Variable Innervation of the Triceps Brachii: Anatomical and Clinical Perspectives in a Narrative Review

TL;DR

This review shows that the triceps muscle's nerve supply is more variable than traditionally taught, with implications for surgery and nerve injury diagnosis.

Contribution

The paper systematically compiles and analyzes existing evidence on triceps brachii innervation variability, highlighting the need for updated anatomical knowledge.

Findings

The axillary nerve frequently contributes to the long head of the triceps in up to 35% of cases.

The medial head often receives innervation from the ulnar nerve, and rare cases show musculocutaneous nerve involvement.

These variations suggest a more complex neural architecture than previously described in standard anatomy texts.

Abstract

Traditional anatomical texts describe the triceps brachii as receiving motor innervation exclusively from branches of the radial nerve. However, growing morphological, electrophysiological, and clinical evidence demonstrates notable variability in its neural supply, particularly to the long and medial heads of the muscle. To clarify these inconsistencies, a narrative review was conducted using PubMed, Scopus, and Google Scholar with search terms related to triceps innervation and nerve variations. After screening 930 records, 27 studies met the inclusion criteria. The articles were reviewed and presented in a table format, comprising original human cadaveric and clinical data. Relevant information on study design, sample size, and specific innervation patterns was extracted and organised, with selection illustrated using a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart. The compiled evidence from cadaveric dissections and clinical case reports reveals frequent deviations from the classic pattern. Numerous studies report that the axillary nerve contributes to the long head, with prevalence ranging from isolated findings to over 35% in certain populations. The medial head has been shown in several investigations to receive branches from the ulnar nerve, and rare cases describe musculocutaneous nerve fibres replacing distal radial innervation. These observations underscore a more complex neural architecture than typically depicted. Recognising such variations is crucial for academic accuracy and clinical practice. It facilitates improved interpretation of nerve injuries, informs surgical and nerve transfer procedures, and supports more precise electrophysiological assessment. Collectively, the evidence highlights the need to update standard anatomical descriptions and encourages continued research into the functional implications of these innervation patterns.

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