Retrograde Intramedullary Femoral Lengthening With Acute Deformity Correction in Children, Adolescents, and Young Adults.

Background: Acquired and congenital limb length discrepancies often coexist with deformities of the distal femur. Lengthening of the femur along its anatomic axis changes the limb's mechanical alignment. Angular correction and lengthening can be achieved at the same site if a retrograde lengthening nail is used with a specific preoperative planning method ("reverse planning") which permits patient-specific selection of the final mechanical axis. Methods: A consecutive cohort series of children, adolescents, and young adults (mean 15.6 ± 4.8 years) undergoing retrograde implantable femoral lengthening between the years 2011 and 2024 were analyzed. Surgical details, lengthening parameters, Limb Lengthening and Reconstruction Society (LLRS)-AIM index, accuracy of final correction, and complications were reviewed and classified. Patients were eligible only if the distal femoral physis was closed. Results: Seventy-three lengthening were eligible in the study period. Average lengthening was 4.2 ± 1.4 cm (range 2.0-8.0 cm), and consolidation index was 39.4 ± 21.9 days/cm. Deformities and length discrepancies were moderately complex, with a mean LLRS AIM score of 6 (range 1-13). Complication rates were similar to previous reports of intramedullary femoral lengthening, comparable between congenital (12 of 31, 39%) and acquired etiologies (16 of 42, 38%). Preoperative coronal alignment ranged from 14° varus to 20° valgus, while final coronal alignment was 0.4° ± 3.4° of neutral (range 7° valgus to 13° varus). Coronal deformities up to 20° and sagittal deformities up to 23° were corrected acutely at the lengthening site. Conclusions: Retrograde intramedullary femoral lengthening with acute deformity correction at the same site is an alternative to antegrade lengthening with separate osteotomy of the distal femur in children and adolescents. The reverse planning method allows reproducible length and deformity correction at the same location. Specific intraoperative technical adjuncts are used to achieve and maintain the desired alignment. Level of Evidence: Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.