Imaging of the Pediatric Elbow

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CHAPTER 12 Imaging of the Pediatric Elbow

INTRODUCTION

Radiography is the primary imaging modality for evaluation of the elbow in children, as it is in adults. Although the radiographic views are the same, the pediatric patient is unique. Injury is the primary reason for evaluating the immature elbow. Children’s reactions to the process of imaging vary greatly, although they are usually related to the patient’s age and the nature of the injury sustained.

Modern radiographic equipment is a cornerstone for obtaining high-quality imaging studies. However, the most important component is a qualified radiologic technologist who understands the child’s anxieties and who has empathy for the child’s fears. Such a technologist is aware of patient and parent anxiety and that the minor motions of the elbow may cause pain. The assistance of an accompanying parent or guardian may be useful and, occasionally, is mandatory when there is insufficient technical help available for positioning. A gentle, friendly approach that is firm but reassuring will yield optimal radiographic examinations of the pediatric elbow.

The basic elbow study consists of anteroposterior and lateral views. The lateral view invariably is obtained first, because the child maintains an injured elbow in the flexed position. The patient is seated beside a radiographic table so that the arm can be elevated parallel to the level of the table top and a 90-degree flexed position can be maintained. The forearm should be supinated gently, with the thumb pointed up, positioning all three bones of the elbow in the lateral projection. The anteroposterior view then is obtained with the forearm positioned up and the elbow extended slowly as much as the injury allows. If necessary, the anteroposterior view can be divided into two segments: one with the humerus parallel to the radiographic film, and the other with the forearm parallel to the radiographic film. This provides better anatomic detail than does a single exposure with the elbow partially flexed and neither component parallel to the film.

Some unstable fractures and dislocations require splinting such that views obtained at right angles are usually sufficient for the initial diagnosis. The fracture or dislocation with obvious clinical deformity is usually less problematic than is the subtle fracture, which may go undetected. When the patient is examined for subtle fractures, the lateral view is extremely important, and positioning should be flawless. This view provides clues concerning the injured elbow, such as the anterior and posterior fat pad signs. It also allows for visual alignment of the distal humeral ossification segments with the shaft of the humerus and with the radius.

In certain instances, a fluoroscopic examination of the elbow may yield valuable information. The examiner can manipulate the elbow to obtain the precise obliquity required to best evaluate a subtle abnormality. Instead of repeating a radiograph multiple times, optimal positioning can be obtained while watching real-time fluoroscopy and then digital fluoroscopic spot radiographs are easily taken.

Tomography, using either a simple linear method or a complex motion system, can be used in the evaluation of growth plates that have closed prematurely following trauma. In most practices, computed tomography has completely replaced conventional tomography. Computed tomography examinations now take only seconds to perform, and sedation is usually not necessary, even in very young infants and children. Using current 64-slice multidetector computed tomography technology (MDCT), isovoxel images can be obtained in all three planes down to 0.6-mm collimation. This allows detailed imaging, with the bony trabecular pattern well seen. Examinations are obtained with the patient in the prone position, with the affected arm held above the head with about 90 degrees of flexion at the elbow. Sagittal and coronal two-dimensional reformatted images as well as three-dimensional reconstructions are then made from the raw data. MDCT is a sensitive (92%) and specific (79%) method of evaluating for radiographically occult elbow fractures.6 MDCT can also use automated tube current modulation to markedly decrease the radiation dose to the patient compared with fixed-tube current techniques. MDCT can also be performed with no image degradation through a cast.3 MDCT with reformatting can better delineate intra-articular fractures (Fig. 12-1). Three-dimensional imaging can also provide additional information and help define the joint relationships to aid surgical planning (Figs. 12-2 and 12-3). The resulting three-dimensional image can be rotated in all planes with computerized subtraction of the adjacent soft tissues and bones, if needed.

Magnetic resonance imaging (MRI) and ultrasonography are increasingly being used to evaluate the elbow. MRI can evaluate cartilage, bone marrow, and soft tissue structures (Fig. 12-4).8 Radiographs do not show bone bruising, or cartilaginous or soft tissue injury and can underestimate physeal injury. MRI is also occasionally used to better define elbow fractures.2 Owing to the length of the MRI examination (at least 20 minutes), children younger than 5 years old will usually need sedation so that optimal MRI images can be obtained. In children with elbow trauma, MRI reveals a broad spectrum of bone and soft tissue injury, including ligamentous injury, beyond that recognized by radiographs. However, the additional information afforded by MRI usually does not change treatment or clinical outcome in acute elbow trauma.9 MRI can be very useful in the evaluation of osteochondritis dissecans (OCD) of the capitellum. MRI provides information about the size, location and stability of the OCD lesion. All of these factors are important when deciding treatment options (see Chapter 20 for more discussion). Unstable OCD lesions in the capitellum have a peripheral rim of high signal or an underlying fluid-filled cyst on T2-weighted images (Fig. 12-5). Stable OCD lesions have no peripheral signal abnormality.12 Loose bodies in the elbow joint can be visualized by MRI or MDCT, but smaller detached bone fragments are usually better visualized using MDCT (Fig 12-6).

Ultrasonography has the ability to dynamically delineate soft tissues and cartilage in detail.13 Soft tissue swelling, a mass (including vascular masses investigated with duplex Doppler and color flow Doppler), joint effusion, and fractures, particularly in infants and young children with unossified or minimally ossified epiphyses, are studied with this modality.1,7 Ultrasound can detect early changes of medial epicondylar fragmentation and OCD of the capitellum, even in the asymptomatic stage in selected populations such as young baseball players.10

As with other portions of the appendicular and axial skeletons, side-to-side comparison may be helpful when one is presented with an unfamiliar or a rare variant. Comparison views need to be obtained only in selected cases,14,15 such as when consultation with the standard text of normal cases is not helpful.5,11,17

NORMAL DEVELOPMENT

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