Boutonniere deformity causes the middle joint in a finger or thumb to bend inward and the end joint to bend outward.

It is possible to correct this using a splint, but sometimes, other treatments are necessary.

Boutonniere deformities can result from injuries to the tendons that run along the backs of the fingers or thumbs. They are different to “swan neck deformities,” which affect the base joint.

This article discusses what boutonniere deformities are, their causes, and some possible treatment options.

Definition

A person may have a boutonniere deformity in the middle joint of any finger or the thumb.
Image credit: Alborz Fallah, 2013
A boutonniere deformity occurs when the middle joint of a finger bends inward, while the joint at the end points outward. It can affect any finger or the thumb.

It is easy to confuse a boutonniere deformity with a swan neck deformity. A swan neck deformity occurs when the base joint of the finger, rather than the middle joint, bends inward.

Diagnosis
To diagnose a boutonniere deformity, a doctor will physically examine the fingers and hand.

They will check the position of each joint to rule out similar deformities, such as swan neck deformity.

The doctor will also assess a person’s medical history. They will look for conditions that increase the risk of a boutonniere deformity, such as arthritis.

They may also use medical imaging, such as X-rays, to check for any signs of bone damage.

Causes and symptoms
A boutonniere deformity can occur due to an injury or an underlying health condition. Damage to the tendon that runs along the back of the finger or thumb joint is usually the primary cause.

The injury usually occurs at the middle phalanx extensor tendon, which is located at the bottom of the tendon. This causes the joint bone to push out through the tendon, creating the deformity.

Rheumatoid arthritis is another possible cause of a boutonniere deformity. Rheumatoid arthritis and similar conditions, such as psoriatic arthritis, can cause inflammation in the tendons of the finger. Over time, this can weaken or damage the tendon, causing the joint to bend.

This irregularity can make it difficult for a person to straighten their finger or thumb. It may also get worse over time.

Boutonniere deformities can lead to problems using the finger. For example, it may be difficult to type on a computer or grip an object.

It is important to get prompt treatment to help prevent the irregularity from getting worse.

Treatment
With early treatment, it is usually possible to correct a boutonniere deformity without leaving permanent damage. Treatments can either be surgical or nonsurgical, depending on the severity of the irregularity.

Splints are a common form of nonsurgical treatment. A splint is a device that can attach to the finger to provide support.

These are useful for keeping the finger in a straight position. Wearing the splint can allow the joints to gradually return to their normal positions.

Splints are most useful when the cause is a tendon injury and the treatment is prompt. The length of time the splint will be necessary for depends on the severity of the injury and the person’s age.

For example, a young person may need to wear a splint for up to 6 weeks, whereas an older adult will wear the split for around 3 weeks.

A doctor or hand specialist will usually check on a person’s progress several times while they are using a splint. During this time, it is best to avoid engaging in contact sports, playing an instrument, or doing any other activities that can cause further damage to the finger.

If the deformity is due to a condition, it may require more than just a splint. For example, a doctor may prescribe corticosteroids to reduce inflammation in the tendons.

When the tendon is severed or other treatments do not work, a doctor may recommend surgery.

During surgery, a health professional may cut an area of the tendon to release pressure on the joint. They may also insert a screw or wiring to straighten the joints, similar to a splint. This fuses the joint in a fixed position.

Surgical treatment is more common when a boutonniere deformity stems from a condition, such as rheumatoid arthritis.

Exercises
When a person is no longer using a splint and the fingers are in the final stages of healing, a doctor may suggest some exercises to stretch the fingers. These can help increase strength and flexibility in the tendon.

For example, they may suggest bending the fingers from the base down toward the palm until they reach a 90 degree angle. Keep the fingers as straight as possible and hold the position for a few seconds.

Or, they may recommend only bending the tips of the fingers slightly toward the palm and holding for a few seconds.

A doctor will advise on if and how often to perform these exercises, as well as when it is best to start. It is vital to discuss any exercises with a doctor or hand specialist before doing them to prevent further injury.