Numerous descriptions regarding the anomalies of the extensor tendons in their course have been reported in the literature. Brunelli et al3 carried out cadaveric research to study the anatomy of EPB on 52 hands. They observed anatomical variations of the EPB with regards to its presence in the first extensor compartment, size, insertion, and function. EPB was noted to be single, thin, ran along with APL in the first compartment except in five cases where EPB traversed in a separate compartment divided from APL by a fibrous septum.
Various studies in the literature have reported the presence of accessory tendons associated with EPB4,5. They have also documented different insertion sites of the tendon. None of these studies have described presence of EPB in other compartments other than in the first compartment either with APL or divided from APL by a septum.
Takayu et al6 reported a rare case where they found two slips of EPL tendon originating from the same muscle belly and inserting to the base of the distal phalanx. EPB was absent in the first compartment. It was considered that one of the two slips of the EPL, on the radial side performed the functions of EPB.
Papaloizos et al7 reported a finding of supernumerary EPL during a cadaveric dissection. The additional extensor tendon traversed ulnar to the principal EPL, in the fourth compartment, separated from the latter by a bony prominence like Lister’s tubercle. This tendon led to the extension of the IP joint of the thumb. EPB was present in its usual first compartment.
Suguira et al2 described an unusual course of EPB in the third compartment in a cadaver, a similar finding in our patient. EPB tendon was identified radial to EPL with insertion to the base of the proximal phalanx. APL was the only tendon in the first compartment. In our patient EPB was seen traversing ulnar to the EPL.
EPL is an undeviating extensor tendon in the third compartment according to Yoshida et al8. An absent EPB in the first compartment was noted only in two of the 52 cases studied by Brunelli et al3. This suggests that an absent EPB in the first compartment during hand reconstructive surgery warrants its exploration in the other compartments just as seen in our case report.
Knowledge of the anomalous variants of the EPB tendon will assist in the reconstructive hand surgery namely repair of the tendon during traumatic injury, spontaneous rupture of the tendon, tendon transfer surgery in spastic hands, reconstruction of ulnar collateral ligament. This also means that a pre-operative evaluation of the tendon by ultrasound or magnetic resonance imaging becomes imperative to be certain of the anatomy and its possibility as a donor in tendon transfer surgery.