Purpose: We have sometimes observed paralysis of the long portion of the triceps in patients operated after traumatic damage to the axillary nerve. In anatomy textbooks, the motor branch of the long portion of the triceps arises from the radial nerve within the triceps. We studied the position of the motor branch of the long portion of the triceps in order to better detail its origin.

Material and methods: Group I: this group included nine patients with trauma-induced lesions of the axillary nerve associated with clinical involvement of the long portion of the triceps. Group II: this group was composed of 20 cadaver specimens of the secondary posterior trunks. Group III: fif-teen approaches to the subclavian plexus with dissection of the secondary posterior trunk. Lesions to the axillary nerve were retrieved from the operation reports in group I. The origin of the motor branch of the long portion of the triceps was identified in group II. The same origin was identified by neurostimulation in group III.

Results: In group I there were six lesions of the axillary nerve situated a mean 10 mm from the division of the secondary posterior trunk and three lesions of the secondary posterior trunk. There were four type IV lesions and five type V lesions. In group II, the motor branch of the long portion of the triceps arose a mean 6 mm from the division of the secondary posterior trunk in 13 cases, at the division in five cases, and 10 mm downstream in two cases, but never from the radial nerve. In group III, the branch of long portion of the triceps arose a men 4.5 mm from the division of the secondary posterior trunk in 11 cases, and at the division in four cases, but never from the radial nerve.

Discussion: In patients with trauma to the axillary nerve with paralysis of the long portion of the triceps, lesions to the axillary nerve occur proximally and are severe. In our study, the motor branch of the long portion of the triceps always arose from the axillary nerve or the secondary posterior branch. This shows that paralysis of the long portion of the triceps is a sign of poor prognosis in patients with traumatic lesions to the axillary nerve. This association is for us an element in favour of a proximal and serious lesion to the axillary nerve.

Conclusion: Involvement of the long portion of the triceps must be searched for in patients with traumatic lesions to the axillary nerve. Paralysis of the long portion of the triceps is a sign of a serious lesion requiring early surgical repair before two months.