The Toyota FJ Cruiser lower control arms (LCA) are prone to damage. The stock arms are not strong enough to holdup to a direct hit on a rock. Once bent the alignment of the rear axle will not longer be correct and the drivablity of the FJ Cruiser will be affected. A number of people have reported bending the LCAs when impacted on a rock.
There are a number of aftermarket manufacturers that have replacement lower control arms that are made with much stronger material and should not bend under hard off road use. The cost of these LCAs varies based on materials used and construction. I have replaced my LCAs with ones provided by All Pro Off-road.