Original Article Age-Related Differences of Bone Mass, Geometry, and Strength in Treatment-Na € ıve Postmenopausal Women. A Tibia pQCT Study Konstantinos D. Stathopoulos, * ,1 Pelagia Katsimbri, 1 Erato Atsali, 2 Eleutheria Metania, 1 Aristidis B. Zoubos, 1 and Grigorios Skarantavos 1 1 Bone Metabolic Unit, First Orthopedic Clinic, University of Athens, ‘‘Attikon’’ University Hospital, Athens, Greece; and 2 Third Pediatric Clinic, University of Athens, ‘‘Attikon’’ University Hospital, Athens, Greece Abstract Most studies addressing the effects of aging on bone strength have focused mainly on (areal) bone mineral densities and bone mineral content (BMC) and less on bone geometry. We assessed age-related differences of bone mass (grams of bone mineral), geometry, and derived strength in 219 treatment-na € ıve postmenopausal women using peripheral quantitative computed tomography of the load-bearing tibia. Subjects were separated in 3 age groups: A 5 48e59 yr (N 5 80), B 5 60e69 yr (N 5 84), C 5 70e80 yr (N 5 55). Three slices were obtained for each individual, at the 4% (trabecular), 14% (subcortical and cortical), and 38% (cortical bone) of tibia length sites. Trabec- ular, subcortical, and cortical BMC (mg per 1-mm slice), volumetric bone mineral densities (mg/cm 3 ), bone cross-sectional areas (mm 2 ), periosteal (PERI_C, mm) and endosteal circumference (ENDO_C, mm), mean cortical thickness (CRT_THK, mm), and Stress Strain Indexes (SSIs, mm 3 ) were studied. Trabecular and cortical BMC and vol- umetric densities were significantly lower in the elder subjects (group C) compared with younger subjects (groups A and B), p ! 0.0005. Cortical area and CRT_THK were significantly lower in group C (vs A and B, p ! 0.0005), whereas total cross-sectional area was higher in group C compared with A and B. ENDO_C was significantly higher in older subjects (group C vs A and B, p ! 0.0005), whereas PERI_C did not differ significantly between the age groups. SSIs were significantly lower in older subjects at the 14% site (group C vs A, p ! 0.0005 and C vs B, p ! 0.005), and at the 38% site (group C vs group A, p ! 0.01). Our results indicate that age-induced differences on bone strength entail significant alterations not only of bone mass, but also of bone geometry. Key Words: Aging; bone geometry; bone strength; postmenopausal osteoporosis; peripheral quantitative computed tomography (pQCT). Introduction Bone mass has been shown to continually change through- out life: it attains peak levels during young adulthood and starts to decline thereafter, but not at a steady rate (1,2). Before menopause, bone loss is, under normal loading condi- tions, considered to be slow, whereas after menopause it is more rapid, primarily because of loss of estrogens (3). With aging, bone loss continues, but also geometrical properties of the bone are altered to compensate for this loss (4e7). In most studies, the effects of aging have been focused on differ- ences of bone mineral content (BMC) and bone mineral den- sity (BMD), using dual-energy X-ray absorptiometry (DXA) of the spine or hip. However, DXA has major limitations in estimating even such parameters, because it measures only areal (mg/cm 2 ) and not volumetric (mg/cm 3 ) densities, and does not discriminate between the trabecular and cortical compartment of the bone. Moreover, many of the factors determining the bone’s resistance to strain and fracture are beyond the scope of DXA (8). In contrast, 3-dimensional techniques such as quantitative computed tomography have been gaining popularity in the study of bone geometry and architecture, because these parameters are also considered Received 08/23/10; Revised 11/26/10; Accepted 11/27/10. *Address correspondence to: Konstantinos D. Stathopoulos, MD, Bone Metabolic Unit, First Orthopedic Clinic, University of Athens, ‘‘Attikon’’ University Hospital, Rimini 1 Chaidari, Athens 12462, Greece. E-mail: kossta51@hotmail.com 33 Journal of Clinical Densitometry: Assessment of Skeletal Health, vol. 14, no. 1, 33e40, 2011 Ó Copyright 2011 by The International Society for Clinical Densitometry 1094-6950/14:33e40/$36.00 DOI: 10.1016/j.jocd.2010.11.004