In order to design future disease modifying osteoarthritis drug (DMOAD) proof of concept studies, this study is being conducted to assess magnetic resonance imaging (MRI) measurements of cartilage morphology and glycosaminoglycan (GAG) content as it relates to the progression of disease in subjects with potentially rapidly progressing OA. The subject population is selected to have higher likelihood of having rapidly progressing OA (i.e., a more rapid joint space narrowing (JSN) compared to general knee OA population and thus, may be more likely to have changes in GAG content and/or cartilage volume. The results of this study may provide a reasonable means to assess DMOAD activity of drugs in development. The non-OA controls are included to determine the rate of change for subjects of similar age. Ideally, results of this study will identify reliable methods for delayed Gadolinium Enhanced MRI of cartilage (dGEMRIC) and MRI cartilage assessment that correlate with OA disease progression as compared to x-ray changes.