Utility of ultrasound imaging in monitoring fracture healing in rat femur: Comparison with other imaging modalities.

Objective: Fractures are common injuries and various imaging modalities are employed to diagnose and monitor bone union. However, the follow-up of fracture healing using ultrasound imaging (US) remains a topic of debate. In this study, we analyzed of fracture healing process and compared US and radiological analyses with histological analyses to clarify the characteristics and limitations of each modality. Methods: An osteotomy model was created using the femur of Wistar rats, and US, radiological (radiography and micro-computed tomography (micro-CT)), and histological analyses were performed. Radiological assessments were conducted for the evaluation of calcified tissue. The gap between the bony callus and cartilaginous callus was measured. Results: US effectively captured changes on the fracture surface, potentially reflecting the early healing processes. Both US and radiographic findings showed strong correlation in terms of the decrease in the bony callus gap. US was unable to distinguish cartilaginous callus from the surrounding soft tissue. During the remodeling stage, micro-CT offered a detailed assessment of the internal fracture surface, whereas US was limited to evaluating the outer bone surface and lacked accuracy in visualizing the entire fracture site. Radiography provided a general overview of the fractures. The decrease in the bony callus gap measured using US correlated with the reduction in cartilaginous callus observed histologically. Conclusion: This study demonstrated that US could be a valuable tool for evaluating fracture healing. Combining fracture management with US and radiological examinations may provide a more accurate assessment of healing progress.