It needs to be specified whether the unknown origin or known medical condition has caused osteoarthritis for the purpose of classification.

 In the clinical criteria, the multi-center study group evaluated the classification of the idiopathic OA of the knee while proceeding with the comparison diagnoses. These diagnoses included para-articular pain and other painful conditions of the knee. From the physical examination, laboratory tests, and medical history to radiographs, various methods were used to develop criteria with varied investigative purposes. 

Apart from the previous criteria, the classification trees or algorithms were used in this criteria classification.