Written by Shamaine Soh, Principal Hand Occupational Therapist at Phoenix Rehab, AHPC A1302343D.Clinically reviewed by Nigel Chua, Principal Hand Occupational Therapist & Director, AHPC A1300362Z.Last reviewed 7 October 2026.
A boutonniere deformity is a finger whose middle knuckle stays bent while the fingertip bends back, because the central slip, the tendon that straightens the middle knuckle, has torn. It usually follows a jammed finger or a cut over the middle knuckle. Treatment starts with a splint that holds the middle knuckle straight, with the fingertip free to bend.
Key takeaways
- A boutonniere deformity is a middle knuckle that stays bent and a fingertip that bends back. The cause is a torn central slip, the tendon that straightens the middle knuckle.
- It usually follows a jammed finger, a dislocated middle knuckle or a cut over the back of the middle knuckle. Rheumatoid arthritis can cause it slowly, with no injury.
- The bent shape can take days or weeks to appear, so a jammed finger that looks minor in the first week can still be a torn central slip.
- A closed injury is usually treated in a splint that holds the middle knuckle straight and leaves the fingertip free to bend. A cut, a crooked finger or a possible fracture needs a doctor first.
- Doctors call a central slip injury chronic once it is more than about 4 weeks old. Late is still worth treating, and a hand surgeon decides on surgery.
What is a boutonniere deformity?
The tendon that straightens each finger runs along the back of it. Over the middle knuckle, the proximal interphalangeal or PIP joint, it splits in three. The middle strip, the central slip, attaches just past the middle knuckle and straightens it. The two side strips, the lateral bands, run either side of the knuckle and carry on to the fingertip.
When the central slip tears, nothing pulls the middle knuckle straight. Over days and weeks the two side bands slide down the sides of the knuckle, below its pivot. From there they bend the middle knuckle instead of straightening it, and they pull the fingertip back.3 Doctors write it as PIP flexion with DIP hyperextension.2
Why is it called boutonniere?
Boutonnière is French for buttonhole. The middle knuckle pushes up through the gap between the two side bands, the way a button goes through a buttonhole.2 You will also see it called a buttonhole deformity, or, before the shape has appeared, a central slip injury.
The bent shape can take days or weeks to appear after the injury.3,4 In the first week the finger often looks like an ordinary jammed knuckle: swollen, sore on top, a little short of straight.
How it happens, in the order to check
1. A jammed finger, or a blow on a bent middle knuckle
A ball that catches the fingertip at netball or basketball. A block at volleyball. A bent finger driven into the floor, a wall or a car door. The middle knuckle is forced to bend further at the moment the tendon is pulling it straight.
2. A middle knuckle that dislocated
A middle knuckle that popped out of place and was pulled back on court can tear the central slip on the way. A finger that looked crooked and was put back still needs a doctor and an X-ray.
3. A cut or a burn over the back of the middle knuckle
A kitchen knife, broken glass, a sharp edge of sheet metal. The tendon sits under thin skin there, so a cut deeper than the skin can divide the central slip even while the finger still straightens. That needs a doctor the same day.
4. Rheumatoid arthritis, with no injury
Long-standing inflammation in the middle knuckle can stretch the central slip until the same shape appears, often on more than one finger. That road is led by your rheumatologist. See rheumatoid arthritis in the hands.
The middle knuckle test (the Elson test)
A surgeon described this test in 1986 to pick up a torn central slip early, before the buttonhole shape shows.1 Doctors and hand therapists use it in clinic. You can try a gentle version once at home, so you know what to ask about. Skip it if the finger looks crooked, if there is a cut, or if it hurts too much to bend.
- Rest your forearm on a table with the injured finger hanging over the edge, so the middle knuckle bends down to a right angle.
- With your other hand, hold the middle section of that finger down. Hold the middle section, not the tip.
- Try to straighten the middle knuckle up against that hand. Push gently.
- Watch the fingertip while you push.
If the middle knuckle pushes up firmly and the fingertip stays soft and floppy, the central slip is probably working. If the middle knuckle has little or no push and the fingertip goes stiff and straight while you try, the central slip may be torn.1 The tip stiffens because the side bands are trying to do the central slip’s job.
The test gives you a clue, and a doctor or a hand therapist should confirm it. A doctor decides whether you need an X-ray. In the first days, pain alone can stop you pushing, which makes the test hard to read.
Boutonniere, swan neck, mallet finger or a jammed finger?
Look at the finger at rest, then at what the middle knuckle and the fingertip do on their own.
| Condition | What happened | Middle knuckle | Fingertip | What it needs first |
|---|---|---|---|---|
| Boutonniere deformity (central slip injury) | A jam or blow on a bent middle knuckle, a dislocation, or a cut over it | Sits bent. Will not come fully straight on its own | Bends back, and is stiff to bend down | A doctor first for a cut, a crooked finger or an X-ray. A splint holding the middle knuckle straight, tip free |
| Swan neck deformity | Often after an untreated mallet finger, a loose volar plate, or rheumatoid arthritis | Bends backward past straight | Droops down | Assessment, and a splint that stops the middle knuckle bending backward |
| Mallet finger | A ball or a blow on the end of a straight finger | Normal | Droops, and will not straighten on its own | A doctor, an X-ray, and a splint holding the tip straight |
| Jersey finger | A gripping finger yanked straight | Bends normally | Will not bend on its own | A doctor the same day, then a hand surgeon |
| Jammed finger or sprain | A ball jams the fingertip, or the finger bends back or sideways | Swollen and sore. Comes straight on its own, and the Elson test is strong | Bends and straightens | Strapping or a splint, and an X-ray if a fracture is likely. See volar plate injury |
Swan neck and boutonniere are mirror images. In a swan neck the middle knuckle bends backward and the tip droops; in a boutonniere the middle knuckle bends down and the tip bends back.
Why the first weeks matter
Doctors call a central slip injury acute in the first weeks and chronic once it is more than about 4 weeks old.3 A closed injury seen within 4 weeks is often treated in a splint. Past 4 weeks a hand surgeon’s opinion comes into it, and results after surgery for a chronic deformity vary with how stiff the middle knuckle has become.3
The change over those weeks is mechanical. The side bands settle below the pivot of the middle knuckle and shorten there, and the fingertip stiffens in its bent-back position.3 Hand surgeons sort a long-standing boutonniere into four grades.5
- Grade 1. A slight deformity that still straightens when someone pushes it.
- Grade 2. A stiff, set bend, with tight side bands and the joint itself still clear.
- Grade 3. The plate on the palm side of the joint and the side ligaments have tightened, with scarring inside the joint.
- Grade 4. All of that, with arthritis in the middle knuckle.
Late is still worth treating. A chronic deformity that still straightens when pushed is often treated with splinting first.6 One that has set over months is a much harder joint to get straight, and some never fully do.
Early or late, the first stop for a middle knuckle that will not straighten is a doctor: your GP, a polyclinic, or the emergency department after a cut or a crooked finger. The doctor decides on an X-ray and refers you to a hand surgeon if the tendon has been cut, a piece of bone has come off, or the joint is unstable. Ask the doctor one question: is the central slip intact?
Boutonniere deformity treatment: who does what
- A doctor (your GP, a polyclinic doctor or the emergency department) examines the finger, decides on an X-ray, puts back a dislocated joint and refers you to a hand surgeon when you need one.
- A hand surgeon repairs a cut central slip, secures a large piece of bone that has come off with it, and decides whether a chronic deformity needs reconstruction.
- A hand therapist makes the splint, teaches the fingertip exercise, measures the middle knuckle at every visit and refers you back to the doctor if something does not add up.
The splint
The splint holds the middle knuckle straight and leaves the fingertip free. It stays on full time, day and night, typically for around 6 weeks, then often at night for some weeks more.3,4 The middle knuckle must not bend at any point in the full-time weeks, including in the shower. If it does, your therapist may restart the count.
At Phoenix the splint is a custom thermoplastic splint, molded to your finger at the first visit and reshaped as the swelling goes down. Your therapist shows you how to take it off for skin care with the finger flat on the table, so the middle knuckle never bends.
The fingertip exercise
With the splint on, bend the fingertip down as far as it goes, hold it there for a few seconds, then let it straighten. Your therapist sets the number, commonly 10 at a time, several times a day. Bending the tip keeps the side bands sliding over the knuckle and stops the fingertip setting in its bent-back position.3
The four stages
In the Phoenix Recovery Protocol the work starts at Calm & Protect: the splint, swelling control and the fingertip exercise. Move & Mobilize brings back middle knuckle bending in steps as the splint comes off, while we check at each visit that the knuckle still straightens on its own. Rebuild & Strengthen loads grip and pinch. Return & Perform tests the tasks themselves: the catch, the block, the keyboard, the wok handle. Most people buddy tape the finger for the first weeks back at ball sport. Your doctor’s or surgeon’s instructions set the weeks.
After a repair or a reconstruction, the Extensor Tendon Repair Recovery Program sets out each stage and what moves you up.
What we measure
- The middle knuckle test, written down. If it points to a torn central slip and you have not seen a doctor, we write to your doctor.
- Extension lag at the middle knuckle. How many degrees short of straight it stops on its own, and how far it goes when we straighten it for you. The gap between the two numbers tells us whether the tendon or the joint is the limit.
- Fingertip bend with the middle knuckle held straight. In degrees. A tip that will not bend in that position means the side bands are tightening.
- Swelling. A tape around the middle knuckle, week to week.
- Fingertip to palm. In centimeters, once bending is allowed.
- Grip and pinch. In kilograms, on both hands, once load is allowed.
Tested, not dated. The plan moves on when the measures say so.
What you can do this week
- Take off any rings on that hand now, before the finger swells further.
- Do the middle knuckle test once, gently. Repeating it tells you nothing new.
- Raise the hand above your heart and use a cold pack wrapped in a cloth for 10 to 15 minutes at a time.
- Do not buddy tape a middle knuckle that will not straighten. Taping lets it bend, which is the movement a torn central slip needs to avoid.
- Do not force the knuckle straight, and do not let a friend pull it.
- Write down the date and how it happened, and take that to the doctor.
- Pain relief and anti-inflammatory medication are a decision for your doctor or pharmacist.
Is this normal?
Usually expected: after a jam, swelling and soreness on top of the middle knuckle for some weeks. A middle knuckle that is stiff to bend when the splint first comes off, after weeks held straight. Thickening around the knuckle that takes months to settle. A knuckle that stops a few degrees short of straight for some weeks after the splint comes off.
Worth getting checked: a middle knuckle that will not come straight on its own a week or more after a jam. A fingertip that has started to bend back. A knuckle that sat straight in the splint and drops back into a bend once the splint is off.
When to see a doctor first
- Call 995 if a finger has been cut or torn off, or a wound is bleeding heavily and firm pressure does not slow it.
- Go to the emergency department now if the finger is cold, pale or blue, if it looks crooked or out of place, or if a cut over a knuckle came from a punch that hit teeth or from a bite.
- See a doctor the same day if the middle knuckle cannot be straightened on its own after an injury, if a dislocated finger was put back on court, or if a cut on the back of the finger goes deeper than the skin, even when the finger still straightens. After a repair, contact your surgeon the same day if you suddenly lose straightening, if the splint breaks or comes off, if the wound is red, leaking or more painful, or if you have a fever.
- See a doctor soon if the middle knuckle is still swollen and tender on top a week after a jam, if the fingertip has started to bend back, or if several fingers are drifting into a bent shape with swollen, stiff knuckles and no injury, which needs a doctor and may need a rheumatologist.
Also on this site: the page on finger joint pain covers what the spot that hurts tells you.
Where are you with this right now?
1. The middle knuckle comes straight, and it is settling
Hold the hand out flat. The middle knuckle comes all the way straight on its own, the fingertip bends and straightens normally, and the swelling goes down week by week. That is a jammed finger or a sprain behaving as expected. Finger sprain covers strapping and the return to ball sport. You do not need us for this, and we would rather say so.
2. It has been weeks, and the knuckle still sits bent
You strapped it to the next finger after the game and called it jammed. Three weeks on, the swelling has eased. The middle knuckle still stops short of straight, and when you lay the hand flat on the desk the fingertip tilts up.
The finger catches on the edge of your trouser pocket. Gloves snag on it. At the keyboard that finger lands on the knuckle instead of the pad. You have stopped going up for rebounds.
Waiting for it to loosen up made sense for a jammed knuckle. A torn central slip has nothing to loosen, and in your own weeks the knuckle has not come straight.
What our patients say
Google reviews from our clinics in Singapore.
The pain is down. Has anyone measured how far that knuckle straightens on its own?
Doctors count a central slip injury as chronic after about 4 weeks, so the date you jammed it is worth knowing. Start with a doctor if there was a cut, if the finger looked crooked, or if nobody has X-rayed it. If you cannot tell a stiff sprain from a torn central slip, one Assessment & Treatment with a hand therapist answers it: we run the middle knuckle test, measure the lag in degrees, and if the tendon is the problem, make the splint that day and write to your doctor.
If the knuckle has been bent for months and no longer straightens when pushed, the Stalled Recovery Review is three weeks with the same hand therapist. The first visit measures the lag at each joint. The next two measure how it responds. The Stiff Finger Joint Recovery Program sets out the stages for a joint that has set.
3. You have had the repair, or you have a date
The surgeon repairs or rebuilds the central slip. The weeks after decide whether the knuckle both straightens and bends. See the Extensor Tendon Repair Recovery Program, or hand therapy after surgery. Your surgeon’s protocol takes precedence.
If it is months on and the knuckle straightens when someone pushes it but not when you ask it to, that gap is worth measuring. The Stalled Recovery Review measures it at each joint and tracks how it responds over three weeks.
All of it runs on the same four stages. The Phoenix Recovery Protocol explains what each stage works on and what you have to meet to move up. No referral needed to start.
Next step
Find out which stage you are in
Pain is the first thing to leave. Movement and strength are the last things trained back, and most people stop before that part is done. One Assessment and Treatment is a single 45-minute appointment at $230, nett, no GST. Your therapist finds what is actually limiting you, treats it in the same appointment, and you leave with your current stage and a written plan.
Prefer to phone? Each of our five clinics has its own number on the clinics page. No referral needed to book.
Related reading
Sources: 1. Elson RA. Rupture of the central slip of the extensor hood of the finger. A test for early diagnosis. J Bone Joint Surg Br. 1986;68(2):229-231. 2. Coons MS, Green SM. Boutonniere deformity. Hand Clin. 1995;11(3):387-402. 3. Boutonniere Deformity. In: StatPearls. Treasure Island (FL): StatPearls Publishing; updated 6 March 2026. NCBI Bookshelf NBK470323. 4. British Society for Surgery of the Hand. Boutonnière injury, patient information leaflet. BSSH; 2008. 5. Žyluk A. The relative motion flexion splinting in the treatment of boutonnière deformity of the finger: presentation of the method and a review of the literature. Pomeranian J Life Sci. 2025;71(3):6-9, reporting the Burton classification (Burton RI. Extensor tendons, late reconstruction. In: Green DP, ed. Operative Hand Surgery. Churchill Livingstone; 1988). 6. Urbaniak JR, Hayes MG. Chronic boutonniere deformity: an anatomic reconstruction. J Hand Surg Am. 1981;6(4):379-383.
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