Radial Nerve Palsy

Clinical features & Diagnosis

Dr Subhakanta MohapatraIPGME&R,Kolkata.INDIA

Anatomy

• Largest branch of the brachial plexus• Arises from the posterior cord of the

brachial plexus (C5–8)• Mixed nerve

Radial Nerve

Course of Radial Nerve (RN) in the arm

In the axilla, RN lies anterior to subscapularis,

teres major and LD

• Sensory supply: Posterior cutaneous nerve of arm

RN leaves the axilla via the triangular space

• Motor supply: long head of Triceps

It then comes to lie along spiral groove on

posterior aspect of humeral shaft along with arteria profunda brachii

• Motor: medial and lateral heads of triceps, Anconeus

• Sensory: posterior cutaneous nerve of forearm, lower lateral cutaneous nerve of arm

RN then leaves the spiral groove by piercing the lateral

intermuscular septum to enter the anterior compartment of the arm, 10-12 cm above the lateral

epicondyle

• Motor supply: Brachialis (lateral part), BR, ECRL

Anterior to lateral epicondyle, RN divides into its terminal branches

• Terminal branches: Posterior Interosseous Nerve (PIN) and Dorsal or Superficial radial sensory nerve

Here it lies b/w brachialis and BR

Radial nerve (C5, 6, 7 , 8, T1) exiting axilla via the triangular space

Brachialis (lateral part)

Anconeus

Triceps brachii

Posterior cutaneous nerve of forearm

Posterior cutaneous nerve of arm

Lower lateral cutaneous nerve of arm

Radial nerve in the spiral groove (posterior aspect of humeral shaft)

Brachioradialis (BR)

ECRL (last branch of radial nerve proper)

Lateral intermuscular septum

BR

ECRL

Dorsal Radial Sensory Nerve

Dorsal digital nerves

Radial styloid

8 cm

Dorsal radial nerve courses through the forearm immediately

deep to the BR

It emerges b/w tendons of BR and

ECRL ≈ 8 cm proximal to radial styloid, to

become subcutaneous

It crosses the anatomical snuffbox

b/w EPB and EPL, dividing into multiple

branches to supply sensation to hand

Course of Radial Nerve (RN) in the forearm

Deep terminal branch → Posterior interosseous nerve (PIN)

Supinator

EIP

EDC and EDM

ECU

ECRB

Superficial terminal branch

Radial Nerve Proper

EPL

EPB

APL

PIN reaches the back of forearm by passing around the lateral aspect of the radius b/w the superficial and deep heads of the Supinator to supply all extensor compartment muscles

Finally, PIN ends by supplying carpal joint sensation

Lower lateral cutaneous nerve of arm

Posterior cutaneous nerve of arm

Posterior cutaneous nerve of forearm

Dorsal radial sensory nerve

Gives sensibility to the dorsum of the hand over the radial two-thirds, the dorsum of the thumb, and the index, long, and half of the ring finger proximal to the distal interphalangeal joint.

Cutaneous innervation from radial nerve

Clinical Features

Functional motor deficitInability to extend the wrist (in case of injury at level of PIN, wrist extension is weak with radial deviation since ECRL innervation is intact)

Inability to extend the fingers at the MCP joints

Inability to extend and radially abduct the thumb

Weakness of grip strength d/t loss of mechanical advantage that wrist extension provides for grasp and power grip

Area of sensory loss in radial nerve injury in the axilla

Unlike the median and ulnar nerves, sensory loss following radial nerve injury is not functionally disabling unless the patient develops a painful neuroma

Sensory Loss

Autonomous sensory zone for radial nerve → dorsum of 1st webspace

The Lateral cutaneous nerve of forearm has a significant overlap pattern with the Superficial radial sensory nerve

Radial Nerve Compression Syndromes

Wartenberg’s syndrome

• Aka: Cheiralgia paresthetica• D/t compression of Superficial radial nerve as it

emerges b/w ECRL and BR, 8 cm proximal to radial styloid

isolated pain or paresthesias over the dorsoradial aspect of the hand

preceding history of trauma to the area (i.e., handcuffs, forearm fracture)

Differentiating Wartenberg’s syndrome from de Quervain’s tenosynovitis

A Tinel’s sign over the superficial sensory radial nerve is the most common exam finding

Clinical features

presence of motor weakness suggests a more proximal site of compression

Also seen in patients who use forearms in pronated position for extended periods → in pronation, the tendons of BR and ECRL approximate and may compress the nerve

▪In WS, pain is exacerbated by pronation, while in DQT pain is elicited with changes in thumb and wrist position▪DQT - normal sensation in the dorso-radial hand▪DQT - pain on percussion over the 1st extensor compartment

Electrodiagnostic testing is of limited value in Wartenberg’s syndrome

Posterior interosseous nerve (PIN) syndrome

• D/t compression of PIN in the radial tunnel• Most common causes include:

▪Tumors such as lipomas, ganglia ▪Rheumatoid synovitis ▪Septic arthritis ▪Vasculitis

The radial tunnel is a 5 cm space bounded by:▪Dorsally: capsule of the radiocapitellar joint ▪Volarly: the BR▪Laterally: the ECRL and ECRB muscles ▪Medially: the biceps tendon and brachialis muscles

Within radial tunnel, there are 5 potential sites of compression: ▪fibrous bands to the radiocapitellar joint between the brachialis and BR ▪the recurrent radial vessels (leash of Henry)▪the proximal edge of the ECRB ▪the proximal edge of the Supinator (arcade of Fröhse)▪the distal edge of the Supinator

BR

Supinator

arcade of Fröhse

ECRL

PIN

Diagnosis

loss of finger and thumb extension

Weak wrist extension with radial deviation (since ECRL innervation is intact)

Intact passive tenodesis effect (rules out extensor tendon rupture)

EMG testing is helpful to confirm the diagnosis and monitor motor recovery

Radial Tunnel syndrome

• Similar to PIN syndrome, it is also d/t compression of PIN in the radial tunnel

• Not considered a true compression neuropathy by some

Radial Tunnel Syndrome is a clinical diagnosis

Radial Tunnel

Syndrome

Tenderness over radial tunnel (lateral proximal

forearm, 3-4 cm distal to lateral epicondyle over the mobile wad)

Pain at ECRB origin with resistance of

middle finger extension

Pain with resisted forearm

supination↑ Pain on combined elbow extension,

forearm pronation, and wrist flexion

Proximal Radial nerve compression

• Compression of the radial nerve proximal to the elbow is uncommon

• Causes: ▪Fibrous arch from the lateral head of triceps ▪After strenuous muscular activity ▪Bony exostosis of humerus ▪Injury in spiral groove: ▫# shaft humerus ▫‘Saturday night palsy’ (neuropraxia) ▫Post injection palsy (chemical neurotmesis)

• Patients present with variable degrees of radial nerve dysfunction

Diagnosis

Mechanism of injury (e.g. sharp penetrating vs. blunt trauma)

Timing of injury

Loss of motor and sensory function

Presence of pain

Interval recovery of function in patients presenting late

History

Assessment of motor function

Assessment of sensory function

Assessment of involved joints

Physical Examination

Individual muscles innervated by the nerve are tested to determine what is functioning and what is not:▪Helps to determine the level of injury▪Guides future surgical planning

▪Elicitation of Tinel’s sign▪Specific sensory testing

Each joint is taken through its passive range of motion to assess for suppleness → presence of fixed joint contractures in delayed presentations is associated with poor treatment outcomes

Specific sensory testsTest Perception Main receptor Comments

Static 2 point discrimination (2PD)

Tactile Merkel cell ▪Evaluates sensory receptor innervation density▪Normal distance: 6mm

Moving 2PD Tactile Meissner corpuscle ▪Normal distance: 3mm

Tuning fork (250 Hz) Vibration Pacinian corpuscle

Tuning fork (30 Hz) Vibration Meissner

Semmes-Weinstein monofilament test

Pressure Merkel

Ten test (moving light touch)

Pressure Merkel ▪Reliability comparable to monofilament test

Cold-heat test Temperature Free nerve endings

•Changes in Vibration and Pressure thresholds are seen in early nerve compression but are unreliable for evaluating nerve lacerations•Changes in sensory receptor innervation density (2PD) are seen in chronic nerve compression but are reliable for evaluating nerve lacerations

Electromyography (EMG)

Nerve conduction studies (NCS) Electrodiagnosti

c testing

Helpful in arriving at a diagnosis in presence of atypical presentations or equivocal clinical findings

Limitations of EDT:▪Evaluates only large myelinated fibres → smaller axons conveying pain and temperature are not assessed▪Changes in unmyelinated nerve fibres, which are the first to be affected in nerve compressions, are not evaluated▪Performing the test before 3-6 weeks post injury can give inaccurate results▪Very proximal or distal nerve injuries are difficult to assess▪Unreliable assessment of multi-level injuries▪Examiner dependant

Nerve conduction studies (NCS)2 electrodes are placed along the course of the nerve. The first electrode stimulates the nerve to fire, and the second electrode records the generated action potential

Amplitude• represents the size of the response• proportional to the number of

depolarizing axons in the nerve

Latency• the delay in response following

stimulation

Conduction velocity

Sensory nerve action potential (SNAP)• Response obtained when the

recording electrodes is placed proximally along the sensory nerve, toward the spinal cord

Electromyography (EMG)

Insertional activity • Activity observed when a needle electrode is inserted into the muscle

▪Fibrillation potentials ▪Fasciculations

• Seen when the muscle is at rest• Absent in normal muscles

Motor unit potentials (MUPs)

• Generated by the muscle during a voluntary contraction

• Evaluates the integrity of neuro-muscular junction

Sequence of events in nerve compression

Focal demyelination

Axonal damage at the compression site

Further axonal loss

Axonal sprouting producing collateral re-innervation

Remyelination following decompression

▪↑Latency▪↓Nerve conduction velocity

Associated Electrodiagnostic findings

▪↓SNAP▪↓CMAP

▪↑Insertional activity▪Fibrillation potentials and fasciculations

▪’Giant’ MUPs

▪Normalization of NCV▪Loss of ‘giant’ MUPs