Normative Bone Mineral Density Measured on CT scan in Children and Adolescents.

STUDY DESIGN: Retrospective chart review.

OBJECTIVE: To provide reference values for HU measured on CT scan of children and adolescents.

SUMMARY OF BACKGROUND DATA: Spine surgeons increasingly use Hounsfield Units (HU) on spine CT as a measure of bone mineral density (BMD). This has not been described in children and adolescents.

METHODS: Pediatric patients who had a spine CT between 2012 and 2022 were identified. Patients who had more than one comorbidity or were syndromic were excluded. Using the bone window, three axial images (cephalad, middle and caudal) of each vertebra were selected. In each axial view, the HU was measured using a Region of Interest (ROI) that included the total cancellous bone area and an ROI excluding the radiolucency present in the posterior vertebral body (Total vs. Limited). HU values were compared between Total and Limited areas, and between the axial images at the cephalad, middle, and caudal levels. Each age category data was estimated and stratified.

RESULTS: A total of 144 patients (79 female, 65 male) from 2 to 17 years old were included. Mean Limited HU was consistently lower than Total HU across all images and lumbar levels except for L1. Limited HU taken mid-vertebral body was also consistently lower than those taken cephalad or caudad. Mean Limited HU across all ages including all levels was 227±50 (range: 109 to 357). Stratifying by age showed a gradual decrease in BMD from age 2 to 10 followed by an increase.

CONCLUSIONS: This is the first study to measure HU on lumbar CTs in children and adolescents. The technique of measuring BMD in adults should be modified in children by using an ROI that excludes the rarefaction present in the posterior vertebral body. Further studies are needed to evaluate the age dependent changes in BMD seen in this study.