Lumbar Vertebrae

Lumbar vertebrae are in the lower back between the thorax and sacrum. Because the weight they support increases toward the inferior end of the vertebral column, lumbar vertebrae have massive bodies, accounting for much of the thickness of the lower trunk in the median plane. Their articular processes extend vertically, with articular facets sagittally oriented initially (beginning abruptly with the T₁₂-L₁ joints), but becoming more coronally oriented as the column descends.

The L₅-S₁ facets are distinctly coronal in orientation. In the more sagittally oriented superior joints, the laterally facing facets of the inferior articular processes of the vertebra above are “gripped” by the medially facing facets of the superior processes of the vertebra below, in a manner that facilitates flexion and extension and allows lateral flexion, but prohibits rotation.

The transverse processes project somewhat posterosuperiorly as well as laterally. On the posterior surface of the base of each transverse process is a small accessory process, which provides an attachment for the intertransversarii muscles. On the posterior surface of the superior articular processes are small tubercles, the mammillary processes, which give attachment to both the multifidus and intertransversarii muscles of the back.

Vertebra L₅, distinguished by its massive body and transverse processes, is the largest of all movable vertebrae. It carries the weight of the whole upper body. The L₅ body is markedly taller anteriorly; therefore, it is largely responsible for the lumbosacral angle between the long axis of the lumbar region of the vertebral column and that of the sacrum. Body weight is transmitted from L₅ vertebra to the base of the sacrum, formed by the superior surface of S₁ vertebra.