The effect of liquid nitrogen exposure on the proliferative phase of Achilles tendon healing in Rattus norvegicus rats

Aim Tendon healing involves a crucial proliferative phase, during which fibroblasts and fibrocytes orches-trate collagen deposition. The use of liquid nitrogen (LN) in orthopaedic oncology may inadvertently affect adjacent tendon tissues. This study aimed to evaluate the impact of LN exposure on the histological features of tendon healing. Methods This experimental study employed a randomized post-test-only control group design involving 24 males Rattus norvegicus, randomly divided into four groups: control (no LN exposure) and three treatment groups exposed to LN for 1, 5, and 10 minutes, respectively, following Achilles tendon transection and re-pair. After a 21-day healing period, histological analysis was performed to assess the counts of fibroblasts, fibrocytes, and collagen content. Statistical analyses included one-way ANOVA, Post-hoc Tukey, and Pear-son correlation (p<0.05 was considered significant). Results LN exposure significantly reduced fibroblast, fibrocyte, and collagen levels compared to controls (p<0.05). The 10-minute group showed the lowest counts. A significant negative correlation was found between LN immersion duration and the number of fibroblasts (r=-0.87), fibrocytes (r=-0.829), and collagen content (r=-0.83) (p<0.05). Conclusion Liquid nitrogen (LN) impairs tendon healing in a dose-dependent manner, likely due to cryo-in-duced cell death and disruption of blood flow. This results in an acellular and avascular tendon matrix, hin-dering the repair process. LN exposure negatively impacts the proliferative phase of tendon healing in rats, suggesting the need for caution in clinical use to prevent damage to surrounding tendinous tissues.