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Objective: Martin-Gruber anastomosis (MGA) is a median-to-ulnar nerve communication in the forearm; three types of MGA occur. Typically, motor fi bres course through the median nerve in the upper arm and elbow, however, they supply the ulnar-innervated muscles of the hand: abductor digiti minimi (ADM) – MGA-I; fi rst dorsal interosseous (FDI) – MGA-II; or adductor pollicis – MGA-III. The objective was to determine the prevalence of MGA in a study group of healthy volunteers. Methods: Two hundred and ninety-two healthy participants (457 arms) were enrolled. Motor and sensory nerve conduction studies of the ulnar and median nerves were performed. Ulnar and median nerve compound muscle action potential amplitudes were obtained on stimulation at the elbow and wrist. Results: We found 109 cases of MGA in 90 arms (MGA-I in 30 arms; MGA-II in 57 arms; MGA-III in 22 arms). We found isolated MGA types in 73 arms, a combination of two types in 15 arms, and occasionally (2 arms) a simultaneous combination of all three types. Conclusion: The prevalence of MGA was 19.7%. Most frequently, we found MGA-II (prevalence = 12.5%). Signifi cance: MGA does not produce any clinical signs. However, it can change EMG results. The neurophysiologist must be able to logically interpret such fi ndings., Úvod: Prevalence Martin-Gruberovy anastomózy (MGA), spojky n. medianus a ulnaris na předloktí se uvádí v rozmezí 15– 39 %. Existují tři různé typy MGA, kdy motorická vlákna jsou v oblasti paže a lokte vedena skrze n. medianus a zásobují svaly ruky inervované n. ulnaris (m. abductor digiti minimi, m. interosseus dorsalis primus či m. adductor pollicis). Soubor a metodika: V pěti EMG laboratořích bylo unifi kovanou technikou vyšetřeno 292 zdravých osob ve věku 20– 67 let, průměr 39,4 let: 166 žen (256 rukou) a 126 mužů (201 rukou), celkem 457 rukou. Byla provedena motorická a senzitivní neurografie n. ulnaris a n. medianus. Pro detekci MGA mělo zásadní význam hodnocení amplitudy CMAP pro n. ulnaris a n. medianus při stimulaci z oblasti lokte a zápěstí. Výsledky: V našem souboru 457 vyšetřených rukou jsme na 90 rukou našli 109 výskytů MGA. U 30 rukou se jednalo o MGA-I, u 57 rukou o MGA-II a u 22 rukou o MGA-III. Izolované typy MGA se vyskytly v 73 případech, Na 17 rukou se vyskytla kombinace dvou, ojediněle dokonce všech tří typů MGA současně. Závěr: V souboru 292 osob zdravých osob jsme na 457 hodnocených rukou našli MGA v 19,7 %. Nejčastěji se vyskytoval typ MGA-II (12,5 %).

Anomalous communications between median and ulnar nerve in the forearm have been widely described during the years. The most common of these anastomosis, known as Martin–Gruber anastomosis (MGA), consists in a neural connection between median and ulnar nerve in the forearm, usually in its proximal part, that results in an anomalous course of the fibers innervating the intrinsic muscles (and rarely cutaneous region) of the hand. Its frequency, firstly described by Gruber in 1870 as 15.2% in 250 studied arms, is currently estimated through neurophysiological and anatomical studies to range between 10% and 40% (Amoiridis, 1992; Rodriguez-Niedenführ et al., 2002; Lee et al., 2005). Much rarer is ulnar to median communication, known as Marinacci communication, where fibers from the ulnar nerve cross over to the median nerve in the forearm (Marinacci, 1964). The knowledge of such anatomical variants is important to explain some electrodiagnostic (EDX) findings. Moreover, its identification is crucial for reaching a correct diagnosis and providing information on prognosis and treatment. We report on two patients who presented with the coexistence of median–ulnar anastomosis and nerve tumors.