The main indications for osteochondral allograft transplantation include a focal full-thickness cartilage or osteochondral lesion that is symptomatic (6,8,20,21). The defects should be large, with diameters approaching 2 cm. Although there is no defined limit as to how large a defect can be, osteochondral allografting is typically limited to large defects up to 10 cm². Improved results are seen with unipolar defects where the opposite surface is still healthy (8). Osteochondral transplant is generally indicated for posttraumatic and osteochondritis dessicans (OCD) lesions; however, this procedure has also been used to treat lesions caused by osteonecrosis (17), as well as tibial plateau fractures (20,42). Allografting is typically indicated for younger patients, who represent the vast majority of patients presenting with these lesions in the clinical setting. Successful clinical results have been noted in the treatment of patellofemoral and unicompartmental chondrosis (26).

Contraindications to osteochondral allograft transplantation include osteoarthritis, particularly when both the tibial and the femoral surfaces are affected. Rheumatoid arthritis (RA) and steroid induced osteonecrosis are considered relative contraindications. Age is also a relative contraindication as patients older than 60 years treated with osteochondral transplantation were found to have worse outcomes than patients younger than 60 (5).

Preoperatively, patients should undergo a thorough history and physical examination. Weight-bearing radiographs to include a full-length standing radiograph to assess alignment are needed (Fig. 44.1). Malalignment may indicate the need to perform an osteotomy in addition to the planned allograft transplant. Magnetic
resonance imaging (MRI) may also be used to evaluate the articular cartilage and soft tissues. Diagnostic arthroscopy is often performed prior to the allograft procedure and allows better characterization of chondral defects and can address associated meniscal or ligamentous injury.

Graft selection is a critical aspect of the preoperative planning process. While freezing of osteochondral allografts decreases the immunogenicity of the tissue, this process destroys both the cell viability and the cartilage matrix (15,38). Cryopreservation of allografts allows preservation of the matrix, but chondrocyte viability is not maintained (41,44). Fresh allografts are recommended for transplant as they have an intact matrix and good chondrocyte viability, compared to frozen or cryopreserved allografts. Based on the drawbacks of freezing and cryopreservation, fresh allograft transplantation is recommended.

Allografts should be obtained within 24 hours of donor death, and stored at 4°C in Lactated Ringer (LR) or culture medium with added cefazolin and bacitracin. Transplant occurring 3 to 7 days after harvest permits retention of cartilage cell viability and matrix constitution (12,28). The avascular bone, which is attached to the allograft, serves as a nonviable scaffold and requires replacement by host bone through creeping substitution (12). With the advent of commercially available osteochondral allografts, complete tissue testing is performed according to the American Association of Tissue Banks guidelines. While this strict screening process aids in the prevention of disease transmission, it may take up to 2 to 4 weeks after donor death for the tissue to become available for transplant. This increased screening time may have a negative effect on graft health as prolonged storage has been shown to decrease chondrocyte viability, although the matrix is likely maintained (1,39,49). Improved graft storage will likely decrease these negative effects. One study demonstrated improved chondrocyte viability and metabolic activity for allografts stored for 14 days in proprietary culture medium, compared to grafts stored in traditional LR solution (4).

In order to obtain an appropriate allograft, the donor must be size matched to the recipient. This is accomplished by measuring the anteroposterior and lateral dimensions of the tibial plateau from standard radiographs or MRI. The donor and host tibial diameters are determined with measurements taken 1 cm below the articular surface. If the patellofemoral joint is to be treated, the widest diameter of the patella should be measured. The donor allograft is determined to be an acceptable size match if both of the measured planes in the host fall within 2 mm of the corresponding regions in the donor.