Does the motor branch of the long head of the triceps brachii arise from the radial nerve?

Abstract

Anatomy textbooks say that the motor branch of the long head of the triceps brachii (LHT) arises from the radial nerve. Some clinical observations of traumatic injuries of the axillary nerve with associated paralysis of the LHT have suggested that the motor branch of the LHT may arise from the axillary nerve. This anatomic study was performed, using both cadaver anatomical dissections and a surgical study, to determine the exact origin of the motor branch of the LHT. From the adult cadaver specimens (group I), 20 posterior cords were dissected from 10 subjects (eight embalmed, two fresh) using 3.5x magnification. The axillary nerve was followed from its onset to the posteromedial part of the surgical neck of the humerus and the radial nerve. We looked for the origin of the proximal branch of the LHT by a meticulous double anterior and posterior dissection. From the surgical group (group II), 15 posterior cords were dissected from 15 patients suffering from a C5-C6 injured paralysis, without paralysis of the LHT. During the surgical procedure, we looked for the origins of the motor branch of the LHT with a nerve stimulator. In group I, the motor branch of the LHT arose in 13 cases from the axillary nerve near its origin, in five cases from the terminal division of the posterior cord itself, and in two cases from the posterior cord 10 mm before its terminal division into the radial and axillary nerves. In no case did we find the motor branch of the LHT arising from the radial nerve. In eight cases, we found some accessory branches that arose near the principal branch. In group II, the motor branch of the LHT arose in 11 cases from the axillary nerve near its origin and in four cases from the terminal division of the posterior cord itself. The motor branch of the LHT never originated from the radial nerve. In four cases, we found some accessory branches that arose near the principal branch of the LHT. These results reveal that the motor branch of the LHT seems to originate most often from the axillary nerve. This contribution could be relevant for surgical treatment of traumatic nerve injuries.

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

“…The findings of some studies challenge the traditional notions of the classic pattern [5,12,14]. Cases of axillary nerve innervation to the long head of the triceps have been documented in cadaveric specimen in several studies [4,5,12].…”

“…The findings of some studies challenge the traditional notions of the classic pattern [5,12,14]. Cases of axillary nerve innervation to the long head of the triceps have been documented in cadaveric specimen in several studies [4,5,12]. Our purpose for this study was to provide innervation data for the long head of the triceps regarding additional brachial plexuses and to determine if our sample would result in findings similar to those in the published series.…”

“…Additionally, we did not attempt to determine if the nerve bundles had motor, sensory, or mixed functionality. Our specimens may not be representative of all populations as they were from a geographic region distinctly different from those in the prior publishes studies [4,5,12]. The actual ancestry data of the individual cadavers were not available.…”

“…Although the textbooks do not describe an innervation to the long head of the triceps other than the radial nerve, some cadaveric studies have noted cases of the motor branch of the long head of the triceps arising from the axillary nerve [5,12,14]. Clinical scenarios of axillary nerve injury with unexpected triceps brachii dysfunction support a cadaver study documenting this variant [14].…”

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

“…Since that time, most of our evidence consists of case studies [5], but there are some larger cadaveric anatomic studies on the subject [3,6]. The current study includes 22 anatomic dissections, a reasonably large number, emphasizing the issue of nerve supply to the long head of triceps.…”