Poor Eddie.
We have had some car seat tether tangles. Having 2 dogs in one seat seems to make things worse. Separate seats are a little better.
If you are stopped, and you trust your dogs not to leave their seats and not climb around the car, untethering is ideal. That is what I do when we stop on errands, although someone always stays in the car. That might be the only reason M&T behave and stay in the seat.
I hope Eddie's leg feels better.