Substance P immunoreactive fibers of synovial tissue in patients with anterior cruciate ligament injury

Substance P, a neuropeptide, exerts proinflammatory effects and transmits the sensation of pain. Substance P immunoreactive fibers of the synovial tissue were examined to investigate the significance of Substance P in the traumatic joint. Biopsy specimens from 15 patients (eight female and seven male) with anterior cruciate ligament (ACL) injury were examined immunohistochemically with semi-quantitative counting to correlate Substance P positive fibers of the synovial tissue with clinical data, pain intensity on a visual analog scale, and serous inflammatory indicators. The total (sum of the three compartments) expression of Substance P in females of 571.9±255.1 cm⁻² was significantly greater than that of males of 241.2±126.6 cm⁻². In the female group, the total number of Substance P immunoreactive fibers was significantly correlated with pain intensity (r=0.804); in the male group, there was no significant correlation with pain intensity. The expression of Substance P in the female infrapatellar fat pad was statistically significantly correlated with pre- and postoperative erythrocyte sedimentation rate as inflammation indicators. In the male group, there was no such correlation. Substance P was well- correlated with pain and inflammatory reaction in the female joint. Neural inflammation and neural pain occur more strongly in female joints.