Swan Neck Deformity: a finger that bends in two directions.

Swan neck deformity describes a finger in which the middle knuckle, the PIP joint, is hyperextended while the fingertip joint, the DIP joint, is bent. The shape resembles a swan's neck. It arises when the delicate balance of tendons and ligaments that normally hold the finger straight is disrupted.

The deformity has several causes. It is commonly seen in rheumatoid arthritis, where chronic inflammation loosens the supporting structures, and it can also follow an untreated mallet injury at the fingertip or develop in fingers that are naturally lax. Some patients have a mild, flexible deformity that is mostly cosmetic, while others develop a stiff, fixed finger that catches and interferes with grip.

Why the finger deforms

The finger is balanced by tendons on the back that straighten it and structures on the palm side that prevent the middle joint from over-straightening. When this balance is lost, often because the volar plate on the palm side becomes lax or the tendon balance shifts, the middle joint drifts into hyperextension and the fingertip drops into flexion. The result is the characteristic swan-neck shape.

Common causes

Swan neck deformity is associated with:

• Rheumatoid arthritis and other inflammatory arthritis
• A prior mallet injury that was not fully treated
• Natural ligament laxity in some patients
• Old injury or imbalance of the finger tendons

Flexible versus fixed deformity

The most important question on examination is whether the deformity is flexible or fixed. A flexible deformity can still be straightened passively and often responds to therapy and splinting. A fixed deformity has become stiff and cannot be passively corrected, which changes the treatment toward surgery. The examination also looks for the underlying cause, since treating rheumatoid arthritis or an old mallet injury is part of addressing the deformity.

Non-surgical treatment

Flexible deformities often respond well to:

• Hand therapy to maintain motion and balance
• A ring or figure-of-eight splint that blocks hyperextension while allowing bending
• Treating the underlying cause, such as rheumatoid arthritis or an old mallet injury

Surgical treatment

For fixed or disabling deformities, surgery rebalances the finger. Depending on the case this may involve soft-tissue procedures that restrain the middle joint, tendon procedures that restore balance, or procedures at the PIP joint itself. The choice is tailored to the individual finger and the underlying cause.

Recovery timeline

Recovery depends on the procedure performed:

1. Early weeks
   Protective splinting holds the corrected position. Hand therapy guides a careful range of motion so the correction is maintained.
2. Weeks 4 to 8
   Progressive motion and strengthening under therapy guidance, with splinting weaned as the finger stabilizes.
3. Beyond 8 weeks
   Return to fuller hand use. Final motion and strength continue to improve over the following months.

What patients commonly misunderstand

A few points worth clarifying:

• Early splinting can do a lot. A small ring splint that blocks hyperextension often restores a smooth grip in flexible deformities, without surgery.
• It is not always from arthritis. Swan neck deformity can follow an old mallet injury or occur in naturally lax fingers, not only in rheumatoid arthritis. The cause guides the treatment.
• Fixed deformities are a different problem. Once a finger becomes stiff and cannot be straightened by hand, splinting alone is unlikely to correct it, and surgery is considered.

This page is general educational content authored by Dr. Lee. It is not a substitute for individual medical advice. Every patient's case is different, book a consultation to discuss yours.