Trauma X-ray - Upper limb

Elbow X-ray

An awareness of normal X-ray appearances of the elbow is essential for the identification of elbow injuries. Elbow injuries often have characteristic radiological appearances, which may only be detected by the presence of soft tissue abnormalities.

There are important considerations when dealing with elbow injuries in children.

Elbow development

Bone structures at the elbow develop within multiple cartilaginous ossification centres. Typically there is ossification in the following order - Capitulum (C), Radial head (R), Internal epicondyle (I), Trochlea (T), Olecranon (O) and External/Lateral epicondle (L).

These centres of ossification become visible from 6 months to 12 years of age and in early adulthood fuse to the humerus, radius or ulna.

Key points

  • Elbow injuries have characteristic appearances
  • Soft tissue abnormality is often the only evidence of bone injury
  • An awareness of elbow development is essential when considering paediatric elbow injuries

Order of elbow ossification centre development

  • C - Capitulum (or Capitellum)
  • R - Radial head
  • I - Internal epicondyle (or medial epicondyle)
  • T- Trochlea
  • O - Olecranon
  • L - Lateral (or external epicondyle)
  • Mnemonic = C R I T O L

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Normal elbow X-ray - 10 year old

  • The red ring shows the position of the External or 'Lateral' epicondyle (L) which has not yet ossified
  • All the other centres of ossification are visible
  • C = Capitulum
  • R = Radial head
  • I = Internal epicondyle
  • T = Trochlea
  • O = Olecranon
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Normal elbow X-ray appearances

On the lateral image there is often a visible triangle of low density lying anterior to the humerus. This is the anterior fat pad which lies within the elbow joint capsule. This is a normal structure.

Anterior humerus line

A line extending from the anterior edge of the humerus should pass through the capitulum with at least one third of the capitulum seen anterior to it.

Radiocapitellar line

A line taken through the centre of the radius should extend so it passes through the centre of the capitulum.

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Normal elbow X-ray - Lateral - (7 year old)

  • Normal anterior fat pad
  • The posterior fat pad is not visible - soft tissue of the triceps muscle is not separated from the posterior edge of the humerus
  • More than one third of the capitulum lies in front of the anterior humerus line
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Normal elbow X-ray - AP - (7 year old)

  • The first three ossification centres are visible
  • C = Capitulum
  • R = Radial head
  • I = Internal epicondyle
  • The Trochlea (T) has not yet ossified (Red ring = predicted position)
  • IMPORTANT RULE - Suspect avulsion of the internal epicondyle if it is absent and there is ossification at the site of the trochlea

Raised fat pad sign

If the anterior fat pad is raised away from the humerus, or if a posterior fat pad is visible between triceps and the posterior humerus, then this indicates a joint effusion. In the setting of trauma this is due to haemarthrosis (blood in the joint) secondary to a bone fracture. This is often the only X-ray sign of a bone injury.

A post-traumatic effusion without a visible bone fracture usually indicates a radial head fracture in an adult, and a supracondylar fracture of the distal humerus in a child.

If there is a joint effusion but no history of trauma, an inflammatory cause should be considered.

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Elbow X-ray - Radial head fracture

  • Adult patient
  • The lateral image shows the anterior fat pad is raised away from the humerus but does not show a fracture
  • Posterior fat pad visible - ALWAYS ABNORMAL
  • A fracture of the radial head is visible on the AP image
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Elbow X-ray - Supracondylar fracture

  • Child patient
  • Visible fracture of the distal humerus
  • A joint effusion (haemarthrosis) raises the fat pads away from the humerus
  • The powerful triceps muscle posteriorly displaces the ulna - taking the capitulum (C) with it
  • The capitulum therefore lies well behind the anterior humerus line
  • REMEMBER - At least one third of the capitulum should lie in front of the anterior humerus line

Elbow dislocation

The radial head may dislocate from the capitulum of the humerus on its own or in combination with dislocation of the ulna from the trochlea. The latter is usually straightforward to identify, but radial head dislocations may be more subtle. The rule to remember is that the midline of the radial shaft, the radiocapitellar line, should pass through the middle of the capitulum.

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Elbow X-ray - Radial head dislocation

  • The radiocapitellar line does not pass through the capitulum
  • In this case the ulna is also dislocated from the trochlea

©Radiology Masterclass 2007 -