One convenient way to repair cartilage defects is to obtain a combination of cartilage with its underlying bone—usually in the shape of a cylinder—and make a corresponding empty hole in which to insert the new “plug”. In this way the cartilage layer is already attached to bone and the blood supply may eventually integrate the new graft into the surrounding tissues. This can be performed either with bone from the patient (autograft) or from a cadaver donor (allograft). Of course there are advantages and problems associated with either source of tissue. A common theme of this idea is that a cartilage replacement plug can be inserted arthroscopically and sized precisely to match the size of the cartilage defect.
Autografts are safe because they come from the patient, and there is no issue of disease transmission. The donor sites for autograft are the peripheral areas of knee cartilage, and the surgeon has to use careful judgment in deciding just how much of this tissue is expendable- The procedure is essentially robbing Peter to pay Paul. So a reasonable autograft, sometimes called a mosaicplasty, is usually a very small cylinder of cartilage and bone, or perhaps several.
Allografts are from a cadaveric donor. Although any good tissue bank performs routine screening for HIV, hepatitis, bacteria, etc., and there are now standards for tissue banks to observe, disease transmission is not an unknown complication of tissue banking. The popular press has exposed several instances of multiple patients receiving diseased tissue in a variety of organ systems. Nevertheless, the concept of pre-packaged osteochondral grafts in a variety of sizes, and without size limitation, is quite attractive. Unlike other tissues, there is not thought to be a significant immune problem when allografts are placed into a joint (immunoprotected).
Fresh allograft material, which has live cartilage cells, is thought to be far more favorable that conventional frozen allografts, although the latter are safer. Very recent developments may allow us to have the best of both worlds—a safe, frozen allograft with live cartilage cells in it. Stay tuned for this possibility in the very near future.