Mateusz Gładysz FESSH prep

FESSH prep Anatomy Martin–Gruber, Marinacci, Riche–Cannieu and Berrettini communications; Lanz classification of the thenar motor branch; electrodiagnostic consequences

Median–ulnar nerve communications and variations of the thenar motor branch

Last reviewed v1.0

FESSH-066Anatomy●●● advanced

Regarding anatomical variations of the median nerve and communications between the median and ulnar nerves:

  1. 1.The Martin–Gruber anastomosis, a median-to-ulnar communication in the forearm, is present in about one in five upper limbs and most often arises from the anterior interosseous nerve.

  2. 2.In pooled anatomical data, the Riche–Cannieu and Berrettini communications are rare, each found in fewer than 5% of hands.

  3. 3.The Marinacci communication — ulnar-to-median fibres in the forearm — is more common than the Martin–Gruber anastomosis.

  4. 4.In Lanz's classification, an extraligamentous course is the commonest pattern of the thenar motor branch, found in about three-quarters of hands.

  5. 5.Unrecognised median–ulnar communications can mislead the interpretation of nerve conduction studies, for example by producing an apparent (pseudo-) conduction block in the forearm.

FESSH marking: +1 per correct statement, 0 for blank, −1 for incorrect. Click the same TRUE/FALSE button twice to clear it.

Question ID
FESSH-066
First published
Last reviewed
Version
v1.0
Answer key and explanations — open after answering

  1. 1. The Martin–Gruber anastomosis, a median-to-ulnar communication in the forearm, is present in about one in five upper limbs and most often arises from the anterior interosseous nerve.

    True

    Roy's meta-analysis of 58 studies (10,562 limbs) found a pooled prevalence of 19.5%, most often unilateral, oblique in course and arising from the anterior interosseous nerve (57.6%). Plutecki's larger meta-analysis found similar prevalences of about 17–21% across cadaveric, fetal and clinical studies.

    • Roy J, Henry BM, PĘkala PA, Vikse J, Saganiak K, Walocha JA, et al.. Median and ulnar nerve anastomoses in the upper limb: A meta-analysis. Muscle Nerve. 2016;54(1):36-47. PMID 26599506
    • Plutecki D, Bonczar M, Walocha J, Chaba-Karnaś W, Nowak A, Kozioł T, et al.. Nerve anastomoses in the upper limb: an up-to-date meta-analysis. Surg Radiol Anat. 2026;48(1). PMID 42758316

  2. 2. In pooled anatomical data, the Riche–Cannieu and Berrettini communications are rare, each found in fewer than 5% of hands.

    False

    Both are common: Roy's pooled prevalences were 55.5% for the Riche–Cannieu anastomosis and 60.9% for the Berrettini anastomosis, with wide confidence intervals. Plutecki found the Berrettini anastomosis in about 68% of cadaveric hands, although less often in fetal and electrophysiological studies.

    • Roy J, Henry BM, PĘkala PA, Vikse J, Saganiak K, Walocha JA, et al.. Median and ulnar nerve anastomoses in the upper limb: A meta-analysis. Muscle Nerve. 2016;54(1):36-47. PMID 26599506
    • Plutecki D, Bonczar M, Walocha J, Chaba-Karnaś W, Nowak A, Kozioł T, et al.. Nerve anastomoses in the upper limb: an up-to-date meta-analysis. Surg Radiol Anat. 2026;48(1). PMID 42758316

  3. 3. The Marinacci communication — ulnar-to-median fibres in the forearm — is more common than the Martin–Gruber anastomosis.

    False

    The Marinacci communication is the reverse of the Martin–Gruber anastomosis and is far less frequent: pooled prevalence 2.04% in Plutecki's meta-analysis and 0.7% in Roy's, against roughly 20% for the Martin–Gruber anastomosis. On nerve conduction studies it can produce a pseudo-conduction block over the forearm on median nerve stimulation.

    • Plutecki D, Bonczar M, Walocha J, Chaba-Karnaś W, Nowak A, Kozioł T, et al.. Nerve anastomoses in the upper limb: an up-to-date meta-analysis. Surg Radiol Anat. 2026;48(1). PMID 42758316
    • Roy J, Henry BM, PĘkala PA, Vikse J, Saganiak K, Walocha JA, et al.. Median and ulnar nerve anastomoses in the upper limb: A meta-analysis. Muscle Nerve. 2016;54(1):36-47. PMID 26599506
    • Meenakshi-Sundaram S, Sundar B, Arunkumar MJ. Marinacci communication: an electrophysiological study. Clin Neurophysiol. 2003;114(12):2334-7. PMID 14652092

  4. 4. In Lanz's classification, an extraligamentous course is the commonest pattern of the thenar motor branch, found in about three-quarters of hands.

    True

    Henry's meta-analysis of 31 studies (3,918 hands) found pooled prevalences of 75.2% for the extraligamentous, 13.5% for the subligamentous and 11.3% for the transligamentous course. A transligamentous course was more frequent in hands with hypertrophic thenar muscles over the transverse carpal ligament, and the authors recommend an ulnar-sided, layer-by-layer approach to carpal tunnel release.

    • Henry BM, Zwinczewska H, Roy J, Vikse J, Ramakrishnan PK, Walocha JA, et al.. The Prevalence of Anatomical Variations of the Median Nerve in the Carpal Tunnel: A Systematic Review and Meta-Analysis. PLoS One. 2015;10(8):e0136477. PMID 26305098

  5. 5. Unrecognised median–ulnar communications can mislead the interpretation of nerve conduction studies, for example by producing an apparent (pseudo-) conduction block in the forearm.

    True

    A 2026 systematic review and meta-analysis of 20 studies lists pseudo-conduction block, mislocalisation of neuropathies, underestimation of carpal tunnel syndrome severity and iatrogenic surgical injury among the consequences of unrecognised communications. Roy's meta-analysis likewise stresses that detailed anatomical knowledge is essential for accurate interpretation of electrophysiological findings.

    • Jeff Walter Rajadurai OR, Prem Regis PA, Supadevi S, Vinoth S. Dissecting neural anomalies and clinical impact of aberrant median and ulnar nerve pathways in the forearm: A systematic review and meta analysis. J Hand Microsurg. 2026;18(3):100446. PMID 41959652
    • Roy J, Henry BM, PĘkala PA, Vikse J, Saganiak K, Walocha JA, et al.. Median and ulnar nerve anastomoses in the upper limb: A meta-analysis. Muscle Nerve. 2016;54(1):36-47. PMID 26599506