This issue of Seminars in Musculoskeletal Radiology highlights several maturation-dependent common variants, potential sites of relative weakness, and pathologic processes that can be encountered on musculoskeletal (MSK) imaging of children. Variants can be normal, associated with physiologic growth and maturation of the immature skeleton. However, these transient developmental changes are often sites of relative weakness, prone to injury from acute insult and/or repetitive overuse, leading to a set of uniquely pediatric pathologies. Variants can also be abnormal and pathologic, the result of congenital malformation, acquired deformity, and/or malalignment.

Thus imaging plays a critical role in the clinical work-up and treatment planning for children with MSK symptoms and complaints. A basic understanding of the normal sequence of development and maturation-dependent changes on radiographs, ultrasonography, computed tomography, and magnetic resonance imaging can help improve diagnostic confidence and provide impact, distinguishing between normal and pathologic variants, anticipating potential sites of injury, and estimating risk for future growth disturbance.

This pediatric-themed issue offers 11 comprehensive articles, which include a general overview of the core principles of development, maturation, and physiologic sites prone to relative weakness, followed by a detailed review of each of the core joints of the upper and lower appendicular skeleton, reviewing location-dependent unique patterns of ossification and maturation-dependent pathologies. Finally, Mohamed and colleagues review the imaging assessment of Gaucher's disease.

As an introduction, the first two reviews summarize the predictable pattern of growth and maturation of the immature skeleton, highlighting endochondral ossification that predominates throughout the long and round bones of the appendicular skeleton. Normal histoanatomy and physiology of the growth plate complex is discussed by Nguyen and Caine, emphasizing the unique contribution of each component of the growth plate complex that includes the physis proper, subjacent vascularity within the growth cartilage, and the ossification front. Salter-Harris classification for acute physeal fractures and characteristic imaging patterns associated with overuse injuries involving the epiphyseal, apophyseal, and secondary growth plate complexes are individually reviewed.

Physeal stress injury (PSI) is an emerging hot topic and further expanded in the review by Caine and colleagues. PSI is a underrecognized and underdiagnosed pattern of injury that is steadily increasing among children, particularly in youth athletes who participate in year-round sports. A fundamental understanding of the underlying pathophysiologic mechanisms can ensure early identification of injury and prompt intervention when tissue changes are still reversible, reducing the risk for cumulative and potentially irreversible damage and future growth disturbance.

Detailed reviews of the upper extremity are anatomically subdivided into the pediatric shoulder girdle, elbow, wrist, and hand. In the shoulder girdle, Farooq and colleagues highlight normal regional development and common pathologies that can be encountered at the immature scapula, clavicle, proximal humerus, and regional soft tissues.

In the elbow, Gendler and colleagues review the normal sequence of radiographic appearance of the six regional ossification centers, assessment of elbow alignment, and identification of elbow effusion. They also describe potential regional congenital deformities and commonly encountered acquired pathologies.

For the pediatric wrist, Rodrigues and colleagues discuss the sequential appearance and variable morphology of the regional ossification centers, age-dependent bone marrow signal intensity, findings of carpal depressions, metaphyseal variants, bipartite carpal bones, and coalitions, highlighting features that distinguish these from fractures, abnormal marrow edema, carpal erosions, and metaphyseal lesions. They present an imaging review of the gymnast wrist, Madelung's deformity, ulnar variance, and soft tissue injuries.

In the pediatric hand, Kan and colleagues provide a comprehensive review on the normal regional development, congenital, and acquired variations as well as traumatic conditions using a multimodality imaging approach.

Detailed reviews of the lower extremity are anatomically subdivided into the pediatric pelvis, hips, knees, ankles, and feet. For the pelvis, Chauvin reviews the predictable pattern of ossification involving the regional bones, synchondroses, and apophyses. She also presents a multimodality imaging review of normal maturation-dependent changes and a highlight of common injuries unique to the pediatric pelvis.

For the hips, Anderson and colleagues discuss normal patterns of growth and maturation of the proximal femur, acetabulum, and the hip joint itself, such as pattern of ossification, acetabular variants and dysplasia, labral findings, femoroacetabular impingement, and regional synovial pathologies.

Yaya-Quezada and colleagues review developmental variants of the pediatric knee, subdivided into those that involve the tibiofemoral and patellofemoral compartments, which include the focal periphyseal edema (FOPE) zone, ossification variants of the femoral condyles, metaphyseal cortical irregularity, the subperiosteal stripe, partite patella, dorsolateral defect, and variant trochlear morphologies.

For the pediatric ankle, Colucci and Sofka provide a comprehensive overview of various physiologically normal findings, variants (os trigonum, Stieda process, accessory ossicles, fibular groove, and soft tissue variants), and maturation-dependent pathologies (patterns of physeal fractures, calcaneal apophysitis, osteochondral lesions, and nonossifying fibromas).

Finally, for the foot, Morgan and colleagues review development and anatomical variants including accessory ossification centers, common symptomatic variants, and acquired pathologies (metatarsal base fractures), as well as a basic approach to assess foot alignment and categorize pediatric foot malalignments.

We sincerely hope that this volume dedicated to pediatric variants in MSK imaging will raise the comfort level of adult general and MSK radiologists interpreting pediatric imaging studies and contributing to pediatric injury management, serving as a reference for subspecialty pediatric general and pediatric MSK radiologists for both reporting and teaching.

Article published online:
29 July 2024

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