Michael W Bowman M.D. FACS
The anatomy of the extensor tendons (tendons that extend or straighten your finger) is very complex. 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. See figure 1. It attaches to a fibrous band called the Sagittal Bands that wrap 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. Thus, as seen in figure 1, the extensor mechanism is complex, elegant and delicate.
A laceration or injury to the top or dorsum of the finger near the middle or PIP joint may injure the Central Slip, causing the finger to droop downward at the PIP joint. 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. The PIP joint is flexed and increased tension through the Lateral Bands out to the terminal tendon at the DIP joint 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 simple inability to completely straighten the middle or PIP joint. After several weeks the finger may become stiff in this deformity as the Lateral Bands become scarred down. 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 complain of both pain and stiffness.
Treatment of an acute traumatic Boutonniere Deformity may be conservative in cases where a stretch injury to the PIP joint and central slip have occurred. 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 been 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 as an outpatient 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 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 begun. Surgical risks with this procedure and clinical condition include anesthesia related risks, wound healing problems or infection, stiffness of the finger.
Treatment of a chronic Boutonniere Deformity first involves mobilizing the stiff joints. This may be accomplished by occupational therapy 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 as an outpatient under general or axillary block anesthesia. Once again an incision is made on the top or dorsum of the finger. The Central Slip and the Lateral Bands must be freed from scar tissue and mobilized to be 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 started in therapy. The pin is usually removed at 4 weeks and mobilization of all 3 joints continued. Surgical risks and risks with this condition are anesthesia related risks, wound healing problems or infection, stiffness of the finger.