Prospective Longitudinal Effects of Intra-articular Corticosteroid Injection on Synovial Fluid Oxygen

Inclusion Criteria: * Participant is willing and able to give informed consent for participation in the study. * Male or Female, aged 18 years or above. * Fulfil American College of Rheumatology/European League Against Rheumatism criteria (ACR/EULAR) 2010 Rheumatoid Arthritis Classification Criteria or fulfil Classification Criteria for Psoriatic Arthritis 2006 (CASPAR). * Participant has been selected for intra-articular corticosteroid injection as part of their routine clinical care. * Selected joint for biopsy must be minimum Grade 2 synovial thickening for large joint (knee) and medium joint (wrist), or minimum Grade 3 synovial thickening for small joint (metacarpophalangeal). Exclusion Criteria: * Current enrolment in any other clinical study involving an investigational study treatment. * Intramuscular, intravenous or intra-articular administration of corticosteroid within 4 weeks prior to baseline visit. * Oral corticosteroid \> 10 mg/day prednisolone or equivalent within 4 weeks prior to baseline visit. * Oral corticosteroid dose not stable for at least 4 weeks prior to baseline visit. * Oral non-steroidal anti-inflammatory drugs (including aspirin \> 75 mg/ day and selective-cyclooxygenase inhibitors) dose not stable for at least 4 weeks prior to baseline visit. * Disease modifying anti-rheumatic drugs (DMARDs) dose not stable for at least 4 weeks prior to baseline visit. * History of septic arthritis. * Participants on warfarin, heparin, low molecular weight heparin, direct oral anticoagulants. Oral anti-platelet agents are permitted. * History of haemophilia.