PAM Light & Laser Therapy 2 — Questions and Answers
Question 1: Which laser classification (Class) is most commonly used in clinical low-level laser therapy (LLLT) for musculoskeletal conditions?
- Class 1
- Class 2
- Class 3B (Correct answer)
- Class 4
Correct answer: Class 3B
Class 3B lasers (1–500 mW) are the most common for clinical LLLT, delivering therapeutic doses without the tissue ablation risk of Class 4.
Question 2: A patient with rheumatoid arthritis is referred for photobiomodulation. Which wavelength range is MOST appropriate to penetrate synovial tissue effectively?
- 200–280 nm (UVC)
- 320–400 nm (UVA)
- 600–700 nm (red visible)
- 780–1000 nm (near-infrared) (Correct answer)
Correct answer: 780–1000 nm (near-infrared)
Near-infrared wavelengths (780–1000 nm) penetrate deepest into tissue, reaching synovial structures up to several centimeters below the skin.
Question 3: The Arndt-Schulz law applied to laser therapy states that:
- Higher doses always produce greater therapeutic effects
- Weak stimuli excite, optimal stimuli enhance, and excessive stimuli inhibit biological activity (Correct answer)
- Laser energy is inversely proportional to wavelength
- Coherent light is required for all photochemical reactions
Correct answer: Weak stimuli excite, optimal stimuli enhance, and excessive stimuli inhibit biological activity
The Arndt-Schulz law describes a biphasic dose-response where sub-threshold stimuli are ineffective, optimal doses stimulate, and excessive doses inhibit.
Question 4: Which property distinguishes laser light from ordinary light produced by a lamp?
- Higher frequency
- Monochromaticity, coherence, and collimation (Correct answer)
- Infrared emission only
- Pulsed output only
Correct answer: Monochromaticity, coherence, and collimation
Laser light is uniquely monochromatic (single wavelength), coherent (waves in phase), and collimated (parallel beams), unlike broadband lamp emissions.
Question 5: When applying low-level laser therapy over a superficial skin wound, the recommended application technique is:
- Scanning the beam rapidly across the entire wound bed
- Contact or near-contact stationary probe placement at grid points (Correct answer)
- Submerging the wound in water and applying laser through the medium
- Applying the probe at a 45-degree angle to maximize scatter
Correct answer: Contact or near-contact stationary probe placement at grid points
Grid-point contact or near-contact application ensures consistent dosing across the wound area and maximizes energy delivery to target tissue.
Question 6: Photobiomodulation therapy is contraindicated directly over which anatomical area due to potential systemic hormonal effects?
- The knee joint
- The thyroid gland (Correct answer)
- The lumbar paraspinals
- The plantar fascia
Correct answer: The thyroid gland
Direct laser application over the thyroid gland is contraindicated because photobiomodulation may alter thyroid hormone synthesis and release.
Question 7: A physical therapist is treating a patient with delayed wound healing using LLLT. Which cellular target is primarily responsible for the photobiomodulation effect?
- Sodium-potassium ATPase pump
- Cytochrome c oxidase in the mitochondrial respiratory chain (Correct answer)
- Collagen cross-links in the extracellular matrix
- Calcium channels in the sarcoplasmic reticulum
Correct answer: Cytochrome c oxidase in the mitochondrial respiratory chain
Cytochrome c oxidase is the primary photoacceptor in mitochondria, absorbing photons to upregulate ATP production and cellular metabolism.
PAM Light & Laser Therapy 2
Which laser classification (Class) is most commonly used in clinical low-level laser therapy (LLLT) for musculoskeletal conditions?