Stellamac, to answer your question from a couple of months ago, I had a revision because the femoral component became loose 9 years after a THR, most likely caused by "bad luck," When the loosening happened starting over a year ago, the pain was on the outside of the hip, but even worse than the pain was a feeling of instability. A couple of times, my hip seemed to suddenly "give way" and I fell to the ground, luckily in my garden both times so it was a soft landing. I never felt groin pain as you say you are experiencing. It seems unfortunate that at 4 months you are still having so much pain. The diagonsis is complicated in your case because of the knee issue. I hope you get some answers. What does your surgeon have to say about this much pain at 4 months out?