Osteochondral allograft transplantation in cartilage repair: Graft storage paradigm, translational models, and clinical applications

Abstract

The treatment of articular cartilage injury and disease has become an increasingly relevant part of orthopaedic care. Articular cartilage transplantation, in the form of osteochondral allografting, is one of the most established techniques for restoration of articular cartilage. Our research efforts over the last two decades have supported the transformation of this procedure from experimental "niche" status to a cornerstone of orthopaedic practice. In this Kappa Delta paper, we describe our translational and clinical science contributions to this transformation: (1) to enhance the ability of tissue banks to process and deliver viable tissue to surgeons and patients, (2) to improve the biological understanding of in vivo cartilage and bone remodeling following osteochondral allograft (OCA) transplantation in an animal model system, (3) to define effective surgical techniques and pitfalls, and (4) to identify and clarify clinical indications and outcomes. The combination of coordinated basic and clinical studies is part of our continuing comprehensive academic OCA transplant program. Taken together, the results have led to the current standards for OCA processing and storage prior to implantation and also novel observations and mechanisms of the biological and clinical behavior of OCA transplants in vivo. Thus, OCA transplantation is now a successful and increasingly available treatment for patients with disabling osteoarticular cartilage pathology.

Keywords: cartilage repair; osteochondral allografts.

Figure 1. Summary of Results for In Vitro Storage of OCA

Chondrocyte viability is higher when OCA are stored at 4°C in TCM with greater nutritional content. TCM with fetal bovine serum (FBS) preserves viability better than serum free media and Lactated Ringers, but there is still substantial cell death versus fresh controls and OCA stored at 37°C, especially at the vulnerable superficial zone. At 4°C, while cells are vulnerable to death and relatively quiescent, cartilage matrix content and structure are maintained, but matrix metabolism is decreased and expression of proapoptotic genes are increased. 37 °C storage of OCA supports long-term chondrocyte viability, especially at the articular surface, but cartilage matrix content can be modulated.

Figure 2. Summary of Results for In Vivo OCA Repair

Implantation of fresh OCA resulted in consistently good (and intact) cartilage repair outcomes with high cartilage cellularity, whereas 4°C stored OCA had variable results, and the cartilage had decreased cellularity and was somewhat susceptible to degeneration. Frozen OCA exhibited clear progression toward failure (erosion), with loss of chondrocytes, reduced proteoglycan content and cartilage stiffness, and associated surface and/or bone collapse.

Figure 3. Relationship of Insertion Parameters and Cartilage Structure in In Vivo Animal Model

Excessive taps during surgical insertion resulted in poor outcomes after 12 months in vivo from Pallante et al.

Figure 4. OCA Survivorship at 12 years by Indication

OCA survivorship varied between ~70–90% for most cartilage indications, with the lowest survivorship (~40%) in patients with osteoarthritis.