Friday, November 7, 2008

Icebergs and Fractures

The word "fracture" comes from the Latin word fractura, meaning "a breach, break, cleft". The word is used in various ways— for example, when icebergs fracture from a glacier, that process is known as "calving":

In medicine, "fracture" is usually used in the context of a bone break. MRI is excellent for depicting acute fractures, because most acute fractures are accompanied by extensive bone marrow edema, as in this radial head fracture in my 14 year-old son:

In the subacute or chronic setting, however, MRI becomes less sensitive for fractures, in part because bone marrow edema often subsides or resolves entirely. This can be particularly problematic in small joints. The bones are smaller, and are often curving in character, creating volume-averaging artifact.

One way to increase the sensitivity of the exam for small chip or avulsion fractures is to use a thin-section 3D (volume) gradient echo sequence. This is often the best sequence for picking up these subtle injuries.

Here are MRI and CT images from a 35 year-old male with a history of trauma four months ago:

(click on image to enlarge)

There is a subtle chip fracture of the lunate (red arrows), which is seen best on the GRE (gradient echo) and CT images. Note how difficult the fracture is to see on the intermediate fatsat (Int FS) image. When reading wrist MRI, I try to scrutinize the 3D GRE images very carefully, as this can often be the only sequence where a fracture is well-seen.

Thus, it's generally a good idea to run a thin-section GRE sequence for wrist MRI. Fractured icebergs off glaciers are easy to see, but small bone chip and avulsion fractures can be hard to detect without this sequence.

Vic David MD

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