Bone Abstracts

Background: Measurement and interpretation of metaphyseal shape in children is difficult. We aim to develop relevant assessment methods using commonly available spiral computed tomography (CT) scanning.

Methods: We analysed 12 pairs of age and pubertal stage matched subjects from a larger group of children recruited into a non-interventional case–control study in which all had suffered trauma; half had sustained a fracture. Each subject underwent anthropometry, pubertal stage self-assessment, LS DXA and spiral CT of the whole of both tibiae. Total area and volumetric trabecular bone density (TBD) were extracted from each 1.25 mm CT slice between the growth plates. Eight nested cylinders were defined within the metaphyseal volume. Metaphyseal extent was defined as being between the growth plate and where TBD reaches 0 in the central 1/8 area. Equal-length datasets were created to allow data comparison. We assessed metaphyseal extent, absolute metaphyseal area at 50% metaphyseal length (50% area) and change in area across the 40–60% metaphyseal length (40–60 Δarea) in relation to tibial length, tibial width at narrowest point and aspect ratio (length:width).

Results: Subjects were aged 5–13 years. Girls: 4/12 controls and 3/12 fractures. Mean tibia length was 29.2±5.1 cm. There was no significant difference in height or tibial length between fractures and controls. Aspect ratio varied from 13 to 19 (median 16).

The proximal metaphysis varied from 11 to 25% tibial length (median 15%); distal metaphysis from 8 to 20% (median 13%). There were no significant differences between fracture and control groups for these parameters or for the ratio of 50% area to shaft width. 40–60 Δarea correlated with age, height, tibial length and height Z-score. 40–60 Δarea of the proximal metaphysis was greater in controls compared to fractures (P=0.02). This was not the case for the distal metaphysis. There was no correlation of aspect ratio or metaphyseal data with LS DXA values.

Conclusion: We have described a method for determining the size and variability of the shape of the tibia and its metaphyses. The combination of observed differences suggests less in-waisting of the proximal metaphysis in children with a history of fracture.