Applied Radiology

Dr. Swischuk is a Professor of Radiology and Pediatrics and Director of Pediatric Radiology at the University of Texas Medical Branch, Galveston, TX.

Long bone fractures are very common in infants and children, and while many are overt and easily recognized, others are subtle and often overlooked. However, radiologists are less likely to miss these fractures if they know what these fractures look like and where they occur. In addition, using comparative imaging views further enhances the ability to detect these fractures so that virtually none of them will be missed.

In assessing the involved extremity for a fracture, it is important to assess the soft tissues (for swelling), the fat pads (for joint fluid and edema), and then the bones. When comparative views are used, edema is detected more readily and abnormalities of the various fat pads occurring around the joints are well visualized. A detailed discussion of these fat pads is beyond the scope of this presentation; nonetheless, they are important, because abnormality of the fat pads may indicate a bony injury.

Types of fractures

There are five basic types of fractures in infants and children, all of which are often very subtle: 1) epiphyseal-metaphyseal (Salter-Harris) injuries, 2) buckle (torus) fractures, 3) hairline fractures, 4) plastic bending fractures, and 5) avulsion fractures.

In regard to epiphyseal-metaphyseal fractures, the most commonly missed of these are the Salter-Harris I and II injuries, in which there is minimal or no displacement of the epiphysis (Figures 1A and B). These fractures, although most common in infants and younger children, also occur in older children and adolescents before the epiphyseal line has been completely obliterated (Figures 1C and D). Epiphyseal-metaphyseal fractures occur most frequently in the wrist and ankle, with the knee and shoulder the next most common locations.

Buckle fractures also are common and result from axial loading on an extremity (ie, falling on an outstretched arm). There are two types of buckle fractures: the classic buckle fracture, in which there is outward buckling of the cortex (Figures 2A and B); and the angled buckle fracture, in which the cortex is merely angled (Figure 2C). In the classic buckle fracture, axial loading is almost pure and the resultant forces are distributed evenly across the metaphysis. As a result, the trabeculae are crushed along the fracture line (sclerosis) and the cortices at either end bulge outwardly. In some cases, bilateral cortical bulging occurs, while in other cases bulging is unilateral. With the angled buckle fracture, in addition to axial loading, some other force (ie, varus, valgus, hyperextension or hyperflexion) is also at play. This other force tends to lateralize the forces across the metaphysis, and rather than an outward cortical buckling fracture occurring, an angled buckle fracture of the cortex occurs on one side (Figure 2C). As opposed to the other type of buckle fracture, which occurs a short distance from the epiphyseal line, the angled buckle fracture occurs adjacent to the epiphyseal line. If forces that produce the angled buckle fracture are more severe, a frank Salter-Harris type II fracture results. Buckle fractures in general most frequently occur in the wrist, ankle, and elbow. Thereafter, they occur around the knee and the shoulder but much less commonly.

In the elbow, angled buckle fractures commonly occur in the proximal radius (Figures 3A and B), while in the wrist they commonly occur in the distal radius (Figures 3C and D). The most prominent forces at play in elbow angled buckle fractures are axial loading and valgus forces. In the wrist, the forces consist of axial loading and hyperextension. Therefore, in the wrist, a buckle fracture occurs posteriorly through the radius, while in the elbow it occurs laterally. In the wrist, if hyperflexion is the other force, an angled buckle fracture occurs anteriorly.

Another angled buckle fracture of the elbow occurs through the distal humerus and can be quite subtle. ^1,2 This fracture occurs both posteriorly (axial loading and hyperflexion), and laterally from associated varus forces (Figure 4). The posterior angled fracture can also be detected with the anterior humeral line. ² This line is designed to pass along the anterior cortex of the humerus and then intersect the capitellum. Normally it intersects the capitellum through its posterior third, but when a plastic bending-buckle fracture of the distal humerus occurs, the line intersects the capitellum more anteriorly (Figures 4A and B).

Angled buckle fractures may also occur through the distal femur with hyperextension of the knee, but they are much less common. However, a special buckle fracture through the upper tibia occurs with hyperextension of the knee. This type has recently has been reported as another toddler's fracture. ³

With hyperextension forces applied to the upper tibia, there is buckling of the anterior cortex and, at the same time, increased concavity of the normal notch for the tibial tubercle (Figure 5). In some cases, there is a visible associated transverse hairline fracture and/or minimal cortical buckling manifest on the anterioposterior view (see Figure 9). Finally, another commonly missed buckle fracture occurs through the base of the first metatarsal as a bunkbed fracture ^4,5 (Figure 6).

Hairline fractures in infants and children also occur, but, again, are more likely to occur at certain sites. In this regard, the most common hairline fracture is the toddler's fracture. ⁶ In these cases there is a tibial spiral fracture involving the tibial metaphysis and diaphysis, but only portions of the fracture are seen on any given view. The findings with this fracture are notoriously subtle (Figure 7). Other hairline fractures occur through the ulna, both transverse and linear (Figure 8). The tranverse fractures result from direct forces applied to the posterior ulna, while the linear fractures result from twisting forces exerted on the ulna as it is locked into the trochlear notch on hyperextension. ⁷ These linear fractures are extremely subtle (Figures 8C and D). Hairline fractures in the form of longitudal spiral fractures also occur in the small bones of the hands and feet. In addition, subtle transverse hairline fractures occur as part of the hyperextension upper-tibial toddler's fracture ³ (Figure 9).

Plastic bending fractures most commonly occur in the forearm, involving the radius and ulna. ⁸ They are "cousins" of the greenstick fracture, and often both fractures are present in a single extremity (Figure 10). Once again, comparative views are essential for detection of these fractures (Figure 11). After the radius and ulna, the most common locations for a bending fracture are in the clavicle (Figure 12) and fibula.

Finally, a few avulsion injuries should be considered. An assortment of avulsion fractures can be seen in the younger child and infant, despite the fact that avulsion fractures usually occur around the hip in older children and adolescents. One of the most commonly missed fractures of this type is the small avulsion fracture that occurs off of the coronoid process of the ulna (Figure 13A). This fracture is usually seen on the lateral view. Medial epicondylar avulsion fractures may also be subtle (Figure 13B), and lateral condylar fractures may be extremely subtle (Figure 13C). In such instances, nothing more than a small sliver of cortex may be visible, minimally avulsed off of the humeral metaphysis (Figure 13D).

Conclusion

Childhood fractures are a common occurrence. Most are overt and are easily detected. However, many are subtle and can be overlooked. The key to avoiding missing these fractures is to know where they occur and what they look like. AR