Goldie, sorry to be replying so late. If it were just the finger, I'd suggest it is carpal tunnel. However, since you also have problems in the elbow, it could be pressure on the nerve, either within the nerve sheath somewhere along its path from the neck down into the hand, or by nerve compression caused by the brachial plexus's covering muscles--the scalenes that lift the 1-2 ribs when you inhale, or by pectoralis minor (beneath your pec major), or, rarely, by the coraconbrachialis which attaches to the coracoid process of scapula and to the upper arm bone.

As for the nerve sheath, nerves are meant to glide freely within the sheath. Standing, if you lift your chin, extending your neck as high as you can and as far away from the affected arm as you can stretch it, and simultaneously extend the affected arm as far as you can, and move the hand into flexion and extension, if the nerve is impinged within the sheath, you may feel tingling/numbness in the elbow or down into the fingers.

With all the research you have done, you're familiar with the term TOS, I assume. The pronator teres is lower than the elbow, so is unlikely to be the cause. Likewise, the interrosseus. So, if it isin't a problem in the spine due to your surgeries, I think it likely stems from thoracic outlet syndrome.

Trigger points within the aforementioned TOS muscles can cause hypertonicity and compression of the brachial plexus nerves.

Cortisone injections into painful joints are common, have been for a time. But research I've read posits the theory that cortisone is actually harmful to the structures of joints, that it causes degeneration of tendons and bursa. Ask your doctors about this research: http://orthopedics.about.com/u/ua/in.../cortisone.htm
Ask whether you should give therapeutic massage a try before going under the knife again.