A Closer Look At Boutonneire and Swan Neck Deformities
Finger deformities can greatly interfere with everyday tasks. Two finger deformities that are complex to treat are a boutonniere deformity and a swan neck deformity. Look at the back of your hand and divide your finger into three sections. A posttraumatic boutonneire deformity is when the middle section bends and the tip of your finger bows. A swan neck deformity is when the middle section bows and the tip of your finger flops down towards your palm. Both of these deformities involve the extensor mechanism of the finger which consists of three muscles and their tendons working intricately together to provide knuckle stabilization and the ability to straighten your fingers. Disruption to these muscles and their tendons, via dislocation, laceration, or blunt trauma causes this extensor mechanism to malfunction.

Because a boutonneire deformity can progress quickly after injury and become permanent, a fast diagnosis is crucial. An Elson test has proven the most reliable test to detect a boutonneire deformity, which involves a hand specialist holding your finger a certain way and asking you to move. Diagnosis should also include an x-ray to rule out any fractures. Once a boutonneire deformity is detected the middle section of your finger is splinted for four to eight weeks and very specific daily exercises are perform with the tip of your finger. Following that time period, the middle section of your finger is given specific exercises but the splint must still be worn at night for another four to six weeks. Surgery is necessary if conservative treatment fails, or if there is coinciding joint damage or a fracture. The surgeon will insert pins into the bone and a splint is worn for at least six weeks followed by pin removal and specific exercises for full return to function. If there is a long standing boutonneire deformity, it is often recommended to simply live with it as the outcomes can result in loss of the ability to flex your finger.

A swan neck deformity can develop over time due to hypermobility of the finger tip joint, tight hand or wrist muscles, or a traumatic event of hyperextension of the middle joint of the finger. Sometimes it is caused by inflammatory arthritis and, if this is the case, the patient should seek help from a rheumatologist. Otherwise, a Bunnell test, or a muscle length test, combined with an x-ray is adequate for diagnosis. Conservative treatment consists of a low-profile splint. If patients elect to have surgery, there are multiple procedural options, all of which involve splinting and very specific finger exercises for a minimum of six weeks.
Mckeon, K., MD and Lee, D., MD. Posttraumatic Boutonniere and Swan Neck Deformities. Journal of the American Academy of Orthopaedic Surgeons . October 2015. Vol. 23, No. 10. Pp. 623-632.