‘On-track’ and ‘off-track’ shoulder lesions

[摘要] The basic concept of shoulder stability is explained in the first section of this article so that the following explanation of bony stability will be better and more easily understood by the readers. The shoulder joint is a ball-and-socket joint. Since the socket (glenoid) covers only one-quarter of the surface of the ball (humeral head),1 it has the greatest range of movement of all the joints in the body. When the arm comes to the limit of shoulder movement, it is defined as the ‘end-range’. The track of the extended arm moved along the end-range creates a large circle around the shoulder joint. The area surrounded by this circle is called the ‘mid-range’ of movement. At the end-range of movement, a part of the shoulder capsule is tight, which prevents a translation of the humeral head on the glenoid socket.2 On the other hand, the shoulder capsule is lax in the mid-range of movement, which allows the humeral head to translate freely in any direction on the glenoid socket. This translation of the humeral head is called laxity. The anterior and posterior drawer tests (load and shift test) and sulcus test are performed with the arm in the mid-range of movement because these tests are aimed to detect the laxity of the shoulder joint.

[学科分类] 神经科学

[关键词] shoulder instability;glenoid bone loss;Hill-Sachs lesion;glenoid track;on-track lesion;off-track lesion