If you cut the palm side of your finger, hand or wrist and afterwards a joint won’t bend on its own, you have a divided flexor tendon until proven otherwise.
This is the important part: a cut flexor tendon does NOT heal by itself.
The muscle up in your forearm pulls the cut end back down the finger like a released elastic, and every day it sits retracted makes the repair harder. The good window is roughly the first two weeks.
Two tendons per finger, and they fail separately
Each finger is bent by two separate cords running up the palm side. (More on the machinery in hand tendon anatomy.)
FDP runs all the way to the fingertip and bends the LAST joint.
FDS stops at the middle bone and bends the MIDDLE joint.
Because they’re separate, you can cut one and keep bending the finger with the other… which is exactly why these get missed in a busy A&E at 1am. The finger still curls. Everyone relaxes. The wound gets stitched.
A finger that still bends is not a finger with intact tendons. It’s a finger with at least one intact tendon.
Test them one at a time
Do this with the uninjured hand doing the holding. It takes fifteen seconds.
- FDP test — hold the middle joint of the injured finger dead straight, then try to bend just the fingertip. Can’t? FDP is likely cut.
- FDS test — hold the OTHER three fingers flat on the table, then try to bend the injured finger at its middle joint. Can’t? FDS is likely cut.
- Sensation — run a fingertip lightly down each side of the finger. The nerves sit right beside the tendons, so a numb strip along one side means the nerve went too.
A partial cut is the sneaky one. The finger still bends, but it hurts badly to bend against resistance, and sometimes there’s a catch or a triggering feeling. Partial tears above about half the tendon can still rupture later, out of nowhere, doing something ordinary.
The zones, and why Zone 2 is the one surgeons swear about
Surgeons divide the palm side into five zones. You only need to care about one distinction.
Zone 2 runs from the crease at the base of the finger to the middle of the finger. Both tendons run there together inside a tight fibrous tunnel, one sliding inside the other, with almost no spare room. Repair anything in that tunnel and the repair site wants to stick to the walls.
That’s why old textbooks called Zone 2 no man’s land. It isn’t a no-go area anymore, but it is still the zone where the result depends most on the rehab that follows.
Cuts closer to the wrist, in Zones 4 and 5, are technically easier but often involve nerves and arteries at the same time, so the tendon can end up the least of it. See nerve repair recovery for how that half behaves.
And if the fingertip won’t bend after a sudden pull rather than a cut — gripping a rugby shirt, a dog lead, a climbing hold — that’s the tendon tearing off the bone, not a laceration. That one is Jersey finger, and it has an even tighter clock.
The window, plainly
- Day 0 to 14 — primary repair. The tendon ends are still reachable, the sheath hasn’t scarred, the muscle hasn’t shortened. This is where the good outcomes live.
- Week 3 to 6 — delayed repair. Harder. The tendon has retracted and the muscle has started to contract. Still often possible.
- Past 6 weeks — usually a two-stage reconstruction with a silicone rod, then a graft, months apart. A much bigger undertaking for a result that is rarely as good.
Nobody gets this window back. That’s the entire reason I write in this much detail about a finger that “still sort of works”.
What happens after the repair
The stitched tendon is at its WEAKEST around week three, right when the hand starts feeling normal and the temptation to use it properly becomes almost irresistible.
So the rehab protocol is not caution for caution’s sake. It’s timed against a real dip in strength. The full week-by-week version is in flexor tendon repair recovery.
The two ways it goes wrong: the repair RUPTURES, or the repair sticks down and the finger stops gliding. Rehab is a constant negotiation between those two failures, which is why it’s supervised rather than handed out on a photocopied sheet.
Go now, not tomorrow, if
- Any joint of the finger won’t bend on its own after a cut
- Part of the finger is numb after a cut
- The wound is over the palm side of a finger crease, even if it looks tiny
- The finger is going red, swollen and very painful to straighten over the following day or two — that’s a sheath infection, and it runs on hours
A glass-cut palm from washing up looks like nothing. A two-centimeter laceration gets four stitches and a plaster, and the tendon underneath quietly retreats up the finger while everyone congratulates themselves on the neat suturing.
Stitching skin is not treating the injury. It’s closing the window.
If a finger won’t bend properly after any cut, ask specifically to be seen by a hand surgeon. Say the words “I can’t bend this joint”.
That sentence changes what happens next.
For the splint used, see the dorsal blocking splint.
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.