T&O - Nerve Territories And Injuries

Question 1

Outline the MRC classification of power assessment

Answer 1

• 5: normal power
• 4: weakness
• 3: inability to use muscle against gravity
• 2: movement with gravity eliminated
• 1: flicker of muscle
• 0: no movement detectable

Question 2

Outline the peripheral territories of brachial plexus branches

Answer 2

INSERT PICTURE

Question 3

Outline the dermatomes of the upper limb

Answer 3

INSERT PICTURE

Question 4

Outline the dermatomes of the lower limbs

Answer 4

INSERT PICTURE

Question 5

Outline the myotomes of the upper limb

Answer 5

C4-Shoulder elevation
C5 – The deltoid muscle (abduction of the arm in the shoulder joint).
C6 – The biceps (flexion of the arm in the elbow joint).
C7 – The triceps (extension of the arm in the elbow joint).
C8 – The small muscles of the hand.
T1- Finger Abduction (ulnar nerve)
T1-Abductor pollis brevis (median nerve)

Question 6

Outline the myotomes of the lower limb

Answer 6

L2 -Hip Flexion
L3,4- Knee Extension
L4 – The quadriceps (extension of the leg in the knee joint).
L5 – The tibialis anterior (upward flexion of the foot in the ankle joint).
S1 – The gastrocnemius muscle (downward flexion of the foot in the ankle joint).

Question 7

Outline two important lesions at the brachial plexus

Answer 7

• Erbs palsy (C5-6): abductors and external rotators paralysed - arm held close to body, internally rotated with loss of sensation to C5/C6 dermatomes
• Klumpke paralysis (C8/T1): rare, result in loss of intrinsic muscles of hand, leading to claw hand with loss of sensation in C8/T1 dermatomes

Question 8

Describe lesions of the radial nerve

Answer 8

(C5-T1)
-low lesions: fracture around elbow or forearm (eg head of radius)
◦ Loss of extension of CMC joints (finger drop) and no sensory loss
-High lesions: fracture of shaft of humerus where nerve is in radial groove
◦ Wrist drop, loss of sensation of dorsum of thumb
◦ Triceps functions normally
-Very high lesions: axilla (crutches or palsy)
◦ Paralysis of triceps and wrist drop + sensory loss

Question 9

Describe lesions of the ulnar nerve

Answer 9

(C8-T1)
-Site: elbow (cubital gunner) or wrist (Guyon’s canal)
-Effects:
◦ Intrinsic hand muscle paralysis —> claw hand
◦ Ulnar paradox: lesion at elbow has less clawing (looks better but is functionally worse) because FDP is paralysed, decreasing flexion of 4th/5th digits
◦ Weakness of finger ad/abduction (interossei)
◦ Sensory loss over little finger/ulnar nerve region is more likely if there is damage at the elbow than at wrist (cutaneous branches enter hand via Guyon’s canal)

Question 10

What is carpal tunnel syndrome?

Answer 10

• Median nerve: first 2 lumbricals and the near eminence (LOAF- lumbricals, opponens polices, abductor and flexor pollicis brevis)
• Carpal tunnel syndrome: parasthesia and pain in distribution of median nerve b/c it is compressed as it passes under flexor retinaculum
*Small patch of skin over then at eminence is spared b/c it is supplied by superficial branch of median nerve

Question 11

What test do you perform to elicit carpal tunnel syndrome?

Answer 11

-Test: Tinel’s sign: tapping over median nerve at wrist to reproduce the symptoms

Question 12

What are possible Rx options for carpal tunnel syndrome?

Answer 12

• Symptomatic Rx: splints across wrist or local steroid injections
• Surgical Rx: (reduced nerve conduction) - decompression by division of flexor retinaculum. Pain will improve but numbness/wasting may not