Underdevelopment of trabecular bone microarchitecture in the distal femur of nonambulatory children with cerebral palsy becomes more pronounced with distance from the growth plate.

SUMMARY: We found that the underdeveloped trabecular bone microarchitecture in the distal femur of children with cerebral palsy (CP) who are unable to ambulate independently becomes more pronounced with increased distance from the growth plate. This suggests that the degree of underdevelopment in trabecular bone in children with CP is greater than previously understood. INTRODUCTION: Children with CP who are unable to ambulate independently have severely underdeveloped trabecular bone microarchitecture in the distal femur. The aim of the study was to determine if the level of underdevelopment in trabecular bone microarchitecture is consistent across the distal femur in children with CP. METHODS: Children with quadriplegic CP and typically developing children were studied (n=12/group, 5-14 years). Apparent bone volume to total volume (appBV/TV), trabecular number (appTb.N), trabecular thickness (appTb.Th), and trabecular separation (appTb.Sp) were estimated in each of 20 magnetic resonance images collected above the growth plate in the distal femur. RESULTS: For the total region, appBV/TV, appTb.N, and appTb.Th were lower (30, 21, and 12%, respectively) and appTb.Sp was higher (52%) (all p≤0.001) in children with CP than in controls. Distance from the growth plate was inversely related to appBV/TV and appTb.N and was positively related to appTb.Sp at the same distance in children with CP and controls (all p<0.01). However, the relationships were stronger (r2=0.87 to 0.92 versus 0.36 to 0.65) and the slopes were steeper in children with CP (all p<0.01). Furthermore, the steepness of the slopes in children with CP was positively related to appBV/TV, appTb.N, appTb.Th, and appTb.Sp for the total region (r2=0.37 to 0.75, p<0.05). CONCLUSIONS: The underdeveloped trabecular bone microarchitecture in the metaphysis of the distal femur in children with CP becomes more pronounced with greater distance from the growth plate. This pattern is most profound in children with the least developed trabecular bone microarchitecture.

Evaluation of the femoral midshaft in children with cerebral palsy using magnetic resonance imaging.

SUMMARY: Magnetic resonance imaging was used to show that children with quadriplegic cerebral palsy and unable to ambulate independently compared to typically developing children have a remarkably underdeveloped femoral midshaft as indicated by a very thin diameter, a very thin cortical wall, and very low strength estimates. INTRODUCTION: The femoral shaft is very susceptible to fracture in children with quadriplegic cerebral palsy (QCP); however, its structure and strength have not been evaluated. METHODS: The volume and width of the middle third of the femur (midfemur) and its cortical wall and medullary cavity were assessed in children with QCP and unable to ambulate independently and typically developing children (n = 10/group) using magnetic resonance imaging (MRI). Estimates of cross-sectional moment of inertia (CSMI), section modulus (Z), and polar moment of inertia (J) were also determined. RESULTS: Total volume of the midfemur and volume of its cortical wall and medullary cavity were substantially lower in children with QCP than controls (51-55%; p < 0.001). In addition, the total midfemur, its medullary cavity and the anterior, posterior, and lateral sections of its cortical wall were thinner (27-43%) in children with QCP (p < 0.001). The midfemur in children with QCP also had remarkably lower CSMI, Z, and J (60-71%; p < 0.001). CONCLUSIONS: Children with QCP who lack the ability to ambulate independently have midfemurs that are very thin with very thin cortical walls and very low estimated strength. The disparity can be detected using MRI.

Trabecular bone microarchitecture in female collegiate gymnasts.

UNLABELLED: Using high-resolution magnetic resonance imaging, we observed more developed trabecular bone microarchitecture in the proximal tibia of female collegiate gymnasts vs. matched controls. This suggests that high-load physical activity may have a positive effect on the trabecular microarchitecture in weight-bearing bone. INTRODUCTION: Participation in physical activities that overload the skeleton, such as artistic gymnastics, is associated with increased areal bone mineral density (aBMD); however, the status of trabecular microarchitecture in the weight-bearing bone of gymnasts is unknown. METHODS: Eight female collegiate artistic gymnasts and eight controls matched for age, height, body mass, gender and race were recruited for the study. Apparent trabecular bone volume to total volume (appBV/TV), trabecular number (appTb.N), thickness (appTb.Th) and trabecular separation (appTb.Sp) were determined using high resolution magnetic resonance imaging. Areal bone mineral density, bone mineral content (BMC) and bone area in the proximal tibia were determined using dual-energy X-ray absorptiometry. Group differences were determined using t-tests. The magnitude of group differences was expressed using Cohen's d (d). RESULTS: Gymnasts had higher appBV/TV (13.6%, d = 1.22) and appTb.N (8.4%, d = 1.45), and lower appTb.Sp (13.7%, d = 1.33) than controls (p < 0.05). Gymnasts had higher aBMD and BMC in the proximal tibia, although the differences were smaller in magnitude (d = 0.75 and 0.74, respectively) and not statistically significant (p > 0.05). CONCLUSION: The findings suggest that high-load physical activity, such as performed during gymnastics training, may enhance the trabecular microarchitecture of weight-bearing bone.

Underdeveloped trabecular bone microarchitecture is detected in children with cerebral palsy using high-resolution magnetic resonance imaging.

UNLABELLED: Using high resolution magnetic resonance imaging, we detected severely underdeveloped trabecular bone microarchitecture in the distal femur of children with cerebral palsy who can not ambulate independently vs. typically developing controls. Furthermore, very good short-term reliability of trabecular bone microarchitecture measurements was observed in both groups of children. INTRODUCTION: Severe forms of cerebral palsy (CP) are associated with very low areal bone mineral density and a very high incidence of fracture in the distal femur; however, the state of trabecular bone microarchitecture has not been evaluated. Furthermore, the short-term reliability of trabecular bone microarchitecture assessment in children using high-resolution magnetic resonance imaging (MRI) has not been determined. METHODS: Apparent bone volume to total volume (appBV/TV), trabecular number, (appTb.N), trabecular thickness (appTb.Th) and trabecular separation (appTb.Sp) were determined in the distal femur of non-ambulatory children with CP and typically developing children using MRI. RESULTS: Children with CP had a 30% lower appBV/TV, a 21% lower appTb.N, a 12% lower appTb.Th and a 48% higher appTb.Sp in the distal femur than controls (n = 10/group; P < 0.001). The short-term reliability of the trabecular bone microarchitecture measures was very good, with coefficients of variation ranging from 2.0 to 3.0% in children with CP (n = 6) and 1.8 to 3.5% in control children (n = 6). CONCLUSIONS: Underdeveloped trabecular bone microarchitecture can be detected in the distal femur of children with CP who can not ambulate independently using high-resolution MRI. Furthermore, MRI can be used to assess trabecular bone microarchitecture in children with a high degree of reliability.

Former college artistic gymnasts maintain higher BMD: a nine-year follow-up.

INTRODUCTION: If higher bone gains acquired from weight-bearing sports during growth persist into old age, the residual benefits could delay or even prevent osteoporotic fractures. The purpose of this study was to determine if the higher areal bone mineral density (aBMD) observed 15 years after competitive training and competition in former female college artistic gymnasts (GYM) compared with controls (CON) is maintained nine years later in this same cohort approaching menopause. In this 9-year follow-up, aBMD changes were also compared between GYM (n=16; aged 45.3+/-3.3 years) and CON (n=13; aged 45.4+/-3.8 years). METHODS: Total body, lumbar spine, proximal femur, femoral neck, leg, and arm aBMD were assessed at baseline and follow-up using dual-energy X-ray absorptiometry (DXA), (Hologic QDR-1000W). GYM had higher aBMD at all sites at follow-up (P<0.05; eta (2)>0.14). RESULTS: While there were no significant differences between groups for percent changes in aBMD at the total body, lumbar spine, total proximal femur, femoral neck, and arm, the change in leg aBMD was significantly different between GYM and CON (P=0.05; eta (2)=0.14). CONCLUSIONS: Former female college artistic gymnasts maintained significantly higher aBMD than controls 24 years after retirement from gymnastics training and competition. This study provides greater insight into the effects of past athletic participation on skeletal health in women approaching menopause.

Bone turnover and body weight relationships differ in normal-weight compared with heavier postmenopausal women.

Low body weight is associated with increased risk for fractures, whereas higher body weight has been shown to be protective against osteoporosis. This study evaluated whether body weight plays a role regulating bone turnover and mass in normal-weight (body mass index (BMI) <25 kg/m2), overweight (BMI 25-29.9 kg/m2) and obese (BMI> or =30 kg/m2) postmenopausal women who were either receiving hormone replacement therapy [HRT(+)] or not [HRT(-)] (total of six groups). Body weight, BMI, total body bone mineral content (TBBMC), and markers of bone formation (serum osteocalcin) and bone resorption (urinary pyridinoline (PYD) and deoxypyridinoline) were retrospectively analyzed in 210 postmenopausal women. The mean age was 67+/-6 years, with mean body weight of 70.8+/-14.2 kg, ranging from 45.0 to 115.5 kg. Body weight was positively correlated with TBBMC ( r=0.50, p<0.0001). There was a lower TBBMC and higher bone formation rate in normal-weight than obese HRT(-) women, but in women taking HRT there were no differences between BMI categories. In addition, in normal-weight HRT(-) women only, PYD and body weight showed a negative correlation (r=-0.39, p=0.01). Among normal-weight, but not overweight or obese subjects, we observed higher TBBMC and lower bone turnover in the HRT(+) compared with the HRT(-) group. Regression models explained 36% of the variance in TBBMC, mainly through body weight. Additional models could only explain 11-15% of the variance in bone turnover. Taken together, these data suggest that among normal-weight but not obese postmenopausal women, higher bone turnover is associated with lower bone mass, and that only normal-weight women show a different bone turnover profile with HRT treatment. Body weight should be considered an important factor in bone metabolism with relevant clinical implications.

Relation of bone mineral density and content to mineral content and density of the fat-free mass.

Differences in the mineral fraction of the fat-free mass (M(FFM)) and in the density of the FFM (D(FFM)) are often inferred from measures of bone mineral content (BMC) or bone mineral density (BMD). We studied the relation of BMC and BMD to the M(FFM) and D(FFM) in a heterogeneous sample of 216 young men (n = 115) and women (n = 101), which included whites (n = 155) and blacks (n = 61) and collegiate athletes ( n = 132) and nonathletes (n = 84). Whole body BMC and BMD were determined by dual-energy X-ray absorptiometry (DXA; Hologic QDR-1000W, enhanced whole body analysis software, version 5.71). FFM was estimated using a four-component model from measures of body density by hydrostatic weighing, body water by deuterium dilution, and bone mineral by DXA. There was no significant relation of BMD to M(FFM) (r = 0.01) or D(FFM) (r = -0.06) or of BMC to M(FFM) (r = -0.11) and a significant, weak negative relation of BMC to D(FFM) (r = -0.14, P = 0.04) in all subjects. Significant low to moderate relationships of BMD or BMC to M(FFM) or D(FFM) were found within some gender-race-athletic status subgroups or when the effects of gender, race, and athletic status were held constant using multiple regression, but BMD and BMC explained only 10-17% of the variance in M(FFM) and 0-2% of the variance in D(FFM) in addition to that explained by the demographic variables. We conclude that there is not a significant positive relation of BMD and BMC to M(FFM) or D(FFM) in young adults and that BMC and BMD should not be used to infer differences in M(FFM) or D(FFM).

Effect of race and resistance training status on the density of fat-free mass and percent fat estimates.

The impact of race and resistance training status on the assumed density of the fat-free mass (D(FFM)) and estimates of body fatness via hydrodensitometry (%Fat(D)) vs. a four-component model (density, water, mineral; %Fat(D,W,M)) were determined in 45 men: white controls (W; n = 15), black controls (B; n = 15), and resistance-trained blacks (B-RT; n = 15). Body density by hydrostatic weighing, body water by deuterium dilution, and bone mineral by dual-energy X-ray absorptiometry were used to estimate %Fat(D,W,M). D(FFM) was not different between B and W (or 1.1 g/ml); however, D(FFM) in B-RT was significantly lower (1.091 +/- 0.012 g/ml; P < 0.05). Therefore, %Fat(D) using the Siri equation was not different from %Fat(D,W,M) in W (17.5 +/- 5.0 vs. 18.3 +/- 5.4%) or B (14.9 +/- 5.6 vs. 15.7 +/- 5.7%) but significantly overestimated %Fat(D,W,M) in B-RT (14.0 +/- 5.9 vs. 10.4 +/- 6.0%; P < 0.05). The use of a race-specific equation (assuming D(FFM) = 1.113 g/ml) did not improve the agreement between %Fat(D) and %Fat(D,W,M), resulting in a significantly greater mean (+/-SD) discrepancy for B (1.7 +/- 1.8% fat) and B-RT (6.2 +/- 4.3% fat). Thus race per se does not affect D(FFM) or estimates of %Fat(D); however, B-RT have a D(FFM) lower than 1.1 g/ml, leading to an overestimation of %Fat(D).

Muscularity and the density of the fat-free mass in athletes.

The purpose of this study was to use estimates of body composition from a four-component model to determine whether the density of the fat-free mass (D(FFM)) is affected by muscularity or musculoskeletal development in a heterogenous group of athletes and nonathletes. Measures of body density by hydrostatic weighing, body water by deuterium dilution, bone mineral by whole body dual-energy X-ray absorptiometry (DXA), total body skeletal muscle estimated from DXA, and musculoskeletal development as measured by the mesomorphy rating from the Heath-Carter anthropometric somatotype were obtained in 111 collegiate athletes (67 men and 44 women) and 61 nonathletes (24 men and 37 women). In the entire group, D(FFM) varied from 1.075 to 1.127 g/cm3 and was strongly related to the water and protein fractions of the fat-free mass (FFM; r = -0.96 and 0.89) and moderately related to the mineral fraction of the FFM (r = 0.65). Skeletal muscle (%FFM) varied from 40 to 68%, and mesomorphy varied from 1.6 to 9.6, but neither was significantly related to D(FFM) (r = 0.11 and -0.14) or to the difference between percent fat estimated from the four-component model and from densitometry (r = 0.09 and -0.16). We conclude that, in a heterogeneous group of young adult athletes and nonathletes, D(FFM) and the accuracy of estimates of body composition from body density using the Siri equation are not related to muscularity or musculoskeletal development. Athletes in selected sports may have systematic deviations in D(FFM) from the value of 1.1 g/cm3 assumed in the Siri equation, resulting in group mean errors in estimation of percent fat from densitometry of 2-5% body mass, but the cause of these deviations is complex and not simply a reflection of differences in muscularity or musculoskeletal development.

Premenarcheal gymnasts possess higher bone mineral density than controls.

PURPOSE: The purpose of this study was to examine bone mineral density (BMD), body composition, dietary intake, physical activity, and energy expenditure (EE) in premenarcheal gymnasts (N = 16; age = 10.5 +/- 1.5 yr) in comparison to age- (+/- 0.35 yr), height- (+/- 2.6 cm), and weight- (+/- 1.5 kg) matched controls (N = 16; age = 10.5 +/- 1.3 yr). It was hypothesized that premenarcheal gymnasts would have higher BMD, fat-free soft tissue (FFST) mass, physical activity, and EE, but lower fat mass, percent body fat, and dietary intake than controls. METHODS: Dual energy x-ray absorptiometry was used to measure whole body, femur, and lumbar spine (L1-4) BMD, FFST, and fat mass. Three-day diet records were used to estimate mean daily dietary energy, macronutrient, and calcium intakes. Physical activity and EE were estimated by the Seven-Day Physical Activity Recall. RESULTS: The BMD means of the gymnasts were significantly higher (P < 0.05) than controls at all sites, except whole body, as were lumbar spine and femoral neck bone mineral apparent densities, despite lower protein intake expressed per kg FFST mass. Fat mass was significantly lower in gymnasts versus controls (P < 0.01) as was percent body fat (P < 0.001). Very hard physical activity during weekdays (P < 0.0001) and estimated EE (P < 0.01) were significantly higher in gymnasts compared with controls. CONCLUSION: Premenarcheal gymnasts have higher BMD than age-, height-, and weight-matched controls.

Impact of bone mineral estimates on percent fat estimates from a four-component model.

PURPOSE: The primary purpose of this study was to determine the impact of bone mineral content (BMC) from QDR 1000/W and DPX-L dual-energy x-ray absorptiometers (DXA(QDR) and DXA(DPX-L) on percent fat (%fat) estimates from a four-component model. A secondary purpose was to test the accuracy of %fat estimates from DXA(QDR) and DXA(DPX-L) using %fat estimates from a four-component model as the criterion. METHODS: Percent fat, fat mass, and fat-free mass (FFM) were determined from DXA(QDR) and DXA(DPX-L) and from a four-component model based on measures of body density from underwater weighing, body water from deuterium dilution, and BMC from DXA(QDR) (4C(QDR)) or DXA(DPX-L) (4C(DPX-L)) in young men (N = 14) and women (N = 10). RESULTS: BMC was significantly lower using DXA(QDR) compared with DXA(DPX-L) (approximately 11%), resulting in slightly lower estimates of %fat and fat mass and slightly higher estimates of FFM from 4C(QDR) than 4C(DPX-L). Although estimates of %fat, fat mass, and FFM from DXA(QDR) and DXA(DPX-L) were not different than those from a four-component model, there was considerable individual variability between methods. Furthermore, %fat from DXA(QDR) was lower than %fat from 4C(DPX-L). CONCLUSIONS: We conclude that using BMC from different DXA instruments has a minimal impact on %fat, fat mass, and FFM estimates from a four-component model. The large variability in %fat estimates between the two DXA instruments and those from a four-component model does not support DXA as a criterion method of body composition. Further studies involving larger sample sizes and specific population groups are needed to assess the validity of body composition measurements from DXA.

Nutrition, physical activity, and bone health in women.

Calcium and vitamin D can significantly impact bone mineral and fracture risk in women. Unfortunately, calcium intakes in women are low and many elderly have poor vitamin D status. Supplementation with calcium (approximately 1000 mg) can reduce bone loss in premenopausal and late postmenopausal women, especially at sites that have a high cortical bone composition. Vitamin D supplementation slows bone loss and reduces fracture rates in late postmenopausal women. While an excess of nutrients such as sodium and protein potentially affect bone mineral through increased calcium excretion, phytoestrogens in soy foods may attenuate bone loss through estrogenlike activity. Weight-bearing physical activity may reduce the risk of osteoporosis in women by augmenting bone mineral during the early adult years and reducing the loss of bone following menopause. High-load activities, such as resistance training, appear to provide the best stimulus for enhancing bone mineral; however, repetitive activities, such as walking, may have a positive impact on bone mineral when performed at higher intensities. Irrespective of changes in bone mineral, physical activities that improve muscular strength, endurance, and balance may reduce fracture risk by reducing the risk of falling. The combined effect of physical activity and calcium supplementation on bone mineral needs further investigation.

In vivo validation of whole body composition estimates from dual-energy X-ray absorptiometry.

We validated whole body composition estimates from dual-energy X-ray absorptiometry (DEXA) against estimates from a four-component model to determine whether accuracy is affected by gender, race, athletic status, or musculoskeletal development in young adults. Measurements of body density by hydrostatic weighing, body water by deuterium dilution, and bone mineral by whole body DEXA were obtained in 172 young men (n = 91) and women (n = 81). Estimates of body fat (%Fat) from DEXA (%FatDEXA) were highly correlated with estimates of body fat from the four-component model [body density, total body water, and total body mineral (%Fatd,w,m); r = 0.94, standard error of the estimante (SEE) = 2.8% body mass (BM)] with no significant difference between methods [mean of the difference +/- SD of the difference = -0.4 +/- 2.9 (SD) % BM, P = 0.10] in women and men. On the basis of the comparison with %Fatd,w,m, estimates of %FatDEXA were slightly more accurate than those from body density (r = 0.91, SEE = 3.4%; mean of the difference +/- SD of the difference = -1.2 +/- 3.4% BM). Differences between %FatDEXA and %Fatd,w,m were weakly related to body thickness, as reflected by BMI (r = -0.34), and to the percentage of water in the fat-free mass (r = -0.51), but were not affected by race, athletic status, or musculoskeletal development. We conclude that body composition estimates from DEXA are accurate compared with those from a four-component model in young adults who vary in gender, race, athletic status, body size, musculoskeletal development, and body fatness.

Comparison of body composition and bone mineral measurements from two DXA instruments in young men.

The purpose of this study was to compare body-composition and whole-body, lumbar spine (LS), femoral neck (FN), trochanter, and Ward's triangle (WT) bone mineral measurements by using the Hologic QDR 1000W (DXAH) and the Lunar DPX-L (DXAL) dual-energy X-ray absorptiometry instruments. In addition, the ability of conversion equations to predict DXAH data from DXAL data were tested. Thirteen healthy young adult males (aged 22.2 +/- 3.6 y, 177.4 +/- 5.3 cm in height, and 72.7 +/- 9.6 kg in weight) were scanned on the same day by using DXAH and DXAL. Whereas measured body mass was not different (P > 0.05) between machines, whole-body fat mass [DXAH-DXAL (DXAdiff) = 1152 +/- 1395 g], percentage fat (DXAdiff = 1.5 +/- 1.7% of body mass), bone mineral density (BMD; DXAdiff = 0.016 +/- 0.023 g/cm2), and bone mineral content (BMC; DXAdiff = 316 +/- 50 g) were lower and whole-body fat-free soft tissue (FFST; DXAdiff = 1781 +/- 1859 g) was higher with DXAH than with DXAL. Lower fat mass (DXAdiff = 2145 +/- 855 g) and BMC (DXAdiff = 216 +/- 36 g) and higher FFST (DXAdiff = 1966 +/- 943 g) in the trunk were primarily responsible for the whole-body differences. Lower BMD and BMC values were found for LS (DXAdiff = 0.145 +/- 0.038 g/cm2 and 3 +/- 2 g, respectively), trochanter (DXAdiff = 0.100 +/- 0.044 g/cm2 and 1.7 +/- 1.0 g), and WT (DXAdiff = 0.195 +/- 0.061 g/cm2 and 1.93 +/- 0.51 g) with DXAH compared with DXAL. DXAH BMD of FN was also lower (DXAdiff = 0.141 +/- 0.032 g/cm2) than with DXAL. Only DXAH whole-body BMC and LS BMD were accurately predicted from DXAL with conversion equations. Predicted DXAH FN BMD was significantly lower than the actual DXAH value (P < or = 0.05), whereas the discrepancy between DXAH and DXAL actually increased for whole-body percentage fat and BMD (DXAdiff = 6.6 +/- 1.3% body mass and 0.020 +/- 0.025 g/cm2). In conclusion, lower whole-body fat mass, percentage fat, and BMC, and higher whole-body FFST with DXAH were due primarily to measurement differences in the trunk. Whereas conversion equations accurately predicted DXAH whole-body BMC and LS BMD from DXAL measurements in young adult males, they did not accurately predict DXAH, percentage fat, and BMD of the whole body and FN BMD.

Density of the fat-free mass and estimates of body composition in male weight trainers.

The purpose of this study was to determine whether the assumed density and composition of the fat-free mass (FFM) and estimates of percent fat (%Fat) from body density by use of the Siri equation (%Fatd) are valid in weight trainers with high musculoskeletal development. Measures of body density by underwater weighing (Db), body water by deuterium dilution, and bone mineral by whole body dual-energy X-ray absorptiometry were obtained in young white men: 14 weight trainers with high musculoskeletal development and 14 non-weight-training controls with average musculoskeletal development. %Fatd was significantly higher (P < or = 0.05) than %Fat estimated from body density, water, and mineral (%Fatd,w,m) by use of a four-component model in weight trainers (17.3 +/- 4.6 vs. 13.2 +/- 5.1%) but not in controls (14.8 +/- 3.1 vs. 14.2 +/- 3.6%). The greater discrepancy between %Fatd and %Fatd,w,m was explained by lower density of fat-free mass (Dffm) in weight trainers (1.089 +/- 0.005 g/ml) than in controls (1.099 +/- 0.007 g/ml). The lower Dffm in the weight trainers was due to higher water (74.8 +/- 1.2 vs. 72.6 +/- 20%) and lower mineral (5.3 +/- 0.6 vs. 5.9 +/- 0.4%) and protein (19.9 +/- 1.4 vs. 21.5 +/- 1.9%) fractions of the FFM. We conclude that, in young white men with high musculoskeletal development, Dffm is lower than the assumed value of 1.1 g/ml and %Fat is overestimated from Db by use of the Siri equation.