I am so sorry
You've received some great advice.
Regarding prognosis, there may be some things you can look into that will help delay the onset of crippling arthritis.
IRAP therapy might be one - at some point down the road.
Keeping his hocks warm is important - especially in Iowa winters.
I have Back On Track hock wrap and Quick wraps for two different horses. I think they are "earning their keep" for the money they cost. Get Back on Track -Therapeutic Horse, Dog, People Products
Did the vet say whether or not wrapping him would help?
I have one horse with torn ligaments and sesamoiditis on the front. I have been keeping his legs wrapped 24/7 since that Loser Farrier cut him too short and the result was those torn tendons. The vet said keeping his legs warm was largely instrumental in saving him.
I wrap with felt, then quilts, then the standing wraps and change them twice a day. The only time he is out of wraps is the few hours he wears the Back-On-Track Quick Wraps. He is on turnout 7 - 12 hours daily, depending which season we are in. He is also my horse that never grows a winter coat, so he wears a blanket when the sun isn't out, it's windy, and the temps are below the mid-40's. It all helps keep him warm, which in turn reduces pain stress and weight loss.
It would be difficult to wrap back legs but not impossible if the vet thinks the added warmth would be beneficial
I hope this helps and the very best to you