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 Baumann angle is the standard coronal-alignment measure after a supracondylar fracture, but it is only useful if you know exactly what it is and where it fails.

View larger

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.

CRITOE is most useful when you also know the approximate ages and the single rule that turns the sequence into a fracture detector.

Ages vary widely and the centres appear earlier in girls, so the order is far more reliable than the exact age - and the order is what makes CRITOE a safety check rather than a memory test.

The medial epicondyle rule

Because the Internal (medial) epicondyle always ossifies before the Trochlea, the trochlea should never be visible without the medial epicondyle also present in its normal position. So if you can see a trochlear ossification centre but the medial epicondyle is absent from where it belongs, the medial epicondyle fragment has been avulsed - and may be incarcerated within the joint (classically after an elbow dislocation that has spontaneously reduced). A rounded ossific density sitting at the joint line is the displaced epicondyle until proven otherwise.

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.

The differential is really a list of injuries that look subtle on a paediatric elbow film. The job of the reader is to separate normal developmental anatomy from a treatment-changing fracture.

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.

Global epidemiology

• Supracondylar humerus fracture is the most common paediatric elbow fracture, accounting for roughly 55 to 70 percent of elbow fractures in children, with a peak incidence between 5 and 7 years of age and a fall on the outstretched hand the usual mechanism.
• Lateral condyle fractures are the second most common (around 12 to 20 percent of paediatric elbow fractures); medial epicondyle avulsions follow, often associated with elbow dislocation.
• The Kappelhof meta-analysis confirms that when a post-traumatic fat pad sign is present, the occult fracture rate is high (44.6 percent), reinforcing effusion as a globally relevant warning sign.
• Distribution is broadly consistent across high- and low-resource settings, though delayed presentation and missed lateral condyle and Monteggia injuries are reported more often where access to follow-up imaging is limited.

Side-by-side guidance

Registry and resource notes

• Paediatric elbow fractures are not tracked by arthroplasty registries; the evidence base is built from trauma series, meta-analyses and observer-reliability studies rather than implant registries.
• High-resource settings can readily obtain internal oblique views, ultrasound and MRI for equivocal cases; the priority in limited-resource settings is a true AP and lateral, disciplined use of alignment lines and fat pads, and robust safety-netting with planned re-review when advanced imaging is unavailable.

• Comparison views of the opposite elbow. Routine contralateral films were once common to "check" an ossification centre. Most paediatric bodies now discourage this because of the extra radiation dose and limited yield; reserve it for genuinely ambiguous cases where it will change management and does not delay urgent care.
• Which sagittal measure to trust. The Baumann angle is widely taught but is highly view-dependent and unreliable in isolation. The anterior humeral line position and the AHL-to-capitellum distance have better reproducibility, so several authors argue these should lead sagittal assessment.
• Grading the posteriorly hinged (Gartland type 2) fracture. Interobserver agreement on Gartland type 2 is poor. The AHL index has been proposed as a more reproducible way to decide which extension injuries need reduction, but it is not yet a universal standard.
• Imaging the occult fracture. When a fat pad sign is the only finding, practice varies between immobilise-and-review, early MRI, or ultrasound. With a 44.6 percent occult fracture rate the safe default is to treat as a fracture; advanced imaging is reserved for cases where confirming or excluding injury changes management.
• The very young elbow. In children under about four years, normal alignment lines frequently miss the middle third of the capitellum, so the under-fours remain the group where over- and under-calling are both most likely.