Figure 1: Diagnostic path for patient #4, a 55-year-old woman with a 3-day history of acute pain in the right hip. Ultrasound scans revealed an intra-articular effusion (white arrows; L = labrum) with distension of the capsule (a, b) whereas the radiograph was unremarkable. T2 weighted MRI scans (d) confirmed effusion in the right hip and ruled out extra-articular abscess formation and advanced osteochondral involvement.