Collagenous fibril texture of the gliding zone of the human tibialis posterior tendon.

UNLABELLED: Light microscopy and scanning electron microscopy was used to describe the collagenous fibril texture of the wrap around region of the human tibialis posterior tendon in human cadavers. In the region where the tendon wraps around the medial malleolus, the anterior part of the tendon directed towards the pulley had the structure of fibrocartilage. This zone started approximately 25-30 millimeters from the navicular insertion. Scanning electron microscopy of the collagen fibril texture revealed three different layers in the fibrocartilaginous zone. The anterior surface was covered by a meshwork of thin unbanded fibrils with a diameter of app. 30 nm. Beneath the superficial network there was an app. 150 microm thick layer of banded collagen fibrils, These fibrils formed lamella-like bundles which intersected at various angles. The main portion of the collagen fibrils lie below this layer and run in a longitudinal direction. The longitudinal fibrils were divided into bundles by loose connective tissue. The location of the fibrocartilage corresponds to the region where the tibialis posterior tendon wraps around the medial malleolus which serves as a pulley. CLINICAL SIGNIFICANCE: Our study documented the existence of a fibrocartilaginous zone with a specific collagen fibril texture that corresponds to a possible site of rupture, as reported by several authors. Due to special collagen fibril texture the fibrocartilage may be more vulnerable to repetitive tensile micro-trauma.