This is a classic example Xue,
There is degenerative arthritis of the STT joint and associated synovial proliferation of the volar / radial carpus joint capsule.
You can also see how the fCR sheath is getting thickened and there is Doppler signal in the FCR sheath and the tendon itself.
So this pattern represents STT arthritis with associated synovitis and FCR tenosynovitis as a result of the STT arthritis.
This is a really common pattern especially in this age group.
Unfortunately the end stage of this is a FCR future.
It does not look imminent in your case as the FCR tenosynovitis is not severe yet.
Steve