Median–Ulnar nerve Connections

The Median and Ulnar nerves don’t give any branches in the arm. In the forearm and the hand, four communications have been described between them: two in the forearm (Martin- Gruber, Marinacci/ Reversed Martin- Gruber anastomosis) and two in the hand (Riche- Cannieu, Berretini anastomosis).¹

Communications in the Forearm

1. Martin-Gruber anastomosis

Median (or anterior interosseous nerve) to Ulnar nerve.

💡 MNEMONIC ➜ “It’s all in the name”- M- goes with- U

It has an autosomal dominant inheritance pattern. It is more common on the right side and has no sex predilection.

2. Marinacci communication /Reversed Martin Gruber anastomosis

Ulnar to Median nerve.

It’s rare compared to Martin Gruber anastomosis.

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Communications in the Hand

1. Riche-Cannieu anastomosis/Cannieu-Riché anastomosis (CRA) or Thenar ansa

Median (recurrent branch) to Ulnar (deep branch) nerve in the thenar region.

It has an autosomal dominant inheritance pattern. Its incidences is 70- 80% (less frequently present in African Americans).

2. Berretini anastomosis

Ulnar to Median nerve (between the common digital nerves arising from them)- aka ramus communicans or superficial communicating branch.

Since many investigators found its incidence to be over 80%, the Berretini anastomosis should be considered a normal structure rather than an anatomic variation. It has no age, sex or race predilections.

Reference

1. Nadire Unver Dogan et al. The communication between the ulnar and median nerves in upper limb. Neuroanatomy 2009-8: 15–19