This may just be your breakthrough. And he may be bringing it about himself.
Whether or not we realise it, when we need to change, part, if not all, of the motivation we find is the"what's in it for me?" factor. This may what galvanises some change in him. Did your husband want to go and have this issue addressed? Does he want the pain to stop? Would he like to find stairs, walking or generally moving around more comfortable?
How far would he go to achieve that?
I'm not sure if you have noticed, or indeed if it has occurred since you've been coming on here, but quite regularly people end up here when they have been rejected for surgery, on the basis of their bloods. Poorer diabetic control can result in poorer healing, and the the danger that any minor infection could run riot.
Not all of those new people arriving here are new diabetics, discovered in the pre-op period, some have been living with diabetes for some time leading up to their pre-ops, but either couldn't or didn't make the desired level of changes required for surgery to take place safely. Being rejected for their surgery is often the catalyst for change.
See what I mean about the "What's in it for me?" factor?
For them, there is a stated requirement to achieve an HbA1c score of X before surgery can occur. The message delivered is, "No surgery for you, for now. Come back when your HbA1c is X and we'll get you scheduled."
The "what's in it for me?" is an HbA1c equals surgery, which equals being pain free, which equals better quality of life. Suddenly better diabetic control isn't the end objective, but a stepping stone to something else.
Whilst I don't want your husband to be rejected for surgery he may well need, but if he wants a change of knee, he may just get motivated to take notice of his diabetes.
What do you think?
And finally, if there is anyone reading this who arrived here in the manner I describe, please don't think I'm judging you. Sometimes change is just too overwhelmingly difficult, and we can't make the change for whatever reason. We've all been there at some stage, for some reason, including me.