Osteoarthritis (OA), the most common joint disease, causes pain and disability and mainly affects the knee, hip and finger joints. Treatment focuses on pain relief, physical therapy and eventually prosthesis. Cartilage proteins are degraded after joint injuries and in OA; joint trauma is a risk factor for OA, but the mechanisms leading to OA are mainly unknown. We study the molecular and structural changes that occur after knee injuries and in OA, and associate them to patient symptoms. We use cartilage explants, blood, urine and joint fluid samples from patient cohorts in order to measure protein fragments by immunological methods and mass spectrometry. Magnetic resonance imaging (MRI) is used to measure the structure and volume of joint tissues. Patient evaluation forms provide clinical data on symptoms, pain and quality of life. Molecular markers are ultimately compared with MRI and clinical data.