Muscles: Upper Limb

Question 1

What four muscles make up the rotator cuff and where so they originate/attach?

Answer 1

These guys are the ones that help stabilize the humeral head into the glenohumeral joint while the shoulder moves. Subscapularis inserts on the lesser tuberosity, the rest (supra, infra, teres minor) insert on the greater tuberosity.

Question 2

Innervation and Function of the rotator cuff muscles

Answer 2

Suprascapular nerve:
- Supraspinatus - Assists deltoid with first 15 degrees of abduction
- Infraspinatus - Externally rotates the arm
Axillary Nerve
- Teres minor - Externally rotates the arm
Subscapular Nerves
- Subscapularis - Internally rotates the arm

Question 3

What muscles, nerves, and functions do we find in the anterior compartment of the arm?

Answer 3

The anterior compartment is fed by the musculocutaneous nerve andontains three flexors:

• Biceps Brachii -Flexes and supinates forearm
• Brachialis - Flexes the forearm
• Coracobrachialis - Flexes and adducts the arm

Question 4

What muscles, nerves, and functions do we find in the posterior compartment of the arm?

Answer 4

Radial nerve feeds this guy, and only one muscle, the triceps brachii, which extends the arm.

Question 5

What muscles, nerves, and functions do we find in the anterior compartment of the forearm?

Answer 5

Pronators and flexors are in this compartment, and all except the flexor carpi ulnaris and the medial part of the flexor digitorum profundus (fed by the ulnar nerve) are fed by the median nerve.

Question 6

What muscles, nerves, and functions do we find in the posterior compartment of the forearm?

Answer 6

Extensors and supinators (except brachioradialis, which flexes the forearm). All are fed by the radial nerve.

Question 7

What are the thenar muscles and what innervates them?

Answer 7

There are four thenar muscles:

Recurrent Branch of the Median nerve
 - Abductor Pollicis Brevis - Abduction
 - Opponens Policis - Opposition
 - Flexor Pollicis Brevis - Flexion
Ulnar nerve
 - Adductor policis - Adduction

Question 8

What are the hypothenar muscles and what innervates them?

Answer 8

All innervated by the ulnar nerve. These guys move the pinky.

• Opponens digiti minimi - Opposition
• Flexor digiti minimi - Flexion
• Abductor digiti minimi - Abduction

Question 9

Fracture of the surgical neck of the humerus secondary to trauma leads to what clinical findings and why?

Answer 9

The nerve affected, due to its close proximity, is the axillary nerve. This leads to impaired shoulder abduction due to the deltoid and lateral rotation due to the teres minor.

Question 10

Shoulder dislocations, often due to outstretched arm injuries in sports, cause what clinical findings and why? What else causes symptoms like this?

Answer 10

Also the axillary nerve. This leads to impaired shoulder abduction due to the deltoid and lateral rotation due to the teres minor.

We see this in electrocution as well

Question 11

A fracture of the mid humerus has what classic clinical features, and why?

Answer 11

The radial nerve runs right along this part.

Thus, we see a wrist drop (note, the triceps is not affected because it gets its branch of the radial nerve much higher).

Question 12

What else causes a wrist drop besides a midhumeral fracture?

Answer 12

Radial dislocation, as with nurse-maid’s or falling on outstretched arm

Question 13

If I shot someone in the anterior biceps, what would happen?

Answer 13

You’d hit their musculocutaneous nerve, causing impairment of elbow flexion and forearm supination

Question 14

Supracondylar fracture of the elbow leads to what clinical findings and why?

Answer 14

Median nerve runs right by here, so we see “the hand of benediction.”

• Impaired wrist flexion, flexion of digits 1-3, and pronation of the forearm.

With this particular fracture, we also see brachial artery interruption and eventual Volkmann ischemic contracture of the forearm/arm

Question 15

What else causes the hand of benediction, but it not linked to any arterial issues?

Answer 15

Fracture of the lateral epicondyle of the humerus.

Question 16

Explain carpal tunnel and what is affected.

Answer 16

Carpal tunnel is what happens when you get fat or old or have volume issues…or are fat.

Your median branch is the one that gets compressed in there the most, leading to sensory/muscular deficits in digits 1-3, impaired thenar muscles BUT palm sensation is intact

Question 17

Fracture of the medial epicondyle of the humerus leads to what

Answer 17

Ulnar nerve damage, so we get:

• impaired interossei muscles
• impaired digit 4-5 flexors and lumbricals
• impaired hypothenars
• impaired wrist flexion on ulnar side

“Claw hand deformity”

Question 18

What happens if we fracture the hook of the hamate?

Answer 18

Like fracturing the medial epicondyle of the humerus, we get ulnar nerve damage, but it happens so distally, the wrist is not affected, so we do not get the impaired wrist flexion.

• impaired interossei muscles
• impaired digit 4-5 flexors and lumbricals
• impaired hypothenars

Question 19

What originates/attaches to the coracoid process of the scapula?

Answer 19

Origin - Coracobrachialis and biceps brachii

insertion - Pec Minor

Question 20

What transverses the scapular notch?

Answer 20

Suprascapular nerve

Question 21

Pec Major vs. Pec Minor innervation and action

Answer 21

Both of them innervated by the medial and lateral pectoral nerves.

Pec Major flexes, adducts, and medially rotates the arm

Minor Depresses the scapula and elevates the ribs.

Question 22

Discuss injury to the posterior cord

Answer 22

This is caused by the pressure of the crosspiece of a crutch, resulting in paralysis of the arm called crutch palsy, which results in loss of function of the extensors of the arm, forearm, and hand, and produces a wrist drop

Question 23

Discuss Erb-Duchenne Paralysis

Answer 23

This is caused by a birth injury or a violent throw from a horse or motorcycle that injures the upper trunk. It results in loss of abduction, flexion, and lateral rotation of the arm, producing a waiter’s tip hand, where the arm tends to lie in medial rotation resulting from paralysis of lateral rotator cuff muscles.

Question 24

Besides Erb’s Palsy, what else can a difficult delivery cause?

Answer 24

Lower trunk injury or Klumpke paralysis. It causes a claw hand.

Question 25

Discuss the extensor compartments of the hand

Answer 25

As the extensor tendons cross the wrist joint, they are arranged into compartments by the extensor retinaculum.

The first dorsal compartment encloses the abductor pollicis longus and the extensor pollicis brevis, the second the extensor carpi radialis brevis and longus, the third the extensor pollicis longus, the fourth the extensor digitorum comminus and the extensor indicis, the fifth the extensor digiti minimi and the sixth the extensor carpi ulnaris.