My surgeon wants to do a hip replacement within a year, but i believe my pain is coming from my back which in the mri showed severe stenosis on l4 and l5 along with bulges and severe compression l3 l4 which is classic pain in my knee and thigh?

Get a second opinion if this is your concern.

It is not uncommon for older folks to have both degenerative arthritic wear-and-tear in both hip and lumbar spine. A search for the primary pain generator may be a worthwhile endeavor and many experienced physiatrists can pinpoint the precise location. Sometimes, it is necessary to operate on both hip and back, but physical therapy may be useful in stabilizing without surgery, albeit temporary.