Bone Strength Index Research Articles

Peak lean tissue mass accrual precedes changes in bone strength indices at the proximal femur during the pubertal growth spurt

Purpose We examined the timing of the age and the magnitude of peak lean tissue mass accrual (PLTV) relative to the age and magnitude of two variables of bone strength [peak cross sectional area velocity (PCSAV), and peak section modulus velocity, (PZV)] at the proximal femur in males and females during the adolescent growth spurt. We hypothesized that the age of PLTV would precede the ages of PCSAV and PZV and that there is a positive relationship between the magnitude of PLTV and both PCSAV and PZV in both genders. Methods 41 males and 42 females aged 8–18 years were selected from the Saskatchewan Pediatric Bone Mineral Accrual Study (1991–2005). Participants' total body lean tissue mass was assessed annually for 6 consecutive years using DXA. Narrow neck and femoral shaft cross sectional areas (CSA) and section modulus ( Z) were determined using the hip structural analysis (HSA) program. Participants were aligned by maturational age (years from peak height velocity). Lean tissue mass, CSA, and Z were converted into whole year velocities and the maturational age of peak tissue velocities was determined using a cubic spline curve fitting procedure. A 2 × 3 (gender × tissue) factorial MANOVA with repeated measures was used to test for differences between age of PLTV and the ages of PCSAV and PZV between genders. Multiple regression analyses were used to examine the relationship between PLTV and both PCSAV and PZV. Results There were no sex differences in the ages at which tissue peaks occurred when aligned by maturational age. There were significant differences between the age of PLTV and both PCSAV and PZV at the narrow neck ( p = 0.001) and femoral shaft ( p = 0.03), where the age of PLTV preceded both PCSAV and PZV when pooled by gender. PLTV was a significant predictor of the magnitude of both PCSAV and PZV at all sites ( p < 0.05). Conclusions These findings support the hypothesis that the age of PLTV precedes the age of PCSA and PZV at the proximal femur. Results support the theory that muscle development is an important factor in affecting bone strength.

Overweight children have poor bone strength relative to body weight, placing them at greater risk for forearm fractures

Introduction: Obesity is thought to be a protective factor for bones in adults but not in children based on the evidence of the greater incidence of forearm fractures in obese children. Our objective was to investigate the effect of adiposity on bone strength in relation to the mechanical challenge placed onto the forearm bones in case of a fall. Methods: Cross sectional areas (CSA) were obtained at the mid- and distal radius by peripheral quantitative computed tomography in 486 children (241 boys), mean age 8.3 years (range 6.9–9.7), participating in the LOOK Project. The following parameters were measured: bone mass and bone CSA (both sites), and muscle and fat CSA (mid-forearm only). Bone strength indices combining bone size and total volumetric density were calculated at each site. Results/Discussion: Overweight children (BMI > percentile equivalent to 25 kg/m2 in adults) have higher bone parameters than normal-weight peers (Z-scores +0.6 to +0.9SD, p Conclusion. Overweight children have stronger bones due to greater muscle size. However, children with high fat mass relative to muscle mass (increased adiposity) have poorer bone strength, independent of weight, which may contribute to the increased risk of fracture in obese children.

Distal Radius Strength: A Comparison of DXA-Derived vs pQCT-Measured Parameters in Adolescent Females

Although quantitative computed tomography (QCT) is considered the gold standard for in vivo densitometry, dual-energy X-ray absorptiometry (DXA) scans assess larger bone regions and are more appropriate for pediatric longitudinal studies. Unfortunately, DXA does not yield specific bone architectural output. To address this issue in healthy, postmenarcheal girls, Sievänen's distal radius formulae [1996] were applied to derive indices of bone geometry, volumetric bone mineral density (vBMD), and strength from DXA data; results were compared to peripheral quantitative computed tomography (pQCT) output. Contemporaneous scans were performed on the left, distal radii of 35 gymnasts, ex-gymnasts, and nongymnasts (aged 13.3–20.4 yr, mean 16.6 yr). For 4% and 33% regions, pQCT measured cross-sectional areas (CSAs) and vBMD; comparable DXA indices were generated at ultradistal and 1/3 regions. Index of structural strength in axial compression was calculated from 4% pQCT and DXA output for comparison; 33% pQCT strength-strain index was compared to 1/3 DXA section modulus. Sievänen DXA indices were significantly, positively correlated with pQCT output ( R = +0.61 to +0.98; p < 0.0001). At the distal radius, in healthy postmenarcheal girls, Sievänen's method yielded potentially useful DXA indices of diaphyseal cortical CSA and bone strength at both the diaphysis (section modulus) and the metaphysis (index of structural strength in axial compression).

Bone Structure and Volumetric BMD in Overweight Children: A Longitudinal Study

The effect of excess body fat on bone strength accrual is not well understood. Therefore, we assessed bone measures in healthy weight (HW) and overweight (OW) children. Children (9-11 yr) were classified as HW (n = 302) or OW (n = 143) based on body mass index. We assessed total (ToD) and cortical (CoD) volumetric BMD and bone area, estimates of bone strength (bone strength index [BSI]; stress-strain index [SSIp]), and muscle cross-sectional area (CSA) at the distal (8%), midshaft (50%), and proximal (66%) tibia by pQCT. We used analysis of covariance to compare bone outcomes at baseline and change over 16 mo. At baseline, all bone measures were significantly greater in OW compared with HW children (+4-15%; p <or= 0.001), with the exception of CoD at the 50% and 66% sites. Over 16 mo, ToA increased more in the OW children, whereas there was no difference for change in BSI or ToD between groups at the distal tibia. At the tibial midshaft, SSIp was similar between groups at baseline when adjusted for muscle CSA, but low when adjusted for body fat in the OW group. At both sites, bone strength increased more in OW because of a greater increase in bone area. Changes in SSIp were associated with changes in lean mass (r = 0.70, p < 0.001) but not fat mass. In conclusion, although OW children seem to be at an advantage in terms of absolute bone strength, bone strength did not adapt to excess body fat. Rather, bone strength was adapted to the greater muscle area in OW children.

Sex Differences in Parameters of Bone Strength in New Recruits

Stress fracture (SF) injuries in new recruits have long been attributed to low bone mineral density (BMD). Low areal BMD assessed using two-dimensional dual-energy x-ray absorptiometry imaging, however, reflects structural density and is affected by smaller measures of bone geometry. Recent studies support a relationship between bone size and SF and indicate that slender bones are more susceptible to damage under identical loading conditions. Peripheral quantitative computed tomography (pQCT) is a three-dimensional imaging tool that provides measures of tissue density and geometry parameters of the tibia, a common site of SF. To evaluate sex differences in parameters of volumetric BMD (vBMD), geometry, and strength of the tibia in new recruits using a novel pQCT image analysis procedure. pQCT images were obtained from 128 healthy men and women (20 male, 108 female, aged 18-21 yr) entering a 4-month gender-integrated combat training program in the Israeli Defense Forces. Tibial scans taken at sites 4% (trabecular bone), 38%, and 66% (cortical bone) from the distal end plate were analyzed using MATLAB to assess whole-bone and regional parameters. Measures included vBMD, geometry (diameter, area, cortical thickness, and canal radius), and strength (moments of inertia and bone strength and slenderness indices). With the exception of normalized canal radius, which did not differ between sexes, all measures of bone geometry (P < 0.0001) and strength (P < 0.0001 to P = 0.07) were greater in men. Women exhibited 2.7% to 3.0% greater cortical vBMD than men, whereas trabecular vBMD was 8.4% lower in women (P < 0.001). These differences remained significant after adjusting for body size. Sex differences in bone geometry and mineralization of the tibia may contribute to a decreased ability to withstand the demands imposed by novel, repetitive exercise in untrained individuals entering recruit training.

Maintenance of exercise-induced benefits in physical functioning and bone among elderly women

This study showed that about a half of the exercise-induced gain in dynamic balance and bone strength was maintained one year after cessation of the supervised high-intensity training of home-dwelling elderly women. However, to maintain exercise-induced gains in lower limb muscle force and physical functioning, continued training seems necessary. Maintenance of exercise-induced benefits in physical functioning and bone structure was assessed one year after cessation of 12-month randomized controlled exercise intervention. Originally 149 healthy women 70-78 years of age participated in the 12-month exercise RCT and 120 (81%) of them completed the follow-up study. Self-rated physical functioning, dynamic balance, leg extensor force, and bone structure were assessed. During the intervention, exercise increased dynamic balance by 7% in the combination resistance and balance-jumping training group (COMB). At the follow-up, a 4% (95% CI: 1-8%) gain compared with the controls was still seen, while the exercise-induced isometric leg extension force and self-rated physical functioning benefits had disappeared. During the intervention, at least twice a week trained COMB subjects obtained a significant 2% benefit in tibial shaft bone strength index compared to the controls. A half of this benefit seemed to be maintained at the follow-up. Exercise-induced benefits in dynamic balance and rigidity in the tibial shaft may partly be maintained one year after cessation of a supervised 12-month multi-component training in initially healthy elderly women. However, to maintain the achieved gains in muscle force and physical functioning, continued training seems necessary.

Overweight Children Have Increased Tibia Bone Density and Bone Strength Attributable To Increased Muscle Mass

To determine differences in bone geometry, estimates of bone strength, muscle size and bone strength relative to load, in women runners with and without a history of stress fracture.We recruited 32 competitive distance runners aged 18–35, with (SFX, n = 16) or without (NSFX, n = 16) a history of stress fracture for this case-control study. Peripheral quantitative computed tomography (pQCT) was used to assess volumetric bone mineral density (vBMD, mg/mm3), total (ToA) and cortical (CtA) bone areas (mm2), and estimated compressive bone strength (bone strength index; BSI, mg/mm4) at the distal tibia. ToA, CtA, cortical vBMD, and estimated strength (section modulus; Zp, mm3 and strength strain index; SSIp, mm3) were measured at six cortical sites along the tibia. Mean active peak vertical (pkZ) ground reaction forces (GRFs), assessed from a fatigue run on an instrumented treadmill, were used in conjunction with pQCT measurements to estimate bone strength relative to load (mm2/N ∗ kg− 1) at all cortical sites.SSIp and Zp were 9–11% lower in the SFX group at mid-shaft of the tibia, while ToA and vBMD did not differ between groups at any measurement site. The SFX group had 11–17% lower bone strength relative to mean pkZ GRFs (p < 0.05).These findings indicate that estimated bone strength at the mid-tibia and mean pkZ GRFs are lower in runners with a history of stress fracture. Bone strength relative to load is also lower in this same region suggesting that strength deficits in the middle 1/3 of the tibia and altered gait biomechanics may predispose an individual to stress fracture.

Tibial Bone Geometry in Chronic Stroke Patients: Influence of Sex, Cardiovascular Health, and Muscle Mass

This study aimed to examine the geometry of the tibia in chronic stroke survivors. Fifty-five ambulatory individuals with chronic stroke were included in the study. pQCT was used to obtain a cross-sectional scan of the tibia at the 30% site on both the paretic and nonparetic sides. Leg lean mass was derived from a total body scan using DXA. Each subject was also evaluated for peak oxygen consumption rate, spasticity, and functional mobility. Paired t-tests were used to compare the pQCT parameters between the two sides. Multiple linear regression analysis was used to identify the significant determinants of tibial bone strength index (BSI). In men, marrow cavity area on the paretic side was significantly greater than the nonparetic side (p = 0.011), whereas the total bone area showed no significant side-to-side difference (p = 0.252). In women, total bone area on the paretic side was significantly smaller than the nonparetic side (p = 0.003), whereas the marrow cavity area had no side-to-side difference (p = 0.367). Peak oxygen consumption (r(2) = 0.739, F(5,49) = 22.693, p < 0.001) and paretic leg lean mass (r(2) = 0.802, F(6,48) = 32.475, p < 0.001) remained independently associated with tibial BSI, after controlling for age, sex, body mass index, years since stroke onset, and physical activity level. The geometry of the tibia in stroke patients showed sex-specific side-to-side differences. The results suggested that, whereas endosteal resorption was apparent in men, periosteal resorption was more predominant in women. The results also highlight the potential importance of promoting cardiovascular health and leg muscle mass in enhancing bone geometry in chronic stroke survivors.

Eight Months of Regular In-School Jumping Improves Indices of Bone Strength in Adolescent Boys and Girls: The POWER PE Study

The POWER PE study was an 8-mo, randomized, controlled, school-based exercise intervention designed to apply known principles of effective bone loading to practical opportunities to improve life-long musculoskeletal outcomes. A total of 99 adolescents (46 boys and 53 girls) with a mean age of 13.8 +/- 0.4 yr (peri- to postpubertal) volunteered to participate. Intervention subjects performed 10 min of jumping activity in place of regular physical education (PE) warm up. Control subjects performed usual PE warm-up activities. Bone mass (DXA and QUS) was assessed at baseline and follow-up along with anthropometry, maturity, muscle power, and estimates of physical activity and dietary calcium. Geometric properties (such as femoral neck [FN] moment of inertia) were calculated from DXA measures. Boys in the intervention group experienced improvements in calcaneal broadband ultrasound attenuation (BUA) (+5.0%) and fat mass (-10.5%), whereas controls did not (+1.4% and -0.8%, respectively). Girls in the intervention group improved FN BMC (+13.9%) and lumbar spine (LS) BMAD (+5.2%) more than controls (+4.9% and +1.5%, respectively). Between-group comparisons of change showed intervention effects only for whole body (WB) BMC (+10.6% versus +6.3%) for boys. Boys in the intervention group gained more lean tissue mass, trochanter (TR) BMC, LS BMC, and WB BMC and lost more fat mass than girls in the intervention group (p < 0.05). Ten minutes of jumping activity twice a week for 8 mo during adolescence seems to improve bone accrual in a sex-specific manner. Boys increased WB bone mass and BUA, and reduced fat mass, whereas girls improved bone mass at the hip and spine.

Improved Peripheral Cortical Bone Geometry after Surgical Treatment of Primary Hyperparathyroidism in Postmenopausal Women

Cortical bone geometry is one of the most important components of bone strength. Excess endogenous PTH or intermittent PTH administration affects cortical bone geometry; however, the changes in cortical bone geometry in patients with primary hyperparathyroidism (pHPT) after parathyroidectomy (PTX) remain unknown. The present study was performed to examine the longitudinal effects of treating endogenous PTH excess on cortical bone geometry in postmenopausal patients with pHPT by using peripheral quantitative computed tomography. Twenty postmenopausal pHPT patients and 30 postmenopausal control subjects matched for age participated in this study. Volumetric bone mineral density (vBMD), cortical bone geometric parameters, polar strength strain index, and polar cross-sectional moment of inertia were measured using peripheral quantitative computed tomography at the radius during the year after PTX. After 1 yr, total and cortical vBMD significantly increased after PTX in the pHPT group (2.9 and 1.6%, respectively), whereas they significantly decreased in the control group (-2.1 and -1.3%, respectively). Significant decreases in cortical thickness and area were observed in the control group (-3.0 and -2.5%, respectively). In contrast, the pHPT group showed increases in cortical thickness and area (8.5 and 7.6%, respectively) as well as polar strength strain index 1 year after PTX. The present longitudinal study showed significant beneficial changes in volumetric BMD, cortical bone geometry, and bone strength index after PTX in postmenopausal women with pHPT.

Bone Geometry, Strength and Muscle Mass in Runners with and without a History of Stress Fracture

Stress fractures are common among distance runners. While low areal bone mineral density has been associated with stress fractures, little is known about the role of bone structure and muscle mass in the pathophysiology of stress fractures. PURPOSE: To determine differences in bone geometry, estimates of bone strength, and muscle size in female runners with and without a history of stress fracture. METHODS: A total of 39 competitive female distance runners ages 18-35, with (SFX, n = 19) or without (NSFX, n = 20) a history of lower limb stress fracture were recruited for this cross-sectional study. Peripheral Quantitative Computed Tomography (pQCT, Orthometrix XCT 3000) was used to assess volumetric bone mineral density (vBMD, mm3), bone area (ToA, mm2), and estimated compressive bone strength (bone strength index; BSI= ToA * ToD2) at the distal tibia (4%). Total (ToA, mm2) and cortical (CoA, mm2= ToA * ToD2) bone area, cortical density, and estimated bone bending strength (stress strain index; SSIp, mm3) were measured at the 15%, 25%, 33%, 45%, 50% and 66% sites. Muscle cross sectional area (MCSA) was measured at the 50% and 66% sites. Questionnaires were used to assess health and training history. RESULTS: Participants in the SFX group had significantly smaller (7 - 8%) CoA at the 45%, 50%, and 66% sites in both the right and left legs (p < 0.05 for all). SSIp was also significantly lower (9 - 10%) at the 50% and 66% sites. Runners with a history of stress fracture also had a smaller MCSA (7 - 8%) at the 66% site in both the legs. The remaining bone parameters, including vBMD were not significantly different between groups. After adjusting for MCSA there were no differences between groups for any measured bone outcomes. CONCLUSION: These findings suggest that bone CoA, strength and MCSA are all lower in runners with a history of stress fracture. However, the lower bone CoA and strength was adapted to the lower muscle size, suggesting interventions to reduce stress fracture risk might be aimed at improving muscle size and strength.

Predisposing Characteristics for Tibial Stress Fracture

Tibial stress fractures (TSF) increasingly affect athletes and military recruits, and are challenging to manage. There is a need to identify the characteristics most associated with the incidence of TSF in order for preventative strategies to be developed, and/or screening to be implemented where appropriate. PURPOSE To identify physical and behavioural characteristics related to incidence of tibial stress fracture in men and women. METHODS Twenty-seven patients (13 M, 14 F) with TSF and 27 age-, sex-, height-, weight-, and activity-matched subjects with no history of stress fracture were recruited. Physical (height, weight, menstrual history, bone parameters, lower limb alignment anomaly) and behavioural (diet, meds, oral contraceptives, training) characteristics were recorded from all subjects via anthropometry, questionnaire, dual-energy x-ray absorptiometry and quantitative ultrasound. Between group differences were examined via one-way ANOVA. RESULTS Stress fracture subjects exhibited shorter femoral necks (FN) with smaller FN area and thinner cortices, but greater lumbar spine (LS) bone mineral density (BMD), bone mineral apparent density (BMAD), stiffness (E) and strength index (IBS). Foot type also differed between groups with 70% of controls having normal feet versus 40% of fractured subjects. There were no other between group differences in any other anthropometric or behavioural variable. Split file analyses revealed subtle sex-specific characteristics. Only foot type differed between groups for men; the control group exhibiting fewer anomalies. All the aforementioned differences in bone parameters were apparent between female groups, with greater FN bone mineral content (BMC) and lower LS BMC in controls also becoming significant. CONCLUSION Foot anomalies appear to be the characteristic most associated with TSF for men; whereas women suffering TSF appear to have smaller bones of the lower extremity, but stronger lumbar spines than those who have never fractured. Supported by US Army MRMC, DAMD17-98-1-8519, and BIOLECTRON, Inc. now EBI, Parsippany, NJ.

Effects of Moderate Zinc Deficiency and Phytase Supplementation on Musculoskeletal Integrity in Exercising Rats

It is not clear how the adaptations to chronic exercise may be affected by a phytase (P) supplemented low zinc (Zn) diet. Phytic acid (PA) is known to form insoluble complexes with nutritionally essential minerals; including Zn. Phytases are enzymes that aid the removal of essential minerals from PA, thus increasing their bioavailability. PURPOSE: To determine the effects of a low Zn diet and supplemental P on bone and muscle in voluntary exercising rats. METHODS: 30 male Sprague-Dawley rats were housed in cages fitted with voluntary running wheels and fed either a 5ppm Zn (ZnLo), 5ppm Zn+1,500 FTU/kg P (ZnLo+P) or a 30ppm Zn (ZnAd) diet for nine weeks, (n=10 per group). In vivo peripheral quantitative computed tomography scans were performed at 10 and 50% of the total tibia length. Cortical content (CCNT) (mg), cortical area (CA) (mm2) and polar strength strain index (SSIp) (mm3) were investigated at the 10 and 50% regions of interest (ROI). Muscle area (MA) (mm2) was additionally investigated at the 50% ROI. A one-way ANOVA and Tukey post-hoc were used to analyze the data. RESULTS: At the 10% ROI, ZnAd exhibited increased CCNT and greater SSIp as compared to ZnLo and ZnLo+P. At the 50% ROI, ZnAd exhibited increased CCNT, CA and greater SSIp as compared to ZnLo and increased MA as compared to ZnLo and ZnLo+P. Additionally at the 50% ROI, ZnLo+P exhibited increased CCNT and MA as compared to ZnLo.TableCONCLUSION: P-supplementation increased mid-shaft CCNT and MA in a moderately Zn deficient sample but did not match the superior indices of bone strength and lean mass that were observed by consuming a 30ppm Zn diet.

Autosome-wide linkage analysis of hip structural phenotypes in the Old Order Amish

IntroductionFracture risk is associated with bone mineral density (BMD) and with other indices of bone strength, including hip geometry. While the heritability and associated fracture risk of BMD are well described, less is known about genetic influences of bone geometry. We derived hip structural phenotypes using the Hip Structural Analysis program (HSA) and performed autosome-wide linkage analysis of hip geometric structural phenotypes. Materials and methodsThe Amish Family Osteoporosis Study was designed to identify genes affecting bone health. BMD was measured at the hip using dual X-ray absorptiometry (DXA) in 879 participants (mean age±SD=49.8±16.1 years, range 18–91 years) from large multigenerational families. From DXA scans, we computed structural measures of hip geometry at the femoral neck (NN) and shaft (S) by HSA, including cross-sectional area (CSA), endocortical or inner diameter (ID), outer diameter (OD) buckling ratio (BR) and section modulus (Z). Genotyping of 731 highly polymorphic microsatellite markers (average spacing of 5.4 cM) and autosome-wide multipoint linkage analysis was performed. ResultsThe heritability of HSA-derived hip phenotypes ranged from 40 to 84%. In the group as a whole, autosome-wide linkage analysis suggested evidence of linkage for QTLs related to NN_Z on chromosome 1p36 (LOD=2.36). In subgroup analysis, ten additional suggestive regions of linkage were found on chromosomes 1, 2, 5, 6, 11, 12, 14, 15 and 17, all with LOD>2.3 except for our linkage at 17q11.2-13 for men and women age 50 and under for NN_CSA, which had a lower LOD of 2.16, but confirmed a previous linkage report. ConclusionsWe found HSA-derived measures of hip structure to be highly heritable independent of BMD. No strong evidence of linkage was found for any phenotype. Confirmatory evidence of linkage was found on chromosome 17q11.2-12 for NN_CSA. Modest evidence was found for genes affecting hip structural phenotypes at ten other chromosomal locations.

The BPAQ: a bone-specific physical activity assessment instrument

A newly developed bone-specific physical activity questionnaire (BPAQ) was compared with other common measures of physical activity for its ability to predict parameters of bone strength in healthy, young adults. The BPAQ predicted indices of bone strength at clinically relevant sites in both men and women, while other measures did not. Only certain types of physical activity (PA) are notably osteogenic. Most methods to quantify levels of PA fail to account for bone relevant loading. Our aim was to examine the ability of several methods of PA assessment and a new bone-specific measure to predict parameters of bone strength in healthy adults. We recruited 40 men and women (mean age 24.5). Subjects completed the modifiable activity questionnaire, Bouchard 3-day activity record, a recently published bone loading history questionnaire (BLHQ), and wore a pedometer for 14 days. We also administered our bone-specific physical activity questionnaire (BPAQ). Calcaneal broadband ultrasound attenuation (BUA) (QUS-2, Quidel) and densitometric measures (XR-36, Norland) were examined. Multiple regression and correlation analyses were performed on the data. The current activity component of BPAQ was a significant predictor of variance in femoral neck bone mineral density (BMD), lumbar spine BMD, and whole body BMD (R(2) = 0.36-0.68, p < 0.01) for men, while the past activity component of BPAQ predicted calcaneal BUA (R(2) = 0.48, p = 0.001) for women. The BPAQ predicted indices of bone strength at skeletal sites at risk of osteoporotic fracture while other PA measurement tools did not.

Increased Plasma Osteoprotegerin Concentrations Are Associated with Indices of Bone Strength of the Hip

Osteoprotegerin (OPG) is an important regulator of bone turnover through its effects on osteoclastogenesis, yet findings from previous studies of circulating OPG and commonly measured bone indices in humans have been conflicting. We conducted a cross-sectional study to evaluate the association between plasma OPG and femoral neck (FN) bone density (BMD) and geometry in a large cohort of women and men. Participants included 1379 postmenopausal women and 1165 men, aged 50-89 yr (mean, 64 yr), in the Framingham Offspring Study. Dual x-ray absorptiometry was used to evaluate FN BMD and geometry (bone width, section modulus, and cross-sectional area at the narrow neck region). Plasma OPG concentrations were measured by ELISA. Sex-specific analysis of covariance was used to calculate means and assess linear trend in BMD and geometry values across OPG quartiles, adjusted for confounders. OPG concentrations were greater in women than men, increased with age, and were greater in smokers and those with diabetes and heart disease. Multivariable-adjusted mean FN BMD in women increased from the lowest to the highest OPG quartile (trend, P < 0.01). However, no linear trend between FN BMD and OPG was observed in men (trend, P = 0.34). Section modulus and bone width increased with OPG in men (trend, P < 0.01), whereas no association between hip geometry indices and OPG was observed in women. Higher OPG concentration may indicate greater skeletal strength in women and men, possibly through reducing bone loss in women and increasing periosteal apposition in men.

Proximal femur mechanical adaptation to weight gain in late adolescence: a six-year longitudinal study.

The effect of weight gain in late adolescence on bone is not clear. Young women who consistently gained weight (n = 23) from 17 to 22 yr of age had increased BMD but a lack of subperiosteal expansion compared with stable weight peers (n = 48). Bone strength increased appropriately for lean mass in both groups but decreased relative to body weight in weight gainers, suggesting increased bone fragility in weight gainers. Weight gain leading to obesity often starts in adolescence, yet little is known about its effects on bone. We used longitudinal data to examine the effects of weight gain in late adolescence (from 17 to 22 yr of age) on proximal femur BMD, geometry, and estimates of bending strength. Participants were classified as either weight gainers (WG, n = 23) or stable weight (SW, n = 48) using a random coefficients model. Weight gainers had positive increases in weight (p < 0.05) at each clinic visit from age 17 onward. Proximal femur DXA scans (Hologic QDR 2000) taken annually from 17 to 22 yr of age were analyzed for areal BMD (g/cm(2)), subperiosteal width (cm), and bone cross-sectional area (CSA) at the proximal femoral shaft. Cortical thickness was measured, and section modulus (Z, cm(3)) was calculated as a measure of bone bending strength. Total body lean (g) and fat (g) mass were measured from DXA total body scans. Over ages 17-22, height remained stable in both groups. Weight remained static in the SW group but increased 14% on average in the WG group (p < 0.05). After controlling for age 17 baseline values, WG had higher BMD (+2.6%), thicker cortices (+3.6%), and greater bone CSA (+2.3%). Increased BMD did not translate to greater increases in bone bending strength (Z). The SW group achieved similar gains in Z by greater subperiosteal expansion. Bone strength index (SI = Z/height) normalized for body weight remained constant in the SW group but decreased significantly in the WG group. In contrast, SI normalized to lean mass did not change over time in either group. Other variables including physical activity, nutrition, and hormone levels (estradiol, testosterone, cortisol) did not differ significantly between groups. These data suggest that weight gain in late adolescence may inhibit the periosteal expansion known to normally occur throughout life in long bones, resulting in decreased bone strength relative to body weight.

Sex-specific developmental changes in muscle size and bone geometry at the femoral shaft

Introduction When expressed as a percentage of the average result in young adults, bone mineral content lags behind bone length before puberty. Even though this observation has led to speculation about bone fragility in children, such relationships could simply be due to scaling effects when measures with different geometrical dimensions are compared. Methods The study population comprised 145 healthy subjects (6–25 years, 94 females). Magnetic resonance imaging and dual-energy X-ray absorptiometry were used to determine femur length, bone mineral content, cortical bone mineral density, cross-sectional bone geometry (bone diameter; cortical thickness; total, cortical and medullary areas; cross-sectional and polar moments of area; bone strength index) and muscle area at the proximal one-third site of the femur. Results were dimensionally scaled by raising two-, three- and four-dimensional variables to the power of 1/2, 1/3 and 1/4, respectively. Sex-differences were also assessed before and after functionally adjusting variables for femur length and weight or muscle size. Results In prepubertal children, unscaled results expressed as percentages of adult values were lowest for variables with the highest dimensions (e.g., moments of area < bone mineral content < cross-sectional areas < femur length). However, when dimensionally scaled, results in children represented similar percentages of the respective average adult values, even after functional adjustments. Before puberty, there was no sex-difference in adjusted bone or muscle variables. After puberty, males had greater total and cortical bone area, bone diameter, moments of area, bone strength index and muscle area than women, both in absolute terms as well as adjusted for femur length and weight. The largest sex-difference was found for muscle area. When compared relative to muscle size, young adult women attained greater total and cortical bone area than men. Conclusions Growth in femoral length, diameter, mass and strength appears well coordinated before puberty. Postpubertal females have narrower femora, less bone strength and muscle size than males. However, when muscle size is taken into account, females have a larger femoral bone cross-section and more cortical bone. These sex-differences likely result from a combination of mechanical and hormonal effects occurring during puberty.

Differential Response of Risedronate on Tibial and Mandibular Bone Quality in Glucocorticoid-treated Growing Rats

Glucocorticoids induce bone loss and retard bone growth in children. In this study we investigated the effect of treatment with risedronate on glucocorticoid -prednisolone- induced decreases in bone density, quality, strength and growth of the tibia and mandible in growing rats. Trabecular and cortical bone structure was measured by peripheral quantitative computed tomography (pQCT) and three-dimensional (3D) micro-computed tomography (micro-CT). Indicators of bone strength were calculated from cortical bone density and the modulus of sections obtained from pQCT analysis. Tibial and mandibular bone sizes were also measured. Prednisolone decreased the bone growth of both tibia and mandible. It also caused deterioration of trabecular and cortical bone structure and strength in the mandible, and in cortical bone in the tibia, but had no effect on trabecular bone in the tibia. Risedronate inhibited the prednisolone-induced decreases in tibial width and mandibular length and height but did not improve the retardation of longitudinal bone growth. Risedronate prevented prednisolone-induced deterioration of trabecular and cortical bone architecture. In the mandible, this protective effect of risedronate was accompanied by an increase in cortical bone density and in bone strength. These findings show that risedronate inhibits prednisolone-induced loss of bone density, structure, decrease in bone strength, and retardation of bone growth in the mandible in young growing rats.

Bone Mass and Body Composition in Children and Adolescents With Primary Hypertension

Because primary hypertension (PH) is associated with calcium metabolism, it is hypothesized that PH may be related to osteoporosis risk. The study aimed to evaluate the relationship between body composition and bone strength in hypertensive adolescents. Total body scans using x-ray absorptiometry (DPX-L, GE Healthcare) were performed in 94 PH children aged 6 to 18 years (21 girls and 73 boys). References of healthy control subjects were used for the calculation of Z scores (age and gender matched), SD scores (height and gender matched), and SDs scores (weight and gender matched). Total body bone mineral density, total body bone mineral content (TBBMC), lean body mass (LBM), and fat mass (FM) were investigated. Relative bone strength index was calculated as the TBBMC:LBM ratio. As evidenced by Z scores, PH case subjects had slightly higher total body bone mineral density, TBBMC, and LBM compared with healthy subjects. Reduced LBM/body weight (BW) Z scores of -1.9+/-1.5 and -1.2+/-1.4, increased FM Z scores of +2.5+/-2.5 and +1.7+/-2.0, and increased FM/BW Z scores of +1.6+/-1.3 and +1.1+/-1.4 were noted in girls and boys compared with healthy subjects, respectively (P<0.001). When increased BW was controlled for, PH girls differed in SDs scores for LBM (-1.4+/-1.7; P<0.01), FM (+1.6+/-2.2; P<0.05), FM/BW (+0.9+/-1.0; P<0.05), and FM/LBM (+1.3+/-1.4; P<0.01) but not for total body bone mineral density (+0.2+/-1.0; P value not significant), TBBMC (-1.2+/-1.6; P=0.07), LBM/BW (-0.7+/-1.0; P=0.07), and TBBMC/LBM (-1.0+/-2.1; P value not significant), when compared with respective SDs scores of -0.3+/-1.1, +0.3+/-1.1, +0.3+/-1.0, +0.3+/-1.0, -0.2+/-1.0, -0.6+/-1.9, -0.3+/-1.0, and -0.2+/-1.0 in PH boys. In conclusion, PH adolescents had increased FM and an imbalanced relationship among BW, FM, and LBM. In PH girls, bone strength, although proper for chronological age and body height, was lower than expected for BW.