[The effect of releasing the medial stabilisers of the knee on the magnitude of correction in opening-wedge high-tibial valgus osteotomy. Anatomy study on cadavers].

PURPOSE OF THE STUDY When a larger opening of high-tibial osteotomy is necessary to achieve good correction of the lower extremity axis, partial release of the attachments of the medial stabilisers of the knee may be required. The aim of the study was to ascertain, in cadaver specimens, the effect of loosening the medial knee stabilisers on the magnitude of correction in medial opening-wedge high-tibial valgus osteotomy. MATERIAL AND METHODS Thirty-eight knees obtained from cadavers of Caucasian race were dissected. Medial opening-wedge high-tibial valgus osteotomy was performed using a dynamic distractor, constructed by us, with a dynamometer to ensure constant force action. Using a kinematic navigation system, the lower leg axis was studied at opening-wedge osteotomy under constant forces of 100 N and 150 N. The change in its angulation was recorded after each step in releasing the medial stabilisers whose structures were gradually made loose, under constant action of the given force, in the following order: superficial portion of the medial collateral ligament, tendons of the gracilis, semitendinosus and sartorius muscles. RESULTS The results were statistically analysed using descriptive statistical methods and the two-sample paired t-test with the level of statistical significance set at p < 0.05. Loosening of the medial stabilisers one by one under a constant load led to a statistically significant change in alignment. The most significant change in angulation, both in clinical and statistical terms, was that of 3.4° occurring after the superficial portion of the medial collateral ligament was made loose under a constant force of 100 N applied to osteotomy. Thus, this loosening contributed by 62% to an overall change of 5.5° in the lower extremity mechanical axis, as compared with the condition not allowing for loosening of the stabilisers. Under a load of 150 N applied to osteotomy, loosening of the medial collateral ligament resulted in a change by 4.1°, which accounted for 56% of an overall change of 7.3° that occurred after all stabilisers were released. On distraction of the osteotomy using a higher force, an increase in a stabilising effect of the pes anserinus was apparent. DISCUSSION The evolution of angle-stable implants has advanced options for reliable fixation of high-tibial corrective osteotomy which involves cutting out a wedge and forcing it open on the medial side. These implants provide stable fixation even when a large correction of the limb mechanical axis is required, and allow for rehabilitation with early weight-bearing. As with a large correction the force needed to make the wedge open is increasing, it is necessary to consider loosening of the medial stabilisers of the knee. According to our knowledge, no study on the effect of individual medial stabilising structures of the knee on the force required to open high-tibial osteotomy with the wedge opened medially has been published. CONCLUSIONS The process of correcting lower extremity alignment by high-tibial opening-wedge valgus osteotomy brings about an increase in tension of the stabilisers on the concave side of the deformity. Our results show an important role of releasing the superficial portion of the medial collateral ligament in the reduction of forces necessary to correct a deformity.