When a patient presents with numbness, weakness or pins and needles in the arm or hand, one or more than one nerv is affected. It can be challenging to identify whether that comes from distal of proximal structure. When you suspect nerve root or peripheral nerve compression, testing is one of the ways to help identify but knowing basic anatomy, causes of injury and understanding history of patients will also be vital. See ulnar nerve compression.
C8 nerve root comes out of between C7 and T1 vertebrae and has sensory and motor function. C8 nerve root compression may manifest with weakness in abductor pollicis brevis, opponent pollicis and lateral two lumbricals, which are innervated by median nerve. Therefore, pinching something with thumb, index and middle finger is a way of testing.
If this is ulnar nerve compression, weakness in these fingers should not show as these are innervated by median nerve (C6-T1) [Pic 1].
*Making a tight circle with thumb and index finger to hold against resistance by clinician is another way to test [pic 2].
*C8 nerve root compression may show weakness in triceps or extension of the wrist, which is C7 myotome as C8 innervates those muscles as well .
C8 dermatome distribution is the little finger, half of the ring finger and hypothenar eminence [pic 3].
T1 nerve root comes out of between T1 and T2, which is a rare nerve root compression. . However, presentation can be similar to ulnar nerve compression. T1 myotome is the finger abduction. Dorsal interossei muscle has a function of finger abduction, which is innervated by ulnar nerve.
T1 dermatome covers ulnar (medial) half of the forearm [pic 3].
Ulnar nerve compression
Ulnar nerve provides motor function to 7 muscles in the forearm and hand.
Flexor carpi ulnaris (flexion and ulnar deviation of the wrist)
Flexor digitorum profundus (4th and 5th) :Flexion of the 4th and 5th digits
·Flexor digiti minimi brevis
·Abductor digiti minimi
·Opponens digiti minimi
·Adductor pollicis (adduction of the thumb)
·Dorsal and palmer interossei (finger adduction and abduction)
·Medial lumbricals (flexion of 4th and 5th interphalangeal joint)
Little finger, half of the ring finger and hypothenar eminence (not in the forearm)
*Make sure to clear and test the cervical joint by ROM, over pressure PROM, palpation, ULNT, Bakody’s test, spurling test and reflex.
* Nerve conduction test might be normal depending on the size of the damaged nerve fibre [4, pic 3].
 Stoker, G. E., Kim, H. J., & Riew, K. D. (2013). Differentiating C8–T1 Radiculopathy from Ulnar Neuropathy: A Survey of 24 Spine Surgeons. Global Spine Journal, 4(1), 1–5. https://doi.org/10.1055/s-0033-1354254
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