Orthopaedics

Swan Neck Deformity Of The Finger

Swan Neck Deformity of the fingers may occur in about 50% of patients suffering from Rheumatoid Arthritis. Ligaments are the structures which balances the normal positioning and movement of the fingers by supporting the finger joints. Muscles hold the fingers and allow flexible movement. The fine movements in each finger is controlled by tendons. But these can get disturbed by disease, injury or shocks. There are chances that the normal functioning and alignment of the finger may also be lost. Mostly it results in a crooked finger, like the swan neck deformity of the finger.

Many surgical procedures are available now to correct this digital abnormality. The first thing to be done is to analyze the deformity accurately prior to the surgery to opt for the most accurate treatment option.

Classification Of Swan Neck Deformity Of The Finger

Nalebuff Swan-neck Deformities Classification
Type I

The PIP joints are flexible to move in all positions.

Type II

The PIP joints is not very flexible, the movement is limited in certain positions.

Type III

The flexibility of the PIP joint is limited in all positions.

Type IV

Stiffened PIP joints with a poor radio graphic appearance.
Basing on the above classification, the surgical treatment is decided.

Welsh and HastingsClassification

They first classsified them into three major types, viz. mobile, snapping or fixed. This classification is based on the ability of the digital intrinsic muscles. They again subdivided swan-neck deformity into the following types:

Type I

PIP joint disease causes it.

Type II

MP joint disease causes it.

But the Nalebuff classification is accepted by most people.</em

What Parts Of The Finger Are Involved To Cause Swan Neck Deformity?

Three phalanges (bones) make up the finger. These phalanges are separated by two joints in each finger called the interphalangeal (IP) joints. The joint which is located towards the end of the finger is named as the distal IP (DIP) joint. Because distal means far away. The middle joint located between the DIP joint and the knuckles is known as the proximal IP (PIP) joint. Because proximal means closer in. The IP joints helps in the movement leading to bending and straightening of your hand.

The extensor tendons allow the straightening of each finger joint. Ligaments allow the bending and balancing the movement of all the fingers together. The strongest ligament is the volar plate. This connects the proximal phalanx to the middle phalanx. As the joint straightens, the ligament tightens, restricting the PIP joint from bending too back or hyper-extending. When the volar plate loosens due to some disease or injury, Swan neck deformity occurs.

How Does Swan Neck Deformity Occur?

The primary cause is unknown. Many factors including Chondrolysis, synovitis and periarticular bone absorption, viral infections and genetic predisposition can also act as triggers.

A hyperextended PIP Joint and a deformed DIP joint are described as a swan neck deformity of the finger. Any conditions that can loosen the PIP joint making it bending beyond limit cause a swan neck deformity of the finger. Rheumatoid arthritis and chronic inflammation of the PIP joint affects the PIP joint by putting a stretch on the volar plate. Hyperextension of the PIP joint makes the extensor tendon to go out of balance. This pulls the DIP joint downward into flexion. This causes the swan neck deformity. Trauma, nerve disorders like cerebral palsy, Parkinson’s Disease or stroke can make the volar plate weak. Hyperextension, rupturing or stretching of the volar plates due to injury can also make the volar plates weak.

Any injury or disease which can disrupt the end of the extensor tendon, may be another cause of drooping of the DIP joint. Without treatment the drooping will not straighten again, causing a Mallet Finger. The tendon will become imbalanced and start pulling the DIP joint. Thus, causing hyperextention of the DIP joint and starting the Swan Neck Deformity of the finger.

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