Brachial Plexus

Question 1

What is the brachial plexus divided into?

Answer 1

The roots, which are the spinal nerves. These are generally the anterior rami of the roots (C5-T1)

Trunks are where the roots may fuse (superior, middle and inferior)

Divisions are where you have swapping and division into anterior and posterior (anterior and posterior)

The cords are where nerves are recombined (lateral, posterior and medial - in relation to axillary artery)

The big terminal branches come off at other points ( musculocutaneous, axillary and radial, median, ulnar )

• C5, C6, C7 - long thoracic to serratus anterior
• subclavian nerve off of superior trunk
• suprascapular nerve off of anterior superior branch
• upper and lower subscapualr nerves and thoracodorsal nerve ( latissimus dorsi) off posterior cord
• lateral pectoral off lateral cord
• medial pectoral, medial cutaneous nerve
  of arm off medial cord ( medial cutaneous nerve of forearm off uln

Question 2

Describe the nervous supply of the motor nerves of the upper limb

Answer 2

• C3-C7 supply shoulder girdle muscles
• C5-C6 supply shoulder joint muscles and elbow flexors
• C7-C7 supply elbow extensors
• C6-C8 supply wrist and coarse hand muscles
• C8-T1 supply small muscles of the hand (fine movements)

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Question 3

What is the benefit of nerve recombination happening in the plexus?

Answer 3

the pattern of cutaneous nerve distribution is very different from the dermatome pattern

Benefit:

• if there is damage to one spinal nerve, it won’t completely knock out the action of a muscle - muscles are usually supplied by more than one nerve
• Similarly, if you damage a peripheral nerve, you don’t damage the supply to the whole of a dermatome - the dermatome will receive some supply from OTHER peripheral nerve

Question 4

What are the common ways to damage the axillary nerve?

Answer 4

shoulder dislocation or fracture at surgical head of humerus because it is emerging just beneath the gleno-humoral (shoulder) joint

Question 5

What are the consequences of damaging the axillary nerve?

How can you assess the nerve damage?

Answer 5

Axillary supplies DELTOID MUSCLE – damaged axillary nerve -> wasting of deltoid muscle

With lack of activity of deltoid over a long period of time, you get wasting of the muscle and there is bumpiness in the shoulder. The underlying skeleton of the shoulder is more visible. Teres minor is also supplied by axillary. There is some sensation supply of the axillary nerve (at the regimental badge). It is the upper lateral cutaneous region of the arm.

You can test for axillary nerve damage by assessing whether there is any abnormal sensation (anaesthesia or paraesthesia in that region) - regimental badge area

Question 6

What can cause a radial nerve damage?

What happens if you damage the radial nerve?

Answer 6

The radial nerve runs closely apposed to the shaft of the humerus, so can be damaged in humeral fractures. There is a radial groove on the shaft of the humerus, where the radial nerve runs. If you have a break or fracture of the humerus, it can damage the radial nerve.

In radial nerve damage, you get WRIST DROP (forearm extensors aren’t working). There is also anaesthesia in the dorsal-lateral aspect of the hand.

If the damage is high enough, patients may also be unable to properly extend the elbow. There is loss of muscle mass evident in both the arm and forearm if the damage is high enough. The higher up the damage (i.e. closer to the plexus), the worse the outcome tends to be. You also get loss of the power grip (most important outcome). Grip is more effective when extensors are shortened.

Question 7

How can you damage the musculocutaneous nerve?

Answer 7

The musculocutaneous nerve comes from the lateral cord -> comes off and goes into the anterior arm -> supplies the anterior arm muscles

This nerve is quite deep, so it is well protected by muscles so not often injured by traum. However, it may be damaged during breast cancer surgery due to harvesting of lymph nodes from the axilla

• It runs from the axilla in that region

Question 8

What are common sites of injury of the ulnar nerve?

Answer 8

The ulnar nerve goes behind medial epicondyle of the humerus - injuries to medial epicondyle of humerus cause injury to the ulnar nerve at the elbow

he ulnar nerve can be damaged at the wrist - e.g by attempted suicide (cutting wrists

Question 9

What happens in an ulnar nerve injury?

Answer 9

Ulnar nerve injury can cause claw deformity.

Lumbrical muscles coming off the tendons of FDP go round and the tendon inserts into the extensor expansion on the proximal interphalangeal joint. Loss of lumbrical contraction means loss of flexion of the MPJs and weakened extension of the IPJs

Other muscles supplies by the ulnar in the hand include interossei. If interossei aren’t getting good supply, you cannot adduct and abduct the digits properly. Many small muscles of the hand are affected but the thumb, index and middle finger movements are largely spared. Loss of sensation is inconvenient but not too debilitating.

Question 10

What is the ulnar paradox?

Answer 10

Ulnar injury at the wrist results in a more severe deformity (clawing) than injury at the elbow

You might normally expect a more proximal injury to result in a more deformed appearance

This is because the ulnar nerve also innervates the ulnar half of FDP -> flexion of the IP joints is weakened -> therefore less claw-like appearance (‘the closer to the paw, the worse the claw’)

Question 11

What causes carpal tunnel syndrome?

Answer 11

As with all enclosed spaces, if you get inflammation, there is a build up of fluid -> COMPRESSION (fairly common)

• Inflammation can result from infection and trauma

Question 12

What does the ulnar nerve supply in the hand?

Answer 12

most of the intrinsic muscles of the hand, EXCEPT for the thenar eminence muscles of the thumb. It also supplies the little finger and half of the ring finger

Question 13

What does the median nerve supply in the hand?

Answer 13

• sensation to the thumb, index, middle and half of the ring finger
• muscles of the thenar eminence are supplied by median after it passes through the carpal tunnel - so compression in the carpal tunnel affects thenar muscles
• There is a cutaneous branch coming off the median nerve, supplying some sensation to the palm.
  This won’t be significantly affected in the long term by carpal tunnel compression

Question 14

What are the consequences of carpal tunnel syndrome?

Answer 14

• long-term effect of carpal tunnel syndrome is wasting of the thenar eminence
• loss of both sensation and fine movement in the lateral digits
• Some ulnar sensation can compensate for digits.

Question 15

What can cause damage to the long thoracic nerve?

Answer 15

The long thoracic nerve runs down the lateral side of the thoracic wall

The thoracic wall is covered by the serratus anterior muscle

It has an attachment at the medial border of the scapula, before forming digitations attaching to ribs

Because the long thoracic nerve is relatively superficial, it can get damaged in trauma and stabbings

Question 16

What are the consequences of damage to the long thoracic nerve?

Answer 16

SERRATUS ANTERIOR: important muscle for stabilising the scapula (stops it from becoming depressed)

Damage to the long thoracic nerve can be assessed by getting a patient to press into a wall

You will see winging of the scapula resulting from the loss of activity of serratus anterior

Question 17

What can cause damage to the upper roots?

What are the consequences of this?

Answer 17

Erb - duchenne palsy

UPPER ROOTS: C5, C6

Damage to the upper roots can result from neck trauma e.g by falling on the head, breaking the neck, can also result during childbirth (the baby’s neck can be stretched during delivery -> damage)

If the upper root is affected, the lateral and posterior cords will be affected. Many muscles will therefore be affected (in the shoulder and anterior arm).

The forearm will be pronated by lack of biceps supination (‘waiter’s tip’ position with upper root injury).

Question 18

What can cause injury to the lower roots?

Answer 18

Common cause is over-abduction due to gripping overhead to break a fall -> stretch of brachial plexus / at childbirth – stretching of the limb can lead to lower root injury

• The affected roots in ‘lower root injury’ involve mainly T1, and sometimes C8
• If T1 is affected, its going to affect the lower trunk and the medial and posterior cords

Question 19

What is the consequence of damage to the lower roots?

Answer 19

Klumke’s Palsy

T1 mainly supplies the small muscles of the hand via the ulnar and median nerves - loss of their activity results in clawed hand. This is because all of the lumbricals are affected -> more pronounced clawing. The affected interossei will result in a deficit of fine movement in the hand.