Imaging in Pediatric Elbow Trauma Workup

Updated: Jul 20, 2017
  • Author: Richard M Shore, MD; Chief Editor: Felix S Chew, MD, MBA, MEd  more...
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Workup

Approach Considerations

Standard radiographic evaluation of the elbow includes imaging in the anteroposterior (AP) and lateral views. Other views may also be helpful. In particular, for lateral condyle fractures, the internal oblique view is often best for demonstrating the fracture and determining the degree of displacement. [13] Because supracondylar fractures may be oriented obliquely on the lateral view, coursing proximally from anterior to posterior, an AP view with cephalad angulation of the x-ray beam may help to better demonstrate such a fracture. Although infrequently used, the capitellum and radiocapitellar joint are best seen on the radiocapitellar view, which is a lateral view with the beam angulated toward the shoulder to project the radiocapitellar joint away from the trochlea and coronoid processes, which otherwise overlap these structures on a standard lateral view. [44]

Evaluation of soft tissues and joint effusions

Evaluation of the soft tissues is important in elbow trauma. Localized soft tissue swelling over the lateral aspect of the elbow should heighten the suspicion for a possible lateral condyle fracture. Similarly, medial epicondyle avulsion fractures are often accompanied by localized soft tissue swelling in the medial aspect of the elbow.

Displacement of the elbow fat pads is an important indicator of an elbow joint effusion (see below). The radiographic posterior fat pad sign is one of the signs most frequently used for occult elbow fracture. [45]

Fat pad signs indicate an elbow joint effusion. La Fat pad signs indicate an elbow joint effusion. Lateral view shows the posterior fat pad, which is always abnormal when seen with the elbow positioned in right-angle flexion. The anterior fat pad is demonstrated and is abnormally elevated. Although the anterior fat pad may be seen without an effusion, it should not be elevated to this degree.

The elbow fat pads are situated external to the synovium and within the fibrous external joint capsule; the posterior fat pad is located in the olecranon fossa and the anterior fat pad in the coronoid fossa. When the elbow is flexed, the posterior fat pad lies deep within the olecranon fossa and is hidden from view by the medial and lateral condyles. Hence, depiction of the posterior fat pad indicates outward displacement by a joint effusion. With elbow extension, the olecranon moves into the olecranon fossa, displacing the fat pad outward, and hence visualization of the posterior fat pad as a sign of effusion is valid only if the elbow is flexed. The coronoid fossa is not as deep as the olecranon fossa, and hence the anterior fat pad may be seen just anterior to the distal humeral cortex even without an effusion. However, if the anterior fat pad is angled outward, it indicates an elbow effusion.

The presence of an elbow effusion alone does not indicate a fracture. In the setting of acute trauma, the presence of an elbow effusion strongly suggests a hemarthrosis, often from a fracture. In other settings, the etiology may be different. Joint effusions resulting from septic arthritis or juvenile rheumatoid arthritis displace the fat pads, and patients with hemophilia often have an elbow hemarthrosis in the absence of fracture or trauma. In addition to circumstances in which visualization of the fat pad may be due to processes other than fracture, there are also circumstances in which the fat pads are not visualized, even though a fracture is present. If the joint capsule is torn by the fracture fragments, blood may escape from the joint, preventing joint distension and fat pad displacement. Marked edema may also obscure the fat pads, preventing their recognition even though they are displaced. Extra-articular fractures, such as those of the medial epicondyle, also do not result in hemarthrosis.

Approximately 70-90% of children with an elbow joint effusion following trauma have a fracture as demonstrated on the initial or follow-up radiographs. In most cases, the fracture is identified initially. A more important question concerns the risk of an occult fracture in those patients with an elbow effusion and no fracture is seen on initial examination.

Using sclerosis or periosteal new bone to indicate a healing fracture, Morewood initially estimated the risk of occult fracture in this setting to be approximately 30%. [46] Subsequent studies have shown considerable variability in this risk. Skaggs et al found healing fractures in 76%, supporting the concept of considering the presence of an effusion to be essentially indicative of an occult fracture. [11] More recently, Donnelly et al reported that the incidence of healing fracture on follow up was only 17%, with the difference likely related to improved radiographic technique and interpretive criteria for recognizing fractures initially. [47] Using multidetector CT at the time of initial injury, Chapman et al found fractures in approximately 50% of children with a postramatic elbow effusion but no fracture seen radiographically. [48]

Hence, although the presence of a posttraumatic elbow effusion in children raises the possibility of an occult elbow fracture, this situation is not synonymous with an occult fracture, as it seems equally likely that a fracture is not present. The clinical decision as to which patients need to be treated for a presumed fracture must be made on the basis of clinical and radiographic findings and knowledge of the associated risks.

The absence of an effusion in children is strong evidence against an intra-articular fracture. Although a torn capsule or marked edema may produce a false-negative fat pad sign, in these circumstances an obvious fracture is usually present. However, in adults, a significant number of fractures are not associated with an identifiable effusion. Therefore, the negative predictability of this sign is less useful in adults than in children. [49]

Use of the anterior humeral and radiocapitellar lines

Two lines may be drawn on radiographs to help in evaluating elbow trauma: the anterior humeral line and the radiocapitellar line (see below).

Normal lines. Lateral view shows the 2 lines used Normal lines. Lateral view shows the 2 lines used for radiographic analysis in patients with elbow trauma. The solid anterior humeral line is drawn along the anterior cortex of the distal humeral metaphysis and should pass through the middle third of the capitellum. Passage of the anterior humeral line either anterior to the capitellum or through the anterior third of the capitellum demonstrates that the capitellum is positioned too far posteriorly; this finding indicates a distal humeral fracture. The dashed radiocapitellar line is drawn through the radial neck and should pass through the capitellum. This relation should be examined on a frontal view as well. Failure of the radiocapitellar line to pass through the capitellum indicates radiocapitellar dislocation.

On a true lateral view of the elbow, a line drawn along the anterior aspect of the distal humeral metaphysis should pass through the middle third of the capitellum, which is also part of the humerus. Since the anterior humeral line evaluates the relative positions of 2 parts of the same bone, malalignment is indicative of a fracture. Specifically, if the anterior humeral line passes either through the anterior third of the capitellum or anterior to the capitellum, it indicates that the capitellum is displaced posteriorly relative to the humeral metaphysis. This displacement most frequently results from an extension-type supracondylar fracture, although posterior displacement of the capitellum may also be seen in lateral condyle fractures.

Although this sign is useful in interpreting findings in most children, caution is needed in young children. When the capitellar ossification center is small, its anterior aspect may still be well within the middle third of the entire capitellum, which is still mostly cartilage. In this case, the anterior humeral line may pass anteriorly relative to the small capitellar ossification center even without a fracture. The exact stage of development at which the capitellum is sufficiently ossified for this sign to be reliable is not certain. Initially, 2.5 years had been suggested along with the indication that occasionally comparison with the position of the capitellum of contralateral elbow may be useful. [22] More recent data suggest that the anterior humeral line reliably passes through the middle third of the capitellum in children older than 4 years. [50]

The radiocapitellar line evaluates the relationship of the proximal radius to the capitellum. Because the radius usually bends in the region of the tuberosity, with the radial neck angled anteriorly and laterally relative to the orientation of the radial shaft, only the most proximal part of the radius should be used for drawing the radiocapitellar line. This line should intersect the capitellum on all views, although in young children, the capitellar ossification center may occupy an eccentric position within the largely cartilaginous capitellum. Since the radiocapitellar line compares the relative positions of 2 adjacent bones, malalignment indicates dislocation.