While dealing with Medicare can be "challenging", I suggest you contact them directly to provide the specifics regarding your wife & your desire to ensure if future injections (post retirement) will be covered.
I believe it is important to cover all the bases so you completely understand what they (Medicare) will pay for or will not prior to your retirement & continuing treatment for your wife.
I your question is a critical one - again be sure you understand all the ramifications.

P. S. do you have "secondary" / "backup" insurance to kick in if Medicare does cover the injections?

Mark