Z-scoring of pQCT-assessed, reference distribution/quality curves in the human tibia to evaluate the efficiency of bone mechanostat.

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

Minneapolis (MN)

Congreso; XXXIV ANNUAL MEETING, Americal Society for Bone & Mineral Research (ASBMR).; 2012

Americal Society for Bone & Mineral Research

In a serial pQCT study (XCT-2000, Stratec - slices taken at every 5% of the tibia height throughout the bone, sites S5 to S95) of sedentary and running-trained men and women aged 20-40 yr (n=10/group) we had shown that bone mass distribution along the tibia reflected a structural adaptation to the variable stress pattern imposed by the mechanical usage of the limb. Now we extend that analysis to describe the relationships between indicators of cortical bone distribution (bending and torsion cross-sectional moments of inertia, MIs, y), mass (BMC, x1), and “quality” (vBMD, proportional to bone tissue stiffness, x2). Correlations between MIs and cortical BMC and between MIs and cortical vBMD were regarded as describing “distribution/mass” (d/m) and “distribution/quality” (d/q) relationships, respectively, at each studied site. The d/m curves were all described by positive exponential equations, while the d/q curves, hyperbolically shaped, were always adjusted to negative exponential functions. All d/m and d/q correlations were significant at every site. The distributions of the r coefficients of both d/m and d/q curves, plotted by site, were described by quasi-symmetrical, bell-shaped curves, reaching a maximum toward the central region of the tibiae in every instance. Both men and trained individuals showed significantly higher MIs and BMC and lower vBMD values than women. The d/m relationships were described by unique curves for all groups, with increasing slopes from the heel to the knee. The d/q relationships were described by separate, parallel curves for men (higher ordinates, lower abscissae) and women, with little or no influence of the trained/untrained condition within sex. Results offer original support to 4 important concepts in Bone Biology: 1. the architectural quality of diaphyseal design concerning bending and torsion strength is proportional to the relative influence of bending and torsion in the varying stress patterns along the bones (known to be maximal toward the central regions) with a significant trend to minimize bone mass; 2. there is a trade-off between cortical bone “quality” (intrinsic stiffness) and distribution, as if both variables were interrelated by a feedback control mechanism of structural diaphyseal stiffness/strength (in agreement with the mechanostat theory); 3. both d/m and d/q relationships are highly related to bone mechanical environment, and 4. the d/q relationships are also affected by sex.