Risk of vertebral fractures in men: relationship to mineral density of the vertebral body.

Abstract

Vertebral fracture is the most frequent manifestation of osteoporosis in women. Because there is a lack of information about bone density and the occurrence of fractures in men with osteoporosis, we evaluated the relationship between vertebral fractures and spinal bone mineral density (BMD) to determine if there is a threshold of BMD below which fractures are likely to occur. Radiographs of the spine and BMD measurements of the lumbar spine as measured by quantitative CT were obtained in 201 men 21-86 years old (mean age, 68 +/- 4 years) who were referred consecutively for osteoporosis screening. Radiographs were interpreted for the presence or absence of vertebral fractures. The probability of fractures was determined after classifying the patients into subgroups according to their quantitative CT values. The relationship of spinal bone mass to spinal fracture was examined by both logistic regression and receiver operating characteristic (ROC) analysis. Seventy-one patients were classified as having definite vertebral compression fractures. Spinal BMD was 132 +/- 34 mg/ml for the 130 men without vertebral fractures and 75 +/- 22 mg/ml for the 71 men with vertebral fractures (p < .001). The number of fractures per patient and the BMD were negatively correlated (r = -0.71, p < 0.0001). When a BMD of 100 mg/ml was given as a fracture threshold, 15% of the patients without fractures were below this value and 14% of the patients with fractures were above this threshold. Quantifying the overlap between values from patients with and without fractures by ROC analysis, the value of 100 mg/ml gave a sensitivity of 86%. Logistic regression showed 105 mg/ml as the most discriminate value, resulting in a sensitivity of 90%. Logistic regression analysis of the predicted fracture probability also indicated that age does not significantly influence the regression curve. We found that direct quantitative CT measurement of the BMD of the vertebral body is a highly efficient approach to distinguish men without vertebral fractures from those with fractures. Thus, a fracture-threshold concept could provide a quantitative criterion to identify men at high risk for vertebral fractures.