Motorized Plate Lengthening of the Femur in Children: A Preliminary Report

Background: Limb lengthening by distraction osteogenesis can be performed with motorized internal devices, but intramedullary implants risk avascular necrosis of the femoral head in young children. A method of internal limb lengthening using a motorized expandable plate has been developed and preliminary results are presented. Methods: Seven skeletally immature patients (ages 2.7 to 9.7 y) with congenital femoral deficiencies underwent femoral lengthening with the use of a magnetic expandable plate. Surgical details, lengthening parameters, Limb Lengthening and Reconstruction Society-Angular deformity, Infection, Motion index, and complications were reviewed and classified according to the modified Clavien-Dindo system. Results: An average lengthening was 4.1 cm (range, 3.3 to 4.4 cm) comprising 18% of initial femoral segment length (range, 14% to 21%). The average lengthening phase was 50.2 days (range, 40 to 57 d) and weight-bearing was initiated at an average of 13 weeks from surgery (range, 8 to 18 wk). Limb deformities and length discrepancies were of moderate complexity, with an Limb Lengthening and Reconstruction Society-Angular deformity, Infection, Motion score of 6.57 (range, 6 to 7). Complication rates were comparable to previously reported methods of femoral lengthening. One patient underwent reoperation for patellar instability and 1 patient experienced radiographic hip subluxation which was observed. Small magnitude varus was observed in regenerate in 3 of 7 cases, none requiring treatment. Preoperative planning consisted of careful localization of the corticotomy site, acute deformity correction at the lengthening site in 3 cases, and implant orientation. Conclusions: Limb lengthening with motorized internal plates is feasible for young children with congenital femoral deficiency for whom intramedullary lengthening is unsafe or if external fixation is to be avoided. However, the fundamental principles of distraction osteogenesis and risks of lengthening for congenital discrepancies remain unchanged. Specific considerations herein include: careful planning of implant length and positioning, adjacent joint protection with adjunctive means, and mitigating deformity of the regenerate during distraction.