Analysis of stored osteochondral allografts at the time of surgical implantation

Background: To date, the morphological, biochemical, and biomechanical characteristics of articular cartilage in osteochondral allografts that have been stored have not been fully described. Hypothesis: Osteochondral allografts procured and stored commercially for a standard period as determined by tissue banking protocol will have compromised chondrocyte viability but preserved extracellular matrix quality. Study Design: Controlled laboratory study. Methods: Unused cartilage from 16 consecutive osteochondral allografts was sampled during surgery after tissue bank processing and storage. Ten grafts were examined for cell viability and viable cell density using confocal microscopy, proteoglycan synthesis via (SO4)-S-35 uptake, and glycosaminoglycan content and compared with fresh cadaveric articular cartilage. Biomechanical assessment was performed on the 6 remaining grafts by measuring the indentation stiffness of the cartilage. Results: The mean storage time for the transplanted specimens was 20.3 +/- 2.9 days. Chondrocyte viability, viable cell density, and (SO4)-S-35 uptake were significantly lower in allografts at implantation when compared to fresh, unstored controls, whereas matrix characteristics, specifically glycosaminoglycan content and biomechanical measures, were unchanged. In addition, chondrocyte viability in the stored allografts was preferentially decreased in the superficial zone of cartilage. Conclusion: Human osteochondral allografts stored for a standard period (approximately 3 weeks) before implantation undergo decreases in cell viability, especially in the critically important superficial zone, as well as in cell density and metabolic activity, whereas matrix and biomechanical characteristics appear conserved. The exact clinical significance of these findings, however, is unknown, as there are no prospective studies examining clinical outcomes using grafts stored for extended periods. Clinical Relevance: Surgeons who perform this procedure should understand the cartilage characteristics of the graft after 21 days of commercial storage in serum-free media.