Transplantation of free perichondrial grafts into rabbit articular cartilage is associated with matrix vesicle calcification.

Autogenous perichondrial grafts from rabbit ear were transplanted into articular cartilage defects in the knee joint. Electron micrographs performed after 2 months revealed calcifications associated with cartilaginous-forming cells and extracellular matrix vesicles. Many of these vesicles contained apatite crystals, particularly in areas adjacent to the calcifying fronts. In these areas the vesicular membrane was occasionally ruptured by the crystals. Many crystals in the calcifying front proper were organized alongside collagen fibers. Examination of sham-operated and normal controls revealed the occurrence of non-calcifying matrix vesicles. The results of the present and previous studies suggest that matrix vesicles occur in normal articular cartilage in a latent form, their calcification being associated with changes of the metabolic state of the tissue.