Influence of Noxious Electrical Stimulation on Chronic Pain From Knee Osteoarthritis

Up to forty-four participants (22 for Aim 1; 22 for Aim 2) with knee OA will be recruited using advertisements, the Legacy Scholars research registry maintained by UNE's Center of Excellence in Aging and Health, from participants with knee OA previously involved in the investigator's research who indicated their willingness to participate in other studies, and from a local orthopedic surgeon group practice. Potential participants will complete a per-participation survey online or by phone that will be used to determine eligibility based on inclusion/exclusion criteria. For Aims 1 and 2, eligible individuals will be asked to defer any plan for knee joint injections until after the testing period. Participants will be asked to refrain from taking any pain medications for at least 4 hours prior to testing. After giving informed consent, individuals who have diabetes will undergo sensory testing to confirm that their sensory detection threshold is no lower than the mean (+ 2 standard deviations) of the detection threshold of healthy older adults which is 1.4 g of force applied by a size 4.17 monofilament. This threshold is based on data collected in our laboratory using the 4-2-1- method of steps. If the individual is unable to perceive 1.4 g stimulus s/he will not continue in the study. Protocol for Aim 1- Data collected for Aim 1 will occur over 4 sessions. The purpose of this aim is to determine the magnitude and duration of the day-to-day effects on clinical pain relief and quantitative sensory tests related to pain after a single NxES treatment. Session 1: In this session we will gain informed consent, then perform a sensory screen (if necessary), collect demographic data and baseline questionnaire data and familiarize participants with the quantitative sensory testing (QST) procedures and to briefly experience the NxES treatment. Session 2: During this session, participants will experience a single treatment with NxES and we will assess changes in pain and function and QST measures before and after the treatment. For the NxES Intervention, a pair of 2x3 inch electrodes will be placed on the medial and lateral sides of the knee. Pulses of electrical current (400 µs biphasic square wave pulses delivered at 50-100 pulses/second; 10-seconds on: 10-seconds off) will be applied for 20 minutes. The amplitude of the current will be increased until the participant rates the pain 50/100 on numeric pain rating scale. Pain intensity and unpleasantness will be assessed every two-min. and amplitude will be increased to maintain the 5/10 pain intensity level during the treatment. QST will be performed immediately after the treatment and 1 hour later. One- to two-minute washout periods will be provided between QST test repetitions and a 20-minute washout period will be provided after the NxES treatment and the post-treatment test of conditioned pain modulation. Sessions 3-4: These sessions will occur 24-hours and 72-hours after session 2 and pain and function along with QST will be performed. Protocol for Aim 2- The purpose of this aim is to determine if there is a cumulative response to NxES treatment on clinical pain and quantitative sensory tests related to pain. Data collected for Aim 2 will begin at least 1-week after the testing for Aim 1 and take place over a 2-week treatment period. Follow-up testing will take place 72-hours and 4-weeks after the last NxES treatment session. Session 1: This session will be used to re-collect baseline questionnaire data and re-familiarize participants with procedures if it has been greater than 2-weeks since participation in Aim 1 or if they declined participation in Aim 1. Session 2: During this session, participants will receive the first NxES treatment and undergo assessment of QST, pain, and function. Session 3-7: These sessions are NxES treatment sessions. Pain and QST assessment will be collected at the beginning of sessions 3,5 \& 7 only. Session 8: No treatments will be performed; post-treatment assessments will occur at 72 hours after session 7. Session 9: No treatments will be performed; post-treatment assessments will be completed 4 weeks after session 7. Sessions 2-7 must be completed within 18 calendar days in order to preserve the fidelity of the intervention dosage.