Degenerative disease in rotator cuff tears: what are the biochemical and histological changes?

The histopathological changes associated with rotator cuff tears include thinning and disorganization of collagen fibers, the presence of granulation tissue, increased levels of glycosaminoglycans, fibrocartilaginous metaplasia, calcification, fatty infiltration, and necrosis of the tendon margin with cell apoptosis. The biochemical changes include an increase in the expression of matrix metalloproteinases (MMPs) and a decrease in tissue inhibitor of metalloproteinases (TIMP) messenger ribonucleic acid expression. Histological evidence of tendinopathy has been found in patients with rotator cuff tear. Biochemical changes include significant increases in MMP1, MMP2, MMP3, and in TIMP1 and TIMP2 levels, not only at the lateral supraspinatus edge, but also in the macroscopically intact portion of the supraspinatus tendon and in the intact subscapularis. The tissue in the ruptured area of the supraspinatus tendon undergoes marked rearrangement at molecular levels. This involves the activity of MMP1, 2, and 3 and supports a critical role of MMPs in tendon physiology. Intact parts of the torn supraspinatus tendon can present the histopathological changes associated with rotator cuff tears. These findings suggest that biochemical changes can already occur in a macroscopically intact tendon and seem to point to a global degenerative process in the shoulder.