UPPER LIMB PERIPHERAL NERVE LESIONS

CERVICAL NERVE ROOT LESIONS (C5-T1)

DERMATOMES (= cutaneous innervation of each nerve root)

• The key is C7
• Cervical Vertebrae with longest spinous process = vertebral prominens = C7
• Longest finger = middle finger
• C7 dermatome centres on middle finger and extends along back of arm
• Successive dermatomes descend down lateral side to hand and ascend along medial side to armpit
• Lateral upper limb
  C5 = shoulder/lateral upper arm, C6 = lateral forearm/hand
• Medial upper limb
  C8 = medial hand/forearm, T1 = medial upper arm/axilla

MYOTOMES (= motor innervation of each nerve root)

Shoulder (starts with C5)

• C5 - Abduct (+ lateral rotation)
• C6,7,8 - Adduct (+ medial rotation)

Big 'wings' arms outstretched

Elbow (starts with C5)

• C5,6 - Flex (+ pronation = 'pulling out the cork'))
• C6,7 - Extend (+ supination = 'paddling with arms'

Wrist (now drop a myotome to C6)

• C6 - Extend
• C7 - Flex

Fingers (drop another myotome to C7)

• C7 - Extend
• C8 - Flex
• T1 - Abduct/Adduct
• To repeat: C5+678 shoulder, C56+C78 elbow, C6+C7 wrist, C7+C8 fingers, T1 intrinsics mm.

BRACHIAL PLEXUS LESIONS

Erb's palsy (C5/C6)

• 'Waiter's tip' - arm dropped to side and shoulder turned in with wrist flexed
• Loss of shoulder abduction, elbow function and wrist extension
• Numb lateral upper limb
• Due to forced lateral flexion of neck

Klumpke's palsy (C8/T1)

• Loss of finger flexion and abduction/adduction
• Numb medial upper limb
• From grabbing handhold above whilst falling

PERIPHERAL NERVE LESIONS

Axillary nerve palsy

• Weak deltoid, numb deltoid
• Often due to shoulder dislocation/fractures

Radial nerve palsy

• Loss of the 'extensors' - elbow, wrist, finger
• Numb lateral arm and 1st web space
• Degree depends on proximity of lesion
• Wrist drop +/- other extensor loss
• Vulnerable in compression (Saturday night palsy) or humeral shaft fractures

Median nerve palsy

• Loss of all finger flexors (except ring/little finger)
• Thenar muscles (except thumb adductor = ulnar n) - can't make OK sign
• Numb thenar eminence
• 'Pointing finger' sign when making fist
• Thenar eminence wasting (if chronic)
• Vulnerable in elbow dislocation
• Part of the 'carpel tunnel syndrome'

Ulnar nerve palsy

• Loss of ring/little finger flexors (FDS/FDP spared in distal lesion) and abduction/adduction
• Numb hypothenar eminence
• 'Claw hand' with extended ring/little fingers at MCP (flexed small joints if FDS/FDP spared)
• Interossei wasting (if chronic)
• Vulnerable in medial elbow trauma ('funny bone')

The radial, ulnar, median nerve quick test::

• Make a fist = median nerve, Make a star = ulnar nerve, Thumbs up = radial nerve
• Thenar sensation = median nerve, Hypothenar sensation = ulnar nerve, 1st web space sensation = radial nerve