Causes of trigger finger
NHS Choices Medical Reference
Trigger finger is caused by a problem in the tunnel that the tendon in your finger runs through (the tendon sheath). This makes it difficult for your tendon to slide through the tunnel and causes the pain and stiffness associated with trigger finger.
Problems with the tendon sheath
The most common problem involves one of the ligaments that make up the tendon sheath, usually the first ligament at the base of your finger. Because of its position, it is exposed to the most pressure in your hand, for example when you grip something. Over time, this ligament can become thicker than it should be.
As the ligament thickens, it partially blocks the opening of the sheath, making it harder for the tendon to slide in and out of the sheath.
When you bend your finger or thumb, the tendon slides down the sheath towards your arm. As you straighten your finger or thumb, the tendon should slide back up the sheath into your finger. If the sheath is partially blocked, the tendon cannot enter the sheath and your finger becomes temporarily stuck in a bent position.
The stuck tendon may suddenly pop past the swollen ligament into the sheath, releasing your finger like the release of a trigger.
Once the tendon in your finger starts getting stuck, the condition usually gets progressively worse. This can happen in one of three ways:
- The constant irritation or friction from the tendon getting stuck can cause the tendon to swell, making it harder for it to fit into the sheath.
- The irritation from the tendon can cause the lining of the sheath to become inflamed (swollen), making the sheath narrower.
- The irritation from the tendon can cause a small growth or lump of tissue (nodule) to form in the sheath, partially blocking it.
As the cycle of irritation repeats itself, the tendon eventually gets stuck and the finger becomes locked in a bent position. Sometimes, the tendon will pop free and your finger will be able to move again, but it may become stuck in a permanently bent position.
The cause of these problems is not fully understood and, in most cases, is never known. However, several things may make trigger finger more likely:
- Trigger finger is up to six times more common in women than men.
- It is more common in children under six years of age or in adults over 40, and is most common in people in their 50s or 60s.
- It is more common if you have injured the base of your finger or palm.
You may be more likely to develop trigger finger if you have any of the following conditions:
- diabetes - a long-term condition that is caused by too much glucose in the blood
- rheumatoid arthritis - a long-term condition caused by a problem with your immune system (the body's defence system), resulting in pain and stiffness in your joints
- gout - a short-term condition that causes inflammation (swelling) in one or more of your joints
- amyloidosis - a condition where abnormal protein called amyloid builds up in organs, such as your liver
- underactive thyroid - your body does not produce enough of certain hormones
- mucopolysaccharide storage disorders - a group of rare disorders that cause progressive physical and sometimes mental disability
- carpal tunnel syndrome - a condition that affects the nerves in your wrist, causing pain and tingling
- Dupuytren's contracture - a condition that causes one or more fingers to bend into the palm of your hand
- De Quervain's disease - a condition that affects the tendons in your thumb, causing pain in your wrist