Orthopaedic Surgery - Swan Neck Deformity

Basics

Swan neck deformity is a characteristic digital deformity consisting of:

Hyperextension of the proximal interphalangeal joint

combined with:

Flexion of the distal interphalangeal joint.

There may also be compensatory:

Flexion at the metacarpophalangeal joint.

Characteristic Posture

The classic deformity therefore consists of:

MCP flexion

PIP hyperextension

and

DIP flexion.

Not every patient demonstrates abnormalities at all three joints.

Mechanism

The deformity develops when the balance between:

Flexion

and

Extension forces

across the finger becomes abnormal.

The essential biomechanical feature is excessive:

Extension force across the PIP joint

relative to available:

Flexion restraint.

Traumatic Causes

Traumatic causes include:

Mallet finger

Flexor digitorum superficialis laceration

and injuries involving the:

Extensor mechanism around the PIP joint.

Other Causes

Swan neck deformity may also result from:

Intrinsic muscle contracture

Volar plate laxity

or

Volar subluxation of the MCP joint.

These mechanisms are particularly important in:

Rheumatoid arthritis.

Epidemiology

Swan neck deformity can occur after:

Trauma

or as part of chronic:

Inflammatory joint disease.

Rheumatoid Arthritis

Among patients with rheumatoid arthritis, the deformity is reported more commonly in:

Women

than in men.

This partly reflects the greater overall prevalence of rheumatoid arthritis in:

Women.

Incidence

Rheumatoid arthritis affects approximately:

0.5–1% of the general population.

Among patients with established rheumatoid arthritis, swan neck deformity may eventually develop in a substantial proportion.

Historical series have reported occurrence in up to:

Approximately half of patients

during the course of longstanding disease.

Short-Term Incidence

Some studies have reported an incidence of approximately:

8% over 2 years

among patients with rheumatoid disease.

Risk Factors

Important risk factors include:

Rheumatoid arthritis

Mallet finger

Digital laceration

Intrinsic muscle tightness

Neurologic spasticity

and

Volar plate laxity.

Sports Injury

Sports participation may predispose to:

Mallet finger

through closed avulsion injury of the:

Distal extensor tendon.

A chronic untreated mallet finger can subsequently lead to:

Swan neck deformity.

Digital Laceration

Dorsal or volar lacerations may disrupt:

Extensor

or

Flexor structures

and alter normal force balance across the:

PIP joint.

Neurologic Disorders

Intrinsic muscle tightness may occur with:

Traumatic brain injury

Stroke

or other conditions producing:

Spasticity.

This can contribute to excessive:

PIP extension.

Rheumatoid Disease

Rheumatoid arthritis may create multiple contributing abnormalities, including:

Intrinsic muscle contracture

Volar plate attenuation

MCP subluxation

and progressive destruction of:

Joint stabilizers.

Etiology

The deformity develops when the net forces acting across the:

PIP joint

favor excessive:

Extension.

This is accompanied by secondary alteration in the:

Distal extensor mechanism

producing:

DIP flexion.

Mallet Finger Mechanism

In chronic mallet finger, loss of terminal extensor function at the:

DIP joint

allows the extensor mechanism to redistribute proximally.

This can increase extension force across the:

PIP joint

and eventually produce:

Swan neck posture.

FDS Injury

Injury or loss of function of the:

Flexor digitorum superficialis

removes an important flexion restraint at the:

PIP joint.

This predisposes the joint to:

Hyperextension.

Volar Plate Laxity

The:

Volar plate

normally resists excessive PIP:

Hyperextension.

Attenuation or laxity permits the PIP joint to move beyond its normal:

Extension limit.

Intrinsic Tightness

Tight intrinsic muscles can increase:

PIP extension

and alter the balance of:

Digital tendon forces.

Associated Conditions

The principal associated systemic disorder is:

Rheumatoid arthritis.

Other associated conditions may include:

Neurologic spasticity

and chronic post-traumatic:

Tendon imbalance.

Diagnosis

Diagnosis is usually made by:

Clinical examination.

The clinician should determine both:

The underlying cause

and whether the deformity remains:

Flexible or fixed.

Signs and Symptoms

The most obvious finding is:

PIP hyperextension

with

DIP flexion.

Functional Symptoms

Patients may report difficulty with:

Grasping objects

Making a fist

Pinch activities

or placing the hand into:

Pockets or gloves.

Pain

Pain may arise from:

Inflammatory arthritis

PIP joint degeneration

or associated:

Tendon pathology.

Some flexible deformities may produce relatively little:

Pain.

History

A detailed history should address:

Prior finger trauma

Mallet finger

Digital lacerations

and symptoms of:

Inflammatory arthritis.

Rheumatologic History

Ask about:

Joint swelling

Morning stiffness

Multiple-joint pain

and personal or family history of:

Rheumatoid arthritis or other inflammatory disease.

Physical Examination

Examine:

MCP

PIP

and

DIP joints

of the affected finger.

Both:

Active

and

Passive range of motion

should be documented.

Comparison Examination

The affected digit should be compared with:

Adjacent fingers

and the corresponding digit of the:

Contralateral hand.

Flexible Deformity

Early swan neck deformity may remain:

Passively correctable.

The patient may also retain nearly full:

Active motion.

Fixed Deformity

With chronic progression, the joints may develop:

Capsular contracture

Tendon shortening

and

Articular degeneration.

The deformity then becomes:

Stiff or fixed.

Finochietto–Bunnell Test

The:

Finochietto–Bunnell test

helps distinguish:

Intrinsic muscle tightness

from

PIP capsular restriction.

Test Technique

Passively flex the:

PIP joint

while comparing motion with the:

MCP joint extended

and then:

Flexed.

Capsular Restriction

If PIP flexion remains equally limited regardless of MCP position, the problem is more consistent with:

Capsular restriction.

Intrinsic Tightness

If PIP flexion improves when the MCP joint is:

Flexed

the limitation is more consistent with:

Intrinsic muscle tightness.

Joint Stability

The PIP joint should also be assessed for:

Volar plate laxity

and excessive:

Hyperextension.

Tendon Examination

Evaluate:

Terminal extensor function

at the DIP joint and function of the:

Flexor digitorum superficialis.

This helps identify the mechanical cause of the:

Deformity.

Imaging

Plain Radiographs

Standard radiographs should include:

PA

Lateral

and

Oblique views.

Radiographic Assessment

Imaging can identify:

Joint-space narrowing

Articular destruction

Subluxation

Fracture

and

Bony mallet injury.

Rheumatoid Disease

In rheumatoid arthritis, radiographs may demonstrate:

Erosions

Joint-space loss

MCP subluxation

and other features of:

Inflammatory arthropathy.

Differential Diagnosis

Important differential diagnoses include:

Boutonnière deformity

Mallet finger

PIP dislocation

and

Nonunion of proximal or middle phalanx fractures.

Boutonnière Deformity

Boutonnière deformity is essentially the opposite digital posture:

PIP flexion

with

DIP hyperextension.

This distinction is important because the underlying tendon imbalance and treatment are:

Different.

Mallet Finger

Mallet finger consists primarily of:

DIP flexion

due to loss of terminal extensor function.

A chronic mallet injury may progress to:

Swan neck deformity.

PIP Dislocation

Prior PIP dislocation may cause:

Volar plate injury

and chronic:

Hyperextension instability.

Treatment

Management depends on:

Cause

Flexibility of the deformity

Joint condition

Symptoms

and

Functional impairment.

General Measures

Flexible deformities can often be managed initially with:

Nonoperative treatment.

Ring Splints

A:

Double-ring splint

or other anti-hyperextension splint may prevent excessive:

PIP extension.

This can substantially improve:

Finger function.

Extension-Block Splint

An:

Extension-block splint

allows PIP flexion while preventing excessive:

Hyperextension.

DIP Splinting

Progressive splinting may also be used to address:

Persistent DIP flexion deformity

and improve:

Distal joint extension.

Hand Therapy

Hand therapy is useful for:

Passive stretching

Joint mobilization

Splint fabrication

and maintenance of:

Functional motion.

Flexible Versus Fixed Deformity

Nonoperative treatment is most effective when the deformity remains:

Flexible

and the articular surfaces are relatively:

Preserved.

Medication

Pain relief may include:

Acetaminophen

or

NSAIDs

when medically appropriate.

Acute Tendon Repair

If an acute extensor or flexor tendon injury requires repair, a:

Digital nerve block

or other suitable anesthesia may be used.

Rheumatoid Arthritis Treatment

When the deformity is secondary to:

Rheumatoid arthritis

management of the systemic disease is essential.

DMARD Therapy

Treatment may require:

Disease-modifying antirheumatic drugs

under the care of a:

Rheumatologist.

Other Rheumatoid Medications

Depending on disease severity, treatment may also include:

Glucocorticoids

NSAIDs

and other:

Analgesics.

Controlling the underlying inflammatory disease may slow progression of:

Joint destruction and deformity.

Surgery

Surgery is considered when there is:

Persistent functional limitation

Pain

Failure of splinting

or progressive:

Fixed deformity.

Flexible Deformity Surgery

When passive motion is preserved, surgery focuses on restoring:

Tendon balance

and preventing excessive:

PIP hyperextension.

Volar Plate Advancement

The volar plate may be:

Advanced or tightened

to improve restraint against:

PIP hyperextension.

Central Slip Tenotomy

Selected deformities may be treated with:

Central slip tenotomy

to reduce excessive extension force across the:

PIP joint.

Intrinsic Release

When intrinsic muscle tightness is the major cause, an:

Intrinsic release

may improve:

PIP flexion.

FDS Tenodesis

The:

Flexor digitorum superficialis

may be used as a:

Tenodesis

to limit excessive:

PIP extension.

Volar Skin Procedure

A:

Volar skin ellipse

at the PIP joint may occasionally be used to restrict:

Hyperextension.

Late-Stage Disease

In advanced disease, chronic deformity may be accompanied by:

Joint arthrosis

and loss of:

Passive correctability.

Arthrodesis

A severely painful or destroyed PIP joint may require:

Fusion

in a functional position.

Arthroplasty

Joint replacement may be considered in selected patients with:

Advanced arthritic destruction

where preservation of some:

Motion

is desirable.

Follow-Up

Patients should be reassessed for:

Progression of deformity

Splint effectiveness

Range of motion

and

Functional improvement.

Rheumatology Follow-Up

Patients with inflammatory arthritis require continued:

Rheumatologic management

to control the underlying:

Systemic disease.

Hand Surgeon Referral

Referral to a:

Hand surgeon

is appropriate when the deformity is:

Progressive

Functionally limiting

Painful

or likely to require:

Operative reconstruction.

Prognosis

Both nonoperative and surgical treatment can produce:

Meaningful deformity correction

and improved:

Hand function.

Recurrence

Recurrence is relatively common because the deformity often results from persistent underlying:

Tendon imbalance

Joint laxity

or

Inflammatory disease.

Flexible Deformities

Flexible deformities generally have a better prognosis with:

Splinting

and

Soft-tissue reconstruction.

Fixed Deformities

Chronic fixed deformities are more difficult to correct because of:

Capsular contracture

Tendon shortening

and

Arthrosis.

Complications

Incomplete Correction

The deformity may not be completely corrected by either:

Splinting

or

Surgery.

Recurrence

Even after successful treatment, excessive PIP extension may:

Recur.

PIP Stiffness

Overcorrection or postoperative scarring may result in:

PIP stiffness.

Loss of DIP Extension

Excessive alteration of extensor balance may produce:

Loss of DIP extension.

Surgical Imbalance

Because correction requires redistribution of complex tendon forces, excessive correction in one direction may produce a new:

Digital imbalance.

Patient Monitoring

Monitoring should include:

Active and passive MCP motion

PIP motion

DIP motion

Joint stability

and progression of:

Functional limitation.

Key Principle

Swan neck deformity is characterized by:

PIP hyperextension with DIP flexion, sometimes accompanied by MCP flexion.

It results from an imbalance in digital tendon forces, commonly associated with:

Rheumatoid arthritis, chronic mallet finger, FDS injury, volar plate laxity, or intrinsic muscle tightness.

The:

Finochietto–Bunnell test

helps distinguish intrinsic tightness from capsular restriction.

Flexible deformities are commonly treated with:

Ring splints, extension-block splints, stretching, and hand therapy.

When deformity is persistent or advanced, surgery may involve:

Volar plate advancement, central slip tenotomy, intrinsic release, FDS tenodesis, arthrodesis, or arthroplasty, depending on the:

Stage of disease and condition of the joint.