Central Sensitization and Alteration of Circulating Neurosteroid

For patients who underwent two-stage replacement of both knee joints (one knee surgery - one week term- the other knee surgery), postoperative pain and analgesic usage with patient-controlled analgesia (PCA) increased at the second stage, which suggests that central sensitization occurs within a short period (one week) in patients who undergo total knee arthroplasty (TKA). Neurosteroids act on NMDA and AMPA receptors, GABAa receptors, and voltage-dependent Ca2+ or K+ channels of sensory neurons to increase invasive or neuropathic pain and, conversely, to exhibit analgesic and anticonvulsant effects. These actions mean that the neurosteroid acts as an endogenous regulator of pain control and central sensitization. The purpose of this study is to confirm that the hypothalamus-pituitary-adrenal (HPA) axis, which is the main body of endocrine neurosteroid, is associated with increased pain sensitivity after TKA. The concentrations of cortisol and dehydroepiandrosterone (DHEA) in the saliva of patients who undergo two-staged bilateral knee replacement surgery (one knee surgery - one week term- the other knee surgery) will be measured at each stage and analyzed for correlation between concentration-related changes of HPA and postoperative knee pain variations.