What are the lumbar foramen and spinal canal made of?

Lumbar foramen consists of the posterior part of vertebral body and vertebral arch. The lumbar foramen are connected to form a lumbar canal, which contains cauda equina nerve from waist 1 to waist 2, and is an important nerve channel. There are two diameters of the hole: the sagittal diameter of the hole is from the posterior edge of the vertebral body to the most prominent joint of the two laminae; The transverse diameter of vertebral foramen is the widest distance between the inner edges of pedicle protruding from both sides. Of the two diameters of spinal canal, sagittal diameter is the most important. Generally speaking, if the sagittal diameter is less than 13mm and the transverse diameter is less than 18mm, it can be defined as spinal stenosis, and if it is less than 10mm, it is absolutely stenosis. Lumbar 3 is the smallest in the sagittal diameter of vertebral foramen. In the case of pathological changes, such as lumbar disc herniation and lumbar spinal stenosis, waist 4 can be the smallest.