Unilateral two-headed extensor digitorum longus muscle: atypical configuration and clinical implications

Abstract

This report describes a new configuration of the extensor digitorum longus (EDL) with two heads and two main tendons divided into four slips. During routine cadaver dissection, unilateral (right) EDL muscle belly and tendon variations were identified. The morphometric measurements of the EDL were conducted using Image J software. Two bellies and two tendons of the EDL muscle were observed in the right leg of an 87-year-old male cadaver. The second belly of the EDL muscle originates 2 cm below the first belly. The tendons originate at the ends of the muscle bellies. First and second tendons split into two more slips after passing through the same tunnel below the extensor retinaculum. The first tendon was divided into two tendon slips attached to the extensor expansion of the second and third toes, whereas the second tendon was divided into two tendon slips attached to the extensor expansion of the fourth and fifth toes on the dorsum of the foot. The width of the muscle belly for the tendons of 2nd and 3rd toes was 1.10 +/- 0.06 cm, while it was 1.39 +/- 0.04 cm for that of the 4th and 5th toes. The developmental variations in the EDL muscles can be asymptomatic. This variant of the EDL muscle may cause entrapment under the extensor retinaculum, potentially restricting ankle dorsiflexion. This limitation can also affect walking. Consequently, paying attention to this variance is crucial for surgical planning and interpretation of radiological scans.