Multi-level Lumbar Disc Issues

Hello. I am being recommended for L5/S1 spinal fusion.  I have already had L4/L5 fused.  Based on the results of a recent MRI (see notes below), please let me know your thoughts on if this would be a logical mode of treatment.  Thank you

L5-S1: Moderate bilateral facet arthrosis is present, with 3 mm of mild grade 1 degenerative anterolithesis of L5 and S1.  There is disc uncovering and a small central/left paracentral disc protusion (with annular fissure/tear) which minimally effaces the ventral thecal sac without central spinal canal stenosis or foraminal stenosis.  

L4-L5: Residual small endplate osteophytes mildly efface the ventral thecal sac and results in mild bilateral foraminal narrowing.  No significant central spinal canal stenosis.

L3-L4: A broad-based disc protusion measuring 4 mm in AP diameter and mild bilateral facet arthrosis are present, resulting in mild effacement of the ventral thecal sac (10 mm AP diameter of the thecal sac) without significant foraminal narrowing.  

L2-L3 Minimal annular bulges with no spinal canal or foraminal stenosis.