It can be bacause of many different reasons. The most common ones are incorrect tire presure, unbalanced wheels, loosen nuts, bad alignment, bad front bearing, and the worst bad steering system. I would start from presure and nuts. You can check also front bearings it's easy but you have to be careful.
Wheel balance
It might be your transmition...
One or more tire out of balance, a bent wheel, or defect in a tire.
Tire out of balance or bent wheel.
Tires and/or wheels out of balance?
If it shakes just driving at around 50 mph then the tires need balancing. If it shakes when stopping you have a warped rotor. Edit: tire balance problems are most noticeable starting at around 35 mph. Balance problems can be undetectable by 50 mph. Can also be a bad tire which will be more noticeable usually at slower speeds. Steering wheel shake normally indicates a problem with the front end while a shake felt in your feet and/or the seat will be in the rear. Shake while braking will usually be a rotor problem, however can be a bent hub or spindle and even loose steering parts. Need to take to a qualified tech for further diagnosis.
Struts themselves cannot cause shaking, I think who ever was assembling your car did not install properly wheels or the alignment was disturbed.
i would really like to know myself
Need more info. Does just the engine run rough or does the steering shake or does the whole vehicle shake betwen 50 and 55 mph?
If it happens when you are driving fast (60-70 MPH) it could be that your wheels are out of alignment.
have your front tires rebalanced.
Most likely your wheels need balanced.