Is your recovery window still open? Free one-page chart ↓
Your Fingers Have No Muscles In Them.
The muscles that bend and straighten your fingers sit in your FOREARM, not your hand. They pull on long cords called tendons that run through the wrist and along each finger. On the palm side, two flexor tendons bend each finger: FDP bends the fingertip, FDS bends the middle joint. On the back, one flattened extensor mechanism straightens all three joints. More than 20 tendons cross your wrist to make this work.
Make a fist and watch your forearm move. That’s where the engine is.
Once you understand that your fingers are operated remotely by cables, most hand symptoms stop being mysterious. Including why a problem at the wrist stops a fingertip working, and why a cut in the palm makes a finger useless.
Most people land on this page for one of three reasons. You cut your hand and someone said the word “tendon”. A finger has stopped bending or straightening and nobody’s sure why. Or a scan report used words like FDP, central slip or A2 pulley and you’d like them in English.
Here’s why it’s worth ten minutes. Tendon problems are where waiting costs the most in the hand. A cut flexor tendon recoils back toward the palm, and after roughly 3 weeks the ends can be too short or too scarred to stitch back together. A fingertip that droops after a jam and doesn’t get splinted early can stay droopy for good.
So here’s the map. The cables, the guides they run through, and where each one goes wrong.
What tendons are in the hand?
Two teams. Flexors on the palm side bend things. Extensors on the back straighten things. Both start as muscles in the forearm and turn into tendons around the wrist.
- Finger flexors. Two per finger, FDP and FDS. Eight in total for the four fingers.
- Thumb flexor. One, flexor pollicis longus (FPL). It bends the thumb tip.
- Wrist movers. FCR, FCU, ECRL, ECRB and ECU move the wrist, not the fingers. Palmaris longus is a thin spare that some people simply don’t have, which is why surgeons like borrowing it for grafts.
- Finger extensors. EDC goes to all four fingers, plus private extra tendons for the index (EIP) and the little finger (EDM). That’s why you can point, and why the little finger can lift on its own when you hold a teacup.
- Thumb extensors. Three. EPL lifts the thumb tip. EPB and APL swing the thumb base out to the side.
Inside the hand there are also small muscles, the lumbricals and interossei, that sit between the bones and weave into the extensor system. They do the fine work. The forearm tendons do the heavy lifting.
Which tendons bend the fingers?
Each finger has TWO flexor tendons, stacked one behind the other.
- Flexor digitorum profundus (FDP). The deep one. Attaches to the last bone and bends the FINGERTIP.
- Flexor digitorum superficialis (FDS). The superficial one. Splits in two, passes around the deep tendon, and attaches to the middle bone. Bends the MIDDLE joint.
The thumb has only one: flexor pollicis longus.
Where a flexor tendon is cut matters as much as which one. Surgeons split the palm side into zones, and each zone has its own repair and its own recovery. See flexor tendon injury by zone.
How do you test if a finger tendon is cut?
Two tendons per finger is why doctors test each joint separately after a cut. You can do the first two yourself, gently, and compare with the other hand.
- FDP test. Hold the middle joint of the finger straight with your other hand. Now bend only the tip. If it bends, FDP is working.
- FDS test. Hold the other fingers flat on the table. Bend the free finger at the middle joint. If it bends, FDS is working. The little finger’s FDS is weak or missing in some people, so check the other hand before you panic.
- The resting cascade. Relax the hand palm up. The fingers curl a little more as you go from index to little finger. One finger lying straighter than its neighbors after a cut is a flexor tendon problem until proven otherwise.
- Extensor check. Hand flat on the table, palm down. Lift each finger off the table on its own. For the central slip, a doctor or therapist uses the Elson test, done with the finger bent 90 degrees over a table edge.
- Scans. Ultrasound shows a gap in the tendon and where the ends have gone. MRI when it’s unclear. For a fresh cut, the surgeon often confirms by looking directly in the operating room.
A finger that still moves after an injury has not proved both tendons are intact. It has proved at least one is. A partly cut tendon can work fine on day one and snap on day five. That’s why a cut over a tendon gets explored, not just stitched.
What are the pulleys in the finger?
Running along the palm side of each finger is a series of fibrous bands, the annular pulleys A1 through A5, holding the flexor tendons tight against the bone.
Without them, bending a finger would lift the tendon away from the bone like a drawn bowstring, and you would lose a lot of power and range.
Two pulleys explain a large share of finger problems:
- A1, at the base of the finger. When the tendon thickens, it catches passing through it. That’s trigger finger, and the thumb has its own version, trigger thumb.
- A2, over the first bone. The strongest, and the one climbers rupture. See climbing pulley injury.
The tendon is the cable. The pulley is the guide it runs through. Almost every finger tendon problem is a fault in one or the other.
Which tendons straighten the fingers?
Straightening is where the hand gets genuinely elegant. It’s not a tendon. It’s a net.
On the back of each finger, the extensor tendon flattens and spreads into a triangular web of fibers called the extensor expansion, and the small muscles inside the hand weave into it.
It divides into three:
- Central slip. Attaches to the middle bone and straightens the MIDDLE joint. Rupture it and the finger buckles into a boutonnière deformity.
- Two lateral bands. Run down each side, rejoin, and attach to the last bone to straighten the TIP. Rupture the end of this and you get mallet finger.
The whole net is one connected system, which is why an injury at one joint changes the position of the joint next door. The slack has to go somewhere. Tip the balance one way and you get a boutonnière. Tip it the other way and the middle joint over-straightens while the tip bends: swan neck deformity.
Holding the extensor tendon centered on the knuckle is a thin sling called the sagittal band. When it tears, the tendon slides into the valley beside the knuckle every time you make a fist. That’s boxer’s knuckle.
Cuts on the back of the hand are zoned too, and the zone decides the splint. See extensor tendon injury by zone.
Which tendons cross the wrist?
On the palm side, nine flexor tendons and the median nerve squeeze through the carpal tunnel. Fixed walls, no room to expand. That’s why swelling there produces carpal tunnel syndrome.
On the back, the extensors pass through SIX compartments, each a separate tunnel.
- 1st compartment. Thumb tendons APL and EPB. Inflammation here is De Quervain’s.
- 2nd compartment. The wrist extensors ECRL and ECRB. Where the 1st compartment muscles cross over them, a few finger-widths above the wrist, you get intersection syndrome.
- 3rd compartment. EPL, the thumb-lifting tendon. It turns a sharp corner around a bony ridge and can fray and snap after a wrist fracture. See EPL rupture.
- 6th compartment. ECU, on the little finger side. It can inflame, or snap in and out of its groove when you turn the palm up. See ECU tendinopathy and subluxation.
Numbered compartments sound like trivia. They’re actually a map: tell someone which compartment hurts and you’ve named the diagnosis. If you’re not sure which tendon is complaining, wrist tendonitis: which tendon is it sorts it by spot.
And the same forearm muscles that move your fingers anchor at the elbow. Outer elbow pain when you grip is the extensor origin, tennis elbow. Inner elbow pain is the flexor origin, golfer’s elbow.
Which tendon problem matches my symptom?
- Finger catches, clicks or locks bent. A1 pulley. Trigger finger or trigger thumb.
- Can’t bend the fingertip after grabbing a jersey, or after a pop while gripping. FDP pulled off the bone. See jersey finger.
- Fingertip droops and won’t straighten on its own. Terminal extensor. Mallet finger.
- Middle joint stuck bent, tip bent back, weeks after a jam. Central slip. Boutonnière.
- Knuckle tendon flicks sideways when you make a fist. Sagittal band. Boxer’s knuckle.
- Thumb-side wrist pain lifting, pouring or carrying a baby. 1st compartment. De Quervain’s.
- Thumb tip suddenly won’t lift, weeks after a wrist fracture. EPL rupture.
- Pop at the base of a finger while climbing. A2 pulley.
- Cut on the palm side and a joint won’t bend. Flexor tendon injury. Cut on the back and a joint won’t straighten: extensor tendon injury.
- Red, swollen sausage finger, held bent, agony to straighten. Possible flexor tendon sheath infection. That’s an ER visit today, not a tendon question.
Why do tendons heal so slowly?
Tendons have a poor blood supply and get much of their nutrition passively, from the fluid in their sheaths. That fluid only circulates when the tendon MOVES.
Hence the central paradox of hand rehab: a repaired tendon must move to heal, but move too hard and the repair ruptures. Goldilocks rehab. Not too much, not too little.
Every flexor tendon protocol you’ll meet is an attempt to solve that one equation. A repair is at its weakest in roughly the first 3 weeks, and isn’t trusted with heavy loads until around 12 weeks.
Gliding distance matters too. A flexor tendon travels several centimeters with a full fist. A tendon stuck down by scar loses that travel, and the finger loses range even though the tendon is perfectly intact.
How long do hand tendon injuries take to heal?
Your surgeon’s protocol wins over anything here. These are the conservative, typical ranges.
- Weeks 0 to 6, protected. After a flexor or extensor repair, a splint full-time, usually around 6 weeks, with therapist-led movement inside it. See flexor tendon repair recovery and extensor tendon repair recovery.
- Weeks 6 to 8, weaning. Splint off for the day, light use only, no forceful gripping or lifting.
- Weeks 8 to 12, building. Gradual strengthening, guided by how the tendon glides.
- 12 weeks onward. Heavy gripping, lifting and contact sport, usually from around 12 weeks. Full range and strength often take 4 to 6 months, sometimes longer.
- Mallet finger without surgery. Splint on 24/7 for 6 to 8 weeks, then nights for a few more weeks.
- Irritated tendons (trigger finger, De Quervain’s). Weeks to a few months with splinting and load changes. Injection or a release if that fails.
In Closing Window terms: a cut or ruptured tendon runs on a CLOSING window measured in days to a few weeks. Irritated tendons usually sit in an OPEN window, where time and load changes are on your side. And a repair that’s getting stuck in scar has its own window, cos scar is most changeable in the first few months.
When can I work, drive and grip after a tendon repair?
- Desk or one-handed work: often within 1 to 2 weeks, in the splint, if the job keeps the hand protected. See returning to work after a hand injury.
- Driving: not in a full tendon splint. Usually once the splint is off and you can grip the wheel firmly, often 8 weeks or more after a flexor repair. See driving after a hand injury.
- Light manual work: about 8 to 10 weeks.
- Heavy manual work: 12 weeks at the earliest, often 3 to 4 months.
- Gym, climbing, contact sport: 12 weeks at the earliest, built up gradually. See the gym after a hand injury.
Exercises: what keeps tendons gliding
Only for tendons that are uninjured, or healed and cleared by your surgeon. Never after a fresh repair unless your therapist set the exercise.
- Tendon glides. Five positions: straight hand, hook fist, full fist, tabletop, straight fist. Hold each 3 to 5 seconds, 10 rounds, 3 to 4 times a day. Each position slides the two flexors a different distance. See tendon glide exercises.
- FDP blocking. Hold the middle joint straight and bend just the tip. 10 reps, 3 times a day.
- FDS blocking. Hold the knuckle straight and bend just the middle joint. 10 reps, 3 times a day.
- Stop rule. Stretch and mild ache are fine. Sharp pain, a pop, or a sudden loss of movement is a stop-and-call.
(This is where hand therapy earns its place: the custom splint after a repair, the early protected movement program, scar work, and catching a tendon that’s sticking or stretching out before it becomes permanent. See what a hand therapist does.)
The short version
- Engine in the forearm, cables in the hand.
- Two flexors per finger, tested separately.
- Pulleys keep the cables down. A1 catches, A2 ruptures.
- Extension is a net, not a rope. One break shifts the neighboring joints.
- Six compartments on the back of the wrist, each with its own condition.
- Tendons need movement to heal, and movement is also what threatens the repair.
More than 20 tendons cross your wrist, none of which you have ever consciously thought about, all cooperating every time you pick up a cup.
Get it checked today if
- A finger is red, swollen like a sausage, held slightly bent, and it hurts a lot to straighten, especially after a cut, bite or prick. Go to the ER.
- You have a cut on the palm, finger or wrist and a joint won’t bend or straighten on its own, or the finger lies out of line with its neighbors. See hand and finger cuts.
- A cut finger is also numb down one side. The nerves run right beside the flexor tendons.
- You felt a pop and now can’t bend the fingertip. A jersey finger repair goes best within about 7 to 10 days.
- A fingertip suddenly droops after a jam. Keep it straight and get it splinted today.
- After a tendon repair you feel a pop, or the finger suddenly stops bending or straightening. Call your surgeon today.
Get it checked if
- A finger clicks, catches or locks.
- A jammed middle joint can’t fully straighten, even if it doesn’t look bent yet.
- The thumb tip suddenly won’t lift, weeks after a wrist fracture.
- Thumb-side or little-finger-side wrist pain hasn’t eased after 2 weeks off the task that set it off.
- A tendon repair is moving less this week than last week.
The muscles live in your forearm. The problems live in the cables. Know which cable, and you know which clock you’re on.
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. A cut finger that won’t bend, or a fingertip that won’t straighten, deserves a look today, not next week.
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.