Trigger Thumb: Why It Locks, and Why It Isn't Quite Trigger Finger

Written by Nigel Chua, hand occupational therapist · 21 years treating fingers, hands, wrists, forearms and elbows · Singapore

Same Mechanism, Different Address

Trigger thumb is a narrowing of the A1 pulley at the base of the thumb, where the single flexor tendon that bends your thumb has to pass through a tunnel that has thickened around it.

The tendon swells.

The tunnel narrows.

Something has to give.

It locks in the BENT position, not the straight one, and that single detail is why trigger thumb behaves worse than trigger finger even though the underlying problem is identical.

You have one joint below the knuckle instead of two. Less room to cheat.

Why the thumb is different

Your fingers are moved by TWO flexor tendons each. Your thumb only has one: flexor pollicis longus.

One tendon, one pulley, one interphalangeal joint.

So when the tendon catches, there is no second tendon quietly taking up slack, and no second joint to absorb the loss of movement.

The lock is more complete… and the stiffness that follows arrives faster.

In clinic, the giveaway is the story: people describe prising the thumb straight with the other hand, usually in the morning, usually for weeks before they mention it to anyone.

What it feels like, in order

A tender lump at the base of the thumb, on the palm side, over the crease
Clicking on bending or straightening
Catching — the movement stalls, then releases with a snap
Locking — the thumb stays bent until you straighten it manually
Fixed flexion — it no longer straightens fully even with help

That last stage is the one that matters. Once the IP joint has sat bent for months, the joint capsule shortens, and releasing the pulley alone won’t hand back the straightening.

The pulley problem is reversible. The joint contracture that follows it often isn’t.

Who gets it most of the time?

Adults: most commonly women between 40 and 60, and it is strongly associated with diabetes. If you have diabetes, trigger digits are more likely to be multiple, more likely to recur, and less responsive to injection.
Children: congenital trigger thumb is its own thing entirely. A baby or toddler with a thumb stuck bent at the tip, with a palpable nodule, is not the same condition and is not managed the same way. That needs a hand surgeon’s opinion, not a wait-and-see.

Also common after a period of heavy, repetitive gripping — secateurs, screwdrivers, a new gym habit built on kettlebells. Not the cause exactly… more the thing that tipped an already-narrow tunnel over.

Treatment, in the order it’s worth trying

Splinting. A small splint holding the MCP joint at 0 to 15 degrees, leaving the IP joint free, worn at night. It works by stopping the tendon repeatedly dragging the swollen segment through the narrowed pulley while you sleep.

Worn nightly for 6 to 10 weeks
Roughly half of early, non-diabetic cases settle on splinting alone
Works best when catching started within the last three months

Corticosteroid injection. Placed into the tendon sheath at the A1 pulley.

First injection: good response in around 60 to 80 percent of non-diabetic thumbs
Response usually noticed within 1 to 2 weeks
Second injection has a lower success rate than the first
Diabetic thumbs respond less well, and blood glucose commonly rises for several days after

Surgical release. The A1 pulley is divided. Day procedure, local anaesthetic, small incision in the palmar crease.

Day 0 to 3: dressing on, thumb moving straight away, gentle and often
Week 1 to 2: stitches out, scar softening begun
Week 3 to 6: grip returning, scar tenderness fading, pushing and gripping through the palm still uncomfortable
Week 6 to 12: scar sensitivity settles; full comfortable load usually back by 3 months

Recurrence after a properly released A1 pulley is uncommon — under 3 percent.

The window

This is a condition where the clock is measured in how long the joint has been stuck, not how long it has hurt.

Clicking and catching, treated within the first three months, mostly resolves without surgery.

A thumb that has been locked bent for over six months has usually added a second problem on top of the first — and now you’re treating two things.

Your thumb is doing a Groundhog Day loop: same catch, same snap, same morning. The loop doesn’t break on its own, it breaks when you change something.

Trigger Thumb: Why It Locks, and Why It Isn’t Quite Trigger Finger