Bone Abstracts

Introduction: FGF3-associated hypophosphatemic rickets (HR) is a rare disorder caused by excessive renal phosphate wasting. Patients may suffer from limb deformities and low turnover femoral fractures have been described. The aim of this study is to evaluate DXA derived hip geometry of adult HR patients using hip structure analysis (HSA).

Materials and methods: Cross-sectional study of HR patients (n=21) at Odense University Hospital compared to age- and sex-matched controls (CON; n=38). Proximal hip DEXA scans were analyzed for bone geometry by use of the HSA programme developed by Beck et al. The analysis included three locations: the narrow neck (NN), the intertrocanteric region (IT), and the femoral shaft (FS).

Results: NN cross-sectional area (CSA) were: (mean±S.D) HR: 3.60±1.06, CON 3.28±0.70 cm², cross-sectional moment of inertia (CSMI) HR: 4.06±1.88, CON 3.63±1.42 (cm²)², section modulus HR: 2.04±0.75, CON 1.86±0.58 cm³, buckling ratio (BR) HR: 9.92±2.52, CON 10.50±2.41, BMD HR: 1.06±0.26, CON 0.98±0.16 g/cm². Results were similar for IT and FS. The shaft neck angle were lower in HR patients: HR: 124.0±5.8, CON 130.1±5.2° (P<0.001); the hip axis length similar: HR: 113±11, CON 114±12 mm. HR and CON patients were at similar age (HR: 40.7±2.4, CON 42.6±2.3 years) and weight (HR: 85.7±5.5, CON 84.2±2.3 kg). HR patients were shorter than controls: HR: 159.2±5.5, CON:173.1±1.8 cm (P=0.004).

Conclusion: The HSA analysis of the hip revealed no major differences in geometry between the groups: BMD, CSA, CSMI, section modulus, and buckling ratio were similar between HR patients and sex-and age-matched controls. The shaft neck angle and height were lower in HR patients.