A rare subtype of the extensor digitorum brevis manus muscle: description and clinical relevance

The extensor digitorum brevis manus (EDBM) is an infrequent anatomical variation on the dorsum of the hand, with an estimated prevalence of 2%. Morphologically, type III is the rarest variant. The purpose of this study is to provide a detailed morphological description of a rare specimen of the EDBM, classified as type III, and to analyze its biomechanical implications and clinical relevance in the differential diagnosis.

A meticulous anatomical dissection was performed on the dorsal surface of the left hand of a male cadaver. Morphometric analysis was conducted using a digital caliper to record the precise dimensions of the muscle belly and its associated tendon.

An accessory muscular structure was identified deep to the tendons of the extensor digitorum muscle, located medially to the extensor indicis muscle. The muscle originated from the dorsal radiocarpal ligament at the distal portion of the radius and inserted into the medial margin of the extensor expansion of the middle finger. This configuration corresponds to the type III variant by Ogura et al., which represents the rarest variant described in the literature.

The EDBM is a significant anatomical variation often misdiagnosed as a ganglion or synovial cyst due to lack of awareness among clinicians. Understanding its rarest subtypes, such as type III, is essential for improving clinical practices and surgical management thereby enhancing the quality of life for symptomatic patients.