Types of Lasers, Mechanisms of Action, Indications, Contraindications, and Parameter Settings

Introduction

Laser therapy, also known as low-level laser therapy (LLLT) or photobiomodulation therapy (PBMT), is an advanced therapeutic modality widely used in physiotherapy to promote healing, reduce pain, and improve tissue function. It uses light to stimulate cellular processes that contribute to tissue regeneration, pain relief, and inflammation reduction. The effectiveness of laser therapy depends on factors such as the type of laser used, the intensity, wavelength, and the treatment parameters applied. This article provides a comprehensive overview of the different types of lasers, the mechanisms behind their therapeutic action, clinical indications and contraindications, and optimal parameter settings for wound healing and pain relief.

Types of Lasers in Physiotherapy

Laser therapy can be classified into low-level lasers (LLLT) and high-power lasers (HPL) based on their output power and the applications they are used for.

1. Low-Level Lasers (LLLT)

Low-level lasers typically operate at lower power outputs (usually in the milliwatt range, <500 mW) and are primarily used for therapeutic purposes. These lasers are non-thermal and do not cause tissue damage when used appropriately.

Characteristics of LLLT:

Power Output: <500 mW (usually in the range of 5-500 mW).
Wavelength Range: Typically between 600 nm and 1000 nm (red and near-infrared).
Tissue Penetration: Due to the lower power output, LLLT has limited penetration but is effective for treating superficial tissues such as the skin, muscles, and joints.

Common Uses: LLLT is used for pain relief, reduction of inflammation, wound healing, and soft tissue injury recovery. It is frequently used in conditions such as tendinitis, muscle strains, ligament sprains, and wound healing.

2. High-Power Lasers (HPL)

High-power lasers, also known as Class IV lasers, have higher power outputs (usually above 500 mW) and are capable of deeper tissue penetration. These lasers are used for more intense therapeutic effects and can stimulate a wider range of biological processes due to their higher energy levels.

Characteristics of HPL:

Power Output: >500 mW, often in the range of 1-10 W.
Wavelength Range: Similar to LLLT, HPL lasers also operate in the red to near-infrared spectrum (600-1000 nm), although some HPL devices use other wavelengths for specialized treatments.
Tissue Penetration: HPL lasers penetrate deeper into tissues compared to LLLT, making them effective for treating deeper muscle layers, joint capsules, and subcutaneous tissue.

Common Uses: High-power lasers are typically used in cases where deeper penetration is required, such as in the treatment of chronic pain conditions, deep musculoskeletal injuries, and joint disorders. They are also used in post-surgical rehabilitation for tissue regeneration.

Mechanisms of Action of Laser Therapy

Laser therapy works primarily through the process of photobiomodulation (PBM), where light is absorbed by tissues and converts into biochemical energy, triggering various cellular responses. The effects of laser therapy are non-thermal, meaning they do not rely on heat to produce their therapeutic effects.

1. Cellular Effects

When light from a laser is absorbed by tissue, it penetrates the skin and is absorbed by mitochondria in the cells, specifically by the enzyme cytochrome c oxidase. This process leads to increased adenosine triphosphate (ATP) production, which is the primary energy source for cells.

Increased ATP Production: ATP is necessary for cellular functions like protein synthesis, cell division, and cellular repair. Increased ATP enhances the efficiency of metabolic processes involved in healing.
Stimulation of Collagen Synthesis: Laser light stimulates fibroblasts to produce collagen, an essential component of tissue repair and wound healing. This is particularly beneficial in the healing of soft tissue injuries and skin wounds.
Increase in Nitric Oxide (NO): Laser therapy promotes the release of nitric oxide, a vasodilator, which improves blood circulation and oxygen delivery to tissues. This results in enhanced nutrient and waste removal, which accelerates healing.

2. Pain Relief Mechanisms

Endorphin Release: Laser therapy can stimulate the release of endorphins, which are natural painkillers produced by the body. Endorphins interact with opioid receptors in the brain and spinal cord to reduce pain perception.
Reduction of Inflammatory Mediators: Laser therapy can inhibit the production of pro-inflammatory cytokines and prostaglandins, which are responsible for pain and inflammation in conditions such as arthritis or acute soft tissue injuries.
Nerve Function Modulation: Low-level lasers can influence nerve function by reducing the sensitivity of nerve endings to noxious stimuli, leading to pain reduction.

3. Tissue Healing and Regeneration

Enhanced Blood Flow: Laser therapy promotes vasodilation (widening of blood vessels), increasing local blood circulation and oxygen delivery to tissues, which accelerates the healing process.
Reduction of Edema: By improving circulation and lymphatic drainage, laser therapy reduces swelling and edema in injured tissues, aiding in faster recovery.
Cellular Proliferation: Laser therapy stimulates the proliferation of cells involved in tissue repair, such as fibroblasts, endothelial cells, and keratinocytes. This is essential for wound healing and the repair of injured soft tissues.

Indications for Laser Therapy

Laser therapy has a wide range of applications in physiotherapy, particularly for musculoskeletal and soft tissue injuries. Below are the key indications:

1. Pain and Inflammation Management

Acute and Chronic Pain: Laser therapy is widely used for the management of pain, including conditions such as low back pain, neck pain, and joint pain.
Inflammatory Conditions: Laser therapy is effective in reducing inflammation associated with conditions like tendinitis, bursitis, arthritis, and fibromyalgia.
Musculoskeletal Injuries: Laser therapy can be used for sprains, strains, and ligament injuries to reduce pain, inflammation, and swelling, and to accelerate tissue healing.

2. Wound Healing

Chronic Wounds: Laser therapy is beneficial for chronic wounds such as diabetic ulcers, pressure sores, and venous ulcers. It stimulates cellular repair mechanisms and accelerates healing.
Post-Surgical Wound Healing: After surgical procedures, laser therapy can enhance tissue repair, reduce scar tissue formation, and improve the cosmetic appearance of surgical scars.
Burns and Abrasions: Laser therapy can be used in the healing of burns and superficial skin injuries by promoting faster tissue regeneration and reducing the risk of infection.

3. Soft Tissue and Joint Disorders

Tendonitis and Tendinopathy: Laser therapy is effective in treating tendon-related injuries, such as tennis elbow, Achilles tendonitis, and patellar tendinopathy, by reducing inflammation and stimulating collagen synthesis.
Muscle Strains and Ligament Sprains: The modality accelerates the healing process by promoting cell regeneration, collagen formation, and enhancing circulation.
Osteoarthritis: Laser therapy can help reduce pain and stiffness in the joints, improving mobility and function in patients with osteoarthritis, particularly in the knee, hip, and shoulder joints.

4. Neurological Conditions

Nerve Regeneration: Laser therapy has been shown to assist in the regeneration of damaged nerves, particularly in conditions like diabetic neuropathy or post-surgical nerve injuries.
Carpal Tunnel Syndrome: Low-level lasers can help reduce pain, inflammation, and swelling in patients with carpal tunnel syndrome, promoting faster recovery.

Contraindications for Laser Therapy

While laser therapy is generally safe, certain conditions may contraindicate its use or require precautions. The following are absolute and relative contraindications:

1. Absolute Contraindications

Pregnancy: Laser therapy should not be applied over the abdomen or pelvic region during pregnancy due to the potential risks to fetal development.
Malignancy: Lasers should not be used over areas of malignant tumors as they may promote tumor growth.
Photosensitivity: Patients who have photosensitivity or are taking medications that cause sensitivity to light (e.g., some antibiotics or chemotherapy drugs) should not undergo laser therapy.
Active Bleeding: Laser therapy should be avoided in areas with active bleeding or hemorrhage, as the increased circulation may exacerbate bleeding.

2. Relative Contraindications

Over the Eyes: Direct application of laser therapy over the eyes should be avoided, especially with high-power lasers, to prevent potential retinal damage.
Over the Thyroid Gland: Caution should be exercised when applying lasers over the thyroid gland, particularly in patients with thyroid conditions.
Over Pacemakers or Implanted Devices: Lasers should not be applied over areas with implanted electrical devices like pacemakers, as the electromagnetic fields could potentially interfere with their operation.

Parameter Settings for Laser Therapy

The effectiveness of laser therapy depends on selecting appropriate parameters, including wavelength, power, energy density (fluence), and treatment duration.

1. Wavelength

Red (600-700 nm): Ideal for superficial conditions, such as skin wounds and surface inflammation.
Near-Infrared (700-1000 nm): Best for deeper tissue penetration, useful in treating musculoskeletal injuries, joint pain, and deep tissue wounds.

2. Power Output

Low-Level Lasers: Power output typically ranges from 5-500 mW. For most musculoskeletal injuries, a typical power output is around 100-300 mW.
High-Power Lasers: Power output ranges from 1-10 W. These are used for deep tissues and larger areas.

3. Energy Density (Fluence)

Energy density is typically measured in J/cm² (joules per square centimeter). The optimal fluence depends on the condition being treated:

Wound Healing: 1-4 J/cm² is effective for promoting cell regeneration.
Pain and Inflammation: 3-6 J/cm² is typically used for reducing pain and inflammation in soft tissue injuries.

4. Treatment Duration

Treatment duration varies depending on the power output and the condition being treated:

Superficial Conditions: 3-5 minutes.
Deeper Conditions: 8-10 minutes, particularly with high-power lasers.

Conclusion

Laser therapy, including both low-level and high-power lasers, is a highly effective and non-invasive treatment modality that has proven benefits in treating a wide variety of musculoskeletal and soft tissue conditions. By understanding the types of lasers, the mechanisms of action, clinical indications and contraindications, and proper parameter settings, physiotherapists can optimize the use of laser therapy for pain relief, tissue healing, and rehabilitation.

References

Chow, R. T., Armati, P. J., & O’Brien, T. A. (2009). Low-Level Laser Therapy: A Practical Introduction. Springer.
Hamblin, M. R., & Demidova, T. N. (2006). Laser Therapy: Photobiomodulation and the Biochemical Effects of Low-Level Laser Therapy. Journal of Photochemistry and Photobiology B: Biology, 85(3), 160-168.
Beams, K. (2014). The Role of Laser Therapy in Pain Management. Physiotherapy Journal, 100(3), 245-251.
Simao, T. F., & Leal, J. P. (2017). The Effects of Laser Therapy in Wound Healing: A Review. European Journal of Physiotherapy, 19(4), 223-229.
Bensoussan, L., & Yip, J. (2012). Laser Therapy for Musculoskeletal Disorders: A Review of Current Evidence. Physiotherapy Research International, 17(3), 171-179.