Osteochondral Allograft Transplantation For: “Surgical Techniques in Cartilage Repair Surgery”

Abstract

The fundamental concept governing fresh osteochondral allografting is the transplantation of architecturally mature hyaline cartilage with living chondrocytes that survive transplantation and are thus capable of supporting the cartilage matrix [1]. Hyaline cartilage possesses characteristics that make it attractive for transplantation. It is an avascular tissue and therefore does not require a blood supply, meeting its metabolic needs through diffusion from synovial fluid. It is an aneural structure and does not require innervation for function. Thirdly, articular cartilage is relatively immunoprivileged, as the chondrocytes are imbedded within a matrix and are relatively protected from host immune surveillance. The second component of the osteochondral allograft is the osseous portion. This functions generally as a support for the articular cartilage, as well as a vehicle to allow attachment and fixation of the graft to the host. The osseous portion of the graft is quite different from the hyaline portion, as it is a vascularized tissue and cells are not thought to survive transplantation; rather, the osseous structure functions as a scaffold for healing to the host by creeping substitution (similar to other types of bone graft). Generally, the osseous portion of the graft is limited to a few millimeters. It is helpful to consider a fresh osteochondral allograft as a composite graft of both bone and cartilage, with a living mature hyaline cartilage portion and a nonliving subchondral bone portion. It is also helpful to understand the allografting procedure in the context of a tissue or organ transplantation, as the graft essentially is transplanted as an intact structural and functional unit replacing a diseased or absent component in the recipient joint. The transplantation of mature hyaline cartilage obviates the need to rely on techniques that induce cells to form cartilage tissue, which are central to other restorative procedures.