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Nerve to Long Head of Triceps

nervus capitis longi musculi tricipitis

The branch of the radial nerve supplying the long head of triceps arises proximal to the spiral groove, at the level of the posterior axilla, before the radial nerve enters the spiral groove. This proximal origin means the long head is spared in radial nerve injuries at or distal to the spiral groove, distinguishing axillary-level from spiral groove-level radial nerve palsy.

Region: Upper Arm

Clinical Relevance

Clinical Notes

The nerve to the long head of triceps is the most proximal radial nerve motor branch and its integrity is the key localising feature in radial nerve injury. In spiral groove palsy (Saturday night palsy), long head triceps function is preserved because its nerve arises proximal to the groove. In posterior cord or axillary-level radial nerve injury, the long head is paralysed alongside all other triceps heads. EMG of the long head triceps localises the lesion level with precision.

Pathology

Common Injuries & Conditions

Radial Nerve Palsy Level Localisation

Preserved long head triceps EMG activity in spiral groove palsy distinguishes this from proximal radial nerve or posterior cord injury, where denervation of the long head indicates the lesion is at or above the axilla.