This is Dr. David
it sounds like the neurosurgeon wants to do a diskectomy to cut out part of the disk at L4 which could be pressing on nerves exiting the spinal cord there and causing pain.
the whole disk is not cut out and so the disk is not replaced.
it sounds like your surgeon wants to do a bone fusion with bars to fuse L3-L5 as well to maintain stability of the spine at that level.
let me know if you have other questions.
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