COLLAGENOUS FIBRIL TEXTURE OF THE HUMAN KNEE-JOINT MENISCI

Anatomical and clinical literature describes the arrangement of collag en fibrils in the human meniscus as being ''arcade-like''. The ''arcad e-like'' orientation, mainly running in a radial direction in the inte rnal circumference and in a circular direction in the external circumf erence, was found in polarization light microscopic studies. This, how ever, does not provide a mechanical explanation for the direction of m eniscus tears. In view of this contradiction collagen fibrils in the m enisci of adults aged from 18 to 85 years were exposed layer-by-layer to study their arrangement by scanning electron microscopy. The result s obtained by this procedure were compared to the path of the split li nes. Scanning electron microscopy reveals three distinct layers in the meniscus cross section: (1) The tibial and femoral sides of the menis cus surfaces are covered by a meshwork of thin fibrils with a diameter of approximately 30 nm. (2) Beneath the superficial network there is a layer of lamellalike collagen fibril bundles on the tibial and femor al surface. In the area of the external circumference of the anterior and posterior segments the bundles of collagen fibrils are arranged in a radial direction. In all other parts the collagen fibril bundles in tersect at various angles. (3) The main portion of the meniscus collag en fibrils are located in the central region between the femoral and t he tibial surface layers. Everywhere in the central main portion of th e meniscus the bundles of collagen fibrils are orientated in a circula r manner. The split lines in the region of the internal circumference of the menisci are arranged in a circular manner, generally running in a radial direction in the portions adjacent to the base. Scanning ele ctron microscopy reveals that the direction of the split lines depends on the orientation of the collagen fibrils in the superficial lamella r layer. The arcade-like path of the collagen fibrils described in the literature can not be confirmed either by scanning electron microscop y or by the course of the split lines. The circular arrangement of col lagen fibrils in the central portion of the meniscus provides a functi onal explanation for the longitudinal orientation of the majority of t ears in the meniscus tissue.