Four Signs. If You Have All Four, GO A&E NOW.
Almost everything else on this site can wait until morning.
This one can’t.
A pyogenic flexor tenosynovitis 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 this article is short and it has one job: help you recognize it.
Kanavel’s four signs
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 pull the finger straight. Sharp, disproportionate pain is the most telling sign of the four, and usually the first to appear.
All four, or three of four in a finger that’s getting worse by the hour: go to an emergency department now. Tonight. Not a GP 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.
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.
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 apologies 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 it isn’t
Three things get mixed up with this, and the difference is where the swelling lives.
- 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 agonising.
- And 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.
What treatment involves
Caught genuinely early, within the first day and with mild signs, some cases settle with admission, intravenous antibiotics, splinting and elevation, watched closely by hand surgeons.
Most need surgery.
The sheath is opened and irrigated, sometimes through two small incisions with a catheter flushing between them, sometimes more extensively. Antibiotics follow, and the finger is elevated and splinted.
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.
- Days 1 to 5: elevation above heart level, almost constantly. Swelling is what turns into stiffness. Gentle movement usually starts within the first days on the surgeon’s instruction.
- Weeks 1 to 4: daily tendon gliding work, several short sessions rather than one long one. Splinting between sessions to stop the finger settling into a bent position.
- Weeks 4 to 12: pushing range, scar management, gradual strengthening.
- Months 3 to 12: whatever range you have at three months is broadly what you keep, with slow gains after that.
Honest outcome expectations: many people get a good functional finger. A meaningful number end up with permanently reduced bend, and the ones who do are overwhelmingly the ones who arrived late.
The short version
Whole finger evenly swollen, resting slightly bent, tender along its length, and severe pain when someone straightens it.
That combination is a surgical emergency regardless of how small the original wound was, or whether you can even remember one.
Emergency department, tonight. The cost of being wrong about this is a wasted evening. The cost of being right and waiting is your finger.
Written by Nigel Chua, hand occupational therapist in practice since 2005. Tens of 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.