Synovial Neuronal Changes in Knee Joint Osteoarthritis

Purpose: The purpose is to study whether pain and inflammation in knee joint osteoarthritis (OA) are associated with local synovial neuronal changes. Methods: Synovial biopsies were harvested from the medial and lateral knee compartments from OA patients undergoing total joint replacement surgery. All patients had predominant pain at the medial joint compartment. Pain and knee joint function were evaluated by knee society score (KSS). Synovial inflammation was analyzed by histopathological analysis and expression of growth associated protein-43 (GAP-43), sensory (SP, CGRP) and autonomic (NPY, VIP, TH) neuropeptides was studied by single and double immunohistochemistry techniques. Results: We observed reduced KSS and increased inflammatory score in synovial membrane of medial knee compartment. A significant increase in GAP-43 [P = 0.001], SP [P = 0.05], CGRP [P = 0.05] and TH [P = 0.05] expression was observed and SP, CGRP and NPY were found to be co-existed predominantly with GAP-43 in synovial membrane collected from medial compared to the lateral knee compartment. Conclusions: Regenerating nerve fibers containing sensory and autonomic neuropeptides are associated with pain and inflammation in knee joint OA.