The Effect of Metabolic Control of Rickets on Deformity Correction Following Hemiepiphysiodesis in Children With X-linked Hypophosphatemic Rickets

Background: X-linked hypophosphatemic rickets (XLH) is a genetic disorder of chronic hypophosphatemia leading to rickets and osteomalacia that often results in lower limb deformities requiring surgical correction. Hemiepiphysiodesis is commonly used to correct angular deformities in skeletally immature patients, but outcomes in XLH are variable, and the influence of metabolic control on surgical outcomes remains unclear. We evaluated the relationship between metabolic control of rickets, measured by serum alkaline phosphatase (ALP), and deformity correction after hemiepiphysiodesis in children with XLH. Methods: We retrospectively reviewed children with XLH from 2 tertiary centers between 2000 and 2021, who underwent hemiepiphysiodesis and had serial lower extremity radiographs from 6 months preoperatively to 2 years postoperatively or until implant removal. Angular correction was assessed using mechanical axis deviation (MAD, mm) and MAD rate of correction (mm/month); metabolic control was evaluated using serum ALP, expressed as percentage of the age-specific and sex-specific upper limit of normal (%ALP-ULN). Correction was defined as MAD=0 mm within 2 years of surgery. Associations between %ALP-ULN, MAD, and MAD rate of correction were analyzed using univariable and multivariable models adjusted for body mass index (BMI) Z-score. Results: Fourteen patients [26 affected limbs, 18/26 (69%) genu varum] who had both preoperative and postoperative radiographs were included. Correction was achieved in 20/26 (77%) limbs (71% of patients) by 2 years postoperatively. All non-corrected limbs (6/26, 23%) had varus deformity. %ALP-ULN at 1 year postoperatively correlated positively with greater residual MAD ( R =0.83, P =0.0014) and negatively with MAD rate of correction ( R =−0.70, P =0.017); which remained significant after controlling for BMI Z-score (MAD: β=0.96, 95% CI 0.23, 1.7, P =0.017; MAD rate of correction: β=−0.06, 95% CI −0.12, −0.01, P =0.036). Conclusions: Postoperative metabolic control of rickets, as assessed by lower ALP, was associated with greater and faster deformity correction after hemiepiphysiodesis in children with XLH, supporting the importance of metabolic optimization and medical management to improve surgical outcomes. Level of Evidence: Level IV—Case Series.