Blood and knee fluid hold clues to why arthritis worsens

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: ALL participants must meet the following criteria: * Male or female, aged ≥18 years of age AND at least one of the following (a-d): 1. A definite diagnosis of knee osteoarthritis , evidenced by consistent knee symptoms and imaging findings, commensurate with non-advanced KL grade changes (KL 0-2 where an X-ray grade is available) 2. A symptomatic degenerative meniscal tear with or without definite imaging findings suggesting knee osteoarthritis 3. Probable early-stage symptomatic knee osteoarthritis without definite imaging changes, fulfilling NICE diagnostic criteria for osteoarthritis: * Age 45 or over * Activity-related knee pain. * Either no morning stiffness or that lasts \<30 minutes 4. A definite clinically significant acute knee injury at the age of 50 or younger at any stage in the past, evidenced by appropriate clinical history of a traumatic knee episode AND documented imaging or surgical confirmation of a relevant structural injury. * Willing to provide at least one of the following samples: synovial fluid or blood (a salivary sample is an acceptable alternative for remote participants with a history of knee injury. This alternative also applies to existing participants from ICHTB/IHKB, for whom no prior DNA sample is currently banked) * Understand English sufficiently to be able to read PIS, ICF and/or Participant Invitation Letter * Provide an ICF, signed by the participant * Be capable of complying with Protocol requirements, i.e. completing study questionnaire packs. Exclusion Criteria: * Known advanced radiographic changes of KOA on available imaging (KL grade 3-4 where available), or other commensurate findings, such as those present on MRI * Knee joint replacement (uni-compartmental arthroplasty or total knee arthroplasty) of the index knee, prior to consent, or planned during current episode of care, or within next 12 months * Other clinically significant knee pathology such as infection or malignancy affecting the index knee joint or surrounding bone (at any time) * Surgery to the index knee in the last 3 months * Any other systemic inflammatory disease (e.g. inflammatory bowel disease), systemic infection, or inflammatory arthritis (e.g. rheumatoid arthritis, psoriatic arthritis, gout) * Systemic/intra-articular steroid use to index knee in the last 3 months * Any use of immunosuppressive drugs or chemotherapy in the last 12 months * Unwilling or unable to provide follow-up data for minimum 2 years and/or maximum 5 years * Pregnancy, expecting to be pregnant, near the scheduled Year 2 or Year 3 X-ray visit. * Other medical reason which would prevent participation, at the discretion of the investigator.