Abstract
BACKGROUND: Achilles tendinopathy is a common degenerative disorder characterized by pain, impaired function, and poor tissue regeneration. Effective treatment remains a challenge due to the tendon's limited healing capacity. Cinnamic acid, a naturally occurring phenolic compound, has demonstrated anti-inflammatory and antioxidant effects in various tissue repair models. However, its therapeutic potential in tendon injury remains unexplored, and this study represents the first study to evaluate its effects in an experimental Achilles tendinopathy model. METHODS: In this experimental study, tendinopathy was induced in male rats via ultrasound-guided collagenase injection into the right Achilles tendon. Animals were randomly assigned to six groups (n = 7 each): Sham, Injury Control, vehicle control (Tendinopathy + DMSO), and three cinnamic acid treatment groups (10, 30, and 90 mg/kg). Cinnamic acid was administered intraperitoneally once daily for four weeks, starting on day 7 post-injury. Tendon healing was evaluated on days 21 and 35 using ultrasound imaging and histological analysis based on semi-quantitative scoring systems. RESULTS: Cinnamic acid treatment led to dose-dependent improvements in tendon healing. Ultrasound scores significantly decreased in the 30 mg/kg group, indicating preservation of echogenicity and reduced neovascularization. Modest improvement was observed with 10 mg/kg, whereas 90 mg/kg showed no significant benefit. Histological findings paralleled the ultrasound results, with the 30 mg/kg group displaying improved collagen fiber organization, normalized nuclear morphology, and reduced inflammation. Both 10 mg/kg and 90 mg/kg groups showed improvements over the injury control group, but the difference between these two doses was not statistically significant. A strong correlation (ρ = 0.794, p < 0.001) between ultrasound and histological scores confirmed the consistency of imaging-based assessment. CONCLUSIONS: These findings support the utility of ultrasound as a non-invasive monitoring tool and highlight cinnamic acid as a promising therapeutic agent for tendinopathy. CLINICAL TRIAL NUMBER: Not applicable.