If Brian Urlacher's opinion matters to anybody then the biggest loss to the Bears defense this year is 2nd year tackle Dusty Dvorcek. Urlacher has gone on record saying that not only has his absence hurt the run defense in general, but it was a knock on his ability to do his job.
In two years as a pro, Dvoracek has only played 1 game. Missing last year to a torn right ACL and this year to a torn left ACL. The word is typically the ACL is stronger after coming back from surgery, so hopefully this will be the end of his bad luck.
For his part, all he can do is keep working.
The one thing we know is when healthy our defensive line is in good shape and perhaps can dominate. The problem is keeping Dvorcek and Harris healthy to go along with Ogunleye, Anderson and/or Alex Brown. Add Anthony Adams, who played well when needed to that and you have something to base a defense on.