SAT-273 Suboptimal Bone Adaptation to Increasing Body Weight in Adolescents across the Nutritional Spectrum of Anorexia Nervosa, Normal Weight, and Obesity

Despite their higher areal bone mineral density (aBMD), adolescents with obesity (OB) have an increase in fracture risk, particularly of the extremities, compared with normal-weight controls (C). Whereas bone parameters that increase fracture risk are well characterized at the other end of nutritional spectrum in anorexia nervosa (AN), these data are lacking in adolescents with obesity. Our objective was to compare bone geometry, microarchitecture, density and strength estimates in adolescents across the nutritional spectrum, to determine whether suboptimal bone adaptation to increased body weight may explain the increased fracture risk in OB. We assessed bone endpoints in 153 adolescents 14-21 years old: 50 OB, 48 C and 55 AN. We used DXA to assess aBMD at the lumbar spine, proximal femur and whole body, high resolution peripheral quantitative CT (HRpQCT) to assess bone geometry, microarchitecture and volumetric BMD (vBMD), and finite element analysis to assess failure load (a strength estimate) at the distal radius and tibia. All HRpQCT and FEA analyses were controlled for age. Groups did not differ for age or height. Per design, weight and BMI were highest in OB and lowest in AN. Areal BMD Z-scores at all sites were highest in OB, intermediate in C and lowest in AN (p<0.03 for all comparisons). At the radius, cortical area and thickness increased progressively from AN to C to OB (p<0.03) while trabecular area did not differ across groups. Compared to C and AN, OB had higher cortical porosity (p<0.03), trabecular number and thickness (p<0.01). Cortical vBMD did not differ in OB vs. C but was lower in AN (p<0.0001). Trabecular and total vBMD increased progressively from AN to C to OB (p<0.04). Of note, plate BV/TV did not differ in OB vs. C, but was lower in AN (p<0.0001); rod BV/TV was higher in OB vs. C and AN (p <0.002). At the tibia, cortical area and thickness increased progressively from AN to C to OB (p<0.002), while trabecular area was higher in OB vs. AN and C (p<0.004). Compared to C and AN, OB had higher cortical porosity (p<0.007) and lower trabecular thickness (p<0.02). Trabecular number increased progressively from AN to C to OB (p<0.02). Cortical vBMD did not differ in OB vs. C but was lower in AN (p<0.02). Trabecular and total vBMD were higher in OB vs. AN and C (p<0.002). Plate BV/TV was comparable in the three groups but rod BV/TV was higher in OB vs. C and AN (p<0.0001). Finally, failure load (a strength estimate) increased from AN to C to OB for the radius and tibia (p<0.04 for all). However, after adjusting for weight, failure load was lower in OB vs. C at both sites (p<0.05), and did not differ from AN. These data demonstrate that not all bone parameters appropriately adapt to an increase in body weight, with cortical porosity, cortical vBMD, and plate BV/TV at the radius and tibia, and tibial trabecular thickness being particularly at risk. These changes may explain the higher risk for fracture in OB than controls.