The functional muscle-bone unit in patients with osteogenesis imperfecta type I

- Muscle force is lower in children and adolescents with OI type I than in healthy age and gender-matched controls.
- Bone strength is lower in children and adolescents with OI type I than in healthy age and gender-matched controls.
- Despite lower muscle force and bone strength, the muscle-bone relationship is similar between OI type I and healthy control.

ContextOsteogenesis imperfecta (OI) type I is a heritable bone fragility disorder that is caused by mutations affecting collagen type I. We recently showed that patients with OI type I frequently have muscle weakness. As muscle force and bone mass are usually closely related, we hypothesized that muscle weakness in OI type I could contribute to increase bone mass deficit in the lower extremities.ObjectiveTo assess the muscle-bone relationship in the lower extremities of children and adolescents with OI type I.SettingThe study was carried out in the outpatients department of a pediatric orthopedic hospital.Patients and other participantsThirty children and adolescents with OI type I (20 females; mean age [SD]: 11.2 years [3.9]) were compared with 30 healthy age- and sex-matched controls (mean age [SD]: 11.1 years [4.5]).Main outcome measuresTibia bone mineral content (BMC; mg/mm) was measured by peripheral quantitative computed tomography to estimate bone strength at the 4% and 14% sites. Lower extremity peak force (kN) was measured by mechanography using the multiple two-legged hopping test.ResultsCompared with age- and sex-matched controls, patients with OI type I had 17% lower peak force (1.3 kN vs. 1.7 kN; p = 0.002) as well as a 22% lower BMC (128 mg/mm vs. 165 mg/mm; p < 0.001). Stepwise regression analysis showed that muscle force and tibia length were positively related to bone strength (r2 = 0.90, p < 0.001) whereas there was no effect of the disease status (OI vs. control).ConclusionsThese results suggest that the muscle-bone relationship is similar between children and adolescents with OI type I and healthy age and sex-matched controls. It also suggests that muscle weakness may contribute to decreased bone strength in individuals with OI type I.