Osteoarthritis and inflammation: a serious disease with overlapping phenotypic patterns.

Globally, osteoarthritis (OA) is the most prevalent arthritic condition in those aged over 60 years. OA has a high impact on patient disability and is associated with a significant economic burden. Pain is the most common first sign of disease and the leading cause of disability. Data demonstrating the increasing global prevalence of OA, together with a greater understanding of the burden of the disease, have led to a reassessment of the seriousness of OA and calls for the designation of OA as a serious disease in line with the diseases impact on comorbidity, disability, and mortality. While OA was traditionally seen as a prototypical 'wear and tear' disease, it is now more accurately thought of as a disease of the whole joint involving cartilage together with subchondral bone and synovium. As more has become known of the pathophysiology of OA, it has become increasingly common for it to be described using a number of overlapping phenotypes. Patients with OA will likely experience multiple phenotypes during their disease. This review focuses on what we feel are three key phenotypes: post-trauma, metabolic, and aging. A greater understanding of OA phenotypes, particularly at the early stages of disease, may be necessary to improve treatment outcomes. In the future, non-pharmacological and pharmacological treatments could be tailored to patients based on the key features of their phenotype and disease pathway.