- Radiological Technique
Two standard projections are always required to properly assess the elbow, and we should never underestimate the importance of the adequate radiologic technique. (Fig 1).
- AP in full extension: Shows the epicondyle, trochlea, olecranon fossa, humeral condyle, and radial head. The coronoid process is seen frontally, and the olecranon overlaps the trochlea. (Fig 1. A)
In a normal situation, the epicondyle will be partially covered by part of the humeral metaphysis.
- Lateral with 90° of flexion: Shows the distal humeral diaphysis, supracondylar crest, olecranon process, and anterior aspect of the radial head. (Fig 1. B)
- Normal anatomy and ossification centre
When considering paediatric elbow injuries, awareness of the elbow development is important. The growing elbow presents 6 cartilaginous centres, that gradually appear and ossify, between ages 1 to 12 (Fig 2), until each fully ossified epiphysis fuses with the diaphysis. We propose de mnemonic “CRITOE” to remember the order in which this ossification centre appear. (Fig 2)
Also, it is important to note that the trochlea often presents two or more ossification centres, which give a “fragmented appearance” that should not be mistaken by a fracture.
- Alignment
There are two important anatomical lines that can help us diagnose dislocation or fracture.
- Anterior humeral line (Lateral X-ray): when a line is drawn along the anterior cortex of the humerus, at least 1/2 of the ossified condyle should be anterior to this line. (Fig 4) If less than 1/2 of the condyle is anterior to this line, there is likely a supracondylar fracture with posterior displacement of the distal fragment.
- Radiocapitellar line (AP and lateral): a line drawn along the central axis of the proximal 2-3 cm of the radius should pass through the centre of the condyle. If it does not, it indicates that the radius is dislocated at the elbow joint. (Fig 4)
Keep in mind, these lines are only useful if the radiological technique is correct.
- Signs of joint effusion
Analysis of the fat pads is performed in the lateral projection where a radiolucent triangular image is identified anterior to the distal third of the humerus. No fat pad is observed on the posterior edge. (Fig 5)
Displacement of the anterior fat pad (sail sign) is abnormal (Fig 6), as well as the visualization of a posterior fat pad (Fig 7), indicating the presence of joint effusion.
Although not all joint effusions are associated with fractures, the presence of a positive fat pad sign should raise suspicion of a hidden fracture (especially displacement of the posterior fat pad).
The absence of a visible fat pad does not rule out a fracture, since the radial neck is typically extracapsular, and a fracture thereof may not result in joint effusion/hemarthrosis or displacement of the fat pads.
- Type of fracture and classification
Supracondylar fracture
They are the most common elbow fractures in children, commonly affecting school age kids under 10 years old. They usually occur due to falling onto an extended arm.
If there is minimal or no displacement of the fracture, it may remain unseen on plain radiograph, with a positive fat pad sign being the only clue.
Usually, there is some displacement, and the anterior humeral line does not pass through the centre of the capitellum but through the anterior third or even anterior to it.
Supracondylar fractures are classified according to Gartland (Figs. 8, 9, 10).
Lateral condyle fractures
These fractures are the second most common pediatric elbow fracture, occurring primarily between the ages of 4 and 10 years. They typically result after a fall onto an outstretched hand, and frequently associate with an olecranon fracture.
Diagnosing lateral condyle fractures can be challenging, as most of the tissue involved in the fracture is cartilaginous, fracture lines often are barely visible. Sometimes the fracture extends through the ossified portion of the capitellum and can be seen. In other cases, magnetic resonance imaging plays an important role in defining the fracture trajectory and assessing articular cartilage involvement.
These fractures are classified according to Milch (Figs. 11 -12) and correspond to Salter Harris type IV epiphyseal fractures.
Treatment is based on the degree of displacement, so it must be noted in the report.
Medial epicondyle avulsion
The medial epicondyle is an apophysis located on the dorsal aspect of the elbow and does not contribute to the longitudinal growth of the humerus. In a lateral projection, especially if the arm is rotated, it may appear excessively posterior and be confused with an avulsion; however, avulsions tend to be located more distal and anteriorly. Often, the medial epicondyle is an extraarticular structure, so an avulsion, does not automatically associate with a positive fat pad sign (fig 13).
Most of these fractures occur in adolescent boys, with the mechanism of injury being acute valgus stress due to a fall with extended forearm or sometimes due to a pull. Half of these fractures are associated with elbow dislocation. When the elbow is dislocated and there is an avulsion of the medial epicondyle, the fragment can interpose between the articular surface of the humerus and the olecranon. When a dislocation is spotted, the first question to ask is, "where is the medial epicondyle located?" When the dislocation is reduced, the fragment may return to its original position or remain trapped in the joint, causing severe damage to the articular surface. Therefore, post-reduction projections should be taken to evaluate it carefully.
During forced valgus mechanism, the joint may temporarily open, and the fragment may become trapped in the joint without dislocation. An avulsed fragment located in the joint can pose diagnostic challenges as it may be superimposed on radiographs.
When the trochlea is not fully ossified, the avulsed fragment may mimic an ossification nucleus.
Proximal radial fractures
In children, these lesions often occur in the radius neck because the metaphyseal bone is fragile due to constant remodelling. They are usually Salter-Harris type II epiphysiolysis.
If there is no displacement, diagnosis can be challenging. If there is less than a 30° tilt of the radial head, patients are treated with cast immobilization. If the tilt exceeds 30°, closed reduction is necessary.
50% of radial neck fractures, as well as dislocations, associate some kind of elbow injury, with olecranon fracture being the most common (fig 14 -15).
When the radial epiphysis is still very small, it can slip and become superimposed. Failure to recognize this injury or if it is unsuccessfully reduced, it may alter the development of the radial head.
Radial head dislocation
Dislocation of the radial head can be easily recognizable, with subtle or overlapping cases being uncommon. Associated injuries should always be sought in all cases.
In the original description by Monteggia, there is a dislocation of the radial head in combination with a proximal ulnar fracture; however, the fracture may be located anywhere along the ulna (fig 16).
Associated olecranon fractures are also a common finding.
Olecranon fractures
Olecranon fractures in children are less common than in adults. As mentioned earlier, they are associated with fractures of the radial neck and radial dislocations (Figs. 14- 15). The apophysis or separation of ossification centers should not be confused with a fracture. The apophysis has sclerotic and wavy margins. The growth plate typically has different oblique positions compared to a fracture line.