Substance-P in symptomatic mediopatellar plica as a predictor of patellofemoral pain

The present study aimed to investigate the expression of a neuropeptide of symptomatic mediopatellar plica (MP) to prove that there was a significant correlation between the expression of substance-P (SP) in MP and patellofemoral pain. The specimens of synovial plica were obtained by knee arthroscopy. Semi-quantitative analysis was used to investigate the expression of SP, and compared the innervation density of SP among the three groups: Blank control (asymptomatic plica), positive control (symptomatic plica with other injuries) and experimental (symptomatic plica without other injuries) groups by the paired t-test, one-way analysis of variance and Student-Newman-Keuls test in 60 patients. The expression levels of SP nerve fibers in the superior plica were 24.60±26.17, 117.36±73.62 and 59.06±44.06 in the blank control, positive control and experimental groups, respectively. The density of nerve fibers in medial plica was 23.23±18.41 in the blank control group, 268.00±71.60 in the positive control group and 255.44±87.91 in the experimental group. The density of nerve fibers of MP was higher compared to that of the superior plica. The density was highest in the positive control group, and lowest in the blank control group in MP. There was a close correlation between the density of SP expression and the degree of patellofemoral pain. The SP expression intensity has an important role in the incidence of patellofemoral pain and is responsible for the pathogenesis of symptomatic MP.