Persistent post-surgical pain (PPSP) remains a problem after knee replacement. “Pain” is not likely to be monolithic or a single entity. It can broadly be divided into mechanical pain that is not continuous and is influenced by movement and non-mechanical pain, which is continuous and is marginally affected by activity. If the cause of mechanical pain can be identified, corrective surgery may help.Non-mechanical pain can be subdivided into three groups as follows: sepsis, neuropathic, and perceived pain. The first two groups can be treated to some extent, but the perceived pain group that is very heterogeneous, remains a significant problem.