Innervation of nociceptors in the menisci of the knee joint: an immunohistochemical study

Using histology, we studied the innervation of nociceptors in the medial an d lateral menisci of the knee joint. Specimens examined were taken from 16 patients during arthroplasty. The patients were 6 men and 10 women, with ag es ranging from 14 to 76 years (mean 56 years). Immunohistochemistry with t he unlabeled antibody biotin-streptavidin method was employed to detect pro tein gene product 9.5 (PGP 9.5) or substance P (SP) in the specimen. The an tibody for PGP 9.5 detected nerve tissues in the menisci, Most but not all of the nerve fibers were associated with blood vessels. Nerve fibers and se nsory receptors were found mainly in the peripheral, vascular zone, represe nting the outer one-third of the meniscus, and the innervated area was wide r in the anterior and posterior hems. Pacinian and Ruffini corpuscles as we ll as free nerve endings were identified in these areas. Larger fibers cour sed circumferentially in the peripheral zone, with smaller branches of nerv e fibers running radially into the meniscus. Nerve fibers positive for SP w ere also detected in the menisci, but were fewer in number. Their branches also were fewer, oriented radially and paralleling blood vessels. This stud y showed that some of the pain in cases of meniscal tear could originate in the meniscus itself, especially with peripheral tears that may be accompan ied by bleeding.