I was wondering if he got OEM parts or aftermarket parts from AutoZone.

Get well Mike!
Dennis
No matter how good modern medicine is, it is very difficult to replace nature's original parts. We can improve things but never get back to nature's original form.
For anyone who has had to go thru this type of surgery, I wish you well and a speedy recovery. I know what you are going thru. Recovery can be painful and slow but if you hang in there, do the therapy, you will improve. You can't rush nature so it will take time.
I have had nothing but spinal problems all my life. The first fusion surgery was in '83 or so. That was in the Stone Age, where bone slivers were cut out of the hip and used to fuse L5 to S1. What a horrible, painful recovery. I had a condition called spondylolysis. The surgery was successful but I was told that in time, this could cause problems at the next level up.
I had two more surgeries last year. With more modern techniques, the three-level neck fusion and a second lumbar fusion (for spondylolisthesis at L4) were not too bad. I now have so much metal in my spine I wonder about setting off metal detectors. In both of the most recent surgeries, the unavoidable nerve irritation and other trauma that was required just to fix the problem resulted in painful recovery. However, I am glad I did both surgeries as there was no way physical therapy was going to solve these problems.
I was lucky to have found a young and very skilled surgeon.