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Abstract., (This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

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.

Background: The aim of this study is to determine the prevalence of Martin-Gruber Anastomosis (MGA) in healthy Egyptian subjects, and to discuss the available literature regarding MGA subtypes and their clinical implications. Methods: An electrophysiological study was conducted in both forearms of 140 healthy subjects. This included the ulnar and median nerves. Compound muscle action potentials were recorded from abductor pollicis brevis, abductor digiti minimi, and first dorsal interosseous muscles. Other measurements included the compound motor action potential amplitude and its innervation ratio. Results: MGA was found in 56 of the 280 forearms. This included 20 men and 36 women. Type II MGA subtype was the most frequent in both genders. The MGA was bilateral in 6 subjects and more frequent on the right side. The highest mean amplitude and innervation ratio were recorded at first dorsal interosseus muscle. Conclusions: The prevalence of MGA in the studied sample of the Egyptian population is 20%. It is important for Hand, Orthopaedic and Neurosurgeons to be aware of this anatomic variation in order to explain paradoxical motor and sensory loss in patients.

Background: Several anatomical variations of the median nerve recurrent motor branch have been described. No previous reports have described the anatomical variation of the ulnar nerve with respect to transverse carpal ligament. In this article, we present a patient with symptomatic compression of the ulnar nerve found to occur outside the Guyon canal due to a transligamentous course through the distal transverse carpal ligament. Methods: A 59-year-old, right-hand-dominant male patient presented with right hand pain, subjective weakness, and numbness in both the ulnar and the median nerve distributions. Electromyography revealed moderate demyelinating sensorimotor median neuropathy at the wrist and distal ulnar sensory neuropathy. At the time of planned carpal tunnel and Guyon canal release, a transligamentous ulnar nerve sensory common branch to the fourth webspace was encountered and safely released. Results: There were no surgical complications. The patient's symptoms of numbness in the median and ulnar nerve distribution clinically improved at his first postoperative visit. Conclusions: We have identified a case of transligamentous ulnar nerve sensory branch encountered during carpal tunnel release. To our knowledge, this has not been previously reported. While the incidence of this variant is unknown, hand surgeons should be aware of this anatomical variant as its location puts it at risk of iatrogenic injury during open and endoscopic carpal tunnel release.

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.)

Aim: To evaluate the existence of nerve innervation of the triceps brachii muscle via the ulnar nerve and its clinical importance in terms of nerve transfer or susceptibility to iatrogenic injuries during surgical procedures., Material and Methods: Thirty-five skeletally mature upper extremities of adult cadavers were included in the present study. The ulnar nerve was revealed from the medial cord to the distal part of the cubital fossa. The existence of the branches of the ulnar nerve and communicant branch of the radial nerve was examined in the brachium. The diameter and length of the variant nerve branches were measured., Results: A nerve branch from the ulnar nerve to the triceps brachii muscle was found in five of the dissected extremities (14.7%). The mean length and diameter of the variant nerve branch were 20.2 mm and 1.46 mm, respectively. The mean distance of the muscle entry point of the variant nerve branch from the bi-condylar line was 8.18 cm., Conclusion: A variant nerve branch via the ulnar nerve can innervate the medial head of the triceps brachii at the distal third of the brachium. This variant nerve branch will be under risk of iatrogenic injury during elbow surgery and it seems to be an option for nerve grafts.

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.)

Two patients with an anteriorly positioned ulnar nerve at the elbow, identified during cubital tunnel release, are presented. Upon encountering an empty cubital tunnel, additional dissection found the ulnar nerve to course posterior to and to penetrate through the intermuscular septum 3 to 5 cm proximal to the medial epicondyle. It then ran anterior to the pronator-flexor mass before entering the forearm between the ulnar and the humeral heads of the flexor carpi ulnaris. Although a rare anatomical anomaly, an anteriorly positioned ulnar nerve is potentially an underreported finding. In individuals with cubital tunnel syndrome, diagnosis and surgical treatment may be negatively affected if the surgeon fails to recognize the aberrant anatomy. Upper extremity surgeons should also be mindful of this rare anomaly when performing elbow arthroscopy or medial epicondyle release to prevent inadvertent injury to the nerve., (Copyright © 2015 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.)

An unusual communication between the radial and ulnar nerves was observed during repair of a fracture of the humerus in an adult patient who presented with unusual physical exam findings. The patient had loss of radial and ulnar nerve motor function, as well as decreased sensation in both nerve distributions. Radial nerve injury following fracture of the humerus is a common condition, and anatomic variations are therefore of importance to clinicians. Communications between branches of the brachial plexus are also not uncommon findings; however there is very little mention of communication between the radial and ulnar nerves in the literature. An appreciation of unusual nerve anatomy is important in explaining unusual finding in patients.