Sharpey fiber: a neglected but crucial collagen fiber in specialized tendon-bone interface

Tendon-bone interface injuries treated with implanted grafts are often characterized by the formation of scar tissue, which exhibits suboptimal morphology and mechanical strength. Sharpey fiber plays a pivotal role in tendon-bone healing by facilitating the transition from indirect to direct graft attachment. This process not only restores the native four-layer structure, enhancing biomechanical integration, but also highlights the growing recognition of Sharpey fiber's crucial role in tendon-bone interface healing. Abundant evidence has shown that these fibers significantly contribute to positive healing outcomes, firmly establishing their importance in this context. However, a comprehensive review focusing specifically on Sharpey fibers is still lacking. This review will examine the composition of the Sharpey fiber, its origin in degradation, as well as its distribution in vivo, and its different functions. The macro- and micro-regulatory factors that modulate Sharpey fiber and thus affect tendon-bone healing, including mechanical stimulation, stem cells, and cytokines, will be discussed to provide theoretical references for a new direction.