Medical reasons why Saints may have passed on RB Tyjae Spears

SonOfNOLA said
There may have been concern that he wouldn’t play out his rookie deal, making it a gamble to select him with the 3rd rounder. Hines Ward and Elway played without an ACL, but it’s different wear and tear for a RB without it long term.

Isn't "not unstable" a good thing? Are knees suppose to be unstable? Maybe that explains why my knee sometimes goes left when I want to go right.