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The Finger That Ends Up Bent Was Almost Always Called a Sprain.
Most extensor tendon injuries of the finger heal without surgery, in a splint worn continuously for 6 to 8 weeks, then at night for a few more weeks. Full strength usually takes about 3 months. The catch is the deadline: splinted in the first 1 to 2 weeks, most do well. Found late, the finger can set bent.
Extensor tendons run along the BACK of your finger, and they are the opposite of their flexor cousins in almost every way: thin, flat, sitting just under the skin, and usually treated with a splint rather than an operation.
That makes them sound minor… they aren’t.
Most extensor injuries have a deadline measured in days to a couple of weeks, and the finger that ends up permanently bent is almost always one that was called a sprain.
Miss that deadline and the fix changes from a plastic splint you wear at home to a reconstruction in the operating room, with a less predictable result.
What is the extensor tendon? It’s a hood, not a cord
On the palm side you have two round cords per finger. On the back you have something more like a flat sheet wrapping over the knuckle, splitting into three slips over the middle joint, then rejoining to reach the fingertip.
That’s why extensor problems show up as a finger sitting in a strange POSITION rather than a finger that can’t move at all.
Cut one part of the hood and the rest keeps pulling… just in the wrong direction. Over weeks, that imbalance is what builds a deformity. (The layout is spelled out in hand tendon anatomy.)
Flexor injuries announce themselves. Extensor injuries deform slowly, which is why they’re caught late.
Extensor tendon zones explained
Surgeons and therapists describe extensor injuries by zone, numbered from the fingertip up. The odd numbers sit over joints, the even numbers between them.
- Zone 1: over the fingertip joint (DIP).
- Zone 2: over the middle bone of the finger.
- Zone 3: over the middle joint (PIP).
- Zone 4: over the first bone of the finger.
- Zone 5: over the big knuckle (MCP).
- Zone 6: back of the hand.
- Zone 7: back of the wrist, where the tendons run under a band of tissue.
- Zone 8: lower forearm.
The thumb has its own numbering. Its most famous problem, a thumb that stops lifting weeks after a wrist fracture, is a ruptured EPL, not stiffness.
The four that matter, by where they sit
Over the fingertip (Zone 1). The tip droops and won’t lift. That’s mallet finger, and the treatment is a splint holding the tip dead straight for 6 to 8 weeks, CONTINUOUSLY. Let it bend once at week four and the clock restarts from zero.
Over the middle joint (Zone 3). A jammed or cut finger that seems fine, then two weeks later starts bending at the middle joint and hyperextending at the tip. The central slip has gone, and what you’re watching is a boutonnière deformity forming. This is the single most-missed hand injury I see. Splinted in the first two weeks it usually does well. Found at three months, it’s a reconstruction.
Over the knuckle (Zone 5). The tendon is held centered on the knuckle by a thin sling. Tear that and the tendon slides into the valley between the knuckles, so the finger drifts sideways and won’t fully straighten from a bent fist. That’s a sagittal band rupture, and splinting works well inside a few weeks and poorly after.
Back of the hand and wrist (Zones 6 to 8). Here the tendons are separate and a cut usually means the finger simply won’t lift at the knuckle. These get repaired surgically, and the recovery is in extensor tendon repair.
The knuckle wound that is not a cut
A small wound over a knuckle, acquired in a fight, from a mouth, is not a laceration. It is an inoculation.
The fist punches the tooth, the tooth pierces the extensor hood and the joint, the hand relaxes, and the puncture in the tendon slides back under intact skin where nobody can see it. Hours later the joint is infected.
Any wound over a knuckle from a tooth needs to be seen today, not tomorrow. The full version is in bites to the hand, and I will keep repeating it because the people it happens to are, understandably, not keen to explain how they got it.
How do I know if I’ve damaged an extensor tendon?
Lifting the finger proves less than people think, because neighboring tendon connections can cheat.
- Fingertip. Rest the hand flat, lift just the tip off the table. Can’t lift, or it lags behind the others? Zone 1.
- Middle joint. Bend the finger over the edge of a table at the middle joint, then try to straighten it against a light push. Weak or painful? Suspect the central slip.
- Knuckle. Make a loose fist, then open the hand. If the finger has to be flicked or pushed to start straightening, suspect the sagittal band.
- Hold, don’t just reach. The useful version of every test is holding the position against gentle resistance, not reaching it once.
In clinic I always test the same finger on the other hand first. Half of what looks abnormal is just how that person is built.
Then imaging. An X-ray shows whether the tendon pulled off a flake of bone (common in mallet finger and at the middle joint) and whether the joint is sitting properly. Ultrasound can show a partial tear or a sagittal band injury when the X-ray is clean. Surgery is usually only on the table for open cuts, a large bone fragment, a joint that won’t stay in place, or an injury found too late for a splint to work.
How long does an extensor tendon injury take to heal?
Your surgeon or therapist’s protocol comes first. These are the typical, conservative ranges.
- Mallet finger (Zone 1): 6 to 8 weeks of continuous splinting with the fingertip straight, then at least 2 to 4 more weeks at night and for risky tasks. Back to normal use around 10 to 12 weeks.
- Central slip (Zone 3, closed injury): the middle joint held straight for 6 to 8 weeks, with the fingertip left free to bend. Then gradual bending and night splinting for a few more weeks.
- Sagittal band (Zone 5): usually 6 to 8 weeks in a relative motion (yoke) splint, which holds the injured finger slightly higher than its neighbors and lets you keep using the hand.
- Repaired tendons (Zones 5 to 8): protected for about 4 to 6 weeks, light use from 6 to 8 weeks, strength and heavier work from around 10 to 12 weeks.
In Closing Window terms, the window is OPEN for the first 1 to 2 weeks after the injury, when a splint does most of the work. It is CLOSING after that, as the ends scar in the wrong place. By around three months a central slip injury is usually a shut window for splinting alone, and the goal shifts to what surgery or longer therapy can still recover.
What exercises help an extensor tendon injury?
Only the ones your therapist has cleared for your zone and your week. The rule is protect the injured part, move everything else.
- During mallet splinting: bend and straighten the middle joint fully, 10 reps, 4 to 5 times a day, with the splint on. Keeps the rest of the finger from stiffening while the tip is held.
- During central slip splinting: fingertip bends with the middle joint held straight in its splint, 10 reps, 4 to 5 times a day. This keeps the side bands from tightening and is half the treatment.
- After the splint comes off: gentle active bending only, 10 reps, 3 to 4 times a day, adding a little more bend each week. No forcing the finger down with your other hand in the first 2 weeks.
- Check for droop daily. If the finger stops straightening as well as it did on the day the splint came off, go back into the splint and tell your therapist.
- Grip and strength from about week 10 to 12, starting with soft putty.
Can I work, drive and play sport with an extensor tendon injury?
- Desk work: usually yes, from the first week, with a finger splint on. Typing is slower but fine as long as the protected joint stays straight.
- Manual work: depends on whether the splint can stay on, dry and intact. Wet or dirty work often means modified duties for 6 to 8 weeks.
- Driving: usually fine with a small finger splint if you can grip the wheel securely. With a hand or wrist splint after a repair, wait until you’re cleared and can control the car in an emergency.
- Ball sports: sometimes possible with the splint protected and taped, if your therapist agrees. Unprotected contact sport usually waits until around 12 weeks.
Two things people get wrong
“It’s only a small droop.” A ten-degree lag at the fingertip is cosmetic. A thirty-degree lag catches on pockets, bags and keyboards for the rest of your life. And an untreated mallet finger is one of the routes to a swan neck deformity further down the finger, because the forces have to go somewhere.
“The splint hurts, I’ll take it off at night.” Night is when the finger bends unsupervised. Splint compliance IS the treatment here, in a way it simply isn’t for most other injuries. If the splint is causing skin problems, that’s a reason to have it refitted, not a reason to stop.
What a hand therapist does differently
A custom splint molded to your finger, not a one-size stack splint that slides off. A skin check every visit, cos white pressure marks over the knuckle are how splints fail. A taught technique for changing or cleaning the splint with the finger held flat on a table so it never bends. And a measured angle every visit, so a returning droop is caught in days instead of months. For the middle-joint version, that’s the PIP extension splint.
Get it checked today if
- There is any wound over a knuckle, however small, especially from a tooth.
- A cut on the back of the hand or finger and the finger won’t lift fully.
- The finger is red, hot and swelling after any knuckle wound.
Get it checked if
- A finger joint droops or lags behind its neighbors after any knock or cut.
- A jammed finger is still swollen at the middle joint after 10 days.
- A finger has started drifting sideways or needs a flick to straighten.
- A thumb has stopped lifting off a flat table weeks after a wrist fracture.
- The droop came back after the splint came off.
On the back of the finger, the injury is rarely dramatic and the deadline is rarely obvious. Those two facts are the same problem.
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 a finger isn’t straightening the way its neighbor does, get it assessed inside the first two weeks. Those two weeks are the difference between a splint and an operation.
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.