Femoral anteversion (FNA) in individuals with X-linked hypophosphatemia (XLH)

Abstract

Background/Introduction: XLH is a rare genetic condition which affects phosphate metabolism, resulting in osteomalacia. Individuals with XLH are also at risk of lower limb deformities and early onset of hip osteoarthritis. These two factors may be linked, as abnormal FNA (femoral torsion) is a risk factor for hip osteoarthritis. The contributions of regional femoral torsion e.g. intertrochanteric torsion (ITT), shaft torsion (ST) and condylar torsion(CT) to FNA differ between clinical groups and are important when planning femoral osteotomies to correct FNA. Purpose: This study aimed to compare FNA and regional femoral torsion of the femur between adults with XLH and controls. Methods: 13 individuals with XLH (5 male, age 49±9y) and 12 age, sex and weight-matched control participants (7 male, age 49±8y) were recruited following ethical approval and informed consent. Magnetic resonance imaging (MRI) scans of the femur were obtained, from which FNA, ITT, ST and CT were measured. Data were normally distributed, therefore group differences were assessed using t-tests. Results: FNA was 29° lower in individuals with XLH than controls (pb0.005). This resulted mainly from lower ITT (pb0.001) and in part CT (pb0.05) whereas ST was similar in the two groups (Fig. 1). Conclusion(s): We observed differences in FNA and regionspecific femoral torsion in individuals with XLH compared to controls. These differences may contribute to clinical problems such as hip osteoarthritis common in XLH. Information on region-specific differences may be useful in planning corrective surgeries. Future work should examine how pharmacological and other interventions in this group affect FNA.