The most common type of tenosynovitis is called "De Quervain tenosynovitis" and is located over the thumb side of the wrist. Basically, two hand muscles can get irritated in your wrist and get compressed, causing major pain.
So, what movements make this injury flare up? Any time you move your thumb away from the middle of your hand or tilt your hand away from the side of your thumb, you're in for some serious discomfort. And for us climbers, that usually means pinch and undercling grip types become unbearable, and eventually all grip types can be affected.
If you suspect you've got De Quervain's, it's important to stop climbing and get it checked out rather quickly. Apart from starting rehabilitation early, you want to make sure it's not something more serious like a pinched nerve.
A quick examination by your GP or physiotherapist will help confirm whether it's tendonitis or not.
Now, let's talk treatment.
If it's a new injury, you might need to limit your wrist mobility with a splint, but make sure you start rehab exercises right away so you don't lose too much strength or mobility. If it's been going on for a while, you can get a little more aggressive with some strengthening and mobilizing exercises, massage, and manual therapy. Just make sure you listen to your body and don't push too hard.
Remember, a common cause of De Quervain's in climbers is a lack of strength in the shoulder and elbow muscles, so make sure you're taking care of those areas too. Also be sure to reflect on your technique as this is also a huge contributor to De quervains in climbers.
Take care of your body and happy climbing!