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Rationale: The incidence of Martin-Gruber anastomosis ranges from 5% to 34%, which is characterized by crossing over from the median to the ulnar nerve and innervating the first dorsal interosseous, thenar or hypothenar muscles. However, the reverse Martin-Gruber anastomosis, or Marinacci anastomosis, is far less discussed and appears in recent literature., Patient Concerns: A 56-year-old man presented to the clinic of a university hospital because of left neck soreness with numbness radiating to the left lateral shoulder. The neck discomfort was aggravated while the neck rotated or tilted to the right., Diagnosis: Higher compound muscle action potential over the abductor pollicis brevis on elbow stimulation than on the wrist was found during upper limb nerve conduction velocity study. Ulnar to median anastomosis was identified., Intervention: We performed cervical spine X-ray and electrophysiological examinations and monitored the patient., Outcomes: We identified that this patient had left C5 and C6 subacute radiculopathy with active denervation and left subclinical ulnar sensory neuropathy, and verified the existence of ulnar-to-median anastomosis., Lessons: We demonstrated a pure motor ulnar-to-median anastomosis without sensory correspondence and higher CMAP over the abductor pollicis brevis on elbow stimulation of the ulnar nerve than on the wrist. The prevalence might be underestimated in a Chinese population-based published study., Competing Interests: The authors have no conflicts of interest to disclose. Patient consent: The patient provided written informed consent for the publication and use of the report., (Copyright © 2021 the Author(s). Published by Wolters Kluwer Health, Inc.)

Anomalous innervations are commonly encountered on electrodiagnostic testing and may be mistaken for a pathological process, especially if seen in multiple nerves. While crossover of median-to-ulnar fibers in the forearm (Martin-Gruber anastomosis) has been frequently described, the corresponding ulnar-to-median crossover (Marinacci anastomosis) is much less commonly seen. There have been no reported cases of both of these anomalous innervations occurring together. We describe a novel case of bilateral Martin-Gruber and Marinacci anastomoses in the same patient. The importance of the case lies in the fact that the multiple pseudo-conduction blocks that result from these crossovers could potentially be misinterpreted as being pathological in nature, illustrating the need for electromyographers to be familiar with common anomalous innervations in the upper extremity and with techniques to identify them.

Median and ulnar nerve interconnections commonly occur in the brachial plexus, forearm, and hand. Each is classified based on location, fiber type (sensory fibers, motor fibers, or both), and directionality (ie, carrying fibers from median to ulnar or vice versa). There are 4 main interconnections found in the forearm and hand: Martin-Gruber and Marinacci anastomoses in the forearm and Riche-Cannieu and Berrettini anastomoses in the hand. The presence of an interconnection may skew electrodiagnostic findings, possibly resulting in misdiagnosis and iatrogenic injury. Clinicians should perform nerve studies of both nerves at proximal and distal stimulation sites to rule out interconnections and guide treatment. This review details anatomy, electrodiagnostic findings, and clinical approach., (Copyright © 2019 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.)

Introduction: The most frequently described anomalous neural connections between the median and ulnar nerves in the upper limb are: Martin-Gruber anastomosis (MGA), Marinacci anastomosis (MA), Riche-Cannieu anastomosis (RCA), and Berrettini anastomosis (BA). The reported prevalence rates and characteristics of these anastomoses vary significantly between studies., Methods: A search of electronic databases was performed to identify all eligible articles. Anatomical data regarding the anastomoses were pooled into a meta-analysis using MetaXL 2.0., Results: A total of 58 (n = 10,562 upper limbs) articles were included in the meta-analysis. The pooled prevalences were: MGA, 19.5% (95% confidence interval [CI], 16.2%-23.1%); MA, 0.7% (95% CI, 0.1%-1.7%); RCA, 55.5% (95% CI, 30.6%-79.1%); and BA, 60.9% (95% CI, 36.9%-82.6%). The results also showed that MGA was more commonly found unilaterally (66.8%), on the right side (15.7%), following an oblique course (84.8%), and originating from the anterior interosseous nerve with a prevalence of 57.6%., Conclusions: As anastomoses between the median and ulnar nerves occur commonly, detailed anatomical knowledge is essential for accurate interpretation of electrophysiological findings and reducing the risk of iatrogenic injuries during surgical procedures. Muscle Nerve 54: 36-47, 2016., (© 2015 Wiley Periodicals, Inc.)

Martin-Gruber anastomosis (MGA) is the most common nerve anastomosis in the upper extremities and it crosses from the median nerve to the ulnar nerve. Proximal MGA is an under recognized anastomosis between the ulnar and median nerves at or above the elbow and should not be missed during nerve conduction studies. We presented two patients with ulnar neuropathy mimicking findings including numbness and tingling of the 4th and 5th digits and mild weakness of intrinsic hand muscles. However, both cases had an apparently remarkable conduction block between the below- and above-elbow sites that was disproportionate to their clinical findings. To explain this discrepancy, a large MGA was detected with stimulation of the median nerve at the elbow. Thus, proximal MGA should be considered in ulnar neuropathy at the elbow when apparent conduction block or/and discrepancy between clinical and electrodiagnostic findings is found.

Purpose: A proximal Martin-Gruber anastomosis (MGA) is an underrecognized anomaly and can mimic ulnar neuropathy at the elbow on electrodiagnostic testing. Martin-Gruber anastomosis is mainly recognized as a crossover from median nerve or its branches to ulnar nerve at the forearm, but may occur at the elbow (proximal MGA). The authors report their experience with MGA at the elbow., Methods: Using standard nerve conduction techniques, the authors prospectively detected electrodiagnostic evidence of a proximal MGA at the elbow over the course of 4 years. An accompanying ulnar neuropathy was diagnosed based on clinical findings, focal conduction slowing, and needle electromyography., Results: A proximal MGA involving branch of ulnar nerve was detected in 16 cases. The detection of proximal MGA to the first dorsal interosseous muscles was more sensitive than to the adductor digiti minimi muscles in their series., Conclusions: A proximal MGA is an underrecognized anomaly. This study is the largest series for proximal MGA in the literature. The authors recommend considering proximal MGA in any cases of ulnar neuropathy at the elbow, especially if the apparent conduction block is not associated with slowing of conduction velocity, and a discrepancy between clinical and electrodiagnostic findings is present.

Introduction: It is important to understand the presence of Martin-Gruber anastomosis in patients with complete ulnar neuropathy at the elbow., Case Report: We describe a patient with complete ulnar neuropathy at the elbow and Martin-Gruber anastomosis in the forearm, mimicking incomplete ulnar neuropathy with complete conduction block in the forearm segment. Ultrasonography of the ulnar nerve around the elbow demonstrated severe swelling of the ulnar nerve, which was compatible with severe ulnar neuropathy at the elbow., Conclusions: This case report demonstrates that combination of ultrasonography with electrophysiological studies can provide more detailed information about the changes of nerve structures and lesion sites., (Copyright © 2012 Wiley Periodicals, Inc.)

Objective: This study aimed to clarify the morphology of the Martin-Gruber anastomosis (MGA) in Chinese., Methods: One hundred and five Chinese upper limbs (36 males and 20 femalese) were dissected to find the connections between medial nerve and ulnar nerve. The MGA was classified as previously described by Lee., Results: MGA was found in 24 cases (22.9%), in 11 of the 36 male and 5 of the 20 female. There was no obvious difference in the frequency of MGA in both upper limbs. Most MGA ulnar position was located at the medial and distal segment of the forearm., Conclusion: MGA anatomy could play important role in forensic diagnosis of ulnar nerve injury in Chinese population.

This study aimed to clarify the morphologic variations of the Martin-Gruber anastomosis (MGA) by tracing the anastomotic fascicles. We used 102 upper limbs, and MGA was found in 39.2%. Among 12 instances of MGA between the branches innervating the flexor digitorum profundus muscle, eight anastomotic branches solely innervated the muscle without crossover from median to ulnar nerve. The results of the present study showed three morphologic features of MGA that could not be detected by an electrodiagnostic method.

The incidence and morphology of the intramuscular Martin-Gruber anastomosis are presented based on the study of 118 human cadavers (55 male, 63 female). The Martin-Gruber anastomosis was found in 25 (21.2%) of the 118 cadavers. It occurred in 11 (20%) of the 55 male cadavers (4 bilateral, 7 unilateral; 5 left and 2 right) and in 14 (22.2%) of the 63 female cadavers (2 bilateral, 12 unilateral; 8 left and 4 right). Therefore, the Martin-Gruber anastomosis was found in 31 (13.1%) of the 236 upper limbs. According to a recent classification (Rodríguez-Niedenführ et al., 2000), pattern I was found in 29 cases (93.5%), corresponding to Type A in 13 (41.9%), Type B in 3 (9.7%) and Type C in 13 (41.9%), whereas pattern II was found in 2 cases (6.5%), both being a duplication of Type IC. Intramuscular Martin-Gruber anastomosis was a single anastomosis that originated in all cases from the anterior interosseous nerve (pattern IC) and then passed through a muscle bundle of the flexor digitorum profundus and behind the ulnar artery to join the ulnar nerve as a single connecting branch. It did not send branches to the flexor digitorum profundus. This intramuscular course was observed in 3 of the 13 cases of Type C anastomosis (23.1%) or 3 cases out of 31 Martin-Gruber anastomoses (10%)., (Copyright 2002 Wiley-Liss, Inc.)

Based on a study of 70 human cadavers (31 male, 39 female) and on cases described previously, we propose a new classification of the Martin-Gruber anastomosis, a neural connection between the median and ulnar nerves in the forearm. The anastomosis was found in 16 (22.9%) cadavers, being bilateral in three (18.7%) and unilateral in 13 (81.3%), five right and eight left. It occurred in eight (25.8%) of the 31 male cadavers and in eight (20.5%) of the 39 females. Therefore, the anastomosis was found in 19 (13.6%) of the 140 forearms. In Pattern I (89.5%) the anastomosis was made by only one branch, whereas in Pattern II (10.5%) it was made by two. The individual branches were classified as Types a, b, and c based on the nature of their origin from the median nerve. Type a (47.3%) arose from the branch to the superficial forearm flexor muscles, Type b (10.6%) from the common trunk, and Type c (31.6%) from the anterior interosseous nerve. Pattern II was a duplication of Type c (10.5%). The anastomotic branch took an oblique or arched course before joining the ulnar nerve, undivided in 15 cases, but divided into two branches in four cases. The anastomosis passed in front of the ulnar artery in four cases, behind it in six, and in nine cases it was related to the anterior ulnar recurrent artery., (Copyright 2002 Wiley-Liss, Inc.)

Although anatomical studies have shown that a crossover of sensory fibers is not rare in forearm Martin-Gruber median-ulnar anastomosis (MGA), it has been electrophysiologically described only in rare subjects. Using a near-nerve needle technique, the possibility of electrophysiologically detecting a forearm median-ulnar crossover of sensory fibers was investigated in 24 arms of 21 subjects with unilateral or bilateral MGA, by stimulating the fifth digit of the hand and recording along the median nerve. Small-amplitude elbow responses were found in the median nerve in 10 of the 24 arms but, in 9, the responses disappeared after lidocaine block of the ulnar nerve distal to the elbow sulcus, indicating their volume-conducted origin. In one subject with carpal tunnel syndrome and a subclinical ulnar neuropathy at the elbow, the elbow response was not affected by the ulnar block, thus confirming the presence of a sensory anastomosis in the forearm. In another subject with MGA, a clear-cut sensory response was recorded in the median nerve at the elbow by stimulating the fifth digit of the right hand but no anesthetic block was performed, because ulnar responses were absent above the elbow sulcus due to a severe lesion at the elbow. Thus, use of a near-nerve recording technique facilitates recognition of median-ulnar crossover of sensory fibers to the fifth digit, which is, however, uncommon., (Copyright 2001 John Wiley & Sons, Inc.)

We dissected 72 upper limbs of fresh cadavers and found 17 cases of the Martin-Gruber anastomosis. The incidence was 23.6%. They can be classified into 5 types. Type I (n = 5, 29.4%): Communication between the anterior interosseous and the ulnar nerves. Type II (n = 3, 17.6%): Communication between the median and the ulnar nerves. Type III (n = 3, 17.6%): Communication between the muscular branches of the flexor digitorum profundus muscle (FDP). Type IV (n = 3, 17.6%): Communication between the anterior interosseous and the ulnar nerves, the muscular branches of the flexor digitorum profundus muscle (FDP) originated from the connection. Type V (n = 3, 17.6%): The anastomotic branch originated from the median nerve and joined the ulnar at two different points as well as connecting with the ulnar branch of the FDP. Through histologic examination, we found the number and size of nerve fascicles which every connection contained to be very different. In one case of type II only one single nerve fascicle was found. We propose the hypothesis that the different amounts of nerve fascicles innervate different amounts of intrinsic hand musculature. The communication which contained one single nerve fascicle only innervate the first dorsal interosseous muscle (FDI).