Common Causes of Shoulder Pain
Shoulder pain is most commonly associated with injuries to the muscles, tendons and ligaments within the shoulder. However, this pain can also originate from the area of the cervical spine and radiate from the neck down into the shoulder and the arms (Figure 1).
There are two main joints within the shoulder, which include the acromioclavicular joint and the glenohumeral joint (Figure 2). The acromion and the clavicle (collar bone) combine to form the AC joint. The coracoid process is a thick curved structure attached to the upper part of the scapula (shoulder blade). The glenohumeral joint is a ball and socket joint, which involves articulation between the head of the humerus and the glenoid fossa of the scapula.
There are five major muslces of the shoulder joint that are responsible for the movement of the shoulder. In the front portion of the shoulder, originating from the scapula, the muscles involved are the subscapularis muscle and the biceps muscles (Figure 3). The supraspinatus is a relatively small muscle that runs from the top portion of the scapula which inserts into the top of the humeral head. From that back position, the muscles of the shoulder joint include the infraspinatus muscle and the teres minor muslces (Figure 3). These muscles of the shoulder combine to form a thick cuff that is important in stabilizing the shoulder as well as elevating and rotating the arm. Elevation of the arm causes squeezing of the bursa located above the supraspinatus tendon and the acromion.
Biceps tendonitis is a condition that affects the area where the biceps muscle meets the front of the shoulder (Figure 5). It usually develops as a result of rotator cuff tendonitis.
Rotator Cuff Tears:
Tears of the rotator cuff are a common cause of pain associated with the shoulder (Figure 6). Most tears occur in the supraspinatus muscle and can be either partial or complete. Complete tears of the rotator cuff usually require surgery.
The labrum is a cuff of tissue surrounding the rim of the glenoid, which helps keep the head of the humerus in place within the shoulder joint. Tears of the labrum are often associated with significant shoulder pathology. There are two most common types of labral injuries, which are a SLAP tear and a Bankart lesion (Figure 7). A SLAP tear occurs at the point where the tendon of the biceps muscle inserts on the labrum. The Bankart lesion occurs when an individual sustains a shoulder dislocation, which ultimately tears the labrum.
The treatment of shoulder pain depends entirely on the cause of the problem.
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