OBJECTIVE: 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. SUBJECTS: 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. METHODS: A visual analogue scale recorded the magnitude and pain relief period for up to 10 hours after stimulation. RESULTS: By day 10, 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 followup 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 day 10 (p < 0.000). However, the TENS40 group produced the longest pain relief period by the follow-up session. CONCLUSION: 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.

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