Anatomy clinical scenarios (upper limb) Flashcards
If there is an issue with one dermatome, where is the problem?
spinal nerve root problem
If there is an issue with multiple dermatomes, where is the problem?
peripheral nerve problem (multiple spinal nerve roots are in a peripheral nerve)
What is a dermatome?
area of skin innervated by a single spinal nerve root
What is a myotome?
group of muscles, or parts thereof, that are innervated by a single spinal nerve root
What is a somite?
paired segmental blocks of mesodermal origin structures occurring dorsally alongside the neural tube
Shoulder abduction primary nerve root
C5
Elbow flexion primary nerve root
C5/6
Elbow extension primary nerve root
C7
Wrist flexion primary nerve root
C7
Wrist extension primary nerve root
C6
Finger flexion primary nerve root
C8
Finger extension primary nerve root
C7
Thumb opposition primary nerve root
C8/T1
Finger abduction primary nerve root
T1
A patient has diminished sensation over the top of her shoulder and lateral arm, which nerve roots are likely to have been affected and why?
C5
nerves that supply skin over shoulder carry fibres from C5 nerve root
C5 nerve root injury, what movements of the upper limb are most likely to be affected?
initiation of shoulder abduction and external rotation absent
nerves that innervate muscles for these actions only carry C5 nerve root
shoulder flexion weakened - nerves that innervate shoulders carry C5 nerve root but this is not the main nerve root used for this action
shoulder abduction + scapula protraction weakened for same reason
C5 nerve root injury (lack of sensation over top of shoulder)
How could the doctor use their knowledge of dermatomes and myotomes to confirm this is a nerve root injury, rather than a peripheral nerve injury?
damage to axillary nerve could also result in absence of shoulder abduction, however, axillary nerve damage would only leave regimental badge area with reduced sensation not whole C5 dermatome
could also ask patient to rotate shoulder joint if they are able to as these movements are brought about by subscapular nerves carrying C5 nerve root so would not be affected if the axillary nerve is damaged
Pectoralis major is a flexor of the shoulder joint, what is the difference in action between the clavicular and sternal heads?
clavicular head = flex shoulder joint from anatomical position
sternal head = flex shoulder joint from extended position
What 2 actions of the shoulder (other than flexion) does pectoralis major contribute to?
adduction
medial rotation
Which muscle is predominantly responsible for holding the medial border of the scapula against the chest wall, preventing winging of the scapula?
serratus anterior
Other than preventing winging, what other action does serratus anterior have on the scapula?
helps to protract scapula
What muscle helps serratus anterior to protract scapula and prevent winging of the scapula?
pectoralis minor
What action tests the deltoid muscle?
shoulder abduction
What action tests the muscles in the anterior compartment in the arm?
elbow flexion
A patient can flex their shoulder and there is no winging of the scapula. But, they experience pain on abduction of the arm, particularly beyond 90 degrees and on resisted elbow flexion. Which muscle is likely to have been affected?
long head of biceps brachii
biceps brachii = primarily flexor of elbow joint (hence pain on resisted flexion, however long head also passes over top of shoulder joint
abduction of shoulder reduces space above the joint, and in this case, compresses the injured long head of biceps, causing pain
What muscle weakness can cause one-sided shoulder weakness - looking dropped on one side?
trapezius
What surgery can cause weakness in the trapezius muscle?
during a lumpectomy, nerve that innervates trapezius (spinal accessory nerve) can be damaged
What examination findings would suggest a weakened trapezius?
weakened shoulder elevation on affected side
unable to abduct affected shoulder beyond 90 degrees
Why does someone with a weakened trapezius struggle to reach higher cupboards in their kitchen?
at 90 degrees of abduction. glenohumeral joint is unable to abduct any further
further abduction requires the trapezius muscle to laterally rotate the scapula
What is the only muscle that moves the upper limb that is not innervated by a branch of the brachial plexus and what is its alternative innervation?
trapezius
spinal accessory nerve (one of cranial nerves that originate directly from the brain)
How does a dislocated shoulder look?
straight down from tip of acromion
shoulder drops straight down
How do you test nerve function of the axillary nerve?
test for sensation over deltoid/regimental badge area
don’t test deltoid function = painful
What nerve is most likely to be affected by shoulder dislocation?
axillary nerve
passes inferior to shoulder joint
Which direction does the humerus move initially during a subluxation or dislocation of the glenohumeral joint?
inferiorly
no muscles under joint
(rotator cuff muscles = anterior, posterior + superior)
How does the shoulder joint capsule contribute to subluxations/dislocations of the glenohumeral joint?
capsule = lax inferiorly
lax for mobility
capsule loose + relatively weak, particularly at inferior aspect
What is the functional reason for a loose shoulder joint?
lax for mobility of shoulder joint
allow greater range of movement during abduction of shoulder
Why should a patient have physiotherapy after a shoulder dislocation?
strengthen rotator cuff muscles
(help hold shoulder in socket)
muscles stronger = joint held more securely
What movements against resistance would help strenghten the rotator cuff muscles?
subscapularis = medial/internal rotation
supraspinatus = abduction
infraspinatus + teres minor = lateral/external rotation
Why may the clavicle be at risk when falling on the upper limb?
clavicle provides only bony attachment of upper limb to trunk
when falling, forces can be transmitted through upper limb + into clavicle, potentially breaking it
Which rotator cuff muscle passes through the sub-acromial space?
supraspinatus
What happens to the sub-acromial space during abduction to 90 degrees and what effect does this have on the rotator cuff muscle passing through?
becomes smaller
can compress the muscle
What anatomical feature is present beneath the acromion to reduce the effect of wear and tear on the rotator cuff tendon?
subacromial bursa
How does the mechanism of the subacromial bursa work?
bursa formed by 2 membranes with small amount of synovial fluid between them (one membrane in contact with underside of acromion, other sits over tendon of supraspinatus)
during movements of shoulder, membranes can glide past each other
reduced friction between supraspinatus + acromion
What happens to the subcromial bursa when the area becomes inflamed?
inflamed (bursitis) = increased synovial fluid produced to try and compensate for increased friction within bursa
as this continues, bursa becomes fluid-filled sac that fills subacromial space and limits shoulder movement