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. (Note: Mnemonic- It’s all in the name- M–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.
Communications in the Hand
1. Riche- Cannieu anastomosis, or Thenar ansa.
Median (recurrent branch) to Ulnar (deep branch) nerve.
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.
- Article: Nadire Unver Dogan et al. The communication between the ulnar and median nerves in upper limb. Neuroanatomy 2009-8: 15–19