Article: Bartell, LR; Fortier, LA; Bonassar, LJ; Cohen, I; (2015) “Measuring Microscale Strain Fields in Articular Cartilage During Rapid Impact Reveals Thresholds for Chondrocyte Death and a Protective Role for the Superficial Layer”, Journal of Biomechanics, 48 (12): 3440-3446
Abstract: Articular cartilage is a heterogeneous soft tissue that dissipates and distributes loads in mammalian joints. Though robust, cartilage is susceptible to damage from loading at high rates or magnitudes. Such injurious loads have been implicated in degenerative changes, including chronic osteoarthritis (OA), which remains a leading cause of disability in developed nations. Despite decades of research, mechanisms of OA initiation after trauma remain poorly understood. Indeed, although bulk cartilage mechanics are measurable during impact, current techniques cannot access microscale mechanics at those rapid time scales. We aimed to address this knowledge gap by imaging the microscale mechanics and corresponding acute biological changes of cartilage in response to rapid loading. In this study, we utilized fast-camera and confocal microscopy to achieve roughly 85 pm spatial resolution of both the cartilage deformation during a rapid (similar to 3 ms), localized impact and the chondrocyte death following impact. Our results showed that, at these high rates, strain and chondrocyte death were highly correlated (p<0.001) with a threshold of 8% microscale strain norm before any cell death occurred. Additionally, chondrocyte death had developed by two hours after impact, suggesting a time frame for clinical therapeutics.
Moreover, when the superficial layer was removed, strain and subsequently chondrocyte death penetrated deeper into the samples (p < 0.001), suggesting a protective role for the superficial layer of articular cartilage. Combined, these results provide insight regarding the detailed biomechanics that drive early chondrocyte damage after trauma and emphasize the importance of understanding cartilage and its mechanics on the microscale.
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Funding Acknowledgement: National Science Foundation [DMR-1056662]; National Institutes of Health [R21-AR062677]; Harry M. Zweig Fund for Equine Research; NSF [DGE-1144153]
Funding Text: This work was supported in part by the National Science Foundation under award no. DMR-1056662, in part by the National Institutes of Health under award no. R21-AR062677, and in part by the Harry M. Zweig Fund for Equine Research. L.R.B. acknowledges support from the NSF Graduate Research Fellowship, No. DGE-1144153. The authors wish to thank Michelle Delco, Corinne Henack, Tsevi Beatus and Brian Leahy for helpful discussions and support with this study.