No abstract

Concerns have been raised regarding the validity of using areal bone mineral density (aBMD) as a substitute for the true volumetric bone mineral density (vBMD) in the pediatric population. We studied 209 normal subjects (109 males), aged 5-27 yr, to examine the influence of age, gender and growth on vBMD. The femoral neck, midthird of the femoral shaft, and the four lumbar vertebral bodies (L1-L4) were studied. Using data on bone width and height obtained by dual energy x-ray absorptiometry, bone volume was calculated with the assumption that all three sites are cylinders. In contrast to aBMD, vBMD of the femoral neck bore no relationship to age or weight in both sexes, but was significantly related to height in females (r2 = 0.07; P = 0.01). Similarly, vBMD of the femoral shaft (vFBMD) did not change with age or height in either sex. In females, a significant inverse relationship was seen between vFBMD and weight (r2 = 0.14; P = 0.001). Male subjects had higher vFBMD than females (mean +/- SD, 0.73 +/- 0.11 vs. 0.70 +/- 0.12; P = 0.047), but no sex difference was seen in vBMD of the femoral neck. Conversely, vBMD of L1-L4 remained age and growth dependent, although the strength of the relationship was weaker than that for aBMD (data not shown). In conclusion, the vBMD of the femoral neck and shaft is independent of age and is less dependent on growth variables in children and young adults than is aBMD. These observations offer a different perspective from our previous concepts of aBMD.

Concerns have been raised regarding the validity of using areal bone mineral density (aBMD) as a substitute for the true volumetric bone mineral density (vBMD) in the pediatric population. We studied 209 normal subjects (109 males), aged 5-27 yr, to examine the influence of age, gender and growth on vBMD. The femoral neck, midthird of the femoral shaft, and the four lumbar vertebral bodies (L1-L4) were studied. Using data on bone width and height obtained by dual energy x-ray absorptiometry, bone volume was calculated with the assumption that all three sites are cylinders. In contrast to aBMD, vBMD of the femoral neck bore no relationship to age or weight in both sexes, but was significantly related to height in females (r2 = 0.07; P = 0.01). Similarly, vBMD of the femoral shaft (vFBMD) did not change with age or height in either sex. In females, a significant inverse relationship was seen between vFBMD and weight (r2 = 0.14; P = 0.001). Male subjects had higher vFBMD than females (mean +/- SD, 0.73 +/- 0.11 vs. 0.70 +/- 0.12; P = 0.047), but no sex difference was seen in vBMD of the femoral neck. Conversely, vBMD of L1-L4 remained age and growth dependent, although the strength of the relationship was weaker than that for aBMD (data not shown). In conclusion, the vBMD of the femoral neck and shaft is independent of age and is less dependent on growth variables in children and young adults than is aBMD. These observations offer a different perspective from our previous concepts of aBMD.

Bone mineral density (BMD) of total body (TBMD), lumbar spine (L2-4), and femoral neck was measured in 266 normal subjects (136 males) aged 4-27 years (mean 13 years) using dual-energy x-ray absorptiometry (DXA). BMD of all sites increased significantly with age until 17.5 years in males and 15.8 years in females, except for femoral neck BMD in females, which peaked at age 14.1 years. Males had higher peak TBMD, which was attributed to greater weight and lean tissue mass. In contrast, despite a later timing, peak L2-4 BMD in males was not different from that in females. Before peak BMD, weight was the best predictor of TBMD and L2-4 BMD in both sexes (r2 ranged from 0.77 to 0.88), whereas femoral neck BMD was predicted equally by height and weight. Longitudinal information collected from 53 (25 boys) of these children, aged 4-16.9 years, showed that the average annualized gain in TBMD was 0.047 g/cm2 for boys and 0.039 g/cm2 for girls. No significant difference in the association between age and BMD (slopes) was found between cross-sectional and longitudinal data for either sex. We conclude that the timing for peak BMD was consistent for total body, lumbar spine, and femoral neck for each sex. The earlier peak BMD in females is most likely related to earlier puberty. The cross-sectional normative data of this study are useful in serving as a standard for serial assessment in health and disease states.

Osteoporosis and fractures are features in adults with Turner syndrome (TS). Using dual-energy x-ray absorptiometry, correcting bone mineral content (BMC) for height and lean mass (LTM) avoids misclassification of short children as osteopenic. Total body (TB), lumbar spine (LS), and femoral neck (FN) dual-energy x-ray absorptiometry scans were performed on 83 patients with TS (aged 4-24 yr). A prepubertal subgroup (n = 17) receiving GH was followed for 24 months. Age z-scores for height, TB BMC, LTM, the BMC/LTM ratio, and LS volumetric bone mineral density (vBMD) decreased significantly (P < 0.001) with age in prepubertal subjects (n = 51) but were constant in the combined pubertal and postmenarchal group (n = 32). Osteopenia was found in 14.5% (TB), 15.8% (LS), and 28.4% (FN) of patients. In the longitudinal subgroup, TB BMC z-scores decreased by -0.28 (0.31) in subjects remaining prepubertal (n = 11) but increased by 0.71 (0.56) in subjects entering puberty (n = 6; P = 0.007). The z-scores for height and LTM increased in both groups. Our results show a height-independent prepubertal decrease in bone mass accrual, which ceased with puberty. Optimizing bone mass in TS may require earlier induction of puberty than currently recommended. However, reduced FN volumetric bone mineral density and a dissociation of bone and muscle measures were age independent, suggesting an additional intrinsic bone defect.

No abstract

Growth hormone deficiency (GHD) in adults and children is associated with decreased lean tissue mass (LTM), increased fat mass and reduced bone mineral density (BMD). The changes in BMD and body composition, 6 and 12 months after ceasing GH treatment, were assessed using dual‐energy X‐ray absorptiometry in eight patients with GHD (age range, 13.8–17.5 years). Seven age‐matched normal subjects who had completed growth were assessed at 0 and 12 months. Total body BMD was low at baseline (p < 0.05) in patients with GHD compared with the predicted values based on sex‐specific regression equations, with height, weight and age taken into account. Total body, lumbar spine and femoral neck BMD increased in the patients and controls at 12 months. LTM decreased significantly by a mean of 1.37 kg in the patients with GHD at 12 months whereas there was a non‐significant increase in LTM in the control group. The percentage of body fat increased in all patients with GHD at 6 and 12 months, from 27.2 ± 11% (mean ± SD) at baseline to 32 ± 9.9% at 12 months (p= 0.009). There was no significant increase in mean percentage body fat in the control group. The ratio of android (trunk):gynoid (legs) fat was calculated using default settings of dual‐energy X‐ray absorptiometry. The mean android:gynoid fat ratio increased, though non‐significantly, in patients with GHD at 12 months, with 6 of 7 showing an increase; no change was observed in the control group. These results indicate that BMD continues to increase 12 months after ceasing GH therapy in adolescents with GHD, but that unfavourable alterations in body composition occur.

No abstract