Relationship between trabecular vertebral body density and fractures: a quantitative definition of spinal osteoporosis.

To evaluate the relationship between vertebral fractures and trabecular vertebral body density (TVBD), as measured by computed tomography (CT), we evaluated 110 female and 38 male patients referred consecutively to our clinic for an osteoporosis evaluation. Number of fractures per patient and TVBD was negatively correlated in both males and females (r = -.64, P less than .001 and r = -.69, P less than .001, respectively). Based on this relationship and that between percent of patients with fracture and TVBD, we devised four different approaches to calculate the fracture threshold. (1) Because the x-axis intercept of this regression line represents the TVBD value at zero fractures, this intercept can be considered the fracture threshold, which was 103 mg/cm3 for females and 132 mg/cm3 for males. (2) Breakpoint analysis of the relationship between the number of vertebral fractures per patient v TVBD gave a fracture threshold value of 98 mg/cm3 for females, but for males we were unable to compute a threshold value because of the small sample size. The percentage of patients with fractures was also negatively correlated with TVBD for males and females (r = -.98, P less than .001, and r = -.94, P less than .001, respectively). (3) the x-axis intercept of this relationship, which represents the fracture threshold, was 123 mg/cm3 for males and 101 mg/cm3 for females. (4) The fracture threshold, calculated as the mean TVBD + 2 SD for patients with fracture(s), was 120 and 92 mg/cm3 for males and females, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)