Boutonniere deformity is a condition where one’s fingers present in a deformed position. Specifically, the joint nearest the knuckle (the proximal interphalangeal joint, or PIP) is permanently bent toward the palm while the farthest joint (the distal interphalangeal joint, or DIP) is bent back away.

The Anatomy Behind the Deformity

This deformity occurs following an injury to the tendons that allow our fingers to straighten as needed. The anatomy of the extensor tendons (tendons that extend or straighten your finger) is very complex, meaning that there are a number of injuries that can interfere with the functions of our fingers.

Let’s take a closer look at this complex anatomy:

  • The muscles for the main extensor tendons to the fingers are located in the forearm. 
  • The extensor tendon to the finger (extensor digitorum) runs on the back or dorsum of the hand, down to the knuckle, or MCP joint. It attaches to a fibrous band called the Sagittal Bands, which wraps around the base of the first finger bone (Proximal Phalanx). This attachment allows the Extensor Digitorum to pull the finger up at the MCP joint and extend the finger at the knuckle. 
  • The Extensor Digitorum then travels further to attach to the Middle Phalanx or middle finger bone. At that point, it is called the Central Slip. Pulling or tension on the Central Slip straightens or extends the middle joint or PIP joint. 
  • Extensions of the Extensor Digitorum called the Lateral Bands extend out from either side of the Extensor Digitorum and are joined by tendons from the small intrinsic muscles located deep in the hand. The Lateral Bands run toward and connect at the last bone, or Distal Phalanx. They form the Terminal Tendon, which is used to extend or straighten the last joint or DIP joint. 
  • The extensor tendons at this level are covered by peritenon, a slick layer of tissue which allows gliding. The extensor tendons, in general, are thinner than the powerful flexor tendons and glide together as a sheet over the finger.

As you can see, the extensor mechanism is complex, elegant and delicate.

The Causes

A laceration or injury to the top (dorsum) of the finger near the middle joint (PIP joint) may injure the Central Slip, causing the finger to droop downward at the PIP joint. When this happens, the Extensor Digitorum retracts and becomes slack, allowing the Lateral Bands to separate and slip down towards the palmar side of the finger. This allows the PIP joint to “buttonhole” or stick up through the extensor mechanism. When the PIP joint is flexed, increased tension moves through the Lateral Bands out to the terminal tendon at the DIP joint. This causes the DIP joint to become hyperextended. This deformity is known as a buttonhole, or Boutonniere Deformity. 

Initially, the finger may be very flexible with a simple inability to completely straighten the middle (PIP) joint. After several weeks, however, the finger may become stiff in this deformity as the Lateral Bands become scarred. In such cases of chronic Boutonniere Deformity, the patient may have difficulty flexing the stiff DIP joint and difficulty straightening the stiff PIP joint.

Patient's with this condition often complain of both pain and stiffness.

The Treatment

Acute Cases

Treatment of an acute traumatic Boutonniere Deformity may be conservative in cases where a stretch injury to the PIP joint and central slip has occurred. In these cases, an extension splint is fitted to the PIP joint, allowing the MCP joint and DIP joint to move. The PIP joint is held in extension for 6 to 8 weeks, allowing the central slip and lateral bands to heal. That is then followed by therapy to mobilize all 3 joints. Success rates with conservative treatment are between 80 to 85%. There may be some minor residual flexion at the PIP joint, but the finger is mobile and very functional.

In cases of laceration to the Central Slip, or cases where conservative treatment of an acute injury has failed, surgery may be required. This surgery is performed on an outpatient basis, with general anesthesia or axillary block anesthesia. An incision is made on the top of the PIP joint and the Central Slip is repaired. The Lateral Bands are mobilized and placed back up on top of the finger. 

In cases where the Central Slip has torn off the middle phalanx or been stretched out, it may be repaired back to the bone with small anchors. A pin may be placed across the PIP joint to hold it straight while the repairs heal. A splint is then applied across the PIP joint and early therapy is started to mobilize the DIP joint and MCP joint during the healing process. Usually, at 4 weeks the PIP joint pin is removed and gentle mobilization techniques are implemented. 

Surgical risks with this procedure and clinical condition include anesthesia-related risks, as well as problems with wound healing or infection. Stiffness of the finger can also occur.

Chronic Cases

Treatment of a chronic case of Boutonniere Deformity first involves mobilizing the stiff joints. This may be accomplished through occupational therapy techniques and/or utilizing a dynamic/progressive splint to straighten the finger. 

Once the finger joints have been straightened and mobilized, the tendon problem can be addressed. 

In a small number of cases, the joint cannot be straightened and a capsulotomy must be performed, where the scar tissue around the joints is released. The surgery is performed on an outpatient patient under general or axillary block anesthesia. Once again, an incision is made on the top (dorsum) of the finger. The Central Slip and the Lateral Bands must first be freed from scar tissue and mobilized, and then placed back in their original position. The central slip is reattached to the middle phalanx at its proper length. The PIP joint is usually pinned with the finger in extension to protect the repair. 

Afterwards, a protective splint is applied to hold the PIP joint in extension. Early mobilization of the DIP joint and MCP joint is addressed in therapy. The pin is then usually removed at 4 weeks and mobilization of all 3 joints is continued as needed. 

Surgical risks and risks with this condition are anesthesia-related, as well as related to problems with wound healing, infection, or stiffness of the finger.