Swan Neck Deformity

A swan neck deformity is a common condition where the fingers bend abnormally.

It often develops gradually and can affect hand function, grip strength, and everyday activities. It may affect one or more fingers.

Swan neck finger is most often linked with arthritis, tendon imbalance, or untreated finger injuries, but it can also occur after trauma or neurological conditions.

Understanding what causes swan neck deformity, common symptoms, how it differs from similar finger problems and the best treatment options is key to making a good recovery.

What Is Swan Neck Deformity?

Swan neck deformity is a degenerative finger condition where:

• The middle joint (PIP joint) bends backwards into hyperextension
• The fingertip joint (DIP joint) bends downwards into flexion
• The knuckle joint (MCP joint) may also bend downwards

This creates the classic “swan neck” appearance, similar to the curve of a swan’s neck, hence the name. It is the opposite of a boutonniere deformity.

Swan neck disease affects the balance of tendons and ligaments that control finger movement. When this balance is lost, the finger can no longer straighten and bend normally. Over time, the deformity may become fixed and difficult to correct.

Although most common in the fingers, swan neck thumb deformity can also occur, particularly in people with rheumatoid arthritis.

What Causes Swan Neck Deformity?

Finger joint deformities occur when the delicate system that controls finger movement is damaged.

This system, known as the extensor mechanism, is a network of tendons and muscles that work together to move and control the finger joints.

Because these structures are carefully balanced, a problem in one part affects the others. If one joint loses the force that normally controls it, another joint may be pulled too strongly in the opposite direction.

Swan neck deformity develops when:

• The extensor tendon on the back of the finger is damaged or weakened
• The volar plate ligament on the palm side of the finger is stretched or torn and becomes lax
• There is resultant tightness in the triangular ligament around the PIP
• Finger muscles become overly tight and shortened (contracture)

Common causes of swan neck deformity fingers include:

1. Arthritis: joint inflammation damages the soft tissues, weakening the tendons, leading to progressive deformity. Rheumatoid arthritis is the most common cause of swan neck deformity finger, and up to 50% of people with RA will develop it
2. Finger Injuries: such as untreated mallet finger, chronic joint sprains, laceration or previous finger fractures
3. Neurological or Muscle Conditions: such as stroke, cerebral palsy, Parkinson’s, muscle spasticity

Swan neck deformity may affect one finger, multiple fingers, or the thumb, depending on the underlying cause.

Symptoms of Swan Neck Deformity

Swan neck finger symptoms usually develop gradually and may worsen over time:

• Middle joint of the finger bends backwards, forming a valley
• Fingertip bends forwards, forming a peak
• Progressive finger stiffness or locking
• Difficulty making a fist and with fine motor tasks like buttoning or writing
• Weak grip and reduced pinch strength
• Pain or swelling (especially with arthritis)
• Snapping feeling when moving the finger

In advanced cases, the finger may become fixed in the deformity, making movement very limited.

Diagnosis

Swan neck disease diagnosis is based on a clinical history and physical examination. Your clinician will ask about symptom onset, progression, previous finger injuries, and signs of arthritis.

They will then carry out a clinical examination where they will:

• Assess finger posture and active/passive movement
• Test joint stability
• Look for signs of arthritis or tendon imbalance

You may also be sent for imaging studies or tests to confirm the diagnosis or rule out other conditions:

• X-rays may be used to assess joint damage or arthritis
• Ultrasound or MRI may be used if tendon injury is suspected
• Blood Tests to help diagnose inflammatory diseases

Early diagnosis is important, as treatment is far more effective before the deformity becomes rigid.

Swan Neck vs Boutonniere Deformity vs Mallet Finger

Although these conditions affect similar joints in the fingers, they are caused by different tendon problems and require different treatment.

• Swan Neck Deformity: Middle joint bends backwards, fingertip droops
• Boutonniere Deformity: Middle joint bends forward, fingertip bends backwards
• Mallet Finger: Fingertip droops due to extensor tendon injury

Correct diagnosis is essential, as splinting the wrong joint can make symptoms worse.

Splint for Swan Neck Deformity

A swan neck deformity splint is commonly used as part of treatment.

Swan neck splints work to correct the finger position by:

• Preventing hyperextension of the middle joint
• Allowing controlled finger flexion
• Improving grip and hand function

Common options include:

• Double Ring splints
• Custom thermoplastic splints

Splints are particularly helpful for people with rheumatoid arthritis or early deformity, and may delay or avoid the need for surgery.