pseudoarthosis

Question regarding a pt I have.

Pt pressented with L posterior knee pain localized for a few months. Pain was intense and got worse with his job which was physical. All Xray and MRI showed no problems with the knee.

I believed the pain was from the back, as pt did report previous falls onto his lower back.

Xray shows a pseudoarthosis of S1-2. This I believe is the cause of the pain in the posterior knee, and pt now complains that the pain even goes to the foot, further confirming this.

What would be the treatment of choice for this? Any ideas?

Many Thanks for you help