Bone Abstracts

Objectives: The clinical assessment of bone mass in children with osteogenesis imperfecta (OI) is normally assessed by DXA. Further information about bone microarchitecture is obtained from bone biopsy which is invasive and requires anaesthetic. High-resolution peripheral quantitative computer tomography (HRpQCT) is an in-vivo imaging modality capable of assessing skeletal microstructure and integrity to a resolution of 80 μm. To date, no HRpQCT studies have included the assessment of children with severe OI.

Methods: We plan to assess skeletal microstructure of the ultradistal radii and tibiae (distal 9 mm) of 22 children with mild to severe OI using HRpQCT (Scanco Medical AG) and DXA in comparison with healthy controls. A further six bisphosphonate naive children with OI will undergo longitudinal microstructural assessment to determine in vivo changes in cortical and trabecular structure following bisphosphonate therapy. During scanning of OI patients an anti-gravity supportive sleeve will be used to prevent fracture.

Results: We scanned a boy with type I OI (15.17 years) who has received 8 years bisphosphonate treatment (6 years risedronate; 2 years pamidronate). We compared him with a healthy male control matched for height (OI 1.60 cm vs control 1.69 cm), BMI SDS (23.8 kg/m² vs 22.3 kg/m²) and Tanner stage (TS3). Subtotal BA (1757 cm² vs 1553 cm²) and subtotal BMC (1294.9 g vs 1195.4 g) were 12.3% and 7.9% greater respectively in our OI patient. Subtotal BMD was 4.34% lower in our OI patient. Radial cortical area (41.7 mm² vs 31.1 mm²), cortical thickness (0.67 mm vs 0.51 mm) and cortical BMD (750 mg/cm³ vs 719.6 mg/cm³) were 29, 27 and 4% higher in our OI patient. In contrast, trabecular spacing (0.407 mm vs 0.464 mm), trabecular number (1.96^1/mm vs 2.16^1/mm) and thickness (0.052 mm vs 0.055 mm) were 13, 10 and 2% lower in our patient with OI. Trabecular BMD was thus 16% lower (121.3 mg/cm³ vs 143.5 mg/cm³). The inhomogeneity of trabecular bone was 45.84% higher for our OI patient suggesting disruption in normal trabecular organisation.

Conclusion: It is well recognised that bisphosphonates improve total body BMD in OI patients. Although our work is preliminary, HRpQCT demonstrated clear differences in the microstructural organisation. Further work determining the impact of bisphosphonate therapy on skeletal integrity and biomechanics (including microfinite element analysis) is merited.

Disclosure: The authors declared no competing interests.