What is a boutonniere deformity?
A boutonniere deformity is a specific finger injury where the middle joint (PIP joint) gets stuck in a bent position while the fingertip joint (DIP joint) hyperextends upward. The name comes from the French word for "buttonhole" — the tendon tears and the joint pokes through the gap like a button through a buttonhole.
This is not the same as a jammed finger or a mallet finger. It involves a specific tendon — the central slip of the extensor tendon — and it creates a distinctive posture that gets worse over time if left untreated.
How it happens in rugby
The most common mechanism is forced bending of a finger that is held straight. In rugby, this happens when:
- A finger gets caught in an opponent's jersey during a tackle and is forcibly bent backward or forward
- A direct blow to the top of the middle joint — such as a ball striking the end of the finger during a pass or catch
- A finger jams against the ground during a fall or ruck clearout
- Hyperflexion of the PIP joint during a grapple or maul — the finger is trapped and bent beyond its normal range
What does it look like?
In the first few days, the injury often looks like a simple jammed finger — swelling and pain at the middle joint, some difficulty straightening it. This is the window where it is most commonly missed. Over the next 1-3 weeks, if the central slip tear is not identified and splinted, the deformity develops:
- The middle joint (PIP) sits in a flexed position and becomes difficult to straighten
- The fingertip (DIP) hyperextends — it points upward when the hand is at rest
- Grip strength is reduced because the finger cannot close properly
- The finger looks crooked from the side — bent at the middle, tipped up at the end
Why early treatment matters
The central slip tear itself is not a difficult injury to treat — but timing makes all the difference. When the tear is identified early (within the first week), splinting the PIP joint in full extension for 6 weeks allows the tendon to heal in the correct position. The lateral bands stay where they belong, and full function is restored in most cases.
When the injury is missed, the lateral bands gradually slip below the joint axis over 1-3 weeks. Once they become fixed in this displaced position, the deformity becomes rigid. At that point, conservative splinting is much less effective, and surgery may be needed to reconstruct the extensor mechanism.
The splinting process
Treatment involves wearing a custom-made or prefabricated splint that holds the PIP joint in full extension. The DIP joint is left free — in fact, actively bending the DIP joint is encouraged because it helps pull the lateral bands back into their correct position above the joint axis.
- The splint is worn continuously for 6 weeks — 24 hours a day, including during sleep
- The splint is only removed for skin care and cleaning — a second person should hold the finger straight while the splint is off
- If the PIP joint bends at all during the splinting period, the 6-week clock resets
- After 6 weeks, gradual weaning from the splint begins — wearing it at night and during activity for another 2-4 weeks
- Active range-of-motion exercises start once the splint is removed during the day
Comparison with mallet finger
| Feature | Boutonniere deformity | Mallet finger |
|---|---|---|
| Tendon injured | Central slip (extensor) | Terminal tendon (extensor) |
| Joint affected | PIP joint (middle) | DIP joint (tip) |
| PIP position | Flexed (bent down) | Normal |
| DIP position | Hyperextended (tipped up) | Flexed (droops) |
| Splint duration | 6 weeks | 6-8 weeks |
| Onset | Gradual (1-3 weeks) | Immediate |
| Deformity direction | Opposite to mallet | Opposite to boutonniere |
Playing with a boutonniere injury
During the splinting phase, most players can continue to train and play with the splint taped securely to the finger. The splint holds the PIP joint straight, and taping prevents it from catching on jerseys or equipment. Discuss with your medical team whether the splint material is approved under your competition's rules — some leagues require soft splinting or padding over rigid splints.
Long-term outlook
When treated early and splinted correctly, most players recover full or near-full function. A small extension lag (5-10 degrees) at the PIP joint is common but does not affect grip strength or playing ability. Chronic boutonniere deformity — where the lateral bands are fixed in the displaced position — is much harder to treat and may require surgical reconstruction with a longer recovery period (3-6 months). The key message: treat it early.