The presence of extensor digiti medii muscle-anatomical variant

This study reports the presence of the extensor digiti medii muscle (EDM) in a population of cadavers dissected by students at a chiropractic college anatomy laboratory and determines its frequency, bilaterality, innervation, and sex differences.

Dissection of upper extremities of 47 human cadavers (24 males, 23 females) was conducted. Both upper extremities were examined for bilaterality. The long extensor tendons were exposed, separated, and cut to expose the EDM. Identifying the innervation of the variant muscle was attempted. The specimens were then photographed.

In this report, the prevalence of EDM is at 7.4%. The EDM was discovered in 5 male cadavers and 1 female cadaver (5:1 ratio). It also revealed that the EDM was prevalent on the left forearm than on the right forearm at a ratio of 5:2. Out of the 47 cadavers studied in this report, only one was observed to have EDM bilaterally (2.1%). In 2 cadavers, the EDM appeared to be supplied by the posterior interosseous nerve. The branch piercing through the extensor indicis muscle continued to give off a small branch entering the belly of the EDM.

The findings obtained in this report support previous observations regarding its prevalence in males more than females. The report also shows that the EDM occurs more in the left forearm than the right forearm as opposed to other reports of equal incidence between left and right forearms. This report also supports one previous study showing that the posterior interosseous nerve innervates the EDM.