How normal is the enthesis by ultrasound in healthy subjects?

Objectives: To explore the prevalence of the ultrasound (US) findings of enthesitis in a group of healthy subjects.
Methods: US assessments of quadriceps, patellar and Achilles tendons, and plantar fascia entheses were performed by a rheumatologist on 82 healthy volunteers focusing on the US findings indicative of "active" inflammation according to the Outcome Measures in Rheumatology (OMERACT) definitions.
Results: Eight hundred and twenty entheses were evaluated in 82 healthy subjects. One or more US findings of "active" inflammation were found in at least one enthesis in 30 out of 82 subjects (34.1%), in 69 out of 820 entheses (8.4%). Entheseal thickening, hypoechogenicity and PD signal were respectively found in at least one enthesis in 23 (28.0%), 11 (13.4%) and 8 (9.8%) out of 82 subjects. Among the 69 entheses showing US features of "active" inflammation, entheseal thickening, hypoechogenicity and PD signal were found as isolated in 61 entheses and in combination in the remaining 8 (entheseal thickening and hypoechogenicity).
Conclusions: Our results show a relatively high prevalence of US findings of "active" inflammation at the lower limb entheses in a group of healthy subjects, thus questioning the discriminant power of the OMERACT definitions for the diagnosis of "active" enthesitis. A combination of grey-scale and PD findings at a specific threshold to be defined could improve both the reliability and clinical usefulness of US.