This prospective, cross-sectional, observational study will include subjects with fibromyalgia (FM), psoriatic arthritis (PsA) and asymptomatic controls. Participants will undergo a research ultrasound (US) exam of the enthesis of the Achilles' tendon, the medial collateral ligament at the femoral epicondyle and the common extensor tendon at lateral epicondyle of the elbow in resting conditions. The research US exam will consist of shear wave elastography (SWE) and radiofrequency (RF) data acquisitions. SWE technology will allow quantification of the shear wave speed (SWS) reporting the elastic stiffness of the tissues under investigation. RF data will be used to estimate quantitative ultrasound (QUS) parameters characterizing the mean intensity μ (akin to B-mode echogenicity), acoustic inhomogeneity (1/alpha), and structural spatial organization of echoes (κ) in the tissue.