Core Content - Core Orthopaedic Concepts - Interpreting Radiographs


The Film

 

When asked to describe a radiograph on the spot, an easy way of giving yourself some ‘thinking time’ is to describe the basics of who and what the film is of.

  1.  What the projection is (AP/Lateral/Oblique or special views like an ankle mortis view)
  2.  What bone or region it is centered on, including the side
  3. Patient name (or initials), age and sex
  4.  When the radiograph was taken
  5. Adequacy of the film. Is it properly centered? Is everything you need to see included?

This will give you something like the following:
This is an AP and a lateral radiograph of the left forearm of Mr AB, a 70 year old man. It was taken on the 5th of March and the film adequately positioned.

 

To properly interpret a radiograph, it is important that the film is centered on the bone or joint that is to be examined, and not part of a larger film. An example would be looking at a wrist joint on a wrist radiograph as opposed to on a forearm radiograph.

This is because a radiograph is taken using a point source for the x-rays and is therfor subject to beam spreading. This means the x-rays hit the detector plate at an increasingly shallow angle when further from the center of the image.

Demonstration of beam spread
Click to Enlarge

If a radiograph of 2 pairs of spheres was taken, as in the diagram to the right, with one pair centered under the beam and one pair far to the side, then the images would be significantly different. The first pair would appear as 2 almost perfect circles with a gap in between. The second pair would appear to touch or overlap and their shapes would be distorted.

The above example is exaggerated,  as in practice the point source is further from the body part, but a radiograph centered on a forearm will still have a view of the wrist that is oblique. When deciding on treatment of a fracture, it is important to bear this in mind as sometimes a very small difference, such as articular displacement of a milimeter, can mean an operation rather than a plaster cast.

 

If you are asked to comment on a radiograph on the spot ,and you think that the film is not adequate, then you could say something like the following:
On this AP of a left forearm, I am suspicious of a distal radius fracture. I would like a further AP and lateral radiograph centered on the wrist to fully assess and describe this.

 

The Fracture

 

Fracture Pattern

Transverse

Oblique

Spiral

Comminuted/Complex

Intra-articular

 

Fracture Location

Diaphyseal – Split into thirds (proximal, middle and distal).

Metaphyseal

Epiphyseal

You can also refer to junctions, for example ‘junction of diaphysis and metaphysis’

 

Anatomic name – Eg radial head, femoral neck

 

Fracture Displacement

Fractures can displace in 3 ways: Translocation, Angulation, Rotation. You should describe the displacement of the distal fracture fragment in relation to the proximal.

When describing fractures below the elbow, you cannot refer to anterior/posterior or medial/lateral as these change due to supination/pronation. You should therefor use Volar/Dorsal and Radial/Ulnar.

 

Translocation

Fracture fragments move away from each other.

If the fragments move towards each other along the long axis of the bone then this is called shortening.

You can quantify the degree of translocation using a percentage of the bone’s width.

 

Angulation