Peripheral Nerves Flashcards
Radial nerve origins
C5-8
Pass through upper, middle and lower trunks then posterior cord of brachial plexus
Radial nerve anatomy in upper arm
As it winds around the humerus or proximal to this it innervates the tricpes.
After course in spiral groove it supplies brachioradialis and ECRL and brevis.
Bifurcates into a superifical (sensory) and deep (motor) branches
Muscles supplied by proximal branches of radial nerve
Triceps
Brachioradiailis
ECRL
ECRB
Superficial branch of radial nerve
In forearm, passes distally into the hand where it supplies skin of the radial aspect of the dorsum of the hand and dorsum of first four fingers.
Deep branch of radial nerve
Passes deep through the fibrous arch of supinator (arch of Froshe) to enter the posterior compartment of forearm
Continuous in this compartment as the purely motor posterior interosseous branch
Innervates
Supinator
Extensor digitorum
Extensor digit mini
ECU
Abductor pollicis longus
Extensor pollicis longus
Extensor pollicis brevis
Extensor indicies
Forearm muscles dupplied by posterior interosseous nerve
Supinator
Extensor digitorum
Extensor digiti minimi
ECU
Abductor pollicis longus
Extensor pollicis longus
Extensor pollicis brevis
Extensor indicis
Supinator function
Forearm supinator
Test with resisted supination
Extensor digitorum
Extensor of 2nd to 5th metacraophalangeal joints
Extensor digiti minimi function
Extensor if fifth MCP
ECU function
Ulnar extenor of the wrist
APL function
Abductor of carpometacarpal joint of thumb
EPL function
Extension of thumb interphalangeal joint
EPB function
Extensor of the MCPJ of thumb
Extensor indicies function
Extensor of index finger
Saturday night palsy
AKA radial nerve palsy
Classically associated with a drunkard who falls asleep with arm hyper abducted across a park bench
Site of compression is in the region of the spiral groove
Why is the triceps preserved in radial nerve palsy (Saturday night palsy)
Because branches of the tricpes originate proximal to spiral groove
Wrist drop
Inability to extend fingers at MCPJ
Supinator weakness
Triceps spared
Absent sensation first dorsal interosseuous
Radial nerve palsy
Compression in the spira groove of humerus/humeral fracture
Why is weakness of supination only partial in Radial nerve palsy
Because it may be accomplished with either biceps or supinator
Posterior interosseous nerve syndrome
Most common syndrome caused by compression at the arcade of Frohse (fibrous arch at the origin of supinator) which may pathologically constrict nerve
Inability to extend fingers at MCPJ, absence of wrist drop and normal sensation
Supintaor spared as branches are given off proximal to PIN entering the arcade of Frohse
Why is wrist drop absent in PIN palsy
The ECR is presreved
The ECU is innervated by PIN so there may be radial deviation of the hand on extension
Why is there no senosry deficit in PIN syndrome
It is purely motor
Inability to extend fingers at MCPJ
No wrist drop but radial deviation on extension of wrist
Presrved sensation
Preserved supinator and triceps
Posterior interosseus nerve syndrome
Arcade of Frohse associated with PIN syndrome/supinator syndrome
Roots of median nerve
C6 to T1
Pasing through upper middle and lower trunks and the lateral and medial cords of the brachial plexus
Median nerve branches proximal to the elbow
None
Median nerve at elbow
Muscles supplied
Pronator teres
Flexor carpi radialis
Palmaris longue
FDS
Prontaor teres function
Forearm pronator
FCR function
Radial wrist flexor
PL
Wrist flexor
FDS
Flexor at the IPJ for 2nd-5th fingers
Contents of the cubital fossa
Really Need Beer To Be At My Nicest
L->M
Radial nerve
Biceps tendon
Brachial artery
Median nerve
Under what is the median nerve found at the elbow?
Behind the biccipital aponeurous (lacertus fibrosus)
How does the median nerve enter the forearm
Between the two heads of pronator teres
Where is the AIN given off?
As it the median nerve passes deep to pronator teres
Anterior interosseous nerve function
Purely motor
Supplies FPL, Pronator quadratus, FDP 1 and 2
FPL function
Flexion of thumb at interphalangeal joint, key function for grip
Pronator quadratus
Pronation of forearm
Function of FDP
Flexion of DIP in 2-4th fingers
Median nerve in the hand
Passes deep to the flexor retinaculum to innervate the LOAF muscle
Lumbricals
Opponens pollicis
Abductor pollicis brevis
Palmar digital nerves-> palmar aspect of thumb, second, third and half of fourth fingers. Raedial aspect of the palm and dorsl aspect of the distal middle phalanges of the sconed, third and half of fourth fingers
Palmar cutaneous bracnh given off proximal to the carpal tunnel and supplies the median eminence and proximal palm on radial aspect of hand
Three major median nerve entrapment syndromes
Pronator teres syndrome
AIN syndrome
CTS
Pronator teres syndrome
Results from entrapment of the median nerve as it passes between the two heads of the pronator teres and under the fibrous arch of the FDS
Compression may be caused by thickened lacertus fibrosus, hypertrophied pronator teres, tight fibrous band of the FDS
Pain in forearm with weakness in hand grip and numbness and tingling in the index finger and thumb.
Similar symptoms to CTS with hand assuming a “benedicton” attitude in severe cases. Nocturnal exacerbation is absent normally
Weakness is variable but often there is no measurable weakness in median nerve innervated muscles
How to differentiate between Hand of Benediction and Ulnar Claw
Ulnar claw usually seen at rest whereas in Hand of Benediction there is weakness on active flexion in the radial three digirs
Pain in forearm
Weakness in hand attitdue
Numbness in median nerve distribution without nocturnal exacerbation
?Pronator teres syndrome
DDx
Ulnar claw or Hand of Benediction
AIN snyfrome
Most commonly due to a constricting band causing entrapment neuropathy near the origin of the nerve
FDP and FPL weakness
Abnormal pinch attitude of the hand
Weakness in pronator quadratus is usually clinically insignificant due to more powerful pronator teres.
No sensory deficit
Abnormal pinch attitude
Extension of hyperextension of the terminal phalanges of the thumb and index finger when the thumb and index finger are opposed
Abnormal pinch attitude of the hand due to weakness in FDP and FPL
Normal sensation
AIN syndrome
CTS
Caused by compression of the median nerve as it passes through the carpal tunnel
Pain anad paraesthesia in wrist and hand awakening patient from sleep
Sensory loss in te ditsirubiton of the palmar digital branches Isensory loss easiest to discern along vola tips of index and middle fingers)
Pain may also involve forearm, elbow or shoulder- classically this pain may radiate from distal to proximal and may be associated with shaking the hand to alleviate pain in contrast to cervical radiculopathy in which movement exacerbates pain.
Motor symptoms are usually late- LOAF muscles affected- weakness in abduciton, opposition and flexion of thumb.
Phalen’s positive
Function of lumbricals
Flex fingers at the MCPJ
Function of opponens pollicis
Opposition refers to the rather complex movement of the thumb which is a combination of flexion, adduction and medial rotation at the first carpometacarpal joint
Function of Abductor pollicis brevis
Abduction of thumb at MCPJ
Phalen’s test
Forcibly dosriflexing affected hand for 60 seconds
Positive test will reproduce symptoms
What is the most reliable assessment of thenar muscle function?
Abductor pollicis brevis
Nocturnal pain and paraesthesia in median distirubtion
Weakness and atrophy in LOAF muscless
Sensory loss
Carpal tunnel syndrome
Contents of carpal tunnel
9 tendons, 1 nerve
4 tendons of the FDS superifically
Median nerve
1 tendon of FPL
4 tendons of FDP
Roots of the ulnar nerve
C7/8/T1
Medial cord of the brachial plexus
Branches of ulnar nerve in arm
None
Ulnar nerve branches at the elbow
Ulnar nerve enters a groove between the medial humeral epicondyle and olecranon process
Groove covered by an aponeurosis formng an osseofibrous canal (cubital tunnel)
Two motor branches- FCU and FDP to fourth and fifth fingers
Boundaries of the cubital tunnel
Roof: Cubital tunnel retinaculum (band of Osbourne)
Laterally: Olecranon
Medially: Medial epicondyle
Floor: elbow joint capsule, posterior band of medial collateral ligament of elbow joint
Ulnar nerve in forearm
Passes between two heads of FCU to take place superifical to FDP
Two sensory branches- palmar cutaneous branch-> skin over hypothenar eminence
Dorsal cutaneous bramnch-> dorsal ulnar aspect of the hand and dorsal aspect of the fifth finger and half of fourth finger
Sensory branches of ulnar nereve in forearm
Palmar cutaneous branch
Dorsal cutaneous branch
Superficial sensory branch is given off as the ulnar nerve enters Guyon’s canal at the wrist
How does the ulnar nerve enter the hand?
Through Guyon’s canal
Borders of Guyon’s canal
Floor- transverse carpal ligament, hypothenar msucles
Roof- Volar carpal ligament
Ulnar border- Pisiform and pisohamate ligament, abductor minimimuscle belly
Radial border- Hook of hamate
Branches of the ulnar nerve in hand
Superficial sensory branch given off proximally in the canal- supplies the distal part of theulnar aspect of th eplam and the palmar aspect of the fifth and half of the fourth finger
Contineus as deep motor branch supplying:
Abductor digiti minimi
Opponens digiti minimi
Flexor digiti minimi
Lumbricals 3 and 4
Interosseous muscles
Addcutor pollicis
Flexor pollicic brevis
Action of abductor digiti minimi
Abducts and flexes 5th finger
Action of opponens digiti minimi
Opposition of the little finger with the tip of the thumb
Deepends hollow of the palm
Action of the flexor digiti minimi
Flexes little finger
Lumbricals action
Flex MCPJ and extend interphalangeals
Interosseous muscle actions function
PAD- palmar adduct
DAB- dorsal abduct
Action of adductor pollicis
Adducts CMCJ of the thumb
Flexor pollicis brevis function
Flexes thumb at MCPJ
Two major syndromes assocaited with ulnar nerve
Cubital tunnel syndrome
Guyon’s canal syndrome
What is a key differentiator between Cubital tunnel and Guyon’s canal syndrome
Dorsal cutaneous nerve which is spared in Guyon’s canal but affected in cubital tunnel
Cardinal features of cubital tunnel syndrome
Numbness and tingling of the ulnar aspect of hand
Weakness variously described as imapirment of hand grip, clumsiness or difficulty buttoning shirt
Atrophy in hypothenar eminence and first interosseous space.
Sensory loss most easily observed in the distal two phalnges of the little finger
Claw hand deformity
Froment’s sign
Claw hand
Results from simultaenous hypextension at the MCPJ and flexion at IPJ
Hyperextension at the MCPJ is due to wekness of rthe lumbricals with unopposed action of the extensor digotorum
Flexion at the IPJ is due to passive tethering pull of the flexor digitorum which occurs when the MCPJ are in extension
Froment’s sign
Due to weakness in adductor pollicis
On grasping a piece of paper between thumb and index finger and pulling
Positive when the patient attempts to compensate for lack of thumb adduction with extension of the PIPJ and felxion of the distal phalangex
Why are the FCU and FDP often spared in cubital tunnel syndrome?
Because they are situated deeply within the nerve and may be spared the more suprifically localted fibres which are compressed first
Differneces between cubital tunnel and CTS
Cubital tunnel less frequently associated with pain with weakness and atrophy early rather than late
Hypothenar wasting
Paraesthesia on medial border of hand
Weakness and clumsiness in hand
Atrophy of the dorsal interossei and hypothenar eminence
Claw hand
Froment’s sign
?Cubital tunnel syndrome
Classification of Guyon’s canal syndrome
Three types based on the site of the compression
Zone 1 to 3 based on site of compression
Guyon’s Canal Syndrome Zone 1
Mixed motor and sensory symptoms
Proximal to bifurcation of the nerve
Common causes of compression: Ganglia and hook of hamate fractures
Guyon’s Canal Syndrome
Zone 2
Surrounds deep motor branch
Predominantly motor symptoms
Common causes include ganglia and hok of hamate fractures
Guyons Canal Syndrome
Zone 3
Surrounds superifical sensory branch
Senosry symptoms only
Common caauses include ulnar artery thrombosis or aneursym
Loss of abductir digiti minimi, abductor pollicis, FDM, dorsal. interossei
Froment’s sign and claw hand
Loss of palmar sensation but not dorsal
Zone 1
Guyon’s canal syndrome
Sensory pattern is due to superifical sensory branch being affected but sparing of the dorsal cutaneous branch
Hypothenar muscles spared (abductor digiti minimi and flexor digiti minimi)
Loss of adductor pollicis and dorsal interossei
Froment’s sign and claw hand
Preserved sensation
Zone 2 Guyon’s canal syndrome
Hypothenar muscle sparing due to early origin
Sensation spared
All hand muscles spared
Loss of palmar but not dorsal sensation over ulnar border
Froment’s and Claw hand absent
Zone 3 Guyon’s canal syndrome
LFC
Direct branch of the lumbar plexus
Provides sesnosry innervation to the skin of the ventrolateral aspect of the thigh
Anatomy of the LFC
Purely sensory nerve dervied from the second and third lumbar nerves of the lumbar plexus
Emerges from lateral aspect of psoas to run obliquely and forward across iliacus
Passes across the iliac fossa medial to ASIS, enters the thigh beneath the inguinal ligament piercing the fascia lata of te lateral thigh.
Supplis the skin of the ventrolateral aspect of the thigh
Meralgia paraesthetica
Syndrome of the LFC
Usually caused by compression of the nerve in the inguinal region.
Characterised by paraesrthesia involving the ventrolateral of th e thigh.
Common in obese individuals whose abdominal girth causes excessive strain on the inguinal ligament
Fat
No motor signs
Paraesthesia in ventrolateral thigh
Meralgia paraesthetica
Saphenous nerve
Terminal branch of femoral nerve in lower limb, provides sensory innervation to the ventromedial aspect of the knee leg and foot
Anatomy of the saphenous nerve
Purely sensory branch of femoral nerve
Originatse below the inguinal ligament and enters Hunter’s canal, crossing the femoral artery from medial to laterally and exits by piercing its root
Divides into two terminal branches- infrapatellar branch supplying ventromedial aspect of the knee and a descneding branch which supplies the ventromedial aspect of the leg and ankle
Saphenous nerve compression syndrome
Occurs at exit point from adductor canal
Characterised by intense pain along medial aspect of the knee with associated numbness in this area and down medial leg.
No motor signs or symptoms
Intense pain along medial aspect of knee and leg
Numbness along medial aspect of knee and leg
Intact motor function
Saphenous nerve entrapment