The prevalence of extensor digitorum brevis manus and its variants in humans: a systematic review and meta-analysis.

Extensor digitorum brevis manus (EDBM) is a rare variant extensor muscle of the dorsum of the hand, which constitutes a diagnostic challenge in clinical practice. The aims of the review are to provide a better estimate of the frequency of EDBM and its association with variables such as ancestry, gender, laterality and side. Twenty-six studies met the inclusion criteria. The pooled rates of the meta-analyses yielded the following values: (a) an overall crude cadaveric prevalence of 4%, (b) an overall true cadaveric prevalence of 2.5%, (c) a true cadaveric prevalence of 2.6 % in European ancestry, (d) a true cadaveric prevalence of 2.3% in Asian ancestry (2.07% in Japanese and 4.2% in Indian), (e) a bilateral occurrence in 26.3%. Non-significant association was found between EDBM presence and ancestry, gender or side. The EDBM muscle was inserted on the index in 77% of cases and on the long finger in the remaining 23%. This is the first evidence-based anatomical review, which addresses the frequency of EDBM in humans.