Laser therapy penetration depth: a near-infrared study on a horse tendon model

M. Monici, A. Gnerucci, T. Falconi, D. Bani, F. Cialdai, F. Fusi, G. Romano
Muscles, Ligaments and Tendons Journal 8 (2):222-228 (2018)

Introduction: Laser therapy is widely used in the management of tendon diseases and injuries, being effective in reducing pain and promoting tissue repair. However, laser transmission properties in the different biological tissues are not completely known. Our aims were: 1) define a method to model and measure the penetration depth (PD), a fundamental optical parameter describing laser transmission in tissues; 2) verify whether PD depends on the tendon type.
Methods: Ex-vivo specimens (horse) were collected from the superficial flexor (SDFT) and suspensory tendons (SL). A dual wavelength near-infrared laser source was used. Laser transmission through tendon samples was measured using an optical bench. The PD was estimated by the Lambert-Beer equation modeling.
Results: PD values are ~0.16 mm for SDFT and ~0.5 mm for SL, respectively, corresponding to a respective power attenuation factor of ~10-3 and ~10-1 mm-1.
Conclusion: Different tendon types show very different PD values. Knowledge of PD allows to quantitatively estimate the light power arriving at any depth in different tissues and biological structures. This methodology is not limited to the tendon case nor to near-infrared sources, allowing for a better understanding of the physical basis of laser therapy, improvement of treatment protocols and dose definition.