Plain radiographs will usually confirm the diagnosis. The lesion is usually located on the lateral side of the medial femoral condyle, seen on an ‘tunnel’ view x ray. Sometimes patients are specifically tender to palpation over the site of the lesion.
Whether the overlying articular cartilage is intact is very important. This cannot be determined on X ray and MRI is generally needed to assess this. If there is a break in the cartilage lining the joint fluid can get behind the loose fragment. If this occurs there is a significant risk that the fragment will completely displace. The outlook is much worse if this occurs.