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
What is the function of the flexor retinaculum?
prevents bowstringing of the long flexor tendons to increase effectiveness by preventing slack forming in the muscles
attaches carpal bones on radial aspect to carpal bones on ulnar aspect, stabilising carpal bones to maintain shape of carpal tunnel
Which tendons pass through the carpal tunnel?
flexor digitorum superficialis (4 tendons)
flexor digitorum profundus (4 tendons)
flexor pollicis longus (1 tendon)
What is compressed in carpal tunnel syndrome?
median nerve
What causes the median nerve to become compressed in carpal tunnel syndrome?
inflammation + swelling of synovial sheaths covering long flexor tendons
Which muscles does the median nerve supply in the forearm?
all muscles except flexor carpi ulnaris + ulnar half of flexor digitorum profundus
Why are the muscles in the forearm that are innervated by the median nerve unaffected in carpal tunnel syndrome?
damage to the nerve is distal to the point at which the muscles are innervated
Which muscles does the median nerve supply in the hand?
LOAF
radial 2 lumbricals, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis (thenar muscles)
Why is loss of sensation of the palm spared in carpal tunnel syndrome?
palmar branch arises proximally and passes over carpal tunnel
(loss of sensation on palm = problem further up arm = test extrinsic muscles)
Why is there no pain/tingling proximal to the wrist joint in carpal tunnel syndrome?
innervation to the wrist joint is proximal to the site of damage of the nerve
What is trigger finger?
nodule in palm of hand that moves when extending and flexing index finger
What is the structure of the flexor sheath of the tendons of the digits of the hand?
tough fibrous structure with retinaculum type pulleys providing a tunnel for tendons of flexor digitorum superficialis + profundus to pass through
originates at proximal aspect of metacarpals and terminates at distal aspect of distal phalanges
What is the extent of the flexor sheath?
metacarpophalangeal joint to distal plalanx and to periosteum of bones either side of digit
What is the function of the flexor sheath?
holds tendons against bones and joints, improving function and effectiveness of muscles
What causes the nodule in trigger finger?
inflammation + swelling of synovial sheath passing beneath pulleys caused sheath to become bunched up and develop into a nodule
Which part of the flexor sheath is commonly involved in causing the nodule to become trapped in trigger finger?
A1 pulley
Explain why the finger gets stuck in flexion rather than extension in trigger finger
flexion is a more powerful action than extension
during flexion, strong flexors pull nodule under pulley
weaker extensors are not powerful enough to pull nodule back through pulley in extension with ease
nodule gets stuck distal to pulley and finger stuck in flexion until additional force applied to pull nodule through the pulley
Treating trigger finger (after an unsuccessful steroid injection) involves dividing the A1 pulley. What would happen if the A2 pulley was also accidentally divided?
tendons would be at increased risk of bowstringing and muscle function would be affected
(bowstringing = tendon coming away from finger)
What is the midprone position?
between pronation and supination (eg holding a mug)
Why do we not use pronators and supinators to achieve the midprone position?
these muscles can work together to bring the forearm into a midprone position however they would struggle to keep the forearm steady and it would vacillate between supination and pronation
What muscle is used to put the forearm in the midprone position?
brachioradialis
What muscles are used to extend the wrist?
extensor carpi radialis longus + brevis
extensor carpi ulnaris
What muscles are used to adduct the wrist?
extensor carpi ulnaris
flexor carpi ulnaris
What muscles are used to abduct the wrist?
flexor carpi radialis
extensor carpi radialis longus + brevis
What muscle is used to extend the digits?
extensor digitorum longus
What muscle is used to extend the thumb?
extensor pollicis longus
What tendon brings about extension of the distal interphalangeal joint?
extensor digitorum (distal attachment = distal phalanx + middle phalanx)
What is a mallet finger deformity and what causes it?
flexed distal interphalangeal joint
can be caused by avulsion fracture of dorsal surface of distal phalanx
attachment of extensor tendon has come away, so there is unopposed flexion of the DIP
What further deformity could occur after a mallet finger if the finger is not splinted in extension and allowed to heal?
swan neck deformity
tendon can shorten backwards
tendon pulls on middle phalanx causing hyperextension of proximal interphalangeal joint
Why did extensor digitorum used to be called extensor digitorum communis, and what is the function of the extra feature?
interconnecting slips between tendons
ensures all tendons work together resulting in a more powerful extension of the digits but limiting independent extension of individual fingers
(index + little fingers have individual extensor muscles to circumvent this problem)
What is PAD and DAB?
palmar interosseous muscles adduct the fingers
dorsal interosseous muscles abduct the fingers
When gripping an object, we first extend our wrist. How do the extensors increase the power in grip?
extension of wrist stretches long flexor tendons, allowing them to work more effectively/generate more power
Why do we have a dedicated muscle to allow us to hold our arm in the midprone position?
brachioradialis allows us to hold this position steadily
Which intrinsic muscles are used to hold a key in a pinch grip?
flexor pollicis longus
1st dorsal interosseous
Which intrinsic muscles are used to grip and manipulate a pencil?
thenar eminence muscles
1st lumbrical
Which muscles are used in the power grip?
flexor digitorum superficialis/profundus
lumbricals
Lack of sensation in the radial 3.5 digits and flexion of digits 4 and 5 towards the palm suggests injury to which nerve?
median nerve
Which muscles does the median nerve supply in the forearm?
all in anterior forearm except flexor carpi ulnaris + medial half of flexor digitorum profundus
Which muscles does the median nerve supply in the hand?
LOAF lateral 2 lumbricals opponens pollicis brevis abductor pollicis brevis flexor pollicis brevis
Which LOAF muscles are usually used to make a fist?
long flexors of anterior forearm (flexor digitorum superficialis + profundus)
Why can the 4th + 5th digits still flex towards the palm in median nerve injury?
medial portion of flexor digitorum profundus is innervated by ulnar nerve and therefore still able to function
Which nerve is compressed in cubital tunnel syndrome?
ulnar nerve
What does tapping an injured nerve cause?
tingling/painful sensation (Tinel’s sign)
Which muscles does the ulnar nerve innervate in the forearm?
flexor carpi ulnaris
medial half of flexor digitorum profundus
With an ulnar nerve injury at the elbow, what will happen when the patient attempts flexion of the wrist?
wrist will deviate laterally (only flexor carpi radialis still functioning)
With an ulnar nerve injury at the elbow, what will happen when the patient attempts extension of the wrist?
normal
no posterior forearm muscles affected
Which muscles does the ulnar nerve innervate in the hand?
all intrinsic muscles apart from LOAF muscles
Why does damage to the ulnar nerve result in clawing of digits 4 and 5?
lumbricals to these digits lost nerve supply resulting in clawing of digits
Which muscles will lose their innervation if the ulnar nerve is damaged at the level of the wrist?
only intrinsic muscles of the hand
What is the ulnar paradox?
more severe ulnar claw when damage is closer to hand (less muscles affected)
clawing occurs when lumbricals are damaged leading to imbalance of flexion/extension within affected digits
if ulnar nerve is damaged at elbow, one of flexors (flexor digitorum profundus) also stops working and therefore there is less severe clawing
damage at wrist = both digital flexors still working = increased clawing
What is Dupuytren’s contracture?
ring and little fingers curled into palm with tight bands and nodules in the skin and fascia holding them tight
muscle power + sensation = normal
Why is supination more powerful when the elbow is flexed?
biceps brachii can also be used as a supinator when the elbow is flexed
What type of joint is the humeroulnar joint?
hinge
How many articulations are there within the elbow joint capsule?
3 (humeroradial, humeroulnar and proximal radioulnar)
What type of joint is the humeroradial joint?
pivot
What type of joint is the proximal radioulnar joint?
plane
What bony features give stability to the elbow joints?
deep articulation between trochlea of humerus and trochlea notch of ulna
What ligamentous structures give stability to the elbow joints?
collateral + annular ligaments
Which joint is most likely to be dislocated if a patient presents with pain at the lateral aspect of the elbow?
humeroradial joint
Why is humeroradial joint dislocation more common in children?
radial head smaller in children meaning it can be more easily pulled through the annular ligament
Why can quickly grabbing a child’s arm result in a dislocation, but swinging by their arms does not?
when a child is expecting their arm to be pulled they can brace their muscles to support the joints of the elbow
Why do the carpal bones primarily articulate with the radius?
during pronation/supination, the ulna stays static with the radius rotating around it
the carpal bones articulate with the radius so that movements of the bone allow the hand to move with it
When falling on an outstretched hand, which forearm bone transmits the force from the hand and why?
radius
forms majot articulation between forearm and wrist
Which carpal bones are more at risk of injury when falling on an outstretched hand?
scaphoid
lunate
What are the boundaries of the anatomical snuffbox and how can you locate it?
tendons of extensor pollicis longus (medially)
tendons of extensor pollicis brevis + abductor pollicis longus (laterally)
ask patient to extend and abduct thumb will make tendons more prominent so you can locate the depression of the anatomical snuffbox
Why is the scaphoid bone more prone to fracture?
has narrowing/neck which is weaker than the surrounding bone
What is the clinical significance of a scaphoid fracture?
fractures of scaphoid interrupt blood supply
if fracture goes undiagnosed + untreated the patient may suffer avascular necrosis of bone
