I mix just about 50/50 venison to pork or ground beef. The fat from these definitely helps, but for stickiness, I go with an egg and maybe breadcrumbs or parmesian/romano cheese. It's kind of like making meatballs, but I use a about 1/2 the amount of egg/bread/cheese.

Meatballs - 1/2 lb venison, 1/2 lb pork or gr. beef
1/2 cup breadcrumbs
1/4 cup grated cheese
3 eggs

burgers - 1/2 lb venison, 1/2 gr. pork or beef
1/8 - 1/4 cup breadcrumbs
1/8 cup grated cheese
1 egg

They taste great and don't fall apart any more than regular beef burgers.
Cheers
Rob