Trabecular bone microarchitecture, bone mineral density, and vertebral fractures in male osteoporosis

Some studies have indicated that the risk of fragility fractures in men inc reases as bone mineral levels decrease, but there is an overlap in the bone mineral density (BMD) measurements between patients with or without fractu res. Furthermore, it has been suggested that the biomechanical competence o f trabecular bone is dependent not only on the absolute amount of bone pres ent but also on the trabecular microarchitecture. In the present study, 108 men (mean age 52.1 years) with lumbar osteopenia (T score < -2.5) were rec ruited to examine the relationships between BMD, architectural changes in t rabecular bone, and the presence of vertebral fractures. Lumbar BMD was ass essed from L2 to L4 in the anteroposterior view with dual-energy X-ray abso rptiometry. At the upper left femur, hip BMD was measured at the transcervi cal site. Spinal X-ray films were analyzed independently by two trained inv estigators, and vertebral fracture was defined as a reduction of at least 2 0% in the anterior, middle, or posterior vertebral height. Transiliac bone biopsy specimens were obtained for all patients. Histomorphometric studies were performed on an image analyzer, and the following parameters were dete rmined: trabecular bone volume (BV/TV), trabecular thickness (Tb.Th), numbe r (Tb.N), and separation (Tb.Sp), interconnectivity index (ICI), characteri zation of the trabecular network (node count and strut analysis), and star volume of the marrow spaces. Spinal radiographs evidenced at least one vert ebral crush fracture in 62 patients (group LI) and none in 46 patients (gro up I). After adjusting for age, body mass index, and BMD, there were no sig nificant differences between the two groups in BV/TV, Tb.Th, or star volume . In contrast, the mean values of ICI, free end-to-free end struts (FF/TSL) , and Tb.Sp were significantly higher, whereas Tb.N and node-to-node struts (NN/TSL) were lower in patients with at least one vertebral fracture. Logi stic regression analysis showed that only ICI, FF/TSL, NN/TSL, and Tb.N wer e significant predictors of the presence of vertebral fracture: odds ratios for an alteration of 1 SD ranged from 1.7 (1.0-3.2) for NN/TSL to 3.2 (1.1 -10.1) for ICI. Patients with at least three vertebral fractures (n = 23) w ere categorized as "multiple fractures." The results of logistic regression showed that spine BMD, BV/TV, and all architectural parameters were signif icant predictors of multiple vertebral fractures: odds ratios for an altera tion of I SD ranged from 2.2 (1.1-4.6) for star volume to 3.7 (1.4-9.7) for ICI. These results strongly suggest that bone trabecular microarchitecture is a major and independent determinant of vertebral fractures in middle-ag ed men with osteopenia.