What Effect Does Light Therapy Have on Tendon Injuries?
I had a patient ask me this week about what effect light therapy – or photobiomodulation (PBM) – has on tendon injuries and I didn’t have a great answer… but now I do! In particular, this patient has a low-grade tear in her high (proximal) hamstring that has still been bothering her after a couple months of therapy. Let’s dive in.
What is Photobiomodulation?
When broken down, PBM simply refers to the use of specific wavelengths of light to modulate biological processes within the body. The most popular natural example of this is vitamin D synthesis: when UV light from the sun hits the skin, it converts specific cholesterol compounds into vitamin D3. In medicine, the most common form of PBM is a laser, with some clinics beginning to adopt the use of LED systems as well. These devices emit red and/or infrared frequencies of light, which have specific effects on the tissues within the body.
How Does Photobiomodulation Impact Tendon Healing?
The most widely recognized effect of PBM is that it increases the amount of adenosine triphosphate (ATP) in the tissues being stimulated. ATP is the energy “currency” of the body and is required for essentially all bodily functions. ATP is created primarily by the mitochondria inside of cells, and PBM acts as a catalyst for ATP production by activating one of the enzymes (cytochrome c oxidase) that makes the process work. Since this process occurs in every part of the body, the utility of PBM can be applied to almost any region, including tendons.
In the case of tendon tears, the injured tissue requires an enormous amount of energy initially in order to remove the damaged cells and create new ones. Later in the injury process, once most of the new tissue has been created, the energy demands of the tendon and surrounding tissues are much less. Based on this framework, laser therapy will likely be much more effective in the early stages of recovery. In later stages, placing graduated stress on the tendon as it is capable of withstanding increased stresses will be more effective.
What Does the Research Say?
Most of the research on PBM for tendon injuries has been done on rats, since the organic occurrence of tendon injuries in humans is relatively low and it is unethical to cut people’s hamstring tendons. One study found that rats with tendon injuries that were treated with PBM exhibited substantially higher ratios of type I collagen vs. type III collagen compared to the control group. This is a good sign, because type I collagen is the type of collagen that gives tendons their strength, whereas type III collagen is the precursor to type I collagen and is less strong. This finding lines up with the theory outlined above, which is that PBM provides tendons with more energy, allowing it to heal and produce the most optimal type of collagen faster.
Another study on rats found that tendons treated with PBM exhibited increased resistance to load compared to the control group. Interestingly, this finding was only found in female rats; there may be some underlying factor that caused this result, or it could just be due to chance. If this finding can be translated to humans, then it would indicate that PBM can be helpful after tendon injuries, in order to improve the resistance of the tendon to stress during the healing process.
I found a couple of studies that examined the use of PBM on tendon injuries in humans, but they were mixed and not of great quality. One study I will share found no difference between time to return to sport between athletes with hamstring injuries that received PBM vs. sham therapy. This could be due to the small number of participants included in the study (11 in each group), meaning that a meaningful difference could have been missed.
Summary
PBM works by increasing the energy production abilities of the mitochondria within cells, which increases the rate at which healing can occur. The majority of the energy needs of a damaged tendon occur early in the repair process, indicating that PBM is likely more effective in the early stages of recovery vs. the later stages. While there is not much research on the use of PBM for tendon injuries in humans, the research in animals indicates PBM likely improves the rate of healing of tendons if used in the first week after the injury.
Western Slope Rehab and Performance is Here to Help
If you are struggling with injuries or have recently been in a motor vehicle accident, we can help. We are a physical therapy company that provides home-based orthopedic services in the Grand Junction, CO, area, as well as telehealth appointments throughout Colorado. If you would like to schedule a free consultation, you can call us as 970-462-9177, or fill out our contact form here.
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