Short-term Safety Profile of Trochanteric-Entry Intramedullary Lengthening Nails in Skeletally Immature Patients.

Background: There are historical concerns with trochanteric-entry intramedullary femoral nailing in skeletally immature patients due to possible proximal femoral growth disturbance, including coxa valga. While more contemporary studies suggest improved safety with modern nail designs, data specific to femoral lengthening nails in patients with substantial growth remaining are limited. The purpose of this study was to evaluate proximal femoral morphology following trochanteric-entry intramedullary lengthening in skeletally immature patients. Methods: A retrospective institutional review board-approved case series was performed in skeletally immature patients with >2 years of growth remaining and a minimum of 1-year radiographic follow-up who underwent antegrade femoral lengthening with a Precice™ nail between 2017 and 2024. Radiographic parameters, including the neck-shaft angle (NSA), mechanical lateral proximal femoral angle (mLPFA), and articulotrochanteric distance (ATD), were measured preoperatively and at latest follow-up. Clinically meaningful coxa valga was defined as a ≥2 standard deviation increase in NSA from baseline. Linear regression analyses were performed to assess the effect of time remaining until skeletal maturity on proximal femoral morphology. Results: Twenty-four femoral lengthenings in 22 patients (mean age 12.2 ± 2.3 years) were included with a mean radiographic follow-up of 23.4 ± 18.8 months. The mean age at nail insertion was 12.2 ± 2.3 years, and the mean lengthening was 46.4 ± 19.5 mm. There were no cases of infection, implant failure, or osteonecrosis. For the series, no significant differences were observed between pre and postoperative NSA, mLPFA, or ATD. One patient (4.2%) treated at age 8.6 years developed progressive coxa valga at long-term follow-up. Regression analysis demonstrated that each additional year of growth remaining was associated with a 1.5° increase in NSA, indicating that greater time remaining until skeletal maturity was associated with valgus-directed postoperative changes in proximal femoral morphology. Conclusions: Trochanteric-entry intramedullary femoral lengthening demonstrates a favorable safety profile in skeletally immature patients with >2 years of growth remaining, with a low risk of proximal femoral growth disturbance, including osteonecrosis. Younger patients with substantial growth remaining may be at higher risk for valgus proximal femoral changes, warranting routine radiographic surveillance until skeletal maturity. Key Concepts: (1)Trochanteric-entry antegrade femoral lengthening appears safe in skeletally immature patients with >2 years of growth remaining, with no noted cases of osteonecrosis.(2)Clinically relevant proximal femoral growth disturbance was uncommon across the series, with no significant postoperative changes in the neck-shaft angle, mechanical lateral proximal femoral angle, or articulotrochanteric distance.(3)The youngest subset of patients with substantial growth remaining may be at higher risk for progressive coxa valga, necessitating routine postoperative radiographic surveillance until skeletal maturity. Level of Evidence: Level 4 (case series).