Significance of granulation tissue in torn supraspinatus insertions: an immunohistochemical study with antibodies against interleukin-1 beta, cathepsin D, and matrix metalloprotease-1.

The pathophysiology of rotator cuff tears can be elucidated by examining the tendinous insertion of the supraspinatus muscle. As seen by light microscopy, the granulation tissue around the insertion of a torn supraspinatus tendon appears to induce osteochondral destruction by means of multinucleated giant cells and chemical mediators. The purpose of this study was to examine the contribution of certain chemical mediators to osteochondral destruction using immunohistochemical analysis of interleukin-beta, cathepsin D, and matrix metalloprotease-1. Sixteen supraspinatus insertions with portions of the greater tuberosity, including eight complete-thickness tears and eight incomplete-thickness tears, were obtained during surgery. Six fresh cadaveric supraspinatus tendons without grossly evident tears served as normal controls. Strong immunoreactivity was found in all 16 torn supraspinatus insertions but not in the six insertions of apparently intact tendons. Macrophages and multinucleated giant cells, which showed immunoreactivity for all three chemical mediators, were often found at the interface between the osteochondral margin of the enthesis and the granulation tissue, suggesting that they may be involved in osteochondral destruction. We therefore concluded that, in addition to repetitive subacromial impingement, this granulation tissue may contribute to the development of rotator cuff tears by weakening the insertion.