Factors Associated with Bone Union Failure After Frozen Autograft Reconstruction in Lower Limb Osteosarcoma

<b>Background/Objectives</b>: Liquid nitrogen-treated frozen autograft is a biological reconstruction method developed at Kanazawa University for malignant bone tumors. However, nonunion between the treated autograft and host bone remains a complication. In this study, we aimed to identify factors influencing bone union in patients undergoing this procedure for osteosarcoma of long bones in the lower extremities. <b>Methods</b>: We retrospectively analyzed 35 osteosarcoma patients (mean age: 18.0 years) with lower limb long bone tumors treated with frozen autograft between 1999 and 2023. Factors assessed included sex, age, tumor location, fixation method (plate or intramedullary nail), technique (pedicle or free freezing), chemotherapy, and bone union. <b>Results</b>: Nonunion occurred in 6 cases: 2/25 with plate fixation (8.0%) and 4/10 with intramedullary nails (40%). The mean union time was shorter with plates (5.8 months) than with nails (7.2 months). Intramedullary nail use was significantly associated with nonunion (<i>p</i> < 0.05). Among plate fixations, nonunion occurred in 5.6% of multiple plates versus 14.3% of a single plate. <b>Conclusions</b>: Intramedullary nail fixation is associated with nonunion in biological reconstructions of long bones, consistent with previous reports. Multiple-plate fixation after frozen autograft with liquid nitrogen for osteosarcoma of the lower limb long bone should be considered.