Lower Ball Joint

Hi, I have a 1990 T-Bird, and I was searching parts out for it that I need, and the auto parts store asked me if it was just the lower ball joint I need or if the ball joint and control arm thing are a 1 piece thing, I told him I have no idea....so can anybody tell me how do I figure out if the lower ball joint can be seperated from the control arm thing or if it is a 1 piece thing? Any help would be much appreciated....thanks :-)

- Brian