Purpose of the study: The tibial slope is an important parameter for knee surgery. Tibial slope designates the inclination of the tibial plateaus in the sagittal plane. The presence of a tibial slope and its value is intimately related to the condylotrochleal profile. The importance of tibial slope in knee disease and knee surgery is now universally recognised.

Material and method: We reviewed 140 cases of anterior cruciate ligament (ACL) ligamentoplasty performed at the institute; 25 failures were identified. After analysis of the position of the tunnels, particularly the femoral tunnels, the most documented cause of failure, as well as other factors of failure, we measured the mean tibial slope in all operated patients.

Results: Subjective Lachmann and the IKDC and ARPEGE scores associated with the dynamic study (TELOS) helped understand why knees can become unstable despite good surgical technique.

Discussion: William and Lissner established a mathematical relations between tibial slope and stress forces applied to the ACL. Dejour and Bonnin demonstrated the effect of the tibial slope on anterior subluxation and single leg stance. The tibial slope should thus be considered for all knee procedures. Bonnin demonstrated that an excessive slope can be a factor of plasty failure.