Trigger finger is also known as stenosing tenosynovitis. The pathology is irritation of the A1 pulley of the finger which occurs by the MCP joint. You may experience “triggering” or a catching of your finger in a bent position. The finger may be difficult to straighten and sometimes you may forcefully have to “untrigger” your finger.
The cause of trigger finger is a narrowing of the sheath that surrounds the tendon in the affected finger. Tendons are fibrous cords that attach muscle to bone. Each tendon is surrounded by a protective sheath — which, in turn, is lined with a substance called tenosynovium. The tenosynovium releases lubricating fluid that allows the tendon to glide smoothly within its protective sheath as you bend and straighten your finger — like a cord through a lubricated pipe.
But if the tenosynovium becomes inflamed frequently or for long periods, the space within the tendon sheath can become narrow and constricting. The tendon can’t glide through the sheath easily, at times catching the finger in a bent position before popping straight. With each catch, the tendon itself becomes more irritated and inflamed, worsening the problem. With prolonged inflammation, scarring and thickening (fibrosis) can occur and bumps (nodules) can form.
Symptoms may progress from mild to severe and include:
- A popping or clicking sensation as you move your finger
- Tenderness or a bump (nodule) at the base of the affected finger
- Finger catching or locking in a bent position, which suddenly pops straight
- Finger locked in a bent position, which you are unable to straighten
Trigger finger more commonly occurs in your dominant hand, and most often affects your thumb or your middle or ring finger. More than one finger may be affected at a time, and both hands might be involved. Triggering is usually more pronounced in the morning, while firmly grasping an object or when straightening your finger.
The A1 pulley and the actual triggering can be visualized under ultrasound as it happens. This area can be targeted for an ultrasound-guided cortisone injection which is typically a successful procedure.