The Hip

Abstract

The hip can be a complex anatomical area to evaluate for disease and pathology given the importance it plays in its role of stabilization and also providing a wide range of movement e.g. in flexion, extension, abduction, abduction, internal and external rotation. The hip is frequently associated with injury and symptoms that can affect patients of all ages depending on the mechanisms of injury, and this is no exception in rheumatology. Routine radiographs of the pelvis including both hips are simple yet important crucial first imaging steps to evaluate for hip pathology. They often complement the use of ultrasound, which can be a commonly used imaging tool as well in Rheumatology, to help assess structures including tendons, ligaments, joints and bursae [1]. In the hip, ultrasound is commonly used to evaluate the joint to look for effusions and synovitis which could be inflammatory in aetiology or simply degenerative with osteophyte production in addition [2]. More laterally, the gluteal tendons and their insertions onto the greater trochanter can be evaluated to assess for tendinopathy and for any adjacent trochanteric bursitis. Other regions assessed on hip ultrasound include various tendon insertions to assess for enthesopathy, tendon tears or muscle injury (the latter more useful in the acute setting) [3]. An evaluation of the cartilage can demonstrate degeneration or the presence of crystal arthritides. The advantages of ultrasound include it is a relatively cheap imaging modality that can be easily accessible by using in a clinic or out-patient setting as an extension to a clinical consultation. There is no ionisation radiation involved and therefore is safely used in all patients including during pregnancy. It can often be used as a dynamic study, whereby live demonstrations of moving tendons and fluid to look for imaging features compatible with ‘impingement’, can place ultrasound ahead of other imaging modalities e.g. internal or external snapping hip syndromes. One important point to remember however, particularly due to the exponential growth of ultrasound use world-wide is that it is ‘operator-dependent’. In the right hands, ultrasound can provide a wealth of validated information and the importance of this is greater as independent review of ultrasound images cannot be optimally assessed at a later date. In this chapter, we will focus on the most relevant areas in the hip that are affected by rheumatological diseases and offer a systematic approach to a comprehensive and thorough examination of this joint, in order to accurately assess for any underlying disease pathology. We also discuss the relevant anatomy, an understanding of which is essential, to perform accurate ultrasound.