Anatomy, Back, Lumbar Vertebrae

Vertebrae, together with intervertebral discs, compose the vertebral column, also referred to as the "spine." The vertebral column extends from the skull to the coccyx and includes the cervical, thoracic, lumbar, and sacral regions. The spine serves several critical functions, including protection of the spinal cord and branching spinal nerves, structural support for the thorax and abdomen, and facilitation of flexibility and mobility. Intervertebral discs permit this mobility while preserving the supportive strength of the vertebral column. The lumbar region contains 5 vertebrae, designated L1 through L5. The intervertebral discs, in combination with the laminae, pedicles, and articular processes of adjacent vertebrae, form spaces through which spinal nerves exit. The lumbar vertebrae collectively produce a lordotic curvature. Typical vertebrae consist of a vertebral body, a vertebral arch, and 7 processes. The vertebral body bears the majority of the axial load transmitted through the vertebral column. The vertebral body is composed of trabecular bone containing red marrow, surrounded by a thin external layer of compact bone. The vertebral arch, together with the posterior aspect of the vertebral body, forms the vertebral canal, which houses the spinal cord. The arch consists of paired pedicles connecting it to the vertebral body and paired laminae extending posteriorly from the pedicles to meet at the midline spinous process. A typical vertebra also contains 4 articular processes, including 2 superior and 2 inferior processes, which articulate with the corresponding articular processes of the adjacent vertebrae above and below. The articulation between the superior and inferior articular facets forms a facet, or zygapophyseal, joint. These joints maintain vertebral alignment, limit the range of motion, and bear weight in certain positions. The spinous process projects posteriorly and inferiorly from the vertebral arch and overlaps the inferior vertebrae to varying degrees, depending on the spinal region. The paired transverse processes project laterally from the vertebral arch in a symmetric fashion. Typical lumbar vertebrae demonstrate several features distinct from those of cervical or thoracic vertebrae. The most prominent distinguishing feature is the presence of a large vertebral body. The spinous process is short and thick relative to overall vertebral size and projects perpendicularly from the vertebral body. The articular facets are oriented predominantly in the vertical plane, with the superior facets directed posteromedially and medially. The facets also exhibit a curved articular surface. This characteristic distinguishes lumbar vertebrae from thoracic vertebrae. A mammillary process is present on the posterior aspect of the superior articular process (see . Lumbar Vertebra). Intervertebral disc thickness generally increases from rostral to caudal levels, with lumbar disc height exceeding that of cervical and thoracic intervertebral discs. Only 1 lumbar vertebra is considered atypical. L5 has the largest vertebral body and transverse processes of all vertebrae. The anterior height of the vertebral body exceeds the posterior height. This configuration contributes to the formation of the lumbosacral angle between the lumbar spine and the sacrum.