There are two fat pads around the wrist that can be utilized in the assessment of wrist injuries. The first is the pronator quadratus fat pad [1], and the second is the navicular fat pad [2]. The pronator quadratus fat pad is seen on lateral views of the wrist and lies along the pronator quadratus muscle (Fig. 7.1a). The navicular fat pad lies just medial to the scaphoid bone and is seen on anteroposterior views of the wrist (Fig. 7.1b). In young infants, this latter fat pad is not visualized with as much consistency as it is in older children. However, this is not so unfortunate because obliteration of the navicular fat pad is utilized primarily for the detection of navicular fractures, and these fractures are not particularly common in infants and young children. Distal radial and ulnar fractures, on the other hand, are quite common, and it is in this regard that displacement and obliteration of the pronator quadratus fat pad becomes most useful.

Determining the presence of fluid in the wrist joint is not possible with plain films and thus one must rely on soft tissue edema to focus ones attention on any possible underlying bony abnormality. In terms of swelling, if the problem is in the wrist proper, swelling will be most pronounced distal to the radial epiphyseal plate (Fig. 7.2c, d), but if the problem is in the distal radius/ulna, swelling is most pronounced proximal to the radial epiphyseal plate (Fig. 7.2a, b).

Although a variety of overt transverse and oblique fractures commonly occur through the distal third of the radius and ulna, these fractures usually are not difficult to detect (Fig. 7.3). At the other end of the spectrum of distal radial and ulnar fractures are the cortical buckle or torus fractures [3]. Both standard buckle and angled buckle fracture are common, but these fractures often can be subtle on AP and oblique views. They are usually more clearly seen on lateral views of the wrist (Figs. 7.4 and 7.5). Indeed, the lateral view is the money view for wrist fractures of the distal radius and ulna, including the relatively uncommon childhood equivalent of the Smith’s fracture (Fig. 7.6).

Epiphyseal/metaphyseal Salter–Harris fractures also are very common in the wrist, especially the distal radius. The most common of these are the Salter–Harris I and II fractures. Types III, IV, and V injuries are relatively uncommon. Salter–Harris type I injuries can be very subtle [4]. In most instances the injury results from falling on the outstretched extremity, and most often it is the distal radial epiphysis which is involved and displaced posteriorly (Fig. 7.7). These Salter injuries can occur even in older children where the epiphysis is basically closed (Fig. 7.8).

Finally in terms of Salter–Harris fractures, it should be noted that chronic stress-induced epiphyseal/metaphyseal fractures of the distal radius and ulna can be seen in gymnasts and other young athletes who overuse the wrist [5–9]. These fractures appear as healing Salter–Harris I epiphyseal/metaphyseal fractures (Fig. 7.9). The problem is one of chronic, repetitive subclinical stress on the wrist and, hence, the gymnast wrist.

Ulnar styloid fractures although appearing innocuous are very important. The reason for this is that they usually herald the presence of an associated significant radial fracture [10]. This occurs because the wrist is encircled by strong ligaments and muscles, and when rotation/impaction injuries occur, the forces involve both the radius and ulna. In terms of the ulna, it is the ulna styloid tip which is fractured and avulsed. If the associated radial fracture is obvious, there is no problem (Fig. 7.10a). However, in lesser cases only the ulnar styloid fracture is apparent on AP views (Fig. 7.10b). In such cases one should look for an almost always present distal radial fracture, either a buckle fracture or a Salter–Harris fracture (Fig. 7.10c). Isolated ulnar styloid fractures can be seen if direct blows to the styloid process are sustained [10].

Old, ununited styloid avulsion fractures may erroneously suggest the presence of a secondary ossification center. I have seen only one such secondary center in my career. Otherwise, the finding should represent an old, ununited fracture of the tip of the ulnar styloid. However, the normal ulnar epiphysis can be bipartite through its midpoint (Fig. 7.10d). In these cases there should be no confusion with a fracture for such fractures basically do not occur.

Galeazzi’s fracture (see Fig. 7.3c, d), which often is associated with radioulnar disassociation, is rare in childhood [11]. The radioulnar disassociation is best evaluated on lateral views and usually is finally delineated with CT scanning [12].

Fractures or dislocations of the carpal bones in infants and young children are uncommon. They are more common in the older child and adolescent, and of these, fractures of the scaphoid bone are most common [13]. The clinical findings in these fractures are similar to those seen in adults (i.e., acute tenderness in the anatomic snuff box), and the fractures result from falls on the outstretched extremity.

In terms of plain film imaging, this fracture can be suspected if there is juxta-navicular soft tissue swelling and/or obliteration of the adjacent navicular fat pad [1, 13]. If the fat pad is intact, it is highly unlikely that a scaphoid fracture is present. In the classic case of a transverse fracture, the findings are not difficult to detect (Fig. 7.11). However, in children an impacted buckle/stress fracture of the scaphoid bone is probably just as common or even more common than the transverse fracture [14–16]. The findings often are very subtle, and comparative views are critical (Fig. 7.12). In puzzling cases, if a question about a fracture is still present, one can resort to nuclear scintigraphy [17] or MR imaging [18–20].