RESUMO
OBJECTIVE: This study evaluated dual-energy x-ray absorptiometry-assessed whole-body bone-muscle relationship (bone mineral content/lean mass [BMC/LM]) as an indicator of its nonmechanical perturbations (ie, systemic) in pre- and postmenopausal women. A total of 3,205 women were studied, either healthy (no fracture [No Fx] groups, 1,035 premenopausal, 1,556 postmenopausal) or with recent fractures (Fx groups, 139 premenopausal, 475 postmenopausal) located at osteoporotic sites (hip, spine, long-bone metaphyses; Type II Fx, n = 386) or at other skeletal sites (Type I Fx, n = 228) to evaluate the impact of decreased muscle mass on fracture incidence before and after menopause. DESIGN: SD-scored graphs of BMC/LM proportionality were obtained from the No Fx groups as normal references. Based on the reference BMC versus LM curves obtained from their respective No Fx pre- and postmenopausal controls, BMC-LM SD scores were calculated for all women with fractures. RESULTS: BMC-LM SD scores in all premenopausal women with fractures and in Type I Fx postmenopausal women were similar to the reference. In contrast, SD scores in Type II Fx postmenopausal women were lower than the reference, especially in those with hip fractures. Except for Type II Fx postmenopausal women, all groups showed linear and similar BMC versus LM curves. Type II Fx postmenopausal women showed nonlinear relationships, with progressively decreasing BMC and BMC-LM SD scores as their LM decreased. CONCLUSIONS: Results suggest that both LM and BMC-LM SD scores can help to differentiate between systemic and mechanical (disuse-related) osteopenia/osteoporosis after menopause. Low LM values or BMC-LM SD scores seem to constitute additional fracture risk factors beyond those usually detected in premenopausal women or in women with other types of fractures. This application of dual-energy x-ray absorptiometry technology may lead to more effective diagnosis and treatment at low cost.
Assuntos
Composição Corporal , Peso Corporal , Fraturas Ósseas/epidemiologia , Osteoporose Pós-Menopausa/epidemiologia , Absorciometria de Fóton , Idoso , Argentina/epidemiologia , Densidade Óssea , Causalidade , Comorbidade , Feminino , Fraturas Ósseas/diagnóstico , Humanos , Pessoa de Meia-Idade , Osteoporose Pós-Menopausa/diagnóstico , Valor Preditivo dos Testes , Valores de Referência , Fatores de Risco , Saúde da MulherRESUMO
Correlations between dual-energy X-ray absorptiometry (DXA)-assessed bone mineral content and lean mass (BMC-LM curves), and between BMC/LM ratio and age ([BMC/LM]-age curves), were analyzed in the whole body (WB), the upper limbs (ULs) and the lower limbs (LLs) of 3,063 healthy Hispanic adults. Groups of 472 men aged 25-87 years, 1,035 premenopausal (pre-MP) women aged 27-54 years, and 1,556 post-menopausal (post-MP) women aged 48-93 years were studied with a GE-Lunar DPX-Plus device. BMC-LM curves confirmed previous observations that BMC and LM masses always correlate linearly, with similar slopes within each region, but differing in intercepts according to gender and hormonal status. Multiple regression tests showed little or no independent interaction of body weight or height with those relationships. [BMC/LM]-age curves were flat in men but showed the positive influence of estrogens throughout the age range in women. Z-scored graphs of all the corresponding relationships were compiled, showing the confidence intervals for means +/-1, +/-2, and +/-3 SDs of the data (+/-1, +/-2, +/-3 z-scores) along BMC-LM and [BMC/LM]-age curves. These charts are proposed as references for assessing how well bone mass (as assessed by BMC) and muscle mass (assumed proportional to LM) follow the natural anthropometric/biomechanical proportionality in Hispanic men and women within the age range studied, employing similar devices. Charts for LLs, showing the lowest variance amongst the studied correlations and approaching the origin as an exclusive feature, could provide the most accurate reference curves. Differences between data from ULs and LLs may provide information about any eventual interaction of body-weight bearing with the general results. The proposed analysis may provide useful information for approaching a differential diagnosis between disuse-related and other types of osteopenias employing only DXA.
Assuntos
Absorciometria de Fóton/métodos , Composição Corporal/fisiologia , Densidade Óssea/fisiologia , Menopausa/fisiologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Braço , Colômbia/epidemiologia , Feminino , Humanos , Perna (Membro) , Masculino , Pessoa de Meia-Idade , Músculo Esquelético/fisiologia , Pós-Menopausa/fisiologia , Pré-Menopausa/fisiologia , Valores de Referência , Estudos RetrospectivosRESUMO
In this article, we summarize the results of six different tomographic/biomechanical rat studies involving hypophysectomy (Hx), ovariectomy, treatment with rhGH, olpadronate, alendronate, and toxic doses of aluminum and the development of a genetic diabetes in the eSS strain. All these conditions induced some interesting and rarely reported effects on postyield bone strength. These effects were generally related neither to the degree of mineralization or the elastic modulus of the bone tissue nor to the preyield behavior of the bones. In two particular cases (Hx, eSS), the elastic modulus of bone tissue varied independently of its degree of mineralization. These results suggest the involvement of some microstructural factor(s) of bone tissue resistance to crack progression (a postyield feature of bone behavior), rather than to crack initiation (the yield-determining factor) in the corresponding mechanism. Changes in collagen or crystal structure may play that role. These changes are relevant to the mechanism of fracture production during plastic deformation, a feature of bone strength that might be independent from mineralization. Therefore, these changes might help to explain some effects of novel treatments on bone strength unrelated to bone mineralization. This questions the belief that the remaining bone mass in metabolic osteopenias is biologically and mechanically normal.
Assuntos
Densidade Óssea/fisiologia , Calcificação Fisiológica/fisiologia , Animais , Doenças Ósseas Metabólicas/fisiopatologia , Feminino , Fraturas Ósseas/fisiopatologia , Humanos , Ratos , Ratos Sprague-Dawley , Estresse Mecânico , Resistência à Tração/fisiologiaRESUMO
This report summarizes some preliminary absorptiometric (DXA, QCT/pQCT) studies from our laboratory, supporting the following assumptions. 1. In Homo sapiens at all ages, natural proportionality between DXA-assessed bone mineral mass (bone mineral content, BMC) and muscle mass (lean mass, LM) of the whole body or limbs is specific for ethnicity, gender, and reproductive status, but not for body weight, height, or body mass index. 2. This proportionality is sensitive to many kinds of endocrine-metabolic perturbations. 3. Percentilized or Z-scored charts of the BMC/LM correlations as determined in large samples of healthy individuals can provide a diagnostic reference for evaluating proportionality in different conditions. 4. Employing exclusively DXA, this methodology can be applied to discriminate between "disuse-related" and "metabolic" osteopenias based on the finding of normal or low BMC/LM percentiles or Z-scores respectively, with important therapeutic and monitoring implications.
Assuntos
Densidade Óssea , Osso e Ossos/diagnóstico por imagem , Músculo Esquelético/diagnóstico por imagem , Osteoporose/diagnóstico por imagem , Absorciometria de Fóton , Osso e Ossos/patologia , Feminino , Humanos , Masculino , Músculo Esquelético/patologia , Tamanho do Órgão , Osteoporose/patologiaRESUMO
Morphological and biomechanical features of the mandible are negatively affected by protein-energy malnutrition, whose effects are apparently dependent on the time of life of application. The aim here was to investigate, in neonatal rats nursed by dams put on a protein-free diet to depress milk production and thus create a state of protein-energy malnutrition in the offspring, subsequent growth and long-term effects by analyzing mandibular dimensions and bone quality in adulthood. Pregnant Wistar rats were fed a 20% protein diet (control) or a protein-free diet (malnourished) to obtain normal or subnormal milk production, respectively. After weaning, the offspring (males) were fed a 20% protein diet for 70 days. The dimensions of their excised mandibles were measured directly between anatomical points; the geometry and material quality of mandibular bone were assessed by peripheral quantitative computed tomography. Pups suckling from malnourished dams weighed 49.4% of those suckling from control dams at weaning; the actual difference between control and malnourished pups was 25.1g, which persisted until day 91 of age, indicating the absence of catch-up growth. As with body size, the mandibular base length, height and area (an index of mandibular size) were significantly smaller in malnourished than control rats at the end of the study. The mandibular cortical area, volumetric cortical bone mineral content and volumetric cortical bone mineral density assessed by peripheral quantitative computed tomography were similar in both groups of rats at the end of the observation period, but there was a significant reduction in the cortical axial moment of inertia in malnourished rats at this time of postnatal life. These findings suggest that catch-up growth was incomplete in rats malnourished during the suckling period and that the adaptation of mandibular bone architecture to body growth was apparently insufficient to attain normal values, thus not allowing complete compensation in mechanical competence at the end of the study because of an inadequate spatial distribution of resistive material through its cross-section rather than qualitative or quantitative impairment of cortical bone.
Assuntos
Mandíbula/crescimento & desenvolvimento , Desnutrição Proteico-Calórica/fisiopatologia , Análise de Variância , Animais , Animais Recém-Nascidos , Fenômenos Biomecânicos , Constituição Corporal , Peso Corporal , Densidade Óssea/fisiologia , Dieta com Restrição de Proteínas/efeitos adversos , Proteínas Alimentares/administração & dosagem , Feminino , Lactação/fisiologia , Masculino , Mandíbula/patologia , Mandíbula/fisiopatologia , Gravidez , Desnutrição Proteico-Calórica/patologia , Ratos , Ratos Wistar , Estatística como Assunto , Estresse Mecânico , Tomografia Computadorizada por Raios X , DesmameRESUMO
La calidad mecánica de cualquier hueso está determinada por la rigidez (micro-arquitectura, grado de calcificación, microfracturas) y distribución espacial (macro-arquitectura) de su material cortical (en cualquier hueso) y trabecular (sólo en cuerpos vertebrales), resultantes de una combinación de modelación y remodelación óseas. Estos procesos están regulados direccionalmente por el "mecanostato" óseo, sistema retroalimentado cuyo estímulo proviene del uso mecánico regional del esqueleto, y cuyo punto de referencia está permanentemente modulado (no regulado) en forma sistémica por el entorno endocrino-metabólico. Todos los tratamientos medicamentosos en uso para las osteopatías, fragilizantes, incluyendo los bisfosfonatos actúan únicamente modificando no-direccionalmente este último factor. Por eso, sus resultados dependen del grado de estimulación del mecanostato por el uso, y sólo pueden estimarse determinando parßmetros de calidad material y de eficiencia arquitectónica ósea. Los bisfosfonatos mejoran la eficiencia mecánica ósea por inhibir la remodelación (que usualmente arroja balances negativos de masa) afectando, en algún grado (menor para los productos de más cercana generación), la mineralización del material rígido. En nuestro medio contamos con tres productos con efectos biomecánicos óseos positivos demostrados: pamidronato, olpadronato y alendronato. En animales intactos, los tres mejoran la macro-arquitectura ósea a cualquier dosis, aunque el pamidronato deteriora la mineralización del material a dosis muy altas. En animales ooforectomizados o inmovilizados, los tres protegen contra la repercusión biomecánica negativa de la osteopenia impidiendo el deterioro de la calidad del material y sin alterar el diseño arquitectónico óseo. También potencian o prolongan los efectos anabólicos óseos de la hPTH. Sus ventajas terapéuticas se fundan en que ninguno de los tres perturba el accionar del mecanostato, dejando intactos los mecanismos regulatorios de la eficiencia mecánica de la estructura ósea por el uso mecánico, o incluso potenciándolos sistémicamente (efecto anti-catabólico). Esta característica explica que sus efectos dependan mucho del uso mecánico del esqueleto en las regiones que se desea mejorar. Está aun por definirse si una inhibición demasiado intensa o prolongada de la remodelación por los bisfosfonatos pudiera deteriorar o no la reparación de microfracturas que la misma provee, con consecuencias biomecánicas potencialmente...
Assuntos
Humanos , Animais , Ratos , Osso e Ossos/efeitos dos fármacos , Doenças Ósseas Metabólicas/tratamento farmacológico , Difosfonatos/farmacologia , Difosfonatos/uso terapêutico , Fenômenos Biomecânicos , Densidade Óssea/efeitos dos fármacos , Remodelação Óssea/efeitos dos fármacos , Relação Dose-Resposta a DrogaRESUMO
La calidad mecánica de cualquier hueso está determinada por la rigidez (micro-arquitectura, grado de calcificación, microfracturas) y distribución espacial (macro-arquitectura) de su material cortical (en cualquier hueso) y trabecular (sólo en cuerpos vertebrales), resultantes de una combinación de modelación y remodelación óseas. Estos procesos están regulados direccionalmente por el "mecanostato" óseo, sistema retroalimentado cuyo estímulo proviene del uso mecánico regional del esqueleto, y cuyo punto de referencia está permanentemente modulado (no regulado) en forma sistémica por el entorno endocrino-metabólico. Todos los tratamientos medicamentosos en uso para las osteopatías, fragilizantes, incluyendo los bisfosfonatos actúan únicamente modificando no-direccionalmente este último factor. Por eso, sus resultados dependen del grado de estimulación del mecanostato por el uso, y sólo pueden estimarse determinando parßmetros de calidad material y de eficiencia arquitectónica ósea. Los bisfosfonatos mejoran la eficiencia mecánica ósea por inhibir la remodelación (que usualmente arroja balances negativos de masa) afectando, en algún grado (menor para los productos de más cercana generación), la mineralización del material rígido. En nuestro medio contamos con tres productos con efectos biomecánicos óseos positivos demostrados: pamidronato, olpadronato y alendronato. En animales intactos, los tres mejoran la macro-arquitectura ósea a cualquier dosis, aunque el pamidronato deteriora la mineralización del material a dosis muy altas. En animales ooforectomizados o inmovilizados, los tres protegen contra la repercusión biomecánica negativa de la osteopenia impidiendo el deterioro de la calidad del material y sin alterar el diseño arquitectónico óseo. También potencian o prolongan los efectos anabólicos óseos de la hPTH. Sus ventajas terapéuticas se fundan en que ninguno de los tres perturba el accionar del mecanostato, dejando intactos los mecanismos regulatorios de la eficiencia mecánica de la estructura ósea por el uso mecánico, o incluso potenciándolos sistémicamente (efecto anti-catabólico). Esta característica explica que sus efectos dependan mucho del uso mecánico del esqueleto en las regiones que se desea mejorar. Está aun por definirse si una inhibición demasiado intensa o prolongada de la remodelación por los bisfosfonatos pudiera deteriorar o no la reparación de microfracturas que la misma provee, con consecuencias biomecánicas potencialmente... (AU)