The best replacement for protrusion is extrusion.

The best alternatives to protrusion are rated as following:
★★★★★  extrusion
★★★★★  herniation
★★★  disc herniation
★  herniated disc
★  disc bulge
★  bulging
★  protraction
★  prolapse
★  bulge
★  rupture
★  disk herniation
  disc extrusion

Your alternative for protrusion is not listed? Suggest!
Speaking about protrusion, one probably shouldn't forget about annular tear.

Other search terms related to protrusion and their ratings are:
★★★★★ annular tear
★★★★ annular fissure
radial tear
an annular tear
You have in mind a companion for protrusion and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of protrusion in all years. Click on graph for more.
protrusion
extrusion
herniation