Paediatric Elbow Radiology and Assessment

Paediatric elbow radiology is difficult because the anatomy visible on X-ray is only the ossified part of a much larger cartilaginous elbow. A fracture may pass through cartilage, an ossification centre may look like a fragment, and malalignment may be subtle unless the view is adequate and the landmarks are used correctly.

The safest approach is not to stare at the film hoping the fracture declares itself. Read every paediatric elbow in the same order: confirm the views, apply CRITOE, draw the anterior humeral line and radiocapitellar line correctly, inspect fat pads, search common fracture sites, and then match the radiograph to swelling, tenderness, nerve function and perfusion.

Common injuries include supracondylar humerus fracture, lateral condyle fracture, medial epicondyle avulsion or incarceration, radial neck fracture, olecranon injury and Monteggia lesion. Soft-tissue signs may be the only clue early. A posterior fat pad after trauma is not a normal finding to ignore; it should trigger concern for occult intra-articular injury when the clinical story fits.

The purpose of this topic is to make the learner safe: know what normal ossification can look like, know where to draw the lines, and know when a subtle film still needs immobilisation, repeat imaging or senior review.

The distal humerus and proximal radius are partly cartilaginous in children. A safe interpretation depends on knowing which landmark is reliable for the child's age.

History

The history guides which part of the elbow radiograph deserves extra attention.

• Fall on outstretched hand or hyperextension injury: supracondylar fracture and radial neck injury are common considerations.
• Direct lateral elbow pain: consider lateral condyle fracture, which can be subtle and clinically important.
• Medial pain after dislocation: look for medial epicondyle avulsion or an incarcerated fragment.
• Forearm pain or deformity: do not stop at the elbow; image the forearm for a Monteggia pattern.
• Pain escalation, paraesthesia, cool hand or colour change: treat as neurovascular warning symptoms.
• Time since injury and analgesia already given: swelling and compartment concern may evolve.

Examination

Inspect the elbow from the front and side. Marked swelling, deformity, skin puckering or bruising supports a significant injury even if the fracture line is subtle. Palpate systematically: supracondylar region, lateral condyle, medial epicondyle, radial head, olecranon, forearm and wrist.

Neurovascular documentation is part of elbow radiology assessment because the X-ray and the hand must be read together.

Avoid forceful range of motion in an obviously fractured elbow. Compare the site of maximal tenderness with the radiograph. A child with lateral condyle tenderness and a barely visible lateral metaphyseal line should not be labelled as a simple sprain without follow-up.

View quality

Start by asking whether the views are adequate. The lateral should be a true lateral with the distal humeral condyles superimposed. An oblique film can make the anterior humeral line and fat pads misleading. If the AP is rotated, Baumann angle and coronal alignment are less reliable.

Anterior humeral line

Draw the line along the anterior cortex of the distal humerus on the true lateral. In most children beyond early childhood, it should intersect the capitellum. If it passes anterior to the capitellum, suspect an extension supracondylar fracture. Do not draw it down the middle of the humeral shaft or through a random vertical line; it is an anterior cortex line.

Radiocapitellar line

Draw the line through the centre of the radial shaft and neck. It should pass through the capitellum on AP and lateral views. If it misses the capitellum on an adequate film, look for Monteggia injury, radial head dislocation, elbow dislocation or radial neck injury. If the film is poor, repeat or obtain adequate imaging before dismissing the finding.

Fat pads and occult injury

A posterior fat pad after trauma is abnormal. A raised anterior fat pad supports effusion. In a swollen painful elbow, effusion without a visible fracture line should still be treated seriously: immobilise, safety-net and arrange follow-up or repeat imaging.

Click to expand

CRITOE describes the usual order in which ossification centres appear around the paediatric elbow: capitellum, radial head, internal epicondyle, trochlea, olecranon and external epicondyle. Exact ages vary, but the order is clinically useful.

• Normal ossification centre mistaken for fracture fragment.
• Occult supracondylar fracture with posterior fat pad only.
• Lateral condyle fracture mistaken for soft-tissue sprain.
• Medial epicondyle avulsion after dislocation.
• Radial neck fracture with subtle angulation.
• Monteggia lesion missed because forearm alignment was not imaged.

Early

• Missed supracondylar fracture.
• Missed pulseless pink or pulseless pale hand.
• Missed lateral condyle displacement.
• Incarcerated medial epicondyle after dislocation.
• Compartment syndrome from swelling or tight cast.

Late

• Cubitus varus after malunited supracondylar fracture.
• Lateral condyle non-union and fishtail deformity.
• Elbow stiffness.
• Chronic radial head dislocation after missed Monteggia lesion.
• Growth disturbance or angular deformity.

Paediatric elbow radiology is a structured search, not a glance for an obvious fracture. The safest reader checks image quality, ossification sequence, alignment lines, fat pads, common fracture sites and the forearm relationship before deciding the film is normal.

The anterior humeral line should pass through the middle third of the capitellum on a good lateral view in most children beyond early ossification. The radiocapitellar line should follow the central axis of the radial neck and pass through the capitellum on every view. If either line seems abnormal, first check whether the view is true; then assume injury until proven otherwise.

A posterior fat pad after trauma is not a normal variant. It should trigger careful search for occult supracondylar, lateral condyle, radial neck or other elbow injury, plus immobilisation and follow-up when the clinical picture fits.

Read every paediatric elbow film in the same order. The order matters because the common failures are predictable: trusting a poor lateral, forgetting CRITOE, drawing the anterior humeral line on the wrong cortex, drawing the radiocapitellar line away from the radial neck, overlooking a posterior fat pad, or stopping at the elbow when the problem is a Monteggia lesion.

The anterior humeral line and radiocapitellar line are not slogans. They are physical landmark checks. If a diagram shows the line in the wrong place, it teaches the wrong anatomy. The anterior humeral line follows the anterior distal humeral cortex. The radiocapitellar line follows the radius, not the ulna, and it must reach the capitellum.

When the radiograph and examination disagree, respect the patient. A child with marked swelling, focal bony tenderness and a posterior fat pad needs immobilisation and review even if the fracture line is not visible. A child with nerve symptoms or poor perfusion needs urgent escalation even before the radiology report returns.

Common pitfalls

• Drawing AHL through the wrong cortex.
• Drawing RCL away from the radial neck.
• Ignoring view quality.
• Missing a posterior fat pad.
• Forgetting the medial epicondyle after dislocation.
• Not imaging the forearm in suspected Monteggia injury.