Carol GT Vance,
The purpose of this study was to test the hypothesis that TENS reduces primary hyperalgesia of the knee induced by joint inflammation. 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). 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. The authors conclude that the results 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.
Physical Therapy, Vol. 87, No. 1, January 2007, pp. 44-51