huummm not sure that good sports physios can thank the NHS for their training.
MRI will not always detect meniscal injuries especially if they flap back over - the MRI diagnostics has to marry up with the clinical exam. Swelling in (not around) the knee is pretty important and locking are key indicators for mensical tears.
But, (always a few buts) the locking is depends on the unocking - do you just waggle your knee around or do you have to physically unlock it using your hands?
Meniscal tears are not per se painful - the meniscus has no blood or nerve supply so it isn't painful when torn - the associated swelling can miff off the synovial lining (like a Tescos bag) around the knee.
Pain down hill is more indicative of a patella tracking issue and sitting is pretty much on the money for tracking issues...
You may have a tracking issue due to the way you're being forced to move because your torn meniscus has made your knee swell and become painful.....or vica versa without the tear - certainly getting stronger won't make a difference, but getting more control, may.
See a decent physio - CT won't shown anything (it's great for boney stuff not soft tissue or patella control issues) and 'scoping is last resort. If you've had a lateral release I'd take a punt that you've (still) got an issue with the way your patella tracks...
Hi James - bit odd really. Over pronation doesn't necessarily cause ankle pain. There are loads of people who over pronate and don't have ankle pain - the OP maybe due to the ankle pain or it may be incidental the pain...either way if orthotics make make anything feel weird, then whip 'em out.
You may have to gradually introduce them to your foot type for a few hours at a time stylee