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Significance of Recognizing Anatomical Variations for Medical Education – an Example of the Triceps Brachii Heads
Author(s) -
McDowell Arthur R,
Wade Michael D,
Ziermann Janine M
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.901.6
Subject(s) - axillary nerve , anatomy , radial nerve , medicine , brachial plexus , scapula , humerus , deltoid muscle
The triceps brachii muscle is the only muscle in the posterior compartment of the arm comprising three heads. The long head originates from the infraglenoid tubercle of the scapula, the lateral head mostly from the dorsal/posterior surface of the humerus proximal to the radial groove, and the medial head mostly from the dorsal/posterior surface of the humerus distal to the radial groove. It is commonly accepted that all heads of the triceps brachii muscle receive motor innervation by the radial nerve. However, scattered reports of alternative innervations to one or more heads of the triceps brachii can be found. In particular the motor innervation to the long head of the triceps (LHT) seems to be variable as was shown by reports of traumatic injuries to the axillary nerve which were associated with the paralysis of the LHT. This implies that the LHT in those cases was innervated by the axillary nerve. Both, the radial and axillary nerve, are terminal branches of the posterior cord of the brachial plexus. The axillary nerve has an anterior and a posterior branch. The latter emerges at the inferior border of the scapula traversing the quadrangular space, giving off a branch to the teres minor, a branch to the deltoid and a superior lateral cutaneous branch. From a posterior view the radial nerve can be seen through the quadrangular space but this nerve is not traversing the space. Given the spatial correlation of the axillary nerve in the quadrangular space, the insertion of the LHT and the relative distance to the radial nerve in this area, an innervation via the posterior branch of the axillary nerve seems plausible. In our study, we dissected 29 arms in 15 cadavers that revealed radial innervation of all triceps heads, with the radial nerve penetrating the muscles from anterior. This opens the clinically relevant question on how high is the incident of axillary innervated LHTs since the axillary nerve is often damaged (compressed, stretched or even severed) during shoulder dislocation and other injuries. Our results will be relevant for surgical procedures of traumatic nerve injuries as well as for therapeutic treatment (physical and occupational therapies).