Transcutaneous Vagal Stimulation in Knee Osteoarthritis (TRAVKO): Protocol of a Superiority, Outcome Assessor- and Participant-Blind, Randomised Controlled Trial.

Current treatments for knee osteoarthritis (KOA) are partially effective. It is, therefore, necessary to find new strategies that can complement the existing ones. In this scenario, transcutaneous vagal stimulation (TVS) neurophysiological effects could be a helpful solution. However, there is no evidence of the efficacy of TVS in KOA. This trial aims to assess the efficacy of TVS in decreasing pain in participants aged 55 years or older with KOA. A randomised controlled, two-arm, double-blind (participants and outcome assessors) and clinical superiority trial will be conducted for 70 patients with KOA. All the participants will carry out an exercise program. It consists of 12 sessions over four weeks. In addition, they will be randomly assigned to (1) active TVS plus physical exercise or (2) sham TVS plus physical exercise. The application of active TVS consists of electronic stimulation of the auricular concha using a portable device. Sham TVS condition consists of the stimulation of the earlobe that does not cause neurophysiological effects. The primary outcome is the reduction in pain intensity. Additionally, functional capacity, physical performance, pain-related interference, pain-related distress, quality of life in older adults and global change will be measured. Assessments will be conducted at the beginning of the study (baseline), at the end of the intervention and after 1 and 3 months of follow-up. This trial will generate evidence regarding the efficacy of TVS in pain perception in individuals with KOA. This information will serve as an input in the clinical decision-making on the use or non-use of TVS in individuals with KOA. Thus, if the efficacy of TVS is confirmed, a new therapeutic tool may be included in the rehabilitation of individuals with KOA.