Alex I think the link research is refering to C-A ligament which I don't believe is the responsible impingment structure for Karen. There are many different reasons for impingement, Type II acromium, SS tendon, biceps tendon are the most typical. In this case the impingement is between the coracoid process and the humeral head as you suggested and C-A ligament is over the acromium, to of the shoulder and would present with a painful arc.
No karen I have not seen this particular impingement but it does seem likely following shoulder procedures. The OS diagnosed you very quickly. What was the definitive test? It should be the Kennedy Hawkins with shoulder flexion, adduction and medial rotation. I would have a follow up and have him inject it with
lidocaine like the following article suggests just to be certain of the diagnosis. It sure would not hurt to get a definitive further sign. You may find this article interesting.
www.jbjs.org.uk/cgi/reprint/72-B/2/314.pdf