The lumbar spine, lumbosacral articulation, and sacroiliac joints are prone to numerous dysfunctions related to mechanical stresses and degenerative changes. Additionally, this region is vulnerable to acute trauma from falls or heavy lifting and chronic strain from repetitive movements, ligamentous laxity, and poor posture. Those with resultant low back and buttock pain syndromes are among the most frequently treated patients seen in the clinic. It is essential that the clinical evaluation include knowledge of the underlying degenerative changes in the spine as revealed on radiographs. The degree of degeneration will affect the ability of the spine to withstand trauma, assume postural changes, and make functional gains in mobility and movement patterns.
Five vertebrae comprise the lumbar spine (Fig. 11-1). The fifth lumbar vertebra is joined to the sacrum via the articulation of the inferior articular processes of L5 to the superior articular processes of the sacrum and, additionally, the L5–S1 intervertebral disk. These articulations define the lumbosacral junction (Fig. 11-2). The transformation of the lumbar lordosis to the convexity of the sacrum at this junction defines the lumbosacral angle. The caudal end of the sacrum articulates with the coccyx.
A three-dimensional (3D) reformatted CT scan of the lumbar spine and sacrum. (A) is an anterior coronal view The spine is normal with the exception of fractures at the tips of the right side transverse processes of L1, L2, and L3. These injuries were sustained by a professional football player during a regular season game as he jumped to catch the ball and was struck in the low back while tackled. An advantage of 3D CT imaging is the ability to visualize difficult-to-see structures that may not lie in cardinal planes. (B) is a sagittal view, showing normal anatomy of the lower lumbar vertebrae and lumbosacral articulation. (Image A courtesy of Tom Hunkele, MPT, ATC.)
(A) Axial CT image of the sacrum and sacroiliac joints. (B) Posterior view of the lumbosacral articulation, sacrum, coccyx, and sacroiliac articulations. The L5 laminae and spinous process are cut away to show the L5 vertebral body and L5–S1 disk.
Lumbar vertebrae are characterized by large bodies that increase in size from the first to the fifth lumbar vertebra (Fig. 11-3). Short pedicles project posteriorly from the body and give rise to paired superior and inferior articular processes. Short, broad laminae unite in midline to form large, blunt, horizontally inclined spinous processes. Transverse processes are slender in the lumbar spine. Spinal nerves exit the intervertebral foramen bounded by coadjacent pedicles. Zygapophyseal joints (more commonly known as facet joints)...