Purpose or Case Report: Determining the underlying etiology of bone fracture in children is an essential part of patient care. Very young patients who may be victims of child abuse, but who may not be able to express themselves, must be distinguished from those who have low bone mineralization due to disease. Quantitative computed tomography (QCT) has been used to evaluate volumetric bone mineral density (BMD) in children, but there is little information on BMD in very young subjects.^1,2 The goal of this study was to demonstrate the feasibility of using QCT to evaluate BMD and volume (Vol) of lumbar vertebral bodies in children and to establish the need for a separate comparative database to evaluate these parameters in subjects less than 6 years.
Methods & Materials: We obtained anonymized QCT scans (80-120kVp, 9.6-580.8mAs, 0.416-0.977mm pixel size, 2-4mm slice thickness) of lumbar vertebrae of 24 male subjects, 15 less than 6 years old (<6yo) and 9 between 13 and17 years old (13-17 yo), who were imaged for unrelated medical reasons in the ER of our institution (Image Analysis INTable phantom; Philips BrillianceTM iCT 3.2, 256 slice scanner). IRB approval to study anonymous data is not required. BMD and Vol of the vertebral body were evaluated on one image in a region of interest (ROI) through the mid-vertebral body (Figure 1). Volume was computed using an assumed 3-mm slice thickness. Student’s t-tests were performed to determine if BMD and Vol at each level differed between subjects of different groups. Linear regression analysis of the two groups separately was used to determine if BMD and Vol at each level were associated with age. A significance level of p<0.05 was used.
Results: BMD was virtually independent of age in the younger group but increased with age at multiple levels in the older group (Tables 1-2, Figure 2). In contrast, Vol in 13-17yo was more than twice that in <6yo at all levels (p<0.002). Volume increased 0.09 to 0.29 cm³/yr in subjects <6yo (0.33 ≤ R² ≤ 0.61, p ≤ 0.04), but was not associated with age in 13-17yo (p>0.7).
Conclusions: This study demonstrated a QCT method for evaluating bone mineralization in very young subjects and showed that a separate normative database is needed for subjects less than 6 years. With future work, this method may be helpful for distinguishing very young patients who may be victims of child abuse from those with low bone mineralization due to disease or a metabolic process.