Elbow fractures on X-ray

Written by the X-Ray Atlas editorial team from the sources listed below · Medical review pending · Updated 24 October 2026 · Level: Intermediate

Elbow fractures are often invisible as a line. Instead, the film tells you indirectly: a joint effusion lifts the fat pads, and the alignment of the radius and humerus changes. If you learn to read the fat pads and two simple lines, the anterior humeral line and the radiocapitellar line, you will catch most significant elbow injuries even when no fracture is seen. This page covers the adult elbow. Children's elbows, with their ossification centres, have a separate module: paediatric elbow.

1. Views and adequacy

A standard elbow series is an AP with the elbow extended and a lateral with the elbow flexed to 90° and the forearm in neutral (thumb up). The lateral is the most informative view, but only if it is a true lateral:

• The distal humerus should form a "figure of eight" or hourglass shape, with the trochlea and capitellum overlapping as concentric circles.
• The olecranon should sit snugly in the trochlear notch.

An oblique or rotated lateral distorts both the fat pads and the lines, so it can create a false positive or hide a true one. If the lateral is not true, say so. A radial head (radiocapitellar) view can show the radial head clear of the ulna when a fracture is suspected but not seen.

2. The fat pad sign

Two pads of fat sit outside the joint capsule but inside the fibrous layer, in the coronoid fossa (anteriorly) and the olecranon fossa (posteriorly). On a true lateral at 90°:

• The anterior fat pad is normally visible as a thin, dark strip lying flat along the front of the humerus. When an effusion pushes it forwards and upwards it forms a triangle, the "sail sign".
• The posterior fat pad is normally hidden in the deep olecranon fossa. If you can see it, it is abnormal. An effusion has pushed it out of the fossa.

In an adult after trauma, a visible posterior fat pad or a sail-shaped anterior fat pad means an intra-articular fracture until proven otherwise, most often an occult radial head fracture. In children the equivalent is a supracondylar fracture.

3. The two lines

Anterior humeral line (lateral view)

Draw a line along the anterior cortex of the humerus and extend it down through the elbow. It should pass through the middle third of the capitellum. If it passes through the anterior third, or misses the capitellum altogether in front of it, the capitellum has moved backwards. This is the classic sign of an extension-type supracondylar fracture, and the same principle applies to distal humeral fractures in adults. In children under about 4 years the line can normally pass through the anterior third, because the capitellum is small and not fully ossified.

Radiocapitellar line (every view)

Draw a line along the long axis of the radial neck and shaft. It should pass through the capitellum on every view, whatever the position of the elbow. If it does not, the radial head is dislocated. An isolated radial head dislocation in an adult is rare, so look straight away for an ulnar fracture: this is the Monteggia fracture-dislocation.

4. Radial head and neck fractures

The radial head fracture is the most common adult elbow fracture, usually after a fall onto an outstretched hand (FOOSH), which drives the radial head into the capitellum. Patients have pain over the lateral elbow and painful forearm rotation.

On the film the fracture may be:

• a thin vertical lucency or a small step in the articular surface of the head;
• a subtle angulation or buckle of the radial neck, which is easy to overlook;
• completely invisible, with only a fat pad sign.

The Mason classification is commonly used: type I undisplaced, type II displaced (partial articular), type III comminuted, with a type IV for fractures associated with dislocation in later modifications. Many undisplaced radial head fractures are managed symptomatically with early movement, so the practical question is whether there is displacement, a block to rotation, or an associated injury.

Look at the wrist too if there is wrist pain: a radial head fracture with disruption of the distal radioulnar joint and interosseous membrane is the Essex-Lopresti injury, which is easily missed and has a poor outcome if untreated.

5. Olecranon, coronoid and distal humerus

• Olecranon fracture: from a direct fall onto the point of the elbow or a triceps pull. Usually transverse. The triceps distracts the proximal fragment, so displacement is common and the gap may widen with flexion. Check the extensor mechanism clinically.
• Coronoid fracture: a small fragment anterior to the trochlea on the lateral view. Easy to dismiss, but it implies the elbow has subluxed or dislocated, so it is a marker of instability.
• Distal humerus fractures: in adults these are often intercondylar (T- or Y-shaped) and intra-articular, typically after high-energy trauma or in older people with osteoporosis. CT is commonly used for planning. Assess the anterior humeral line and the condyles.
• Capitellar fractures: a crescent-shaped fragment displaced upwards and forwards on the lateral, sometimes producing a "double arc" of the capitellum and trochlea.

6. Elbow dislocation and the terrible triad

Most elbow dislocations are posterior (or posterolateral): the radius and ulna sit behind the distal humerus on the lateral view. They are usually obvious. The important work is finding associated fractures:

• The "terrible triad": posterior dislocation plus radial head fracture plus coronoid fracture. It is unstable and generally needs surgery.
• Medial epicondyle avulsion, especially in adolescents, which can become trapped in the joint after reduction.
• Fractures that only become visible on the post-reduction film.

Check the brachial artery and the median and ulnar nerves before and after reduction, and always obtain post-reduction AP and lateral views.

7. Pitfalls and mimics

• A non-true lateral can make a normal anterior fat pad look raised or hide a posterior fat pad.
• Normal apophyses and ossification centres in adolescents (the olecranon apophysis, medial epicondyle) can mimic fractures. They are smooth and corticated. See paediatric elbow.
• Radial neck fractures are subtle; trace the cortex of the neck on both views.
• Forgetting the forearm: a radial head dislocation means a Monteggia injury until proven otherwise, and wrist pain with a radial head fracture should prompt imaging of the wrist.
• A normal film does not exclude an occult fracture. If there is an effusion but no visible fracture, local practice is usually to treat as a radial head fracture with early review.

Red flags: act now

What to focus on, by role

Role	Priorities
Medical student	Fat pads, the two lines, and the radial head fracture as the commonest adult injury.
Nurse / ENP	Recognise the fat pad sign and know local pathways for "effusion, no fracture seen". Check distal neurovascular status.
Junior doctor	Check the radiocapitellar line on every view, examine the wrist, get post-reduction films, and recognise the terrible triad.
Radiographer	Obtain a true lateral at 90°. Consider a radial head view when the fat pads suggest an occult fracture.
Advanced / FRCR	Subtle radial neck angulation, capitellar shear fractures, Essex-Lopresti and coronoid fragments.

Practise on real upper limb X-rays →

References

1. Radiology Masterclass. Elbow X-ray gallery. radiologymasterclass.co.uk
2. Radiopaedia. Anterior humeral line. radiopaedia.org
3. Radiopaedia. Elbow fat pad sign. radiopaedia.org
4. Radiopaedia. Monteggia fracture-dislocation. radiopaedia.org
5. NICE NG38. Fractures (non-complex): assessment and management. nice.org.uk

For education only. Not a substitute for a formal report, senior review or your local policy. Never use this page to make decisions about a real patient.