Low-Level Laser Therapy and Cryotherapy in Tendinopathy Treatment. Clinical, biological, and biophysical effects of low-level laser therapy alone and in combination with cryotherapy

Abstract

Introduction: Low-level laser therapy (LLLT) and cryotherapy are applied to the human skin to trigger biological actions in the underlying tissue. LLLT modulates biological processes by emitting energy-charged photons to pathological tissue, whereas cryotherapy produces its effect on pathology through the reduction of tissue temperature. When a treatment leads to an unexpected clinical event, the underlying mechanisms involved are often uncertain. This thesis is based upon such a clinical observation, and a reversed translational research approach was used to further investigate the biophysical and biological effects of combining LLLT and cryotherapy in tendinopathy treatment. Aim of Thesis: The overall purpose of this thesis is to investigate the clinical, biophysical, and biological effects of LLLT alone and in combination with cryotherapy for the treatment of tendinopathy. Methods: This thesis consists of three studies. In Study I, a systematic review with metaanalysis was performed to determine the effectiveness of LLLT for shoulder tendinopathy. A structured search for relevant studies up to May 2013 was executed. Two independent assessors rated the included studies according to the Physiotherapy Evidence Database (PEDro) scale. Intervention quality assessments were performed according to World Association for Laser Therapy (WALT) guidelines. The included trials were sub-grouped by intervention quality and the use of other physiotherapy interventions. Study II was a basic in-situ research study of repeated measurements. The optical energy (from two different Class 3B lasers) penetrating the Achilles area of healthy adults was measured before and after 20 minutes of cryotherapy. In Study III, a blinded multiple-armed randomized controlled trial (RCT) design with a post intervention test only was used to investigate the biological effects of LLLT and cryotherapy, both alone and in combination with each other. The study sample comprised in vivo rat Achilles tendons. Results: Optimal LLLT can offer clinically relevant pain relief and initiate a more rapid course of improvement, both alone and in combination with physiotherapy interventions in patients suffering from shoulder tendinopathy. The systematic review identified parallel cryotherapy treatment as a possible confounder to LLLT, as it may induce inhibitory effects and negatively influence treatment outcomes. The penetration of laser energy increased significantly (p<0.01) through Achilles skin and tendons, for both lasers and at all time points, after 20 minutes of cryotherapy. Increased LLLT energy penetration occurred when mean skin temperature was 4.8°C (SD±3.6), resulting in a significant reduction in the Achilles tendon (p=0.03) and skin-tendon-skin thickness (p=0.05). The biological effect of LLLT (3J) one hour after tendon trauma significantly (p<0.05) reduced pro-inflammatory interleukin (IL)- 1ß expression in the presence of the highest median levels of IL-10 (p=0.06) across all treatment groups. Cryotherapy alone failed to reach statistical significance over no treatment for all the targeted cytokines. The parallel treatment of LLLT and cryotherapy produced an anti-inflammatory “add-on” effect and significantly reduced the expression of all targeted cytokines except IL-10. Biomechanical and histology results suggested that the order of therapy administration was essential, showing superior results when LLLT followed cryotherapy. Conclusion: This thesis reveals that the parallel treatment of cryotherapy and LLLT can negatively influence the clinical effects of LLLT in shoulder tendinopathy treatment. The optical properties of healthy skin and tendons are altered by cryotherapy, which significantly increases the penetration of laser energy irradiation. The order of therapy administration determined if a positive or negative biological response in injured rat Achilles tendons occurred.