Aim: The main objective of the IMPAACT study is to describe the histological findings of PsA Achilles enthesitis, and to a) Characterize and b) Quantify the immune-competent cell presence in tendon specimens obtained from the mid-portion and entheseal site of the Achilles tendon from PsA patients with enthesitis using immunohistochemistry and a stereological technique for the quantification. And secondly, to compare these observations with a) Those in healthy Achilles tendons, and b) Those in mono-symptomatic, non-PsA, chronic Achilles tendinopathy. Secondly, to examine whether one or more of the immune-competent cell types in the PsA tendons are associated with 3-months remission rate of Achilles tendon pain, or with baseline a) Ultrasonic findings of the Achilles tendon; b) PsA disease activity; c) Tendon protein analyses; d) Risk factors of cardiovascular disease; e) Blood biomarkers of systemic inflammation; and f) Fecal microbiota composition.