As they say, "life happens". I hope and trust that you and your husband will get through this fine after a time. Seventy-two used to be old, but not anymore. If he's physicially fit, it will help him heal quickly from the surgury.
It cracked me up when you mentioned the first diagnosis of "mild" arthritis. The definition of "mild" is when it's happening to somebody else.
I just remembered. My 95 year old dad broke his ankle (the knob on the fibula) clear through. After six weeks, he's walking on it with the doctor's OK. I expect the cast will come off on Friday. Hopefully, you'll have the same quick (or quicker) healking.