A Unique Bilateral Variation of the Extensor Carpi Radialis Longus: A Case Report

Abstract

A novel combination of variations involving the extensor carpi radialis (ECR) muscle group was observed bilaterally in a 75-year-old female cadaver during routine dissection. An accessory tendon was observed arising from the extensor carpi radialis longus (ECRL) and traveling with the primary tendon through the second compartment of the extensor retinaculum. While the primary tendon inserted on the base of the second metacarpal, as is typical of ECRL, the accessory tendon inserted on the base of the third metacarpal. This insertion is typical of the extensor carpi radialis brevis (ECRB) muscle. Additionally, bilateral agenesis of the ECRB was reported. Thirty-two additional forearms were assessed for similar variations, with none being observed. This combination of variations adds to the literature regarding the ECR muscle group, while also being of interest to clinicians, specifically regarding tendon reconstructive procedures as well as accessing the distal radial artery via the anatomical snuffbox.

Keywords: anatomical variation; extensor carpi radialis brevis; extensor carpi radialis longus; forearm; forearm extensors; tendon.

Figure 1

Classical anatomy of the right posterior forearm. Dissection of the posterior compartment of the right forearm showing the typical anatomy of its musculature (ER: extensor retinaculum, ECRL: extensor carpi radialis longus, ECRB: extensor carpi radialis brevis, EPL: extensor pollicis longus, EPB: extensor pollicis brevis, APL: abductor pollicis longus, ED: extensor digitorum).

Figure 2

Dissection of the left posterior forearm. Dissection of the posterior compartments of the left forearm showing the muscles in this compartment, as well as their tendons passing beneath the extensor retinaculum (A). The extensor retinaculum was removed to show the tendons originating from a single extensor carpi radialis longus muscle belly (B,C) (ER: extensor retinaculum, ECRL: extensor carpi radialis longus, EPL: extensor pollicis longus, EPB: extensor pollicis brevis, APL: abductor pollicis longus, ECU: extensor carpi ulnaris, ED: extensor digitorum).

Figure 3

Dissection of the right posterior forearm. Dissection of the posterior compartments of the right forearm showing the muscles in this compartment, as well as their tendons passing beneath the extensor retinaculum (A). Removal of the extensor retinaculum allowing the tendons originating from a single extensor carpi radialis longus muscle belly to be observed (B,C) (ER: extensor retinaculum, ECRL: extensor carpi radialis longus, EPL: extensor pollicis longus, EPB: extensor pollicis brevis, APL: abductor pollicis longus, ECU: extensor carpi ulnaris, ED: extensor digitorum).