DOI: https://doi.org/10.21203/rs.3.rs-2235260/v1
Nine extensor tendons originate from the dorsal aspect of the forearm and course across the dorsal wrist to insert either to the metacarpals or the phalanges of the digits and thumb. These tendons are covered by the synovial sheaths which in turn pass through the fibro-osseous tunnels formed by the extensor retinaculum at the distal radio-ulnar joint (DRUJ), organised as the six extensor compartments1.
Extensor pollicis brevis (EPB) traverses in the first compartment along with Abductor pollicis longus (APL) tendon. Extensor pollicis longus (EPL) runs in the third compartment. Many variations of the course of the EPB have been reported in the literature. Suguira et al 2 reported a variant course of EPB tendon out of the first compartment, in the third compartment along with EPL, as observed in a cadaveric study. A very few reports are found in the literature describing these variations in clinical scenarios. We report the rare finding of EPB tendon accompanying EPL tendon in the third compartment observed during an emergency trauma surgery.
A gentleman aged 60 years, right-handed presented to the emergency with an injury to the left thumb. He sustained a deep laceration over the dorsum left hand (anatomical snuff box region) while cutting fruit with a long kitchen knife. He was unable to extend the thumb and complained of pain over the injured site. Sensation over the first webspace and thumb was intact. He was able to flex the thumb at the inter-phalangeal (IP) joint as well perform abduction and adduction. There was no bony deformity. Plain radiographs of the left hand showed no fractures. Plans of the surgery namely exploration of the laceration, extensor tendon repair, post-operative immobilisation and physiotherapy were explained.
Surgery was performed under Regional Anaesthesia (Axillary block). The oblique laceration was explored, and the transected distal end of the extensor tendon was identified. A passive pull of the cut end of the tendon demonstrated extension of the IP joint of the thumb and therefore, the tendon was noted to be EPL (Fig 1). The latter was accompanied by another tendon located on the ulnar side, with its insertion to the base of the proximal phalanx. The passive traction or pull of the second tendon demonstrated extension of the thumb at the metacarpo-phalangeal (MCP) joint. There was no demonstrable abduction of the thumb. On proximal exploration two tendons were retrieved from the same fascial pulley of the third compartment. The first compartment showed only one tendon with its insertion to the base of the first metacarpal, which is that of APL. EPB was absent in the first compartment. Therefore, tendon traversing ulnar to EPL in the third compartment with its distal insertion to the base of the proximal phalanx is EPB, demonstrating its variant course in the third compartment (Fig 2). The anomalous tendon was thin and flat. The tendons were repaired using the Modified Kessler’s technique using Polypropylene 3-0 for the core sutures and Polypropylene 4-0 for the epitendinous repair. Skin was closed using Polypropylene 4-0. Post-operatively, the hand was immobilised with thumb in full extension and wrist in 20-30 degrees extension using the Plaster of Paris (POP) slab. He was treated with oral antibiotics for a week. Skin sutures were removed on 12th post-operative day. POP was continued for 4 weeks. Mobilisation of the thumb with active and passive physiotherapy was initiated from the 5th post-operative week. At the end of 8 weeks patient had complete recovery of extension of the IP and MCP joints of left thumb.
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.
Funding
The authors did not receive support from any organisation for the submitted work.
Competing interests
Both authors declare they have no financial or non-financial interests. No conflicts of interest.
Consent
Informed consent was obtained from the patient for the use of data and photographs for publication. The consent has been formally documented in the medical record.
Ethical approval
No ethical approval required.
Authors Contribution
A Rangarajan: Data collection, Data compilation, Manuscript writing
KG Bhaskara: Manuscript writing
Availability of data and materials
Available with the Corresponding author.