Enthesitis, inflammation of the tendon insertion, is a common feature of spondylo arthritis, including psoriatic arthritis (PsA). Enthesitis is currently measured by eliciting tenderness at the insertion, but this tenderness could also be caused by wear and tear in the tendon related to overuse, ageing and/or overweight and is possibly related to metabolic disease as well. Diagnostics by physical examination alone proved to be unreliable: although soft tissue swelling and tenderness can be found, bony changes will be missed. To allow detection of inflammation at the enthesis, standardized methods are needed but yet unavailable.

Ultrasound (US) is valid for the detection of additional fluid, increased blood flow, changes in soft tissue structure and breaks in cortical bone. Previous studies showed that US can differentiate between affected entheses and entheses of healthy controls. However, in these studies often only one or two entheses were evaluated and the US findings were not combined with clinical data.

In this study we aim to combine clinical data and US data per enthesis in healthy subjects, patients with recently diagnosed PsA and patients with longer existing PsA and we aim to describe the distribution of the 5 elementary US lesions in the 7 bilateral enthesis (according to the MASEI method) in those 3 groups.