Lecture 7+8 - SQ

Question 1

1. Where in the arm is the radial nerve at most risk of injury?

Answer 1

1. The radial nerve is at risk of a crushing injury where it lies next to bone in the spiral groove at
   the back of the humeral shaft.

Question 2

2. How does the motor nerve supply to the primary pronators and supinators of the forearm
   differ?

Answer 2

2. The primary supinator, the supinator muscle, is innervated as an extensor via the radial nerve.
   The primary pronators, the pronator quadratus and pronator teres, are innervated as flexors
   via the median nerve

Question 3

3. What are the palpable bony landmarks of the distal radius and ulna?

Answer 3

3. For the ulna, one can palpate most of the posterior surface of its shaft, head, and styloid
   process. For the radius, one can palpate much of the posterior surface at its distal end, plus
   its dorsal tubercle (Lister’s tubercle) and styloid process

Question 4

4. What is the origin and distribution of the cutaneous nerves of the forearm?

Answer 4

4. The medial cutaneous nerve of the forearm comes from the medial cord and innervates the
   skin on the ulnar side of the forearm. The lateral cutaneous nerve of the forearm is the
   terminal branch of musculocutaneous nerve (off of the lateral cord) and innervates the skin
   on the radial side of the forearm. Lastly the posterior cutaneous nerve to the posterior surface
   of the forearm comes from the radial nerve.

Question 5

5. Describe how the radial, ulnar, and median nerves enter the forearm.

Answer 5

5. The ulnar nerve descends toward the elbow medial to the medial head of the triceps. It then
   runs posterior to the medial epicondyle of the humerus (“the funny bone”) and enters the
   forearm between the flexor carpi ulnaris and the flexor digitorum profundus.
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   The median nerve approaches the elbow immediately medial to the brachial artery. In the
   cubital fossa it dives below the pronator teres to innervate it and other flexors on the radial
   side of the forearm (except for brachioradialis). The radial nerve enters the elbow region
   from the posterior surface but moves forward just lateral to the brachialis and deep to the
   biceps tendon. In the cubital fossa it sends a deep branch to the supinator and its superficial
   branch continues down the forearm ultimately to the dorsum of the hand.

Question 6

6. Where in the forearm and wrist are the ulnar and median nerves most at risk of entrapment?

Answer 6

6. The ulnar nerve is at greatest risk of compression injury where it runs posterior to the elbow
   and medial to the olecranon process. The ulnar nerve can also be compressed where it enters
   the hand between the hook of the hamate and the pisiform bone. The median nerve can be
   entrapped in several places, most commonly the carpal tunnel, but also at the superior edge
   of the interosseous membrane, deep to the pronator teres.

Question 7

7. If the musculocutaneous nerve is severed, is elbow flexion still possible?

Answer 7

7. Yes, weak elbow flexion is still possible. The muscle primarily responsible for this action is
   the brachioradialis, since the biceps and the brachialis would be paralyzed.

Question 8

8. If the radius is broken proximal to the insertion of the pronator teres management of the
   injury is more complex than if the break occurs distal to the insertion—why is this so?

Answer 8

8. If the radius is broken proximal to the insertion of pronator teres on the radius the elbow end
   of the radius can be twisted into the supine position by spastic contraction of the supinators
   unopposed by the pronators. The distal end of the radius conversely can be twisted into the
   prone position by the unopposed pronators. Together this can lead to serious misalignment of
   the radius at the break site. This uncoupling of pronators from supinators doesn’t take place,
   if the break is distal to the pronator teres’ insertion.

Question 9

9. What is the function of the palmaris longus?

Answer 9

9. The palmaris longus is a weak flexor of the wrist. By inserting on the palmar aponeurosis, it
   also helps to curl the palm.

Question 10

10. What would be the motor deficit if the median nerve were cut at the elbow?

Answer 10

10. There would be loss of pronation, weakness in wrist flexion, weakness in radial deviation of
    the hand, loss of thumb mobility, and loss of digital mobility. Complete or partial loss of
    muscle innervation will create imbalances with muscles that have not been affected.

Question 11

11. What is “students’ elbow”?

Answer 11

Student’s elbow is a friction bursitis involving the superficial olecranon bursa.

Question 12

12. What structure protects the brachial artery during venipuncture of the median cubital vein?

Answer 12

12. The bicipital aponeurosis

Question 13

13. Where is the best place to take a pulse for the brachial artery?

Answer 13

13. A good place to get a pulse for the brachial artery is about mid shaft on the humerus, where
    the artery lies in the groove between the biceps and the triceps. The artery has to be
    compressed laterally against the humerus in order to take the pulse here.

Question 14

14. What motions of the elbow would be hindered if the ulnar nerve were severed in the arm?

Answer 14

14. None. The ulnar nerve does not innervate any prime movers of the elbow.