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Four Signs. If You Have All Four, GO TO THE ER NOW.
If your whole finger is evenly swollen, resting slightly bent, tender along the palm side, and agony when someone straightens it, go to the ER now. Those are Kanavel’s four signs of a flexor tendon sheath infection (pyogenic flexor tenosynovitis). It’s a surgical emergency: most cases need the sheath washed out in the operating room, plus IV antibiotics. Then expect around 6 to 12 weeks of hand therapy to stop the tendon scarring stiff.
Almost everything else on this site can wait until morning.
This one can’t.
A flexor tendon sheath infection is bacteria growing inside the closed tunnel that your flexor tendon slides through. It’s a sealed space with poor blood supply, which makes it a very good incubator and a very bad place for your immune system to fight.
Left for a day or two, the tendon inside that tunnel can die. What follows is a finger that never bends properly again, and occasionally a finger that has to come off.
So the first half of this article has one job: help you recognize it. The second half is for after the surgeon has done their part, cos that’s when the stiffness fight starts.
Kanavel’s four signs: how to check your finger
A surgeon named Allen Kanavel described these over a century ago and they’ve never needed improving. Check all four.
- The finger rests slightly bent. Not held bent by you. Resting bent, because that’s the position where the swollen sheath is least stretched.
- The whole finger is swollen, evenly. Sausage-shaped, base to tip, rather than swollen around one joint or one spot.
- It’s tender along the whole tendon, down the palm side of the finger and often into the palm itself. Not tender at one point. Tender along a line.
- Straightening it hurts severely. Have someone gently straighten the finger. Sharp, disproportionate pain is the most telling sign of the four, and often the first to appear.
All four, or three of four in a finger that’s getting worse by the hour: go to the ER now. Tonight. Not a doctor’s appointment on Thursday.
A whole finger swollen like a sausage, resting bent, that screams when you straighten it. Those three sentences are the entire diagnosis.
Is a flexor sheath infection an emergency?
Yes. In Closing Window terms, this window is CLOSING from the first hours, not the first weeks.
Most hand problems give you weeks to decide. This one gives you hours to a day or two. Pus inside the sheath raises the pressure in a tunnel that can’t expand, which squeezes the tendon’s blood supply. And the longer the tendon sits in pus, the more its smooth gliding surface turns into scar.
Get the timing wrong in one direction and you’ve spent an evening in the ER for something that turned out to be a sprain. Get it wrong in the other and you keep a finger that won’t make a fist. Only one of those mistakes is permanent.
How it starts, and why the wound looks so unimpressive
This is the part that fools people.
The entry point is usually tiny:
- A splinter.
- A fish bone or a fish spine.
- A rose thorn.
- A cat’s tooth.
- A needle at work.
- A strand of hair.
Something so small you may not remember it, and something that has already scabbed over by the time the finger blows up.
The palm side of the finger is where it matters, because that’s where the sheath sits closest to the skin. A small puncture there, on the front of the finger or in the crease lines, can deposit bacteria directly inside the tunnel. A cat bite is the classic way in: small holes, deep teeth.
Then there’s a gap of a day or two while nothing much happens, followed by a finger that swells and stiffens fast.
(I’ve had patients apologize for wasting my time on the way to hospital, because the cut was so small. The size of the wound tells you nothing about what went through it.)
What else it could be
Three things get mixed up with this, and the difference is where the swelling lives.
- Paronychia or felon. A paronychia sits at the nail fold. A felon sits in the fingertip pad. Both are infections, both matter, and neither swells the whole finger evenly.
- A jammed or sprained finger. Swells mostly around one joint, and straightening it is uncomfortable rather than agonizing. There’s usually a clear moment it got hit.
- Gout. Gout can produce a red, hot, exquisitely painful finger that looks close enough to this to fool anyone, including me. Which is one of the reasons the assessment happens in a hospital and not on a website.
If the problem is one joint that won’t let you move it at all, or redness in the skin with a finger that still bends, read cellulitis or septic arthritis. The same rule applies there: when in doubt, go tonight.
How it’s diagnosed
Mostly with the hands and eyes of someone who has seen it before. The four signs carry the diagnosis. Tests support it:
- Examination. Kanavel’s signs, the wound if there is one, and how far the redness has spread into the palm.
- Bloods. White cell count and inflammation markers (CRP, ESR). Helpful, but normal bloods don’t rule it out.
- X-ray. Looks for a retained splinter, fish spine, tooth fragment or needle tip.
- Ultrasound. Sometimes used to look for fluid inside the sheath when the picture is unclear.
How it’s treated: antibiotics or surgery?
Caught genuinely early, within the first day and with mild signs, some cases settle with admission, IV antibiotics, splinting and elevation, watched closely by hand surgeons. If it isn’t clearly better quickly, it goes to the operating room.
Most need surgery.
The sheath is opened and washed out, sometimes through two small incisions with a thin catheter flushing between them, sometimes more extensively. Antibiotics follow, and the finger is elevated and splinted. Your surgeon and the infection team decide the antibiotic course, not this page.
Then the second half of the problem starts, and this is my half.
Why the stiffness afterwards is the real fight
Infection inside a tendon sheath does what nothing else does: it turns the smooth gliding surface into scar. The tendon that used to slide freely now drags.
So the rehab is a race.
You need movement early enough to keep the tendon gliding while the scar is still soft, and gentle enough not to damage a tendon that has just been through an infection and an operation.
Recovery after a flexor sheath washout, week by week
Your surgeon’s protocol comes first. This is what the usual path looks like.
- Days 1 to 3: a splint usually holds the hand in the safe position (knuckles bent, fingers straight) so the ligaments don’t shorten. Hand above heart level, almost constantly. Swelling is what turns into stiffness. See normal wound healing or infection for what the incisions should look like.
- As soon as your surgeon allows, often within the first few days: gentle movement starts. Full bend and full straighten of the fingers that are allowed to move, several times an hour while awake.
- Weeks 1 to 4: daily tendon gliding work, several short sessions rather than one long one. Splinting between sessions so the finger doesn’t settle into a bent position.
- Weeks 4 to 12: pushing range, scar work once the wounds have healed (see scar management after hand surgery), gradual strengthening.
- Months 3 to 12: whatever range you have at three months is broadly what you keep, with slow gains after that.
In my experience, most fingers treated early are back to daily function within about 3 months. A finger that arrived late may never get every last degree of bend back.
Exercises after flexor tenosynovitis surgery
Only once your surgeon or hand therapist has cleared you to move. Gentle, never forced through sharp pain.
- Tendon glides. Five positions in a row: fingers straight, hook fist (knuckles straight, finger joints bent), full fist, tabletop (knuckles bent, fingers straight), straight fist (fingertips to the base of the palm). Hold each 3 to 5 seconds. 10 rounds, 5 to 6 times a day.
- Blocking. Support the finger just below the middle joint with your other hand and bend only that joint. Then the same for the end joint. 10 each, 3 to 4 times a day, usually from around week 2 to 3 when your therapist says the tendon can take it.
- Straightening. Rest the hand flat on a table and gently press the finger straight. Hold 10 to 20 seconds, 5 times, 3 to 4 times a day. A finger that stays bent at rest is a finger that’s stiffening.
The trap: waiting for the swelling to go down before moving. It doesn’t work that way round. Movement helps clear the swelling. See stiff hand and fingers after a cast, splint or surgery.
When can I work, drive and use my hand normally?
Typical ranges after surgery for a sheath infection. Your surgeon’s advice overrides these.
- Desk work: often 1 to 2 weeks after discharge, once the wound is dry and you can type with the hand elevated between tasks.
- Wet or dirty work (kitchens, cleaning, farming, healthcare): not until the wounds are fully healed, usually 2 to 3 weeks or more, and with gloves after that.
- Heavy manual work: often 6 to 12 weeks. Grip strength is the slow part.
- Driving: once you can grip the wheel firmly, are off strong painkillers, and could control the car in an emergency. Often 2 to 4 weeks.
- Gym and racquet sports: usually from around 8 to 12 weeks, building up gradually.
Who needs a lower threshold
Diabetes (see the diabetic hand), immune-suppressing medicine including biologics and long-term steroids, chemotherapy, and kidney disease. In these groups the usual signs, fever and severe pain included, can be muted while the infection moves. If you’re in one of these groups, “maybe tomorrow” becomes “go now.”
Many people get a good, functional finger back after this. A meaningful number end up with permanently reduced bend, and the ones who do are overwhelmingly the ones who arrived late.
Get it checked today if
Go to the ER now if:
- A whole finger is swollen evenly, resting bent, and straightening it is severe pain.
- The finger is tender along the palm side from tip to palm.
- Redness or swelling is spreading into the palm, or red streaks are tracking up the arm.
- You have a fever of 38°C (100.4°F) or higher, shivering, or feel properly unwell.
- A puncture wound on the palm side of a finger is followed by a finger that’s swelling and stiffening over a day or two.
See a doctor today if:
- A small wound on the front of a finger is red and sore, but the finger still bends and straightens.
- You’re on antibiotics for a finger infection and it isn’t clearly better at 48 hours.
Call your surgeon today if (after surgery)
- Fever, increasing redness, fresh pus, or pain that’s climbing after it had settled.
- The finger is moving LESS at week 2 than it was at the end of week 1.
- New numbness down one side of the finger.
Puncture wounds from bone, fins and hooks are a classic way in for this infection. See butcher and meat processing hand injuries and fishing hand injuries.
The wound was tiny. The deadline isn’t. Go tonight, then fight for the bend.
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. If you have the four signs above, stop reading and go.
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.