An alternative mechanical parameter for assessing the viability of articular cartilage

Abstract

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 = ɛr/ σi, which combines indentation stress σi with near-instantaneous rebound ɛr 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 5 s 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.