Variations in the Innervation of the Long Head of the Triceps Brachii: A Cadaveric Investigation

Abstract

Background Some leading anatomy texts state that all three heads of the triceps brachii are innervated by the radial nerve. The posterior cord of the brachial plexus bifurcates to terminate as the radial and axillary nerves. Studies have noted the presence of axillary innervation to the long head of the triceps brachii muscle, patterns different from the classic exclusive radial nerve supply. An understanding of these variations may assist the clinician in the assessment of shoulder weakness and in preoperative and operative planning of radial and axillary neuropathies. Questions/Purpose We aimed to further investigate, in cadaver dissections, the prevalence of axillary nerve contribution to the innervation of the long head of the triceps brachii. Methods We performed bilateral brachial plexus dissections on 10 embalmed cadavers combining anterior axillary and posterior subscapular approaches. Two additional unilateral cadaveric brachial plexuses were dissected. The posterior cords were fully dissected from the roots distally. The radial and axillary nerves were followed to their muscle insertion points, the dissections were photographed, and the length of branching segments were measured.

Innervation of the Long Head of the Triceps Brachii in Humans—A Fresh Look

“…The figure represented in Erhardt and Futterman () indicates that the branch from the axillary nerve enters the tendinous region of the LHT as was previously described by Aszmann et al (). The latter study describes that the motor branch to the teres minor gives off an articular branch at the level of the LHT insertion, and at this point a small branch to the tendinous insertion and the adjacent capsular region could be identified in 7 out of 25 specimens (Aszmann et al, ).…”

“…Currently 22 studies cite de Sèze et al () and 12 Rezzouk et al () [NB: Table focuses mainly on studies citing de Sèze et al (); only two citations of Rezzouk et al () were found to be additionally relevant for this study]. Nanjundaiah et al (), Bertelli and Ghizoni (), Seema and Gangadhar (2015), Yılmaz et al (), Erhardt and Futterman (), and Howard () cite both de Sèze et al () and Rezzouk et al () without recognizing the identical study groups.…”

“…The latter study describes that the motor branch to the teres minor gives off an articular branch at the level of the LHT insertion, and at this point a small branch to the tendinous insertion and the adjacent capsular region could be identified in 7 out of 25 specimens (Aszmann et al, ). This description indicates a sensory rather than a motor branch and Erhardt and Futterman () admit that they did not study the character of the nerve (sensory or motor). We also, did not verify the characteristic of the nerves in our study but could only identify the radial nerve penetrating the muscular portion of the LHT.…”

“…One cadaver had a bilateral radial innervation of the LHT, both unilateral dissected cadavers had axillary innervation, and the other 9 cadavers showed a mix of innervation patterns (pattern I: dual = axillary and radial unilateral, radial on other side; pattern II: dual innervation bilaterally; pattern III: axillary innervation on one side and radial on the other side; Table ). Erhardt and Futterman () conclude that the sole radial innervation of the LHT is not the dominant pattern and added that they “… found four other studies that looked at axillary innervation of the long head of the triceps; of the 62 total cadaver shoulders examined in those studies, 71% were found to have nonclassic innervation patterns.” It is not surprising that two out of the four studies are Rezzouk et al () and de Sèze et al (), which correspond to 10 cadavers each (totaling 20 cadavers = 40 cadaver shoulders). The other two studies are Nanjundaiah et al () (see above; 1 cadaver = 2 shoulders) and Aszmann et al () (25 upper extremities).…”

“…The other two studies are Nanjundaiah et al () (see above; 1 cadaver = 2 shoulders) and Aszmann et al () (25 upper extremities). This clearly does not add up to 62 shoulders; however, the discussion of Erhardt and Futterman () reveals the problem as they describe that de Sèze et al () “ dissected 20 posterior cords from 10 cadaveric specimens ” and Rezzouk et al () “ dissected 15 posterior cords ” what would add up to 20 + 15 + 2 + 25 = “ 62 cadaver shoulders ”. But, the 15 refers to “… quinze patients successifs ayant eu un abord du plexus infra claviculaire dans le cadre de paralysies post‐traumatiques C5‐C6 … ” (15 patients who had an infraclavicular plexus approach in post‐traumatic C5‐C6 paralysis) (Rezzouk et al, ).…”