Relationships between pQCT indicators of bone mass, mineral density, design and strength in forearms and legs of normal men and pre and post MP women

GUSTAVO ROBERTO COINTRY; RICARDO FRANCISCO CAPOZZA; SEBASTIÁN EDUARDO FERRETTI; SARA FELDMAN; NÉSTOR MATÍAS FRACALOSSI; LEANDRO SARRIO; PAOLA REINA; MARÍA VICTORIA FERRETTI; MARÍA CAROLINA FERULLO; GABRIELA MARCHETTI; EMILIO ROLDÁN; JOSÉ LUIS FERRETTI

Nashville (USA)

Congreso; XXVII Annual Meeting, Americal Society for Bone & Mineral Research (ASBMR); 2005

Americal Society for Bone & Mineral Research

Aim. To describe the interrelationships between different bone properties and the muscle interaction with their biological determination, employing pQCT. Methods. The natural associations between pQCT indicators of bone mass (BMC, cortical area, trabecular density), design (CSMIs), mineral density (cortical vBMD) and strength (BSIs) and of muscle strength (CSA) in forearm (4 and 66% sites) and legs (4, 14, 38 and 66% sites) of 40 men, 60  pre-MP women and 100 post-MP women aged 25-85a were analyzed following biomechanical criteria. Results. Indicators of bone mass, design and strength were higher in men than in pre-MP women. Mass and strength (not design) indicators decayed significantly after MP. Cortical vBMD, higher in women than men, decayed more dramatically than the other indicators after MP. Distribution/mass (MI/CortCSA) and distribution/quality (MI/CortvBMD) curves showed that MIs tended to stabilize after MP, despite the bone mass reduction. The intracortical distribution of vBMD felt dramatically, with a discuntinuity of the areas of highest-density voxels (>1.0 cm-1 attenuation threshold) after MP. The natural, 1:1 and 1:1.5 proportionalities between trabecular and cortical BMC in 4% vs 14% and vs 38% leg sites respectively also decayed after MP. All bone indicators correlated with muscle area in both 66% sites showing a single, saturation relationship for men and pre-MP women, and a lower slope for Post-MP women. Interpretation. Results suggest that 1. Bone mass varies allometrically with body size and biomechanically with the regional muscle strength in fertile individuals, suggesting thag trhe method could evaluate the biomechanical control of bone modeling by bone mechanostat. 2. Estrogen deficiency determines a loss of mass and especially mineralization (enhanced microporosity) of cortical bone (stimulation of remodeling), maintaining the diaphyseal design relatively stable, thus slowening (yet not completely preventing) the development of bone fragility. 3. Bone mechanostat remains healthy (yet metabolically disturbed) after MP. Its status should be evaluated before diagnosing osteoporosis based only in the severity of the osteopenic condition (BMD t-scores). 4. Comparison of BMC between predominantly trabecular or cortical sites in the same individual allows detecting a faster deterioration of the former compared to the latter, as determined in "systemic" (primary or endocrine-metabolic) osteopenias. 5. In practice, a Z-scorization of the described natural relationships will provide suitable reference charts for an original, biomechanical diagnosis of osteoporosis, and a differential diagnosis between "disuse" and "systemic" osteopenias (disuse would correspond to a normal bone/muscle proportionality; a systemic disturb would tend to reduce both the bone/muscle proportionality and the trabecular/cortical bone mass ratio), with important therapeutic implications (exercise in the first case, drugs or hormones in the second one).