Secondary Deformity After Hemiepiphysiodesis in Hypophosphatemic Rickets: The Role of Metabolic Control

Overcorrection during hemiepiphysiodesis has been a common practice to prevent deformity recurrence resulting from the rebound phenomenon. This study aims to investigate the deformity progression following hemiepiphysiodesis for children with rickets.

Records of children with X-linked hypophosphatemic rickets, who underwent hemiepiphysiodesis, were reviewed. Data included demographics, age, body mass index (BMI) percentile, and metabolic status as the alkaline phosphatase percentage above upper normal limits (%ALP-UNL). Radiographs were measured. Children who did not achieve correction to a neutral mechanical axis deviation (MAD) were excluded. Data were compared between children who had progressive secondary deformity in the opposite direction to the initial deformity (Group A) and children who did not (Group B).

A total of 10 children were included (Group A: 7 and Group B: 3). Group A had a younger age at the time of the index surgery (7.1±2 vs. 9.0±1 y, P =0.005) and at the time of plate removal (8.7±2.3 vs. 10.5±1 y, P =0.03), had similar MAD at the time of plate removal (13±10 vs. 6±7 mm, P =0.093), similar BMI percentile at the time of plate removal (75±14 vs. 55±38%, P =0.26), and higher value of %ALP-UNL (119±66 vs. 28±53%, P =0.01). Group A had a higher MAD at the last follow-up compared to the time of plate removal and in the same direction (28±8 vs. 13±10 mm, P =0.0003). Group B had rebound with a mean MAD change of 12±7 mm in the direction of the initial deformity.

This study suggests that while hemiepiphysiodesis is successful for the correction of knee malalignment in children with rickets, caution needs to be taken to avoid overcorrection. Younger age at surgery and poor metabolic control could predispose to secondary deformity in the direction of the overcorrection.