I suspect that Bertognali or maybe I read it is a POD Physician Owned Distributor of spine hardware. Please correct me if I am wrong.
I also think (correct me) that ProDisc is a Johnson & Johnson product that has been a disaster. I think J&J bought the company Synthis that developed the disk.
The FDA approved the ProDisk-L that alone makes me wary.
The disk is a ball and socket. There are many problems with a ball and socket design. It will be the first spinal segment to move and it will move further than it should. That will cause a myriad of problems. IMO the best disk is one that acts like a real disk. Currently the only lumbar disk that acts like the real thing is the M6 made in Sunnyvale CA by a small company called Spinal Kenetics.
What is going to stop a segment from rotating too far? Think about it.
I am not a mechanical engineer but common sense tells me that when you repair a machine you need to use the correct part. We can theorize and discuss the many possible factors but we and most surgeons would be guessing.
Maybe a motion X ray would show what is going wrong. I suspect that due to over rotation nerves are being pinched but that is a guess. The implant may have migrated or Dr B was sloppy. I hear that he is. An Xray would show that.