Bone Abstracts

Radiographs of the second metacarpal are used to assess bone strength development in paediatric populations. Children with achondroplasia and osteogenesis imperfecta (OI) have known differences in bone strength. Details of how bone strength develops and compares within these populations to unaffected children are lacking. A data set for patients with achondroplasia and OI was established.

A retrospective IRB-approved review of bone-age films (n=67; 1–11 films/patient) from patients (5 months–16 years+3 months old) with achondroplasia (six males; ten females) or OI (nine males; 11 females) was conducted. A sample of modern controls (diagnosis: leg-length discrepancy) matched historical measurements from the Bolton-Brush collection (6 months–16 years). Metacarpal length (Le) was measured from the proximal end to the most distal ossified end along the midshaft axis. Outer and inner diameters were measured at 50% and 60% of the length, averaged, and used to calculate total cross-sectional area (Tt.Ar) and cortical area (Ct.Ar) using a circular approximation. To adjust for differences in body size, we compared robustness (Tt.Ar/Le) and relative cortical area (RCA=Ct.Ar/Tt.Ar) among groups.

Achondroplasia patients tend to have both robusticity and RCA values above the most robust Bolton-Brush tertile (Figure 1A). This robust phenotype was consistent with the reduced longitudinal growth seen in achondroplasia patients. Increased RCA values were unexpected and may indicate deregulated mass-accumulation. In contrast, OI patients followed the Bolton-Brush pattern of decreased robusticity and increased RCA, but not the distribution. OI patients all fell in the most slender tertile (Figure 1B). No sexual dimorphism was noted in this study (Figure 1C).

The lack of sexual dimorphism in the dysplasia populations is in contrast to that reported in the unaffected population. We suggest that the underlying dysplasia overrides the sex-specific effects on bone strength development. The contribution of the specific mutation is unknown and needs to be further studied.

Disclosure: Dr. Raggio sits on the Medical Board of the Osteogenesis Imperfecta Foundation.

Figure 1