Chapter 35 - Nerve Compression Syndromes

Question 1

what physiologic factors affect nerve conduction velocity?

Answer 1

myelin thickness, internodal distance, age, temperature

Question 2

intrinsic risk factors for compression neuropathies

Answer 2

female, pregnancy, rheumatoid, diabetes, hypothyroid

Question 3

what finding on NCV studies is UNAFFECTED in a pre-ganglionic injury?

Answer 3

SNAPs - sensory nerve action potentials

Normal even is the patient is clinically absent sensation

Key diagnostic feature for pre-ganglionic injury

Question 4

what findings on emg are associated with denervation?

Answer 4

fibrillations AND positive sharp waves

Question 5

what part of the brachial plexus does the median nerve come from

Answer 5

it is the terminal branch of the medial and lateral cord

Question 6

what nerve roots make up the median nerve?

Answer 6

C5-T1

Question 7

what are anomalous connections between the median and ulnar nerves in the proximal forearm?

Answer 7

martin-gruber connections - these people get abnormal exam findings

Question 8

what are anomalous connections between the median and ulnar nerves in the distal forearm?

Answer 8

ricke-cannieu connections

Question 9

define the carpal tunnel

Answer 9

hook of the hamate medially, transverse carpal ligament superficially, carpal bones deep, and scaphoid tubercle/trapezium radially

Question 10

contents of the carpal tunnel?

Answer 10

4 tendons of the fds
4 tendons of the fdp
FPL
median nerve

Question 11

palmar cutaneous nerve - where does it branch?

Answer 11

5 cm proximal to wrist crease, radiopalmar part of median nerve

Question 12

describe the common branch patterns of the recurrent motor branch of the median nerve?

Answer 12

extraligamentous (distal to the TCL) - 50%
subligamentous (proximal to the TCL but stays in CT until it exits distally) - 30%
transligamentous (pierces the ligament) - 20%

Question 13

diagnosis of CTS (AAOS guidelines)

Answer 13

1. numbness/paresthesias in wrist, palmar aspects of the: thumb, index and radial half of long finger
2. clumsiness, weakness, night pain
3. atrophy if longstanding
4. positive tinels, phalens, Durkans most sensitive and specific
5. sensation along the radial aspect of the palm should be normal (palmar cutaneous nerve branches 5cm proximal to wrist)

Question 14

NCV/EMG findings in CTS

Answer 14

Distal sensory latency >3.5ms
distal motor latency >4ms
end stage - fibrillations and sharp waves (denervation)

Question 15

benefit of endoscopic CTR over open?

Answer 15

decreased post op pillar pain and earlier return to work

Question 16

pronator syndrome

Answer 16

mixed motor and sensory
causes of compression - ligament of struthers (between supracondylar ridge of humerus and median epicondyle), anconeus epitroclearis, bicepital aponeurosis, pronator teres

Question 17

median nerve anatomy at the antebrachial fossa

Answer 17

median nerve passes between deep (ulnar) and sueprficial (humeral) heads of the pronator teres, passes deep to fibrous arch of FDS, emerges beneath radial aspect of FDS belly to long finger

Question 18

median nerve anatomy in the forearm

Answer 18

radial nerve and AIN supply pronator teres, FCR, PL, FDS, radial half of FDP, FPL, and PQ

Question 19

AIN innervates

Answer 19

FDP to IF, LF, PQ, FPL

Question 20

median nerve proper innervates

Answer 20

pronator teres, FCR, PL

Question 21

Ulnar nerve anatomy

Answer 21

terminal branch of the medial cord of the brachial plexus

C7-T1 contributions

Question 22

what mm does the ulnar nerve innervate?

Answer 22

FCU, FDP to RF and SF, two ulnar lumbricals, interossei (all), adductor pollicis, deep head of fpb, hypothenar mm

Question 23

six sites of cubital tunnel compression

Answer 23

1. arcade of struthers (fascial band formed by medial intermuscular seuptum
2. anconeus epitrochlearis
3. medial epicondyle
4. osborne’s fascia (proximal band between two heads of fcu)
5. arcuate ligament - roof of carpal tunnel
6. proximal arch of fdp

Question 24

EMG findings in cubital tunnel syndrome

Answer 24

denervation (fibrillations and sharp waves) in first dorsal interosseous, abductor digiti minimi, and fdp (FCU may or may not be involved)

Question 25

what differentiates guyon’s canal syndrome from cubital tunnel syndrome?

Answer 25

guyon’s canal syndrome does. NOT have sensation changes over the. ulnar dorsal border of the hand (dorsalulnar sensory nerve branches BEFORE guyon’s canal)

Question 26

zones of guyon’s canal

Answer 26

1: prior to the bifurcation of the branches: produces mixed motor and sensory changes
2: just after bifurcation while the deep motor brance is coursing ulnar toward the hamate - pure motor sx (fpb, all the intrinsics except the ulnar two lumbricals)
3. only the superficial branch - sensory only

Question 27

most common cause of guyon’s compression

Answer 27

space occupying lesion - ganglion cyst

also think of hook of hamate fracture, ulnar artery pseudoaneurysm in athletes

Question 28

radial nerve anatomy

Answer 28

posterior cord of the brachial plexus

c5-c8 +/- T1 nerve roots

Question 29

what is the radial arm relationship to the deltoid tuberosity?

Answer 29

radial nerve lies directly posterior to the humerus at the level of the deltoid tuberosity

Question 30

radial nerve is at risk what distance from the acromion?

Answer 30

10cm

Question 31

radial nerve is at risk what distance from the lateral epicondyle?

Answer 31

10 cm proximal - where it pierces the lateral intermuscular septum (14cm from joint line)

Question 32

PIN syndrome features

Answer 32

motor loss without any sensory changes

wrist extension is intact bc ercl innervated by radial nerve proper

Question 33

what fracture pattern(s) is PIN syndrome common in>

Answer 33

Monteggia fracture dislocations and radial head fracture dislocations

Question 34

radial tunnel syndrome

Answer 34

pure pain syndrome - no weakness

pain with resisted supination with arm and wrist in extension, pain with passive pronation with wrist flexion

often condused with lateral epicondylitis

Question 35

radial sensory nerve compression (cheiralgia paresthetica aka wartenberg syndrome)

Answer 35

SBRN compression 2/2 watch, handcuffs, cast

if idiopathic it is likely compression between the BR and ECRL tendons

9 cm proximal to radial styloid (remember intersection syndrome is 5cm proximal to listers)

Question 36

what muscle(s) does compression of the nerve at the suprascapular notch affect and what nerve?

Answer 36

suprascapular nerve (c5/6), supraspinatus AND infraspinatus

Question 37

what muscle(s) does compression of the nerve at the spinoglenoid notch affect and what nerve?

Answer 37

suprascapular nerve (c5/6), infraspinatus ONLY

Question 38

what does weakness of the infraspinatus cause functionally?

Answer 38

weakness in external rotation

Question 39

where does the musculocutaneous nerve arise off the brachial plexus?

Answer 39

lateral cord

c5-7

innervates the coracobrachialis, the brachialis, and the biceps then becomes LABCN

Question 40

where does the axillary nerve come off the brachial plexus?

Answer 40

posterior cord

innervates teres minor and deltoid

Question 41

what runs with the axillary nerve in the quadrangular space?

Answer 41

posterior humeral circumflex a

Question 42

how to differentiate PIN v Radial tunnel syndromes

Answer 42

PIN motor deficits only
Radial tunnel - pain only

EMG helps with PIN, does not help with radial tunnel