The extensor pollicis longus muscle (EPL) plays an important part in the function of the thumb.1 The clinical assessment of the EPL function can be challenging in cases where the EPL is intact but dysfunctional due to pseudoparalysis like an overly elongated tendon in severe shortening malunion of distal radius fracture, or in cases of the EPL tendon dislocation over Lister’s tubercle.2

The available specific clinical assessment tests like active retropulsion and passive tenodesis effect3 require the EPL to have good power function in the former, and normal anatomical course and length for the latter.4

Preoperative knowledge regarding the EPL integrity is vital for the hand surgeon as the management of the EPL dysfunction can differ dramatically. Adjunct radiological tests like ultrasonography and magnetic resonance imaging, or exploratory surgery, can help to determine the diagnosis, however, it is more efficient to have a simple clinical test to examine the integrity of the EPL.

We describe a simple clinical test to ascertain the integrity of the EPL tendon further.

ANATOMICAL CONSIDERATIONS

The EPL is a forearm muscle that originates from the dorsum of the mid-ulna shaft and adjacent interosseous membrane. It becomes a tendon and passes into the third extensor wrist compartment just proximal to the extensor retinaculum where it runs into a narrow and oblique groove at the dorsal aspect of the distal radius before changing direction over a bony Lister’s tubercle pulley. It then courses straight to insert into the dorsum of the base of the distal phalanx of the thumb. At the metacarpophalangeal (MCP) extension hood region, the EPL receives fibrous expansions from the abductor pollicis brevis and the adductor pollicis that act to extend the interphalangeal (IP) joint to neutral position only while the EPL can hyperextend the IP joint. Thus, the EPL is the only muscle that hyperextends the thumb IP joint.5 With complete extension at the carpometacarpal (CMC) and the MCP joints of the thumb the EPL becomes a weak extensor as the muscle becomes abundant in length. Similarly, the flexor pollicis longus (FPL)—the antagonist of the EPL—becomes significantly weak or even dysfunctional when the wrist is at full flexion. This plays an important role in the application of the test described.

TECHNIQUE

In this test the elbow is stabilised on the examination table in flexion and full passive pronation. The wrist is passively flexed and ulnarly deviated, and the thumb is placed passively at full abduction and hyperflexion at the CMC and the MCP joints. The IP joint is kept free. The examiner’s thumb maintains this position by placing it on the proximal phalanx of the patient’s thumb (Fig. 1A).

FIGURE 1:

A and B, Artwork illustration describing the test to assess the integrity of the extensor pollicis longus tendon. Notice the thumb interphalangeal joint remains hyperextended (1A) even when challenged by the examiner (1B), indicating an intact extensor pollicis longus.

The test is negative (intact EPL tendon) if the IP joint hyperextends and resists flexion attempt (Fig. 1B). Alternatively, the test is positive if the IP joint remains flail and slightly flexed when the EPL tendon is ruptured.

EXPECTED OUTCOMES

The described test is based on placing the patient’s EPL into the longest possible course and line of pull by pronating the forearm fully, flexing and ulnarly deviating the wrist, and placing the thumb into full passive flexion and abduction to isolate the IP joint. The IP joint therefore becomes the point of focus to exaggerate any changes to detect the integrity of the EPL.

The test can also be used to assess the integrity of the long flexor tendon of the thumb—the FPL. In this case a reverse manoeuvre is used in the clinical assessment where the elbow is stabilised over the examination table in flexion and full supination with the wrist in full passive extension and radial deviation. The thumb is then extended fully and passively at the MCP and the CMC joints by placing the examiner’s finger over the proximal phalanx of the thumb in a gentle downwards force (Fig. 2A). The test is negative when the IP joint adopts a flexion position where the FPL is intact and the joint will resist further passive extension (Fig. 2B). The IP joint remains flail otherwise.

FIGURE 2:

A and B, Artwork illustration describing the test in a reverse manoeuvre to assess the integrity of the flexor pollicis longus tendon.

In conclusion, the described test is simple, intuitive and useful in the advanced assessment of the thumb EPL and FPL integrity and function.

LIMITATIONS

There are no observed absolute limitations from performing this test, but like most clinical examination techniques and manoeuvres, this test might be hard to perform in patients with stiff or painful elbow, wrist, and thumb joints, or in patients that are noncompliant.

ACKNOWLEDGMENTS

The author is grateful for the Artwork Illustrations produced by Sara Malkawi from the University of Bradford, Bradford, UK.

REFERENCES 1. Gelb RI. Tendon transfer for rupture of the extensor pollicis longus. Hand Clin. 1995;11:411–422. 2. Hunt DD. Dislocation of the extensor pollicis longus tendon in Smith’s fracture of the radius: a case report. J Bone Joint Surg Am. 1969;51:991–994. 3. Andre-Thomas T. Le tonus du poignet dans la paralysie du nerf cubital [The wrist tone in ulnar nerve palsy]. Paris Med. 1917;25:473–476. 4. Bunnell ST. Tendon transfers in the hand and forearm. Instr Course Lect. 1949;6:106–110. 5. Austin NM Levangie PK, Norkin CC. The wrist and hand complex. Joint Structure and Function: A Comprehensive Analysis. Philadelphia, PA: FA Davis Co; 2005:305–352.