*muscle* tightness I would associate with spasticity.. joint tightness not really. need more info.
if muscle spasticity, you could evaluate your magnesium intake from diet (mag is an essential nutrient .. often serum mag is low- to mid-normal in ms patients vs high-normal (or even higher) in healthy controls - make sure you get 600mg per day and not too many magnesium depleting foods/drinks in the mix)
most ppl don't get enough dietary mag. it can manifest in a wide variety of different ways.
if you decide to follow up re magnesium, there's lots of info the read up on re testing, interpreting results, food options, best supplemental forms and so on.
best thing about magnesium is that it helps support hundreds of other processes in the body as well, not just helping muscles relax.
of course it all depends what you mean by knee tightness