This information has been prepared to help patients and their families better understand the diagnosis and treatment options of rotator cuff disease and injury. Before discussing specific problems of the rotator cuff, it will help to review some of the basic anatomy of the shoulder and the rotator cuff. Some of the illustrations which accompany this handout will help you to get a general idea of the anatomy and to visualize it better.
The shoulder is not a true ball and socket joint like the hip. One side is round, and the other side is flat. The round side is called the humeral head, and the flat side is called the glenoid. This relationship resembles more like a golf ball sitting on a tee, rather than a classic ball and socket. The bones that form the shoulder joint, therefore, do not provide much, if any, built-in stability because of their shape.
The structures that do provide stability are the ligaments. These ligaments surround the joint; they are attached to the humeral head on one side and the glenoid on the other. These ligaments are in the front of the shoulder, the underneath-side of the shoulder (deep in the arm-pit), and the back of the shoulder; together they form a “hammock” to support the ball within the glenoid socket. On top of the shoulder joint and overlaying the ligaments in the front and the back of the shoulder are a group of tendons.
These tendons originate from four muscles which together, as a group, are called the rotator cuff. For those of you who are more interested in anatomic details, the names of the muscles and tendons that comprise the rotator cuff are: the subscapularis, in the front or anterior aspect of the shoulder; the biceps tendon, also in the front of the shoulder; the supraspinatus, which covers most of the top; and the infraspinatus and teres minor muscles, which comprises the posterior or back.
The ligaments described above which provide stability to the joint are actually underneath or deep to the rotator cuff tendons, primarily the subscapularis and the infraspinatus / teres minor tendons. These rotator cuff muscles (and tendons) do also act to support and stabilize the shoulder, but their main function is to move the arm and shoulder. The ligaments are called the glenohumeral ligaments and are named according to their position; the superior and middle glenohumeral ligaments are in the front of the shoulder; the inferior glenohumeral ligament lies at the bottom or in the arm-pit; and the posterior glenohumeral ligament which is found in the back, all of which contribute to give the joint stability.
As mentioned above, the ligaments provide stability to the shoulder. The muscles and tendons provide some degree of support and stability to the shoulder, but their main function is to move the arm and shoulder. The combination of different muscle groups that surround the shoulder [i.e. the rotator cuff muscles, the large deltoid muscle (which covers the outside of the shoulder), as well as some other muscles, like the pectoralis major (chest muscle)], work together in a rather complex fashion to allow you to move the shoulder through a remarkable range of motion.
Other important structures related to the shoulder and influence rotator cuff disease and injury are the acromion (which is the bone on top of the shoulder) and the collarbone or clavicle which joins to the acromion. This joint is called the acromioclavicular joint or the AC joint. The acromion and the AC joint can develop spurs, particularly in the older age groups, which can irritate and abrade the rotator cuff and cause abnormal wear and tear of the rotator cuff.
- Next >>