The effects of romosozumab combined with active vitamin D 3 on fracture healing in ovariectomized rats

Background: In this study, we investigated the potential acceleration of fracture healing and the bone mineral density-increasing effects of the combination therapy of romosozumab and active vitamin D 3 on fractures in ovariectomized rats. Methods: Ovariectomy was performed on forty 24-week-old female Sprague–Dawley rats. After 8 weeks, the rats underwent removal of the periosteum and osteotomy of the femoral shaft followed by osteosynthesis with intramedullary nailing to create fracture models. After surgery, the 40 rats were divided into four groups: the C group (control), the R group (romosozumab, 25 mg/kg, once a month via subcutaneous injection), the VD group (active vitamin D 3 , 0.2 µg/kg, twice a week via subcutaneous injection), and the R + VD group. A further 10 rats were prepared as the sham group. Ten weeks postintervention, both femurs were removed from all rats, and blood was collected. Soft X‑ray imaging was used to evaluate bone union, and microcomputed tomography (micro-CT) was used for bone morphometric evaluation. Toluidine blue staining of undecalcified specimens was used for histopathological evaluation, and bone turnover marker levels were measured using enzyme-linked immunosorbent assay. Results: Bone morphometry analysis by micro-CT revealed increased mineral density of the trabecular bone in rat femurs from the R + VD group, demonstrating the effectiveness of combination therapy with romosozumab plus active vitamin D 3 . However, no differences in bone union evaluated using soft X-ray imaging were observed, demonstrating no acceleration of fracture healing. Conclusions: Although combination therapy with romosozumab and active vitamin D 3 increased the trabecular bone volume, there was no evidence that it could accelerate fracture healing.