A rotator cuff tear occurs when the tendons that form the rotator cuff weaken and tear. The rotator cuff surrounds the ball-like humeral head of the upper arm. The rotator cuff comprises four muscles—the subscapularis, the supraspinatus, the infraspinatus and the teres minor—and their musculotendinous attachments The tendons that attach these four muscles in the shoulder area to the humerus, fuse together to form the rotator cuff. The tendons of these muscles come under stress from activities that require lifting and rotation of the arm often in a throwing type motion. Any abnormalities of the shoulder joint can aggravate the stress, especially joint looseness (laxity), muscle imbalance, rubbing of the front edge of the shoulder blade (acromion) on the rotator cuff (impingement syndrome), bone spurs, and bursitis. As the tendons become irritated, inflammation develops (tendinitis). Circulation to the rotator cuff decreases with age and the tendons themselves degenerate over time. Eventually, this can lead to weakening and even tears in the rotator cuff.
Tears are described as either partial-thickness tears or full-thickness, depending on the amount of tissue damage. Partial-thickness tears do not go all the way through the cuff, although a large surface area may be involved. Full-thickness (complete) tears create a gap in the rotator cuff with concomitant loss of function (range of motion and strength). Tears are classified as acute or chronic depending on onset. Acute tears are the result of forceful injury to the shoulder and straining of the tendon beyond its mechanical limits. Chronic tears occur from repetitive wear and tear of the rotator cuff and are more common as we age. Conditions that may predispose an individual to a rotator cuff tear include impingement syndrome, bone spurs, instability of the shoulder (glenohumeral) joint, or congenital abnormalities of the shoulder.
Incidence and Prevalence: Rotator cuff tears may affect from 5% to 40% of the population (Malanga, “Rotator”). Cadaver studies showed that 39% of individuals over the age of 60 have full-thickness tears (Malanga, “Rotator”). Since some partial and full-thickness rotator cuff tears produce no symptoms, it is difficult to estimate incidence and frequency.