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Clinical case:

A 36 yo female was whacked with a skateboard across her hand by an assailant. She presents to the ED with this laceration. 

What is concerning about this injury, and how would you test for it?

A small laceration over the extensor surface of the  proximal interphalangeal joint.  What is the concern with an injury like this?
A small laceration over the extensor surface of the proximal interphalangeal joint. What is the concern with an injury like this?

Answer:

The depth and location are concerning for an injury to the extensor tendon mechanism at the proximal interphalangeal joint (PIP).

Due to the complexity of the extensor mechanism of the finger, this isn’t always an obvious injury.  Furthermore, failure to detect this injury can lead to serious complications.

This video describes Elson’s test, used for early detection of PIP central slip extensor tendon laceration.  Read on to learn more about the relevant anatomy, pitfalls in the diagnosis, and for an explanation of the test and a simple modification in further detail.

Anatomy Primer

The extensor tendon of the digit is not just a simple single tendon–it’s actually a complex network of 12 extrinsic extensor tendons that originate in the proximal forearm and pass across the wrist in 6 separate compartments beneath the extensor retinaculum.

Extensor Tendon Anatomy. Adapted from
Extensor Tendon Anatomy. Adapted from “Extensor Tendon Repair in the Emergency Department,” by Calabro JJ, Hoidal CR, and Susini LM.

The common extensor divides at the PIP into a central slip and two lateral bands.

If the central slip is avulsed, the lateral bands will be freed, and may migrate volarly to actually become flexors of the finger.  This leads to an odd appearance of the finger known as the Boutenniere deformity.

Central Slip Lac

This typically takes weeks to occur, but if you miss the injury to the central slip on presentation, you are putting the patient at risk. Furthermore, it is a condition that is very tough for a hand surgeon to reverse once it occurs.

Diagnostic Pitfalls

It pays to be aware of a few diagnostic pitfalls:

  • PITFALL! The extensor tendons are thin and tend to retract out of the field of view when severed.  Without intimate knowledge of hand anatomy, a tendon injury can easily be missed by visual inspection alone.  Furthermore, a detailed exploration may require extension of the skin wound, which not all providers are prepared to do.
  • PITFALL! Simply testing extension at the PIP can miss a central slip injury.  A patient with intact lateral bands will maintain the ability to extend the digit (albeit, weakened).

Diagnosis: Elson’s Test

Elson’s test is the most well known test to diagnose an injury to the central slip before complications occur.  Here’s how it’s done:

  • The patient bends the PIP 90° over the edge of a table and extends the middle phalanx against resistance.
  • In the absence of central slip injury (negative test), extension is strong AND the DIP remains floppy because the extension force is now placed entirely on maintaining extension of the PIP joint, so the lateral bands are not activated.
  • In the presence of central slip injury (positive test) there will be weak PIP extension, AND the DIP will extend abnormally and become rigid.

The “Modified” Elson’s Test

I find this test easy to understand when I read about it, but in actual practice it can be a little tough to feel confident when you are testing relative strength of extension in the PIP and to judge abnormal extension in the DIP.  That was the case with this patient.

Here’s a trick that can help in this situation.  It’s an interesting modification of the Elson test published in 2006 in the British Journal of Hand Surgery:

  • The injured and uninjured contralateral finger are placed knuckle to knuckle in 90 degree PIP flexion, with the middle phalanges pressed against each other. The patient is then asked to extend both DIPs.
  • If the two fingers remain in a symmetrically semi-flexed position, then there is no injury.
  • A finger with a central slip injury will be able to extend the DIP more than in a non-injured hand.
Abnormal modified Elson's test.  The injured finger (blue tourniquet) should not be able to extend this much, but the key to making the diagnosis is the asymmetry.
Abnormal modified Elson’s test. The injured finger (blue tourniquet) should not be able to extend this much, but the key to making the diagnosis is the asymmetry.
By way of comparison: a normal modified Elson's test, where the distal phalanges are limited in extension.  Again, the key is assessment of the symmetry.
By way of comparison: a normal modified Elson’s test, where the distal phalanges are limited in extension. Again, the key is assessment of the symmetry.

There you have it–a few ways to make sure you don’t miss an injury with some serious sequelae. For another interesting case involving a specialized test for a tendon injury, click here.

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