Focal chondral defects of the knee, due to trauma or other conditions such as osteochondritis dissecans, often fail to heal on their own and may be associated with pain, loss of function, disability and the long-term complication of osteoarthritis. The ideal resurfacing technique would eliminate the symptoms, restore normal biomechanics of the knee joint, and prevent the long-term emergence of osteoarthritis and the necessity for total knee replacement. Various methods of cartilage resurfacing have been investigated including marrow-stimulation techniques, such as subchondral drilling, microfracture, and abrasion arthroplasty, all of which are considered standard therapies and all of which attempt to restore the articular surface by inducing the growth of fibrocartilage into the chondral defect.
The use of both fresh and cryopreserved allogeneic osteochondral grafts has been encouraging. Cryopreservation decreases the viability of cartilage cells and fresh allografts may be difficult to obtain. There are concerns regarding infectious diseases when using allografts (from a donor other than the recipient). For these reasons, autologous (one's own tissue from one location to another) grafts have been under investigation as an option to increase the survival rate of the grafted cartilage and to eliminate the risk of disease transmission. Autografts have been limited by the small number of donor sites; thus allografts are typically used for larger lesions. Single grafts have been harvested from the patella, femoral condyle, and proximal part of the fibula. In an effort to extend the amount of available donor tissue, investigators have used multiple, small osteochondral cores harvested from various non-weight-bearing sites of the knee. Several systems are available for performing this procedure, the MosaicPlasty System™ (Smith and Nephew) and Osteochondral Autograft Transfer System® (OATS®, Arthrex, Inc.), and the COR™ and COR2™ Systems (DePuy-Mitek). Although MosaicPlasty and OATS may use different instrumentation, the underlying principle is similar; i.e., the use of multiple osteochondral cores harvested from a non-weight-bearing region of the femoral condyle and autografted into the chondral defect. These terms have been used interchangeably to describe the procedure. In contrast to autologous chondrocyte implantation (ACI), in which separate surgical procedures are required to harvest and then transplant the cultured chondrocytes, with osteochondral autografting the harvesting and transplantation can be performed during the same surgical procedure.
Preparation of the chondral lesion involves debridement and preparation of recipient tunnels. Multiple individual osteochondral cores are harvested from the donor site, typically from a peripheral non-weight-bearing area of the femoral condyle. Donor plugs range from six-mm to 10 mm in diameter. The grafts are press fit into the lesion in a mosaic-like fashion into the same-sized tunnels. The resultant surface consists of transplanted hyaline articular cartilage and fibrocartilage, which is thought to provide “grouting” between the individual autografts.
Although each system may use different instrumentation, the underlying principle to obtain the autografts is the same and to transfer the cartilage or bone plugs from one area to another damaged area. These procedures may be performed with either an open approach or arthroscopically. The resurfacing concept is similar to a hair transplant. Clinical studies have begun by using osteochondral grafts to repair chondral defects of the hip, patella, tibia, and ankle.