Pathological conditions affecting the hip and knee joints occupy a particular place amongst the important orthopaedic entities affect ing the extremities. On the one hand they are relatively frequent and on the other they mean for the patient limitation of his ability to walk, because of their considerable detrimental effects. A purposeful basic treatment of these joint diseases (and here osteoarthritis takes pride of place) is only possible if it stems from a reliable biomechanical analysis of the normal and pathological stressing of the joint in question. Whilst the situation in the hip can be considered to be fundamentally clarified, a comprehensive representation of the knee is still lacking, particularly when taking into account the latest knowledge of biomechanics. Recently our concepts of the kinematics of the knee have been completely changed, but the clinically important question of articular stressing remains unanswered. Dr. Maquet has carried out pioneer work in this field for some years in adapting, by analogy, to the knee joint principles already accepted for the hip joint. Since the knee is not a ball and socket joint, a complicated problem arises for which new thoughts are necessary. The results of the numerous operations carried out by Dr. Maquet according to the biomechanical considerations demon strate that his thinking is fundamentally correct. Above all, it is here again proven (as earlier in the case of the hip) that healing of osteoarthritis depends decisively on reducing and evenly dis tributing joint pressure.