Bone Abstracts

Background: Case series show improved vertebral size and shape with intravenous bisphosphonate use in children with osteogenesis imperfecta (OI); however, two studies of risedronate showed no such improvement. We have re-examined the data from a dose-ranging risedronate study to determine whether other factors, in particular relating to body composition, contribute to vertebral shape in OI.

Methods: We randomly assigned 53 children with moderate to severe OI to receive 0.2, 1, or 2 mg/kg per week risedronate for 2 years. Children naïve to bisphosphonates were recruited if they had phenotypic OI with one or more of: recurrent fractures affecting mobility; two or more crush-fractured vertebrae; or fractures causing bony deformity and requiring surgical correction. We measured body composition by DXA (GELunar Prodigy, software v4.0). Annual lateral thoracic and lumbar spine films were reviewed by three independent radiologists. Vertebrae were classified according to size and shape. Height loss was assessed as none (0–10%), moderate (10–50%) or severe (>50%). Shape was assessed as normal or showing single-end-plate, double-end-plate, or anterior-wedge deformity. Anterior wedging was the most severe deformity and single-end-plate deformity the least. Films were assessed in pairs for each child. Vertebral architecture was also globally assessed as ‘improved’, ‘the same’ or ‘worse’.

Results: There was no difference in the percentage of ‘improved’ vertebrae between the dose groups. Weight z-score was inversely related to ‘improved’ vertebral architecture irrespective of treatment dose; each 1 S.D. increase in resulted in a fall of 10.3% in ‘improved’ vertebrae (P=0.05). The relationship with % change in fat mass was of a similar magnitude but did not reach significance; the opposite relationship was observed for lean mass. There was no clear relationship with risedronate dose. The number of non-vertebral fractures sustained was negatively correlated with vertebral ‘improvement’ (r²=0.22, P=0.003).

Conclusions: The prevention of fractures is key to improving outcome in OI. It would appear that weight and fat mass gain may contribute to vertebral deformity. Therapeutic intervention should attend to both aspects in order to optimise patient outcome.

Disclosure: The authors declared no competing interests.