Myotome values for the upper limb appear to have been established in the early twentieth century based on historical work. Supraclavicular brachial plexus injuries present with a pattern of neurological loss consistent to the nerve roots affected. Recent advances in radiological imaging and intraoperative nerve stimulation have allowed confirmation of the affected nerve roots.

The records of 43 patients with partial injuries to the supraclavicular brachial plexus were reviewed. The injuries covered the full range of injury patterns including those affecting C5, C5-6, C5-7, C5-8, C7-T1 and C8-T1 roots. All cases with upper plexus injuries had surgical exploration of the brachial plexus with the injury pattern being classified on the basis of whether the roots were in continuity, ruptured, or avulsed, and, if seen in continuity, the presence or absence of a response to stimulation. For lower plexus injuries the classification relied on identification of avulsed roots on Magnetic Resonance Imaging. Muscle powers recorded on clinical examination using the MRC grading system.

In upper plexus injuries paralysis of flexor carpi radialis indicated involvement of C7 in addition to C5-6, and paralysis of triceps and pectoralis major suggested loss of C8 function. A major input from T1 was confirmed for flexor digitorum superficialis, flexor digitorum profundus (FDP) to the radial digits, and extensor pollicis longus. C8 was the predominant innervation to the ulnar side of FDP and intrinsic muscles innervated by the ulnar nerve with some contribution from C7.

A revised myotome chart for the upper limb is proposed.