The distribution of the thickness of cartilage as well as of the subchondral mineralization reflects the various stresses on the joint compartments. Both long bones of the lower arm participate in load bearing. The humeroradial and humeroulnar parts of the joint are incongruent. The capitulum humeri is slightly smaller than the corresponding fovea, whereas the radius of the trochlea is bigger than that of the incisura trochlearis. Therefore, the medial compartment can be seen as a dynamic pressure-transmitting system. The collateral ligaments limit the degree of flexion and extension together with the olecranon and coronoid process. In the extreme flexed position the insertion regions of the ligaments at the humeral crests are twisted. This may explain why the corresponding entheses consist of fibrocartilage. Some molecular components of these regions can become targets of autoimmune reactions. The rotational movements are restricted by soft tissues and muscles.