Assessment of bone density in children and adolescents by quantitative CT of one lumbar vertebra only

Aim: The aim of this study was to determine whether measuring the trabecular bone density in one lumbar vertebra (L) instead of three has an effect on the assessment of bone density in children. Materials and Methods: Bone density was measured in 70 patients (38 male, 32.female), ages I to 22 years (mean age 12.4, median 13 years) using a Somatom Balance Scanner (Siemens). The trabecular bone density was measured (1-cm slice, 80 kV, 81 mAs) in L1 through L3. Results: The mean bone density in the lumbar vertebrae was 139.9 mg/ml calcium-hydroxylapatite per ml bone in L1,133.9 in L2, and 131.7 in L3, and the mean of all three vertebrae was 135.2 mg/ml. Measurements in L1 were 4.7 mg/ml (standard deviation [SD] 4.7 mg/ml) above the mean value of the three upper lumbar vertebrae. The density in L2 was 1.3 mg/ml below the mean (SD 3.1 mg/ml). On average, L3 was 3.5 mg/ml below the mean (SD 4.6 mg/ml). This minor systematic deviation in the measurement values for the individual vertebrae from the mean value was so low that there was no statistical evidence for a deviation from an ideal regression line. Conclusions: When using an adequate technique, especially accurate analysis of the topogram (scout view) and the tomogram, measurement of the bone density of one lumbar vertebra provides satisfactory information regarding the trabecular bone density in children, but the values differ in the three upper lumbar vertebrae. The bone density of L2 is close to the mean of the upper three vertebrae. In the case of pathologic values or a pathologic trabecular pattern, three vertebrae should be measured.