This competing renewal focuses on using Magnetic Resonance (MR) imaging at 3 Tesla to study oint degeneration and the manifested changes in articular cartilage, subchondral bone, peri-articular trabecular bone and bone marrow. Articular degeneration and progression of osteoarthritis (OA) may be preceded and/or accompanied by changes in subchondral and trabecular bone, and bone marrow. This competing renewal grant aims to utilize the strengths of our research environment and group and extend the study of OA to include trabecular bone structure measures, Tip of cartilage, and MR (proton) spectroscopy to characterize the adjoining bone marrow, in the study of OA. Using accepted parameters such as cartilage volume and T2 relaxation for comparison, we hypothesize that: ¿ T2 and T1p are independently associated with cartilage loss and longitudinal progression of OA; Changes of trabecular bone micro-architecture is associated with cartilage loss and progression of OA; MR spectroscopy (MRS) marrow fat/water contents are correlated with histological measurements, and bone marrow edema characteristics are different between OA and acute injury; In addition to size of bone marrow edema, bone marrow edema fat/water and unsaturated/saturated fat composition are associated with cartilage loss and progression of OA. To address these we have the following aims: SPECIFIC AIM I: To evaluate the relationship of T2. T-inrelaxation times, and trabecular bone structure to cartilage loss and OA progression. Three groups of subjects (n=35/group) will be studied longitudinally for three years for Specific Aim I: healthy control population of subjects with no history of knee impairment; Group II, patients with mild arthritic symptoms and radiographic changes (Kellgren Lawrence score of 2); Group III,patients with severe pain and functional limitations associated with knee arthritis (KL score of 3,4). SPECIFIC AIM II: To examine the MRS based water/fat compositions of bone marrow edema for patients with OA and acute injuries, and to evaluate their relationship to cartilage loss and OA progression. An additional cohort consisting of consist of patients with acute anterior cruciate ligament (ACL) injuries with associated osseous contusion (n=20) will also be followed.