Figure 1 Enthesitis versus synovitis Figure 1 | Enthesitis versus synovitis. a | Schematic drawing of a diarthrodial joint showing the joint caspsule with the synovial membrane and tendons inserting into periosteal bone. Synovitis is characterized by inflammation of the synovial membrane. Enthesitis is defined as inflammation of the entheses, the insertion sites of tendons and ligaments to the bone surface. Enthesitis can occur with secondary synovitis. b | Enthesitis is usually periarticular but can also occur at sites distant from the joints (indicated by red circles), such as the Achilles tendon, the plantar fascia, the epicondyle or the anterior longitudinal ligament insertion at the vertebral edges. PsA, psoriatic arthritis; RA, rheumatoid arthritis; SpA, spondyloarthritis. Schett, G. et al. (2017) Enthesitis: from pathophysiology to treatment Nat. Rev. Rheumatol. doi:10.1038/nrrheum.2017.188