Bone Abstracts

Cystic fibrosis(CF) results in low volumetric bone mineral density(vBMD), poor muscle strength and increased fracture risk in young patients. The aim of this study was to compare bone and muscle variables measured by peripheral and high-resolution QCT (pQCT and HR-pQCT) and jumping mechanography (JM) In CF children and healthy controls. We hypothesised that CF children have lower muscle force and power (Fmax and Pmax) than controls which may contribute to CF-related bone disease.

216 children (65 CF) aged 8–16 years had pQCT scans and JM measurements; 176 (25 CF) had HR-pQCT scans. Fmax and Pmax were measured using JM. Volumetric BMD, CSA, stress strain index (SSI) and microarchitecture were measured at the 4% (pQCT), 66% (pQCT) and 8% (HR-pQCT) sites of the tibia. Group differences, with appropriate interactions, were tested using multiple regression adjusting for maturity and body size and, in a separate model, additionally for Fmax and Pmax. Data are presented as β-coefficient (%) and P-value.

CF children had lower vBMD (6–8%, P<0.001), smaller bones (10%, P<0.001) with less cortical CSA (4%, P<0.01) and thinner trabeculae (12%, P<0.05). After adjustment for Fmax and Pmax, cortical vBMD (4%, P<0.001) and BV/TV (29%, P<0.01) were lower in CF children. CF children had lower cortical vBMD (P<0.001) and Tb.Th (P<0.05) compared to controls at the same stage of puberty, a difference that was greater at late puberty. The CF group had lower total vBMD (P<0.05), BV/TV (P<0.001), and Tb.N (P<0.01) compared to controls for a given Fmax and this difference was greater at higher Fmax. There was a negative relationship between Pmax and BV/TV (P<0.01) and Tb.N (P<0.05) in CF children and in controls. BV/TV and Tb.N did not differ with greater Pmax in controls.

Group differences in bone measures existed after adjusting for sex, maturity, and body size. The attenuation of group differences, except BV/TV, after adjustment for Fmax and Pmax indicates a role for muscle in bone development. The interactions suggest a less efficient adaptation to muscle forces in bones of CF and possible worsening bone disease with puberty, both of which may contribute to the increased fracture risk in CF adolescents and adults.

Disclosure: The authors declared no competing interests.