Study designs of evaluations included in the review
Randomised controlled trials (RCTs) were eligible for inclusion in the review. Both parallel and crossover design studies were included in the review.
Specific interventions included in the review
Studies that compared any form of ENS with placebo for any duration were eligible for inclusion. Studies could combine ENS with other treatments if the same concomitant treatment was given to all treatment groups or the patient controlled the amount of the concomitant treatment. Studies that compared ENS with a potentially active control treatment or a control of unknown effectiveness were excluded. The included studies used the following forms of ENS: high-, low- and variable-frequency transcutaneous nerve stimulation (TENS), acupuncture-like TENS, and high-, low- and variable-frequency percutaneous electrical nerve stimulation (PENS).
Participants included in the review
Studies of individuals with chronic musculoskeletal pain at any site, of at least 3 months' duration, were eligible for inclusion in the review.
Outcomes assessed in the review
Studies that measured pain at rest were eligible for inclusion. Eligible studies were required to assess pain either at baseline and following treatment or as a single measure of degree of pain relief following treatment. All scales assessing pain were eligible for inclusion. Studies assessing only load bearing, joint mobility or other indirect aspects of pain relief were excluded from the review.
How were decisions on the relevance of primary studies made?
Two reviewers independently assessed studies for inclusion in the review