Prevalence of musculocutaneous nerve variations: systematic review and meta-analysis

We aimed to establish the prevalence of the musculocutaneous nerve (MCN) variations and the probability of the variation being pure or mixed in the same plexus. We applied the principles of evidence-based anatomy to find, appraise, and synthesize data through a meta-analysis of anatomical studies. The variations were grouped based on the presence and location of the communicating branch with the median nerve and the origin of branches to anterior arm muscles. Forty-three cadaveric studies met the inclusion criteria, providing data from 4124 plexuses. The overall pooled prevalence of plexuses with MCN variations was 20%. Based on the classification applied in our study, the pooled prevalence of variations was 17% in region 1A, 20% in region 1B, 36% in region 2 and 49% in region 3. Importantly, 64.58% of variations in region 1A and 74.14% of variations in region 1B were mixed, i.e., associated with a variation in another region. The odds of finding another variation in the presence of a variation in region 2 or 3 were equal 0.37 and 0.52, respectively, demonstrating a significantly lower probability of finding mixed variations involving these regions, when compared with region 1A. Variations of the MCN are most common in the part distal to the exit from within or beneath the coracobrachialis muscle. Proximal variations are more often associated with another variation located along the nerve. These findings can assist health care professionals in the treatment of brachial plexus lesions.