Possible reason for Spondylolisthesis?

I have been diagnosed with spondylolisthesis in my L5 and surgery has been discussed with me to correct it. They can not give me much of a clear answer to what caused this. I have both of my hips replaced due to RA. Right hip resurfaced using metal on metal in 2009 (I was 25). I walked bone on bone for 2 years before I had it replaced. Left hip total replacement using ceramic on plastic in 2011 (Now 28). They wanted to replace them both at the same time in 2009 but elected to do the right one only. The doctors felt that it may be best to wait as long as I could with the left hip due to my age and to stress the replaced right hip more to slow down the wear on the unreplaced left hip. I instantly had problems with the metal on metal hip resurfacing (I do not have the recalled J&J, I have a Smith and Nephew BHR). While in PT they could feel it click and they were unsure of what was causing this. The surgeon said it was normal and would go away in a few months. It never did, and a little over a year out of surgery the hip started to squeak and grind. I see the surgeon again and Im told it is the media putting ideas in my head due to the hip recall (I did not know there was one at the time) I went to see a revision doctor about the right hip and for him to replace the left hip, he told me my ion levels are high. He said that after the left hip heals to stress it more then the right in hopes it would help the right hip stop grinding. With the ion levels being high, 2 MRI's of the right hip did not show anything out of the normal. I did what I was told and stressed the left hip more. While at home working on our house I took a large step over some things (I had nothing heavy in my hands) and stepped over using my left leg and when I put all of my weight on my left leg I felt a crunch and it felt to be in my left hip. The pain was so sharp it almost put me to my knees. The pain was similar to before I had a hip replacement. I kept walking but my lower back hurt. This happened in Sept of 2011. I went to see the surgeon who replaced the left hip and he felt that it was my back that was the source of my pain and xrays showed some narrowing in my lower back. I have a MRI done and see a spine surgeon who confirmed the spondylolisthesis in my L5. Its pushed inward and rubbing on the left side of my pelvis. Surgery has been discussed to fix the problem, I am very physically fit due to my job and weigh 160lbs.
Ok now to my question. I know that the bodys reaction to the metal debris is as it collects it starts to turn the bone soft (where its collecting) and I wonder if this could be the cause for the fracturs in my L5? They can see its not from the RA. They cant give me a direct cause for the problem but it could be from putting a lot of my body weight on the right hip for so long and then shifting all of that weight to the left hip. They cant give me much of a answer of why the resurfacing is failing either. But if the failing of the resurfacing is a real possibility for the problem in my back what do i do? Have a revision on the right hip first and then surgery on my back? or the other way around? Both the hip and spine surgeon's are talking about this together but its been almost 2 weeks with no answer.

First I want to start out by saying my mom has RA and I am sorry all the pain you have already gone though. I need some questions answered so I can give you the most best answers. Did the spine doc say how much your L5 is moving forward? There is 5 grades of moving for your information. I treat football players with spondylolistehesis and the football players are able to play without pain. The question really comes down to if the spondylolistehesis is unstable affecting leg weakness or bladder symptoms.

The spine doctor has said its a 5mm shift. It was a really quick visit with him and I only seen him once. PT was discussed and if that did nothing then surgery was the next step. I set up a appt to go to PT and they called a day before my appt and said my health insurance would not cover me unless I have had prior surgery done to my back. I called my spine doctor and I left a message for him and he called me back later the same day and he said that he did not think PT would have worked anyway and talked alittle bit more about surgery.
I feel a lot of pressure on the left side of my pelvis when I sit or stand. I have deep muscle pain in my left leg that stops at my knee. As time goes on it is feeling weaker and weaker and at the end of the day its hard to lift my left leg up to walk up stairs or even walk ingeneral. No bladder issues as of now.