Effect of Osteochondral Graft Insertion Forces on Chondrocyte Viability

Abstract

Background Because chondrocytes are responsible for articular cartilage matrix synthesis and maintenance, reduced chondrocyte viability could compromise graft survival, healing, and clinical outcome. Hypothesis Typical forces used in osteochondral grafting reduce the viability of the chondrocytes in the graft. Study Design: Controlled laboratory study. Methods Osteochondral grafting was performed in 4 fresh-frozen cadaver knees (n = 16 per knee). Impact force was measured during extrusion of the donor graft from the harvester into the recipient site, seating the graft flush with the articular surface of the surrounding cartilage using a tamp, and recessing the graft surface below the recipient articular surface. The magnitudes of forces measured during cadaver surgery (200,400, and 800 N) were reproduced using a drop-tower apparatus on 80 fresh osteochondral grafts harvested from knee blocks provided by tissue banks. Cell viability and glycosaminoglycan release in media were measured at 48 hours after injury. Results Forces were relatively low (range, 124-356 N) during graft extrusion from the harvester into the recipient defect or during flush seating (range, 191-418 N) of the graft. Attempts to recess the graft generated significantly greater force (range, 147-685- P < .01). When the donor graft length was 2 mm longer than the depth of the recipient hole, the mean impact force generated was even higher (range, 240-1114 N) than the force seen in a donor graft of equal length. No reduction in viability was seen at 200-N and 400-N impacts. However, a significant decrease in chondrocyte viability was seen in the group impacted with 800 N (only 50% of cells were viable, compared with 91 % in the sham group; P < .01). Glycosaminoglycan levels in culture media did not correlate significantly with insertion force. Conclusion Typical graft insertion forces did not significantly reduce chondrocyte viability. However, increased graft length relative to the depth of the recipient hole and attempts to recess the graft generated higher forces, which reduced chondrocyte viability. Clinical Relevance Any theoretical benefits of cancellous bone compaction that may occur in grafts that are recessed or are longer than the recipient holes must be balanced against the potential reduction in chondrocyte viability.