Spine—My Back Is Killing Me
S. Elizabeth Ames, MD, FAAOS
Emmanuel Menga, MD, FAAOS
Dr. Menga or an immediate family member has received royalties from Evolution Spine and serves as a paid consultant to or is an employee of Evolution Spine and Globus Medical. Neither Dr. Ames nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.
Low back and neck pain are encountered in routine clinical evaluation and in emergent settings. Evaluation requires a comprehensive understanding of common conditions that affect the spine including myofascial conditions, spinal stability, or neurologic function. Assessment must focus on face-to-face patient evaluation, including the history of the current episode and previous experiences. There are three goals—to rule out high-risk conditions, to understand contributing factors, and to create a clinical diagnosis based on history and physical examination and confirm with imaging and other modalities. The diagnosis is supported by patient-reported symptoms, knowledge of anatomy, the overall physical examination, and neurologic assessment of spinal cord health (myelopathy) and nerve root function (radiculopathy). Specific etiologies such as tumor, spinal trauma and instability, and spinal infections may require immediate treatment; others such as degenerative processes can often be managed nonsurgically before surgical intervention is considered.
Prevalence of spine-related pain in the general population: 20% to 30%
No substantial studies assess the effect of race on back pain; there are variable reports on the effect of sex.
Pain incidence peaks at ages 20 to 60 years for Americans (which has a substantial effect on the workforce), with limited information about elderly patients.
In 2016, low back and neck pain accounted for the third highest US health care spending at $87.6 billion and low back pain accounted for 3% to 4% of emergency department visits.1
Up to 85% of patients presenting with axial spine pain have nonspecific etiologies, making diagnosis and treatment difficult.
Radiculopathy is irritation of a nerve root causing symptoms in the distribution served by that nerve; usually occurs secondary to the degenerative process in the spinal column but can relate to tumor, trauma, or other conditions.
Lumbar radiculopathy has an estimated prevalence of 9.8 cases per 1,000 in the lumbosacral spine.
Prior history of axial low back pain is a well-established risk factor.
Cervical radiculopathy is similar and known to peak in the sixth decade in both males and females.
Myelopathy is the leading cause of spinal cord dysfunction in adults worldwide.
Clinical diagnosis with cumulative symptoms that can include weakness, dysfunction of gait and balance, hand function, bowel and bladder dysfunction resulting from spinal cord compression.
Degenerative processes, hypertrophy, or calcification of vertebral structures can lead to narrowing of the spinal canal.
These changes are classically associated with aging but can be aggravated by trauma, or related to encroachment of the spinal cord by tumor, infection, or instability from trauma.
The spinal cord travels through the cervical and thoracic spine and then variably extends over the proximal lumbar spine and ends as the conus most commonly at the thoracolumbar junction.
Most lumbar and sacral spine levels are composed of nerve roots, but upper lumbar lesions may generate symptoms more consistent with spinal cord/conus cord injury.
The spinal column is integrated, interdependent, and dynamic.
The spine is a series of specific anatomic structures from the base of the skull to the tip of the coccyx.
The functional spinal unit—vertebral structures over two levels and the intervening disk—is important to understand from both structural and biomechanical points of view (Figure 1).
Classically this has been described as three columns: the anterior column (anterior two-thirds of the vertebral body), the middle column (posterior one-third of the vertebral body and ligaments, pedicles, and neural elements), and the posterior column (the lamina, spinous process).2
The three columns of the spine are consistent throughout the spine and relevant to evaluating spinal trauma and the bony stability of the spine.
Each region of the spine has morphologic variations that help support posture, provide mobility, and protect the spinal cord and nerve roots.
The anatomy review here focuses on a basic foundation that supports the process of initial patient evaluation; it is not comprehensive.
There are many anatomic terms in the spine that are not used consistently in a clinical setting; clinical terms are included in parentheses where relevant.
Each vertebra consists of two parts: a ventral body deep to anything palpable and a dense cortical posterior structure called the dorsal vertebral arch (posterior elements) (Figures 1 and 2).
The arch consists of the osteochondral joints (facets), lamina, two transverse processes, and spinous process.
It also carries the posterior ligaments and extensor musculature (not discussed in this chapter).
The structures of the posterior arch vary by spinal region, and some of these structures and the spinal erector muscles are palpable.
The vertebral bodies are deep structures that consist of end plates, trabecular bone, and a cortical shell.
They are accompanied by the vascular and neurologic structures that supply the extremities.
Anterior and middle structures
The anterior column is made up of vertebral bodies and disks.
Vertebral size increases craniocaudally, reflects the importance as a load-bearing structure, and correlates with ability to resist fracture and mechanical stress.
Each region demonstrates changes that imply function; for example, the lumbar and cervical bodies are slightly higher in the front, and the thoracic vertebrae have specialized processes to support the rib cage.
The end plates support the intervertebral disk, a fibrocartilaginous structure that connects two vertebral bodies.
Intervertebral disk size and shape vary from region to region, but the intrinsic structure is the same.
Two components: a semifluid mass called the nucleus pulposus and concentric fibrous lamellae called the anulus fibrosus.
The nucleus resists compression and is integrated with the chondral end plates and the anulus fibrosus.
The anulus fibrosus is composed of fibrous lamellar bands that are predominantly vertical in orientation; it connects the vertebral bodies and resists tension forces and torsion.
The connection to the vertebral bodies blends with the vertebral periosteum and the longitudinal ligaments through Sharpey fibers.
The disk is metabolically active but has limited vascularity.
The peripheral vascular plexus of the anulus fibrosus and the vessels adjacent to the cartilage of the end plate and bone/disk interface are the sources of nutrients.
Ligaments are found both anteriorly and posteriorly.
Two major ligaments accompany the vertebral bodies: anterior longitudinal ligament, posterior longitudinal ligament, and the ligamentum flavum.
The anterior longitudinal ligament extends along the ventral surface from the skull to the sacrum.
The deep fibers adhere to the anterior surface of the vertebra and are only loosely attached to the anterior anulus fibrosus of the disk.
The posterior longitudinal ligament is closely applied to the posterior anulus fibrosus and less integrated with the vertebral bodies.
The lamina is the roof of the spinal canal.
Primarily cortical and less vulnerable to trauma or disease than other areas
Continuous with the pars, the facets, the pedicles, and the spinous process and one of the most common anatomic structures encountered in spinal procedures
The central nerve canal is directly below the lamina.
Cervical facet joints oriented to allow significant rotation; lumbar facet joints oriented to allow flexion and extension with limits on rotation
Size varies but structure is the same; all have hyaline cartilage surface, supportive capsule, and nutrition typical of other joints in the body
True synovial joints with synovial membrane, hyaline cartilage, and a fibrous capsule
Pars articularis—area between the facets and lateral aspect of the lamina
Resists translation forces, particularly at C2 and L5; respective clinical examples are a hangman’s fracture or isthmic spondylolisthesis
Roofs the lateral part of the spinal canal and contributes to the opening the nerve roots use to exit the spine (foramen)
The pedicles of the vertebra above and below are the superior and inferior boundaries of the intervertebral foramen.
The foramina are spaces that allow the nerves to exit.
The foraminal floor is disk structures and ligaments, and the roof includes the facet joints.
Degenerative changes and tumor, trauma, and congenital disorders all affect the size of the foramen.
The pedicles are primarily cortical and reliably sized and oriented.
Pedicles connect the posterior elements with the anterior vertebral body.
The relationship between the pedicle and landmarks is well defined at most levels, and easily confirmed with imaging.
Neural elements are closely applied in all regions, and vascular elements in some. These characteristics have made pedicle instrumentation a surgical workhorse particularly in the lumbar spine.
The 24 vertebrae of the spine are divided by region; the regions are determined by overall alignment and individual anatomic features that are most evident in the posterior column.
Four anatomic regions—cervical, thoracic, lumbar, and sacral
Three biomechanical transition zones—cervicothoracic, thoracolumbar, and lumbosacral—carry equal importance.
By convention the spine is defined in two planes: coronal (looked at from the front or back) and sagittal (looked at from the side).
A third plane—axial—defines much of the space available for the neurologic elements.
All three planes are important to clinical evaluation.
Alignment and anatomy are closely related but also affected by external forces such as gravity and motion.
Four regions to the spinal column—cervical (C1-7), thoracic (T1-12; characterized by the presence of ribs), lumbar (L1-5), and a conjoined sacrum
Each is built to respond to the forces it experiences (Figure 3).
In the cervical region, C3-6 are relatively uniform in shape and design (Figure 4).
Cervical vertebrae carry the least weight in the spine.
The neural canal is filled by the spinal cord, and the nerve roots have short, nearly horizontal transitions out of the canal.
The vertebral artery (Figure 5) travels directly through bone structure in the cervical spine, which affects risk of injury both traumatic and surgical.
The cervical disks are accessible through anterior dissection of the neck with safe access to structures affecting the cord and roots; posterior access is more difficult.
The posterior bone structures are small, but instrumentation techniques are available including pedicle access at C7.
The atlantoaxial complex—occiput, C1, and C2—forms a complex articulation that allows rotation of the head.
C1 is a bony ring that can be thought of as similar to a standard vertebra without the body.
Embryologically the body of C1 has become the dens of C2, a prominence arising from the body of C2. C1 rotates around C2, supported primarily by ligaments (Figure 6).
It is critical to understand this relationship in detail when assessing patients with either high-impact and low-impact trauma.
The course of the vertebral artery is closely applied to the posterior ring of C1, risking injury with surgical dissection.
The posterior arch of C2 is substantial, and the inferior processes are typical of the rest of the cervical spine.
C2 is also the end vertebra of the cervical lordosis.
For both these reasons C2 is often included in surgical constructs.
Figure 6 Superior view drawing shows the relationship between C1 and the odontoid of C2. (Reproduced with permission from Anatomical Chart Company © Wolters Kluwer. All rights reserved.)
The cervicothoracic junction is an area of high stress and rapid transition, with stress coming from the highly mobile cervical spine meeting the stiffer, rib-bound thoracic spine.
The anterior anatomy of this region is important to know because airway, esophagus, great vessels, and the sternoclavicular junction are closely spaced to the spine.
C7 is a transitional vertebra.
The inferior portion of the body is relatively larger than the superior portion and the spinous process is also large and distinct.
All 12 thoracic vertebrae connect to ribs.