De Quervain’s tenosynovitis is a painful, inflammatory condition of the tendons on the backside of the thumb at the wrist. Tendons are tough bands of connective tissue and they are the “connectors” between muscle and bone. They transfer the energy from the muscle to the bone when a muscle contracts so we can move through different ranges of motion. Tendons are very resistant to tearing but don’t have a lot of stretch to them.
Think of them as small ropes that glide smoothly through a tunnel. If the tunnel narrows, the rope can fray and start to look like the end of a mop.
In De Quervain’s, there is a narrowing of the tunnel where tendons of two muscles that help move the thumb pass through. These two muscles are the abductor pollicis longus and extensor pollicis brevis and can be seen at the base of the thumb/wrist when moving the thumb back and forth.
Things like picking up, baking (stirring motion), or playing the guitar without ever doing so in the past are a couple examples of this. Regardless, normal hand, wrist, and thumb movements can end up causing pain and a lot of discomfort!