Inadequate pain control after total knee replacement (TKR) is associated with poor functional recovery and the development of new chronic pain syndromes in older adults. Current methods are inadequate for controlling the severe pain experienced during postoperative physical therapy. This project is the next phase in an overall program of research on the use of balanced non-pharmacologic and pharmacologic strategies to improve movement-evoked pain and enhance function. This application fits with the NINR Strategic Plan's Area of Research Emphasis, Promoting Health and Preventing Disease, by evaluating a new approach to transcutaneous electrical nerve stimulation (TENS) therapy to decrease pain, improve function, and prevent the development of new chronic pain syndromes in older adults after TKR.
The aims of this study are to: 1) test the efficacy of intermittent, intense (high amplitude) TENS, applied intermittently as a supplement to current pharmacologic therapy during recovery activities, on postoperative hyperalgesia (i.e. pain sensitization) and movement-evoked pain after TKR;2) determine the effect of pain intensity on function and the development of new chronic pain syndromes after TKR;and 3) validate the proposed model by exploring the pathways through which predictor variables influence postoperative hyperalgesia, movement-evoked pain, and function. A prospective, randomized, experimental design will be used to compare the efficacy of active TENS to placebo TENS and standard care in 321 patients (106 per group). TENS will be used during exercise sessions for 6 weeks after TKR. Hyperalgesia will be measured using quantitative sensory testing, pain intensity using a verbal 0-20 numeric rating scale, function using active flexion and the Iowa Gait Test, and chronic pain syndrome using the Brief Pain Inventory. Multiple subject characteristics, surgical variables, and rehabilitation variables will be measured and controlled for in the GEE analyses. It is hypothesized that TENS decreases pain with movement by reducing hyperalgesia. Minimizing the severe pain experienced during required activities in the immediate postoperative period will improve functional recovery and prevent the development of new chronic pain syndromes. Innovative aspects of this project are that it distinguishes pain with movement (the type of pain largely uncontrolled with current pain treatments) from pain at rest and uses a new TENS approach to target movement-evoked pain after surgery. This study translates bench (animal model) science to human subjects by testing the effect of TENS on hyperalgesia. Management of pain after knee surgery is critical to return of function and avoiding the development of new chronic pain syndromes in older adults. By improving functional status, older adults can retain independence and possibly reduce their health care utilization and costs. Management of pain after knee surgery is critical to return of function and avoiding the development of new chronic pain syndromes in older adults. By improving functional status, older adults can retain independence and possibly reduce their health care utilization and costs.
