Early diagnosis of knee osteoarthritis is evoked in two situations: fortuitous discovery on a normal X-ray or in front of symptoms. In the latest condition the diagnosis is usually easy. This diagnosis could be more difficult when the X-rays are normal or when the pain has a pseudo inflammatory rhythm. In those conditions, MRI is very useful, eliminating other differential diagnosis. Thus, it is rare to prescribe an arthrography coupled with TDM to detect the cartilage lesions. The early diagnosis of OA implies preventive therapies, mainly non-pharmacological ones. The discussion of surgery is rarely contemplated at this early stage. If so, preventive osteotomy for malalignement should be considered.