group 2 (5 knee pairs), sectioning of the superficial MCL was restricted to the anterior border to mimic the surgical exposure for an HTO. To account for the interindividual variability of ligamentous laxity, only increments of MJO within knee pairs were statistically evaluated. Stress radiography did not reveal any significant differences in increments of MJO between knee pair specimens with complete versus partial release of the superficial MCL. We disproved our hypothesis and concluded that the anterior fibers of the superficial MCL do play a crucial role in maintaining valgus stability in this biomechanical setting. Therefore, the release of the superficial MCL for open-wedge HTO should be kept to a minimum to decrease the potential of late valgus instability. This is especially important in patients with small wedge sizes and medial compartment laxity since the anterior MCL fibers are the main contributor to medial joint stability and the re-tentioning effect of the remaining MCL fibers is presumably decreased.