Approach to Pediatric Elbow

What Are the Standard Radiographic Views of the Pediatric Elbow?

Anteroposterior (AP) and lateral projections are the standard radiographic views obtained in the evaluation of the pediatric elbow. The AP view is performed in full extension, with the forearm supinated. The lateral view is acquired with the elbow flexed at 90 degrees, the forearm in neutral position, with the wrist in a true lateral position, thumb up. Obtaining a true lateral is essential for accurate interpretation. Recognizing the hourglass or figure-of-eight morphology of the distal humerus is a quick technique for confirming adequate positioning of the lateral radiograph ( Fig. 13.1 ).

When Are Additional Views Helpful?

Oblique views can occasionally be helpful for specific injuries, including lateral condyle and medial epicondyle fractures. Comparison views of the contralateral elbow are occasionally helpful, particularly in the case of distinguishing a fracture from an ossification variant. In the majority of cases, however, additional views are not necessary.

When Are Other Imaging Modalities Useful?

When additional imaging evaluation is required, ultrasound and/or magnetic resonance imaging (MRI) is often the next imaging modality. Ultrasound is user/technologist and site dependent. The use of ultrasound, however, should always be considered, particularly in younger children who may require sedation for MRI. MRI is most commonly used in athletes with chronic repetitive injuries, although radiographs should always be acquired first. For traumatic injuries, acute or chronic, MRI is typically performed either without contrast or after arthrography. Indications for MRI with intravenous contrast include evaluation for infection, inflammatory arthritis, and/or masses. Computed tomography (CT) is rarely indicated.

F: Fat Pads: Joint Effusion = Fracture (Most Likely)

Displacement of the fat pads indicates the presence of a joint effusion. A positive fat pad sign indicates high likelihood for fracture.

What Is the Significance of the Posterior Fat Pad Sign?

Presence of a posterior fat pad sign is always abnormal. The posterior fat pad is anatomically positioned within the intercondylar depression (olecranon fossa) of the distal humerus, and in the normal elbow it is obscured by overlying bone on the lateral radiograph (see Fig. 13.1 ). In the presence of a joint effusion the posterior fat pad is displaced posteriorly, allowing for its visualization ( Fig. 13.2 ). The presence of a posterior fat pad raises significant suspicion for a fracture.

O: Overt Findings and Outlines

First the forest, then the trees: Always evaluate for obvious soft tissue injuries and obvious fractures and/or dislocations. This is akin to the physical examination and sets pretest probability of an abnormality. For example, patients with medial epicondyle avulsion fractures typically present with marked medial soft tissue swelling. Even if a fracture is not initially detected, the abnormal soft tissue swelling prompts a closer inspection. Occasionally, honing in on a small osseous finding may distract from the bigger picture. Soft tissue swelling and inflammatory stranding are important to note, particularly because radiologists often do not examine the child and may have a limited history. Use soft tissue clues to get a general gestalt of whether the study is normal or abnormal.

After general characterization of the forest, scrutinize individual trees. Trace outlines of each bone, particularly the distal humerus and proximal radius, for any subtle contour deformities and/or buckle fractures. Examples of subtle abnormalities seen in common fractures include subtle cortical disruptions in supracondylar and lateral condyle fractures and mild cortical buckling of the proximal radius in radial neck fractures.

O: Ossification Centers

Radiographic evaluation of the pediatric elbow is unique due to the variable appearance of the ossification centers about the elbow, which undergo transformation from cartilaginous at birth, progressively ossifying, and subsequently fusing during childhood and adolescence.

What Is the Significance of CRITOE?

There are six centers of secondary ossification in children. At birth, these centers are all cartilaginous, and therefore not visible by plain radiography until they begin to ossify. The age at which ossification and fusion occur varies, but fortunately the sequence of ossification is predictable: Capitellum, Radial head, Internal (medial) epicondyle, Trochlea, Olecranon, External (lateral) epicondyle (CRITOE). Familiarity with this pattern is critical to the interpretation of pediatric elbow radiographs ( Boxes 13.2 and 13.3 ) ( Fig. 13.3 ).

BOX 13.2

CRITOE Checklist

• ▪

  C = capitellum

• ▪

  R = radial head

• ▪

  I = internal (medial) epicondyle

• ▪

  T = trochlea

• ▪

  O = olecranon

• ▪

  E = external (lateral) epicondyle

BOX 13.3

CRITOE Pearls

CRITOE , Capitellum, Radial head, Internal (medial) epicondyle, Trochlea, Olecranon, External (lateral) epicondyle.

• 1.

  Ossification centers appear and fuse earlier in girls than boys.

• 2.

  Capitellum ossifies first, often by 6 months of age, and is typically well formed by 1 year of age in both girls and boys.

• 3.

  Lateral epicondyle ossifies last, typically by 10–12 years of age.

• 4.

  Medial epicondyle is the last ossification center to fuse to the distal humerus, typically during mid to late teenage years.

• 5.

  Trochlea, lateral epicondyle, and olecranon have multiple ossification centers and can normally appear fragmented or irregular.

• 6.

  Variants include CIRTOE and CRIOTE.

Knowing the exact age at which ossification occurs is less important than sequence, with both ethnic and sex variability. A general rule of thumb used by some is 1-3-5-7-9-11 years. Girls ossify and fuse earlier than boys by an average of 2 years.

Are There Any Variants of CRITOE?

Variants of CRITOE are rare but have been reported. One of the more common ossification sequence variants includes the appearance of the medial epicon dyle before the radial head, more commonly in girls (CIRTOE) ( Fig. 13.4 ). Case reports also include the olecranon before the trochlea (CRIOTE). In these rare cases, comparison with the contralateral elbow may be useful when the clinical history and imaging findings are not congruent. However, normal development can also be asymmetrical.

L: Lines

The anterior humeral line (AHL) and the radiocapitellar line (RCL) confirm normal alignment of the elbow. Disruption of either line is suspicious for fracture and/or dislocation. Remember that proper positioning of the elbow is paramount to avoiding pitfalls, particularly the lateral view; otherwise, the use of these lines can be misleading. In addition, both the AHL and RCL are less reliable in infants and toddlers, related to small and possibly eccentric ossification centers seen during early stages of physiologic ossification.

What Is the Anterior Humeral Line?

The AHL is a vertical line drawn parallel to the anterior cortex of the distal humerus on the lateral radiograph. This line normally bisects the middle third of the capitellum ( Fig. 13.5A ). Disruption of this line is suggestive, but not pathognomonic, for a supracondylar fracture (see Fig. 13.5B ).