A Segmental Approach to Imaging of Sports-Related Injuries of the Pediatric Elbow

The elbow is a complex articulation comprising the radius, ulna, and humerus. The radius and ulna function in concert with the distal humerus to allow flexion and extension at the elbow, while the radius and ulna separately allow supination and pronation. As a main transfer point of forces between the upper and lower arm, the elbow serves as the insertion site for a number of muscle tendons, all of which exert substantial forces at their attachment sites. During infancy, the elbow’s articular surfaces cannot be seen radiographically, as they are not as yet ossified. As the child grows, an ordered progression of ossification occurs at the secondary centers as the elbow joint gradually reveals its structure. The capitellum is the first secondary ossification center to ossify, occurring at about 1 year of age. Next, the radial head ossifies at about 3 years of age, followed by the internal (medial) epicondyle at 5 years, the trochlea at 7 years, the olecranon at 9 years, and finally the lateral epicondyle at 11 years. The progression lends itself to an easy mnemonic (“CRITOE”) with the ossification progressing approximately every 2 years in most cases. Some variability in the age of ossification of the various centers is common. When faced with an unusual pattern of ossification, views of the contralateral elbow can be very helpful. In truly difficult cases, advanced imaging may be needed, primarily ultrasound and magnetic resonance imaging (MRI). The configuration of the various ligaments and tendons about the elbow is the same as in the adult. The ulnar collateral ligament (UCL) medially has anterior, posterior, and transverse bands of which the anterior and posterior bands are most important. The anterior band spans the gap from the medial epicondyle to the sublime tubercle (Figure 1A). The posterior band is the weaker of the two and extends from the medial olecranon to the posterior aspect of the medial epicondyle (Figure 1B). Laterally, the radial collateral ligament and the lateral band of the UCL are the main restraints to varus stress, with the latter being the primary support. Both arise from the lateral epicondyle. The lateral band of the UCL wraps along the underside of the radius, cradling it, and inserts on the lateral ulna at the supinator crest (Figure 1A). The annular ligament, as its name suggests, encircles the radial head with insertions on the posterior and anterior aspects of the ulna at the radial notch. Figure 1. Twelve-year-old boy. A, coronal T2 fat-saturated magnetic resonance. The anterior band of the ulnar collateral ligament stretches from the underside of the medial epicondyle to the sublime tubercle (arrowheads). The lateral band of the ulnar collateral ... Given its varied appearance and multiple-tendon and ligamentous appearance, a multimodality approach to elbow imaging is best. Especially in pediatrics, radiographs remain the mainstay of initial investigation, since they are fast and inexpensive and usually include sufficient information to guide therapy in the majority of cases. However, other modalities make substantial contributions to the diagnosis and care of both acute and chronic injuries about the elbow through childhood and adolescence. Computed tomography scanning with its multiplanar capability is adept at producing highly intelligible images with excellent resolution. Ultrasound has the advantage of not requiring ionizing radiation but tends to be a more focused examination without the ability to obtain a global picture of the joint. MRI is the primary advanced imaging modality, as it does not require ionizing radiation and can visualize bone as well as articular, physeal, and epiphyseal cartilage. The key to understanding elbow injuries in the child is an appreciation of the weak links in the structure of the elbow. The physis is a mainly columnar aggregation of chondrocytes with scant intervening matrix. As such, it is always weaker than bone and is much more likely to fail in the face of acute or chronic repetitive trauma. Much of pediatric elbow imaging focuses on the evaluation of the multiple growth centers and their physes about the elbow. The distal humerus also includes a thin supracondylar portion, which, when exposed to the force of the olecranon, is much more likely to fracture compared with the more substantial physes at the larger portion of the distal humerus. Supracondylar fractures are common as an acute sports injury, as are lateral and medial condylar fractures. In many cases, after acute trauma no fracture will be noted on conventional radiographs. However, prominent anterior and posterior fat pads indicate a joint effusion and alert the physician of the likelihood of an occult fracture (Figure 2). The elbow can then be immobilized. Follow-up films done 10 to 14 days later will commonly show periosteal reaction, indicating that a fracture had indeed occurred. Figure 2. Six-year-old boy. Lateral view of the elbow demonstrates a prominent anterior far pad (arrowhead) and posterior fat pad (arrow). A fracture of the proximal ulna is present (curved arrow) As children grow and mature, they participate in sports in a more goal-directed manner. In addition to a greater time actually playing sports, a greater amount of time is spent practicing. The greater load of repetitive motion leads to an increased incidence of overuse injuries about the elbow. As the ossification centers about the elbow develop and mature, the pattern of injury changes as well. In the United States, sports-related injuries of the pediatric elbow mainly result from baseball and gymnastics. During throwing, the arm is extended posteriorly, or “cocked,” and then accelerated forward to propel a projectile toward the target. During the late phase of cocking and early acceleration, a large hyperextension and valgus force is placed on the elbow. The result is a lateral compressive force centered on the developing capitellum laterally where the pattern of injury depends on the state of maturation of the capitellum. A great tensile or distractive force is concurrently borne by the medial supporting structures. Here again, the injury changes with age as the skeleton goes through its predictive pattern of maturation. Although the actual mechanism of injury is identical to the syndrome of valgus extension overload common in adult professional baseball pitchers, the appearance changes since the skeletal structures are different. A typical pattern of injury emerges. Laterally, Panner disease is seen first. This injury is thought to be an osteochondrosis of the capitellum seen in athletic individuals less than about 12 years old. In athletes older than 11 years, osteochondritis dissecans (OCD) occurs and is akin to OCD elsewhere in the body, as at the femoral condyles and talus. As can be seen, there is some overlap in the age ranges in the 2 syndromes reflecting to a certain extent their common etiologies. In skeletally mature individuals, true osteochondral fractures of the capitellum may occur. Medially, injuries also progress in a fairly predictable manner. In younger adolescents, the medial epicondyle with its relatively weak physis is mainly affected. As physeal fusion nears, the focus of the injury shifts to the UCL as the main restraint to valgus forces is overcome. At the medial margin, many mixed forms are present such that partial tears of the UCL may coexist with chronic physeal injury at the medial epicondyle. Interestingly, chronic physeal injury at the medial epicondyle weakens it and may result in a complete avulsion of the entire medial epicondyle with displacement. Posteriorly, the main injury is to the olecranon at the level of the physis. Here the triceps caused a chronic avulsive injury to the olecranon physis and persistence of the olecranon physis. In addition to injuries related to throwing a baseball, elbow injuries related to gymnastics are also very common. The pursuit of excellence in gymnastics requires long hours of training in which the same routines and exercises are practiced repetitively such that the arms are subjected to a remarkable degree of repetitive stress. Injuries at the wrist are well documented and include a range on injuries whose manifestation depends on the skeletal maturation of the athlete. Elbow injuries are also common and include some of the same injuries that baseball players sustain especially laterally. Apart from acute fractures, football injuries are underrepresented in the scope of injuries about the elbow. The reason for this discrepancy is related to the actual shape of the football as opposed to the baseball. A baseball is small and round and fits easily into the palm of the hand. It is meant to be thrown, and indeed, all the players on the field, not just the pitcher, throw the baseball an enormous number of times. In contradistinction, the football is not a ball that is easy to throw. It is far heavier than a baseball and does not lie well in the hand. It is much more difficult to throw hard so that the throwing motion is far less extreme in terms of the acceleration of the arm and the extent of cocking that occurs during throwing. In addition, most of the players on a football team do not ordinarily throw the ball. In fact, most of the players on a team do not touch the ball at all during the course of the game.