Author: Frederick A. Matsen III, M.D.
The most common type of rotator cuff tear is a failure of the tendon attachment to the tuberosity. The most common location for this tear is at the anterior aspect of the supraspinatus tendon near the biceps tendon. Details on the patterns of rotator cuff failure can be seen here. Some cuff tears are traumatic occurring when an unexpected load is applied to the arm, such as a fall or a sudden lift with the arm away from the body. These mechanisms are explained in some detail here.
However the great majority of rotator cuff tears are degenerative, arising without injury. These degenerative rotator cuff tears increase with age. It as has also been shown that the cuff tendon becomes stiffer with age. It is apparent that the prognosis for surgical repair of a stiff degenerative tendon is worse that that for repair of a traumatic tear of otherwise healthy tendon.
A number of factors have been identified that increase the risk of rotator cuff tearing, including advanced age, smoking, anabolic steroids, and steroid (cortisone) injections. While it takes a major force to tear the tendon of a young healthy shoulder, the rotator cuff of a shoulder with the risk factors may fail without any noticeable injury. Thus it is useful to distinguish cuff tear (i.e. a traumatic injury) from cuff wear (i.e. failure without an injury) in that this distinction has major implications in selecting treatment.
The types and severity of rotator cuff tears varies widely as shown here.
Interestingly and importantly a high percentage of cuff tears are asymptomatic.
While it used to be said that cuff tears were caused by 'impingement', the evidence does not support this etiology.
See more of the Rotator Cuff Book here.