DISPOSITION OF COLLAGEN FIBRILS IN HUMAN TENDONS

Fixed and unfixed human tendons originating from cadavers and postoper ation specimens were examined using inclined parallel beams of light i n a reflecting mode. Along the tendon, numerous planes, constantly inc lined to the axis, were observed edge-on at the surface and within the interior. Their angle of inclination, with respect to the distal end was very nearly +/-50 degrees. The planes consisted of individual segm ents arranged in steps which were on average 190 x 50 mu m. Similar co nfigurations were also observed with the scanning electron microscope. Using this technique, the segments were identified with collagen bund les turning at a sharp angle with respect to the axis of the tendon at the level of the inclined plane. Crimped planes were found to be irre gularly distributed along the tendons. On longer flatter tendons the a verage distance between planes was in the range of 1-12 mm. On stretch ing, the inclined pattern disappeared and was rapidly reestablished in the previously observed position when the strain was released. It is suggested that the observed structure forms a mechanism which is respo nsible for the appearance of the first part or 'foot' region of the te ndon's stress-strain diagram.