[Morphological variations of the lumbar foramina during flexion-extension and disk collapse]

The authors have studied, on anatomical preparations, the variations in shape and size of 38 intervertebral foramina during flexion-extension movements, on spines which were free of degenerative lesions; they also studied the same variations following an isolated disc collapse. The cast technique takes into account the bony prominences, the bulge of the disc anteriorly, and the capsulo-ligamentous structures posteriorly. In flexion, all the diameters of the foramina are maximum. In extreme extension, all diameters decrease significantly; the pedicles come closer together, the disc bulges posteriorly and the ligamentum flavum pushed by the superior articular process of the underlying vertebra, projects forward. When the height of the disc is preserved, the reduction in size of the foramen does not compress the nerve root. A moderate disc collapse of 4 mm decreases all the diameters and under those circumstances, lumbar extension results in a sufficient decrease of the diameter of the foramen to threaten the nerve root, even in the absence of posterior articular osteophytes.