In this study, the investigators use the clinical documentation and imaging data of MRI to do research. Clinical subjects were divided into two groups: osteoarthritis patients and healthy controls without osteoarthritis. Differences of MRI data were studied between two groups.

In this study, the investigators applied high precision MRI technique (with as less as a slice thickness of 0.35 mm and without inter-slice gap), and calculated not only the IPFP maximal sagittal area and IPFP volume, but also the quantitated signal, and compared the differences between healthy controls and osteoarthritis patients. This is an observational cross-sectional study without specific interventions to the subjects. MRI is a regular examination in our hospital. And all subjects are included for the reasons of osteoarthritis (need MRI) and healthy controls (pain but not osteoarthritis, also need MRI). The investigator does not assign specific interventions to the subjects of the study.

Inclusion Criteria:

• Patients with clinical knee osteoarthritis;
• The healthy controls who require MRI test.

Exclusion Criteria:

• Contraindications to magnetic resonance imaging;
• Rheumatoid arthritis patients;
• Gout;
• Hemophilic arthritis;
• Subjects who take non-steroidal anti-inflammatory drugs (NSAIDs);
• Subjects who take lipid-lowering agents;
• Subjects who have the history of knee trauma;
• Subjects who have the history of knee operation;
• Subjects who have the disease of musculoskeletal tumor near knee;
• Subjects who have joint loose bodies.

Subjects who come to see doctors requiring knee MRI test.