A Rare Supernumerary Extensor Pollicis Longus Tendon: Two Cases Report

This report corresponds to two rare cases in which the accessory extensor pollicis longus was discovered during dorsal wrist surgery of wrist trauma in young people with the need of reconstruction of the scapholunar ligament. These variations consist in two bellies and two tendons of the extensor pollicis longus, coexisting and with the origin in different compartments and the same insertions in the distal phalange of the thumb.

Although a series of anatomical variations of dorsal tendons of the hand have been reported, only few reports of variations of the extensor pollicis longus (EPL) can be found and usually in cadaveric studies. Cauldwell et al reported an incidence of anomaly in the EPL tendon of 1% in a study with 263 cadavers. This rare frequency probably is due to the embryological stability of the EPL [1,2].

It could be one of the least variable muscles of the forearm. Doubling of the extensor longus is not infrequent, and the ulnar portion of the muscle sometimes passes beneath the dorsal anular ligament with the common extensor. The extensor pollicis longus is reported to be absent in about 1.5% of individuals. A slip from the tendon of the long extensor to the extensor indicis is occasionally seen. A rarer variation is an additional extensor between the extensor indicis and extensor pollicis longus, with a double tendon and insertion into both digits. This additional extensor can replace the extensor pollicis longus or extensor indicis [3]. We present two surgical cases with different variations of the long extensor tendon of the thumb.

Case report 1: our first patient was a 19-year-old male medical student who was taken to surgery for treatment of a trans-scaphoid perilunate fracture dislocation after falling off a bicycle. During the surgical approach, an abnormal configuration of the EPL extensors was observed: two tendons corresponding with the EPL. More proximal dissection revealed a separated belly for each EPL tendon, coming from different compartments (Figure 1): one from the third compartment and its course corresponded to the extensor pollicis longus itself (Figure 2) and the anomalous tendon from the fourth compartment (Figure 3). When each tendon was retracted individually, the distal phalanx of the left thumb extended.

Figure 1: Overview of Two Tendons Directed to The Distal Phalanx of The Thumb

Figure 2: Extensor pollicis longus tendon emerging from the third compartment.

Figure 3: supernumerary extensor pollicis longus tendon emerging from the fourth dorsal compartment. It’s remarkable the lesser thickness of the accessory tendon.

Case report 2: our second patient was a 27-year-old male metalworker and engineering student who was taken to surgery for reconstruction of scapholunate ligament. This patient was been previously operated on the opposite hand and no anatomical variation has been noticed. As the first case, was observed two tendons corresponding to EPL, with different origin compartments – third and fourth – and inserting in the distal phalanx of the thumb. By retracting both tendons, the distal phalanx of the left thumb was extended (Figure 4).

Figure 4: supernumerary extensor pollicis tendon emerging from the fourth dorsal compartment.

Variations in tendon anatomy are important during surgeries involving repair, transfer of tendons and other conditions. Wood, in 1868, first reported the existence of a supernumerary long extensor to the thumb. Kaplan and Nathan, in 1969, described an accessory muscle and tendon arising adjacent to extensor indicis within the fourth compartment and running parallel to the EPL [4,5].

Beatty et al reported accessory muscle belly arose from the tendon of extensor pollicis longus and lay within the third extensor compartment causing pain and clicking. Culver, in 1980, and Talbot, in 2013, described findings of a supernumerary extensor tendon supplying both index finger and thumb [6,7,8].

Türker et al, in 2010, proposed a two-part classification after a meta-analysis of various reports available in the literature. The first part corresponding to supernumerary long extensor tendons to the thumb divided it in six subtypes. And the second part divided in four subtypes the aberrant interconnections between the long extensor tendon to the thumb and neighboring tendons (Table 1) [9].

Table 1: Classification of ELP variations in two subtypes.

According to these classifications, both the cases reported in this study were 1a separated bellys, with origin in different compartments (third and fourth) and the insertion in the distal phalange of pollicis [9].

Our cases are relevant since they are wrist traumas in young people with the need of reconstruction of the scapholunar ligament, among other associated techniques. The fact is that they are reconstructive procedures for the biomechanics of the wrist and hand, so it requires anatomical and biomechanical knowledge to reestablish function in the best possible way. The anatomical variations of EPL were occasionally found during the surgical procedure.

The clinical implication of accessory EPL tendons is not clear. Most reports were originated from cadavers, and some studies have shown an association with routine dorsal wrist pain and limitation of range of movement of the thumb [1,2,4]. Even in asymptomatic cases, such ours, there is a concern about the impact of these anomalies on surgical procedures in the forearm, wrist, and hand. Once the stability function was unknown, if these supernumerary tendons are cut or damaged, the surgeon will may face difficulty in establishing anatomy or even reestablishing stability [8].

This article presents two case reports of incidental findings during surgical procedures of rare anatomical variations in the extensor pollicis longus. Our findings may help to increase awareness of such anatomical variation and increase the chance of success of surgical treatment in trauma and planning of reconstructions, tendon repairs and transfers, in addition to avoid possible biomechanical iatrogenic changes after surgery.