Comparison of Photobiomodulation and Anti-Inflammatory Drugs on Tissue Repair on Collagenase-Induced Achilles Tendon Inflammation in Rats

Background: Tendinopathy is characterized by pain, edema, and structural changes in tendon tissue. Objective: In this animal study we decided to compare the short- and medium-term effects of low-level laser therapy (LLLT), dexamethasone, and diclofenac on inflammation and tendon tissue repair in collagenase-induced tendinitis. Materials and methods: Two hundred five female Wistar rats were randomly divided into five groups. Animals in the control group were given a saline injection and the experimental groups received a collagenase injection (100g/tendon) in the peritendinous Achilles and received no treatment, LLLT (3J, 810nm, 100mW), diclofenac (1.1mg/kg), or dexamethasone (0.02mg/kg). Histological analyses were performed at 10 time points up to 60 days (n=5/group each time point), and included an assessment of the severity of inflammation, collagen fiber content, and organization. Results: Collagenase injection induced a severe inflammatory reaction with significant reduction in collagen content for 48h, and disorientation of collagen fibers lasting between 14 and 21 days. Diclofenac and dexamethasone reduced inflammatory signs during the first 2 days, although there was prolongation of the inflammatory phase and slower normalization of tendon quality, particularly in the dexamethasone group. LLLT prevented hemorrhage, reduced inflammation severity, and preserved tendon morphology compared with the other groups. Conclusions: LLLT showed a significant superiority over commonly used anti-inflammatory pharmaceutical agents in acute collagenase-induced tendinitis. (AU)