Importance Of Donor Chondrocyte Viability in Osteochondral Allografting

OBJECTIVES: Osteochondral allografting (OCA) provides a biologic treatment option for functional restoration of large articular cartilage defects in multiple joints. While successful outcomes after OCA have been linked to viable donor chondrocytes, the importance of donor cell viability has not been comprehensively validated. The purpose of this study was to use a canine model to determine the importance of donor chondrocyte viability at the time of implantation with respect to functional success of femoral condylar OCAs based on gross, cell viability, histologic, biochemical, and biomechanical outcome measures. METHODS: With IACUC approval, adult female dogs (n = 16) were implanted with 8-mm cylindrical osteochondral allografts from male dogs in the lateral and medial femoral condyles of one knee. Osteochondral allografts were preserved for 28 or 60 days after procurement and chondrocyte viability was quantified prior to implantation. Two different storage media, temperatures and time points were used in order to obtain a spectrum of %chondrocyte viability at the time of implantation. A successful outcome was defined as an osteochondral allograft that was associated with graft integration, maintenance of hyaline cartilage, lack of associated cartilage disorder, and lack of fibrillation, fissuring, or fibrous tissue infiltration of the allograft based on subjective radiographic, arthroscopic, gross, and histologic assessments at 6 months after implantation. RESULTS: Chondrocyte viability ranged from 23% to 99% at the time of implantation. All successful grafts had greater than 70% chondrocyte viability at the time of implantation and no graft with chondrocyte viability <70% was associated with a successful outcome. Live-dead stained sections and histologic findings with respect to cell morphology suggested that successful grafts were consistently comprised of viable chondrocytes in lacunae, while grafts that were not successful were comprised of non-viable chondrocytes with infiltration of fibroblasts from the surrounding recipient tissues. In situ PCR (FISH) assays were performed in an attempt to distinguish donor (male) cells from recipient (female) cells. Unfortunately, this technique was exceptionally difficult to perform on intact articular cartilage sections, and consistent, repeatable data could not be obtained from this testing. However, the data did support histologic and live-dead data, which strongly suggested that successful grafts retained viable donor (male) chondrocytes and unsuccessful grafts degraded and were replaced by fibrous tissue populated with recipient (female) fibroblasts. CONCLUSION: Viable chondrocytes in osteochondral allografts at the time of transplantation are primarily responsible for maintenance of donor articular cartilage health long term. Optimizing chondrocyte viability in all aspects of osteochondral allografting - including procurement, processing, storage, transportation, and surgical implantation - needs to be a primary focus for clinical use of OCA.