The two main causes of rotator cuff tears are injury from lifting something heavy or falling, and a slow wearing down of the tendon over time. Degeneration of the tendon occurs as people age and is more common in the dominant arm, says the American Academy of Orthopaedic Surgeons.
Several factors increase the chance of a degenerative tear caused by a worn-down tendon. One factor is repeating the same motion in the shoulder over and over, which is usually seen in baseball pitchers, tennis players, painters or carpenters, according to the American Academy of Orthopaedic Surgeons. As a person ages, the blood supply lessens in the shoulder tendon, making it harder for the tendon to repair itself. Bone spurs in the arm rub the shoulder tendon when the arms are lifted, causing weakness in the tendon.
A tear in the rotator cuff in younger people is usually the result of an injury, as reported by the American Academy of Orthopaedic Surgeons. A fall on an outstretched arm or lifting something heavy with a jerking motion are the most common injuries. The rotator cuff may also tear if the collarbone is broken or the shoulder is dislocated. Tears caused by injury usually cause extreme pain and weakness in the arm.