Coxa Vara Deformity in Fibrous Dysplasia/McCune-Albright Syndrome: Prevalence, Natural History and Risk Factors, a two-center study.

This study aimed to evaluate the prevalence of and risk factors for coxa vara deformity in patients with Fibrous Dysplasia/McCune-Albright Syndrome (FD/MAS). This study was conducted at the National Institutes of Health and Leiden University Medical Center. All patients with any subtype of FD/MAS, FD involving the proximal femur, ≥1 X-ray available and age <30 years were included. X-rays were scored for the neck-shaft angle (NSA). Varus deformity was defined as NSA <110 o or >10 o below age-specific values. Risk factors for deformity were assessed by nested case-control analysis, comparing patients and femurs with and without deformity, and by linear mixed effects model, modelling temporal NSA decrease (the natural course of the NSA) in non-operated femurs with ≥2 X-rays. Assessed variables included growth hormone excess, hyperthyroidism, hypophosphatemia, >25% of the femur affected, calcar destruction, radiolucency and bilateral involvement. In total 180 patients were studied, 57% female. Mean baseline age was 13.6 (±SD 7.5) years; median follow-up 5.4 (IQR 11.1) years. 63% were diagnosed with MAS. 94 patients were affected bilaterally; 274 FD-femurs were analyzed; 99 femurs had a varus deformity (36%). In the nested case-control analysis, risk factors were: presence of MAS (p<0.001), hyperthyroidism (p<0.001), hypophosphatemia (p<0.001), high percentage of femur affected (p<0.001), calcar destruction (p<0.001). The linear mixed effects model included 114 femurs, identified risk factors were: growth hormone excess (β=7.2, p=0.013), hyperthyroidism (β=11.3, p<0.001), >25% of the femur affected (β=13.2, p=0.046), calcar destruction (β=8.3, p=0.004), radiolucency (β=3.9, p=0.009), bilateral involvement (β=9.8, p=0.010). Visual inspection of the graph of the model demonstrated most progression of deformity if NSA <120 o with age <15. In conclusion, in tertiary care centers, the prevalence of FD/MAS coxa vara deformity was 36%. Risk factors included presence of MAS, high percentage of femur affected, calcar destruction, radiolucency, NSA <120 o and age <15. This article is protected by copyright. All rights reserved.