Transcutaneous electrical nerve stimulation in experimental acute arthritis

Transcutaneous electrical nerve stimulation (TENS) is applied for the relief of various types of pain, including rheumatoid arthritis and osteoarthritis. This study evaluated the influence of TENS on intraarticular (IA) temperature and pressure and synovial tissue of inflamed rabbit joints. Four hours after induction of acute bilateral hind joint arthritis by single intraarticular injection of urate crystals, the knees of 14 anesthetized rabbits were fixed at 90° between femur and tibia. TENS was supplied from an electrical stimulator to the left knee joint while the other joint was unstimulated as a control. A microprobe needle for temperature measurement was inserted into the knee joint. Intraarticular pressure was recorded by polygraph connected to an IA needle. Readings were carried out at 10-min intervals three times before and four times after 5min of TENS. A significant increase in IA temperature from mean 36.2C to 36.6C and significant reduction of IA pressure (mean decrease of 0.8mmHg, from 2.5mmHg to 1.7mmHg) were found in the stimulated joints, which also showed a reduction of synovial fluid volume and total leukocyte count in comparison to the controls. While the nonstimulated synovial membrane showed massive leukocytic infiltration with neutrophilic exudate and fibrin clot in the intraarticular cavity, the stimulated synovial membrane demonstrated moderate homogeneous leukocytic infiltration through all layers, with absence of inflammatory exudate in the intraarticular cavity. These results suggested that the analgesic effect of TENS on arthritis may be partially attributed to decrease in IA synovial fluid pressure, volume, and leukocyte count. Therefore, TENS may be useful for reducing pain from inflammatory arthritis.