True/False for Axilla and Brachial Plexus

Brachial Plexus and Axillla True False

• explanations come from a mix of Hollinghead, Chung, wikipedia, Duke’s orthopedic encyclopdedia (online), and Moore
• Aqua Italics---False
• Yellow Bole---True
• Red---notes from after comparing to message board

1. The dorsal scapular nerve arises from the posterior cord of the brachial plexus (no, the thoracodorsal nerve arises from the posterior cord while the dorsal scapular arises from the lateral)
2. A lesion of the upper root of the brachial plexus would weaken protraction of the scapula (well, protraction of the scapula is caused by pectoralis major and minor (medial and lateral pectoral nerves from medial and lateral cords), levator scapulae (dorsal scapular from C5 root), and serratus anterior (intercostals nerves and long thoracic). So, a lesion in the upper root (C5) would affect levator scapulae and the pectorals.
3. The long thoracic nerve is derived from the lower 3 roots of the brachial plexus (no, it’s derived from the upper three roots)
4. A lesion of the long thoracic nerve would severely weaken protraction of the scapula (yes, the long thoracic nerve, also called the “external respiratory nerve” innervates the serratus anterior which helps in depression of the scapula.
5. A lesion of the long thoracic nerve would affect complete abduction of the arm (true because the long thoracic innervates the serratus anterior which assists in abduction of the arm by rotating the scapula upward)
   • Dr. Evey has promised to be less ambigious on the exam as this question has two answer depending on your interpretation.See Message Board.
6. A lesion of the middle subscapular would weaken lateral rotation of the arm ( False. The middle subscapular nerve is an alternate name for the thoraco dorsal nerve coming off of the posterior cord and going to innervate the latissimus dorsi. So, a lesion of this nerve would affect medial rotation because the latissus dorsi wraps around to insert on the anterior portion of the humerus, making it a medial rotator)
7. A lesion of the lower subscapular nerve would weaken medial rotation (The lower subscapular nerve from the anterior cord innervates the subscapularis and the teres major muscle. The teres major muscle causes medial rotation (along with adduction) and the subscapularis muscles also causes medial rotation and adduction.
8. A complete lesion of the posterior cord and its branches would cause uncompensated loss of medial rotation. Muscles that cause medial rotation are: subscapularis (lower subscapular), teres major (lower subscapular), lattisumus dorsi (thoracodorsal), deltoid (axillary), and pectoralis major (lateral and medial pectorals). All of these nerves come from the posterior cord EXCEPT the lateral/medial pectoral. So, only the pectoralis major would still be working to cause medial rotation.
9. A complete loss of the posterior cord and its branches would cause uncompensated loss of arm abduction from approximately 15 - 90 degrees. The first 15 degrees of rotation is caused by the supraspinatus muscles, innervated by the supraspinal nerve from the lateral cord. From 15 to 90 degrees, rotation is caused by the deltoid, which is innervated by the axillary nerve from the posterior cord. From 90 to 120, abduction is caused by the ?????
10. Entrapment of the suprascapular nerve at the superior transverse scapular notch could cause uncompensated loss of arm abduction from 0 - 15 degrees and compensated loss of medial rotation of the arm. The suprascapular nerve comes from the lateral cord and cross through the superior scapular notch deep to the superior transverse scapular ligament to innervate the supra spinatus and infraspinatus muscle. So, entrapmen of this nerve would cause loss of abduction from 1 to 15 since that is caused by the supraspinatus. As for medial rotation, the supraspinal nerve only innervates the infra- and supraspinatus muscles, and neither of them act in medial rotation. The supraspinatus abducts and the infraspinatus laterally rotates. So, this statement is not true.
11. A lesion of the lower subscapular nerve would cause weakened (compensated) arm adduction. The lower subscapular nerve innervates the subscapularis (medial rotation and adduction) and the teres major (medial rotation and adduction).
12. A lesion of the axillary nerve would weaken every possible movement at the glenohumeral joint with the exception of abduction from 0 - 15 degrees. Well, the axillary nerve innervates deltoid and teres minor. 0-15 would not be affected b/c that is caused by the supraspinatus innervated by the suprascapular nerve, so that part of the statement is true. However, with deltoid and teres minor, that affects (deltoid) abduct, adduct, flex, extend, rotate arm medially and laterally) and (teres minor)adduct and rotate medially. So the deltoid takes part in everything the shoulder does except the beginning of abduction. This statement is true afterall. *interesting debate going on about this…waiting for response. Pretty sure it’s true
13. A total lesion of the median nerve would cause ape hand. Ape hand is a deformity cause by the extension of the thumb in the same plane as the fingers / flattened thenar eminence. It is related to lesion of the medial nerve at the elbos or wrist.
14. A total lesion of the ulnar nerve would cause claw hand. Claw hand is an atrophy of the interosseous muscles of the hand with hyperextentsion of the MP joint and flexion of the interphalangeal joint. It results from lesion of the ulnar nerve below the wrist and/or lesion of ulnar and median nerves.
15. A total lesion of the radial nerve would cause wrist drop. Wrist drop is when the hand hangs limply and one is unable to extend the wrist to move it. Also called radial nerve palsy. Results from lesion of radial nerve.
16. A lesion of the radial nerve at the spiral groove would cause loss of extension at the elbow. Although the radial nerve does innervate the triceps brachii which is responsible for extension, the course is important. It leaves the brachial plexus and goes through anterior compartment of the arm, the courses posteriolaterally to the posterior compartment with the profunda brachii just below the lower border of teres major. It enteres the posterior compartment between the the long and lateral heads of the tricep. It lies on the fibers of the hmedial head which arise from the medial groove. So, if you get a lesions at the spiral groove, the triceps should still function.
    • Our classmates pegged this as true, but when you look at the branching patterns it should be false. A grad student, “Danger” posted a correction that agrees with me.
17. A lesion of the radial nerve at the spiral groove would the wrist to be flexed and adducted. The radial nerve innervates the extensors, so a lesion would mean no extensors to counterbalance the flexors so you’re always flexed (like wrist drop). As for adduction, I don’t think a lesion of the radial nerve would lead to constant adduction because adduction is caused by flexor carpi ulnaris (ulnar) and extensor carpi ulnaris (ulnar), so adduction would definitely be possible. But, abduction is caused by flexor carpi radialis (median), extensor Capri radilias longus (radial), extensor carpi radialis brevis (radial), abductor pollicus longus (radial), extensor pollicus longus and brevis (radial). So normally adduction is caused by two muscles w/ ulnar innervation and counterbalanced by 1 muscle of median innervation and five muscles of radial innervation. So yeah, w/o the ulnar nerve you’d probably get more adduction than abduction.
    • it all depends on the counterbalancing…Dr. Evey said to scrath this question.
18. A lesion of the ulnar nerve at the ulnar groove would cause the wrist to be extended (no) and abducted (yes). All the sources talking about ulnar nerve mention loss of the ability to adduct, but not loss of the ability to flex. You’d still have flexor carpi radialis to flex (but it’d go lateral) and sometimes palmaris lonus. So, you’ wouldn’t be extended. As for being abducted, a lesion at the ulnar groove would lead to abduction b/c you’d lose the ability to adduct with the flexor carpi ulnaris.
19. A lesion of the ulnar nerve within the anterior compartment of the arm would cause the wrist to be extended (no) and abducted (yes). False…see above. This lesions is event higher, so same thing applies. If the lesion were at the wrist, you wouldn’t see a loss of abduction
20. The ulnar nerve enters the anterior arm by passing through the heads of origin of the flexor carpi ulnaris.
    • 18 and 19: weird questions, but Dr. Evey’s general comment is to assume that a health wrist needs all muscles to function and a lesion prevents that, so think about the consequences. So apparently these should be true?

Ulnar Nerve Injuries:  Injury to the ulnar nerve in the distal part of the forearm can have motor/sensory loss to hand  Denervates most of the intrinsic hand muscles  Loss of adduction  When you try to flex, you get abduction  Leads to clawhand---patient can’t make a fist b/ceaus of paralysis of intrinsic hand muscles  Try to fist, get…hyperextended metacarpophalangeal joints

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Comments and Suggestions

• In response to question 18, can someone speak to the the constant muscle tone that exists in a properly innervated muscle? If this tone is strong enough, in a rested position, the wrist would be extended and abducted. -- RayBradford - 03 Oct 2006 - 21:23

• As a note to #12: The pectoral major muscle is innervated by the medial and lateral pectoral nerves which come from the medial and lateral cords, which are not affected by a lesion of the axillary nerve. The abduction added by the deltoid would be minimal when compared with the the pectoralis major. -- RayBradford - 03 Oct 2006 - 21:18

• The dorsal scapular nerve does not arise from the lateral cord. It arises from the root/trunk of C5. -- RayBradford - 03 Oct 2006 - 21:06

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