Re: Pre/Post-Surgery Strengthening
Ask your local physical therapist.
Pre- Squatting/step ups/etc. all can definitely be done, but it depends on the person if they can handle it and such.
Post- generally therapists will stick with "proven" protocol and they'll progress you fairly slowly because they don't want to risk reinjury
YOu definitely want ot be doing activity to prevent atrophy and such, but no one here is going to give any recommendations because it's case by case.