Small flake, big problem: an unreported cause of extensor pollicis longus tendon rupture

Abstract

Fracture of the base of the third metacarpal with associated avulsion of the extensor carpi radialis brevis tendon is a rare injury. We report such a fracture and the unusual resulting complication of division of the extensor pollicis longus tendon by the avulsed bony fragment. Careful monitoring using lateral radiographs is needed to make the diagnosis and displacement of the avulsed fragment warrants open reduction and internal fixation.

Avulsion fracture at the insertion of either of the radial extensors of the wrist is a rare injury. Isolated avulsion of the extensor carpi radialis longus (ECRL) tendon from the base of the second metacarpal has been described in the literature only 10 times.^1,2 Isolated avulsion of the insertion of the extensor carpi radialis brevis (ECRB) tendon from the base of the third metacarpal has been described only 6 times.^3,4

Rupture of the extensor pollicis longus (EPL) tendon is a well-known injury, with a multifactorial aetiology.⁵ Attrition rupture of the EPL caused by an avulsed fragment of bone from the long radial wrist extensor (ECRL) has been reported in the literature only twice.^6,7 We report, for the first time, a rupture of the EPL tendon caused by the avulsed fragment of bone attached to the ipsilateral ECRB tendon.

Case history

A 35-year-old man was performing a martial arts manoeuvre and punched a plank of wood with the his right, dominant hand. His forearm was pronated, his elbow straight, and his wrist slightly flexed. He felt immediate pain in his wrist. He attended the local accident and emergency department where he was found to be bruised and swollen over the dorsum of his right hand and wrist. X-ray showed a fracture at the base of the third metacarpal (Fig. 1). This was treated conservatively in a full cast, extending from the proximal forearm to the mid-palm, immobilising the wrist. The cast remained for 5 weeks. Two weeks following removal of the cast, the patient was tying his shoelaces and felt a sudden sharp pain at the base of his right thumb radiating to his elbow. He was immediately unable to extend the interphalangeal joint of his right thumb.

Figure 1.

Fracture of the base of the third metacarpal with an avulsion fragment visible over the proximal carpal row.

He was referred to the Hand Trauma Clinic where he was found to have tenderness in the anatomical snuffbox that radiated to the common extensor origin. He was unable to retropulse his right thumb, with clinical rupture of the EPL tendon (Fig. 2). A true lateral radiograph of the wrist showed an avulsed flake of bone at the level of the proximal carpal row. An ultrasound scan of the area confirmed complete rupture of the EPL tendon at the level of the fragment and avulsion of the ECRB tendon in continuity with the flake of bone.

Figure 2.

Inability to extend the thumb from the table-top position is pathognomic of EPL dysfunction.

At operation, the frayed distal stump of EPL was found lying next to the avulsed fragment of third metacarpal base (Fig. 3). The proximal stump of EPL had retracted and primary repair was not possible. The EPL tendon was reconstructed using an extensor indicis proprius tendon transfer and Pulvertaft weave. The ECRB was replaced into its anatomical position and the bony fragment was reattached to the base of the third metacarpal using a compression screw (Fig. 4). Postoperatively, the patient was placed in a protective cast, and early hand therapy was commenced on his thumb. At 3 months, he has rehabilitated well. X-ray has confirmed union of the fracture and, although he lost a grade of power in thumb extension, he has a functional EPL. His wrist extension on the right is approximately 20º less than on the normal left side, but this is expected to improve with further physiotherapy. He is back at full-time work.

Figure 3.

The frayed distal stump of the severed EPL tendon (white arrow) is found next to the avulsed fragment of bone attached to ECRB (dark arrow).

Figure 4.

The avulsed fragment is reduced and held with a lag screw.

Discussion

The causes of EPL rupture are well documented. Although spontaneous rupture of EPL is most commonly associated with rheumatoid disease, there is a wealth of information in the literature concerning post-traumatic rupture. This is most commonly seen following fracture of the distal radius, although it has been described following first and second metacarpal fracture, triquetral fracture, and even fracture of the scaphoid.⁵ It is also a known complication due to attrition over prominent metalwork following fracture fixation.⁸

Isolated fractures of the base of the third metacarpal, however, are rare injuries. The position of the patient’s upper limb at the time of his injury (wrist flexed, forearm pronated, elbow extended) ensured that the ECRB tendon was at its maximum length. Added to the force of the insult, this combination of factors was enough to cause his injury. In such cases, examination reveals tenderness and swelling at the base of the third metacarpal. It is essential that lateral radiographs are taken to identify any avulsion fragments, not only to avoid the sequelae described here but, more importantly, to ensure preservation of ECRB function. The role of the ECRB tendon is to extend the wrist and provide a stable platform during gripping, whereas the ECRL is more important for radial deviation of the wrist.⁹ It is, therefore, important to salvage ECRB function where possible.

Fracture of the base of the third metacarpal may be adequately treated by immobilisation provided that any avulsed fragments of bone remain in good alignment and the function of ECRB is preserved. It may be necessary to perform regular lateral X-rays to ensure that the fragment is not becoming further detached. In cases where the avulsed fragment is displaced, we advise open reduction and internal fixation in order to re-establish the articular anatomy, to preserve extensor tendon function, and to prevent late attrition rupture of neighbouring extrinsic digital extensor tendons.