Defining radiographic osteoarthritis for the whole knee

To determine in the knee which individual radiographic feature or combination of features in the patellofemoral and tibiofemoral joints correlate best with a nonradiographic definition of clinical osteoarthritis in order to recommend a definition of radiographic osteoarthritis for use in studies.

Using data from the Framingham Osteoarthritis Study, we tested the correlation of clinical OA, defined as frequent knee pain plus crepitus, with a variety of definitions of radiographic OA including those based on individual radiographic features, e.g. > or = grade 2 osteophyte 0-3 scale, and new definitions that included alternative combinations of features, [e.g. either > or = grade 2 osteophyte or joint space narrowing > or = grade 2 (0-3 scale) with a bone feature (such as cyst, sclerosis, or grade 1 osteophyte)]. We performed analyses looking at participants who had obtained both weight-bearing anteroposterior (AP) and lateral radiographs of both knees.

In 519 participants, we found that the definitions of radiographic osteoarthritis best correlated with clinical OA were definite osteophyte > or = grade 2' (efficiency 62.4-67.1%) and an 'alternate definition' of either osteophytes > or = grade 2 or joint space narrowing > or = grade 2 with a bony feature of OA (efficiency 62.8-68.1%). A recursive partitioning analysis selected the 'alternate definition' as best. Also, we found that adding lateral views to the AP view improved the diagnostic test performance of the best performing radiographic definitions.

We suggest that a knee should be characterized as having radiographic OA if there is either an osteophyte of grade 2 or greater severity (0-3 scale) present or the presence of moderate to severe joint space narrowing (> or = 2 on a 0.3 scale) with co-occurrence of a bony feature in the compartment affected.