Time-Dependent Changes in the Structure of Calcified Fibrocartilage in the Rat Achilles Tendon-Bone Interface With Sciatic Denervation.

The enthesis transmits a physiological load from soft to hard tissue via fibrocartilage. The histological alterations induced by this physiological loading remain unclear. This study was performed to examine the histomorphological alterations in the collagen fiber bundle alignment and depth of collagen interdigitation between the calcified fibrocartilage and the bone. We examined the Achilles enthesis of rats with sciatic denervation to explore the mechanical effects of structural changes in the enthesis. The parallelism of the collagen fiber bundles was significantly reduced 8 weeks after denervation. However, the depth of collagen interdigitation significantly increased at 2 and 4 weeks after denervation and then significantly decreased 8 weeks after denervation. In conclusion, a lack of muscle loading induced structural alterations in the distal calcified fibrocartilage. These findings suggest that while structural changes in the enthesis are necessary for the development of physiological loading, structural deformities are required in the long term. Anat Rec, 300:2166-2174, 2017.