Other studies have suggested that inflammatory mediators and neurotrophic factors, such as nerve growth factor present in the subchondral bone, also play a role in regulating osteoarthritis pain.4 Moreover, the involvement of NE in modulating bone remodeling has been reported.62 Substances like PGE2 produced during this process also play regulatory roles over osteoarthritis-related pain.19 Consequently, sympathetic nerves may indirectly influence osteoarthritis pain by regulating bone remodeling. This evidence concerns the gene NGF and osteoarthritis.