I have simultaneous Lumbar Stenosis and Arthritis of the hip. How do I know which condition is causing the bulk of my pain?

I have severe lumbar stenosis ( diagnosed in 2003), which had caused sharp pain in both legs.
Over the years the pain situation changed to where, my right leg pain was greatly reduced but my left leg got worse.
Also, in the left leg, I lost 1/2 inch in leg length. Recently, my orthopedic surgeon X-Rayed my left hip and announced that I had severe cartilage damage. He recommended that I have total (left) hip replacement.
My question is:
How do I distinguish which condition ( Hip or Stenosis) is causing the greater pain?
Thank you.
murrays