Swan Neck Deformity

If the middle joint of a finger is in extended (bent back) position more than normal and also the end joint is in flexed (bent down) position, than it is known as swan neck deformity.

Pathophysiology: The intercalated joint collapse in the concept of Landsmeer which means that collapse of a joint in one direction and it will result in deformity of the next distal joint in the opposite direction. It’s kind of “Z” deformity.

Swan neck classification:

I: PIP joint flexible in all positions
II: PIP motion limited.
III: Fixed PIP joint contracture but x-ray is okay
IV: X-ray shows arthritic changes

Causes:

The most common cause of swan neck deformity is rheumatoid arthritis. Other possible causes are given below-

Other types of arthritis.
Untreated mallet finger – a condition often caused by injury.
Poorly healed fracture in the finger.
Other direct trauma to finger that has weakened the ligaments surrounding the PIP joint.
Nerve damage that causes muscle spasms.
Severely jammed tip of finger.
Tightened hand muscles due to injury.
Looseness of the fibrous plate inside the hand located at the base of the fingers.
Loose finger ligaments.
Ruptured finger tendon or tendons.
Some genetic conditions, such as Ehlers-Danlos syndrome.

Sign & Symptoms:

Pain
Swelling of the PIP joint
Laxity of the volar plate
Snapping and locking of the fingers
Hyperextension of the PIP and flexion of the DIP

Diagnosis:

Rheumatoid arthritis (RA)—most common cause of swan neck deformity
Chronic inflammation loosens the volar plate, making PIP susceptible to hyperextension
As a result, extensor tendon tightens causing DIP to pull into flexed position
Other findings: X-ray.