Definition and classification of early osteoarthritis of the knee.

With the emerging interest in regenerative medicine and tissue engineering, new treatment modalities being developed for joint disorders including joint surface lesions and articular cartilage defects. The clinical outcome of these novel approaches appears rather unpredictable and is due to many reasons but definitely also linked to the patient profile. As a typical example, symptomatic articular cartilage lesions can be presented in an otherwise normal joint, or associated with several other joint tissue alterations including meniscal lesions and abnormalities of the underlying bone. The outcome of novel treatments may well be influenced by the status of the whole joint, and the potential to develop osteoarthritis. To better identify the patients at risk and responders to certain treatments, it is of use to define and most importantly classify patients with "early osteoarthritis". Here, classification criteria for this group of patients are presented, allowing a more defined and accurate inclusion in clinical trials in the future.