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Transcutaneous Electrical Nerve Stimulation at Both High and Low Frequencies Reduces Primary Hyperalgesia in Rats With Joint Inflammation in a Time-Dependent Manner

CGT Vance, PT, MA, is Associate, Graduate Program in Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, Iowa
R Radhakrishnan, PhD, was Research Investigator, Pain Research Program and Graduate Program in Physical Therapy and Rehabilitation Science, University of Iowa, at the time of the study. He is currently affiliated with the College of Pharmacy, Western University of Health Sciences, Pomona, Calif
DA Skyba, DC, PhD, is Assistant Professor of Neuroscience, Department of Basic Sciences, Palmer College–Florida, Port Orange, Fla
KA Sluka, PT, PhD, is Professor, Pain Research Program and Graduate Program in Physical Therapy and Rehabilitation Science, 1-252 MEB, University of Iowa, Iowa City, IA 52242 (USA)

Address all correspondence to Dr Sluka at: kathleen-sluka{at}uiowa.edu

Background and Purpose: Clinical studies of transcutaneous electrical nerve stimulation (TENS) have used a variety of outcome measures to assess its effectiveness, with conflicting results. It is possible that TENS is effective on some measures of pain and not on others. The purpose of this study was to test the hypothesis that TENS reduces primary hyperalgesia of the knee induced by joint inflammation.

Subjects: Male Sprague-Dawley rats were used in this study.

Methods: Inflammation of the knee joint was induced by intra-articular injection of a mixture of 3% kaolin and 3% carrageenan. Primary hyperalgesia was measured as the compression withdrawal threshold of the knee joint before and after the induction of inflammation (4 hours, 24 hours, and 2 weeks) and after sham TENS treatment, treatment with high-frequency TENS (100 Hz), or treatment with low-frequency TENS (4 Hz).

Results: The compression withdrawal threshold was significantly reduced at 4 hours, 24 hours, and 2 weeks after the induction of inflammation. Either high-frequency TENS or low-frequency TENS completely reversed the compression withdrawal threshold when applied at 24 hours or 2 weeks after the induction of inflammation but not when applied at 4 hours after the induction of inflammation.

Discussion and Conclusion: These data suggest that TENS inhibits primary hyperalgesia associated with inflammation in a time-dependent manner after inflammation has already developed during both acute and chronic stages.