Hi Susan,
All the same precautions for electrical stimulation with pads should be followed with Needle stimulation. Of course, we would not touch the prosthesis with the needle and stim the area. The other variables are how close you can get to the knee and where the needles are placed determines the path of the stim so certainly would not do an A/P or M/L arrangement to the joint. Putting needles in the quads or the hams with stim is something I have done but I avoid getting any closer to the prosthesis.
Hope that helps