Imaging of the hip and lower extremities

The painful hip is a common clinical problem in all age groups. Magnetic resonance imaging (MRI) is an invaluable tool to assess the hip joint because of its ability to directly visualize bone marrow, cartilage and soft tissues in multiple planes. MR arthrography (MRa) using intra-articular contrast material is the standard method for imaging labral lesions and cartilage degeneration and trauma. Understanding normal hip anatomy and common variants is important, in order to accurately detect and localize areas of pathology and to prevent misinterpreting normal structures as diseased. Plain radiographs should always be available when reporting MRI because basic measurements allow assessment of underlying deformities which might explain the clinical and MRI findings. The most important to know are: joint space width (JSW), CE angle, VCA angle, alpha angle and acetabular retroversion. Among the disorders causing hip pain, osteoarthritis (OA) is the most common one. Age is a risk factor strongly correlated with OA. Early OA is related to CAM type femoroacetabular impingement, developmental dysplasia and previous trauma, inflammation or infection. The diagnosis of OA is based on a combination of radiographic findings and characteristic symptoms. The progression of OA traditionally has been measured using radiographic JSW. Weight-bearing radiographs centered on the hip are the most reproducible and reliable ones. The sequence of degeneration includes the following radiographic findings: joint space narrowing, osteophyte formation, subchondral sclerosis, and cyst formation. In cases that radiographs show minor changes and high clinical suspicion of early disease, OA can be confirmed with MRI and/or MRa.

Knee pain is one of the most prevalent musculoskeletal symptoms which is increasing together with the steady increase in life expectancy and the prevalence of obesity. MRI is the imaging modality of choice for the evaluation of knee disorders, offering a comprehensive evaluation of the bone marrow, the soft tissues and the articular cartilage. As an imaging modality it combines high sensitivity and specificity aiding the investigation and differential diagnosis of pathology such as cruciate ligament and meniscal tears, which cannot be visualized with plain radiographs. This lecture will provide the outlines of the normal cross-sectional anatomy of the knee with a special focus on MRI. An outline of pathology missed or identified on plain films will be provided before focusing on more detail in MR imaging anatomy which is extremely important for the evaluation of knee pathology and the differential diagnosis between anatomical variations and clinically relevant knee lesions. Finally, an outline of meniscal lesion evaluation with the use of MRI will be providing since they are one of the most commonly injured knee structures. The combination of imaging with data provided from the clinical examination and medical history can lead to the correct diagnosis and this is why the knowledge on the normal anatomy as well as variants can lead to the successful diagnosis and the avoidance of unnecessary diagnostic arthroscopic procedures.

This presentation will review common causes of groin pain arising from the hip and from the symphysis pubis. In relation to hip pain the talk will focus on the role of the acetabular labrum in maintaining hip stability in normality, dysplasia and in patients with forms of impingement. The talk will outline appearances on non contrast MR studies and following arthrographic evaluation. The presentation will then review common pathologies in the symphysis pubis that can contribute to the development of groin pain contrasting symptoms and appearances of micro tearing of the adductor longs attachment (superior cleft sign) with appearances of micro tearing at the short adductor attachment (secondary cleft sign) with appearances of primary osteitis pubis.

MRI is excellent for depicting normal ankle anatomy and it can elegantly demonstrate ligamentous injuries of the ankle and associated conditions after ankle sprain. In 85% of all ligament ruptures, the lateral ligament complex is affected and the anterior talofibular ligament is the most often ruptured ligament followed by the calcaneofibular ligament. Additionally, dedicated MRI protocols can delineate the cartilage, as well as the appearance of acute and chronic osteochondral lesions of the talus. Recent advances in MRI include 3D isotropic ankle joint imaging. Subchondral microfractures, osteochondral fractures and solely chondral fractures are different manifestations of impaction injuries, the two last-mentioned affect the articular surface. Since osteochondral lesions of the talus may eventually result in post-traumatic osteoarthritis, recognition of early cartilage damage and associated lesions may help determining the proper treatment of the patient to delay or prevent progression to osteoarthritis. Additionally, osteochondral injuries can often explain persisting symptoms. MRI, where necessary complemented by CT-arthrography, has become a decisive tool in diagnosing and characterizing cartilage lesions of the ankle. In case of disrupted cartilage layers and fluid around undetached fragments as well as in case of a dislodged fragment operative treatment may be indicated after consideration of the patient’s general clinical condition. The interventional procedures, which have been developed for the repair of such lesions, essentially include abrasion, microfracture, autologous osteochondral transplantation, allograft transplantation, and (matrix-associated) autologous chondrocyte implantation. MRI enables the non-invasive assessment of the repair tissue, the success of implantation, and the state of cartilage maturation.

The last decade has seen a constant rise in the number of patients diagnosed and treated for femoroacetabular impingement (FAI). However, there are ongoing controversies about the accuracy of measurements for assessing FAI and an associated overdiagnosis of FAI. This refresher course covers the pathophysiology of FAI, the classic osseous hallmarks, and the characteristic damage to the articular cartilage and labrum. It gives an overview of state-of-the art FAI imaging with different radiological modalities, including the use of traction at MR arthrography, and addresses possible pitfalls when evaluating the hip joint. Additional anatomical factors are described that contribute to the development of FAI, such as abnormal femoral antetorsion and acetabular version. And finally, the relevance of the different parts of the diagnostic algorithm for evaluating FAI are discussed.

Groin pain in the athlete is a complex process with different researchers focusing on the symphysis pubis joint, the adductor longus enthesis, pubic subchondral stress fractures, lower abdominal muscle abnormalities as well as inguinal muscular and aponeurotic tears. There is also confusion over terminology with, for example, osteitis pubis and sportsman’s hernia encompassing many different potential conditions for different clinicians. In reality there is a lot of crossover with many or all of the above regions thought to be involved by chronic shearing forces acting through the symphysis pubis and surrounding soft tissues. This lecture will review: (1) Biomechanics and functional anatomy of the anterior pelvis in relation to athletes especially kicking sports. (2) Theories and nomenclature for the pathogenesis of chronic groin pain in athletes. (3) Imaging findings in symptomatic and asymptomatic athletes focussing on the use of MR imaging. (4) The interpretation of these findings and what research shows they relate to in terms of diagnosis, prognosis and decision making for treatment.

This lecture will focus on MRI for the assessment of muscle injuries at the hip and thigh using fluid sensitive sequences. Muscle injuries include a large variety of imaging patterns from occasionally subtle changes in muscle strain to complete muscle tears. Exercise-related chronic changes such as delayed onset muscle soreness, compartment syndrome, and muscle hernias, as well as complications of muscle injuries such as myositis ossificans may be encountered. The MRI appearance of a muscle contusion may be similar to a muscle strain/tear. Mild post exercise oedema can persist for some time and can mimic a low grade muscle strain injury. 35% of all soccer injuries are muscle injuries and they are the most frequent cause for missing a game. The myotendinous junction is the weakest link in the muscle-tendon-bone chain. The widely used grading system for muscle injuries divides muscle injuries in four grades (grade 0: normal MRI, i.e., functional injury of the muscle, grade 1: oedema, grade 2: partial rupture, grade 3: complete tear). However, this grading system is only a rough estimate, because grade 2 injuries comprise a wide range from tiny fibre discontinuities to subtotal muscle ruptures. Measures of the longitudinal length as well as the percentage and volume of the muscle injury in MRI have some predictive value with respect to time to return to sports activities. Moreover, injury to the intramuscular component of the tendon has prognostic significance. A complete tear (grade 3) may require surgery.