Cartilage viability and catabolism in the intact porcine knee following transarticular impact loading with and without articular fracture.

Posttraumatic arthritis commonly develops following articular fracture. The objective of this study was to develop a closed joint model of transarticular impact with and without creation of an articular fracture that maintains the physiologic environment during loading. Fresh intact porcine knees were preloaded and impacted at 294 J via a drop track. Osteochondral cores were obtained from the medial and lateral aspects of the femoral condyles and tibial plateau. Chondrocyte viability was assessed at days 0, 3, and 5 postimpact in sham, impacted nonfractured, and impacted fractured joints. Total matrix metalloproteinase (MMP) activity, aggrecanase (ADAMTS-4) activity, and sulfated glycosaminoglycan (S-GAG) release were measured in culture media from days 3 and 5 posttrauma. No differences were observed in chondrocyte viability of impacted nonfractured joints (95.9 ± 6.9%) when compared to sham joints (93.8 ± 7.7%). In impacted fractured joints, viability of the fractured edge was 40.5 ± 27.6% and significantly lower than all other sites, including cartilage adjacent to the fractured edge (p < 0.001). MMP and aggrecanase activity and S-GAG release were significantly increased in specimens from the fractured edge. This study showed that joint impact resulting in articular fracture significantly decreased chondrocyte viability, increased production of MMPs and aggrecanases, and enhanced S-GAG release, whereas the same level of impact without fracture did not cause such changes.