Upper Limb CAS 2

Question 1

What are the 3 myotactic reflexes of the upper limb?

Answer 1

1) Biceps tendon reflex – spinal segment/nerve roots C5 & C6
2) Triceps tendon reflex – spinal segment/nerve roots C7 & C8
3) Brachioradialis (supinator) reflex – spinal segment/nerve roots C5 & C6

Question 2

Define reflex and what a reflex pathway consists of

Answer 2

A reflex is an involuntary response to a stimulus. This depends on the integrity of the reflex arc. Typically, a reflex pathway consists of:
1) afferent (sensory) neurones conveying impulses from sensory receptors in the muscle spindle to the spinal cord (CNS)
2) efferent (motor) neurones running from the anterior grey columns of the spinal cord (CNS) to the effector organ which is the limb muscle.
The reflex arc may be monosynaptic or multi synaptic. Most of the myotatic reflex arcs are monosynaptic.

Question 3

Why does a reflex occur?

Answer 3

When the tendon of a muscle is tapped with a tendon hammer, it causes stretching of the muscle spindles. This stimulus travels to the spinal cord, which then stimulates the efferent motor neurones in the anterior grey columns (horns). This results in involuntary contraction of the main muscle whose tendon was stretched by tapping.

Question 4

What is the law of reciprocal innervation?

Answer 4

In the same limb the flexor and extensor muscles cannot contract simultaneously. The afferent nerves responsible for flexor reflex muscle action must have branches to synapse with the extensor motor neurons of the same limb to inhibit the extensor muscle contraction.

Question 5

What would abnormally exaggerated myotactic reflexes indicate?

Answer 5

Higher centres of the brain influence the spinal segmental reflex arc which results in the modulation of the resultant motor activity. In other words, abnormally exaggerated myotatic reflexes lead to a clinical picture of an upper motor neurone lesion.

Question 6

What does areflexia indicate?

Answer 6

If there is disorder in any of the components of the reflex arc (muscle spindles, afferent sensory neurones, efferent motor neurones and the effector organs - the muscle itself) there will be complete absence (areflexia) of reflexes which is suggestive of a lower motor neurone lesion.

Question 7

What is the grading system for reflexes?

Answer 7

0 Absent
1+ Decreased, but still present (hypo-reflexic)
2+ Normal
3+ Hyper-reflexic
4+ Clonus: Repetitive shortening of the muscle after a single stimulation

Question 8

What is a dermatome and myotome?

Answer 8

An area of skin supplied by a single spinal nerve root of the spinal cord segment is referred as a dermatome. A similarly innervated region of a skeletal muscle is called a myotome.

Question 9

What kind of effect would loss of a single spinal nerve root have?

Answer 9

On the skin, the adjacent dermatomes (for example C4, C5, C6) overlap considerably. Therefore, loss of a single spinal nerve root may not produce any detectable sensory loss in that dermatome. In order to detect a significant sensory loss at least three adjacent dermatomes should be affected. However, there is no overlap (for example C4 and T2 or C5 and T1) across the axial lines of the limb.

Question 10

What would damage to a single peripheral nerve cause?

Answer 10

Peripheral nerves carry nerve components from several spinal segments (or roots) to muscles and skin areas. Therefore, damage to a peripheral nerve may result in a wide ranging effects on more than one dermatomal area or myotomes. This may affect large areas of skin and several muscles.

Question 11

What sensation modalities can be tested?

Answer 11

Light touch, localization of touch, two point tactile discrimination, pain, pressure, temperature, vibration, sterognosis, passive joint movement, and postural sensibility.

Question 12

What upper limb region does dermatomal segment C4 consist of?

Answer 12

Shoulder

Question 13

What upper limb region does dermatomal segment C5 consist of?

Answer 13

Lateral side of arm

Question 14

What upper limb region does dermatomal segment C6 consist of?

Answer 14

Lateral side of forearm and thumb

Question 15

What upper limb region does dermatomal segment C7 consist of?

Answer 15

Middle and ring finger

Question 16

What upper limb region does dermatomal segment C8 consist of?

Answer 16

Medial side of hand, forearm and little finger

Question 17

What upper limb region does dermatomal segment T1 consist of?

Answer 17

Medial side of forearm and arm.

Question 18

What upper limb region does dermatomal segment T2 consist of?

Answer 18

Axilla

Question 19

What dermatomal segments does musculocutaneous nerve innervate?

Answer 19

C5, C6 & C7

Question 20

What dermatomal segments does median nerve innervate?

Answer 20

C6, C7, C8 and T1

Question 21

What dermatomal segments does radial nerve innervate?

Answer 21

C5 to T1

Question 22

What dermatomal segments does ulnar nerve innervate?

Answer 22

C7, C8, T1

Question 23

How can a upper limb mononeuropathy come about?

Answer 23

Can result from damage to a single peripheral nerve distal to the brachial plexus

Question 24

What can a upper limb mononeuropathy result in?

Answer 24

Such an injury can lead to signs of deformity, weakness and sensory loss that are characteristic to the function of the particular nerve. The location where the lesion/injury has occurred along the course of the nerve can also be determined by the testing of the nerve.

Question 25

What is the most prevalent cause of mononeuropathies?

Answer 25

Mechanical injury (resulting from compression or trauma) is the most prevalent cause of the mononeuropathies; the median nerve at the wrist (carpal tunnel syndrome), ulnar nerve at the elbow or radial nerve compression at the spiral groove. Less common but important causes such as malignancy and inflammation should also be considered.

Question 26

What could a mono-neuritis multiplex suggest?

Answer 26

When multiple peripheral nerves are involved and these do not relate to compression sites; a vasculitis or an antibody-mediated response against the peripheral nerves should be suspected.

Question 27

What is the common mode and location of injury for musculocutaneous nerve?

Answer 27

Stab wound to upper arm

Question 28

What would the clinical findings be if musculocutaenous nerve is damaged?

Answer 28

Sensory loss in lateral forearm. Motor deficit characterised by weak elbow flexion, weak wrist supination and absent bicep reflex. Deformity resulting from wasting of biceps.

Question 29

What is the common mode and location of injury for axillary nerve?

Answer 29

Fracture of surgical head of humerus or compression injury from shoulder dislocation or crutches in armpit

Question 30

What would the clinical findings be if axillary nerve is damaged?

Answer 30

Sensory loss in Sergeant’s patch, Markedly weak shoulder abduction (15-90 degrees) and weak shoulder flexion, extension and external rotation and wasting of deltoid.

Question 31

What is the common mode and location of injury for radial nerve?

Answer 31

Fracture of proximal/shaft humerus or proximal radius. Compression from crutches on armpit sleeping on arm or armpit on chair (Saturday night palsy)

Question 32

What would the clinical findings be if radial nerve is damaged?

Answer 32

Sensory loss in posterior arm and forearm plus radial area of hand. Weak elbow extension, Absent triceps reflex, Weak wrist extension, Weak finger MCP joint extension. Wasting of triceps and posterior compartment of forearm and wrist drop (on attempted wrist extension).

Question 33

What is the common mode and location of injury for median nerve?

Answer 33

Supra condylar fracture of humerus.

Compression in carpal tunnel in wrist.

Question 34

What would the clinical findings be if median nerve is damaged?

Answer 34

Sensory loss in median distribution of hand and thenar eminence. Weak forearm pronation, Weak wrist flexion, Weak wrist abduction, Weak finger flexion (DIP joint of ring and littler finger preserved), Weak thumb abduction and opposition. Wasting of anterior forearm, Wasting of thenar eminence, Hand of Benediction (on attempted finger flexion).

Question 35

What is the common mode and location of injury for ulnar nerve?

Answer 35

Medial epicondylar fracture, Compression at Guyons tunnel in wrist.

Question 36

What would the clinical findings be if ulnar nerve is damaged?

Answer 36

Sensory loss in ulnar distribution of hand and hypothenar eminence. Weak wrist flexion, Weak wrist adduction, Weak finger flexion of ring and little finger at the MCP and DIP joints, Weak extension at the IP joints in ring and little finger, Weak finger abduction, adduction and opposition. Wasting of hypothenar eminence and intrinsic muscles of hand Claw Hand (on attempted finger flexion).