Exploring Factors Linked to Worsening Over Time in People With Early-stage Knee Osteoarthritis and Those With Prior Proven Acute Knee Injury.

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.