Wall slides as rehab, but now lots of road cycling. I have very big and strong quads, but never do squats, indeed I physically can't due to abnormally tight calf muscles (however much I stretch)
If you can't do squats for whatever reason, your physio should be giving you alternatives. If s/he can't, find a physio who is more knowledgeable!
Of course, you should be working all the muscle groups around the knee, as well as hips, glutes and make sure your feet are aligned and gait is correct
