Harrie,
I do not have "trigger finger" (yet!) but a lot of hand joint pain on Arimidex. I was looking at the John Hopkins' website, and, apparently, there are a number of patients on Arimidex/Aromasin with a similar problem submitting questions. Lillian Shockley, who answers the questions, said that she has told all of the AI drug companies about the high number of questions she is receiving about this symptom. Just wanted to let everyone know that this is not an unusual side effect. The only way we will get proper medical attention for it is to continue to speak up to our doctors and the drug companies. Thanks for posting this question here.
FYI, here is a link to the Mayo Clinic Website with more info on trigger finger:
http://www.mayoclinic.com/health/trigger-finger/DS00155
Hopeful