Fractures are common in children, with ≤ 50% of boys and 40% of girls fracturing by 18 years of age, and with reduced BMD observed in fracture cases. The highest incidence coincides with puberty, when there is a transient reduction in volumetric vBMD and cortical thickness. We hypothesize that deficits in cortical thickness and increased cortical porosity are present in children with fractures.

We recruited 54 children (52% males) with low-trauma fractures and imaged their distal metaphyses of the contralateral radius and tibia using high-resolution pQCT (XtremeCT). Cortical porosity, degree of mineralization (tissue mineralization density), and transitional zone dimensions (area between hard cortex and trabecular bone) were determined using StrAx1.0 software. Fracture case was compared to 54 age- (11.9±2.9 vs. 11.7±2.8yrs), height- (152.4±16.7 vs. 150.7±15.2cm) weight- (46.6±15.6 vs. 45.8±15.3kg) and maturity-matched controls.

Bone cross-sectional area was similar in cases and controls (224±66 v 208±59mm²) however distal radius cortical vBMD was 5% lower in cases (773±114 vs. 819±135mgHA/cm3, p<0.05) due to their 6% higher porosity (53±8 vs. 50±9%, p<0.05) and 3% lower tissue mineralization density (61±3 vs. 63±3%, p<0.0001). Differences were most evident in pre-pubertal boys (n=26) in whom fracture cases had 26% thinner cortices (0.30±0.07 vs. 0.41±0.12mm, p<0.01), and a 9% wider transitional zone (2.77±0.19 vs. 2.55±0.30μm, p<0.05) than controls. Fracture cases had greater trabecular area (107±27 vs. 84±28mm², p<0.05) with thicker (0.08±0.01 vs. 0.07±0.0mm, p<0.01), fewer (1.8±0.2 vs. 2.1±0.3 1/mm, p<0.01) and more separated trabeculae (0.49±0.08 vs. 0.41±0.06mm, p<0.01) than controls. Similar bone structural deficits were observed at the tibia with 6% lower cortical vBMD (p<0.05), 2% lower tissue mineralization density (p<0.001), and 9% higher porosity (p<0.05) observed in cases than controls.

We infer that material and structural abnormalities in the cortex contribute to bone fragility during accelerated growth in children and predispose to fractures should a fall occur.