Incidence and management of secondary deformities after megaendoprosthetic proximal femur replacement in skeletally immature bone sarcoma patients

Introduction Megaendoprosthetic reconstruction of bone defects in skeletally immature patients has led to the development of unique complications and secondary deformities not observed in adult patient cohorts. With an increasing number of megaendoprosthetic replacements performed, orthopedic oncologists still gain experience in the incidence and type of secondary deformities caused. In this study, we report the incidence, probable cause and management outcome of two secondary deformities after megaendoprosthetic reconstruction of the proximal femur: hip dysplasia and genu valgum. Materials and methods Retrospective analysis of 14 patients who underwent primary and/or repeat reconstruction/surgery with a megaendoprosthetic proximal femur replacement between 2018 and 2022. Results Mean patient age was 9.1 years (range 4–17 years). Stress shielding was observed in 71.4%. Hip dislocation was the most frequent complication (50%). While four dislocations occurred without an underlying deformity, secondary hip dysplasia was identified in 58.3% ( n = 7/12) of intraarticular resections and reconstructions, leading to dislocation in 71.4% ( n = 5/7). A genu valgum deformity was observed in 41.6% ( n = 5/12). The incidence of secondary hip dysplasia and concomitant genu valgum was 42.9% ( n = 3/7). Triple pelvic osteotomy led to rebound hip dysplasia in two cases (patients aged