Loaded and Unloaded Magnetic Resonance (MR) Imaging of Meniscus-Cartilage-Trabecular Bone in Osteoarthritis

Inclusion Criteria: * Men and women * At least 35 years of age * Mild OA patients with arthritic knee symptoms and KL score of 1-2 * Severe OA patients with arthritic knee symptoms and KL score of 3-4 * Knee symptoms in OA patients is defined as pain, aching, or stiffness on most days of a month during the past year or use of medication for treatment of knee pain on most days of a month during the past year * self reported knee pain (defined as medial compartment knee pain at least 1 day per week during each of the 6 weeks prior to participation) and at least 3 of the following 6 clinical indicators: Age\>50 years; morning stiffness\<30 minutes duration; crepitus on active motion; tenderness of the bony margins of the knee joint; bony enlargement at the knee; and lack of palpable warmth of the synovium Exclusion Criteria: * current use of investigational drug * conditions other than OA which limit lower extremity function and mobility and/or would confound the evaluation of function (e.g., clinically significant spinal disc degeneration, painful or dysfunctional feet, peripheral vascular disease, lumbar radiculopathy, trochanteric bursitis, hip pain, lumbar pain) * Patients with metallic fragments in the eyes, vascular clips, pacemakers, and other contraindications to MRI * History of joint replacement, intra-articular fracture, osteotomy, arthroplasty or meniscectomy of the signal knee * History of other disease that may involve the study joint including systemic inflammatory disease, crystalline disease, knee infection of the signal knee, avascular necrosis, Paget's disease or tumors * Self reported heart condition that limits any daily physical activity * Patients who are pregnant