1. The avascular zone in the tendon of the supraspinatus near its insertion was not seen in the other tendons comprising the rotator cuff, except for the superior portion of the insertion of the infraspinatus which, on occasions, showed a small avascular area. The biceps tendon, however, also showed an avascular zone as it coursed over the head of the humerus. It is suggested that the anatomical disposition of these tendons makes them subject to constant pressure from the head of the humerus, which tends to wring out the blood supply to these tendons when the arm is held in the resting position of adduction and neutral rotation.

2. Although this study did not produce any evidence that the relative avascularity of the tendons over a prolonged period could be indicted as the sole cause of the degenerative changes that so commonly occur, it was noted that the degenerative changes occurred first and that they were always most extensive in the areas of avascularity. It was also observed that the zones of relative avascularity preceded, and were not the result of, the degenerative changes.

3. With the onset of tendon degeneration, secondary vascular phenomena were observed. Firstly, there was a reaction that appeared to be a foreign body inflammatory response with the development of vascular tufts of granulation tissue. It was thought that these vascular changes were secondary to the breakdown in the tendons and were not the cause of the breakdown as previously suggested by Anderson and Moore. it was noted, moreover, that with the progression of degenerative changes in the supraspinatus tendon, the tendon became much attenuated and, as it did so, the zone of relative avascularity appeared to extend. This secondary shut-down of the vascular bed might well be caused by an increased tension in the tendon. In those tendons in which spontaneous rupture had occurred, it was noted that the major part of the tendon proximal to the rupture was avascular and showed evidence of much degenerative change. This study therefore suggests that in the operative repair of such lesions it is necessary to excise the degenerate avascular tendon in order to effect a sound repair. It is also suggested that detachment of the supraspinatus muscle from the supraspinous fossa in order to advance the whole muscle belly is the only technique possible to enable the surgeon to replace healthy tendon directly into bone, as suggested by Debeyre and his colleagues.