The Anatomy of the Low Back and the Limitations of Diagnostic Imaging of This Area

AuthorSamuel D. Hodge, Jr./Jack E. Hubbard
ProfessionSkilled litigator, is chair of the department of legal studies at Temple University/Professor of Neurology at the University of Minnesota
The Anatomy of
the Low Back and
the Limitations of
Diagnostic Imaging
of This Area
Routine X-rays or
MRIs for patients with
low-back pain does
not lead to improved
pain, function or
anxiety level, and
there were even some
trends toward worse
Roger Chou, M.D.
Scope of Low Back Problems1
The incidence of low back pain is a major economic problem globally. The medical litera-
ture reveals that at least 80 percent of the population experience back pain at least once
in their lifetime and 25 percent of these individuals will have recurrent discomfort within
one year.2 Simply put, low back pain is the price that humans have paid in going from a
four-legged creature to an upright one. And, it is quite an expensive price since the esti-
mated cost of low back pain is more than $90 billion annually.3 Nevertheless, most back
pain sufferers do quite well, with 60 percent recovering after only six weeks4 and 80 to 90
percent becoming asymptomatic by the twelfth week after onset of symptoms.5 Implicit
in these figures is the fact that a minority of people with chronic low back pain6 account
for the majority of the costs in treating this disorder.7 As the literature demonstrates,
70 percent of the cost associated with low back pain is generated by only 20 percent of
Workers greatly influence these statistics.9 Approximately 2 percent of all employees
in the United States receive compensation for back injuries each year,10 and a mere 10
percent of those employees account for 70 percent to 80 percent of the costs associated
with this malady.11 Only 4.5 percent to 8 percent of disability claims involving low back
pain last longer than one year, and those claims that exceeded one year account for 64.9
percent to 84.7 percent of all of disability cases.12 In the vast number of instances, an
episode of low back pain limits a worker’s regular activity for at least 30 days.13 Less than
half of those individuals who miss 26 weeks of employment never return to their jobs and
almost none return to work if off more than 104 weeks.14 Demographically, low back pain
is the most common reason for disability in those under the age of 45 years.15
A number of diagnostic tests are available to help physicians discover the origins
of low back pain. These imaging modalities range from conventional x-rays to highly
sophisticated magnetic resonance imaging (MRI) scanning where few back abnormalities
escape detection. Unfortunately, such imaging is not infallible, for not every abnormality
is clinically significant and there can be legitimate pain complaints in the absence of an
abnormal diagnostic test. This chapter discusses the anatomy of this region of the spine
and explores the limitations of low back diagnostic imaging.
Anatomy of the Low Back
The regions of the spine are adeptly explained in Kostel v. Schwartz as “three main groups
of vertebrae—the cervical vertebrae atop the spinal column, of which there are seven; the
thoracic vertebrae, situated below the cervical vertebrae, of which there are twelve; and
the lumbar vertebrae situated at the end. As discussed previously, the letters C, T, and L
are used, respectively, to designate cervical, thoracic and lumbar vertebrae. The sacrum is
located at the base of the spinal column, and below it, the coccyx or ‘tailbone.’ The five
sacral and four coccygeal vertebrae are fused and together are considered one bone.”16
The term low back typically refers to the lumbar and sacral (lumbosacral) regions of the
spine as well as the coccyx (tailbone).
To be more specific, the lumbar spine17 is the lower portion of the spine, where it curves
inward toward the abdomen, the region of the lumbar. The lumbar spine begins approxi-
mately five or six inches below the low tip of the shoulder blade, connecting with the tho-
racic spine at the top end and extending downward to connect with the sacrum at its lowest
end. The term “lumbar” is taken from the Latin lumbus, “lion,” describing its power and
flexibility (i.e., lifting and bending). The lumbosacral region is the lumbar plus the sacrum.18
Figure 9-1. The lumbosacral angle is formed at the juncture of the long axes of the lumbar
region of the spine and sacrum.19 The region’s major components are bones, joints, liga-
ments, disks, muscles, and nerve roots. Any of these structures can be a pain generator, a
fact that contributes to the difficulty in diagnosing the cause of a person’s low back pain.20
The lumbar spine has several important features:
The lower the vertebral segment, the more weight it must support.
The lumbar spine joins the sacrum at the lumbosacral joint (L5-S1). This area
allows the pelvis and hips to swing when a person walks and runs.
The lowest two spinal segments of the lumbar spine, L4-L5 and L5-S1, support
the most weight, so they are the most prone to degradation and injury.
The spinal cord ends around T12-L1. At this juncture, nerve roots continue down
the vertebral column, forming the cauda equina.
Because the spinal cord ends at the lowest portion of the thoracic spine, a lum-
bar problem such as a herniated disk or lumbar stenosis does not cause injury to
the spinal cord.21 However, all of the nerves going to the legs, bladder, and rectal
sphincter go through the lumbar spine as the cauda equina, which can be injured,
resulting in paralysis of the legs and bowel/bladder incontinence.
The bones of the low back consist of five lumbar vertebrae and two sets of fused bones, the
sacrum and coccyx. The five sacral vertebrae fuse together in adults and four coccygeal ver-
tebrae join together to create the coccyx.22 Bones themselves are not pain sensitive; it is the
membrane covering these structures, the richly innervated periosteum,23 that causes dis-
comforts from bone trauma, such as a fracture,24 or a nontraumatic cause, such as cancer.
Like the rest of the spine, the five lumbar vertebrae are stacked on top of each other like
napkin rings. They are labeled L1 to L5 consecutively; the L1 vertebra is located around
the level of the belly button. Figure 9-2. These vertebrae have massive bodies and rugged
lamina and lack costal facets for rib attachment. The lumbar vertebrae are large because
the body weight they support increases at the end of the spine25 such that the L5 vertebra
is the largest of all movable vertebrae because it supports the weight of the entire upper
body.26 The lumbar vertebrae are most frequently involved in back pain because of their
weight-bearing responsibility and stresses along the spine.27 The lumbar region has a
lordotic curve, meaning that it is has the shape of a backwards “C.” By way of analogy, if
one views the entire spine from the right side it appears to have an “S”-like shape, with
the lumbar region at the bottom of the “S.”28 Figure 9-2.
9-1a: Posterior view of the lumbo-
sacral region of the spine superim-
posed upon the human form. This
termination region of the spine
extends from the L1 vertebra to
the sacrum. The sacroiliac (SI) joints
are the points of attachment of
the sacrum to the pelvis. In a thin
person, the SI joints are visible as
two dimples on either side of the
low back.
9-10b: Side and front view of
the lumbosacral region of the spine
showing its attachment to the
pelvis. The lumbosacral region
consists of five lumbar vertebrae
and the single upside-down tri-
angular-shaped sacrum formed by
fusing of the sacral vertebrae. The
sacrum is attached to the ilium of
the pelvis at the sacroiliac (SI) joint.
The entire weight of the upper
body is carried by and exerted
onto the lumbosacral region. The
coccyx (“tailbone”) is attached at
the end of the sacrum and has no
known function.
In addition to their role in supporting the weight of the upper portion of the body, the
lumbar vertebrae allow movement in the low back, provide for muscle attachment to the
spine, and protect the nerve roots that extend from the spinal cord through openings in
the spine on their journey down into the legs. These functions are reflected in the design
and shape of these bones. For example, the massive, roughly kidney-shaped body of each
vertebra is built to support the trunk as it bears the vertical weight. Figure 9-1. In the
spinal vertebrae, a delicate vertebral arch extends posteriorly from the vertebral body to
create an opening known as the spinal canal or vertebral foramen,29 through which nerve
roots extend downward from the spinal cord.30 Figure 9-3. The vertebral arch attaches to
the vertebral body by paired pedicles, like struts. Bony processes extend outward from the
sides of the vertebral arch as the transverse processes,31 which serve as the attachment for
muscle, and complete the structure as the lamina.32 The term pedicle may sound familiar to
many trial lawyers because of the various lawsuits involving pedicle screws. Because this
bony part projects rearward, they are accessible to physicians for “pedicle fixation,” the
placement of screws passing through the pedicle and into the vertebral body.33 Figure 9-3.
The vertebral arch terminates as the spinous process, which can be felt as the bony
bumps vertically arranged underneath the skin of the back.34 Each vertebra has two pairs
of vertebral joints, the facets, that connect adjacent vertebrae and allow forward, back-

To continue reading

Request your trial

VLEX uses login cookies to provide you with a better browsing experience. If you click on 'Accept' or continue browsing this site we consider that you accept our cookie policy. ACCEPT