MSK · Hand

Trigger Finger — Why It Catches and What Imaging Shows

A finger that clicks, catches or locks has a mechanical explanation. Ultrasound can show it happening in real time — though the diagnosis rarely needs a scan at all.

Open hand with the other hand supporting a bent finger

The tendons that bend your fingers run through a series of narrow tunnels, held close to the bone by a set of pulleys. Trigger finger happens when the tendon thickens, the first pulley narrows, or both — and the tendon no longer glides smoothly. It catches, then releases with a snap. Classically it is worst in the morning, and often the finger has to be straightened with the other hand.

It is more common in people with diabetes, in those with rheumatoid arthritis, and after repetitive gripping — but plenty of people get it with none of those.

Honestly

Do you need a scan?

Usually not. Trigger finger is a clinical diagnosis — the history of catching, the tender nodule at the base of the finger, and the snap on examination are enough for a GP or hand specialist. We would rather say that plainly than imply a scan is a required step.

Where a scan genuinely helps: when the diagnosis is uncertain and something else is suspected; when the finger is locked and someone needs to know what is going on before intervening; when a lump in the palm needs characterising; and when a planned injection would benefit from imaging guidance elsewhere. Ultrasound shows tendon thickening, the state of the pulley, fluid in the sheath, and — uniquely — the catching itself as you bend and straighten the finger.

Not Always Trigger Finger

What else causes a catching or bending finger

What you notice Commonly
Catching and snapping, tender nodule at the base of the finger on the palm side Trigger finger
A finger drawing gradually into the palm with a firm cord in the palm, no catching Dupuytren’s contracture
Painful swollen finger joints, stiffness in the morning across several joints Inflammatory arthritis — see your GP
Sudden inability to straighten a fingertip after a knock Mallet finger — needs prompt assessment
A fixed lump on the tendon sheath, no triggering Giant cell tumour of tendon sheath or ganglion

A hot, spreading infection in the hand is an emergency

A finger that becomes swollen, red and severely painful — particularly after a cut or bite, held slightly bent and agonising to straighten — needs same-day hospital assessment. Hand infections spread along tendon sheaths quickly. Go to A&E rather than booking a scan.

At IUS London

How the appointment runs

  1. 1
    BookingNo referral, no preparation. 30 minutes. Tell us which finger and what it does.
  2. 2
    The scanThe tendon and pulley examined at rest, then watched as you bend and straighten the finger so the catching can be seen as it happens.
  3. 3
    What we assessTendon thickening, pulley appearance, fluid in the sheath, and any lump in the palm characterised properly.
  4. 4
    ResultsExplained on screen as we scan, written report usually within two hours for your GP or hand surgeon. We do not give injections or operate.
FAQs

Your questions answered

Will trigger finger go away on its own?
Some mild cases settle with avoiding provoking grips and sometimes night splinting. Many persist and need treatment — steroid injection is often the first step, with a small surgical release if that does not work or the finger keeps locking.
Do I need a scan to diagnose it?
Usually no. The history and examination are enough. A scan helps when the diagnosis is uncertain, a lump needs characterising, or the picture does not fit.
Why is it worse in the morning?
Fluid accumulates in the sheath overnight and the hand is unused, so the first movements meet the most resistance. It typically eases as the finger is worked through the day.
Is it caused by typing?
Sustained forceful gripping is more associated with it than keyboard work. Diabetes and inflammatory arthritis are stronger risk factors than any particular activity.
Can it affect the thumb?
Yes — trigger thumb is common and behaves the same way, with catching at the base of the thumb.
Can you inject it for me?
No — we provide diagnostic imaging only. If an injection is what you need, your GP or a hand specialist arranges it, and our report gives them the detail.
Related

Where to go from here

WristWrist Pain and Hand Numbness

Carpal tunnel and the other causes of a numb hand.

Read the guide →ElbowTennis or Golfer’s Elbow?

Telling the common elbow tendon problems apart.

Read the guide →ScansOther MSK Scans

Calf, hamstring, groin and other soft tissue areas.

See scans →

When the picture does not fit

Tendon, pulley and any palm lump assessed with the finger watched in motion — explained on screen as we scan, with the written report usually within two hours for your GP or hand surgeon.

From £169
Hand ultrasound scan

Hand scan

5a Lucerne Mews
Kensington, London W8 4ED
3 mins from Notting Hill Gate

This article is general information about trigger finger, not individual medical advice. A hot, red, severely painful finger — especially after a cut or bite — needs same-day hospital assessment. See NHS guidance on trigger finger. We provide diagnostic ultrasound only; we do not offer injections or surgery.

Written and clinically reviewed by the HCPC-registered sonographers who perform this scan at IUS London — a CQC-registered diagnostic ultrasound clinic (Provider ID 1-2775844974). Your own findings are explained to you at the scan and set out in your report.

Author: Yianni Kiromitis, Senior Sonographer, HCPC RA38415 — over 20 years’ experience in NHS and private ultrasound
Medically reviewed: 9 August 2026