Small Group Session I

(answers are shown in red)

Lesions of the Brachial Plexus

Case 1
Your patient is recovering from radiation treatment for her breast cancer. She seems to be
doing fine but you notice she does have some difficulty moving her right arm. She has
difficulty raising her right arm laterally to the side of her head. When you ask her to push
hard against the wall, a protrusion occurs on the right side of her upper back.

1. What nerve do you think was damaged as a result of her radiation treatment?

The long thoracic nerve can be compromised as a result of radiation treatment for
breast cancer.

2. What muscle(s) were damaged as a result of the nerve damage? Was the muscle
paralyzed or just weakened?

The long thoracic nerve innervates the serratus anterior muscle which becomes
paralyzed.

3. Analyze the mechanism involved in full abduction of the arm to the side of the head.
What muscles are responsible for each component of full abduction? Why was your
patient not able to fully perform this task?

Complete abduction of the glenohumeral (shoulder) joint occurs in 3 phases:

• Start or initiation of abduction.
  
• Abduction of the humerus to the horizontal (level with the shoulder).
  
• Terminal phase or moving the humerus to the side of the head.
  

The first phase involves action of the supraspinatus muscle, which is responsible for
starting abduction. The second phase primarily involves the deltoid muscle. This
muscle acts to raise the humerus to approximately shoulder level. The final phase
involves rotation of the scapula concomitant with humeral abduction. In order for the
humerus to be able to move up to the head, the greater tubercle must be able to clear
the acromion. This involves external rotation by the posterior deltoid and teres
minor muscles. In addition, the scapula has to be upwardly rotated. Upward rotation
of the scapula involves simultaneous actions of the trapezius and serratus anterior
muscles.

In complete abduction of the should joint, humerus and scapula move in synchronous
rhythm called the scapulohumeral rhythm. Every 2-3 degrees of humeral abduction is
accompanied by a 1-2 degrees of upward rotation of the scapula.

4. Demonstrate how you would assess scapular movements.

Movement	Assess	Prime Movers
Elevation	Raise the scapula in an upward direction by shrugging the shoulders	Levator scapula Upper Trapezius Rhomboids
Depression	Lower scapula then forcibly depress by reaching towards the floor	Pectoralis major Pectoralis minor Lat. dorsi
Protraction	Moving the scapula away from the midline. Hunch shoulders forward	Pectoralis minor Serratus anterior
Retraction	Bringing the scapulae towards the vertebral column	Trapezius Rhomboids
Upward Rotation	Moving the inferior angle of the scapula laterally while rotating the glenoid cavity upwards	Serratus anterior Upper Trapezius
Downward Rotation	Moving the inferior angle of the scapula medially while rotating the glenoid cavity downwards	Lat. Dorsi Pectoralis Minor Rhomboids

Case 2
You are examining a patient who fell off a ladder while painting his house, injuring his right
shoulder. The patient complains of pain in the area of the shoulder and he has difficulty
moving his arm. You notice that his acromion is visible and that most of his arm
movements are weak. You test for sensation and find a small area of loss just below the
point of the right shoulder. Movements of the scapula and elbow were normal and you
could detect no additional sensory loss.

1. Would you expect to see any bone fractures on an X- Ray of the shoulder area? If you
do, where would you expect to find the fracture?

Yes, in the area of the surgical neck of the humerus.

2. Do you suspect that nerve damage has occurred? If so, what nerve(s) were injured?

The location of the fracture and the symptoms presented by this patient suggests that
there was damage to the axillary nerve.

3. What muscle(s) would be affected?

The axillary nerve innervates the deltoid and teres minor muscles.

4. Describe the movement of the shoulder that would be affected and would the movement
be lost or weak?

The most noticeable effect would be on shoulder abduction. The patient could begin
abduction using the supraspinatus muscle. However, without the deltoid, the arm could
not be raised to the level of the shoulder. Flexion and extension of the shoulder would
be greatly weakened because of the loss of the deltoid muscle. Outward rotation would
be much weaker because of the loss of the deltoid and teres minor. Inward rotation would
be somewhat weakened because of the loss of the anterior deltoid. However, the sub-
scapularis acts as a strong inward rotator.

Case 3
Your teen-age son comes home from his first date with his high school's prom queen. He
looks nervous and he is rubbing his forearm. You ask him what is wrong and he tells you
they went to a movie. When they came out, his hand was "tingling" and he could not lift
his wrist. You ask him if he had his arm around his date and he replies, somewhat
ashamed, the he did have his arm around herfor most of the movie. You examine him
and find the parasthesia ("tingling" is most noticeable along the radial side of the dorsum
of his wrist. He also has difficulty extending his wrist, especially when his forearm is in
the prone position, and can not make a tight fist. You laugh and tell him he has a classic
case of "Saturday Night Palsy", not to worry and he will be better in the morning.

1. What was the cause of his symptoms?

The likely cause of the symptoms was having his date's shoulder compress the radial
nerve within his axilla resulting in a temporary loss of radial nerve function. This is
similar to having ones "legs fall asleep" after sitting in a certain position. The inability
to extend the wrist is called drop wrist.

2. Was there nerve involvement and, if so, what nerve(s).

The radial nerve is the only nerve affected based upon the young man's symptoms.

3. What muscles were affected? Were they paralyzed or weakened?

The radial nerve is the "great extensor nerve" because it supplies the prime extensors
of the elbow, wrist and metacarpophalangeal joints. In this case it appears the
extensor carpi radialis longus & brevis and the extensor carpi ulnaris were
affected. The muscles were temporarily paralyzed but function will return as soon as
the nerve recovers from compression.

4. Could the son extend his wrist and make a tight fist if his forearm was in the supine
position? Explain your answer.

Yes, with the forearm in the supine position, gravity will force the wrist into extension.
This is an exapmle of a passive movement. That is, movement resulting from some-
thing other than muscle contraction.

5. Based upon the site of the injury, what other movements of the upper limb would be
affected? __________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________

Case 4
You are called to examine a psychiatric patient who has been hospitalized for 6 months
suffering from depression. You are called to consult because this individual has difficulty
doing routine tasks with his hands. He has difficulty grasping objects between his thumb
and forefinger. He also has difficulty holding his cigarette between his 1st. and 2nd.
fingers. Your examination finds he has reduced sensation along the medial side of his
palm and the 4th. finger. He has weakened wrist flexion, his 3rd. and 4th. fingers are
"clawed" and there is evidence of muscle wasting on the muscle mass on the dorsal side
of his hand between the thumb and first finger.

1. You suspect the symptoms are a result of nerve damage. What nerve would you expect
is involved and where is the most likely site for it to have be damaged?

The symptoms indicate a problem with the intrinsic muscles of the hand. The nerve
involved is the ulnar nerve. The most likely site of the lesion is in the proximal forearm.
Depressed patients often sit with their elbows on a table and their head supported by their
fingers for long periods of time. Such a position often leads to ulnar nerve damage as the
nerve crosses posterior to the medial epicondyle of the humerus ("funny bone").

2. Explain the sensory and motor symptoms by discussing those muscles that are affected.
Why were the 3rd. and 4th. fingers "clawed" and why could he not hold his cigarette?

The ulnar nerve is sensory to the medial (ulnar) portion of the palm and dorsum of the
hand and to the 4th and ulnar portion of the 3rd fingers. The clawing of the 3rd and 4th
fingers result from weakness to the 3rd and 4th lumbrical muscles and all of the
interossei muscles supplied by the ulnar nerve. The above muscles have many actions,
but both the interossei and lumbricals can flex the metacarpophalangeal joints (MP)
and extend the interphalangeal joints (IP). The latter action is exerted via the insertion
of these muscles on the dorsal digital (extensor) expansion. The lumbrical muscles are
better extensors of the IP joints while the interossei are better flexors of the MP joints.
Damage to these muscles reduces their ability to act. Therefore, the MP joints, lacking a
strong flexor, are pulled into a hyperextend position by the action of the extensor
digitorum. The IP joints, lacking a strong extensor, are pulled in a flexed position,
especially the proximal IP joint by the action of the flexor digitorum superficialis. The
ability to hold objects between adjacent fingers is dependennt upon the action of the
interossei muscles acting to abduct and adduct the MP joints. With ulnar nerve
damage, these muscles are unable to function properly and abduction and adduction of
the MP joints is impossible. Thus, he was not able to hold his cigarette between his
fingers.

3. Why is the wasting of the muscle mass on the dorsum of his hand a clue to the nerve
involved?

The fleshy prominence on the dorsum of the hand between the 1st and 2nd fingers is
made by the 2 heads of the 1st dorsal interosseous muscle. This muscle, as all dorsal
interossei, acts to flex and adduct the MP joint. This muscle is usually larger than the
other dorsal interossei because of the frequent participation of this muscle, along with
the thumb, in grasping and holding objects. This muscle is frequently used when one
performs a precision grip. The ulnar nerve supplies this muscle and, when this nerve is
lesioned, the the muscle will exhibit flaccid paralysis and wasting.

4. Are any of the muscles acting on the thumb affected? If so, what movement(s) of the
thumb would be involved?

The adductor pollicis is the most important muscle acting on the thumb that is
supplied by the ulnar nerve. The deep head of the flexor pollicis brevis, when present,
is also supplied by the ulnar nerve. Because adductor pollicis is damaged as a result
of an ulnar nerve lesion, the thumb is usually hyperabducted and extended (hitch
hiker's position).

Case 5
You have put on a lot of weight and decide to join a gym and to work out on a regular basis.
Your routine includes weight training, stationary bicycle and using the stair master start.
Visions of a svelte you result in your becoming very enthusiastic about your work out
routines. After about 3 months, you go to you doctor because you notice a tingling
sensation along the palmar surface of your thumb and first 2 fingers. This tingling has
gotten a lot worse in the past few weeks. You also notice your grip is weakening , you
have difficulty flexing your wrist using weights you were used to using, and you have
difficulty performing a percussion grip for any length of time (writing with a pencil). You
have no difficulty supinating your forearm, extending your wrist or flexing the distal phalanx
of your thumb.

1. What does your physician think is the cause of your symptoms?

The tingling (parathesia) along the palmer side of the thumb and first 2 fingers suggests
median nerve involvement. The motor symptoms also suggest median nerve damage
because they suggest weakened wrist flexion, finger flexion and, possible, the use of the
thenar muscles.

2. Do you think an X-Ray or MRI would reveal anything significant?

An x-ray will probably not be helpful since there is no incident of bone damage or trauma.
An MRI would be more useful because it is much more sensitive to demonstrating soft
tissue involvement. But, this is very expensive and may not show much in this instance.
A good physical exam should confirm your suspeicions that the median nerve is involved.
A good physical examination can also help localize the site of the lesion.

3. What muscles are involved and how does their involvement explain you symptoms?

The sensory symptoms indicative of a median nerve lesion but are not helpful in localizing
the site of the lesion. The weakening of the grip can indicate problems with the flexor
digitorum superficialis and flexor digitorum profundus. Weakened wrist flexion also
also indicates problems with the wrist flexors, primarily the flexor carpi radialis. That
these muscles are weak tells you that the median nerve is involved but that the problem
(lesion) did not cause total interruption of nerve function. These symptoms also indicate
the lesion is within the proximal forearm and not more distally because the median nerve
innervates the finger flexors and srist flexors high up in the forearm. Lack of involvement
of these muscles would indicate the lesion occurred after these muscles were innervated.
One would expect that weakened wrist and finger flexion would also weaken elbow flexion
(lifting heavy weights) because these muscles act as synergists in elbow flexion. Difficutly
performing the precision grip indicates weakness of the thenar muscles. The primary
muscle involved in this particular movement is the opponens pollicis. The muscle
responsible for flexing the distal phalanx of the thumb is the flexor pollicis longus. This
muscle is innervated by the deep (anterior interosseous) branch of the median nerve. This
branch is usually as soon as the nerve enters the forearm. It is obvious that this branch
has been spared in this case.

4. What can you do to help improve the situation?

The most likely case is the median nerve is damaged within the proximal portion of the
forearm. The most likely cause for this is entrapment of the median nerve between the
2 heads of origin of the pronator teres muscle. The reason for this is likely related to
increased exercise using your forearm muscles improperly. Rest, proper instruction on
the use of the exercise machines and physical therapy should help.

Case 6
You notice your young child's left upper limb is not developing normally so you take her to
her doctor. You explain that your child's birth was not an easy one and forceps were used
in her delivery. Otherwise, things have been unremarkable. Your child has a fair amount of
manual dexterity and can easily grasp objects with her fingers. However, her shoulder and
arm do not seem to work properly. Examination reveals the following: Atrophy of shoulder
and arm musculature, inability to abduct the shoulder, and loss of sensation along the
posterior lateral surface of the arm. The forearm is in a prone position, the arm adducted
and the elbow is in a partially flexed position. The doctor explains that your daughter has
Erb's palsy, possibly resulting from the delivery at birth. Use your knowledge of the
anatomy of the upper limb and your Segmental Innervation Chart to answer the following:

1. Explain the anatomy of Erb's palsy including the branches of the brachial plexus that are
involved.

Erb's palsy occurs when the C5 and C6 roots of the brachial plexus are damaged causing
them to be avulsed from their connections to the spinal cord. All muscles supplied by
these nerve roots will become paralyzed, flaccid and atrophy. Those muscles innervated
by either or both of these roots as well as axons derived from other roots will become
weakened. Examining the Segmental Innervation chart indicates the following nerves
contain axons only from C5,6: dorsal scapular nerve, suprascapular nerve, axillary nerve,
upper and lower subscapular nerves. In addition, the branches of the musculocutaneous
nerve supplying the biceps and brachialis muscles and the branch of the radial nerve
supplying the brachioradialis muscle are also involved.

2. Indicate those muscles that would be affected by this condition. For each muscle
affected, give the function(s) of that muscle and state whether the muscle is weak or
paralyzed.

Examining the Segmental Innervation Chart shows that the following muscles are inner-
vated by branches of the brachial plexus containing axons derived from only C5 and C6:
deltoid, supra and infraspinatus, subscapularis, teres minor, rhomboids, biceps,
brachialis and brachioradialis. These muscles will be paralyzed. Muscles containing
axons from either C5 or C6 and from other roots of the brachial plexus will be weakened.
These include: serratus anterior, extensor carpi radialis longus and brevis, pectoralis
major (sternal head) and latissimus dorsi.

3. What movements of the shoulder and elbow joint would the patient be able to perform?

A patient suffering from Erb's palsy loses most movements of the shoulder girdle and
elbow. Adduction and extension of the shoulder is possible because the latissimus
dorsi and sternal head of the pectoralis major can function.

4. How are movements of the scapula affected?

Elevation of the scapula (levator scapula) and retraction of the scapula (trapezius) are
possible because these muscles are not innervated by the brachial plexus. Protraction
of the scapula is weak but is possible. The scapula will be slightly upwardly rotated
because of the action of the trapezius and, to a lesser extent, the serratus anterior.

5. Would you expect this individual to be prone to shoulder dislocations? Explain your
answer.

Movements should be performed with the shoulder supported by the examiner because
patients with C5,6 palsy are prone to shoulder dislocations.