Chapter 35 - Nerve Compression Syndromes Flashcards
what physiologic factors affect nerve conduction velocity?
myelin thickness, internodal distance, age, temperature
intrinsic risk factors for compression neuropathies
female, pregnancy, rheumatoid, diabetes, hypothyroid
what finding on NCV studies is UNAFFECTED in a pre-ganglionic injury?
SNAPs - sensory nerve action potentials
Normal even is the patient is clinically absent sensation
Key diagnostic feature for pre-ganglionic injury
what findings on emg are associated with denervation?
fibrillations AND positive sharp waves
what part of the brachial plexus does the median nerve come from
it is the terminal branch of the medial and lateral cord
what nerve roots make up the median nerve?
C5-T1
what are anomalous connections between the median and ulnar nerves in the proximal forearm?
martin-gruber connections - these people get abnormal exam findings
what are anomalous connections between the median and ulnar nerves in the distal forearm?
ricke-cannieu connections
define the carpal tunnel
hook of the hamate medially, transverse carpal ligament superficially, carpal bones deep, and scaphoid tubercle/trapezium radially
contents of the carpal tunnel?
4 tendons of the fds
4 tendons of the fdp
FPL
median nerve
palmar cutaneous nerve - where does it branch?
5 cm proximal to wrist crease, radiopalmar part of median nerve
describe the common branch patterns of the recurrent motor branch of the median nerve?
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%
diagnosis of CTS (AAOS guidelines)
- numbness/paresthesias in wrist, palmar aspects of the: thumb, index and radial half of long finger
- clumsiness, weakness, night pain
- atrophy if longstanding
- positive tinels, phalens, Durkans most sensitive and specific
- sensation along the radial aspect of the palm should be normal (palmar cutaneous nerve branches 5cm proximal to wrist)
NCV/EMG findings in CTS
Distal sensory latency >3.5ms
distal motor latency >4ms
end stage - fibrillations and sharp waves (denervation)
benefit of endoscopic CTR over open?
decreased post op pillar pain and earlier return to work
pronator syndrome
mixed motor and sensory
causes of compression - ligament of struthers (between supracondylar ridge of humerus and median epicondyle), anconeus epitroclearis, bicepital aponeurosis, pronator teres
median nerve anatomy at the antebrachial fossa
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
median nerve anatomy in the forearm
radial nerve and AIN supply pronator teres, FCR, PL, FDS, radial half of FDP, FPL, and PQ
AIN innervates
FDP to IF, LF, PQ, FPL
median nerve proper innervates
pronator teres, FCR, PL
Ulnar nerve anatomy
terminal branch of the medial cord of the brachial plexus
C7-T1 contributions
what mm does the ulnar nerve innervate?
FCU, FDP to RF and SF, two ulnar lumbricals, interossei (all), adductor pollicis, deep head of fpb, hypothenar mm
six sites of cubital tunnel compression
- arcade of struthers (fascial band formed by medial intermuscular seuptum
- anconeus epitrochlearis
- medial epicondyle
- osborne’s fascia (proximal band between two heads of fcu)
- arcuate ligament - roof of carpal tunnel
- proximal arch of fdp
EMG findings in cubital tunnel syndrome
denervation (fibrillations and sharp waves) in first dorsal interosseous, abductor digiti minimi, and fdp (FCU may or may not be involved)
what differentiates guyon’s canal syndrome from cubital tunnel syndrome?
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)
zones of guyon’s canal
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
most common cause of guyon’s compression
space occupying lesion - ganglion cyst
also think of hook of hamate fracture, ulnar artery pseudoaneurysm in athletes
radial nerve anatomy
posterior cord of the brachial plexus
c5-c8 +/- T1 nerve roots
what is the radial arm relationship to the deltoid tuberosity?
radial nerve lies directly posterior to the humerus at the level of the deltoid tuberosity
radial nerve is at risk what distance from the acromion?
10cm
radial nerve is at risk what distance from the lateral epicondyle?
10 cm proximal - where it pierces the lateral intermuscular septum (14cm from joint line)
PIN syndrome features
motor loss without any sensory changes
wrist extension is intact bc ercl innervated by radial nerve proper
what fracture pattern(s) is PIN syndrome common in>
Monteggia fracture dislocations and radial head fracture dislocations
radial tunnel syndrome
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
radial sensory nerve compression (cheiralgia paresthetica aka wartenberg syndrome)
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)
what muscle(s) does compression of the nerve at the suprascapular notch affect and what nerve?
suprascapular nerve (c5/6), supraspinatus AND infraspinatus
what muscle(s) does compression of the nerve at the spinoglenoid notch affect and what nerve?
suprascapular nerve (c5/6), infraspinatus ONLY
what does weakness of the infraspinatus cause functionally?
weakness in external rotation
where does the musculocutaneous nerve arise off the brachial plexus?
lateral cord
c5-7
innervates the coracobrachialis, the brachialis, and the biceps then becomes LABCN
where does the axillary nerve come off the brachial plexus?
posterior cord
innervates teres minor and deltoid
what runs with the axillary nerve in the quadrangular space?
posterior humeral circumflex a
how to differentiate PIN v Radial tunnel syndromes
PIN motor deficits only
Radial tunnel - pain only
EMG helps with PIN, does not help with radial tunnel
