FINGER DEFORMITY

SWAN NECK & BOUTONNIERE

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What is a Swan Neck Deformity?

The swan neck deformity of a finger got its name because the injured finger looks like an ugly ducking (just kidding, the finger looks like a swan). The finger becomes hyperextended at the first knuckle joint (PIP: proximal interphalangial joint) and flexed at the second finger joint (the DIP).

This deformity can be seen in the advanced stages of rheumatoid disease, or it can be seen after an injury to the finger was not correctly treated (usually a Mallet finger, see talk).

With bad finger arthritis, the metacarpal-phalangeal joint moves forward (volar), and this causes the the PIP to hyperextend leading to a similar imbalance. The cause of this deformity is an imbalance at the PIP joint, which over time weakness the volar plate, which becomes lax (like an old rubberband that lost its spring), and allows the joint to move out of place.

Treatment includes splinting (nonsurgical) or surgery to tighten the volar plate and correction of the tendons to provide better balance, including a central slip tenotomy, which weakness the hyperextension force.

What is a Boutonniere Deformity?

A Boutonnere is the name for someone who used to sew buttons professionally and this name is given to a finger deformity that they used to develop after many years of hard work with their fingers.

The deformity is the opposite of a swan neck, and in this type, the PIP is hyperflexed, while the DIP is extended. It can be caused by trauma to that finger, specifically an injury to the central slip (which lies over the PIP joint) which is a ligament that helps with straightening of the finger (extrinsic extension occurs from muscles outside the hand). If its disrupted you cannot extend your finger. The other cause is injury to the triangular ligament, another ligament in the hand with helps with intrinsic extension (extension from muscles within the hand: lumbricles). The collateral bands, which are like harness around the finger, slip down and turn muscles that used to extend the finger, into muscles that flex the finger.The injury to the central slip is diagnosed with a Elson test. The PIP joint is placed over a table and forced to extend.