Inadequate pain control after total knee replacement (TKR) is associated with poor functional recovery, increased length of stay, and development of new chronic pain in older adults. Current methods are inadequate for controlling the severe pain experienced during post-op physical therapy. Pain control treatments that address movement-evoked pain during recovery need to be investigated. The primary purpose of this study is to test the effect of intermittent, intense (high amplitude) transcutaneous electrical nerve stimulation (TENS), applied as a supplement to current pharmacologic therapy during recovery activities, on postoperative hyperalgesia, pain with movement, active flexion, and walking function after TKR. A secondary purpose is to validate the proposed model by exploring the pathways through which predictor variables influence postoperative hyperalgesia and movement-evoked pain, and development of chronic pain after TKR. A prospective, randomized, experimental design will be used to compare the effect of active TENS, placebo TENS, and analgesia alone in 321 patients with osteoarthritis scheduled to have a TKR. It is hypothesized is that older adults who receive intermittent, intense TENS during exercise sessions for 6 weeks after TKR will have significantly less movement-evoked pain, less postoperative hyperalgesia, greater active flexion, and increased walking function than those who receive placebo TENS or no TENS therapy. The intervention is not expected to significantly influence pain at rest. This study is the next phase in an overall program of research on the use of non-pharmacologic interventions as a supplement to pharmacologic strategies to improve pain control with movement, enhance function, and prevent the development of new chronic pain syndromes. This project is innovative because it distinguishes pain with movement (the type of pain largely uncontrolled with current pain treatments) from pain at rest and targets the effect of TENS on pain with movement after surgery. This study also translates bench (animal model) science to human subjects by testing the effect of TENS on hyperalgesia. Management of pain with movement during the post-operative period is critical to return of function and avoidance of additional sources of chronic pain in older adults. By improving functional status, older adults can retain independence and possibly reduce their health care utilization and costs.
