Elbow your way into reporting paediatric elbow fractures – A simple approach

Paediatric elbow trauma is common. Radiographic diagnosis of the various fracture types is critical due to the overlapping clinical presentations and to avoid misdiagnosis that can result in growth disturbances. A systematic approach to reporting, supported by an understanding of the age-dependent variation in developmental anatomy of the elbow, is indispensable to the radiologist in tackling these challenging injuries.


Introduction
Paediatric elbow trauma is common.Radiographic diagnosis of the various fracture types is critical due to the overlapping clinical presentations and to avoid misdiagnosis that can result in growth disturbances.A systematic approach to reporting, supported by an understanding of the age-dependent variation in developmental anatomy of the elbow, is indispensable to the radiologist in tackling these challenging injuries.
We now discuss a practical and simple guide to post-traumatic paediatric elbow radiographic reporting.

Step 1 -Evaluate radiographic technique
Initial radiographic interpretation consists of the anteroposterior (AP) and lateral projections.
The AP should be performed with the elbow in full extension and the forearm supinated (Figure 1).For the true lateral projection, the elbow should be flexed 90 degrees with the forearm supinated (Figure 2).The cassette should be centred on the elbow joint with its long axis parallel to the forearm.In an optimal lateral projection, the posterior supracondylar ridges of the humerus are superimposed and the olecranon process is viewed in profile (Figure 3).Radiographic landmarks are unreliable and significant pathology can be obscured in a suboptimal lateral projection.The internal oblique view is useful in the demonstration of lateral condyle fractures and in assessing the degree of displacement. 2e routine use of comparative views is not recommended as it comes at a considerable cost of radiation exposure to the child. 3In addition, several studies have shown that the routine use of comparative views was a predominant choice of inexperienced clinicians, did not alter patient management in the majority of cases and therefore could not be justified. 4,5,6,7ep 2 -Look for soft tissue swelling and joint effusion Localised soft tissue swelling either over the medial or the lateral aspects of the elbow should raise suspicion of a medial epicondylar or lateral condylar fracture.
The elbow fat pads are situated external to the synovium.On a true lateral radiograph with 90 degrees of flexion the normal anterior fat pad is within the coronoid fossa and is seen as a radiolucent line parallel to the anterior humeral cortex; the posterior fat pad is pressed deep into the olecranon fossa by the triceps tendon and the anconeus muscle and is invisible. 8Distention of a structurally intact joint causes displacement of the fat pads -the posterior fat pad moves posterior and superior and becomes visible; the anterior fat pad becomes more sail-like (Figure 3).A false negative fat pad sign may occur in poor positioning, in capsular rupture or in the setting of significant extracapsular abnormality. 8Approximately 70%-90% of children with an elbow effusion will have a visible fracture; however, there is wide debate in the literature about the presence of radiographically occult fractures in the setting of a joint effusion at presentation -radiographic follow-up by Donnelly et al reported 54% of patients showing healing fractures. 9More recent studies looking at MRI and MDCT show occult fractures in the majority of patients, although they do stress that these investigations did not significantly alter management. 10,11.The standard protocol for suspected occult fractures in most institutions remains posterior elbow splinting with follow-up radiographs at 7-10 days.

Step 3 -Evaluate alignment
The anterior humeral and radio-capitellar lines should be used to gauge elbow alignment.
The anterior humeral line is drawn along the anterior cortex of the humerus and should bisect the middle third of the capitellum.Since the line evaluates the relative positions of two parts of the same bone, malalignment indicates a fracture -in most cases, posterior displacement of the capitellum in a supracondylar fracture.This sign relies on adequate ossification of the capitellum and therefore is reliable in children over the age of 4 years only. 12In younger children when the capitellar ossification centre is still small, the anterior humeral line may not pass through the ossified portion (Figure 4).
The radiocapitellar line evaluates the relationship of the proximal radius to the capitellum on all views.If the integrity of this line is compromised, then dislocation should be suspected (Figure 5).Step

-Identify ossification centres
Although ossification of the elbow is complex, this knowledge is essential to all practitioners involved in the evaluation of paediatric trauma.The ossification appears earlier in girls than in boys and there is wide variation between individuals of the same sex.In boys, with the exception of the capitellum, an average delay of two years is seen when compared to girls and there are also differences between population groups. 13,14,15The sequence of appearance of the six centres of secondary ossification is mostly predictable (Table 1) and is best remembered by using the acronym CRITOL (Figure 6).
It should be noted that there are no specific reference data about the timing and sequence of ossification in South African children, and a previous study showed differences in the sequence of ossification in Chinese children when compared to the reported standards. 14 Step 5 -Look for distal humeral fractures a) Supracondylar fracture (50%-70%) (Diagram 1) • T!PS • Lateral view most helpful -look for posterior fat pad.
• Anterior humeral line abnormal in 94% cases (Figure 7).• Baumann's angle predicts varus deformity.Malunion causes a varus abnormality, the severity of which is measured on the true AP projection by the Baumann angle, which uses radiographically identifiable landmarks to compare the healed with the normal elbow (Figure 8).Although primarily a cosmetic deformity, it may cause pain and late development of posterolateral elbow instability, which can be corrected with a valgus osteotomy.

Not to be missed look-alike -Non-accidental injury (NAI)
• T!PS • Non-mobile infant.
• History will be suspicious.
• Bucket handle or corner fracture of distal humerus.
• Requires full skeletal survey.
• Lateral soft tissue swelling is the clue on AP view.
• Cortical breach is posterior on lateral view.
• Need to document amount of displacement.
• Look for medial soft tissue swelling.
• Always confirm normal position in a child >6 years.
• If no epicondyle seen, look for entrapment in the joint (Figure 11).
• Often difficult to differentiate from medial epicondyle fracture.• May be difficult to see extent; external oblique projection helpful (Figure 12).
• Lateral soft tissue swelling may be only finding.
• Internal oblique projection may be helpful ( Figure 13).
• Look for sagittal component that splits medial and lateral condyles and extends to articular surface ( Figure 14).
• Radius and ulna not aligned with humerus on lateral.
• Look for soft tissue swelling.
• Look for associated fractures of medial and lateral condyles and radial neck.• Look for elbow dislocation (Figure 16).
• Posterior fat pad is a clue.
• Oblique views are helpful.

Conclusion
A systematic approach to paediatric elbow reporting in the post-traumatic setting is an asset for everyday radiological practice.Knowledge of the developmental anatomy of the elbow underscored by an understanding of common mimics and pitfalls is fundamental.

FIGURE 1 :
FIGURE 1: Positioning for the anteroposterior (AP) projection.The elbow should be in contact with and in the middle of the cassette in full extension with the forearm supinated.

FIGURE 2 :FIGURE 3 :FIGURE 4 :FIGURE 5 :
FIGURE 2: Positioning for the lateral projection.The elbow should be flexed at 90 degrees with the forearm supinated and thumb superior.

FIGURE 6 :FIGURE 7 :
FIGURE 6: Timeline of the appearance of ossification centres.

FIGURE 8 :FIGURE 9 :
FIGURE 8: Baumann's angle (shown) is formed by the intersection of a line drawn perpendicular to the humeral shaft and a line along the physis of the lateral condyle.A normal Baumann's angle within the paediatric population ranges from 85 -89 degrees.It is important to compare angles between the normal and abnormal side, a difference of more than 5 degrees predicts a possible varus deformity.

FIGURE 10 :FIGURE 11 :
FIGURE 10: (a) Undisplaced right lateral condyle fracture (long arrow).Note lateral soft tissue swelling (short arrow).(b) Displaced right lateral condyle fracture (arrow).(c) Internal oblique showing left lateral condyle fracture that was suspected but not visible on the AP projection. 16

FIGURE 12 :
FIGURE 12: Left medial condyle fracture in a 4 year old.Note the medial soft tissue swelling (short arrow) and the subtle fracture line involving the medial condyle (long arrow).

FIGURE 13 :
FIGURE 13: A 12-year-old with direct blow to elbow. the lateral soft tissue swelling and linear fracture through the lateral epicondyle (arrow).

FIGURE 14 :
FIGURE 14: Intercondylar fracture that extends sagittally to the articular surface (black and white arrow) splitting the medial and lateral condyles (white arrows).

FIGURE 15 :
FIGURE 15: (a) Lateral projection in neonate with a swollen elbow shows marked soft tissue swelling.Ulna and radius appear posteromedially displaced (arrow).(b) AP projection with line drawn along radial shaft that intersects with expected position of the capitellum excluding dislocation and implying a transcondylar fracture.