This deformity results from an imbalance of forces in the finger. As stated in our blog about Boutonniere deformities, the various muscles and their tendons which act upon the fingers work in perfect equilibrium, balancing the forces which act to pull into flexion or extension. Disruption to this equilibrium results in changes in posture, movement and function. The swan-neck position is described as hyperextension of the PIP joint and flexion of the DIP joint and it results from a ‘collapse’ between the three phalanges of the finger. So how does this happen?

The lateral bands drift dorsally and sit atop the PIP joint, pulling it into hyperextension and resisting flexion. The tough oblique retinacular ligament around the DIP joint tightens and resists extension. 

mallet-bout-swan

(Image courtesy of www.kleisertherapy.com)

Some of the common causes of swan-neck deformities include chronic damage to the volar plate which is designed to prevent hyperextension of the PIP Joint; loss of the FDS tendon which is responsible for flexion at the PIP joint; a chronic mallet injury that has not been addressed; and destabilisation of joints due to inflammatory disease such as rheumatoid arthritis. Mallet injuries and volar plate injuries are not uncommon, and we see them particularly in ball sports when the PIP joint hyperextends or sustains a dorsal dislocation.

 fingeranatomy

(Image courtesy of www.jaaos.org)

Movement in the finger can be both difficult and painful with a swan-neck deformity as the tight bands struggle to descend over the PIP joint and tend to abruptly ‘snap’ over the joint when flexing. A painful sensation around the PIP joint is often reported.

While swan neck deformities sometimes require surgical intervention, we regularly resolve them with splinting to retrain the soft tissues and restore the delicate balance between flexion and extension that exists at each joint, and throughout the whole hand. Using splints and a therapy home program, we are able to slowly restore length to the tightened lateral bands and ligament. This way we can regain the equilibrium and restore normal movement.

With chronic conditions such as rheumatoid arthritis or cerebral palsy that can cause swan-neck deformities, or if your deformity does not respond to conservative treatment, you may require surgical intervention to make long-term improvements. In this case, your therapist liaises closely with your surgeon pre- and post-surgery to ensure your rehab is timely and effective, in order to maximise your outcome.

If you have questions about this deformity, talk to a hand therapist about what may be causing this for you and what treatment options are available.

Written by Louise Brown, Senior Occupational Therapist