Pathology and pathogenesis of bursal-side rotator cuff tears viewed from en bloc histologic sections.

Histologic sections from 12 en bloc surgical specimens were studied in order to clarify the pathogenesis of bursal-side rotator cuff tears (BSRCTs). The specimens consisted of the bony insertion, the partially torn area, and the musculotendinous junction of the supraspinatus tendon. There were eight men and four women, with an average age of 48.7 years. Trauma was noted in three instances. All patients exhibited clinical evidence of subacromial impingement, which was confirmed at surgery. Histologic sections were stained with azan or hematoxylin and eosin. All the tears developed from within 1 cm of the insertion. The depth of the tears varied from a superficial flap to a nearly full-thickness tear. Microscopically, the sections demonstrated several abnormalities in addition to degeneration. At the site of insertion and in the distal stump, local disruptions of the normal four layers of enthesis and areas of hypervascularity were observed in all sections. The proximal stumps were rounded, retracted, and avascular, with abundant chondrocytes. No active repair was noted in the proximal stumps. The pathogenesis of BSRCTs appears to be related to: (1) a combination of aging and precarious vascularity of the tendon, (2) repetitive movements of the arm at above-horizontal levels, (3) injury, and (4) especially subacromial-tendon impingement.