Mechanobiology of tendon adaptation to compressive loading through fibrocartilaginous metaplasia

Tendons that wrap around bones often undergo fibrocartilaginous metaplasia. In this paper, we examine the biomechanical causes and consequences of thi s metaplasia. We propose an adaptation rule in which tissue permeability ch anges in response to local cyclic hydrostatic pressures associated with phy sical activity. The proposed rule predicts the development of a low-permeab ility region corresponding to the fibrocartilaginous region in a representa tive wrap-around tendon. A poroelastic finite element model is used to exam ine the time-dependent fluid pressures and compressive stresses and strains in the solid constituents of the tendon's extrafibrillar matrix. The low p ermeability in the adapted fibrocartilaginous region maintains fluid pressu res, protecting the solid constituents of the tendon's extracellular matrix from high compressive stresses and strains that could disrupt the matrix o rganization. Adaptation through fibrocartilaginous metaplasia therefore all ows wrap-around tendons to function effectively over a lifetime without sus taining excessive mechanical damage due to cyclic compressive loading.