taVNS in Veterans With Knee OA (AVAHCS)

Inclusion Criteria: * Clinical diagnosis of knee osteoarthritis according to the American College of Rheumatology (ACR) criteria, confirmed by radiologic evidence of the same. * Moderate to severe knee pain, as assessed by the Defense Veterans Pain Rating Scale (DVPRS), a validated pain scale (score ≥4) * Willingness to discontinue current knee osteoarthritis (OA) pain medications (except permitted rescue medication such as acetaminophen/paracetamol) during the trial * Ability to provide informed consent and comply with all study procedures * Ambulatory and able to attend all study visits Exclusion Criteria: * History or evidence of inflammatory joint disease (e.g., rheumatoid arthritis, spondyloarthropathy), secondary or metabolic causes of arthritis, or significant trauma to the knee within 3 months prior to screening * Recent or planned major knee surgery on the index knee (arthroplasty or arthroscopy within 6 months) * Received intra-articular corticosteroid or hyaluronic acid injections in the index knee within 12 weeks prior to screening, or systemic corticosteroids within 30 days * Contraindications to transcutaneous auricular vagus nerve stimulation (taVNS), such as: * Metal implants above the neck * Active ear infection, recent ear trauma, or chronic ear/facial pain * Prior vagus nerve surgery (including vagotomy) or ongoing vagus nerve stimulation (VNS) therapy for another condition * Severe comorbidities (e.g., uncontrolled liver/kidney disease, active malignancy, uncontrolled hypertension or cardiovascular disease, uncontrolled diabetes with neuropathy) * Participation in another interventional clinical trial within the past 2 months * Inability to provide informed consent or comply with protocol requirements (e.g., significant cognitive impairment) * Any unstable or severe psychiatric disorder that, in the investigator's opinion, would compromise safety or compliance