Long head of the triceps brachii and axillary nerve injury: anatomy and clinical aspects

Purpose of the study Earlier work has demonstrated possible paralysis of the long head of the triceps brachii (LTB) after surgical repair of traumatic injury to the axillary nerve. Anatomy textbooks describe the motor branch of the LTB arising from the radial nerve within the body of the triceps. We studied the position of the motor branch for the LTB to determine its exact origin. Material and methods Three groups were studied: Group I included 9 traumatic injuries of the axillary nerve associated with clinical involvement of the LTB; Group II included 20 secondary posterior trunks dissected from cadaver specimens; Group III included 15 dissections of the infraclavicular plexus with complete dissection of the secondary posterior trunk. The position of the axillary nerve injury was retrieved from the operative reports for Group I. The precise origin of the motor branch for the LTB was identified for Group II Neurostimulation was used to identify the origin of the motor branch for the LTB in Group III. Results For Group I: injury to the axillary nerve was situated 10 mm (mean) from the bifurcation of the secondary posterior trunk in 6 cases and at the bifurcation in 3. Type IV injury was identified in 4 cases and type V in 5. For Group If: the motor branch for the LTB arose 6 mm (mean) from the bifurcation of the secondary posterior branch in 13 cases, at the bifurcation in 5, and 10 mm proximally in 2, but never from the radial nerve. For Group Ill: the motor branch for the LTB arose 4.5 mm (mean) from the bifurcation of the secondary posterior trunk in 11 cases, at the bifurcation in 4, and never from the radial nerve. Discussion Observed injuries to the axillary nerve with an associated paralysis of the long head of the triceps brachii were located proximally and were severe. Our dissections always located the motor branch of the LTB arising from the axillary nerve or the secondary posterior branch. We thus deducted that associated LTB paralysis is a sign of poor prognosis. In patients with axillary nerve injury it is a sign favoring a proximal and severe lesion of the axillary nerve. Conclusion When examining patients with traumatic injury involving the axillary nerve, it is important to search for paralysis of the long head of the triceps brachii. If present, it is a sign of a severe axillary nerve lesion requiring early repair at 3 months.