[Chronic anterior and internal instabilities of the knee. Theoretical study. Clinical and radiological diagnosis].

Antero-medial instability of the knee comprises 96 p. 100 of all knee instabilities. In most instances, the instability is moderate and cannot be analyzed without an adequate understanding of the anatomy and mechanics of the joint. They usually occur after forced movement in medial rotation which ruptures the anterior cruciate ligament and may rupture the postero-medial ligament. Less frequently, they appear after a strain in abduction, flexion and lateral rotation. Some degree of hyper-extension may be added to the primary causal strain. Diagnosis is mainly based on the physical examination which determines the type of surgical procedure that should be made. An anterior draw sign and a click in medial rotation are present when the anterior cruciate ligament is torn. When these signs are very marked, it implies an associated tear of the postero-medial ligament. Standard X-rays and arthrography are most important. Arthroscopy is not of great value and only makes it possible to visualize the meniscus lesions which are important for prognosis. The author describes an original concept of the mechanics of rotation of the knee and the pathogenesis of lesions of the medial capsulo-ligamentous layer.