Indication and treatment of pathological tibial slope

Abstract

Tibial slope describes the posterior inclination of the tibial plateau (mean in a healthy population: 8.8°; range: 6–12°). Biomechanical and clinical studies have shown that an abnormal tibial slope influences the stability of the knee joint. An increased tibial slope is considered a risk factor for recurrent instability after anterior cruciate ligament (ACL) reconstruction. A slight or negative inclination of the tibial plateau, on the other hand, can contribute to the development of posterior instability. If an abnormal tibial slope is present in combination with clinical symptoms (instability, hyperextension), it can be described as pathological. In this case, corrective osteotomy may be indicated. Depending on their relationship to the tibial tuberosity, various osteotomy techniques (supratubercular, tubercular, and subtubercular osteotomy) are possible for correction of an elevated tibial slope. In recent years, the subtubercular osteotomy has largely become the preferred approach. The situation is more difficult when an increased posterior tibial slope is combined with a double varus situation (varus ≥ 5°; joint line conversion angle, JLCA ≥ 2°), because a varus deformity ≥ 5° cannot be adequately corrected with an anterior closing-wedge osteotomy. In this case, a modified medial opening-wedge osteotomy is required, in which the hinge of the osteotomy is relocated anterolaterally, and a small wedge is removed from the ascending osteotomy. The indication for correcting a decreased posterior slope may be recurrent posterior instability or genu recurvatum with hyperextension. For more severe deformities (negative slope), an osteotomy with detachment of the tibial tuberosity is usually required. For minor deformities, a subtubercular osteotomy or a biplanar osteotomy at the level of the tibial tuberosity may be sufficient. In the case of a combination of posterolateral instability and a varus deformity (varus > 5°, JLCA > 2°), combined correction of varus and slope can be reliably achieved using a medial opening-wedge osteotomy.