Vertebral Strength and Estimated Fracture Risk Across the BMI Spectrum in Women.
Somewhat paradoxically, fracture risk, which depends on applied loads and bone strength, is elevated in both anorexia nervosa and obesity at certain skeletal sites. Factor-of-risk (Φ), the ratio of applied load to bone strength, is a biomechanically based method to estimate fracture risk; theoretically, higher Φ reflects increased fracture risk. We estimated vertebral strength (linear combination of integral volumetric bone mineral density [Int.vBMD] and cross-sectional area from quantitative computed tomography [QCT]), vertebral compressive loads, and Φ at L4 in 176 women (65 anorexia nervosa, 45 lean controls, and 66 obese). Using biomechanical models, applied loads were estimated for: 1) standing; 2) arms flexed 90°, holding 5 kg in each hand (holding); 3) 45° trunk flexion, 5 kg in each hand (lifting); 4) 20° trunk right lateral bend, 10 kg in right hand (bending). We also investigated associations of Int.vBMD and vertebral strength with lean mass (from dual-energy X-ray absorptiometry [DXA]) and visceral adipose tissue (VAT, from QCT). Women with anorexia nervosa had lower, whereas obese women had similar, Int.vBMD and estimated vertebral strength compared with controls. Vertebral loads were highest in obesity and lowest in anorexia nervosa for standing, holding, and lifting (p < 0.0001) but were highest in anorexia nervosa for bending (p < 0.02). Obese women had highest Φ for standing and lifting, whereas women with anorexia nervosa had highest Φ for bending (p < 0.0001). Obese and anorexia nervosa subjects had higher Φ for holding than controls (p < 0.03). Int.vBMD and estimated vertebral strength were associated positively with lean mass (R = 0.28 to 0.45, p ≤ 0.0001) in all groups combined and negatively with VAT (R = -[0.36 to 0.38], p < 0.003) within the obese group. Therefore, women with anorexia nervosa had higher estimated vertebral fracture risk (Φ) for holding and bending because of inferior vertebral strength. Despite similar vertebral strength as controls, obese women had higher vertebral fracture risk for standing, holding, and lifting because of higher applied loads from higher body weight. Examining the load-to-strength ratio helps explain increased fracture risk in both low-weight and obese women.
Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Katherine N
KN
Bachmann
Harvard-MIT Health Sciences and Technology Program, Massachusetts Institute of Technology, Cambridge, MA, USA.|Center for Advanced Orthopedic Studies, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
Alexander G
AG
Bruno
Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Miriam A
MA
Bredella
Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Melanie
M
Schorr
Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Elizabeth A
EA
Lawson
Department of Radiology, Massachusetts General Hospital, Boston, MA, USA.
Corey M
CM
Gill
Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.|Pediatric Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Vibha
V
Singhal
Neuroendocrine Unit, Massachusetts General Hospital, Boston, MA, USA.
Erinne
E
Meenaghan
Neuroendocrine Unit, Massachusetts General Hospital, Boston, MA, USA.
Anu V
AV
Gerweck
Department of Psychiatry, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Kamryn T
KT
Eddy
Cambridge Eating Disorders Center, Cambridge, MA, USA.
Seda
S
Ebrahimi
Walden Behavioral Care, Waltham, MA, USA.
Stuart L
SL
Koman
Walden Behavioral Care, Waltham, MA, USA.
James M
JM
Greenblatt
Walden Behavioral Care, Waltham, MA, USA.
Robert J
RJ
Keane
Klarman Center, McLean Hospital and Harvard Medical School, Belmont, MA, USA.
Thomas
T
Weigel
Klarman Center, McLean Hospital and Harvard Medical School, Belmont, MA, USA.
Esther
E
Dechant
Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.|Pediatric Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Madhusmita
M
Misra
Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Anne
A
Klibanski
Harvard-MIT Health Sciences and Technology Program, Massachusetts Institute of Technology, Cambridge, MA, USA.|Center for Advanced Orthopedic Studies, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
Mary L
ML
Bouxsein
Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Karen K
KK
Miller
D000293:Adolescent; D000328:Adult; D000856:Anorexia Nervosa / Q000150:complications / Q000453:epidemiology / Q000378:metabolism; D015519:Bone Density; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008875:Middle Aged; D008954:Models, Biological; D009765:Obesity / Q000150:complications / Q000453:epidemiology / Q000378:metabolism; D012307:Risk Factors; D016103:Spinal Fractures / Q000453:epidemiology / Q000209:etiology / Q000378:metabolism; D013131:Spine / Q000378:metabolism*; D016474:Weight-Bearing
BIOMECHANICS; BONE QCT; OSTEOPOROSIS