Development of radiographic changes of osteoarthritis in the "Chingford knee" reflects progression of disease or non-standardised positioning of the joint rather than incident disease

Objective: To ascertain the extent to which the "Chingford knee" (that is, contralateral knee of the middle aged, obese, female patient with unilateral knee osteoarthritis (OA)) is a high risk radiographically normal joint as opposed to a knee in which radiographic changes of OA would have been apparent in a more extensive radiographic examination. Methods: Subjects were 180 obese women, aged 45-64 years, with unilateral knee OA, based on the standing anteroposterior (AP) view. Subjects underwent a series of radiographic knee examinations: semiflexed AP, supine lateral, and Hughston (patellofemoral (PF)) views. Bony changes of OA were graded by consensus of two readers. Medial tibiofemoral joint space width was measured by digital image analysis. Knee pain was assessed by. the WOMAC OA Index after washout of all OA pain drugs. Results: Despite the absence of evidence of knee OA in the standing AP radiograph, only 32 knees (18%) were radiographically normal in all other views. Ninety four knees (52%) exhibited TF knee OA in the semiflexed AP and/or lateral view. PF OA was seen in 121 knees (67%). Subjects with PF OA reported more severe knee pain than those without PF OA (mean WOMAC scores 9.9 v 8.3, p < 0.05). Conclusion: The Chingford knee is not a radiographically normal joint. The high rate of incidence of OA reported previously for this knee (similar to 50% within two years) may also reflect progression of existing OA or changes in radioanatomical positioning at follow up that showed evidence of stable disease that was present at baseline.