Trigger finger is a painful condition that causes the fingers or the thumb (then called trigger thumb) catch or lock when bent. In the early stages there might be just some discomfort at the base of the digit and the locking may be only in the morning but the digits can then pop out and extend without much pain. As the condition worsens, the catching sensation, the locking, the popping, and the pain become more constant and it becomes more and more painful to straighten the digit. Eventually, the finger becomes more permanently locked or stiff, unable to fully extend or to flex without excruciating pain. Trigger finger is also called stenosing tenosynovitis because it is a stenosis (from ancient Greek meaning abnormal narrowing) that causes inflammation of the tendon (teno-) and its surrounding synovial tissue (-synovitis).
Symptoms Associated with Trigger Finger:
- Random lockup in the finger
- Pain straightening or bending
- Difficulty extending the finger
- Swelling & Stiffness
What Causes Trigger Finger?
Our digits bend because they are connected to the muscles in our forearm by tendons. When the muscles contract, they pull on the tendon and this pull draws the finger into flexion. Our tendons function like bicycle cables. Just like bicycle cables, they have a central cable and a surrounding sheath that guides the cable and provides the counterforce for flexion. The sheath of our tendons consists of a series of pulleys that keep the tendon aligned with the bones of the finger. With wear and tear, overuse, and in predisposed individuals, the cable function eventually degenerates.
Just like a worn out cable, a knot forms that prevents it from gliding within the sheath and it becomes more and more difficult for the tendon knot to pass though the pulley at the base of the finger. Once the knot eventually passes through the tight pulley, it “button holes” through it and becomes unable to come out again, causing the finger to lock in flexion. Every time it passes through the tight pulley the tendon gets inflamed and swells.
This swelling makes it even more difficult to pass through the pulley the next time again which then causes even more swelling. A vicious circle gets established as more attempts to bend the digit makes things even worse. This is why the first treatment is rest and arresting this vicious loop by injecting cortisone that can stop the inflammatory swelling response to irritation.
Trigger finger is commonly seen in diabetics and in patients with inflammatory conditions such as rheumatoid arthritis. Trigger finger is commonly associated with carpal tunnel syndrome because this same swelling of the tendons can also cause the nerve to be compressed at the wrist (see Carpal Tunnel Syndrome).