LCA is your "lower control arm" bushings. The LCA is the part that connects the lower part of your wheel hub to the bottom of the car, by the engine. If any of these suspension parts should fail while you're driving, it will be pretty bad. The wheel might not fall off, but it will come loose from the car, resulting in major damage and most likely a crash.

 

Oh yea, and the bushings are what the LCA piviots on underneath the car.