I was told today (by someone in the field) that disc protrusion is NOT a risk factor for disc herniation. Here is the context: On MRI, I pointed to a small but obvious disc protrusion at C5-C6 and asked…how much more likely is that one to herniate compared to this one (a “normal” disc at C6-C7)? This requires some assumptions, of course. I was surprised at the answer. I suppose I just assumed that a bulging disc stressed the annulus. Maybe not.
PS. Thank you for providing this great forum. There are some really insightful threads here. The current ACDF ?levels thread is brilliant. I suspect the OP is much better off for having found this forum!
A disc bulge in the annulus has a higher chance for a disc herniation than a normal disc. Use simple logic and reasoning for this one. The annulus has 30 layers of collagen fibers. Each one has to develop a tear in it for the nucleus to extrude through the defect. A bulging disc already has failure of the annular wall to some extent. It may be partial tears of some of the layers with stretch injury to some of the other layers. In any case, this bulge is a weakened spot in the wall and less force needs to be generated to fully tear through all the layers.