Rotator cuff injuries

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http://lazahealth.org/rotator-cuff-injuries/

The tendons of the four muscles comprising the rotator cuff muscle group create a musculotendinous cuff around the glenohumeral joint on its anterior, posterior, and superior aspects.  These tendons are fused to the underlying capsule of the shoulder joint and has a critical role in maintaining the stability of the shoulder joint.

The four rotator cuff muscles are
subscapularis
infraspinatus
teres minor
supraspinatus

Wear and tear of the rotator cuff tendons is caused by repeated abduction and flexion. Such movements require the tendons to rub against the acromion and coraco-acromial ligament, and cause cuff tears or rupture over time. Under normal circumstances, the large subacromial bursa that extends laterally beneath the deltoid reduces some of this friction. Degenerative changes to the subacromial bursa, medically known as subacromial bursitis, increases the risk of developing supraspinatus tendinitis as the most vulnerable tendon likely to be damaged is the tendon of the supraspinatus. The term, “pericapsulitis” may also be used to refer to this phenomenon.  The classic symptoms include spasm of pain in the middle range of abduction when the diseased area impinges on the acromion.

A patient may be asked to maintain 90° abduction against mild resistance acting downwards on the forearm to test for partial tear of the rotator cuff.  The patient is unable to abduct 90° in extensive rupture of the cuff. The compensatory strong contraction of the deltoids pulling the humerus upwards towards the acromion and rotation of the scapula and shoulder girdle allows for up to 45° abduction in cases  of extensive cuff tears. The first 15° of abduction may require mechanical assistance if the supraspinatus tendon is in an advanced stage of tendinitis and has either calcified or ruptured as the primary function of the supraspinatus muscle is to hold the head of the humerus in the glenohumeral fossa at the initial stages of abduction.

Rotator cuff tendinitis is a common cause for shoulder pain and may be caused by overuse or may arise spontaneously without a known cause.  It is typically aggravated by excessive overhead activity of the upper limb.