BIOCHEMISTRY AND BIOMECHANICS OF HEALING TENDON - PART II - EFFECTS OF COMBINED LASER THERAPY AND ELECTRICAL-STIMULATION

Purpose: In previous studies we demonstrated that early mechanical loa ding and laser photo-stimulation independently promoted tendon healing . Thus, we tested the hypothesis that a combination of laser photother apy and mechanical load would further accelerate healing of experiment ally tenotomized and repaired rabbit Achilles tendons. Methods: Follow ing surgical tenotomy and repair, the tendons of experimental and cont rol rabbits were immobilized in polyurethane casts for 5 d. The repair ed tendons of experimental rabbits received mechanical load via electr ical stimulation-induced contraction of the triceps surae 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 mechani cal load increased the maximal stress, maximal strain, and Young's mod ulus of elasticity of the tendons 30, 13, and 33%, respectively. Howev er, MANOVA revealed no statistically significant differences in these biomechanical indices of repair of control and experimental tendons. B iochemical assays showed a 32% increase in collagen levels (P < 0.05) and an 11% decrease in mature cross-links in experimental tendons comp ared with that in controls (P > 0.05). Electron microscopy and compute r morphometry revealed no significant differences in the morphometry o f the collagen fibers and no visible differences in the ultrastructure of cellular and matrical components of control and experimental tendo ns. Conclusions: These findings indicate that the combination of laser photostimulation and early mechanical loading of tendons increased co llagen production, with marginal biomechanical effects on repaired ten dons.