Baastrup’s disorder is the fictitious belief that the spinous processes will abut each other under extension and will cause significant pain from the bones compressing into each other. This is simply not true as in all my years of treating patients, I have never seen this disorder but I have seen many patients with spinous processes that abut without pain.
Most active individuals who have extension pain have either facet disorders (see website under lumbar spine facet disorders) or have a pars or facet fracture (see isthmic spondylolisthesis).
One of the trademarks of isthmic spondylolisthesis is tight hamstrings.
Dr. Corenman