post deleted! A new person, maybe figured it'd help. Will PM and correct.
Knuckles are the sirloin tips. They can be used as roasts, as steaks, thick for London Broil or thin for sandwich steak, made into cube steaks. As I'd said, chuck would be a better choice for grinding, either blade chuck or arm chuck; sirloin tip is more tender and less flavorful for grinding. (The tougher the meat, the more flavor.)