Effect of normobaric intermittent hypoxia on bone tendon junction healing: A rat model

Effect of normobaric intermittent hypoxia on bone tendon junction healing: A rat model Objective: The aim of this study is to investigate the biomechanical and histological effects of normobaric intermittent hypoxia on the healing process of the bone-tendon junction. Considering the challenges encountered in the natural healing processes of the bone-tendon junction, the potential impact of normobaric intermittent hypoxia on this process was explored. Materials and Methods: In this study, 64 adult female Wistar-Albino rats were used. The subjects were divided into two main groups: control and experimental, with each main group further divided into two subgroups for biomechanical and histological analyses. The intermittent hypoxia application involved exposing the subjects to an average of 10.5% oxygen level for 5 hours a day, 5 days a week. The rats were subjected to an 8-week follow-up period during which the healing processes of surgically induced Achilles tendon injuries were evaluated. Two observation points were determined with samples taken at the 4th and 8th weeks. Biomechanical analyses were conducted using a Testometric (M500-50CT, UK) device, while histological evaluations were performed using Safranin-O and Picro-Sirius stains, assessed microscopically according to Bonar, Movin, and Nourissat scoring systems. Results: Significant improvements were observed in the biomechanical strength and histological structure of the healing bone-tendon junction in the experimental group subjected to intermittent hypoxia. At the end of the 8th week, the experimental group showed statistically significant higher values in extension at break, maximum extension, stress at break, and maximum stress compared to the control group (p-values: 0.016, 0.031, 0.016, 0.033, respectively). Evaluations according to Bonar, Movin, and Nourissat scoring systems indicated that the experimental group had significantly lower Bonar and Movin scores than the control group, demonstrating better healing (p-values: 0.009, 0.004, respectively). Additionally, the parameter analyses of these scoring systems revealed significant findings at the 8th week: increased collagen content in the Bonar scoring system, decreased hyalinization in the Movin scoring system, and improved collagen organization in the Nourissat scoring system compared to the control group (p-values: 0.009, 0.041, 0.015, respectively). Conclusion: This study demonstrates that intermittent hypoxia application has beneficial effects on the healing process of the bone-tendon junction. Biomechanical and histological findings indicate that intermittent hypoxia supports the reformation of the enthesis structure by reducing scar tissue formation and enhancing the tendon's elasticity, load-bearing capacity, extension capacity, and stress tolerance. These results suggest that intermittent hypoxia could be a potential therapeutic approach in the treatment of orthopedic injuries. Key words: normobaric ıntermittent hypoxia,bone-tendon junction,healing process