An alternative mechanical parameter for assessing the viability of articular cartilage

This paper is a sequel to previously published findings showing that mechanical indentation alone cannot clearly discriminate between normal and degraded articular cartilage. Consequently, the structural elasticity potential Rc = epsilon r/sigma i, which combines indentation stress sigma i with near-instantaneous rebound epsilon r following unloading, is hypothesized as a potential cartilage assessment parameter, which arguably measures the integrity of the collagen fibre-proteoglycan entrapment system. To establish the validity of our hypothesis, samples of normal intact, artificially degraded, and osteoarthritic bovine cartilage were subjected to quasi-static compression at 0.1 s(-1) and 0.025 s(-1) to 30 per cent strain and then unloaded. A significant reduction in recovery was observed for artificially and naturally degraded samples in the first 5s following unloading (p < 0.01). The structural elasticity potential provided a considerable improvement over the results obtained using the individual indentation and rebound parameters to distinguish between paired normal and artificially degraded samples and indicated a high statistical significance of p < 0.005 when applied to the differentiation of normal and osteoarthritic samples.