Nerve vs Root

Who Cares?

Neurologists
Physiatrists
Neurosurgeons
Internal medicine residents who are studying for Canadian boards
in the meantime, these notes may help as a reference in your studies...

A Few Helpful Pointers

Radiculopathies are often painful (focal neuroapthies often aren't)
Radiculopathies are a proximal lesion (i.e. spinal nerve root)
- affects ventral ramus (which supplies all limb muscles)
- affects dorsal ramus (which supplies paraspinal muscles)
  - invaluable for localization on EMG studies
  - ...unfortunately clinical exam of paraspinal muscles is not very fruitful
- for neurology residents: recall that radiculopathies spare the dorsal root ganglion and so the SNAP is preserved within the region of sensory anomaly
Radiculopathies affect motor and sensory nerves
- a pure motor or pure sensory deficit affecting one limb is likely a focal neuropathy or partial plexopathy (infrequently, a motor neuronopathy or sensory neuronpathy)
Radiculopathies are accompanied by loss of deep tendon reflexes (DTRs)
- ...although theoretically any muscle can be tested for a DTR, only certain ones can be tested conveniently/reliably, so not all roots are associated with a reflex.

C5 radiculopathy

Clinical
- Pain: neck, shoulder
- Numbness: lateral aspect of arm and shoulder
- Weakness: shoulder abduction, external rotation, elbow flexion, forearm supination
Motor
- Shoulder abduction: deltoid (C5, C6), supraspinatus (C5, C6)
- External rotation: infraspinatus (C5, C6)
- Elbow flexion: biceps (C5, C6), brachioradialis (with the forearm in mid-pronation) (C5, C6)
- Forearm supination: biceps (C5, C6)
Sensory
- Dermatome: lateral shoulder and upper arm, extending to lateral aspect of the elbow
- ASIA sensory point: on the lateral (radial) side of the antecubital fossa just proximal to the elbow
Reflexes
- Biceps (C5, C6)
- Brachioradialis (C5, C6)

Axillary neuropathy

Motor
- Shoulder abduction: deltoid (C5, C6)
- External rotation: teres minor (C5, C6)
Sensory
- supplies a small patch on the lateral aspect of the inferior shoulder and upper arm
Reflexes
- none

C7 Radiculopathy

Clinical
- Pain: neck, shoulder, hand, middle finger
- Numbness: palm, index and middle finger
- Weakness: elbow extension, wrist extension (radial aspect), forearm pronation, wrist flexion
Motor
- Elbow extension: triceps (C6, C7, C8)
- Wrist extension: extensor carpi ulnaris (C7, C8)
- Forearm pronation: pronator teres (C6, C7) (median nerve)
- Wrist flexion: flexor carpi radialis (C6, C7)
- Finger extension: extensor digitorum communis (C7, C8)
Sensory
- Dermatome: dorsal and palmar hand (region quite variable), middle finger
- ASIA sensory point: on the dorsal surface of the proximal phalanx of the middle finger
Reflexes
- Triceps (C6, C7, C8)

Radial neuropathy

Motor
- Elbow extention: triceps (C6, C7, C8)
- Elbow flexion: (forearm mid-pronated): brachioradialis (C5, C6)
- Radial wrist extension: extensor carpi radialis longus (C5, C6), extensor carpi radialis brevis (C5, C6)
- Forearm supination: supinator (C6, C7)
- Posterior interosseus nerve (pure motor branch of radial nerve, all C7, C8):
  - Ulnar wrist extension: extensor carpi ulnaris (C7, C8)
  - Finger extension: extensor digitorum communis (C7, C8), extensor digiti minimi (C7, C8), extensor indicis proprius (C7, C8)
  - Thumb extension: extensor pollicis brevis (C7, C8), extensor pollicis brevis (C7, C8)
  - Thumb abduction (in a plane at 90^o to the hand): abductor pollicis brevis (C7, C8)
Sensory
- high lesions (above the origin of the posterior cutaneous nerves of the arm and forearm) produce sensory loss with posterior arm, forearm, extending to the dorsal hand
- the more common sensory deficit is restricted to the dorsal aspect of the hand (within the distribution of the superficial cutaneous radial nerve)
Reflexes
- Triceps (C6, C7, C8)
- Brachioradialis (C5, C6)

C8 Radiculopathy

Clinical
- Pain: shoulder, medial forearm, medial hand, 4th and 5th digits
- Numbness: medial forearm, medial hand, 4th and 5th digits
- Weakness: elbow extension, wrist extension (ulnar aspect), distal finger flexion, distal thumb flexion, finger abduction, finger adduction
Motor
- Elbow extension: triceps (C6, C7, C8)
- Wrist extension (ulnar aspect): extensor carpi ulnaris (C7, C8)
- Finger extension: extensor digitorum communis (C7, C8), extensor indicis proprius (C7, C8)
- Distal finger flexion: flexor digitorum profundus (I & II and III & IV) (C7, C8)
- Distal thumb flexion: flexor pollicis longus (C8, T1)
- Finger abduction: dorsal interossei (C8, T1) - first dorsal interosseus (FDI) and abductor digiti minimi (ADM) most clinically relevant
- Finger adduction: palmar interossei (C8, T1)
- Thumb abduction: abductor pollicis brevis (C8, T1)
Sensory
- Dermatome: lateral aspect of dorsal and palmar hand, may be quite variable
- ASIA sensory point: on the dorsal surface of the proximal phalanx of the little finger
Reflexes
- Triceps (C6, C7, C8)

Ulnar neuropathy

Motor
- Wrist flexion: flexor carpi ulnaris (C7, C8)
- Finger flexion (4rd & 5th digits): flexor digitorum profundus III & IV (C7, C8)
- All hand intrinsics (C8, T1): palmar and dorsal interossei, lumbricals III & IV, abductor/opponens/flexor digiti minimi, except for the median-supplied "LOAF" muscles (lumbricals I & II, opponens/abductor/flexor pollicis brevis)
Sensory
- origin above the elbow:
  - medical cutaneous nerve of the arm (sensation to medial arm)
  - medical cutaneous nerve of the forearm (sensation to medial forearm)
- origin above the wrist:
  - palmar cutaneous branch (sensation to palm)
- origin distal to the wrist:
  - superfical terminal branches (sensation to lateral aspect of 4th digit, and to 5th digit)
Reflexes
- none (well, you can test finger flexors of 4th and 5th digits, might not be very useful in practice)

L4 Radiculopathy

Clinical
- Pain: back, anterior thigh, occasionally medial lower leg
- Numbness: anterior thigh, occasionally medial lower leg
- Weakness: hip flexion, hip adduction, knee extension
- Note that L4, L3-4, L2-3-4, etc. radiculopathies have nearly identical clinical presentation
Motor
- Hip Adduction: adductor longus, adductor magnus (L2, L3, L4) (obturator nerve)
- Knee extension: quadriceps femoris (rectus femoris, vastus lateralis/intermedius/medialis) (L2, L3, L4)
- Hip flexion: mostly iliopsoas (L1, L2, L3) but quadriceps does do some hip flexion so there may be weakness
Sensory
- Dermatome: medial leg below the knee
- ASIA sensory point: over the medial malleolus
Reflexes
- Patellar (quadriceps femoris) (L2, L3, L4)

Femoral neuropathy

Motor
- Knee extension: quadriceps femoris (rectus femoris, vastus lateralis/intermedius/medialis) (L2, L3, L4)
Sensory
- medial and intermediate cutaneous nerve of the thigh (anterior and medial thigh above the knee)
- saphenous nerve (medial leg below the knee)
Reflexes
- Patellar (quadriceps femoris) (L2, L3, L4)

L5 Radiculopathy

Clinical
- Pain: back, buttock, lateral thigh, dorsum foot, great toe
- Numbness: lateral calf, dorsum foot, webspace between 1st and 2nd toe
- Weakness: Hip abduction, knee flexion, foot dorsiflexion, toe extension and flexion, foot inversion and eversion
Motor
- Hip abduction: gluteus medius and gluteus minimus (L4, L5, S1) (superior gluteal nerve)
- Knee flexion: semitendinosus (L5, S1, S2), semimembranosus (L5, S1, S2), biceps femoris short head&long head (L5, S1, S2) (sciatic nerve)
- Foot dorsiflexion: tibialis anterior (L4, L5) (major action)
- Foot inversion: tibialis anterior (L4, L5) (minor action), tibialis posterior (L5, S1) (tibial&sciatic nerve)
- Foot eversion: peroneus longus (L5, S1), peroneus brevis (L5, S1)
- Toe extension: extensor hallucis longus (L5, S1), extensor digitorum longus (L5, S1), extensor digitorum brevis (L5, S1)
- Toe flexion: flexor digitorum longus (L5, S1, S2)
Sensory
- Dermatome: lateral aspect of the leg below the knee, extending to the dorsum foot and webspace between 1st and 2nd toe
- ASIA sensory point: on the dorsum of the foot over the 3rd metatarsal phalangeal joint
Reflexes
- medial hamstrings [semitendinosus (L5, S1, S2), semimembranosus (L5, S1, S2)]
- in practice I find these rather hard to obtain (and usually not necessary to discriminate peroneal neuropathy vs L5)

Peroneal neuropathy

now called the fibular nerve (to avoid confusion with perineal)
Motor
- Superficial branch:
  - Foot eversion: peroneus longus (L5, S1), peroneus brevis (L5, S1)
- Deep branch:
  - Foot dorsiflexion: tibialis anterior (L4, L5) (major action)
  - Foot inversion: tibialis anterior (L4, L5) (minor action)
  - Toe extension: extensor hallucis longus (L5, S1), extensor digitorum longus (L5, S1), extensor digitorum brevis (L5, S1)
Sensory
- Superficial branch:
  - lateral aspect of the leg below the knee, extending to dorsum foot, excluding webspace between 1st and 2nd toe
- Deep branch:
  - webspace between 1st and 2nd toe
Reflexes
- None

S1 Radiculopathy

Clinical
- Pain: back, buttock, lateral or posterior thigh, posterior calf, lateral or plantar foot
- Numbness: posterior calf, lateral or plantar aspect of foot
- Weakness: hip extension, knee flexion, foot plantarflexion
Motor
- Hip extension: gluteus maximus (L5, S1, S2) (inferior gluteal nerve)
- Knee flexion: semitendinosus (L5, S1, S2), semimembranosus (L5, S1, S2), biceps femoris short head&long head (L5, S1, S2)
- Foot plantarflexion: gastrocnemius, soleus (S1, S2)
- Toe flexion: flexor digitorum longus (L5, S1, S2)
- Foot intrinsic muscles: abductor hallcuis, abductor digiti minimi, interossei (S1, S2)
Sensory
- Dermatome: distal posterior calf, lateral and plantar aspect of foot
- ASIA sensory point: on the lateral aspect of the calcaneus
Reflexes
- Achilles tendon (gastrocnemius and soleus) (S1, S2)

Sciatic neuropathy

Motor
- Sciatic nerve (before it divides into peroneal&tibial nerves):
  - Knee flexion: semitendinosus (L5, S1, S2), semimembranosus (L5, S1, S2), biceps femoris short head&long head (L5, S1, S2)
- Peroneal (fibular) nerve:
  - Foot eversion: peroneus longus (L5, S1), peroneus brevis (L5, S1)
  - Foot dorsiflexion: tibialis anterior (L4, L5) (major action)
  - Foot inversion: tibialis anterior (L4, L5) (minor action)
  - Toe extension: extensor hallucis longus (L5, S1), extensor digitorum longus (L5, S1), extensor digitorum brevis (L5, S1)
- Tibial nerve:
  - Foot eversion: peroneus longus (L5, S1), peroneus brevis (L5, S1)
  - Foot plantarflexion: gastrocnemius, soleus (S1, S2)
  - Toe flexion: flexor digitorum longus (L5, S1, S2)
  - Foot intrinsic muscles: abductor hallcuis, abductor digiti minimi, interossei (S1, S2)
Sensory
- Peroneal (fibular):
  - lateral aspect of the leg below the knee, extending to dorsum foot, including webspace between 1st and 2nd toe
- Tibial
  - distal toes and plantar aspect of the foot
- Sural (supplied by fibular and tibial)
  - lateral aspect of foot
- ...therefore lesions of the sciatic trunk will affect sensation to lateral leg below the knee and the entire foot
  - high sciatic trunk lesions may involve the posterior cutaneous nerve of the thigh and affect sensation to posterior leg and thigh
Reflexes
- medial hamstrings [semitendinosus (L5, S1, S2), semimembranosus (L5, S1, S2)]
- Achilles tendon (gastrocnemius and soleus) (S1, S2)

References

references in bold are highly recommended

Guarantors of Brain (2000). Aids to the Examination of the Peripheral Nervous System. Saunders Limited.
American Spinal Injury Association (ASIA) scale - accessed at http://www.asia-spinalinjury.org/
Levin, K. (2008). Diseases of the nerve roots. Continuum (Minneapolis, Minn.), 14(3, Spinal Cord, Root, and Plexus Disorders), 134–155.