THE DISTAL TENDON OF THE BICEPS BRACHII - STRUCTURE AND CLINICAL CORRELATIONS

The structure and blood supply of 42 distal biceps tendons were invest igated by means of light and electron microscopy as well as by immunoh istochemistry. Possible structural causes for the rupture of the tendo n are discussed. The distal biceps tendon wraps around the radius duri ng pronation of the forearm. In this area the tendon is exposed to pre ssure and shearing forces in addition to those caused by tension. Two fibrocartilaginous areas were regularly observed. Large chondrocyte-li ke cells were found inside the fibrocartilage. As an expression of str ain, the extracellular matrix is rich in acidic glycosaminoglycans and stains intensely with toluidine blue at pH 1. Electron microscopy sho wed a granular pericellular matrix that increases in size towards the gliding surface. Type I collagen is the main component of the distal b iceps tendon. Type II collagen is found in tendon fibrocartilage but n ot in traction tendons. The gliding surface of the tendon is made up o f reticular fibres that are equivalent to type III collagen. Monoclona l antibodies revealed the presence of dermatansulfate, keratansulfate and chondroitin-C as well as chondroitin-6-sulfate. Blood vessels are usually absent in fibrocartilage, as was shown with a polyclonal antib ody against the basement membrane component laminine. There are signif icant differences between the extracellular matrix of traction and gli ding tendons, which may be responsible for the location of tendon rupt ure.