Psoriatic enthesitis: an update from the GRAPPA 2013 Annual Meeting.

The enthesis, attachment site of ligaments, tendons, and joint capsules to bone, has emerged as a complex structure or entheseal organ that dissipates stress to maintain homeostasis. Entheses are also anatomically and functionally integrated with adjacent bursa, fibrocartilage, and synovium in a synovial entheseal complex that may trigger inflammation in response to biomechanical stress. Recent studies have suggested that inflammation in psoriatic arthritis (PsA) arises in the enthesis based on imaging and anatomical data. In this review, the anatomy of the enthesis from a functional perspective is discussed, and the data that support a central role for enthesitis in PsA are outlined. In addition, new animal models that implicate Th17 and tumor necrosis factor pathways in enthesitis are highlighted along with new data that question the primacy of the enthesis in the early stages of PsA. Finally, future studies that incorporate new technologies are outlined. Those studies may address the contribution of entheseal inflammation to initiation and perpetuation of key pathophysiologic pathways in the psoriatic joint.