This study examined the optimal stimulation duration of transcutaneous electrical nerve stimulation (TENS) for relieving osteoarthritic knee pain and the duration (as measured by half-life) of post-stimulation analgesia.
Thirty-eight patients received either: (i) 20 minutes (TENS20); (ii) 40 minutes (TENS40); (iii) 60 minutes (TENS60) of TENS; or (iv) 60 minutes of placebo TENS (TENS(PL)) 5 days a week for 2 weeks.
A visual analogue scale recorded the magnitude and pain relief period for up to 10 hours after stimulation.
By Day10, a significantly greater cumulative reduction in the visual analogue scale scores was found in the TENS40 (83.40%) and TENS60 (68.37%) groups than in the TENS20 (54.59%) and TENS(PL) (6.14%) groups (p < 0.000), such a group difference was maintained in the 2-week follow-up session (p < 0.000). In terms of the duration of post-stimulation analgesia period, the duration for the TENS40 (256 minutes) and TENS60 (258 minutes) groups was more prolonged than in the other 2 groups (TENS20 = 168 minutes, TENS(PL) = 35 minutes) by Day10 (p < 0.000). However, the TENS40 group produced the longest pain relief period by the follow-up session.
40 minutes is the optimal treatment duration of TENS, in terms of both the magnitude (VAS scores) of pain reduction and the duration of post-stimulation analgesia for knee osetoarthritis.