Friday, August 1, 2008

Korn and the Extensor Pollicis Longus

My teenage son recently went through his musical Korn phase. Delicate music, this is not. Lots of ear-splitting, pounding guitar, twisted transistors, and a drummer that loves to pound his kit:

Photo by Mark McLauglin

Drumming has been around for a few hundred years, and it should come as no surprise that drummers can get injured from their repetitive acrobatics. In 1876 Duplay described "drummer boy's palsy" in Prussian drummers, due to rupture of the extensor pollicis longus (EPL) tendon. Patients with rupture of the EPL tendon present with pain and loss of thumb extension.

The EPL tendon is classically torn as a result of a distal radius fracture. In this setting, the tendon usually ruptures at the level of Lister's tubercle, typically one to three months following the fracture. The EPL can also experience attritional tearing in the setting of systemic diseases such as rheumatoid arthritis, lupus, and gout. Rarely, the EPL tendon can be torn at the level of the distal phalanx of the thumb.

The EPL tendon can also rupture due to trauma, although this is less common. Twenty-eight year old gentleman, who sustained an injury playing lacrosse, and complained of dorsal wrist pain, radiating to the thumb. Axial T2-weighted image reveals a small amount of fluid surrounding the EPL tendon, which is markedly abnormal in signal:

On sequential coronal images, the EPL tendon (yellow arrows) is still continuous, but has a striated appearance, and it is surrounded by a thin rim of increase fluid:

Note the normal cross-over of the EPL tendon over the extensor carpi radialis brevis [ECRB] tendon (green arrows). These images define the presence of a partial tear of the tendon, with reactive inflammatory fluid in the tendon sheath.

The patient was treated conservatively, but several weeks later suffered an additional traumatic event, and presented with acute loss of thumb extension, with a recurrence of dorsal wrist pain radiating to the thumb. An EPL rupture was diagnosed clinically, but an MRI was obtained to exclude a concurrent intercarpal ligament injury. An axial T2-weighted image reveals that the third dorsal compartment, which normally houses the EPL tendon, is nearly empty, with only a small amount of debris in the tendon sheath:

A coronal image better depicts the fluid in the essentially empty tendon sheath:

A slightly more anterior coronal image identifies the torn, retracted EPL tendon (red arrow).

Ruptures of the EPL tendon are not repaired directly. This situation has not changed for many decades, as demonstrated from this letter in the British Medical Journal in September, 1937:

EPL ruptures are treated with a tendon transfer, typically using the extensor indicis.

The EPL tendon can be challenging to image on MRI, due to the thin nature of the tendon, and the complications of magic angle artifact. Nonetheless, with high-resolution, thin section MR imaging, much information can be gained.

Vic David MD

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