Dissecting neural anomalies and clinical impact of aberrant median and ulnar nerve pathways in the forearm: A systematic review and meta analysis.

Abstract

Aberrant communications between the median and ulnar nerves in the forearm and hand are clinically important anatomical variants that can significantly influence electrophysiological interpretation and surgical decision-making. This systematic review and meta-analysis aimed to synthesize available anatomical and electrophysiological evidence on the prevalence, subtypes, and clinical implications of median-ulnar nerve anastomoses, including Martin-Gruber, Marinacci, Riche-Cannieu, and Berrettini connections. A comprehensive search of major databases identified 20 eligible studies encompassing electrophysiological, anatomical, and clinical designs. Meta-analysis was performed using event-rate methodology with logit transformation under a random-effects model. The pooled prevalence of Martin-Gruber anastomosis (MGA), derived from six studies, was approximately 21%, indicating that nearly one in five individuals demonstrates median-to-ulnar nerve communication in the forearm. Subgroup analysis revealed a higher prevalence in healthy populations (≈25%) compared with carpal tunnel syndrome (CTS) populations (≈8-10%), suggesting that median nerve compression may obscure electrophysiological detection of MGA. Cadaveric studies reported lower detection rates (≈6%), reflecting methodological differences. Subtype analysis demonstrated that Type II MGA was more prevalent than Type I, with pooled prevalence estimates of approximately 62% and 31%, respectively, highlighting substantial anatomical variability. Considerable heterogeneity was observed across subgroup analyses, reflecting differences in population characteristics and electrophysiological protocols. Beyond MGA, Marinacci anastomosis was uncommon (≈0.7-4%), whereas Riche-Cannieu and Berrettini anastomoses were frequent, with reported prevalences exceeding 50% in anatomical and electrophysiological studies. Clinically, these variants are highly relevant, as unrecognized nerve communications may lead to pseudo-conduction block, mislocalization of neuropathies, underestimation of CTS severity, and iatrogenic injury during forearm or hand surgery. These findings underscore the necessity of incorporating anatomical awareness and targeted electrophysiological strategies into routine clinical practice.