The presence of extensor digiti medii muscle—anatomical variant

Abstract

Objective: 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. Methods: 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. Results: 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. Conclusion: 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.

The prevalence of the extensor indicis tendon and its variants: a systematic review and meta-analysis

“…Four studies reported the gender composition of their results [5,23,42,45]; out of 37 EMP, 16 were found in males and 22 in females. Four studies reported the side composition of their results [5,10,23,42]; out of 31 EMP, 7 were bilateral, and 17 unilateral of which 11 were on the right side and 6 on the left side.…”

A Cadaveric Study on the Anomalous Extensors of the Hand

“…The incidence of EMP has been reported to be 1% to 12% in cadaver studies, in the current study it is 9.3%. Table1 reports the incidence of EMP in literature [13,[15][16][17][18]. EMP is observed more frequently in males than females, but it is not frequently described in anatomical dissections since it is a small muscle in width and is covered by the tendons of ED [19].…”

“…Authors & Year of study Country Number. of specimens Incidence % Von Schroeder and Botte (1995) [13] California 43 12 Jonathan S. Carlos (2011) [15] Southern California 94 7.4 Dass et al(2011) [16] Indian 100 9 Suwannakhan A et al (2016) [17] Thailand 100 8 K. Ozturk et al (2020) [18] Turkey The EDBM can be a good source for tendon transfer for restoration of malfunctioning muscles like in case of damaged extensor pollicis longus [24]. A close physical examination of hand for differential diagnosis of tenosynovitis or a ganglion cyst becomes imperative where in the ganglion becomes prominent with wrist flexion and in active extension EDBM becomes prominent [23].…”

Extensor digitorum muscle tendon to the index finger from the extensor carpi radialis brevis: a cadaveric case report

“…Becoming thoroughly acquainted with the extensor tendons' variants may be helpful for hand surgeons in planning tendon graft surgery [3,25] and allowing them to successfully perform tenosynovectomy for the treatment of de Quervain's syndrome [3,19]. The detailed anatomical knowledge of the extensor tendons is a determining factor in preserving healthy tendons during orthopedic procedures, hence accounts for good patient outcomes and improves their quality of life [3,5].…”