Clinical and radiological outcomes of using locked intramedullary nails in the treatment of severe frontal plane lower limb deformity in adolescents with hypophosphatemic rickets (mid-term results)

INTRODUCTION: Lower limb deformities in patients with hypophosphatemic rickets are multi-apical and require multiple osteotomies for correction. Intramedullary nails (IMNs) are used to fix multiple osteotomies. Authors of this studyaimed to assess the clinical and radiographic outcomes of using IMNs for correcting lower limb deformity in adolescents with hypophosphatemic rickets. METHODS: This prospective study included patients with hypophosphatemic rickets who underwent deformity correction between November 2020 and November 2023 using IMNs, with a minimum follow-up of 2 years. Clinical outcomes were assessed using the Lower Limb Deformity-Scoliosis Research Society (LD-SRS) score. Radiographic outcomes measured included the mechanical tibiofemoral angle (mTFA), mechanical axis deviation (MAD), mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA), and Stevens' knee joint zoning. RESULTS: Twenty patients (25 limbs and 35 bones) were included (mean age: 16 years; range: 13-22 years). The LD-SRS score improved from 3.2 ± 0.4 preoperatively to 4.3 ± 0.7 postoperatively. Preoperative mechanical tibiofemoral angle was 27.8° ± 12.1° and 17.33° ± 7.9° in the varus and valgus groups, respectively, improving to 3.4° ± 6.4° and 2° ± 5.2°, respectively. Preoperative mechanical axis deviation was 82.2 ± 35.6 mm and 41.8 ± 22.2 mm in the varus and valgus groups, respectively, improving to 9.2 ± 20.1 mm and 4.6 ± 12.6 mm, respectively. Preoperative mechanical lateral distal femoral angle was 102.4° ± 9.7° and 77.9° ± 9.8° in the varus and valgus groups, respectively, improving to 89.9° ± 3.1° and 88.1° ± 3.1°, respectively. Preoperative mechanical medial proximal tibial angle was 78.7° ± 8° and 89.7° ± 3.9° in the varus and valgus groups, respectively, improving to 88.6° ± 3.4° and 88.2° ± 2.9°, respectively. Preoperative Stevens' knee joint zoning was Zone 3 in all patients, improving to Zone 1 in 16 limbs, Zone 2 in eight limbs, and Zone 3 in one limb. CONCLUSION: Correction of severe frontal plane lower limb deformities in adolescents with hypophosphatemic rickets using IMNs yields good clinical and radiographic outcomes at 2-year follow-up.