Study design
A double-blinded randomized controlled trial was designed for the purposes of this study. During the first visit, participants were screened and randomly allocated into three groups: LLLT with a wavelength of 808 nm, LLLT with a wavelength of 660 nm, and the sham control group with LED red light. The randomization was performed by the researcher (Y.L.Y.) based on the block randomization method. The block size was 3 for 1:1:1 randomization of 3 groups. Three laser machines were set with the parameters and labeled with only numbers 1 to 3 before the experiment started. Thus, both participants and the examiner were blinded to the input settings of all machines. Only the researcher who was in charge of data processing and analysis took responsibility for the setup information. In addition, the same orthopedic surgeon evaluated the K-L radiographic scale grades while the same licensed physical therapist took the responsibility for applying the laser machines and the evaluation and assessment. The study protocol was prospectively registered to ClinicalTrials.gov before the first participant was enrolled. The clinical trial number was NCT04828252 (Trial registered on 03/02/2021 and posted on 02/04/2021). Prior to the data collection, the participants were informed of the full treatment protocol and signed an informed consent approved by the Institutional Review Board (IRB) of National Cheng Kung University Hospital following the declaration of Helsinki. The ethics protocol number was A-ER-109-187.