Hip, pelvis and sacro-iliac joints

Hip and groin pain in athletes is common and clinical presentation is often non-specific. Causal pathology represents a complex scenario in athletes, with improper diagnosis serving as a cause of delayed return to sports. Radiologists play an essential role in guiding the work-up of athletes with hip pain. This chapter provides an overview on hip and pelvis anatomy and biomechanics and discusses strategies for imaging assessment. Magnetic resonance imaging (MRI) is often the modality of choice for evaluating many of the injuries observed, although preliminary evaluation with conventional radiography and use of other imaging modalities such as ultrasonography (US), computed tomography (CT) and bone scintigraphy may be supplementary or important in some situations. With the main focus on MRI, the authors present abnormalities of the pelvis and hip joint and the surrounding soft tissues that can occur in athletes: intra- and extra-articular hip impingement syndromes, labral and cartilage disease, microinstability of the hip, bone and myotendinous injuries of the pelvis and sacroiliac dysfunction. Muscle injuries, stress fractures, thigh splints and apophyseal injuries are particularly important to consider in young athletes and may be acute or related to chronic repetitive microtrauma. The authors highlight current concepts of femoroacetabular impingement (FAI), labral tears and cartilage abnormalities. Tear of the ligamentum teres is now recognized as a potential cause of hip pain and instability, best evaluated with MR arthrography (MRA). Greater trochanteric pain syndrome encompasses a group of conditions leading to lateral hip pain, with US playing an increasingly important role for both evaluation and image-guided treatment. Snapping hip syndrome and sacroiliac joint pathology are also important considerations. Innovation has been the catalyst for the transformation of hip imaging, as the arrival of new modalities and the widespread introduction of MRI resulted in a paradigm shift from bone morphology analysis to integrated soft tissue, joint and cartilage assessment. Understanding the pathophysiology through the visualization of osseous structures and detailed depiction of soft tissues has become part of routine imaging and has had a major impact on therapeutic decision-making.