Page 47 - Veterinary Laser Therapy in Small Animal Practice

Tissue healing 33

an experiment in which laser treatment was found to 5.3 Muscle healing
restore collagen fiber alignment in damaged tendons
to the point that no significant difference was found Three tissue types of muscle are recognized: skeletal,
between the groups with standard treatment and 5 cardiac, and smooth muscle. The response of these
days of laser application. [140] Better collagen organi- three to LT has been documented, with different aims
zation and functional recovery after LT has also been and fields of application. While the main applications
described in other experimental studies. [141] Animal of LT in skeletal muscle are related to injury recovery
models also show that LT can improve remodeling of and sports medicine, recovery of ischemic infarct is the
the extracellular matrix during the healing process in focus when treating cardiac muscle.
tendons through simultaneous activation of matrix The precursors for skeletal muscle cells are called sat-
metalloproteinase 2 (MMP-2) and stimulation of col- ellite cells, which become activated and differentiated
lagen synthesis. [142, 143] An increase in tenocyte migra- when there is muscle damage. Laser can promote muscle
tion has also been described; the effect is mediated by a repair by increasing the number of myofibers and sat-
protein called dynamin 2. [144] ellite cell survival, proliferation, and differentiation, as
But having said great things about the in vitro and reported both in vitro and in vivo [146, 147] and by having
experimental results with tendons and ligaments, there anti-inflammatory and pro-angiogenic effects. [148] It
really are few clinical studies. One of them evaluated increases the biochemical activity of the muscle, which
the effect of LT on the recovery of digital flexor tendon can be monitored with acetylcholine receptors, cyto-
injuries in humans and found a significant effect on chrome c oxidase expression, and creatine kinase activity.
edema reduction but no effect on analgesia or hand- [63, 149, 150] Also, transplantation of myogenic cells is being
grip strength. [145] Again, a different treatment protocol studied as part of the treatment of injuries with extensive
might find different results, and more clinical trials muscle tissue loss, and their survival and functionality
should be performed to validate – or not – the good seems to improve after being treated with LT. [151]
results obtained in animal models. We still need to find In cardiac muscle, LT has the potential to reduce
out the best way to get light into our bodies in the same infarct size following induction of myocardial infarc-
way that we do in rats and rabbits! tion in rats and dogs. [152] When mesenchymal stem

In a recent double-blinded study on standardized core lesions surgically created in the superficial digital flexor
tendons of horses, some accelerated healing was noticed. Briefly, the recovery from this type of injury is broken
down into two phases: inflammatory and remodeling. These typically manifest themselves firstly with the lesion
getting bigger until about 5 weeks, then secondly turning a corner and starting to gradually decrease in size. In the
study, this exact behavior was confirmed for the control group, as it had been in previous studies using this same
surgical model, with the tipping point of transition from inflammatory to remodeling at week 5. For the laser group,
there were several interesting points.

• The initial slope was significantly greater in the laser group. This means that the inflammatory
process was enhanced (by almost a factor of 2).
• In fact, the tipping point was achieved on average about 2 weeks early in the laser group than in
the control group (again, statistically significant).
• Once the remodeling phase began (2 weeks earlier than in controls), the rate of healing was significantly better
in the laser group than in the controls.
• After that tipping point, the average lesion size in the laser group was lower than in the control group AT EVERY
measurement point EVEN THOUGH it was higher in the laser group at the tipping point.

This represents a supra-natural response rate within the natural structure of tendon healing, which falls very nicely
in line with the fundamental mechanisms of laser. Also worth noting is that this model is a condensed timetable for
the real-world analog (and purposefully so, with almost full healing in 13 weeks, while these injuries usually take
many more months to heal).

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