During spinal extension, intervertebral foramina narrows by approximately what percentage?

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When the spine extends, the openings for the exiting nerves (the intervertebral foramina) become smaller because the posterior parts of the joint line up closer together. The facet joints glide in a way that brings the superior and inferior articular processes nearer, narrowing the foramen height. This change is a modest one, typically around twenty percent, rather than a large shift. That level of narrowing is enough to influence nerve root space, especially in people with existing foraminal stenosis or disc bulges, and helps explain why symptoms can worsen with extension. The larger percentages would imply a much bigger and less typical change for a healthy spine, so about twenty percent is the best estimate.