Biochemistry and biomechanics of healing tendon: Part II. Effects of combined laser therapy and electrical stimulation

In previous studies we demonstrated that early mechanical loading and laser photo-stimulation independently promoted tendon healing. Thus, we tested the hypothesis that a combination of laser phototherapy and mechanical lead would further accelerate healing of experimentally tenotomized and repaired rabbit Achilles tendons. Methods: Following surgical tenotomy and repair, the tendons of experimental and control rabbits were immobilized in polyurethane casts for 5 d. The repaired tendons of experimental rabbits received mechanical lead via electrical stimulation-induced contraction of the triceps aurae for 5 d. In addition, experimental tendons were treated with daily doses of 1 J · cm^-2 low intensity helium-neon laser throughout the 14-d experimental period. Results: The combination of laser photostimulation and mechanical lead increased the maximal stress, maximal strain, and Young's modulus of elasticity of the tendons 30, 13, and 33%, respectively. However, MANOVA revealed no statistically significant differences in these biomechanical indices of repair of control and experimental tendons. Biochemical assays showed a 32% increase in collagen levels (P < 0.05) and an 11% decrease in mature cross-links in experimental tendons compared with that in controls (P > 0.05). Electron microscopy and computer morphometry revealed no significant differences in the morphometry of the collagen fibers and no visible differences in the ultrastructure of cellular and matrical components of control and experimental tendons. Conclusions: These findings indicate that the combination of laser photostimulation and early mechanical loading of tendons increased collagen production, with marginal biomechanical effects on repaired tendons.