Andy, most of the revisions are the result of a poor configuration. If you are still better than prep-op, why are you worried? Are you bad and getting worse?
The big risk of anterior revisions has to do with the great vessels being difficult to remobilize. L5-S1 is well below the bifurcation of the great vessels, so they are not in the way. While any anterior spine surgery is a big deal, retrieval at L5-S1 does not have anywhere near the risk involved at L4-5. Having said that, I've observed several explantations, including L3-4, L4-5 and L5-S1.
Mark
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