Figure 3 Location of joint space narrowing (JSN) and the JSN score in standing anteroposterior (AP) and Lyon schuss (LS) radiographs of 202 osteoarthritis knees. (A) Identification of definite JSN (score >1 in either tibiofemoral compartment) in the LS radiograph among the 73 knees classified as not having definite JSN (score <2 in both tibiofemoral compartments) in the standing AP radiographs. Most often, lateral JSN was identified in the LS radiograph. Among the 38 knees without definite JSN in the LS radiograph, none was found to have definite JSN in the concurrent standing AP radiograph. (B) Differences between the standing AP and the LS radiographs with respect to the location of JSN and to JSN in knees with definite (score >1) JSN in the standing AP radiograph.