Sensory innervation and inflammatory cytokines in hypertrophic synovia associated with pain transmission in osteoarthritis of the hip: a case-control study

Objective. To clarify the sensory innervation and inflammatory cytokines in hypertrophic synovia associated with pain transmission in OA of the hip. Methods. A piece of the synovium was extracted during reconstruction surgery in 50 patients with OA of the hip as an inflammatory synovium and in 12 patients with femoral neck fracture as a normal synovium. Each sample was immersed in fixative solution, sectioned on a cryostat, and then processed for immunohistochemistry using antibodies as follows: neuron-specific class III beta-tubulin (TuJ-1) as a general marker for nerve fibres, calcitonin gene-related peptide (CGRP) for sensory nerve fibres, nuclear factor kappa B (NF-kappa B) for the protein complex controlling the transcription of DNA in cellular responses to painful stimuli, and TNF-alpha for cytokines involved in acute inflammation. The number of immunopositive cells and fibres were counted using a fluorescence microscope. Results. In the inflammatory synovium of OA of the hip, TuJ-1 was positive in 46% (23 hips). Of those positive for TuJ-1, 78% (18 hips) were also positive for CGRP, but 22% (5 hips) were negative for CGRP. NF-kappa B was positive in 68% (34 hips). Of those positive for NF-kappa B, 76% (26 hips) were also positive for TNF-alpha, but 24% (8 hips) were negative for TNF-alpha. In normal synovia, all four substances were negative. Conclusion. We suggest sensory innervation and inflammatory cytokines in hypertrophic synovia are associated with nociception in OA of the hip. Trial registration: University Hospital Medical Information Network, ext-link-type=uri xlink:href=http://www.umin.ac.jp xmlns:xlink=http://www.w3.org/1999/xlink>www.umin.ac.jp, UMIN000001335.