A swan-neck deformity, typically defined as proximal interphalangeal joint (PIP) hyperextension with concurrent distal interphalangeal joint flexion, occurs in approximately 50% of patients with Rheumatoid Arthritis.

This deformity is not unique to Rheumatoid Arthritis, because it may also be congenital or traumatic in nature. Multiple surgical procedures are available for the correction of this digital abnormality. The deformity of the finger or fingers must be staged accurately to use the most appropriate surgical technique. The staging of the deformed finger is based on the condition of the articular cartilage (determined by radiography) and on the flexibility of the proximal interphalangeal joint.

Welsh and Hastings classified swan-neck deformity as mobile, snapping, or fixed, on the basis of the condition of the digital intrinsic muscles and subdivided swan neck deformity into 2 types:^[1]

• Type I – Caused primarily by proximal interphalangeal joint involvement
• Type II – Caused primarily by metacarpophalangeal joint involvement

Nalebuff classifies swan-neck deformities into 4 types: ^[2]

• Type I – proximal interphalangeal joints are flexible in all positions.
• Type II – proximal interphalangeal joint flexion is limited in certain positions.
• Type III – proximal interphalangeal joint flexion is limited in all positions.
• Type IV – proximal interphalangeal joints are stiff and have a poor radiographic appearance.

The Nalebuff classification guides in the choice of surgical treatment for swan neck deformity, and became the more widely accepted one.

Swan-neck deformity is common in persons with Rheumatoid Arthritis. It occurs as the end result of rheumatoid synovitis of the metacarpophalangeal joint (MP), proximal interphalangeal joint, and/or distal interphalangeal joints, which disrupts the balance of flexion and extension forces acting across a joint.

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