Hi Diane,
This is in the correct area for paratendinitis and rheumatoid is certainly going to be a predisposing factor for such synovial proliferation.
The unusual thing about this one is it is focal and localised, more like a rheumatoid nodule of synovial proliferation compared to the more common diffuse paratendinitis appearance.
I still think it is the correct diagnosis but more rheumatoid nodule version of it.
The clip is great as part of the nodule is stuck to the tendon itself while the rest floats freely.
It almost flips on itself during dynamic movement.
Great case,
Steve