Patients › Hand
Infected Flexor Sheath (Pyogenic Flexor Tenosynovitis)
What you're feeling¶
The infection sits inside the tunnel of tissue that wraps around the bending tendons of your finger or thumb. That tunnel is called the flexor tendon sheath. When it fills with infection, the whole finger becomes painful, swollen and tender along its full length, from the tip down to the palm.
The pain is usually worst when you try to straighten the finger. Keeping the finger bent eases it a little, so many people hold the finger curled up. Pressing on the front of the finger hurts. The swelling can involve the whole finger evenly, which can make it look like a simple skin infection at first. This condition is often mistaken for that, so it is worth knowing the difference matters.
Everyday tasks that bend the finger become hard. Buttoning a shirt, gripping a kettle handle, typing or holding a phone can all flare the pain. You may notice the finger feels stiff and heavy, and you may avoid using the hand altogether.
This infection tends to get worse quickly rather than coming and going. It usually starts after a cut, prick or puncture wound that let bacteria in, most often a common skin germ called Staphylococcus aureus. Sometimes the entry wound looks minor or has already healed over.
Not every classic sign shows up in every person, so a finger that is painful, swollen and held bent after an injury should always be checked promptly. Your surgeon may use an ultrasound scan to help tell this infection apart from a surface skin infection.
Acting early matters. The infection is in a closed space, so pressure builds and the tendons can be damaged. Prompt treatment protects the tendons and gives the finger the best chance of moving well afterwards. Even with quick antibiotics and surgery, some stiffness in the finger is common while it heals.
What's actually happening¶
Inside your finger or thumb, the bending tendons run through a snug tunnel of tissue called the flexor tendon sheath. Think of the tendons as smooth cords, like ropes that pull the finger bent, and the sheath as the sleeve they slide through. The sheath keeps the cords lubricated and gliding freely with every movement.
When bacteria get into that closed sleeve, they multiply in a space with nowhere to expand. The lining becomes inflamed and fills with infected fluid, which presses on the tendons and the delicate gliding surfaces around them. That pressure is why the whole finger swells evenly, why pressing along the front of the finger hurts, and why holding the finger bent feels more comfortable than straightening it. Straightening stretches the infected sleeve, so it hurts most at that moment.
The infection does not always stay put. In some people the sleeve of the small finger connects to a larger fluid channel in the palm, and the thumb has a similar connection on the other side. These channels can carry infection up toward the wrist, which is why early treatment matters so much.
Left alone, the pressure and the bacteria can damage the tendon cords themselves. The tendons can die off or become stuck to the surrounding tissue by scar tissue as it heals. Either problem can leave the finger stiff, bent or unable to move, and in severe cases the loss can extend to much of the hand. This is why this infection is treated as urgent rather than watched.
Doctors describe how advanced the infection is using a simple three-level system based on what the finger looks like before treatment. Early infections caught quickly often need less surgery, while more advanced ones, where the finger is already very swollen, tense or unresponsive to antibiotics, usually need an operation to open the sleeve and wash it out. Nearly all cases need that surgical washout at some point, and the sooner it happens, the better the finger's final movement tends to be.
What we can do about it¶
Dr Kieran Hirpara, an upper-limb surgeon at Mater Private Hospital Rockhampton, starts with the least invasive options that suit your condition. Patients are generally referred to our clinic by their GP; if a physiotherapist has suggested you see us, you will still need a referral from your GP in order to be eligible for the Medicare rebate. At the clinic we take a history, examine your finger and arrange imaging such as an ultrasound scan where it helps.
This infection is treated as urgent, so we rarely start with self-management or physiotherapy alone. Antibiotics given through a drip are part of the care, and they work best when started promptly. If the finger has not yet developed thick pus, we may try washing the tendon sheath out through a small cut at the bedside in the emergency department. During that washout we take a sample of the fluid for testing, flush the sheath with sterile salt water and apply a bulky dressing. If that fluid turns out to be pus, we take you to the operating room.
If there is obvious pus already draining from a wound, or a collection of pus you can feel under the skin, we go straight to the operating room. There we open the sheath through small incisions, wash out the infection and leave a small tube in place so the sheath can be rinsed continuously afterwards. Acting quickly like this protects the tendons and gives your finger its best chance of moving well.
Even with prompt treatment, complications are common. Some people are left with a stiff finger that does not bend or straighten fully, and in severe cases the affected finger can come to need amputation. This is true no matter which treatment approach is used, which is why we treat the infection early rather than watching and waiting.
What to expect¶
With prompt treatment, most infections settle. The usual plan is a washout of the tendon sheath plus antibiotics, and a single washout with the wound closed and 10 days of antibiotics has resolved uncomplicated infections. Catching it early and treating it quickly gives your finger its best chance of good movement, because delay is what tends to cost function.
Even so, be prepared for some stiffness. Even otherwise healthy people who get prompt antibiotics and surgery can expect the finger to remain somewhat stiff afterwards. The finger may not bend or straighten fully for some time, and therapy and gentle use over the following weeks and months help it loosen. How much movement you regain depends on how advanced the infection was before treatment, which is why doctors grade it before operating.
Without treatment, the outlook is much worse. The infection does not burn itself out, and the pressure inside the closed sheath keeps building. The tendons can be destroyed or scarred in place, leaving the finger stiff, bent or unable to move. In severe infections, function can be lost or the finger may need amputation, even when treatment has been timely and thorough.
When to see someone¶
This infection is time-critical, so do not wait to see whether it settles. Go to an emergency department if your finger or thumb becomes painful, swollen and held bent after any cut, prick or puncture wound, even one that looked minor or has healed over. The same applies if the whole finger is tender along its length from tip to palm, or if pressing on the front of the finger hurts. Ask for a specialist review if a finger that was already being treated is not improving with antibiotics, or if the swelling becomes tense and the finger stops responding. Not every classic sign appears in every person, so trust the pattern rather than waiting for all of them. Acting the same day protects the tendons, because delay is what costs movement.
Advanced reading: the deeper science (optional)
This section goes further than you need for your own treatment decisions. An infected flexor sheath is worth the extra reading because it is the one hand infection that is a genuine emergency, and because two of the things that most determine how it ends were decided before you reached hospital — one of them years before.
The diagnosis rests on four signs from the 1930s that have never been properly tested¶
Allen Kanavel described four signs of an infected flexor sheath: a finger swollen along its whole length rather than in one spot, held slightly bent, tender all the way along the tendon sheath rather than over one joint, and, the most useful of the four, severe pain when someone gently straightens the finger [1].
Nearly a century later, those four signs are still how the diagnosis is made, and their sensitivity, specificity and interobserver reliability have never been properly established [1]. That is a remarkable gap for a diagnosis whose delay costs fingers.
The practical consequence is the part worth carrying: not all four signs appear in every case, particularly in children, and the absence of one or more does not exclude the diagnosis [1]. A finger that fails only one of Kanavel's tests is not a finger that has been cleared.
How it is drained changes how well the finger moves afterwards¶
Once the diagnosis is made the sheath has to be decompressed, and there are two broad ways to do it: open the sheath surgically, or pass a fine catheter into it and irrigate through a much smaller wound.
A systematic review covering 763 patients found that catheter irrigation produced better range of motion than open washout, and that using antibiotics as part of treatment, rather than relying on drainage alone, also improved movement [2].
Note that this is the opposite of the position on a felon, where a properly drained pulp abscess needs no antibiotic at all. The difference is the anatomy: a felon is a closed pocket you can empty completely, while a sheath is a long tube lined with the very surface the tendon must glide against. You cannot debride it clean without damaging what you are trying to save, so the antibiotic does work the surgery cannot.
The risk of losing the finger is mostly a property of the patient¶
This is the least comfortable finding and the most useful one. In the pooled series, amputation rates were driven overwhelmingly by background health rather than by surgical technique: 39% in patients with diabetes, 64% with renal failure, and 71% with peripheral vascular disease, all statistically significant [2].
Those numbers describe a different disease from the one a healthy person with a splinter injury has. They are why an infected sheath in someone with diabetes or poor circulation is treated with more urgency and a lower threshold for repeat washout, and why the honest answer to "will I keep the finger" depends more on the answer to "what else is going on with your health" than on anything that happens in theatre.
Why the delay matters more than almost anything else¶
The sheath is a closed space with a poor blood supply and a tendon inside it that depends on gliding. Pus under pressure inside that space does two things at once: it strangles the tendon's blood supply, and it seeds the adhesions that later limit movement. Both are time-dependent, which is why early treatment consistently improves outcomes [2] and why the standard advice for this specific infection is an emergency department rather than a GP appointment [3].
Stiffness afterwards is common even when everything is done correctly and promptly. How much stiffness is set largely by how long the sheath was under pressure, which is the one variable a patient can influence, by coming in early.
References for the advanced reading
- Kennedy CD, Huang JI, Hanel DP. In brief: Kanavel's signs and pyogenic flexor tenosynovitis. Clin Orthop Relat Res. 2016;474(1):280-284.
- Giladi AM, Malay S, Chung KC. A systematic review of the management of acute pyogenic flexor tenosynovitis. J Hand Surg Eur Vol. 2015;40(7):720-728.
- Goyal K, Speeckaert AL. Pyogenic flexor tenosynovitis: evaluation and management. Hand Clin. 2020;36(3):323-329.