Distribution of substance-P nerve fibers in intact and ruptured human anterior cruciate ligament: a semi-quantitative immunohistochemical assessment.

Abstract

Numerous studies have reported qualitative and quantitative analysis of nerve supply in the anterior cruciate ligament; however, as yet relatively little is known about the distribution of substance-P nerve endings in the human anterior cruciate ligament. The objective of this work was to evaluate the distribution of substance-P nerve fibers in intact human anterior cruciate ligament, and determine if rupture of the ligament has any influence on occurrence of these receptors. The intact anterior cruciate ligament group (group 1) of osteoarthritis knee, undergoing total knee arthroplasty, consisted of nine patients (eight females) with a mean age of 65.3 years at surgery. The anterior cruciate ligament rupture group (group 2) consisted of 20 patients (18 males and 2 females) with a mean age of 27.8 years at reconstruction. Healing time of the torn ligament in vivo, determined by the time period between the rupture and reconstruction, lasted from 1 to 40 months and the patients were divided into 3 groups (I, II and III) embracing diverse time periods. All harvested anterior cruciate ligaments were sectioned in thirds so that there was a proximal, middle and distal third for each ligament. The distribution of nociceptive receptors was studied by immunohistochemistry with monoclonal antibody to substance-P, including the semi-quantitative assessment. No significant difference was found between the number of substance-P nerve fibers in the proximal, middle and distal third of the intact anterior cruciate ligament (p>0.05). During the first 4 months after injury (group I) the mean number of neuropeptide-containing fibers was greater in the proximal than in the distal third (p=0.048996). The number of SP-positive nerve fibers in the proximal third decreased between 5 and 12 months after rupture, in a statistically significant manner (p=0.045864). This study showed that distribution of the nociceptive nerve supply, positively stained for substance-P, is equal among the intact anterior cruciate ligament. The substance-P nerve ending density was significantly affected by the injury as well as by the time since rupture. The results of this study provide immunohistochemical evidence suggesting that between 1 to 4 months after rupture the site of the injury undergoes neurogenic inflammation, which could have an influence on the healing course of the torn ligament.