Elbow radiograph (an approach)

Elbow radiographs are common and oftentimes difficult to interpret without a solid systematic search strategy. 

Systematic review

Choosing a search strategy and utilizing it consistently is a helpful method to overcome common errors seen in diagnostic radiology. The order in which you interpret the radiograph is personal preference. A recommended systematic checklist for reviewing musculoskeletal exams is: soft tissue areas, cortical margins, trabecular patterns, bony alignment, joint congruency, and review areas. Review the entire radiograph, regardless of perceived difficulty. Upon identifying an abnormality, do not cease the review, put it to the side and ensure to complete the checklist.

Soft tissue

Assess all soft tissue structure for any associated or incidental soft tissue signs. In the case of the elbow, this will involve assessing for secondary signs of joint effusion.

The sail sign

On the lateral radiograph, inspect for the displacement of the anterior and posterior fat pads embedded in the two layers of the joint capsule. The anterior fat pad is normally seen as a faint line running with the distal humerus, whilst the posterior fat pad is not seen in normal radiographs. 

Elevation of these fat pads, known as the sail sign indicates a joint effusion and should raise suspicion of an occult fracture. 

Common fractures to consider in this setting:

• adult: radial head fracture
• child: supracondylar fracture

Bone cortex

Check each bone in turn:

• pay particular attention to structures that are superimposed i.e. the coronoid process

Bony alignment

There are a few useful lines worth committing to memory (particularly helpful in pediatric presentations):

• anterior humeral line
  • drawn down the anterior surface of the humerus on the lateral projection it should intersect the middle 1/3 of the capitellum
  • if the line does not intersect this point, distal humeral fracture such as a supracondylar fracture should be considered
  • in some cases (patients under 4 years) the line will pass through the anterior third and these are normal
• radiocapitellar line
  • drawn along the radial neck on the lateral and AP view it will intersect the capitellum
  • if abnormal consider a radial head dislocation or subluxation which should then prompt you to consider a fracture-dislocation such as a Monteggia fracture-dislocation
• carrying angle
  • the axis of a radially deviated forearm and the axis of the humerus which should be, 14° in women and 11° in men,  away from the body ²
  • varus malalignment, consider cubitus varus

Joint congruency

One should inspect for smooth, concurrent bony alignment in all views.

• AP
  • the radial head should have an articulation with the capitellum
  • clear congruity of the trochlea of the distal humerus and the trochlea notch of the proximal ulna
• lateral
  • the outline of the posterior olecranon fossa and the anterior coronoid fossa should make a 'figure 8' indicating a well-positioned lateral
  • the radial head should have articulation with the capitellum, a useful tool when trying to differentiate from the trochlea
  • smooth joint space between the trochlea notch of the ulna and the distal humerus

Ossification centers

Although only applicable to younger patients many larger centers will still get occasional pediatric presentations and therefore it would be amiss to leave this out. Review the ossification centers of the elbow, they should appear in the following order ³: 

• capitellum: 2-24 months
• radial head: 3-6 years
• internal (medial) epicondyle: 4-7 years
• trochlea: 8-10 years
• olecranon 8-10 years
• external (lateral) epicondyle: 10-13 years

Understanding the order is important, and systematically reviewing the radiograph can ensure one does not miss subtle pathology such as a medial epicondyle fracture.

For a more in-depth approach to pediatric elbows see, pediatric elbow radiograph (an approach)

Review areas

• the proximal portion of the humerus 
• radial head (often superimposed, additional views can be performed)
• alignment of the ulna and radius (consider larger fracture-dislocation injuries) 
• coronoid process (quite rare however easily missed)