Bone Abstracts

Objective: Osteogenesis imperfecta (OI) is most commonly caused by a defect in the genes that produce type I collagen. Clinical features include low bone mass, fractures and spinal abnormalities. Pars defects are abnormalities in the pars interarticularis of vertebrae. There is a higher incidence of pars defects in the lumbar spine in children with OI compared to the normal population. Abdominal muscle weakness and altered spinal postures are common presentations in the children assessed in a national regional OI service. We therefore hypothesised that children who present with weakness in their abdominal muscles have a higher incidence of pars defects in the lumbar spine.

Method: 51 children were assessed by specialist physiotherapists in the OI clinic. The age range was 5–15 years and all had a clinical diagnosis of type 1 or type 4 OI. All were ambulatory with a brief assessment of motor function (BAMF) score of ≧9. Abdominal strength was assessed by the child’s ability to sit up from a lying position. Weakness was identified if the child needed to push through their arms to achieve a sitting position. Lateral spinal x-rays were formally reported for all children.

Results: Of the 51 children, 36 required the use of their arms to get into sitting from a lying position indicating weakness in their abdominal muscles. Of these, five had confirmed pars defects. Of the remaining 15, five also had confirmed pars defects.

Conclusion: Abdominal weakness was identified in 70% of the children studied. Only 14% of this group had pars defects on x-rays. The data from this sample did not demonstrate a higher incidence of pars defects in OI children with abdominal weakness. However, all ten children with pars defects presented with altered postures in sitting and/or standing. The assessment of abdominal weakness was limited as it only measured trunk flexion during one activity. It did not assess the strength of abdominals and other trunk muscles involved in postural stability. Development of a more objective assessment of truncal muscle strength is needed in order to investigate the relationship between weakness and pars defects in children with OI.

Disclosure: The authors declared no competing interests.