Standing anteroposterior (AP) radiograph of the knees reveals bilateral medial femorotibial compartment narrowing and sharpening of the tibial spines; this finding is typical of osteoarthritis.
http://emedicine.medscape.com/article/392096-imaging

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Note added at 30 mins (2010-07-16 22:18:41 GMT)
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Each knee image was also assessed for osteophytes,
joint space narrowing and sclerosis of the medial and lateral
compartments, and tibial spine sharpening
http://www.phy.mtu.edu/~lshamir/publications/OA_diag.pdf