Non-invasive (pQCT) Analysis of Different Patterns of Structural/Biomechanical

RICARDO FRANCISCO CAPOZZA; SARA FELDMAN; PABLO ANDRÉS MORTARINO; PAOLA REINA; PAMELA RANSDALE; JOSÉ LUIS FERRETTI; JOERN RITTWEGER; GUSTAVO ROBERTO COINTRY

San Diego (California)

Congreso; XXXIII ANNUAL MEETING, American Society for Bone & Mineral Research (ASBMR).; 2011

In a serial pQCT study of the leg (XCT-2000, Stratec, Germany) of sedentary healthy men and women aged 20-40 y (n=10/10, J Anat 216:470,2010) 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. This study extends that observation to further 10/10 men and women of similar age chronically trained in long-distance running, aiming to analyze the interrelationships between indicators of bone mass (total and cortical BMC -ToC, CtC-, cortical cross-sectional area -CtA-, material “quality” (cortical vBMD -CtD-) and diaphyseal design (periosteal perimeter -PoPm-, thickness -CtTh-, circularity, and moments of inertia -MIs- of the CtA) as determined in slices taken at every 5% of height throughout the bone (sites S5 to S95), and of muscle force (maximal calf muscle cross-sectional area -MA-). As previously observed, all the allometrically-related indicators (ToC, CtC, CtA, PoPm, MIs, MA) were higher, while CtD was lower, in men than women and in trained than in sedentary individuals (p<0.05-p<0.001). All allometric bone indicators correlated positively with MA (p<0.05-p<0.01). Circularity was maximal while ToC and MIs were minimal toward S15. ToC increased proximally, especially at sites closer to the knee. The MIs increased geometrically with bone height from S30 upwards. CtTh increased toward the central diaphysis and decrease more proximally. The analysis of all individuals together showed single-curve correlations between MIs and bone mass indicators, CtD and MA, with a maximal significance toward the central region of the bones. All these associations were independent of the degree of physical activity. Results suggest that there would be three regions of the human tibia in which the structural features correspond specifically to three different patterns of usage-derived stress. In these regions the available bone mass would tend to be distinctly distributed in order to optimize predominantly the resistance to 1. uniaxial compression (distal end of the bone, approximately from S5 to S30), 2. anterior-posterior or lateral bending and torsion (central diaphysis, S30-S70), and 3. bi-axial compression (proximal end of the bone, S75-S95). This distribution would be highly oriented by the contractions of regional muscles, and were shown to be independent of the gender, anthropometric characteristics and degree of activity of the individual.