Use of Fresh Osteochondral Allograft for Chondral and Osteochondral Defects in the Knee

Introduction

Fresh osteochondral allografts are composite grafts consisting of a living mature hyaline cartilage portion anchored to a nonliving subchondral bone portion, forming an intact osteochondral functional unit that replaces a damaged corresponding tissue in the recipient joint.

Increasing demand for allografts has been met with advancements in tissue procurement and increased availability of fresh donor tissue from commercial entities as opposed to university-based specialized transplantation centers, which in the past had limited availability to orthopedists in the community.

The advantage of fresh osteochondral allografting is the transplantation of mature hyaline cartilage with viable chondrocytes, which survive hypothermic storage and transplantation while maintaining their metabolic activity and sustaining the surrounding collagen matrix. Investigations have focused on extending the storage interval of fresh human osteochondral allograft tissue. Ball et al. compared the effects of different storage media on human osteochondral allograft tissue when stored hypothermically in either lactated Ringer’s solution or a standard culture media containing amino acids, glucose, and inorganic salts. The standard culture media demonstrated superior storage properties as measured by chondrocyte density, viability, and metabolic activity. Biomechanical properties of the matrix remained relatively intact in both media. Chondrocyte viability essentially remained unchanged from baseline for up to 14 days in the standard media, at which time viability was 90.5% in standard media versus 80% in lactated Ringer’s solution.

Graft Procurement and Storage

Availability of suitable graft tissue remains the limiting factor. Fresh osteochondral allografting is associated with inherent challenges related to tissue recovery, storage, and timely delivery for treatment.

Recovery, processing, and testing of donor tissue follow guidelines established by the American Association of Tissue Banks (AATB) and is under the authority of the US Food and Drug Administration (FDA). Most tissue banks have a 24-hour time limit for retrieval of tissue from refrigerated cadaveric donors in a sterile operating room environment following strict sterile technique. Donors between the ages of 15 and 40 years are generally considered for inclusion in the donor pool if their articular surfaces pass direct inspection for cartilage quality.

It is the policy of tissue banks to hold transplants for a minimum of 14 days to allow completion of microbiologic and serologic testing prior to release. Hence the actual surgical implantation is delayed by 3 to 6 weeks after procurement compared with university center clinical practice of implanting allografts usually within 1 week of harvest. Although results using this traditional fresh tissue protocol have been good even in mid-term follow-up, the effects of prolonged allograft storage on clinical outcomes have not yet been determined.

Use of fresh-frozen grafts improves graft availability, reduces immunogenicity, and may be appropriate for bulk allografting in major osseous reconstruction as encountered in musculoskeletal tumor cases. However, deep freezing of chondrocytes within their extracellular matrix (usually at −80°C) practically eliminates all viable chondrocytes in the articular cartilage portion of osteochondral grafts. Furthermore, clinical experience indicates that the articular matrix in frozen allografts deteriorates over time, presumably because insufficient surviving cells are present within the matrix to maintain tissue equilibrium. However, retrieval studies have demonstrated that with fresh, cold-stored osteochondral allografts, viable chondrocytes are present and mechanical properties of the matrix are maintained many years after transplantation.