At a Glance - Swan neck deformity vs boutonniere deformity

Contributed by Dr Jean Watkins, a retired GP in Hampshire

Severe swan neck deformity
Severe swan neck deformity

Swan neck deformity

  • Occurs in about 50 per cent of rheumatoid arthritis (RA) cases, but may also occur as a congenital phenomenon or following trauma.
  • Develops with hyperextension of the proximal interphalangeal (PIP) joint and flexion of the distal interphalangeal (DIP) joint.
  • May affect one or more fingers but not the thumb.
  • The deformity is initiated by a flexor synovitis that increases the flexor pull on the metacarpophalangeal joint.
  • Extending the fingers causes stretching of the collateral ligaments at the PIP with hyperextension at this joint and reciprocal flexion at the DIP.
  • Severe cases may suffer joint destruction and contractures.
  • Causes considerable disability.


  • Tests that confirm the diagnosis of RA include: rheumatoid factor, which is positive in 80 per cent of cases; analysis of synovial fluid to distinguish from non-inflammatory and infectious arthritis; ESR and X-ray.
  • Surgery should be considered when the patient cannot actively flex the PIP joint.
  • Early referral for assessment is important.

Boutonniere deformity


  • May develop in cases of progressive arthritis or following trauma.
  • Occurs in about half of patients with RA.
  • Presents with flexion of the PIP and hyperextension of the DIP.
  • May affect one or more fingers, including the thumb.
  • In RA, follows chronic synovitis in which the PIP joint is forced into flexion which increases tension on the DIP extensors.
  • Following trauma, the finger is semi-flexed and movement of the joints decreased.
  • May not develop for two to three weeks following injury.
  • In RA, symptoms may be mild, moderate or severe, when the PIP joint can no longer be passively extended.


  • Check for history of recent injury.
  • Tests as for swan neck deformity will help in the diagnosis of RA.
  • Initial treatment with splinting may be helpful after trauma or in RA when symptoms are mild.
  • In RA, moderate and severe cases may be helped by surgery. However, surgical reconstruction of the joint and/or complications can reduce function.

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