about radial nerve anatomy,course,clinical syndromes,nerve conduction study and EMG protocol

1. RADIAL NEUROPATHY
DR AHAMED SUBIR H

2. Radial Nerve
• Originates as the terminal branch of the
posterior cord of the brachial plexus:
– roots from C5, 6, 7, 8, & T1.
– Largest branch of brachial plexus

4. Course of Radial Nerve
• Largest terminal branch of posterior cord
• Enters posterior aspect of humerus through lower
triangular interval
– Teres major (superior)
– Long head triceps (medial)
– Humerus (lateral)
• Gives posterior cutaneous nerve of arm in axilla

6. Course of Radial Nerve
• Comes to lie in distal part of spiral groove with
profundi brachii artery
– Beneath lateral head of triceps and proximal to origin of
medial head
• Gives branches to triceps, anconeus and inferior
lateral cutaneous nerve of arm
• Through lateral intermuscular septum 10-12cm
above lateral epicondyle

9. Course of Radial Nerve
• In anterior compartment of arm lies between
brachialis and brachioradialis
– 1-3 accessory branches to brachialis
– Large branch to BR (sometimes this branch given
by superficial radial below elbow)
• ECRL generally innervated proximal to elbow
joint

11. Course of Radial Nerve
• Enters the forearm anterior to lateral epicondyle
– More specifically over articulation between capitulum and
radial head
• ECRB innervated distal to elbow joint either PIN or
superficial branch
• At some point 3cm above or below divides into:
– Superficial radial
– PIN

13. Course of Superficial Radial Nerve
• Runs over supinator,PT and FDS
• Lies under BR with radial artery on its ulnar side from
1/3 of the way down forearm
• Passes posteriorly through tendon of BR proximal to
radial styloid
• Passes over tendons of snuffbox
• Terminates as cutaneous branches to dorsum of
hand and lateral 3.5 digits short of nailbeds

17. INNERVATIONS

18. Cutaneous Innervation
• Posterior cutaneous nerve of arm
• Inferior lateral cutaneous nerve of arm
• Posterior cutaneous nerve of forearm
• Superficial branch of radial nerve

22. Motor Innervation
• Muscular branches of radial nerve above elbow:
– Triceps
– Anconeus
• After this, it wraps around humerus in the spinal
groove
– Brachoradialis
– ECRL
• Then after 3 -4 cm after lateral condyle bifurcates

23. • Superficial branch- superficial radial sensory
nerve
• Descends distally into forearm over radial
bone –sensation over
– Lateral dorsum of hand
– Part of thumb
– Proximal dorsal phalanges of index,middle and
ring finger
• It is palpable over extensor tendons of thumb

26. Motor Innervation
• Deep branch- deep radial motor branch below
elbow:
– ECRB (varied innervation: superficial or PIN)
– Supinator
• After it enters supinator muscle
• PIN:
– Superficial
• EDC, ECU,, EDM
– Deep
• APL, EPL, EPB, EI
– It has sensory (not a pure motor)

28. Posterior Interosseous Nerve
• Gains access to posterior forearm by diving
posterior and laterally through ligament of
Frohse and the interval between the two
heads of supinator
• Arcade of Frohse is a fibrous arch originating
lateral epicondyle superior part of superficial
layer of supinator

31. Posterior Interosseous Nerve
• After exiting the supinator divides into deep
and superficial muscular branches
– Superficial
• EDC, ECU, EDM
– Deep
• APL, EPL, EPB, EI

32. CLINICAL SITUATIONS

33. RADIAL NEUROPATHY AT SPIRAL
GROOVE
• Most common radial neuropathy
• Why? Bcoz Juxtraposed to humerus
• Causes-prolonged immobilisation ( saturday
night palsy)
-strenous muscle effort
-# humerus
- infarction from vasculitis
There is compression and demyelination of radial
nerve

35. • Wrist drop and finger drop( EI,EDC,ECU,ECRL)
• Mild weakness of supination( supinator)
• Elbow flexion weak(brachioradialis)
• Elbow extension is spared
• Sensory disturbance only in the distribution of
superficial radial sensory nerve
• In isolated radial neuropathy- ulnar & median spared.
• Test in neutral position- finger abduction by placing
hand over a flat surface

36. RADIAL NEUROPATHY AT AXILLA
• From prolonged compression-crutches
• There is additional weakness in extension
(triceps and anconeus) and
• sensory disturbance along arm and forearm
(posterior cutaneous nerve of arm and
forearm)
• DD-proximal posterior cord lesion –normal
deltoid( axillary N) and latissmus dorsi
(thoracodorsal N)

37. POSTERIOR INTEROSSEOUS
NEUROPATHY
• Entrapment in arcade of Frohse
• Other causes-ganglion, cyst ,tumours
• Similar to spiral groove lesion clinically
• Wrist and finger drop with sparing of extension
• Differentiating features from spiral groove lesion
– Sparing of brachioradialis,ECRL and brevis ,triceps
– Able to extend wrist weakly with radial tilt
– No sensory findings
However pain in forearm-deep sensory fibres

39. SUPERFICIAL RADIAL SENSORY
NEUROPATHY
• Superficial location
• Cheiralgia paraesthetica
• Tight fitting watches,bandss,bracelets,hand
cuffs
• No weakness

40. RADIAL TUNNEL SYNDROME
• Isolated pain and tenderness in extensor
forearm
• thought to result form compression of PIN
• No neurologic signs and normal Edx
• Increased painn with manuevers that contract
ECR (resisted extension of middle finger)
or supinator( resisted supination)

41. Differential diagnosis of wrist drop
• PIN
• Radial nerve in spiral groove
• Radial nerve in axilla
• Posterior cord
• C7 root
• CNS

42. • C7 –extend wrists and fingers with sparing of
non radial C7 muscles
• If severe C7 radiculopathy-weakness of
pronator teres and FCR-weakness of arm
pronation and flexion
• Central lesions- increased tone,DTR ,slowness
of movement and associated findings and
altered sensation beyond radial nerve
distribution

43. DD

44. ELECTROPHYSIOLOGIC EVALUATION-
NCS

45. ELECTROPHYSIOLOGIC EVALUATION-
NCS
RADIAL MOTOR STUDY
• EIP muscle –G1- 2 finger breadth proximal to
ulnar styloid
• G2 – over ulnar styloid
• Stimulate –in groove between biceps and
brachioradialis,below and above
• CMAP 2-5 mV
• Compare with contralateral side

46. RADIAL MOTOR STUDY

47. Recommended NCS protocol for Radial
neuropathy
• Radial motor study-EI –stimulating forearm, elbow,below
and above spiral groove-bilateral studies
• Ulnar motor study –Abductor digiti minimi at wrist,below
and above groove in flexed elbow position
• Median Motor study-Abductor pollicis brevis at wrist and
antecubital fossa
• Median and ulnar F responses
• Superficial radial sensory nerve -extensor tendons to
thumb,stimulating forearm
• Ulnar sensory study-recording digit 5 –stimulating wrist
• Median sensory-recording digit 2 or 3 –stimulating wrist

48. Results
• PIN(axonal)- normal superficial radial SNAP, low
amplitude distal radial CMAP
• PIN(demyelinating)- normal superficial radial
SNAP, normal amplitude distal radial CMAP with
motor conduction block between forearm and
elbow
• PIN(mixed axonal & demyelinating)- normal
superficial radial SNAP, low amplitude distal
radial CMAP with motor conduction block
between forearm and elbow
• Radial neuropathy at spiral groove (axonal lesion ) -
reduced superficial radial SNAP, low amplitude
distal radial CMAP ,No motor conduction block
across spiral groove
• Radial neuropathy at spiral groove (demyelinating)-
Normal superficial radial SNAP, Normal amplitude
distal radial CMAP with motor conduction block
across spiral groove
• Radial neuropathy at spiral groove (mixed axonal &
demyelinating lesion )- reduced superficial radial
SNAP, Low amplitude distal radial CMAP with motor
conduction block across spiral groove
• Radial neuropathy at axilla (axonal lesion )-
reduced superficial radial SNAP, low
amplitude distal radial CMAP .
• Radial neuropathy at axilla (demyelinating
lesion )- Normal superficial radial SNAP,
Normal amplitude distal radial CMAP with
normal motor study to above spiral groove
• Superficial radial sensory neuropathy-
Reduced superficial radial SNAP, normal
radial motor study

49. Technical considerations
• Placing G1 over EI-initial positive deflection-
volume conducted potentials from nearby radial
innervated muscles(EPB and EPL)
• Difficult accurate surface measurements-
circutaneous course
• These 2 together cause factitiously fast CV
• But we look for conduction block and axonal loss
• PIN are pure axonal- so no conduction block- so
distal CMAP decreased proportional to the axonal
loss

50. Demyelinating lesion in spiral groove

51. RADIAL SENSORY STUDY
• Superficial sensory radial is easy to stimulate
& record
• G1 – extensor tendons of thumb
• G2 – 3 to 4 cm distally
• Stimulation – 10 cm proximally over radius
• Always compare the other side
• If demyelinating – normal SNAP

52. RADIAL SENSORY STUDY

53. Radial SNAP

54. • 3 situations with normal SNAP( when clinically
sensory signs +)
– Hyper acute axonal loss
– Lesion proximal to dorsal root ganglion
– Lesions caused by proximal demyelination(radial
groove and axilla)
• In PIN – usually normal SNAP

55. Wrist drop with normal SNAP-DD
• PIN
• Lesions caused by proximal demyelination(radial
groove and axilla)
• C7 radiculopathy
• CNS lesion
• Hypercute axonal loss injury < 4 days

56. ELECTROPHYSIOLOGIC EVALUATION-
EMG

57. ELECTROPHYSIOLOGIC EVALUATION-
EMG
• To distinguish
• PIN
• Lesion inradial groove and axilla
• C7 radiculopathy
• CNS lesion- MUAP configuration and
recruitment will be normal in weak muscles,
but decreased activation of normal
configuration MUAPs will be seen

58. EMG PROTOCOL
• Atleast 2 PIN muscles( EI,ECU,EDC)
• atleast 1 radial innervated muscle proximal to
bifurction of main radial nerve near elbow but
distal to spiral groove( Brachioradialis,ECRL)
• atleast 1 radial innervated muscle proximal to
spiral groove( triceps,anconeus)
• At least one non radial posterior cord innervated
muscle(deltoid & Latissmus dorsi)
• Atleast 2 non radial C 7 innervated muscle ( PT,
Flexor digitorum,superficialis,cervical paraspinals)

59. • In pure demyelinating lesions with conduction
block only abnormality will be decreased
recruitment of MUAPs in weak muscles

60. THANK YOU