Influence of physical activity on the distribution of human cortical tissue as a function of its mass and its mechanical quality

PAOLA REINA; GUSTAVO ROBERTO COINTRY; LAURA NOCCIOLINO; SARA FELDMAN; JOSÉ LUIS FERRETTI; JOERN RITTWEGER; RICARDO FRANCISCO CAPOZZA

Baltimore (MD)

Congreso; XXXV ANNUAL MEETING, American Society for Bone & Mineral Research (ASBMR); 2013

Increasing evidence shows that bone mechanostat would optimize bone structural stiffness as a function of the usage-derived peak strains sensed by osteocytes. One mechanism proposed to achieve this homeostatic control of bone structure is the spatial orientation of modeling drifts as a function of the maximal loads determined by customary mechanical usage of the skeleton. To test that hypothesis, we analyzed the correlations between pQCT indicators of the mass (BMC), the mechanical ?quality? (vDMO, a variable known to vary linearly with bone tissue stiffness), and the efficiency of the spatial distribution of cortical tissue to resist deformation in bending or torsion (cross-sectional moments of inertia, MIs) in slices taken at every 5% of the tibia length, as well as the maximal cross-sectional muscle area (MA) of the calf, in 22 males and 20 females aged 25-35 years who either had sedentary habits or were trained in long-distance running during more than 8 years. All MIs (y) correlated with cortical CMO following positive, exponential relationships (?distribution/mass? curves, d/m) and with cortical vDMO following negative, hyperbole-like relationships (?distribution/quality? curves, d/c) in all bone sites. The distribution of correlation coefficients of both d/m and d/c curves along the bone were described by bell-shaped curves, with maximum values toward the central region of the diaphyses, reflecting the predominance of the usual bending and torsion stresses over that of compression stress. The residual values of both the d/m and d/c curves correlated linearly with MA (p<0.001) in every group and also in all the individuals analyzed as a whole (?bone/muscle? relationships, b/m). Results verify no less than 3 correlative hypotheses: 1: That the preferential distribution of the available bone cortical tissue in specific sites across the diaphyseal section results from the directional optimization of local modeling drifts (d/m curves), 2. That that geometrical adaptation is more evident in sites where the bone tissue is less stiff (d/c curves), and 3. That local muscle strength and/or usage is synergic with those two manifestations (b/m curves). In addition, the collected evidence a. supports the proposed role of bone mechanostat with inedit arguments for the human skeleton, and b. offers a basis for developing reference graphs suitable for a comparative diagnosis of the mechanostat condition in individual cases.