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.