The Effects of High-Intensity Laser Therapy vs. Low-Level Laser Therapy on Functional Ability and Quadriceps Architecture in Patients with Knee Osteoarthritis: A Single-Blinded Randomized Clinical Trial

<b>Introduction:</b> This study aimed to compare the effects of high-intensity laser therapy (HILT) and low-level laser therapy (LLLT) on the disability and architecture of the quadriceps in patients with knee osteoarthritis (OA). <b>Methods:</b> Ninety-eight patients with knee OA (KOA) were selected by convenience sampling and then divided into three groups: control, LLLT and HILT. Disability was determined using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Quadriceps structures including thickness, fascicle length and pennate angle of the vastus lateralis (VL) and thickness, volume and fiber angle of vastus medialis obliquus (VMO) muscles were assessed using ultrasonography. All evaluations were performed before interventions, immediately after interventions, and one month later. Between-group data were analyzed with two-way ANOVA and paired-samples t-test. <b>Results:</b> The within-group comparisons of WOMAC scores before, after and at a one-month follow-up showed significant differences between the groups (<i>P</i><0.001). The VMO thickness revealed significant increases after the treatment in both HILT (<i>P</i><0.001) and LLLT (<i>P</i>=00.03) groups. The between-group comparison revealed a significantly lower score of WOMAC in the HILT group compared to the other groups after a one-month follow-up (<i>P</i>=00.03). VMO thickness showed a significant increase in the HILT group after the treatment (<i>P</i>=0.002). The VL structures and VMO fiber angle and volume did not exhibit significant changes in within-group and between-group comparisons (<i>P</i>>00.05). <b>Conclusion:</b> Both HILT and LLLT may improve functional ability and VMO thickness in patients with knee osteoarthritis. After a one-month follow-up, functional ability was greater in the HILT group.