I don't know if you can diagnose anything from this, but the x-ray shows degeneration of the medial compartment in the antero-posterior view (see arrow). Could be consistent with several degenerative diseases or conditions. Also seems like there is some osteophyte formation along bone margin. Could indicate a chronic condition. Compare tibial medial margin with normal knee x-ray: Google Bilder-resultat for http://www.accessexcellence.org/RC/VL/xrays/1knee/knenorml.jpg
Not sure if I can give a diagnosis. But there is surely some degeneration going on. Narrowing of medial compartment and Osteophyte formation of medial margin (see arrow) tells us this is probably a chronic degenerative illness.