Hold up
How fast were you driving when it locked up? And to be clear, you are saying the steering wheel locked up and could not turn one bit yes? Not that you just lost the normal boost that makes the steering feel light and springy. I'm sorry but I have real trouble believing a car can be designed and approved such that its failsafe state in the case of an electrical or sensor problem is that the STEERING WHEEL LOCKS TIGHT. How crazy would that be if you are driving on Pacific Coast Highway at speed and the sensor blips at that point and you are then flying off the cliff because you can't turn the car at all? Seriously I have never heard of this and it doesn't make sense at all.
I smell a troll here, given all the other MDX bashing happening, but willing to listen. At least the others all admitted that "well I guess when I say the steering and brakes FAILED, they didn't really stop working completely, which is why I was able to pull over safely......"