ESPE Abstracts (2016) 86 RFC2.4

aCHU de Besançon, Besançon, France; bAPHP, CMR Calcium-Phosphore, Bicêtre Paris Sud, Le Kremlin Bicêtre, France; cAPHP, Necker-Enfants Malades, Paris, France

Background: XLHR is due to mutations in the PHEX gene leading to unregulated production of FGF23, hence hypophosphatemia and decreased renal 1,25OH-vitamin D hydroxylation. Amongst other features, XLHR is characterized by leg bowing of variable severity. Phosphate supplements and oral 1,25OH-vitamin D, partially or, in some cases, fully restore the limb straightness. For severe or residual limb deformities, orthopaedic surgery may be recommended.

Objective: To retrospectively assess the results of surgical limb correction in XLHR children.

Methods: We analysed the relapse incidence and the post-surgical complications in 49 XLHR children (19M, 30F) bearing a PHEX mutation (mean age at diagnosis 5.6 years (±6.5)) who underwent at least one leg surgery.

Results: At first surgery, the mean age was 13.4 years (±5.0), 70% of the patients had a genu varum. Except for 3 transient epiphysiodeses, most surgical corrections were done through osteotomies. 14/49 (29%) of the patients relapsed after the 1st surgery. The age at surgery was inversely correlated with the risk of relapse. The number of additional surgeries significantly decreased with age (2.0 (±0.9), 1.7 (±0.9) et 1.2 (±0.35) in children <11 years, between 11 and 15, and >15 years; P<0.001). Above the age of 11 years, patients having a good metabolic control of the rickets (normal alkaline phosphatases) seem to present with a lower incidence of relapse (28% vs 44% in children<11 years). 20% of the patients had complications (different from the recurrence of the bony deformity) including pseudarthrosis, infection or fractures.

Conclusion: We report here the largest series of surgical procedures in XLHR. Our results confirm that phosphate supplements and vitamin D analogues therapy is the first line of treatment in XLHR to correct the leg bowing. Early surgeries are associated with a high risk of relapse of the limb deformity. Such procedures should be recommended, as a multidisciplinary decision, only in patients with severe distortion leading to mechanical joint and ligaments complications, or for residual deformities once growth plates are fused.

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