A bit old of a comment to reply to but I found this interesting because I just got a new car and am finding I have a milder version of this kind of problem with it - because of fancy new technology.
My old car was a 1998 Subaru Impreza, an automatic without cruise control. Up to that car I had always driven manual but it was a hand-me-down (well, as were the others). I drove that car from NY to CA and back - going across 7 times in total - and never felt like I needed cruise control. When you really get in the groove of your car you can rest your foot very comfortably in just the right spot on the accelerator and just let it sit there (until you run out of gas, in some parts of the country), and you can make subtle changes in speed almost instinctively when needed.
The few times I’d tried cruise control in other cars it seemed pointless, because even on those big open drives you do usually have to change your speed quite a lot because of other drivers etc., so I really never missed having it. (As an aside I did once drive somebody else’s manual car that had cruise control, which was an interesting oddity to me.)
But now, my new car has adaptive cruise control. It’s awesome - though you do feel very disconnected from the driving. I use it pretty much any time I go on the freeway - even, or especially, in heavy traffic, because it does all the work for me, keeps a consistent distance from the car ahead (you control the distance if you want), and dramatically improves gas mileage over my regular driving style, which is not even particularly aggressive.
However, here’s where the problem comes in. You can use adaptive cruise control almost all the time - way, way more than you could realistically use old-style cruise control. With regular cruise control, the only times it seems usable are times when you could relatively safely have both feet flat on the floor - not times when quick reactions may be needed.
But you can (and, honestly, should) use adaptive cruise control in times when quick reactions are often needed (e.g. when someone quickly cuts into your lane at a much lower speed). The car will put on the brakes and come to a complete stop by itself if it thinks it will hit something, however, I don’t feel it’s particularly wise to trust that - so realistically you have to awkwardly hover your foot over the brake pedal. You can’t rest it on the pedal, because the amount of force required (for either pedal) is quite small.
I don’t know if this becomes painful for most people or not, but I injured my knee in college (I jumped out of a tree I climbed at the top of a mountain on a field trip - I studied geology) - minor injury, really, but it never really went away. Really the only thing that particularly aggravates it is the positions your legs go in when driving a car (and I never put socks on or tied my shoes the same way again). With my old car I never had an issue (and it’s a small car, not a ton of leg room or anything), and now because of new technology (not that I’m forced to use it), I do sometimes have a problem.
tl;dr - a new technology, adaptive cruise control, causes knee pain because you have to hover your foot over the brake pedal and can’t rest on something solid