Anisotropic response of the human knee joint meniscus to unconfined compression.

The response of meniscal tissue to axial, radial and circumferential compressive forces was measured at physiologically relevant levels of load in eight pairs of human knee joint menisci. Compression was unconfined and uniaxial. Stress strain data were fitted to a two-parameter exponential model. The tissue was found to be significantly stiffer to axial compressive forces than to radial and circumferential forces. No significant difference was found between the responses to circumferential and radial forces.

Radial fibre proportions in human knee joint menisci. Measurement by scanning optical microscopy.

The proportions of medial and lateral knee joint menisci represented by radially orientated collagen (COL) were measured in 42 specimens from 24 hospital patients examined post-mortem. Images of the fibre bundles were obtained by the 488-nm laser confocal scanning of hydrated, fixed radial blocks taken from the anterior, middle and posterior regions of the menisci after staining with picro-Sirius red. Measurements of the percentage of each image occupied by fluorescent, doubly refractile COL were made by means of a Kontron IBAS image analyser, after interactive segmentation. In areas adjoining the outer, lateral parts of both the medial and lateral menisci, the proportion of all samples identified as radial COL was 7.56 +/- 0.28%. The corresponding figure for areas near the inner, medial edges of the menisci was 17.80 +/- 0.80%. However, no relationship was demonstrable between age and sex and meniscal radial fibre optical density, and there was no difference between the proportion of radial fibres in the anterior, middle or posterior regions.

Age-related changes in the compressive strength of cancellous bone. The relative importance of changes in density and trabecular architecture.

UNLABELLED: Compressive testing to failure in the weight-bearing axis was done on 255 specimens of cancellous bone that had been machined from forty-four femora from human cadavera. The donors had ranged in age from twenty to 102 years at the time of death. After mechanical testing, the apparent density and trabecular architecture were determined. Linear regression analysis showed that the compressive strength decreased by 8.5 per cent each decade (p < 0.001). Apparent density and volume fraction also decreased significantly with age (p < 0.001). Histomorphometric analysis demonstrated that the surface-to-volume ratio and the mean separation of the trabecular plate increased with age, whereas the mean thickness and connectivity of the trabecular plate decreased. Both bivariate and multivariate analyses demonstrated that age-related changes in apparent density played an important role in the decrease in mechanical strength, accounting for a 92 per cent reduction. Microstructural changes were highly correlated with apparent density and therefore had little independent effect. Thus, similar to the situation with cortical bone, the quantitative changes in aging cancellous-bone tissue, rather than the qualitative changes, influenced the mechanical competence of the bone. CLINICAL RELEVANCE: This study provides information concerning the difference in the properties of human cancellous bone as a function of age. Because of the importance of changes in apparent density, non-invasive means can be used to estimate the mechanical properties of cancellous bone in vivo. Thus, it may be possible to predict the risk of fracture and to explain further some aspects of the mechanics of fracture in the elderly.

Age-related changes in the tensile properties of cortical bone. The relative importance of changes in porosity, mineralization, and microstructure.

Tensile testing to failure was done on 235 cortical specimens that had been machined from forty-seven femora from human cadavera. The donors had ranged in age from twenty to 102 years at the time of death. After mechanical testing, the porosity, mineralization, and microstructure were determined. Linear regression analysis showed that the mechanical properties deteriorated markedly with age. Ultimate stress, ultimate strain, and energy absorption decreased by 5, 9, and 12 per cent per decade, respectively. The porosity of bone increased significantly with age, while the mineral content was not affected. Microstructural analysis demonstrated that the amount of haversian bone increased with age. Both bivariate and multivariate analyses demonstrated the importance of age-related changes in porosity to the decline in mechanical properties. Changes in porosity accounted for 76 per cent of the reduction in strength. Microstructural changes were highly correlated with porosity and therefore had little independent effect. Mineral content did not play a major role. Thus, the quantitative changes in aging bone tissue, rather than the qualitative changes, influence the mechanical competence of the bone.