Orthopaedic Surgery - Pronator Syndrome

Basics

Pronator syndrome is a compressive neuropathy of the:

Median nerve in the proximal forearm.

It typically presents with:

Vague aching pain in the proximal volar forearm

Paresthesia in the median nerve distribution

and sometimes:

Mild weakness of median nerve–innervated muscles.

The disorder is considerably less common than:

Carpal tunnel syndrome.

Anatomy

The median nerve enters the proximal forearm and passes through or beneath several structures that may potentially compress it.

Important sites include:

Ligament of Struthers

Lacertus fibrosus

Between the humeral and ulnar heads of pronator teres

Fibrous arch of flexor digitorum superficialis

The anterior interosseous nerve branches from the median nerve distal to the proximal forearm region.

Pathophysiology

Compression of the median nerve proximal to its major motor and sensory branches may affect:

Motor fibers

and

Sensory fibers.

This explains why pronator syndrome can produce sensory symptoms involving both:

The radial digits

and

The palm.

Palmar Cutaneous Branch

The palmar cutaneous branch of the median nerve arises proximal to the carpal tunnel.

Therefore, proximal median nerve compression can produce sensory symptoms in the:

Thenar eminence or central palm.

This helps distinguish pronator syndrome from:

Carpal tunnel syndrome, in which palmar cutaneous sensation is usually preserved.

Prevention

There is no specific established preventive strategy.

Reducing excessive repetitive forearm loading may be helpful in individuals whose symptoms are clearly activity related.

Epidemiology

Pronator syndrome is:

Rare.

It most commonly presents in:

Middle-aged adults, often around the fifth decade of life.

Sex

Historical series have reported a female predominance, with women affected approximately:

Four times more often than men.

Because the disorder is uncommon, precise incidence and prevalence remain poorly defined.

Risk Factors

Potential anatomic or mechanical risk factors include:

Supracondylar process of the humerus

Repetitive pronation and supination

Repetitive elbow or wrist flexion

Hypertrophied forearm musculature

Supracondylar Process

A supracondylar process is an uncommon bony projection from the distal humerus.

It may be connected to the medial epicondyle by the:

Ligament of Struthers.

The median nerve can occasionally be compressed beneath this structure.

Genetics

There is no known Mendelian inheritance pattern.

Etiology

The exact cause is often:

Poorly defined.

The syndrome is believed to result from mechanical compression of the:

Median nerve in the proximal forearm.

In many patients, no single compressive structure can be definitively identified clinically.

Diagnosis

Diagnosis is based mainly on:

History

Physical examination

and exclusion of other median nerve disorders.

Electrodiagnostic studies are often more useful for excluding alternative diagnoses than for confirming pronator syndrome itself.

Signs and Symptoms

The characteristic clinical picture includes:

Proximal forearm pain

Median-distribution paresthesia

and sometimes

Mild motor weakness.

Sensory Symptoms

Paresthesias may involve the median nerve distribution, including:

Thumb

Index finger

Middle finger

Radial half of the ring finger

Unlike carpal tunnel syndrome, symptoms may also involve:

The palm or thenar eminence.

Pain

Pain is usually located in the:

Proximal volar forearm.

It may become worse with:

Forearm pronation and supination

or repetitive upper-extremity activity.

Night Symptoms

Pronator syndrome generally produces:

Few or minimal nocturnal symptoms.

Prominent nighttime numbness or awakening is more characteristic of:

Carpal tunnel syndrome.

Motor Weakness

Weakness may involve median nerve–innervated muscles such as:

Pronator teres

Flexor carpi radialis

Palmaris longus

Flexor pollicis longus

Flexor digitorum superficialis

Flexor digitorum profundus to the index and middle fingers

Thenar muscles

Radial two lumbricals

However, objective weakness is often:

Mild or absent.

Physical Examination

A complete neurologic and vascular examination of the upper extremity should be performed.

Sensory Examination

Assess sensation in:

Thumb

Index finger

Middle finger

Radial half of the ring finger

and

Palm over the thenar eminence.

Sensory change in the palm supports a lesion proximal to the:

Carpal tunnel.

Motor Examination

Assess strength of:

Forearm pronation

Wrist flexion

Thumb flexion

Index and middle finger flexion

Thumb opposition and abduction

Provocative Testing

Different provocative maneuvers may help localize the suspected level of compression.

A test is considered suggestive when it reproduces the patient’s:

Typical pain or paresthesia.

Lacertus Fibrosus Compression

Compression beneath the lacertus fibrosus may be provoked by:

Resisted elbow flexion with the forearm supinated.

This tensions the bicipital aponeurosis over the median nerve.

Pronator Teres Compression

Compression between the heads of pronator teres may be provoked by:

Resisted forearm pronation with the elbow extended.

Reproduction of the patient’s symptoms supports this site.

Flexor Digitorum Superficialis Arch

Compression at the FDS arch may be suggested when symptoms are reproduced by:

Resisted PIP joint flexion, particularly of the middle finger.

Tinel Sign

Percussion over the proximal course of the median nerve may produce:

Tingling or radiating paresthesia.

A positive Tinel sign can support the diagnosis but is not specific.

Scratch-Collapse Test

The scratch-collapse test has been described for proximal median nerve compression.

Its diagnostic accuracy is variable, so it should be interpreted only as part of the:

Overall clinical examination.

Laboratory Tests

No routine laboratory tests are useful for diagnosing isolated pronator syndrome.

Laboratory studies may be obtained only when there is concern for:

Inflammatory disease

Metabolic neuropathy

or another systemic disorder.

Imaging

Plain Radiographs

Radiographs are not routinely required.

They may be useful when there is concern for:

Supracondylar process

Bony deformity

Previous fracture

or another structural abnormality.

Supracondylar Process and Ligament of Struthers

When a supracondylar process is present, the median nerve may be compressed beneath a fibrous band extending to the medial epicondyle known as the:

Ligament of Struthers.

MRI or Ultrasound

Advanced imaging may be useful when a:

Mass

Ganglion

Tumor

or other space-occupying lesion is suspected.

Ultrasound may also demonstrate:

Dynamic nerve compression

or local nerve enlargement in selected cases.

Electrodiagnostic Studies

Electromyography and nerve-conduction studies may be obtained to:

Exclude carpal tunnel syndrome

Exclude cervical radiculopathy

Exclude anterior interosseous neuropathy

Identify more proximal median nerve injury

Limitations of Electrodiagnostic Testing

Electrodiagnostic studies are often:

Normal or nondiagnostic

in pronator syndrome.

Only a minority of patients demonstrate clear evidence of proximal median nerve compression.

Therefore, a normal study does not completely exclude the diagnosis.

Differential Diagnosis

Important alternatives include:

Carpal tunnel syndrome

Anterior interosseous nerve syndrome

Cervical radiculopathy

Median nerve lesion at another level

Flexor-pronator muscle strain

Anterior Interosseous Nerve Syndrome

Anterior interosseous nerve syndrome is primarily a:

Motor neuropathy.

It causes weakness of muscles such as:

Flexor pollicis longus

Index flexor digitorum profundus

Pronator quadratus

but does:

Not produce sensory loss.

This distinguishes it from pronator syndrome.

Carpal Tunnel Syndrome

Carpal tunnel syndrome usually causes:

Median-distribution paresthesia

with prominent:

Night symptoms.

The:

Palmar cutaneous branch is spared

because it passes superficial to the carpal tunnel.

Thus, numbness over the thenar eminence or palm favors a more proximal median nerve lesion.

Treatment

General Principles

Initial treatment is nearly always:

Nonoperative.

Management focuses on reducing mechanical irritation and allowing the nerve to recover.

Rest

Temporary rest from aggravating activity is often recommended.

Activity Modification

Patients should reduce activities involving:

Repeated pronation-supination

Forceful gripping

Repeated elbow flexion

Heavy wrist-flexor strengthening

if these reproduce symptoms.

Splinting

Temporary rotational or forearm immobilization may be used in selected patients to reduce repetitive nerve irritation.

Prolonged immobilization should be avoided because of the risk of:

Stiffness

and

Weakness.

Physical and Occupational Therapy

Therapy may include:

Stretching of the flexor-pronator musculature

Median nerve-gliding exercises

Range-of-motion exercises

Soft-tissue mobilization

Activity and ergonomic modification

Nerve Gliding

Median nerve–gliding exercises aim to improve:

Neural mobility

and reduce mechanical irritation during forearm motion.

Exercises should not provoke persistent:

Pain or paresthesia.

Medication

NSAIDs may be used for:

Short-term pain relief

when appropriate.

Medication does not correct fixed mechanical compression.

Surgery

Surgical decompression may be considered when there is:

Failure of prolonged conservative treatment

Progressive motor weakness

Significant functional loss

or a clear structural compressive lesion.

Timing of Surgery

A trial of approximately:

3–6 months of conservative management

is often appropriate before surgery when weakness is not progressive.

Earlier intervention may be considered for:

Progressive motor deficit

or definite structural compression.

Surgical Decompression

Surgery involves exploration of the median nerve through the proximal forearm and release of all potential compression sites.

Structures Released

Potential sites include:

Ligament of Struthers

Lacertus fibrosus

Pronator teres

Fibrous arch of flexor digitorum superficialis

Ligament of Struthers

If present and compressive, the ligament is:

Released or excised.

Lacertus Fibrosus

The bicipital aponeurosis may be released when it is contributing to:

Median nerve compression.

Pronator Teres

The median nerve may be decompressed between the:

Humeral

and

Ulnar heads

of pronator teres.

FDS Arch

A distinct fibrous arch at the origin of:

Flexor digitorum superficialis

may form an important distal site of compression.

When encountered during surgery, it should be:

Adequately released.

Referral

Referral to a hand or peripheral nerve specialist is appropriate for:

Progressive weakness

Significant motor deficit

Failure of conservative treatment

Diagnostic uncertainty

Follow-Up

Patients undergoing nonoperative treatment should be reviewed periodically to monitor:

Pain

Paresthesia

Motor strength

Response to activity modification

Prognosis

The overall prognosis is generally:

Good.

Historical series suggest that approximately:

90% of patients

may improve with either conservative or operative management, although persistent symptoms can occur.

Surgical Outcomes

No single operative technique has been conclusively shown to be superior.

Successful surgery depends primarily on:

Correct diagnosis

and

Complete release of the relevant compression sites.

Complications

The main complication is:

Persistent or recurrent symptoms.

Potential surgical complications include:

Scar sensitivity

Incomplete decompression

Iatrogenic nerve injury

although major nerve injury is uncommon.

Patient Monitoring

Patients should be followed regularly during conservative treatment to evaluate:

Median nerve sensation

Forearm pain

Motor function

Thenar strength

Progression or resolution of symptoms.

Key Principle

Pronator syndrome is a proximal median nerve entrapment syndrome characterized by proximal forearm pain, median-distribution paresthesia including the palm, and usually little or no motor weakness.

It differs from carpal tunnel syndrome because:

The palmar cutaneous branch may be involved and nocturnal symptoms are less prominent.

Initial treatment consists of:

Activity modification, therapy, nerve-gliding exercises, and temporary splinting, while persistent symptoms or progressive motor weakness may require:

Surgical decompression of the median nerve at all potential proximal forearm compression sites.