Various hardware failures requiring revision surgery; examples include screw misplacement, screw loosening, breaking or pull out, cage migration, rod breaking, etc. Risk of neural injury during insertion of the implants; especially the screws. Risk of more surgeries down the line due to degeneration of the levels adjacent to the fused level(s). Failure of bone healing i.e., fusion to occur, may result in persistent or recurrent worsening of pain, or problems with instrumentation. Other unforeseen risks.