A boutonniere deformity is a finger injury where the middle joint bends downward and the fingertip angles upward, creating a distinctive zigzag shape. It happens when a specific tendon on the back of the finger tears or stretches, disrupting the delicate balance of forces that keep the finger straight. Without treatment, a mild, correctable bend can progress into a stiff, permanent deformity.
How the Deformity Develops
Each finger has an extensor tendon that runs along the back of the hand and splits into three parts at the knuckle. The middle part, called the central slip, attaches to the base of the middle bone and is responsible for straightening the middle joint (the PIP joint). Two side parts, called lateral bands, continue further down the finger and straighten the fingertip joint (the DIP joint).
When the central slip tears, the middle joint loses its ability to fully straighten. But the damage doesn’t stop there. The lateral bands, no longer held in place, gradually slide down toward the palm side of the finger. Once they slip below the axis of the middle joint, they actually start pulling it into flexion instead of extension. Every tendon crossing the middle joint now bends it rather than straightening it. Meanwhile, those same displaced lateral bands pull harder on the fingertip joint, hyperextending it. The result is the characteristic posture: a flexed middle joint and a hyperextended tip.
The name “boutonniere” comes from the French word for buttonhole. The head of the middle bone pokes through the torn tendon like a button through a buttonhole.
Common Causes
The most frequent cause is a forceful blow to a bent finger, such as jamming it during sports. A ball striking the tip of an extended finger or a fall onto an outstretched hand can rupture the central slip. Cuts or lacerations over the back of the middle joint can sever it directly.
Rheumatoid arthritis is the other major cause. Chronic inflammation in the middle joint gradually weakens and stretches the central slip until it fails. Burns and crush injuries to the hand can also trigger the deformity. In rheumatoid patients, boutonniere deformity is common enough that it has its own treatment pathway, sometimes ending in joint fusion when the cartilage deteriorates.
Stages of Severity
The deformity is classified into three stages based on how much the joint has stiffened and whether the cartilage is damaged:
- Stage 1: Mild swelling with a slight extension lag of 10 to 15 degrees. The joint can still be passively straightened to full extension.
- Stage 2: The middle joint sits at 30 to 45 degrees of flexion. It may be only partially correctable or fully fixed, but the joint surfaces are still intact.
- Stage 3: A fixed flexion contracture with erosion of the joint cartilage. At this point, the damage is structural and permanent without surgery.
The progression from stage 1 to stage 3 can happen over weeks to months if the injury goes unrecognized. This is one reason early diagnosis matters so much: a flexible deformity responds well to splinting, while a fixed one often requires surgery.
How It’s Diagnosed
A boutonniere deformity can be subtle in its early stages. The finger may just look slightly swollen at the middle joint with a minor lag in straightening. Clinicians use a specific physical test to confirm the diagnosis.
You’ll be asked to curl your fingers around the edge of a table, then try to straighten the injured finger against resistance while the examiner presses down on the middle bone. If you can’t straighten the middle joint against that pressure, the central slip is impaired. X-rays help rule out fractures, particularly avulsion fractures where a small chip of bone gets pulled away with the tendon.
Splinting and Conservative Treatment
For acute injuries where the joint is still flexible, the standard treatment is splinting the middle joint in full extension for four to six weeks. During this time, the joint must stay completely straight at all times, with no exceptions, to allow the central slip to heal in the correct position. Even brief bending can disrupt the repair.
While the middle joint is immobilized, you’ll actively exercise the fingertip joint. Bending and straightening the tip over the edge of the splint, holding each position for about five seconds, helps pull the lateral bands back into their correct position on the top of the finger. This is a critical part of the process, not just a supplementary exercise.
After the initial immobilization period, gentle bending of the middle joint begins. A hand therapist will typically provide an angled board, and you’ll practice bending toward it, repeating 10 times every one to two hours. Each week, the angle increases depending on your progress. Nighttime splinting continues for another four to eight weeks to protect the healing tendon while you sleep.
Splinting alone yields a successful outcome in roughly 75 percent of cases when started early. For mild, passively correctable deformities, dynamic splinting (a spring-loaded splint that gently pushes the joint toward extension while allowing some movement) can help reduce the extension lag over time.
When Surgery Is Needed
Surgery becomes necessary in a few situations: when an avulsion fracture has displaced a bone fragment, when there’s an open wound that needs cleaning and direct repair, or when conservative treatment fails to restore function. Chronic deformities that have become partially or fully fixed often require surgical intervention after a period of therapy to regain as much passive motion as possible.
Several surgical approaches exist depending on the specific problem. Direct repair of the central slip works well for acute injuries. For chronic cases, surgeons may cut the terminal tendon near the fingertip to rebalance the forces across the finger, relocate the lateral bands back to their proper position, or reconstruct the torn tendon using a graft. In rheumatoid patients with a painful, stiff, and arthritic joint, fusing the middle joint in a functional position is sometimes the best option for reliable pain relief.
Recovery Timeline
Full recovery typically takes three to four months, whether treated with splinting alone or surgery. The first three weeks are the most restrictive. The middle joint stays locked in extension at all times, and the only active exercises target the fingertip joint.
From week three onward, controlled bending of the middle joint begins with gradually increasing range. Most people notice steady improvement in flexibility over weeks four through eight, though grip strength and fine motor control take longer to return. The final weeks of recovery focus on strengthening and regaining full use of the hand for daily tasks.
Patience during recovery is essential. Pushing the joint too hard or too early risks re-rupturing the healing tendon and starting the process over. On the other hand, delaying treatment or skipping therapy sessions increases the chance of a permanent contracture. The best outcomes happen when people follow the splinting schedule precisely and commit to the graduated exercise program under the guidance of a hand therapist.