This study assessed the effectiveness of TENS in decreasing pain and hyperalgesia and increasing function following total knee arthroplasty (TKA). We hypothesized participants using TENS during rehabilitation exercises would: 1) report significantly lower pain during range-of-motion (ROM) and fast walking but not at rest; 2) have less hyperalgesia; and, 3) have better function than participants receiving Placebo-TENS or Standard Care. The researchers also hypothesized that change in ROM pain would vary based on psychological characteristics (trait anxiety, pain catastrophizing and depression) and treatment group. This prospective, randomized study used intent-to-treat analyses on 317 subjects after primary, unilateral TKA. Assessors, blinded to treatment allocation, measured pain, function (ROM and gait speed), and hyperalgesia (quantitative sensory tests) postoperatively and 6 weeks after surgery. Analgesic intake, anxiety, depression, and pain catastrophizing were also assessed. TENS participants used it 1-2 times/day at 42 mA (on average) and had less pain postoperatively during active knee extension (p=0.019) and fast walking (p=0.006) than Standard Care participants. TENS and Placebo-TENS were not significantly different. TENS participants who scored low on anxiety and pain catastrophizing had a greater decrease in ROM pain at 6 weeks than those scoring high on these factors (p=0.002 and 0.03). Both TENS and Placebo-TENS participants had less postoperative mechanical hyperalgesia (p=0.03 – 0.01) than Standard Care participants.
Supplementing pharmacologic analgesia with TENS during rehabilitation exercises reduces movement pain postoperatively but a placebo influence exists and the effect has dissipated by 6 weeks. Patients with low anxiety and pain catastrophizing may benefit most from TENS.