Objective: The primary objective is to explore whether central sensitization and/or abnormal CPM responses are present in (a subgroup of) patients who will receive shoulder arthroplasty for osteoarthritis, and whether shoulder arthroplasty produces change in these measures of the endogenous pain modulatory system. The secondary objective, in case patients with altered endogenous pain modulation are found, is to explore if change in pain over time, psychological factors and coping strategies differ between patients with and without altered pain modulation. Study design: An exploratory prospective observational cohort study. Study population: Patients (age 18 years or older) who are scheduled to undergo shoulder arthroplasty for osteoarthritis, at the Reinier Haga Orthopaedic Centre. Intervention (if applicable): Not applicable. Main study parameters/endpoints: The main study parameters are CPM and TS values at baseline and at 3 and 6 months after surgery, as well as the absence/presence of allodynia at baseline and at 3 and 6 months after surgery. Nature and extent of the burden and risks associated with participation, benefit and group relatedness: The burden of participation will consist of completing questionnaires at baseline and at three and six months after surgery. In addition, subjects will undergo psychophysical testing at 3 moments, which can lead to redness or a burning sensation of the skin during the first 24 hours after testing. The investigators do not expect any additional risks associated with participation. There is no direct benefit for the subjects.