Bruno Beber Machado

MRI of subchondral fractures: a review

Several authors have recently emphasized the role of magnetic resonance imaging (MRI) in the diagnosis of subchondral fractures. There is increasing interest about this type of fractures, mostly because they have been implicated in the genesis of some well-known destructive articular conditions whose cause was previously undetermined, such as distal clavicular osteolysis, rapidly progressive osteoarthritis of the hip, spontaneous osteonecrosis of the knee and adult-type Freiberg’s infraction. Subchondral fractures may ultimately lead to bone collapse, secondary osteonecrosis and severe articular damage, and there may be rapid progression of joint destruction over a period of weeks to months. It has been suggested that timely diagnosis might potentially improve the outcome and avoid the onset of destructive joint disease, making MRI even more important in this setting. The fracture line usually appears as a band of low signal intensity in the subchondral bone plate, adjacent to the articular surface, most often surrounded by bone marrow edema. In this article the authors review the most relevant imaging features of subchondral fractures in several joints, stressing the importance of early recognition for a better outcome.

Imaging Assessment of the Pediatric Spine: Selected Topics

The spine of children and adolescents is frequently affected by diseases, some of them inherent to skeletally immature patients, such as juvenile idiopathic arthritis and Scheuermann’s disease, and others that are nonspecific of the pediatric group but present peculiarities when children are affected, such as isthmic spondylolisthesis and spondylodiscitis. Awareness of the imaging presentation of these conditions is paramount to the differential diagnosis and to guide therapeutic decision making. Some musculoskeletal disorders that present spinal involvement are discussed elsewhere in this book and will not be discussed in this chapter.

Peculiar Aspects of the Anatomy and Development of the Growing Skeleton

Many radiologists – even experienced and renowned professionals – do not feel comfortable with pediatric studies, including those related to the immature musculoskeletal system. The most important cause of this antipathy is, by far, lack of familiarity with the normal appearance of the growing skeleton and its developmental peculiarities; this unawareness is a barrier both to recognition of normal patterns and to the diagnosis of pathological findings. The purpose of this chapter is to provide the reader with a brief review of the anatomical, histological, and physiological bases of osteoarticular development, which are crucial for interpretation and understanding of pediatric imaging.

Selected Dysplastic and Developmental Abnormalities of the Immature Joint

Developmental abnormalities and skeletal dysplasias comprise one of the most controversial, extensive, and complex subjects in pediatrics. This miscellaneous chapter will provide a concise review of imaging findings in selected conditions that are particularly prone to affect the immature joint. This selection is inevitably arbitrary and includes abnormalities of the bones and of the soft tissues, based mostly in their frequency, their clinical relevance, their importance for the differential diagnosis, and the potential impact of imaging for their diagnosis and management. Pseudotumoral articular and periarticular dysplastic conditions (such as focal fibrocartilaginous dysplasia and dysplasia epiphysealis hemimelica) are discussed in Chap. 6.

Musculoskeletal Disorders Related to Pediatric Hematologic Diseases

The vast majority of hematologic diseases (hemoglobinopathies, coagulopathies, or malignancies) lead to some kind of osteoarticular involvement. Such involvement is often responsible either for the clinical presentation or for some of the most disabling features of these conditions. It is not uncommon for the radiologist to be the one who first suggests the diagnosis. Awareness of the imaging appearance of the main pediatric hematologic diseases is essential in order to avoid diagnostic errors and allow timely institution of treatment.

Juvenile Idiopathic Arthritis

The term juvenile idiopathic arthritis (JIA) encompasses a heterogeneous group of chronic arthritides that share the following features: (1) disease onset before 16 years of age and (2) a minimum duration of 6 weeks. For many years, it was named juvenile rheumatoid arthritis (mainly in the American literature) and chronic juvenile arthritis (mostly in European texts). It is an autoimmune inflammatory disease of unknown etiology that occurs most often in females, whose main target tissue is the synovium. Synovitis is present since the very early stages of JIA, with gradual development of synovial hyperplasia and hypercellular pannus, which eventually erodes cartilage and bone. Even though this diagnosis is essentially a clinical one, recent therapeutic advances have drastically changed the role of imaging in its management. Children with JIA must be diagnosed as soon as possible, aiming at a benign course and a better outcome with timely introduction of treatment. Magnetic resonance imaging is especially useful as it allows for early demonstration of abnormal findings, monitoring of disease progression, and accurate assessment of treatment response.

Accidental and Non-accidental Articular Injuries in the Skeletally Immature Patient

The notion that children are not small adults is proverbial in medicine. This is also valid for osteoarticular trauma, as the immature musculoskeletal system responds to traumatic injuries differently from the adult organism. Lesions due to acute high-energy trauma, which are discussed in this chapter, differ from those caused by overuse/anomalous stress, such as the sports-related injuries studied in Chap. 10. Special emphasis will be put on articular injuries, although some extraarticular lesions typical of the pediatric age group are also described. In addition to accidental traumatic injuries, this chapter will also cover non-accidental trauma, given the importance of imaging as an objective evidence of child abuse. A concise approach will be used in the following topics, highlighting the imaging appearance of the most frequent lesions. Pediatric trauma is an extensive and complex issue and an in-depth study of it is beyond the scope of this brief review.

Imaging Methods and the Immature Joint: An Introduction

The last decades of the twentieth century and the beginning of the twenty-first century have witnessed unparalleled improvements in diagnostic imaging. Until the 1960s, plain radiographs were the only technique available in this field. In time, however, sophisticated imaging methods were gradually added to the diagnostic arsenal, and even radiographs have entered into the digital arena. Each of these imaging methods has singularities to be considered in the assessment of immature joints, and both the radiologist and the requesting physician must be familiar with them. The requesting physician is supposed to have an open-minded and receptive attitude, consulting the radiologist whenever a doubt arises (e.g., “which imaging method is the most appropriate for this patient in this specific clinical setting?”) and providing all the relevant information for each case. Accordingly, the radiologist must perform the requested imaging study and interpret the findings under the light of the clinical picture. Analyzing the images without taking the clinical background into account is dangerous and may lead to an erroneous – and potentially catastrophic – diagnosis.

Juvenile Spondyloarthropathies and Pediatric Collagen Vascular Disorders

The juvenile spondyloarthropathies comprise a group of conditions characterized by inflammation of the sacroiliac joints and of the spine, association with HLA-B27 antigen, and disease onset before age 16. This group encompasses juvenile ankylosing spondylitis, juvenile psoriatic arthritis, reactive arthritis, arthritis associated with inflammatory bowel disease, and the undifferentiated forms of spondyloarthropathy. In addition to the axial skeleton, the juvenile spondyloarthropathies also affect the peripheral joints, mostly in the lower extremities, and prominent enthesopathy is often present. Peripheral arthritis usually predominates during the initial stage and sacroiliitis/spondylitis are late findings, so that children with early-stage juvenile spondyloarthropathies may be incorrectly diagnosed as having classic juvenile idiopathic arthritis. Classic radiographic criteria employed for adult-type disease are fairly insensitive for early diagnosis of juvenile spondyloarthropathies. Therefore, imaging methods such as ultrasonography (US) and magnetic resonance imaging (MRI), which are more sensitive, have become more and more important, given that early diagnosis and timely introduction of treatment are paramount for improved outcome and better quality of life. Pediatric collagen vascular disorders are multisystemic autoimmune diseases of unknown etiology, which are similar in many ways to their adult counterparts. Nonetheless, peculiarities in the presentation and in the evolution of the juvenile forms of collagen diseases make them unique, thus deserving separate study. Even though osteoarticular manifestations are not the more relevant in most patients, some imaging findings are quite typical, and it is important for the radiologist to be acquainted with them. The following paragraphs will discuss the major juvenile spondyloarthropathies and the juvenile forms of dermatomyositis, systemic lupus erythematous, scleroderma, and mixed connective tissue disease.

Infectious Arthropathies and Related Diseases

Musculoskeletal infection in children often poses a diagnostic challenge, so much greater as the younger the patient is. Although joint aspiration remains indispensable for definitive diagnosis, imaging is a valuable tool in the workup. No matter the etiologic agent, early and accurate definition of the infectious origin of the arthritis is paramount in order to minimize structural damage and to avoid complications and long-term sequelae. This chapter will emphasize the articular component of musculoskeletal infections as well as related diseases that should be considered in the differential diagnosis, such as transient synovitis and chronic recurrent multifocal osteomyelitis. Spinal infection will be addressed in Chap. 11.