The five lumbar vertebra are the most massive in the vertebral column because of their role as weight bearing structures ( -- -- ). Lumbar vertebrae L1 through L5 are considered to be typical, because they each have a vertebral body and are interconnected through intervertebral disks that help to distribute and absorb forces due to heavy loads. L4 and L5 have limited motion because of their strong attachment to the sacrum through the iliolumbar ligaments. The superior articular facet faces posteriorly and medially, and the inferior articular facet faces laterally and anteriorly. The heavy superior articular processes bear the mammillary processes; their facets are slightly concave, while those of the inferior articular processes are slightly convex. The synovial joints between the upper lumbar vertebrae for the most part approach the sagittal plane, for the facets of the superior articular processes face largely medially, those of the inferior largely laterally. However, the inferior articular process of the fourth lumbar vertebra tend to be less sagittally and more nearly frontally placed, so that they hook over the superior articular processes of the fifth lumbar vertebra and help prevent the column from sliding forward on the inclined upper surface of the sacrum.
as he presents an overview of the lumbar spine.
In the lumbar region the facets are orientated at a 90 degree angle to the transverse plane and at a 45 degree angle to the coronal plane. The unique alignment of the facets of lumbar vertebrae L1-L5 allows normal amounts of flexion, extension and bilateral sidebending, but very little rotation. The orientation of lumbosacral facets is significantly differant from typical facets in the lumbar vertebrae. This transition to a coronal orientation creates a bony block that prevents the top of the lumbar spine (the upper vertebral column) from sliding forward off the top of the sacrum due to gravity and forward-directed shear forces. The unique orientation of the lumbar facets results in coupled movements of sidebending and rotation to opposite sides in the neutral and backward-bending positions () -- and to the same side in flexion ()
the morphology of L1.
the morphology of L2.
the morphology of L3.
the morphology of L4.
the morphology of L5.
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