Histopathology Findings of Low-Level Laser Therapy Effectiveness on Achilles Tendon Repair in Rabbit Model

Abstract

Background: Low-level laser therapy (LLLT) has been utilized to treat tendinitis and various other musculoskeletal conditions. The current study assessed the impact of LLLT (650 and 750 nm) on tendon repair in rabbits.

Materials and methods: Fifteen 2-year-old male New Zealand White rabbits were divided into three groups: control, 650 nm laser and 750 nm laser therapy. After applying Achilles tendon-destructive surgery on their right legs, rabbits underwent LLLT, and tendon repair was assessed using histopathology and immunohistochemistry (IHC) findings. All data were analysed using SPSS version 21, considering a significant level <0.05.

Results: The study's histopathological and immunohistochemical analysis revealed that LLLT at 650 and 750 nm significantly improved tendon healing compared to the control group (p < 0.05). The treated groups exhibited better organized tendon fibres with reduced discontinuity, collagen fibre waviness, and inflammatory response (p < 0.05). Both laser wavelengths showed similar results with no significant differences between them (p > 0.05), but both were notably better than the control group in reducing inflammation, enhancing fibre structure, and lowering levels of collagen type I (Col-I); collagen type III (Col-III); transformer growth factor beta (TGF-β); galectin-3 (galectin-3); VGF nerve growth factor inducible; vascular endothelial growth factor (VEGF), indicating a more effective healing process with LLLT.

Conclusion: Due to our findings, LLLT at 650 and 750 nm effectively reduced inflammation, improved structural integrity, and enhanced the organization of collagen fibres for Achilles tendon repair in rabbits.

Keywords: Immunohistochemistry findings; histopathology finding; low‐level laser therapy; rabbit; tendon repair.

FIGURE 1

Microscopic view of the structure and arrangement of collagen fibres in the Achilles tendon of rabbits. (A) Control group, (B) 650 nm laser group, (C) 750 nm laser group. The images were captured at a scale of 10 µm using a 40× lens, 50 µm using a 10× lens. After 42 days, the collagen fibre structure in the control group was significantly disrupted, with strands appearing discontinuous and wavy. In contrast, the 650 and 750 nm laser groups exhibited only slight interruptions, with a reduction in strand length and wavelength.

FIGURE 2

Effectiveness of Achilles tendon repair of rabbits in 650 and 750 nm laser therapy groups compared to the control group. The immunohistochemistry (IHC) findings revealed significant differences between the control group and both laser therapy groups (650 and 750 nm) across all evaluated markers. *Tukey's multiple comparisons test; adjusted p < 0.05 with 95% CI. A) For Col‐I, both laser therapy groups showed significantly higher levels compared to the control, with mean differences of 28.93 (22.88–34.99) for 650 nm and 33.89 (27.83–39.94) for 750 nm (p < 0.0001), and no significant difference was observed between the two laser groups (p = 0.1139). B) For Col‐III, both laser groups exhibited significantly higher levels than the control, with mean differences of 25.6 (16.64–34.55) and 29.1 (20.14–38.05) for the 650 and 750 nm groups, respectively (p < 0.0001), whereas the difference between the laser groups was not significant (p = 0.6148). C) TGF‐β levels were significantly elevated in both laser‐treated groups compared to the control, with mean differences of 27.74 (21.42–34.06) and 30.15 (23.83–36.47) for the 650 and 750 nm lasers, respectively (p < 0.0001), with no significant inter‐laser group difference (p = 0.6319). D) Galectin‐3 levels were also significantly higher in both laser groups compared to the control, with mean differences of 18.36 (9.085–27.64, p = 0.001) for 650 nm and 24.22 (14.94–33.49, p = 0.0001) for 750 nm, though the difference between the laser groups was not statistically significant (p = 0.2572). E) For VGF, the laser groups showed significant increases compared to the control (p < 0.0001), with mean differences of 35.9 (28.77–43.03) and 39.64 (32.51–46.76) for the 650 and 750 nm groups, respectively, but no significant difference was observed between the laser groups (p = 0.3927). F) VEGF was significantly higher in the laser groups compared to the control, with mean differences of 16.14 (8.388–23.89, p = 0.0007) for 650 nm and 18.56 (10.81–26.31, p = 0.0003) for 750 nm. The difference between the two laser groups for VEGF was not significant (p = 0.7532). Col‐I, collagen type I; Col‐III, collagen type III; TGF‐β, transformer growth factor beta; VEGF, vascular endothelial growth factor; VGF, VGF nerve growth factor inducible.

FIGURE 3

Immunohistochemistry (IHC) findings of Achilles tendon repair of rabbits in control, 650 and 750 nm laser therapy groups of rabbits. The images were captured at a scale of 100 µm using a 20× lens. Col‐I, collagen type I; Col‐III, collagen type III; TGF‐β, transformer growth factor beta; VEGF, vascular endothelial growth factor; VGF, VGF nerve growth factor inducible.