Irisin and its role in fracture healing: A comparative study with hyaluronic acid and platelet-rich plasma in a rat model.

Objectives: This study aims to investigate the effects of local irisin (IR) injections on closed femoral fractures in rats and to compare its efficacy to platelet-rich plasma (PRP) and hyaluronic acid (HA).

Materials and methods: A total of 64 male Wistar albino rats were divided into four equal groups: a control group that received no treatment and three experimental groups that received local injections of HA, PRP, or recombinant IR at the fracture site. All rats underwent a standard bilateral closed femoral shaft fracture and intramedullary fixation. Each group was further divided into two subgroups, sacrificed at Week 2 and Week 4. The right femurs were used for radiological examination with micro-computed tomography (micro-CT) and subsequent histological analysis, while the left femurs were reserved for biomechanical testing.

Results: By Week 2, the IR and PRP groups showed statistically significantly higher scores for the transformation of fibrous cartilage into bone tissue compared to the control group (7.88±0.6, p=0.0001, and 6±0.8, p=0.036, respectively). By Week 4, transformation scores in the IR group increased to 9.25±0.7, statistically significantly exceeding the control group (p=0.0001). Bone volume was also statistically significantly greater in the IR group (5.21±0.5 mm³ at Week 2; 5.94±0.8 mm³ at Week 4) compared to the control group (p=0.001) and the PRP group (p=0.003) at Week 2, and compared to the control group (p=0.001), the HA group (p=0.042), and the PRP group (p=0.014) at Week 4. Additionally, maximum strength in the IR group was statistically significantly higher than in the control group (p=0.0001) and the PRP group (p=0.048) at Week 2. By Week 4, the IR group was also statistically significantly higher compared to the control group (p=0.0001), the HA group (p=0.037) and the PRP group (p=0.009).

Conclusion: The present study is one of the first to demonstrate the potential of administering local IR via injection into the fracture hematoma to accelerate fracture healing. The superior efficacy of IR over HA and PRP may be explained by its ability to enhance osteoblast activity, promote vascularization, and reduce inflammation, creating an optimal environment for bone regeneration. Unlike PRP, which primarily delivers growth factors, and HA, which supports cell migration and proliferation, IR appears to directly influence the bone microenvironment, expediting callus transformation. These findings suggest that IR may play a significant role in improving outcomes for patients at risk of delayed union. However, further clinical trials in humans are necessary to confirm its efficacy and safety for clinical applications.