Immunohistochemical analysis of mechanoreceptors in the human posterior cruciate ligament - A demonstration of its proprioceptive role and clinical relevance

Although long-term studies report successful results with total knee arthro plasty (TKA), performed with or without posterior cruciate ligament (PCL) r etention, controversy exists as to which is preferable in regard to patient outcome and satisfaction. The possible proprioceptive role of the PCL may account for a more normal feeling of the arthroplasty. Although the PCL has been examined using various histological techniques, immunohistochemical t echniques are the most sensitive for neural elements. Therefore an immunohi stochemical study was designed to determine the patterns of innervation, th e morphological types of the proprioceptors, and their immunohistochemical profile. During TKA, samples were obtained from 22 osteoarthritic PCLs and subjected to immunohistochemical analysis with mouse monoclonal antibodies against neurofilament protein (NFP), S100 protein (S100P), epithelial membr ane antigen (EMA), and vimentin (all present in neuromechanoreceptors). Thr ee normal PCLs from cadaveric specimens were also obtained and analyzed for comparison. Five types of sensory corpuscles were observed in both the nor mal and the arthritic PCLs: simple lamellar, Pacini-like, Ruffini, Krause-l ike, and morphologically unclassified. Their structure included a central a xon, inner core, and capsule in lamellar and Pacini corpuscles and variable intracorpuscular axons and periaxonal cells in the Ruffini and Krause-like corpuscles. The immunohistochemical profile showed the central axon to hav e NFP immunoreactivity, periaxonal cells to have S100P and vimentin immunor eactivity, and the capsule to have EMA and vimentin immunoreactivity. Nerve fibers and free nerve endings displayed NFP and S100P immunoreactivity. Th e immunohistochemical profile of the PCL sensory corpuscles is almost ident ical to that of cutaneous sensory corpuscles. Some prior histological studi es of the PCL reported Golgi-like mechanoreceptors, and others found encaps ulated corpuscles but no Golgi-like structures. This report determined the innervation of the PCL by the more sensitive immunohistochemical means, rev ealing four major types of encapsulated mechanoreceptors. The plentiful and varied types of encapsulated mechanoreceptors found in even the arthritic PCL suggests a rich proprioceptive role. It is controversial as to whether preservation of the PCL at TKA improves postoperative proprioception. Our f indings tend to support those clinical reports of improved proprioception a fter PCL-retaining versus PCL-substituting TKAs. The presence of many and v aried types of mechanoreceptors may account for the improved stair climbing reported in patients with PCL-retaining TKA and may contribute to patient satisfaction and a more normal feeling after TKA.