Could the Topping-Off Technique Be the Preventive Strategy against Adjacent Segment Disease after Pedicle Screw-Based Fusion in Lumbar Degenerative Diseases? A Systematic Review

Figure 2

The definitions of “index level” and “supra-adjacent level” in our manuscript. “Index level” represents the disc level just above the fusion construct. “Supra-adjacent level” represents one disc level above the index level. The fusion levels in selected manuscripts ranged from 2 to 5 vertebrae levels, which were not, respectively, presented herein.