[The median functional slope of the tibia. Principle. Technique of measurement. Value. Interest].

The tibial slope is an important datum in knee surgery; the levelling by a uni- or bicompartmental prosthesis preserving both cruciate ligaments requires to maintain this slope. The postoperative rehabilitation of the A.C.L. plasties, especially those performed with a patellar tendon and the surgical cure of a genu recurvatum, must integrate this notion. Even if the anatomical slopes are usable in prosthetic surgery, they do not seem precise enough in the field of A.C.L. and tibia recurvatum surgery. In these indications, the authors propose to determine the functional tibial slope defined as being the complement of the angle formed by the tangent to the tibial medial plateau and the lateral mechanical axis of the leg. Measured to an average of 7 degrees on 238 knees, the average median functional slope cannot be deduced from anatomical slopes; it must be measured on a lateral teleradiographic view of the lower limb, the knee being in full extension and X-rayed in true posterior and inferior lateral view.