Hello -
While morning joint stiffness is often associated with
arthritis, since this has been ruled out, the next most likely cause is something called "trigger finger", in which the tendons that control the finger become irritated, thickened, and eventually cause the finger to actually assume the curved attitude of pulling a trigger (even though it may not be one's index finger, the tradition finger used for pulling triggers). If that's what's going on, yours hasn't reached that point yet, and may not, but it may eventually get to that point. Otherwise what happens is the finger becomes stiff, sore, and may move in a jerking fashion when flexed or extended. It's a sort of tendinitis, and in your case it may remain no more than that. Since it is inflammatory in nature (even if it's not
arthritis), it should respond to non-steroidal anti-inflammtories such as iburprofin or naproxyn. You can try this and see if it helps. Sometimes these medications can actually give the inflamed part relief long enough to heal and the problem doesn't recur.
I hope this is helpful to you. Best of luck with this.