C8 and T1 innervation of forearm muscles

•C8/T1 myotomal innervation of the forearm muscles was investigated based on clinical weakness and EMG findings.•Median-innervated forearm flexor muscles, such as flexor digitorum superficialis and flexor digitorum profundus of the index finger, were dominantly innervated by the T1 root.•Ulnar-innervated forearm flexor muscles, such as flexor carpi ulnaris and flexor digitorum profundus of the little finger, were dominantly innervated by the C8 root.

ObjectiveC8-dominant innervation of ulnar-innervated and T1-dominant innervation of median-innervated intrinsic hand muscles have been suggested, although less is known regarding forearm muscles. We aimed to determine myotomal innervation of the forearm muscles based on the clinical and electromyographial findings of patients with C8 or T1 lesions.MethodsMedical Research Council scale and EMG findings were retrospectively reviewed in 16 patients with C8 lesions (2 postmedian sternotomy C8 plexopathy and 14 C8 radiculopathy) and 9 patients with T1-dominant lesions (8 true neurogenic thoracic outlet syndrome and 1 T1 radiculopathy).ResultsClinical and EMG findings revealed T1-dominant innervation of the flexor digitorum superficialis, flexor digitorum profundus of the index finger, abductor pollicis brevis, and flexor pollicis longus muscles, and C8-dominant innervation of the flexor carpi ulnaris, flexor digitorum profundus of the little finger, and digit extensors innervated by the posterior interosseous nerve. The first dorsal interosseous, and abductor digiti minimi muscles seem to be innervated by both C8 and T1 roots.ConclusionsC8-dominant innervation of ulnar-innervated muscles and T1-dominant innervation of median-innervated muscles are also evident for forearm flexor muscles.SignificanceSuch an additional evidence for myotomal innervation will improve localization in clinical as well as electrophysiological diagnoses.