Bone Abstracts

Background: At present, clinical assessment of bone strength in children predominantly relies bone mass measurement using absorptiometry (DXA) or QCT densitometric approaches. However, bone strength is not only dependent on mass/density, but also structural and material mechanical properties. Currently no technique measures bone mechanical properties. Recently, a new micro-indentation device, the reference point indentation (RPI) instrument has been validated for the measure of cortical bone fracture resistance in adult subjects.

Aim: To establish safe and effective protocols for using the RPI instrument in infants and children.

Methodology: We planned to perform RPI testing on bone samples from 18 children aged 0–16 undergoing orthopaedic operations where bone was routinely excised. The RPI parameters for total indentation distance (TID) and indentation distance increase (IDI) were measured at 3, 5 and 7N force. The RPI parameters were compared with participants’ vitamin D, PTH and calcium levels. Scanning electron microscopy (S.E.M.) of bone samples was carried out to quantify damage cause by RPI testing.

Preliminary results: Of the 18 samples obtained, only 5 had cortices >2 mm and were suitable for testing. In these samples, S.E.M. analysis showed that micro-indentations using the three forces (3, 5 and 7N) did not cause cracks greater than microcracks formed physiologically in cortical bone; crack length was statistically greater for the 7N force (194.9 μm 95% CI 136.0–253.9) compared with either 3N (124.7 μm, 95% CI 101.0, 148.3) or 5N force (116.8 μm, 95% CI 97.1, 136.5); P=0.001 and P=0.005 respectively. There was no difference between 3N and 5N. There was no clear correlation of RPI outputs and measures of vitamin D homeostasis within this limited group.

Conclusion: Preliminary results suggest RPI testing using 3N and 5N indentation forces is safe on children’s bone with a cortical bone thickness of over 2 mm. Further testing will ensure the RPI instrument is safe to use on children of all ages and on children with metabolic bone diseases such as osteogenesis imperfecta, who have fragile bones.