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Swan-Neck Deformity – Causes & Treatment

Swan-neck deformity is a finger deformity characterized by hyperextension of the middle joint and flexion of the end joint. It is most commonly associated with rheumatoid arthritis.

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Things worth knowing about "Swan-neck deformity"

Swan-neck deformity is a finger deformity characterized by hyperextension of the middle joint and flexion of the end joint. It is most commonly associated with rheumatoid arthritis.

What is Swan-Neck Deformity?

Swan-neck deformity is a distinctive abnormal posture of the finger in which the proximal interphalangeal (PIP) joint – the middle finger joint – is hyperextended, while the distal interphalangeal (DIP) joint – the end joint – is held in a flexed position. The term refers to the curved shape of the finger, which resembles the neck of a swan.

Causes

Swan-neck deformity can result from a variety of diseases and injuries:

Rheumatoid arthritis: The most common cause. Chronic inflammation damages joint capsules, ligaments, and tendons, leading to the typical deformity.
Trauma: Injuries to the extensor tendon at the DIP joint (e.g., mallet finger) can secondarily cause a swan-neck deformity.
Systemic lupus erythematosus (SLE): Ligament laxity caused by the systemic disease leads to abnormal joint positioning.
Cerebral spasticity: Muscular imbalances due to neurological conditions.
Connective tissue disorders: Such as Marfan syndrome or Ehlers-Danlos syndrome.

Symptoms

Swan-neck deformity is primarily recognized by its characteristic appearance:

Hyperextension of the middle finger joint (PIP joint)
Flexion of the end joint (DIP joint)
Reduced grip strength and fine motor function
Pain, swelling, and stiffness, particularly in inflammatory conditions
Difficulty bending the finger, as the hyperextended PIP joint blocks normal movement

Diagnosis

Diagnosis is mainly clinical, based on observation and physical examination of the finger position. Additional investigations may include:

X-rays: To assess joint changes and bone structure.
MRI (Magnetic Resonance Imaging): When tendon involvement is suspected or for detailed evaluation of soft tissues.
Laboratory tests: When rheumatoid arthritis or other systemic diseases are suspected (e.g., rheumatoid factor, CRP, ANA).

Classification

Swan-neck deformity is classified according to the Nalebuff classification into four types, depending on the flexibility of the PIP joint and the presence of additional changes:

Type I: Flexible PIP joint in all positions, no or minimal joint changes.
Type II: Restricted PIP joint flexion depending on the position of the MCP joint.
Type III: Restricted flexion regardless of MCP joint position.
Type IV: Stiff PIP joint with radiographic joint changes.

Treatment

Conservative Treatment

In early or mild cases, conservative measures are the first-line approach:

Splinting: Specialized finger orthoses (e.g., silver ring splints) hold the PIP joint in a slightly flexed position to prevent hyperextension.
Physiotherapy and occupational therapy: Targeted exercises to improve grip function and correct muscular imbalance.
Medication: Treatment of the underlying condition, e.g., with NSAIDs, corticosteroids, or disease-modifying antirheumatic drugs (DMARDs) for rheumatoid arthritis.

Surgical Treatment

In advanced or fixed deformities, surgical intervention may be necessary:

Tendon corrections: Reconstruction or rerouting of tendons to restore balance of joint forces.
Arthrodesis (joint fusion): In severe joint damage, the joint is surgically fused to achieve pain relief and stability.
Joint replacement (endoprosthesis): In selected cases, the destroyed joint can be replaced with a prosthesis.

References

Niethard, F. U., Pfeil, J., Biberthaler, P.: Duale Reihe Orthopadie und Unfallchirurgie. 8th edition, Georg Thieme Verlag, Stuttgart 2017.
Nalebuff, E. A.: Diagnosis, classification and management of rheumatoid thumb deformities. Bulletin on the Rheumatic Diseases, 1968;19(2):489-496.
World Health Organization (WHO): Musculoskeletal conditions. Fact Sheet, 2023. Available at: https://www.who.int/news-room/fact-sheets/detail/musculoskeletal-conditions

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