ESTABLISHMENT OF A BONE REGENERATION MODEL FOR THE SECOND STAGE OF THE MASQUELET TECHNIQUE USING MICE

The Masquelet technique is widely recognized as an effective treatment for large bone defects; however, its underlying mechanisms remain incompletely understood. In previous basic research, large animal models such as sheep and goats, as well as small animal models like rabbits and rats, have been utilized. However, reports on Masquelet models using mice remain limited. We reported on the characteristics of the induced membrane in the first stage of the Masquelet technique using a mouse model. In this study, we aimed to establish a second-stage bone regeneration model and present our findings. Eleven male C57BL/6J mice (24 weeks old) were used. A mouse-specific plate (RISystem AG) was placed on the midshaft of the right femur, and a 2-mm bone defect was created. A cylindrical polymethylmethacrylate (PMMA) spacer was inserted into the defect. Two weeks after the initial surgery, the second-stage surgery was performed, where the spacer was removed, the ends of the femur were refreshed. And allogenic crushed femoral bone from separate individuals was transplanted within the induced membrane. Bone regeneration was evaluated using X-ray and CT imaging at 4, 6, and 8 weeks after bone grafting. At 8 weeks, the mice were euthanized, and histological evaluation using hematoxylin and eosin (HE) staining was performed on the harvested femoral samples. CT imaging revealed that the transplanted bone graft was gradually resorbed from both femoral ends and replaced with new bone, leading to the eventual union of the regenerated femoral ends, restoration of cortical continuity, and reopening of the medullary cavity. At the 8 weeks after bone grafting, bone union was achieved in 7 out of 11 mice. Histological analysis with HE staining confirmed the regeneration of the cortex and medullary cavity, consistent with the CT findings. In samples exhibiting nonunion, varying degrees of bone regeneration were observed, including complete absence of regeneration or failure of union despite contact between the bone ends This study represents the first report of bone regeneration evaluation using the Masquelet technique in a mouse model. Similar to other animal models, bone regeneration was observed; however, improvements such as increasing the bone union rate remain necessary. The advantages of the mouse model include its low cost, ease of management, and the potential for studies utilizing genetically modified models, making it a promising platform for elucidating the mechanisms underlying the Masquelet technique.