RESUMEN
The pQCT-assessed Bone Strength Indices (BSI's, SSI) depend on the product of a 'quality' indicator, the cortical vBMD (vCtD), and a 'design' indicator, one of the cross-sectional moments of inertia or related variables (MIs) in long bones. As the MIs vary naturally much more than the vCtD and represent different properties, it could be that the variation of the indices might not reflect the relative mechanical impact of the variation of their determinant factors in different individuals or circumstances. To understand this problem, we determined the vCtD and MI's in tibia scans of 232 healthy men and pre- and post-MP women, expressed in SD of the means calculated for each group, and analyzed the independent influence of 1 SD unit of variation of each factor on that of the indices by multiple correlations. Results showed: 1. that the independent influence of the MIs on the indices was generally larger than that of the vCtD, and 2. that in post-MP women the influence of the vCtD was larger than it was in the other groups. This confirms the view that inter-individual variation of vCtD is comparatively small, and that mechanical competence of human bone is mostly determined by 'design' factors.
Asunto(s)
Huesos/diagnóstico por imagen , Huesos/fisiología , Adulto , Anciano , Anciano de 80 o más Años , Fenómenos Biomecánicos , Densidad Ósea/fisiología , Femenino , Humanos , Masculino , Persona de Mediana Edad , Posmenopausia , Premenopausia , Tomografía Computarizada por Rayos XRESUMEN
Some pharmacologic effects on bone modeling may not be evident in studies of remodeling skeletons. This study analyzes some effects of olpadronate on cortical bone modeling and post-yield properties in femurs diaphyses (virtually only-modeling bones) of young rats by mid-diaphyseal pQCT scans and bending tests. We studied 20/22 male/female animals traetad orally with olpadronate (45-90 mg/kg/d, 3 months) and 8/9 untreated controls. Both OPD doses enhanced diaphyseal cross-sectional moments of inertia (CSMI) with no change in cortical vBMD and elastic modulus. Yield stiffness and strength were mildly increased. Post-yield strength, deflection and energy absorption were strikingly enhanced. Ultimate strength was enhanced mainly because of effects on bone mass/geometry and post-yield properties. The large improvement of post-yield properties could be explained by improvements in bone geometry. Improvements in bone mass/geometry over weight-bearing needs suggest an enhanced modeling-related response to mechanical stimuli. Effects on tissue microstructural factors (not measured) could not be excluded. Results reveal novel olpadronate effects on bone strength and toughness unrelated to tissue mineralization and stiffness, even at high doses. Further studies could establish whether this could also occur in modeling-remodeling skeletons. If so, they could counteract the negative impact of anti-remodeling effects of bisphosphonates on bone strength.
Asunto(s)
Conservadores de la Densidad Ósea/farmacología , Remodelación Ósea/efectos de los fármacos , Calcificación Fisiológica/efectos de los fármacos , Difosfonatos/farmacología , Análisis de Varianza , Animales , Fenómenos Biomecánicos , Densidad Ósea/efectos de los fármacos , Diáfisis/anatomía & histología , Diáfisis/fisiología , Relación Dosis-Respuesta a Droga , Módulo de Elasticidad , Elasticidad , Femenino , Fémur/anatomía & histología , Fémur/fisiología , Masculino , Ratas , Ratas Wistar , Caracteres Sexuales , Programas Informáticos , TomografíaRESUMEN
In a pQCT study of running-trained and untrained men and women we had shown that bone mass distribution along the tibia was adapted to the usage-derived stress pattern. To study the possible association between the efficiency of diaphyseal design and bone material stiffness, we extend the analysis of the same sample to correlate pQCT indicators of the distribution (CSMIs), mass (BMC), and density (vBMD) of cortical bone tissue as descriptors of "distribution/mass" (d/m) or "distribution/quality" (d/q) relationships. The d/m and d/c curves followed positive (exponential) and negative (hyperbolic-like) equations, respectively. Distribution curves of r coefficients throughout the bone were all bell-shaped, reaching a maximum towards the mid-diaphysis. The CSMIs and BMC were higher, and vBMD was lower in men than women and in runners than non-runners. The d/m relationships were described by unique curves for all groups while d/q relationships were better adjusted to separate curves for men and women. Results support that: 1. diaphyseal design reflects the relative influence of bending/torsion stress along the bones, tending to minimize bone mass; 2. there is a trade-off between cortical bone "quality" and distribution; 3. d/m and d/q relationships are related to bone mechanical environment, and 4. d/q relationships are affected by sex.