The Pediatric Elbow: A Review of Fractures, Part 1
By Deborah Pate, DC, DACBR
The elbow fracture is one of the most common fractures in children. Assessing the elbow for fracture can be difficult because of the changing anatomy of the growing skeleton and the subtlety of some of these fractures. It's important to be aware of the radiographic signs of fracture in the elbow, along with knowing the appearance and fusion of the ossification centers in the pediatric patient, to avoid confusing an ossification center with a fracture fragment. Of course, alignment and radiographic positioning are also extremely important in making a diagnostic assessment.
When reviewing an X-ray study for trauma, it's best to have a methodical way of viewing the study. Perform (at the very least) two views of the elbow at 90° to each other, AP and lateral. Positioning is very important, particularly in the growing skeleton. Alignment of the joint cannot be assessed unless the positioning is accurate.
The two most common errors in positioning are: 1) elbow is lower than the shoulder, which projects the capitellum onto the ulna; and 2) elbow is higher than the wrist, which will make the capitellum and the head of the radius appear anterior, and the epicondyle appear posterior, making it difficult to assess the alignment. In a true lateral view, the elbow and the shoulder should be in the same plane and the wrist should be higher than the elbow to compensate for the normal valgus position of the elbow. The thumb should be up to keep the radius from rotating.
Once X-rays are taken, it's a matter of reviewing the films methodically. Four questions should be kept in mind when reviewing pediatric trauma cases (when in doubt, have the films reviewed by a radiologist):
Is There Joint Effusion?
The way to evaluate joint effusion in the elbow is to look for a positive fat pad sign. Normally, when the elbow is flexed to 90°, the anterior fat pad may be seen just anterior to the joint; the posterior fat pad is not seen because it is located in the intercondylar fossa. With joint distention, the fat pads are displaced away from the joint in the anterior aspect; the fat pad will be elevated away from the joint and the posterior fat pad will be visible.
If a positive fat pad sign is not present in a child, significant intra-articular injury is considered unlikely; but on the other hand, if a visible fat pad sign is demonstrated without the appearance of a fracture, the patient should be treated as having a non-displaced fracture and should be splinted for two weeks and then re-evaluated. It is generally agreed that in the case of trauma, a displaced posterior fat pad is virtually pathognomonic of the presence of a fracture.
Is the Alignment Normal?
There are two important lines that help in the assessment of normal alignment of the elbow. These are the radiocapitellar line and the anterior humeral line. The radiocapitellar line is drawn through the center of the radial neck and should pass through the center of the capitellum. Even if the positioning isn't optimal, the capitellum should always be in alignment with the radius, since they articulate with each other. This should be true in both the AP and the lateral views. If not, there is a dislocation of the radius and one should look for other signs of fracture.
The anterior humeral line is drawn on a lateral view along the anterior surface of the humerus; it should pass through the middle third of the capitellum. In cases of supracondylar fracture, the anterior humeral line usually passes through the anterior third of the capitellum or in front of the capitellum, due to posterior bending of the distal humeral fragment.
Are the Ossification Centers Normal?
There are six ossification centers around the elbow joint. They appear and fuse to the adjacent bones at different ages. The order of appearance is as follows: capitellum, radius, medial epicondyle, trochlea, olecranon and lateral epicondyle. This order never varies, but the ages at when they appear is variable and differs between individuals. In general, the capitellum appears at 1-3 years, medial epicondyle at 3-5 years, trochlea at 5-7 years, olecranon at 7-9 years and lateral epicondyle at 9-11 years. The age of appearance isn't nearly as important as is the order of appearance, because this never varies. (Mnemonic is Cover My Truck Of Love; no, I didn't make it up.)
Editor's Note: Look for part 2 of this article, which outlines pediatric elbow fractures by type, in the September 2011 issue.
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