Deformity correction in children with hereditary hypophosphatemic rickets

Abstract

X-linked hereditary hypophosphatemic rickets can induce various multiplanar deformities of the lower limb. We evaluated our ability to correct these deformities and assessed complications and recurrence rates in 10 children (eight girls and a pair of twin boys) followed from early childhood to skeletal maturity. We performed 37 corrective operations in 10 children. Depending on the patient's age, external fixation was used in 53 segments: Kirschner wires in 18, DynaFix in three, the Taylor Spatial Frame device in 13, and the Ilizarov device in 19. Internal fixation with intramedullary nailing was performed in 12. After bone consolidation, we radiographically determined the mechanical axis at an average distance of 0.5 cm medial to the center of the knee. The average mechanical lateral distal femoral angle was 85 degrees (range, 83 degrees-92 degrees) and the average mechanical medial proximal tibial angle was 91 degrees (range, 85 degrees-92 degrees). Deviation of the mechanical axis and knee orientation lines was increased at the followups conducted during a period of 5 to 12 months. Additional followups revealed a recurrence rate of 90% after the first corrective procedure and 60% after a second procedure.

Level of evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Fig. 1

An anteroposterior radiograph shows the lower limbs of a 2.5-year-old girl with XHPR at initial presentation. The knees show the distinctive cupping and widening of the growth plates. Laboratory data: phosphate, 0.58 mg/dL; alkaline phosphatase, 935 U/L.

Fig. 2

An anteroposterior radiograph shows the lower limbs of the patient in Fig. 1 after surgical correction in both lower legs (femur, tibia, and fibular osteotomies and Kirschner wire fixation) at the age of 4 years. Laboratory data: phosphate, 2.2 mg/dL; calcium, alkaline phosphatase, 776 U/L.

Fig. 3A–B

Anteroposterior radiographs show the lower limbs of the patient in Fig. 1 (A) with obvious recurrent deformity and (B) 4 months after correction of both legs at the age of 5 years (distal tibial and fibular osteotomies). Laboratory data: phosphate, 2.4 mg/dL; alkaline phosphatase, 641 U/L.

Fig. 4A–C

Anteroposterior radiographs show the left lower limb of the patient in Figure 1 (A) at the age of 10 years and (B) after surgical correction using an external fixation device and (C) at the 12-month followup after removal of the fixation device. Laboratory data: phosphate, 2.7 mg/dL; alkaline phosphatase, 721 U/L.

Fig. 5A–D

(A, B) Anteroposterior radiographs show the left leg of the patient in Fig. 1 at the age of 15 years. Anterior radiographs show the legs (C) after surgical correction and (D) at the 24-month followup. Laboratory data: phosphate, 2.3 mg/dL; alkaline phosphatase, 189 U/L.

Fig. 6

Alignment of the lower limb was assessed by measuring the MAD, the knee orientation lines, the mLDFA, and the mMPTA according to the method described by Paley et al. [18].