Background: There is a high prevalence of chronic pain in the US, with nearly half of adults experiencing chronic pain. Chronic pain is associated with impaired mobility, specifically ambulation. Treatment for chronic knee pain is complex given that pain is not only due to peripheral sources, but also due to alterations of the central nervous system (CNS). Majority of physical therapy (PT) interventions involve a bottom-up approach targeting the peripheral pain sources and many patients (\ 66%) do not respond to this treatment approach. Noninvasive brain stimulation techniques such as transcranial direct current stimulation (tDCS) is a novel and promising option for a top-down intervention that can have neuromodulatory effects on the CNS and may better target central factors associated with chronic pain. Purpose: To determine if tDCS delivered to the primary motor cortex in conjunction with individualized PT will result in greater improvements in pain and function compared to sham tDCS with individualized PT in individuals with chronic knee pain.

Methods: This study will be performed at outpatient PT clinics at the University of Illinois Hospital. Eligible participants will include patients with chronic knee pain (duration \> 3 months) who have not undergone surgery to this area and are scheduled to receive formal PT intervention. Subjects will be randomized to the active tDCS + PT group or sham tDCS + PT group and will receive the intervention for 8 sessions. Outcomes include pain ratings, pressure pain thresholds, patient specific functional scale, lower extremity functional scale, quadriceps strength, knee range of motion, 2-minute walk test, 5 time sit to stand, patient health questionnaire-2, and Central Sensitization Inventory. Impact: The use of adjuvant therapies such as tDCS have the potential to optimize rehabilitation treatment for individuals with chronic pain by offering a more comprehensive treatment that targets peripheral and central sources of pain.