Posterior Tibial Slope: Understand Bony Morphology to Protect Knee Cruciate Ligament Grafts

Abstract

Improved understanding of the biomechanical significance and clinical repercussions of tibial slope on cruciate ligament function has sparked a newfound clinical interest in this morphological feature. Using either magnetic resonance imaging or lateral tibia radiographs, the anterior-posterior angulation of the tibial plateau relative to the tibial shaft can be measured. Clinical and biomechanical studies have reported that increased posterior tibial slope (PTS) places significantly increased tension on the native and reconstructed anterior cruciate ligament (ACL), leading to an increased risk of failure. It has also been suggested that increased PTS of the lateral tibial plateau has a greater impact on ACL forces and anterior tibial translation than PTS of the medial tibial plateau. Conversely, a decreased PTS has been shown to be a risk factor for recurvatum deformity, posterior cruciate ligament (PCL) injury, and posterior tibial translation and has been linked to single bundle PCL reconstruction failure. In the setting of ACL insufficiency with a PTS greater than 12°, anterior closing wedge osteotomy has been shown to be protective for ACL reconstructions. Alternatively, some surgeons have advocated for the addition of lateral extraarticular stabilization procedures in the setting of increased PTS. Further, in the setting of PCL insufficiency with an anteriorly directed, or flat, PTS, anterior opening wedge osteotomy has shown encouraging results. In addition, double bundle PCL reconstructions should be strongly considered in the setting of anteriorly directed, or flat, tibial slope.