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The Injury That Looks Fine on Day One and Bends Three Weeks Later
Boutonnière deformity is a finger stuck bent at the middle joint, with the fingertip pulled backwards. It comes from a torn central slip, the tendon strap that straightens the middle joint.
Caught in the first few weeks, it’s treated with a splint holding the middle joint dead straight, full time, for about 6 weeks, plus fingertip bending exercises. Then 4 to 6 more weeks of weaning. Most people are back to normal use by around 3 months, without surgery.
The name comes from the French for buttonhole, because the knuckle pokes through the tendon like a button through cloth.
And here is the thing that makes this injury genuinely dangerous, which almost nothing else on this site does:
On the day it happens, the finger usually looks normal. The deformity develops over the following one to three weeks, quietly, while everyone involved is treating it as a jammed finger.
Buddy-tape it, “give it time”, and by week 3 the middle joint has curled and started to stiffen in that bend. Now a 6-week splint job has become months of casting, with a less certain finish.
What is boutonnière deformity, and what’s actually happening in there?
The tendon that straightens your finger doesn’t arrive at the middle joint as one cord. It splits into three straps.
The middle one, the central slip, attaches to the top of the middle bone and is what actually straightens the middle joint. The two outer ones, the lateral bands, run down either side and past the middle joint to straighten the fingertip. (The full map is in extensor tendon injuries by zone.)
Boutonnière is the central slip tearing off.
Straight after that happens, the finger still works reasonably well, because the two side straps are intact and can still partly do the job. Sore, swollen, a bit weak…reads exactly like a bad jam.
But those side straps were being held up on top of the joint by the central slip. With it gone, they gradually slide down the sides of the finger, and once they slip below the axis of the joint, their pull reverses.
They stop straightening the middle joint and start bending it. And because they’re now pulled tight, they yank the fingertip backwards at the same time.
(That’s the deformity. It isn’t a new injury at week 3. It’s the same injury finishing its slow collapse.)
How does a boutonnière injury happen?
Four routes, and they’re worth knowing because two of them get missed constantly.
- A forced bend of a straightened finger. Ball to the fingertip, finger caught and jammed downwards.
- A cut over the top of the middle knuckle. Obvious at the time, and still frequently underestimated.
- A dislocation where the joint went forwards rather than backwards. This is the one I flagged in the dislocation article: it damages the central slip, and if it gets splinted the standard way it becomes a boutonnière over the next few weeks.
- Inflammatory arthritis. In rheumatoid arthritis the same slip gets eroded rather than torn, and the same collapse follows slowly over years.
How is a central slip injury diagnosed before the finger bends?
Since waiting for the finger to bend means waiting too long, there’s a specific test for catching it early. It’s called the Elson test.
Hang the injured finger over the edge of a table so the middle joint is bent to a right angle. Now try to straighten that middle joint against gentle resistance, while somebody watches the fingertip.
If the central slip is intact, the fingertip stays floppy and relaxed.
If it’s torn, the side straps have to do all the work, and the fingertip goes rigid and kicks backwards.
The other early signs:
- Tenderness on TOP of the middle knuckle, pinpointed, rather than on the sides (sides point more to a collateral ligament sprain).
- A lag of about 20 degrees or more when you try to fully straighten that joint in the first week.
- An X-ray, mainly to look for a flake of bone pulled off the top of the middle bone, or a joint that isn’t sitting square. A normal X-ray does NOT rule out a central slip tear, cos the tendon doesn’t show up on it.
- Ultrasound, sometimes, when the examination is unclear.
By the time it looks like a boutonnière, the easy treatment window has already closed.
Which window are you in?
This injury runs on a clock. Name the window, find where you are in it, act while it’s open.
- OPEN (roughly the first 3 weeks): the joint still straightens fully when someone gently pushes it straight. A splint started now has the best odds.
- CLOSING (weeks to a few months): the bend is showing and the joint resists being pushed straight. Still fixable without surgery in many cases, but the straightening has to be won back first, slowly.
- SHUT for the original goal (a fixed, long-standing bend): the goal changes from “perfect finger” to “a finger that works and doesn’t catch on things”. Casting, splinting and sometimes surgery still help…the finish line just moves.
Can boutonnière deformity be fixed without surgery?
Usually, yes, if it’s caught early. This is a splinting problem, and the splinting is beautifully specific.
The middle joint gets held dead straight, continuously, for around 6 weeks. Same discipline as mallet finger: continuously means continuously, and letting it bend restarts the clock.
But the fingertip is deliberately left OUT of the splint, and you’re given exercises to bend that fingertip actively, many times a day.
That’s not a comfort measure. Bending the fingertip pulls the side straps back up over the top of the joint where they belong, and stops them tightening in their collapsed position. The splint protects the healing slip; the fingertip exercises stop the collapse happening around it. Both halves, or it doesn’t work.
How long do you wear a splint for boutonnière?
- Type: a middle-joint extension splint, usually a small custom-molded thermoplastic finger gutter or cylinder splint, sometimes a cast. The fingertip joint stays free.
- Hours: 24 hours a day, including showers and sleep, for about 6 weeks. If it has to come off for skin care, the finger is kept flat on a table so the middle joint never bends.
- Weaning: from about week 6, the splint comes off for short exercise sessions, then for longer periods. Nights and risky activities usually stay splinted until around weeks 10 to 12.
- Restart rule: if the middle joint droops again when the splint is reduced, you go back a step. It’s not failure, it’s the tendon telling you it needs longer.
What exercises help a boutonnière injury?
Your therapist will set the exact program. In my experience, a typical early version looks like this:
- Fingertip bends, in the splint (from week 1): with the middle joint held straight in the splint, bend the fingertip as far as it goes, hold 3 seconds, relax. 10 reps, every 2 hours while awake.
- Big knuckle bends (from week 1): bend the finger at the knuckle where it meets the hand, keeping the splinted joint straight. 10 reps, same sessions. Keeps the rest of the hand from stiffening while one joint is locked out.
- Gentle middle-joint bending (from about week 6, when cleared): small active bends, 10 reps, 3 to 4 times a day, increasing range a little each week. Active only…no forcing it with the other hand.
- Straightening check: after each session, the joint should still straighten fully on its own. If it doesn’t, cut back and tell your therapist.
Boutonnière recovery time, week by week
Your surgeon or therapist may give you different dates. Use theirs.
- Weeks 0 to 6: middle joint splinted straight full time, fingertip bending exercises daily. Swelling control alongside: hand up, and gentle compression if your therapist suggests it.
- Weeks 6 to 8: splint weaned gradually, often kept for nights and risky activities. Gentle active bending of the middle joint begins.
- Weeks 8 to 12: range and strength rebuild. A small residual loss of the last few degrees of straightening is common and usually doesn’t matter functionally.
- Months 3 to 12: swelling around that knuckle keeps receding slowly, same long tail as any middle-joint injury. A slightly thicker knuckle can be permanent.
What if the finger is already bent? Late boutonnière and surgery
Caught late, once the joint has stiffened into the bent position, it’s a much looooooonger road: serial casting or static progressive splinting to regain the straightening first, over weeks to months, and only then any question of surgery.
Surgery enters earlier in a few specific cases:
- An open cut through the tendon over the knuckle. That gets washed out and repaired, not just splinted.
- A large bone fragment pulled off with the tendon, or a joint that won’t sit square.
- An established deformity that still limits function after a proper course of casting and splinting.
Reconstructive surgery for an established boutonnière has a mixed reputation among hand surgeons for a reason. Results are modest, and you still need the stiffness sorted before most surgeons will operate.
Can I work, drive and play sport with a boutonnière splint?
- Desk work: usually within days, splint on. Typing with one finger splinted straight is clumsy, not harmful.
- Manual work: light duties with the splint on in the first 6 weeks if the splint stays protected and dry. Heavy gripping usually waits until around weeks 10 to 12.
- Driving: often possible with a single finger splint, as long as you can grip the wheel and control the car in an emergency. Check with your doctor and your insurer. See driving after a hand injury.
- Ball and contact sports: not in the first 6 weeks. After that, often with a protective splint or taping for another 4 to 6 weeks, if your surgeon or therapist agrees. Unrestricted play is usually around 3 months.
What a hand therapist does differently
- Molds the splint to hold the joint at 0 degrees, not “roughly straight”, and remolds it as the swelling falls, cos a loose splint lets the joint creep back into a bend.
- Measures the straightening lag with a goniometer each visit, so drift gets caught in degrees, not by eye.
- Checks the skin over the knuckle. Constant pressure on a swollen finger can break skin down quickly.
- Times the weaning to what the tendon shows, not to the calendar alone.
The short version
A jammed or dislocated middle knuckle that’s tender on TOP and can’t quite straighten is a central slip injury until someone proves otherwise, and it will look almost normal for two more weeks while it quietly collapses.
Six weeks of a splint now beats months of casting later, and beats an operation with modest odds after that.
Get it checked today if
- There’s a cut over the middle knuckle, however small. Tendon damage and joint infection both start here.
- The finger was dislocated and is still out of shape, or it went back in but won’t straighten fully.
- The fingertip is numb, white, cold or blue.
- The skin under your splint is white, blistered or broken, or the finger is throbbing and darkening inside it.
Get it checked if
- A jammed finger is tender on top of the middle knuckle and can’t fully straighten after a few days.
- The fingertip kicks back on the table test above.
- The middle joint is starting to bend and the fingertip to tip back, 1 to 3 weeks after an injury.
- The joint droops again each time the splint is reduced.
The tendon tears in a second. The bend takes three weeks. That’s your head start…use it.
Written by Nigel Chua, hand occupational therapist in practice since 2005. Thousands of hands, wrists and elbows assessed and treated. My credentials are here. This article explains; it doesn’t examine. A finger that can’t fully straighten at the middle joint after an injury needs looking at this week, not when it starts to bend.
Every article on this site is written using the Closing Window Method: name the window your condition runs on, find where you are in it, and act while it’s still open.