Knee pain often comes with the advice to never do lunges. We think that's silly. Knee mobility and quad strength can often be recovered with minimal to no aggravation of symptoms if utilizing the appropriate progression.
This video demonstrates an example of how the split squat (lunge) can be adjusted and modified to a various levels of intensity and ability.
Specific prescription and dosages are keys to success. Speak with your physical therapist if you are not sure where to get started.