Ultrasound imaging for the rheumatologist III. Ultrasonography of the hip.

Ultrasonography (US) is a reliable and useful diagnostic tool for the assessment of hip pathology. It depicts changes within the coxo-femoral joint (synovitis, erosions, osteophytes) and in the adjacent peri-articular tissues (calcifications, tendonitis, enthesitis, bursitis) in many rheumatic diseases (rheumatoid arthritis, spondyloarthritis, osteoarthritis, polymyalgia rheumatica ) and in some orthopaedic disorders (septic arthritis, trauma, abscess, painful hip after arthroplasty). It is commonly used both in adults and in children. In the assessment of hip joint pathology, US exerts considerable diagnostic supremacy over physical examination. In fact, by virtue of its size and position, reliable physical examination of the hip is often difficult thus making US particularly useful as a bedside tool for the evaluation of a painful hip. Hip US has also proven to be of great practical benefit when performing aspiration and injection within the joint and in the periarticular soft tissues. The relatively limited acoustic windows available to the US beam is the principal limitation to hip US thereby making detailed examination of some important structures impossible together with the interpretation of power Doppler signal sometimes unreliable. In addition, the deep location of the hip can confer further problems to US scanning in obese or particularly muscular subjects.