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871
CHAPTER 40
LOW BACK PAINKaren P. Barr and Mark A. Harrast
Low back pain has become a costly burden to society and a
leading cause of disability and loss of productivity. This chapter
outlines the anatomy and biomechanics of the lumbar spine and our
current understanding of the physi-ology of low back pain. We
discuss the clinical evaluation and treatment of various etiologies
of low back pain and leg pain caused by lumbar spine disease.
Epidemiology
Low back pain is a symptom, not a disease, and has many causes.
It is generally described as pain between the cos-tal margin and
the gluteal folds. It is extremely common. About 40% of people say
that they have had low back pain within the past 6 months.233
Studies have shown a lifetime prevalence as high as 84%.240 Onset
usually begins in the teens to early 40s. Most patients have short
attacks of pain that are mild or moderate and do not limit
activities, but these tend to recur over many years. Most episodes
resolve with or without treatment. The median time off work for a
back injury is 7 days, and many people with low back pain never
alter their activity. A small percentage of low back pain becomes
chronic, however, and causes significant disability. In most
studies about half of the sick days used for back pain are
accounted for by the 15% of people who are home from work for more
than 1 month. Between 80% and 90% of the health care and social
costs of back pain are for the 10% who develop chronic low back
pain and disability. Just over 1% of adults in the United States
are permanently disabled by back pain, and another 1% are
temporarily disabled.151
The percentage of patients disabled by back pain, as well as the
cost of low back pain, has steadily increased dur-ing the past 30
years. This appears to be more from social causes than from a
change in the conditions that cause low back pain. The two most
commonly cited factors are the increasing societal acceptance of
back pain as a reason to become disabled, and changes in the social
system that pay benefits to patients with back pain.238
Anatomy and Biomechanics of the Lumbar Spine
General ConceptsThe lumbar spine has a dichotomous role in terms
of func-tion, which is strength coupled with flexibility. The spine
per-forms a major role in support and protection (strength) of the
spinal canal contents (spinal cord, conus, and cauda equina) but
also give us inherent flexibility, allowing us to place our limbs
in appropriate positions for everyday functions.
The strength of the spine results from the size and arrangements
of the bones, as well as from the arrange-ment of the ligaments and
muscles. The inherent flexibility results from the large number of
joints placed so closely together in series. Each vertebral segment
can be thought of as a three-joint complexone intervertebral disk
with vertebral end plates, and two zygapophyseal joints. The
typical lordotic framework of the lumbar spine assists with this
flexibility but also increases the ability of the lumbar spine to
absorb shock.
The VertebraeThe bony anatomy of the lumbar spine consists of
five lum-bar vertebrae. A smaller percentage of the population has
four (the fifth vertebrae is sacralized) or six (the first sacral
segment is lumbarized). Anatomic variants also exist consist-ing of
a partially lumbarized S1. The lumbar vertebrae have distinct
components, which include the vertebral body, the neural arch, and
the posterior elements (Figure 40-1). The vertebral bodies increase
in size as you travel caudally in the spine. The lower three are
typically more wedge-shaped (taller anteriorly), which helps create
the normal lumbar lordosis. The structure of these large vertebral
bodies serves its weight-bearing function well to support axially
directed loads; however, they would fracture more routinely were it
not for the shock-absorbing intervertebral disks placed
stra-tegically between the vertebral bodies.
The sides of the bony neural arch are the pedicles, which are
thick pillars that connect the posterior elements to the vertebral
bodies. They are designed to resist bending and to transmit forces
back and forth from the vertebral bodies to the posterior elements.
The posterior elements consist of the laminae, the articular
processes, and the spinous pro-cesses. The superior and inferior
articular processes of adja-cent vertebrae create the zygapophyseal
joints. The pars interarticularis is a part of the lamina between
the supe-rior and inferior articular processes (Figure 40-2). The
pars is the site of stress fractures (spondylolysis) because it is
subjected to large bending forces. This occurs as the forces
transmitted by the vertically oriented lamina undergo a change in
direction into the horizontally oriented pedicle.23
The JointsThe Intervertebral Disk
The intervertebral disk and its attachment to the vertebral end
plate are considered a secondary cartilaginous joint, or symphysis.
The disk consists of the internal nucleus pulpo-sus and the outer
annulus fibrosus. The nucleus pulposus is the gelatinous inner
section of the disk. It consists of
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872 SECTION 4 Issues in Specific Diagnoses
water, proteoglycans, and collagen. The nucleus pulposus is 90%
water at birth. Disks desiccate and degenerate as we age and lose
some of their height, which is one reason we are slightly shorter
in our geriatric years.
The annulus fibrosus consists of concentric layers of fibers at
oblique angles to each other, which help to with-stand strains in
any direction. The outer fibers of the annu-lus have more collagen
and less proteoglycans and water than the inner fibers.19 The
varying composition supports the functional role of the outer
fibers in acting like a liga-ment to resist flexion, extension,
rotation, and distraction forces.
The main function of the intervertebral disk is shock absorption
(Figure 40-3). It is primarily the annulus, not the nucleus, that
acts as the shock absorber. (The nucleus is primarily a liquid and
is incompressible.) When an axial load occurs, the increase in
force in the incompressible nucleus pushes on the annulus and
stretches its fibers. If the fibers break, then a herniated nucleus
pulposus results.
The Zygapophyseal Joints
The zygapophyseal joints (also known as Z joints and facet
joints) are paired synovial joints, that is, they have a synovium
and a capsule (Figure 40-4). Their alignment or direction of joint
articulation determines the direction of
motion of the adjacent vertebrae. The lumbar zygapophy-seal
joints lie in the sagittal plane and thus primarily allow flexion
and extension. Some lateral bending and very little rotation are
allowed, which limits torsional stress on the lumbar disks.
Rotation is more a component of thoracic spine motion. The majority
of spinal flexion and exten-sion (90%) occurs at the L4L5 and L5S1
levels, which contributes to the high incidence of disk problems at
these levels.
Biomechanics
Because flexion loads the anterior disk, the nucleus is
dis-placed posteriorly.111 If the forces are great enough, the
nucleus can herniate through the posterior annular fibers. The
lateral fibers of the posterior longitudinal ligaments are
thinnest, however, making posterolateral disk hernia-tions the most
common (Figure 40-5). The posterolateral
Superiorarticular
facet
Transverseprocess
Spinousprocess
Inferiorarticular
facet
Pedicle
Vertebralbody
Inferiorvertebral
notch
Lamina
FIGURE 40-1 Lateral view of the lumbar vertebrae. (Modified from
Parke WW: Applied anatomy of the spine. In Rothman RH, Simeone FA,
editors: The spine, ed 4, Philadelphia, 1999, Saunders.)
12
3
FIGURE 40-2 An oblique dorsal view of an L5 vertebra, showing
the parts of the vertebral arch: 1, pars interarticularis
(crosshatched area); 2, pars lami-naris; and 3, pars pedicularis.
The dotted line indicates the most frequent site of mechanical
failure of the pars interarticularis. (Modified from Parke WW:
Applied anatomy of the spine. In Rothman RH, Simeone FA, editors:
The spine, ed 4, Philadelphia, 1999, Saunders.)
A
B
C
DFIGURE 40-3 The mechanism of weight transmission in an
intervertebral disk. A, Compression increases the pressure in the
nucleus pulposus. This is exerted radially onto the annulus
fibrosus, and the tension in the annulus increases. B, The tension
in the annulus is exerted on the nucleus, preventing it from
expanding radially. Nuclear pressure is then exerted on the
vertebral end plates. C, Weight is borne, in part, by the annulus
fibrosus and by the nucleus pulposus. D, The radial pressure in the
nucleus braces the annulus, and the pressure on the end plates
transmits the load from one vertebra to the next. (Modified from
Bogduk N: The inter-body joint and the intervertebral discs. In
Bogduk N, editor : Clinical anatomy of the lumbar spine and sacrum,
ed 3, Edinburgh, UK, 1977, Churchill Livingstone.)
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873CHAPTER 40 Low Back Pain
portion of the disk is most at risk when there is forward
flexion accompanied by lateral bending (i.e., bending and
twisting). The zygapophyseal joints cannot resist rotation when the
spine is in flexion. This increases torsional shear forces in the
lumbar spine, making rotary movements in a forward-flexed posture
probably the most risky for lum-bar disks.
The LigamentsThe two main sets of ligaments of the lumbar spine
are the longitudinal ligaments and the segmental ligaments. The two
longitudinal ligaments are the anterior and posterior longitudinal
ligaments. They are named according to their position on the
vertebral body. The anterior longitudinal ligament acts to resist
extension, translation, and rotation. The posterior longitudinal
ligament acts to resist flexion. Disruption of either ligament
primarily occurs with rota-tion rather than with flexion or
extension. The anterior longitudinal ligament is twice as strong as
the posterior longitudinal ligament.
The main segmental ligament is the ligamentum fla-vum, which is
a paired structure joining adjacent laminae. It is the ligament
that is pierced when performing lumbar punctures. It is a very
strong ligament but is elastic enough
to allow flexion. Flexing the lumbar spine puts this liga-ment
on stretch, decreasing its redundancy and making it easier to
pierce during a lumbar puncture.
The other segmental ligaments are the supraspinous,
interspinous, and intertransverse. The supraspinous liga-ments are
the strong ligaments that join the tips of adjacent spinous
processes and act to resist flexion. These ligaments, along with
the ligamentum flavum, act to restrain the spine and prevent
excessive shear forces in forward bending. This is supported by
electromyographic studies that have shown that there is no active
contraction of the erector spinae and hip extensor muscles when
resting in lumbar flexion.
The MusclesMuscles With Origins on the Lumbar Spine
These muscles can be divided anatomically into posterior and
anterior muscles. The posterior muscles include the latissimus
dorsi and the paraspinals. The lumbar paraspi-nals consist of the
erector spinae (iliocostalis, longissimus, and spinalis), which act
as the chief extensors of the spine, and the deep layer (rotators
and multifidi) (Figures 40-6 and 40-7). The multifidi are tiny
segmental stabilizers that act to control lumbar flexion because
they cannot produce enough force to truly extend the spine. Their
most impor-tant function has been hypothesized to be that of a
sensory organ to provide proprioception for the spine, given
the
CCAC
FIGURE 40-4 A posterior view of the L3L4 zygapophyseal joints.
On the left, the capsule of the joint (C) is intact. On the right,
the posterior capsule has been resected to reveal the joint cavity,
the articular cartilages (AC), and the line of attachment of the
joint capsule (dashed line). The upper joint capsule (C) attaches
further from the articular margin than the posterior capsule does.
(Modified from Bogduk N: The zygapophysial joints. In Bogduk N,
editor : Clinical anatomy of the lumbar spine and sacrum, ed 3,
Edinburgh, UK, 1977, Churchill Livingstone.)
Nerve rootcompressionin the lateral
recess
Caudaequina
Posterolateralherniated
nucleuspulposus
Nucleuspulposus
Defectin anulusfibrosus
Anulusfibrosus
FIGURE 40-5 Posterolateral intervertebral disk herniation.
Iliocostalis thoracis
Longissimus thoracis
Spinalis thoracis
Iliocostalis thoracis
Longissimus lumborum
Iliocostalis lumborum
FIGURE 40-6 The intermediate layer of back muscles: the erector
spinae.
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874 SECTION 4 Issues in Specific Diagnoses
predominance of muscle spindles seen histologically in these
muscles.
The anterior muscles of the lumbar spine include the psoas and
quadratus lumborum. Because of the direct attachment of the psoas
on the lumbar spine, tighten-ing this muscle accentuates the normal
lumbar lordosis.
This can increase forces on the posterior elements and can
contribute to zygapophyseal joint pain. The quadratus lumborum acts
in side bending and can assist in lumbar flexion.
Abdominal Musculature
The superficial abdominals include the rectus abdominis and
external obliques (Figure 40-8, A). The deep layer con-sists of
internal obliques and the transversus abdominis (Figure 40-8, B).
The transversus abdominis has received significant attention
recently as an important muscle to train in treating low back pain.
Its connection to the thora-columbar fascia (and consequently its
ability to act on the lumbar spine) has probably been the major
reason it has received such attention of late.
Thoracolumbar Fascia
The thoracolumbar fascia, with its attachments to the
transversus abdominis and internal obliques, acts as an abdominal
and lumbar brace. It decreases some of the shear forces that other
muscles and lumbar motions cre-ate. This abdominal bracing
mechanism results from con-traction of these deep abdominal
muscles, which creates tension in the thoracolumbar fascia, which
then creates an extension force on the lumbar spine without
increasing shear forces.75
Pelvic Stabilizers
The pelvic stabilizers are considered core muscles because of
their indirect effect on the lumbar spine, even though they do not
have a direct attachment to the spine. The gluteus medius
stabilizes the pelvis during gait. Weakness or inhibition of this
muscle results in pelvic instability, which introduces lumbar side
bending and rotation, creating increased shear or torsional forces
on the lumbar disks.
The piriformis is a hip and sacral rotator and can cause
excessive external rotation of the hip and sacrum when it is tight.
This can result in increased shear forces at the lumbosacral
junction (i.e., the L5S1 disk or Z joints).
Semispinalis capitis
Semispinalis cervicis
Spinalis thoracis
Multifidus
FIGURE 40-7 The deep back muscles: the multifidi.
Serratusanterior
Anterior layer ofrectus sheath
Externaloblique
5th costalcartilage
Anterior layerof rectus sheath
Externaloblique
Anterior superioriliac spine
Rectusabdominis
A
Serratusanterior
Anteriorlayer ofrectus
sheath
Externaloblique
(cut edges)
Internaloblique
Anteriorsuperior
iliac spine
Rectusabdominis
Posteriorlayer ofrectussheath
Transversusabdominis
Internaloblique
Rectusabdominis
Pectoralismajor
BFIGURE 40-8 A, The superficial abdominal muscles. B, The deep
abdominal muscles.
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875CHAPTER 40 Low Back Pain
Some practitioners also believe that other pelvic floor muscles
act to maintain proper positioning of the spine and are an
important focus of some spine rehabilitation programs.
Biomechanical Lifting in Relation to Muscular Activity and Disk
Loads
The activity of the lumbar muscles correlates well with
intradiskal pressures (i.e., when back muscles contract, there is
an associated increase in disk pressure). These pres-sures change
depending on spine posture and the activity undertaken. Figure 40-9
demonstrates the changes in L3 disk pressure under various
positions and exercises.149,150 Adding rotation to the already
flexed posture increases the disk pressure substantially. Comparing
lifting maneuvers, it has been shown that there is not a
significant difference in disk pressure when lifting with the legs
(i.e., with the back straight and knees bent) versus lifting with
the back (i.e., with a forward-flexed back and straight legs).6,7
What decreases the forces on the lumbar spine is lifting the load
close to your body because the farther the load is from the chest,
the greater the stress on the lumbar spine.7
The NervesThe conus medullaris ends at about bony level L2, and
below this level is the cauda equina. The cauda equina con-sists of
the dorsal and ventral rootlets, which join together in the
intervertebral neuroforamen to become the spinal nerves (Figure
40-10). The spinal nerve gives off the ventral primary ramus. The
ventral primary rami from multiple levels form the lumbar and
lumbosacral plexus to inner-vate the limbs. The dorsal primary
ramus, with its three branches (medial, intermediate, and lateral),
innervates the posterior half of the vertebral body, the paraspinal
muscles, and the zygapophyseal joints, and provides sen-sation to
the back. The medial branch is the most impor-tant to remember
because it innervates the zygapophyseal joints and lumbar multifidi
and is the target during radio-frequency neurotomy for presumed
zygapophyseal joint pain (Figure 40-11).24
Pathophysiology and Pain Generation
The Degenerative Spine CascadeKirkaldy-Willis et al.108 have
supplied us with the most accepted theory describing the cascade of
events in degen-erative lumbar spine disease that results in
spondylotic changes, disk herniations, and eventually multilevel
spinal stenosis (Figure 40-12). At the heart of this theory is the
fact that, although the posterior zygapophyseal joints and the
anterior intervertebral disks are separated anatomically, forces
and lesions affecting one certainly alter and affect the other. For
example, axial compressing injuries can
75 100 150 220 140 185 27525
%
A
%
150 180 210 100 140 130 35BFIGURE 40-9 A, Relative change in
pressure (or load) in the third lumbar disk in various positions in
living subjects. B, Relative change in pressure (or load) in the
third lumbar disk during various muscle-strengthening exercises in
living subjects. Neutral erect posture is considered 100% in these
figures; other positions and activities are calculated in
relationship to this. (Modified from Nachemson AL, Waddell G,
Norlund AI: Epidemiology of neck and low back pain. In Nachemson
AL, Johnsson B, editors: Neck and back pain: The scientific
evidence of causes, diagnosis, and treatment, Philadelphia, 2000,
Lippincott Williams & Wilkins.)
Arachnoid
Subarachnoidspace
Pia
Dura
Dorsal root
Ventral root
Dorsal rootganglion
Dural sleeve
Spinal nerve
Ventral ramus
Dorsal ramusFIGURE 40-10 A lumbar spinal nerve, its roots, and
meningeal coverings. The nerve roots are invested by pia mater, and
covered by arachnoid and dura as far as the spinal nerve. The dura
of the dural sac is prolonged around the roots as their dural
sleeve, which blends with the epineurium of the spinal nerve.
(Modified from Bogduk N: Nerves of the lumbar spine. In Bogduk N,
editor : Clini-cal anatomy of the lumbar spine and sacrum, ed 3,
Edinburgh, UK, 1977, Churchill Livingstone.)
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876 SECTION 4 Issues in Specific Diagnoses
damage the vertebral end plates, which can lead to degen-erative
disk disease, which eventually stresses the posterior joints,
leading to the common degenerative changes seen in them over time.
Torsional stress can injure the posterior joints and the disks,
which in turn leads to increased stress on both these elements,
resulting in further degenerative changes over time. When these
degenerative changes affect one level, such as L4L5, a chain
reaction occurs, placing stress on the levels above and below the
currently affected level, and eventually resulting in more
generalized multi-level spondylotic changes.
In studying lumbar degenerative disease, the question of which
came first (disk degeneration or zygapophyseal joint degeneration)
always arises. Fujiwara67 has answered this by studying multiple
magnetic resonance images (MRIs) of aging spines. He hypothesizes
that disk degeneration pre-cedes zygapophyseal joint
osteoarthritis, and that it might take 20 years for zygapophyseal
joint disease to occur after the onset of disk degeneration.
To describe the degenerative cascade in more detail, we will
separate our discussion of the changes that occur in the posterior
joints from those in the disk, but fully real-izing that they both
can occur simultaneously and affect each other (see Figure 40-12).
The degenerative changes that occur in the zygapophyseal joints
from aging and repetitive microtrauma are similar to those that
occur in the appendicular skeletal joints. The process begins with
synovial hypertrophy, which eventually results in cartilage
degeneration and destruction. With lessened and weak-ened cartilage
and capsular laxity, the joint can become unstable. With the
repetitive abnormal joint motion that results from this
instability, the bony joint hypertrophies. This narrows the central
canal and lateral recesses, poten-tially impinging nerve roots.
A similar process occurs anteriorly at the disk level from
repetitive microtrauma of primarily shearing forces. Tears in the
annulus are thought to be the first anatomic sign of degenerative
wear. When the annulus is weakened enough, typically
posterolaterally, the internal nucleus pulposus can herniate.
Internal disk disruption can occur without herniation, however,
because age and repeated stresses act-ing on the spine cause the
gelatinous nucleus to become more fibrous over time. Tears in the
annulus can progress to tears in the fibrous disk material,
resulting in internal
disk disruption without frank herniation. All this results in a
loss of disk height, which causes instability (because the
end-plate connection to the disk is degenerated), as well as
lateral recess and foraminal narrowing and poten-tial nerve root
impingement. The loss of disk height also places new stresses on
the posterior elements, resulting in further instability of the
zygapophyseal joints and further degeneration and nerve root
impingement.
Although this theory offers an explanation as to how the spine
ages, it is still unclear why there is such a marked disconnect
between the anatomic changes in the spine associated with aging,
and back pain. Many patients with normal spine anatomy suffer from
back pain, occasionally disabling pain, and many patients with
marked degenera-tive changes on imaging are nearly or fully pain
free. As a result, several theories have been developed to explain
the occurrence of back pain.
Transverseprocess
Spinalnerve
Ventralprimary
ramus
Dorsalprimary
ramus
Superiorarticularfacet
Medialbranch
Zygapo-physealjoint
Inferiorarticularfacet
FIGURE 40-11 Observe that the innervation of the zygapophyseal
joints derives from the medial branch off the dorsal primary
ramus.
Posteriorjoints
Three jointcomplex
Intervertebraldisk
Synovialreaction
Circumferentialtears
Cartilagedestruction Herniation
Radialtears
Osteophyteformation
Internaldisruption
Capsularlaxity Instability
Loss diskheight
Subluxation Lateral nerveentrapment
Diskresorption
Enlargementarticular process
(and laminae)
One-levelcentral
stenosis
Osteophytesat back ofvertebralbodies
Effect of recurrent strainsat levels above and
below the original lesion
Multilevel degenerative lesions
Multilevel spinal stenosis
FIGURE 40-12 The spectrum of degenerative change that leads from
minor strains to marked spondylosis and stenosis. (Modified from
Kirkaldy-Willis WH, Wedge JH, Yong-Hing K, et al: Pathology and
pathogenesis of lumbar spondylosis and stenosis, Spine 3:319-328,
1998, with permission of Lippincott Williams & Wilkins.)
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877CHAPTER 40 Low Back Pain
Radiculitis and RadiculopathyMany patients with radicular pain
have no neural impinge-ment noted on MRI. Studies have shown that
disk hernia-tions can cause an inflammatory response.131,136,187
The mechanism stems from the fact that the nucleus pulpo-sus is
highly antigenic as a result of being in an immu-noprotected
setting in nonpathologic states. When the fluid of the nucleus
pulposus is exposed to neural tissue of the spinal canal and
neuroforamen through a defect in the annular fibers, an
autoimmune-mediated inflamma-tory cascade begins. The inflammatory
mediators gener-ated can cause swelling of the nerves. This can
alter their electrophysiologic function, sensitizing these neurons
and enhancing pain generation without specific mechanical
compression.
The mechanism of mechanical compression of the nerve roots has
been studied as well.13,184,185 Compression of nerve roots can
induce structural and vascular changes as well as inflammation.150
Neural compression can result in impairment of intraneural blood
flow, subsequently decreased nutrient supply to the neural tissue,
local isch-emia, and formation of intraneural edema. This can set
off an inflammatory cascade similar to that described above.
Mechanical stimulation of lumbar nerve roots has also been shown to
stimulate production of substance P, the neuropeptide known to
modulate sensory nocicep-tive feedback.13 With these biochemical
reactions, the local structural effects of mechanical compression
(demy-elination and axonal transport block) just compound the
symptomatic response.
Pain of Spinal StenosisThese mechanisms could also be
responsible for neuro-genic claudication symptoms of lumbar
stenosis. Newer theories, however, also support a spinal vascular
role in stenosis symptoms.
If mechanical compression were the sole problem in spinal
stenosis, decompressive surgeries would be the only needed cure. We
know that this is untrue, and conse-quently alternative theories on
the pathogenesis of symp-tomatic spinal stenosis have been studied.
Two theories supporting a vascular component to symptoms of spinal
stenosis are the venous engorgement and arterial insuffi-ciency
theories.1
In the venous engorgement theory, the spinal veins of patients
with stenosis dilate, causing venous congestion and stagnating
blood flow.45 This pooling of blood in the spinal veins increases
epidural and intrathecal pressures, leading to a microcirculatory,
neuroischemic insult (i.e., an ischemic neuritis), which in turn
leads to the typical neu-rogenic claudication symptoms of
stenosis.
The arterial insufficiency theory of spinal stenosis is based on
the arterial dilatation of the lumbar radicular vessels during
lower limb exercise to provide increased blood flow and nourishment
to the nerve roots. In patients with spinal stenosis, this reflex
dilatation might be defective.14Because patients with spinal
steno-sis are typically elderly, they are also at higher risk for
atherosclerosis, which in turn just amplifies the arterial
insufficiency.
Pain Generators of the Lumbar SpineThe low back is an
anatomically diverse set of structures, and there are many
potential sources of pain. One useful strategy to clarify these
potential sources of pain is learning what low back structures are
innervated (and can transmit pain through neural pain fibers) and
what structures have no innervation (Box 40-1).
The sinuvertebral nerve innervates the anterior vertebral body,
the external annulus, and the posterior longitudinal ligament. The
posterior longitudinal ligament is a highly innervated structure
and can play a significant role in low back pain perception with
lumbar disk herniations. The medial branch of the dorsal primary
ramus innervates the zygapophyseal joints and interspinous
ligaments, as well as the lumbar multifidi. The other small
branches of the dor-sal primary ramus innervate the posterior
vertebral body and other lumbar paraspinal musculature and fascia.
The anterior longitudinal ligament is innervated by the gray rami
communicans, which branch off the lumbar sym-pathetic chain. The
internal annulus fibrosus and nucleus pulposus do not have
innervation and in nondisease states cannot transmit pain.
Because many structures are potentially a source of pain,
theories have been developed to help practitioners deter-mine the
cause of a particular patients pain. Some of the most common ones
are described below.
Segmental Dysfunction
Segmental dysfunction can occur when either a segment is too
stiff or too mobile. A segment encompasses the disk, the vertebrae
on each side of the disk, and the muscles and ligaments that act
across this area. Excessive stiffness is thought to be caused by
arthritic and ligamentous changes. Excessive mobility, also called
instability, or potentially better termed functional instability,
can be the result of tissue damage, poor muscular endurance, or
poor mus-cular control, and is usually a combination of all three
factors. Structural changes from tissue damage, such as strained or
failed ligaments that cause joint laxity, vertebral
A useful classification system to understand the potential
sources of low back pain depends on knowing what structures are
innervated (and can transmit pain) and what structures have no
innervation.Innervated structures Bone: Vertebrae Joints:
Zygapophyseal Disk: Only the external annulus and potentially
diseased
disk Ligaments: Anterior longitudinal ligament, posterior
longitudinal ligament, interspinous Muscles and fascia Nerve
rootNoninnervated structures Ligamentum flavum Internal annulus
Disk: Nucleus pulposus
BOX 40-1
Potential Pain Generators of the Back
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878 SECTION 4 Issues in Specific Diagnoses
end-plate fractures, and loss of disk height, can lead to
seg-mental dysfunction because of the altered anatomy. Mus-cles
also provide a critical component of spinal stability. This is of
particular interest to the physiatrist because it can be affected
by exercise. In normal situations, only a small amount of muscular
coactivation (about 10% of maxi-mal contraction) is needed to
provide segmental stability. In a segment damaged by ligamentous
laxity or disk dis-ease, slightly more muscle coactivation might be
needed. Because of the relatively gentle forces required to perform
the activities of daily living, muscular endurance is more
important than absolute muscle strength for most patients. Some
strength reserve, however, is needed for unpredict-able activities
such as a fall, a sudden load to the spine, or quick movements. In
sports and heavy physical work, both strength and endurance needs
increase. For example, in rapid breathing caused by exertion, there
is rhythmic contraction and relaxation of the abdominal wall. A fit
person can simultaneously provide spine support with abdominal wall
muscles and meet breathing demands, but a less-fit person might not
be able to do so and therefore could more easily become injured or
have pain.139 This biomechanical model is particularly complex in
the spine because of the presence of global movement patterns and
segmental movement patterns. Two interrelated muscular tasks must
be carried out at the same time: maintaining overall posture and
position of the spine, and control of individual intersegmental
relationships. Sufficient but not excessive joint stiffness is
required at the segmental level to prevent injury and allow for
efficient movement. This stiffness is achieved with specific
patterns of muscle activ-ity, which differ depending on the
position of the joint and the load on the spine. The inability to
achieve this stiffness, and the resulting segmental problems, is
thought to be a factor in low back pain.178
Muscular Imbalances and Neural Procession Problems
There appear to be consistent muscular problems in patients with
chronic low back pain. Some of these factors might exist preinjury
and make the spine more suscepti-ble to injury, and some are
adaptations to injury. Just as is seen in other areas of the body
(such as the knee), muscle function and strength around the spine
are altered after injury.177 Studies have shown abnormal firing
patterns in the deep stabilizers of the spine and transversus
abdomi-nus with activities such as limb movements, accepting a
heavy load, and responding to balance challenges. Other researchers
have found strength ratio abnormalities and endurance deficits in
patients with low back pain, such as abnormal flexion to extension
strength ratios and lack of endurance of torso muscles.140
Studies of lumbar paraspinals have found several abnor-malities
in patients with low back pain. Multiple imaging studies have
demonstrated paraspinal muscle atrophy, particularly of the
multifidi, in patients with chronic low back pain.178 Recovery of
the multifidi does not appear to occur spontaneously with the
resolution of back pain.91 Biopsies of multifidi in patients with
low back pain also show abnormalities. Atrophy of type 2 muscle
fibers is found, and internal structural changes of type 1 fibers
that give them a moth-eaten appearance are seen. In a study
of patients undergoing surgery for lumbar disk hernia-tions with
duration of symptoms from 3 weeks to 1 year, multifidi biopsies
collected at the time of surgery showed type 2 muscle atrophy and
type 1 fiber structural changes. Biopsies were repeated 5 years
postoperatively. Type 2 fiber atrophy was still found in all
patients, in both those who had improved with surgery and those who
had not. In the positive outcome group, however, the percentage of
type 1 fibers with abnormal structures had decreased, and in the
negative outcome group there was a marked increase in abnormal type
1 fibers.175 Increasingly strong scientific support is found for
the multifactorial nature of low back pain, which includes both
structural and dynamic factors.
This gives a theoretical basis for treatment aimed at improving
spine biomechanics as a means of treating low back pain, along with
other treatments aimed at pain man-agement. The research in this
area is intriguing but not yet conclusive. It is unclear whether
these muscular abnormal-ities are the result of back pathology that
leads to pain, or the cause of back pain. Study results conflict
regarding consistent deficits in patients with back pain. This
again reflects the heterogeneous nature of the group of patients
classified as having low back pain, and that different fac-tors
predominate for different patients.
Psychosocial Factors and Low Back Pain
Pain is an individual experience, and biomechanical and
neurologic factors alone do not explain much of the vari-ance seen
clinically in patients with back pain. Multiple psychosocial
factors have been found to play a role in low back pain. This is
briefly discussed here and more thoroughly discussed in the chapter
on chronic pain (see Chapter 42), as these issues are shared by
multiple painful conditions and not just low back pain.
Depression, Anxiety, and Anger. It appears that between 30% and
40% of those with chronic back pain also have depression.115 This
rate is so high because depressed patients are more likely to
develop back pain and to become more disabled by pain, and because
some patients with persistent pain become depressed. Patients who
are depressed are at increased risk of developing back and neck
pain. In a recent analysis of factors leading to the onset of back
and neck pain, those in the highest quartile for depression scores
had a fourfold increased risk of devel-oping low back pain than
those in the lowest quartile for depression scores.39 Strong
evidence also shows that psy-chosocial factors are closely linked
to the transition from acute pain to chronic pain and disability.
In a study of 1628 patients with back pain seen at a pain clinic,
those with a comorbid diagnosis of depression were more than 3
times more likely to be in the worst quartiles of physi-cal and
emotional functioning on the 36-Item Short-Form Health Survey than
those who were not depressed.70 Mul-tiple other studies have found
that depression, anxiety, and distress are strongly related to pain
intensity, duration, and disability.118
Research has also shown a high correlation with anger
measurements and pain, thought to be related to deficient opioid
modulation in those with high anxiety, anger, and fear
reactivity.32 Patients with posttraumatic stress disorder have a
high incidence of chronic low back pain as well.201
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879CHAPTER 40 Low Back Pain
Patient Beliefs About Pain and Pain Cognition. Beliefs about
back pain can be highly individual and are often not based on
facts. Some patients with back pain, espe-cially those with chronic
low back pain that keeps them from working, have a great deal of
fear about back pain. These include fears that their pain will be
permanent, that it is related to activity, and that exercise will
damage their back. This set of beliefs is referred to as fear
avoidance. For example, studies have found that patients with
chronic low back pain who perform poorly on treadmill exercise
tests,191 walk slower on treadmill tests,2 and perform more poorly
on spinal isometric exercise testing3 were the ones with more
anticipation of pain than those who did well on these tests.
Fear-avoidance beliefs rather than actual pain during testing
predicted their performance. Fear-avoidance levels explain
self-reported disability and time off work more accurately than
actual pain levels or medical diagno-sis does.127 This finding has
led Waddell and other experts to state that the fear of pain may be
more disabling than pain itself.234
A large, population-based study found that subjects with high
levels of pain catastrophizing, characterized by exces-sively
negative thoughts about pain and high fear of move-ment and injury
or reinjury (kinesophobia), who had back pain at baseline were much
more likely to have especially severe or disabling pain at
follow-up evaluation compared with those who did not catastrophize.
For those without back pain at the initial questionnaire,
catastrophizers were more likely to have developed low back pain
with disabil-ity at follow-up evaluation than
noncatastrophizers.171 Thought processes, such as the presence of
catastrophizing, are not limited to back pain and are often part of
a larger pattern of relationships and thought processes.
Patients beliefs about pain and their approach to deal-ing with
pain have been consistently found to affect out-comes. Fortunately,
changes in these beliefs and cognitive patterns are possible.
Multidisciplinary pain programs have proven effective in decreasing
fear-avoidant beliefs and catastrophizing (see Chapter 42).205
These changes in beliefs can also improve function. For example,
a study in which a group of patients with chronic low back pain
underwent a cognitive behavioral treatment program found that,
although there were not significant changes in pain intensity,
those with reductions of fear-avoidance beliefs had significant
reductions in disability. Changes in fear-avoidant beliefs
accounted for 71% of the variance in reduction in disability in
this study.252
Centralization and Pain
The experience of nociception is processed by the body in
complex ways. The theory that pain is a simple loop from injury to
perception of injury is much too simplistic. Pain processing begins
in the spinal cord and continues exten-sively in the brain, and the
ultimate pain that someone experiences is the sum of multiple
descending and ascend-ing faciliatory and inhibitory pathways.
Extensive evidence now supports the theory that persistent pain
might be caused by central sensitization, which could help explain
why often no pain generator is found in chronic low back
pain.46
The History and Physical Examination of the Low Back
A complete history and physical examination is important in the
evaluation of low back pain to determine the cause of the symptoms,
rule out serious medical pathology, and determine whether further
diagnostic evaluation is needed.
The HistoryAs with any pain history, features of back pain that
should be explored include location; character; severity; timing,
includ-ing onset, duration, and frequency; alleviating and
aggra-vating factors; and associated signs and symptoms. Each of
these features can assist the clinician in obtaining a diagnosis
and prognosis and determining the appropriate treatment. The causes
of back pain are often very difficult to determine. For as many as
85% of patients, no specific cause for back pain is found.50 One of
the main purposes of the history is to rule out rare but serious
causes of back pain. Elements of historical information that
suggest a serious underlying con-dition as the cause of the pain
such as cancer, infection, long tract signs, and fracture are
called red flags (Box 40-2). When these are present, further workup
is necessary (Table 40-1).
Children 55 years old
History of violent trauma Nonmechanical nature of pain (i.e.,
constant pain not
affected by movement, pain at night) History of cancer Systemic
steroid use Drug abuse HIV infection or other immunocompromised
patients Unintentional weight loss Systemically ill, particularly
signs of infection such as fever
or night sweats Persisting severe restriction of motion or
intense pain with
minimal motion Structural deformity Difficulty with micturition
Loss of anal sphincter tone or fecal incontinence, saddle
anesthesia Progressive motor weakness or gait disturbance Marked
morning stiffness Peripheral joint involvement Iritis, skin rashes,
colitis, urethral discharge, or other
symptoms of rheumatologic disease Inflammatory disorder such as
ankylosing spondylitis
suspected Family history of rheumatologic disease or
structural
abnormality
BOX 40-2
Red Flags: Most Common Indications From History and Examination
for Pathologic Findings Needing Special Attention and Sometimes
Immediate Action (Including Imaging)
Modified from Nachemson A, Vingard E: Assessment of patients
with neck and back pain: A best-evidence synthesis. In Nachemson
AL, Johnsson B, editors: Neck and back pain: the scientific
evidence of causes, diagnosis, and treatment, Philadelphia, 2001,
Lippincott Williams & Wilkins.
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880 SECTION 4 Issues in Specific Diagnoses
Besides determining a diagnosis, a purpose of the history is to
explore the patients perspective and ill-ness experience. Certain
psychosocial factors are valu-able in determining prognosis (Box
40-3). Factors such as poor job satisfaction, catastrophic thinking
patterns about pain, the presence of depression, and excessive rest
or downtime are much more common in patients in whom back pain
becomes disabling. These are called yellow flags because the
clinician should proceed with caution, and further psychologic
evaluation or treat-ment should be considered if they are present.
Some of these psychosocial factors are addressed by specific
ques-tions, and some become evident through statements that
patients make during the history as they describe their illness
experience. Questions about, for example, what patients believe is
causing the pain, their fear and feel-ings surrounding this belief,
their expectations about the pain and its treatment, and how back
pain is affecting their lives (including work and home life) can
yield valu-able information. Many of these yellow flags are better
prognostic indicators than the more traditional medical
diagnoses.235
The Physical ExaminationTable 40-2 outlines a thorough
examination of the lumbar spine.
Observation
Observation should include a survey of the skin, muscle mass,
and bony structures, as well as observation of overall posture
(Figures 40-13 and 40-14), and the position of the lumbar spine in
particular. Gait should also be observed for clues regarding
etiology and contributing factors.
Palpation
Palpation should begin superficially and progress to deeper
tissues. It can be done with the patient standing. To ensure that
the back muscles (Figure 40-15) are fully relaxed, pal-pation is
often done with the patient lying prone, perhaps with a pillow
under the abdomen to slightly flex the spine into a position of
comfort. It should proceed systematically to determine what
structures are tender to palpation.
Range of Motion
Quantity of Range of Motion. Several methods can be used to
measure spinal range of motion (ROM). These include using a single
or double inclinometer; measuring the distance of fingertips to
floor; and, for forward flexion, the Schober test (measuring
distraction between two marks on the skin during forward flexion).
Of these methods, the double inclinometer has been shown to
correlate the clos-est to measurements on radiographs.77,210
Fingertip to floor has good interrater and intrarater reliability,
but this takes into account the movement of the pelvis and is
affected by structures outside the spine, such as tight
hamstrings.168 The Schober test is commonly used to assess a
decrease in forward flexion in ankylosing spondylitis. It is
sensitive for this condition but is not specific. General figures
for nor-mal ROM are forward flexion, 40 to 60 degrees; extension,
20 to 35 degrees; lateral flexion, 15 to 20 degrees; and rota-tion,
3 to 18 degrees. Studies to determine normal ROM in asymptomatic
adults have found large variations within the normal range.165 It
is unclear what the significance of decreased ROM is in patients
with back pain because many people without back pain also have
limited range. ROM
Table 40-1 Sensitivities and Specificities of Different Elements
of the History and Examination for Some Specific Causes of Low Back
Pain
Disease or Group of Diseases
Symptom or Sign Sensitivity Specificity
Spinal malignancy
Age >50 yr 0.77 0.71
Previous history of cancer
0.31 0.98
Unexplained weight loss
0.15 0.94
Pain unrelieved by bed rest
0.90 0.46
Pain lasting >1 mo 0.50 0.81
Failure to improve with 1 mo of conservative therapy
0.31 0.90
Erythrocyte sedimenta-tion rate >20 mm
0.78 0.67
Spinal infection
Intravenous drug abuse, urinary tract infec-tion, skin
infection
0.4
Fever 0.27-0.83* 0.98
Vertebral tenderness Reasonable Low
Age >50 yr 0.84 0.61
Compression fracture
Age >70 yr 0.22 0.96
Corticosteroid use 0.66 0.99
Herniated interverte-bral disk
Sciatica 0.95 0.88
From Nachemson A, Vingard E: Assessment of patients with neck
and back pain: A best-evidence synthesis. In Nachemson AL, Johnsson
B, editors: Neck and back pain: the scientific evidence of causes,
diagnosis, and treatment, Philadelphia, 2001, Lippincott Williams
& Wilkins.*The sensitivity of fever.
Presence of catastrophic thinking: there is no way the patient
can control the pain, that disaster will occur if the pain
continues, etc.
Expectations that the pain will only worsen with work or
activity
Behaviors such as avoidance of normal activity, and extended
rest
Poor sleep Compensation issues Emotions such as stress and
anxiety Work issues, such as poor job satisfaction and poor
relationship with supervisors Extended time off work
BOX 40-3
Some Common Yellow Flags Associated With the Development of
Chronic Disabling Pain Suggesting Additional Attention May Be
Necessary
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881CHAPTER 40 Low Back Pain
can also change depending on the time of day, the effort the
patient expends, and many other factors.255
Quality of Range of Motion. The examiner should record whether
there are abnormalities in the patients movement pattern during
ROM, such as a catch in the range or whether it causes pain. This
might give clues to the diagno-sis. For example, pain with forward
flexion can signify disk disease, and pain with extension can
indicate spondylolis-thesis, zygapophyseal joint disease, or spinal
stenosis.
The Neurologic Examination
The neurologic examination of the lower limbs can rule out
clinically significant nerve root impingement and other neurologic
causes of leg pain (Tables 40-3 and 40-4). The physical examination
should logically proceed to discover whether a particular root
level is affected by combining the findings of weakness, sensory
loss, diminished or absent reflexes, and special tests such as
straight leg-raising sign. Upper motor neuron abnormalities should
also be ruled
out. The accuracy of the neurologic examination in diag-nosing
herniated disk is moderate. The accuracy can be increased
considerably, however, with combinations of find-ings.50 The
sensitivity and specificity of different findings for lumbar
radiculopathy have been well studied (Table 40-5).
Orthopedic Special Tests to Assess for Relative Strength and
Flexibility
Back pain can be caused by deconditioning, poor endur-ance, and
muscle imbalances. This makes it important to identify any
inefficient or abnormal movement patterns of muscles that control
the movement of the spine and the position of the pelvis.
Because of their stabilizing effect on the spine, abdomi-nal
muscle strength and endurance is important. Several different ways
can be used to measure abdominal muscle strength and control
(Figures 40-16 and 40-17). One grad-ing system assesses whether the
patient is able to maintain a neutral spine position while adding
increasingly more challenging leg movements (Figure 40-18).
Table 40-2 Physical Examination for Low Back PainExamination
Component Specific Activity Reason for This Part of the
Examination
Observation Observation of overall posture Determine whether
structural abnormality or muscle imbalances are present
Observation of lumbar spine Further define muscle imbalance and
habitual posture
Observation of the skin Search for diagnoses such as psoriasis,
shingles, or vascular disease as cause of the pain
Observation of gait Screen the kinetic chain and determine
whether muscular, neurologic, or joint problems are contributing to
symptoms
Palpation Bones Search for bony problems such as infection or
fracture
Facet joints Identify whether specific levels are tender
Ligaments and intradiskal spaces Determine whether these are
tender
Muscles Search for trigger points, muscle spasms, muscle
atrophy
Active range of motion Forward flexion Amount, quality if
painful
Extension
Side bending Same, also side to side differences
Rotation
Neurologic examination Manual muscle testing of L1S1 myotomes
Determine weakness
Pinprick and light touch sensation, L1S1 dermatomes
Determine sensory loss
Reflexes: patellar, hamstring, Achilles Test injury to L4, L5,
or S1 roots if diminished, upper motor neuron disease if brisk
Balance and coordination testing Signs of upper motor neuron
disease
Plantar responses Same
Straight leg raise Neural tension at L5 or S1
Femoral nerve arch Neural tension at L3 or L4
Orthopedic special tests Abdominal muscle strength Determines
weakness and deconditioning
Pelvis stabilizer strength, i.e., gluteus medius, maximus,
etc.
Determines weakness and deconditioning
Tightness or stiffness of hamstrings Determines areas of poor
flexibility
Tightness or stiffness of hip flexors
Tightness or stiffness of hip rotators
Prone instability test Signs of instability
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882 SECTION 4 Issues in Specific Diagnoses
Besides determining the strength of the abdominals, strength
testing of the back muscles and pelvic stabiliz-ers, such as the
hip abductors, can be useful. Assessing for areas of relative
inflexibility is also important. Com-monly performed tests are hip
flexor flexibility, hamstring flexibility, other hip extensors
length, and gastrocnemius/soleus length. Balance challenges, such
as the ability to maintain single-footed stance, the ability to
lunge or squat, and other functional tests are also helpful to
determine a patients baseline status.
Orthopedic Special Tests for Lumbar Segmental Instability
Many clinicians and researchers believe that one cause of
mechanical low back pain is segmental instability that responds to
specific stabilization treatments. Therefore accu-rately
identifying this group from other forms of low back pain could be
important. These special tests include passive intervertebral
motion testing and the prone instability test.
Passive Intervertebral Motion Testing. The patient lies prone.
The examiner applies a firm steady pressure over the spinous
process anteriorly and assesses the amount of vertebral motion and
whether pain is provoked.90
Prone Instability Test. The patient lies prone, with the torso
on the examining table and the legs over the edge of the table with
the feet resting on the floor. The examiner performs passive
intervertebral motion test-ing at each level and notes provocation
of pain. Then the patient lifts the legs off the floor, and the
painful levels are repeated. A positive test is when the pain
dis-appears when the legs are lifted off the table. This is
because the extensors are able to stabilize the spine in this
position.90,138
Examining the Area Above and Below the Lumbar Spine
Generally in musculoskeletal medicine, the joint above and the
joint below the painful area should be assessed to make sure
nothing is missed. This is a good idea for the examination of the
lumbar spine as well. ROM of the hip joints should be assessed, and
a quick screen of the knee and ankle joint can determine whether
pathology in these areas is contributing to the back problem. The
tho-racic spine can be quickly screened as well during ROM and
palpation.
>3030
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883CHAPTER 40 Low Back Pain
Illness Behavior and Nonorganic Signs Seen on Physical
Examination
Multiple reasons can explain why patients with back pain might
display symptoms out of proportion to injury. Ill-ness behaviors
are learned behaviors and are responses that some patients use to
convey their distress. Several stud-ies have found that patients
with chronic low back pain and chronic pain syndrome experience
significant anxiety during the physical examination, even to the
level expe-rienced during panic attacks. This complicates the
assess-ment by altering the clinical presentation of the condition.
This anxiety is generally manifest as avoidance behavior, such as
decreased ROM or poor effort with muscle test-ing.81 Other reasons
for illness behavior include a desire to prove to physicians how
disabling the pain is and malin-gering. One way to assess for
illness behavior on physical
examination is to perform parts of the examination to search for
Waddells signs. Waddells signs are forms of ill-ness behavior.234
They are nonorganic findings on physical examination that correlate
with psychologic distress. They are as follows: Inappropriate
tenderness that is widespread or
superficial Pain on testing that only simulates loading the
spine,
such as light pressure applied to the top of the head, which
reproduces back pain, or rotating the hips and shoulders together
to simulate twisting without actu-ally moving the spine, which
reproduces back pain
Inconsistent performance when testing the same thing in
different positions, such as a difference in outcome of the
straight leg-raising test with the patient supine versus
sitting
Regional deficits in strength or sensation that do not have an
anatomic basis
Overreaction during the physical examinationFindings in three of
these five categories suggest psy-
chologic distress and also suggest that other parts of the
physical exam that require patient effort or reporting of symptoms
might be inaccurate.
Clinical Evaluation: Diagnostics
Imaging StudiesImaging of the lumbar spine should be used in the
evalua-tion of low back pain if specific pathology needs to be
con-firmed after a thorough history and physical examination.
Plain Radiography
Conventional radiographs are indicated in trauma to eval-uate
for fracture and to look for bony lesions such as tumor when red
flags are present in the history. As an initial screen-ing tool for
lumbar spine pathology, however, they have very low sensitivity and
specificity.73 Anteriorposterior and lateral views are the two
commonly obtained views. Oblique views can be obtained to examine
for a spondy-lolysis by visualizing the pars interarticularis and
the Scot-tie dog appearance of the lumbar spine (Figure 40-19).
Lateral flexionextension views are obtained to check for dynamic
instability, although the literature does not sup-port their
usefulness.55 They are potentially most helpful from a surgical
screening perspective when evaluating a spondylolisthesis. They are
commonly obtained in post-trauma and postsurgical patients.
Magnetic Resonance Imaging
MRI is the preeminent imaging method for evaluating degenerative
disk disease, disk herniations, and radiculop-athy (Figure 40-20)
(see also Chapter 7). On T2-weighted imaging, the annulus can be
differentiated from the inter-nal nucleus, and annular tears can be
seen as high-intensity zones. These zones are of unclear clinical
significance but are thought to be potential pain generators.
Adding gadolinium contrast enhancement helps to identify
structures with increased vascularity. Contrast is always indicated
in evaluating for tumor or infection or to determine scar tissue
(vascular) versus recurrent disk
Table 40-3 Factors That Affect PostureReason for Abnormality
Clinical Example
Bone structure Compression fractures
Scheuermann disease
Ligamentous laxity Hyperextension of the knees, elbows
Muscle and fascial length Tight hamstrings that cause a
posterior pelvic tilt
Weak and long abdominal muscles that allow an anterior pelvic
tilt
Body habitus Obesity or pregnancy causes changes in force and
increased lumbar lordosis
Neurologic disease Spasticity causes an extension pattern of the
lower limb
Mood Depression causes forward slumped shoulders
Habit Long-distance cyclists have increased thoracic kyphosis
and flat spine from prolonged positioning while riding
Erector spinaemuscles
Iliaccrest
L45 intervertebraljoint
Sacroiliac joint
FIGURE 40-15 Anatomy of the low back surface anatomy.
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884 SECTION 4 Issues in Specific Diagnoses
herniation (avascular) in postsurgical patients with recur-rent
radicular symptoms.
The downside of MRI is that, although it is a very sen-sitive
test, it is not very specific in determining a definite source of
pain. It is well established that many people with-out back pain
have degenerative changes, disk bulges, and protrusions on MRI.
Boden et al.21 demonstrated that one third of 67 asymptomatic
subjects were found to have a substantial abnormality on MRI of the
lumbar spine. Of the subjects younger than 60 years, 20% had a disk
hernia-tion, and 36% of those older than 60 had a disk herniation
and 21% had spinal stenosis. Bulging and degenerative disks were
even more commonly found. In another study
of lumbar MRI findings in people without back pain, Jen-sen et
al.97 demonstrated that only 36% of 98 patients had normal disks.
They found that bulges and protrusions were very common in
asymptomatic subjects, but that extru-sions were not. In a more
recent study in 2001, Jarvik con-firmed these findings.96
Computed Tomography
Because of the resolution of anatomic structures in MRI, it has
essentially replaced computed tomography (CT) scanning as the
imaging study of choice for low back pain and radiculopathy. CT
scanning is still more useful than MRI, however, in evaluating bony
lesions. CT scans are
Table 40-4 Lumbar Root Syndromes
Root Dermatome Muscle WeaknessReflexes or Special Tests Affected
Paresthesias
L1 Back, over trochanter, groin None None Groin, after holding
posture, which causes pain
L2 Back, front of thigh to knee Psoas, hip abductor None
Occasionally front of thigh
L3 Back, upper buttock, front of thigh and knee, medial lower
leg
Psoas, quadricepsthigh wasting Knee jerks sluggish, protein
kinase B-positive, pain on full straight leg raise
Inner knee, anterior lower leg
L4 Inner buttock, outer thigh, inside of leg, dorsum of foot,
big toe
Tibialis anterior, extensor hallucis
Straight leg raise limited, neck flexion pain, weak knee jerk,
side flexion limited
Medial aspect of calf and ankle
L5 Buttock, back and side of thigh, lateral aspect of leg,
dorsum of foot, inner half of sole, and first, second, and third
toes
Extensor hallucis, peroneals, gluteus medius, ankle
dorsiflexors, hamstringscalf wasting
Straight leg raise limited to one side, neck flexion pain, ankle
jerk decreased, crossed leg-raising pain
Lateral aspect of leg, medial three toes
S1 Buttock, back of thigh, and lower leg Calf and hamstrings,
wasting of gluteals, peroneals, plantar flexor
Straight leg raise limited Lateral two toes, lateral foot,
lateral leg to knee, plantar aspect of foot
S2 Same as S1 Same as S1, except peroneals Same as S1 Lateral
leg, knee, heel
S3 Groin, inner thigh to knee None None None
S4 Perineum: genitals, lower sacrum Bladder, rectum None Saddle
area, genitals, anus, impotence
From Maguire JH: Osteomyelitis. In Braunwald E, Fauci AS, Kasper
DL, et al, editors: Harrisons principles of internal medicine, ed
15, New York, 2001, McGraw-Hill.
Table 40-5 Lumbosacral Radiculopathy in Patients With
Sciatica*
Finding Sensitivity (%) Specificity (%)Positive Lumbrosacral
Radiculopathy
Negative Lumbrosacral Radiculopathy
Motor examination
Weak ankle dorsiflexion 54 89 4.9 0.5
Ipsilateral calf wasting 29 94 5.2 0.8
Sensory examination
Leg sensation abnormal 16 86 NS NS
Reflex examination
Abnormal ankle jerk 48 89 4.3 0.6
Other tests
Straight leg-raising maneuver 73-98 11-61 NS 0.2
Crossed straight leg-raising maneuver 23-43 88-98 4.3 0.8
From McGee SR: Evidence-based physical diagnosis, Philadelphia,
2001, Saunders.NS, Not significant.*Diagnostic standard: for
lumbosacral radiculopathy, surgical finding of disk herniation
compressing the nerve root.Definition of findings: for ipsilateral
calf wasting, maximum calf circumference at least 1 cm smaller than
on contralateral side; for straight leg-raising maneuvers, flexion
at hip of supine patients leg, extended at the knee, causes
radiating pain in affected leg (pain confined to back or hip is a
negative response); for crossed straight leg-raising maneuver,
raising contralateral leg provokes pain in the affected leg.
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885CHAPTER 40 Low Back Pain
also useful in the postsurgical patient with excessive hard-ware
that can obscure MRIs, and in patients with implants (aneurysm
clips or pacemakers) that preclude MRI.
Myelography
In myelography, contrast dye is injected into the dural sac and
plain radiographs are performed to produce images of the borders
and contents of the dural sac (Figure 40-21). CT images can also be
obtained after contrast injection to produce axial cross-sectional
images of the spine that enhance the distinction between the dural
sac and its sur-rounding structures. This is typically reserved as
a potential presurgical screening tool but has been used less with
the advancement of MRI.
Scintigraphy
Radionuclear bone scanning is a fairly sensitive but not
specific imaging modality that can be used to detect occult
fractures, bony metastases, and infections. To
increase anatomic specificity, single-photon emission computed
tomography (SPECT) bone scanning is used to obtain bone scans with
axial slices. This allows the diagnostician to differentiate uptake
in the posterior ele-ments from more anterior structures of the
spine. The diagnostic use of this study with regard to altering
clini-cal decision-making is controversial. Studies have been
published demonstrating that the use of SPECT can help identify
patients with low back pain who might benefit from Z-joint
injections.172
A
B
CFIGURE 40-16 Trunk raising forward: grading. The curl trunk
sit-up is per-formed with the patient lying supine and with the leg
extended. The patient posteriorly tilts the pelvis and flexes the
spine, and slowly completes a curled trunk sit-up. Kendall states
that the crucial point in the test for the abdominal muscle
strength is at the moment the hip flexors come into strong action.
The abdominal muscle at this point must be able to oppose the force
of the hip flexors in addition to maintain the trunk curl. At the
point where the hip flex-ors strongly contract, patients with weak
abdominal muscles will tilt the pelvis anteriorly and extend the
low back. A, A 100% or normal grade is the ability to maintain
spinal flexion and come into the sitting position with the hands
clasped behind the head. B, An 80% or good grade is the ability to
do this with the forearms folded across the chest. C, A 60% or fair
grade is the ability to do this with the forearms extended forward.
A 50% or fair grade is the ability to begin flexion but not
maintain spinal flexion with the forearms extended forward.
(Modified from Kendall FP, McCreary EK: Trunk muscles in muscle
testing and function, Philadelphia, 1983, Williams and
Wilkins.)
90
75
60
45
30
15
0
50% 60%70%
80%
90%
100%
A
B
CFIGURE 40-17 Leg lowering: grading. In the second test, the
patient raises the legs one at a time to a right angle, and then
flattens them back on the table. The patient slowly lowers the legs
while holding the back flat. A 100% or normal grade is the ability
to hold the low back flat on the table as the legs are lowered to
the fully extended position. An 80% or good grade is the ability to
hold the low back flat and lower the legs to a 30-degree angle. A,
A 60% or fair plus grade is the ability to lower the legs to 60
degrees with the low back flat. B, The pelvis tilted anteriorly and
the low back arched as the legs were lowered. C, The final
position. Kendall notes that this second test is more important
than the first (see Figure 40-16) in grading muscles essential to
proper posture, and that often patients who do well on the first
test do poorly on the second. (Modified from Kendall FP, McCreary
EK: Trunk muscles in muscle testing and function, Philadelphia,
1983, Williams and Wilkins.)
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886 SECTION 4 Issues in Specific Diagnoses
Electromyography
Electromyography is useful in evaluating radiculopathy because
it provides a physiologic measure for detecting neurogenic changes
and denervation with good sensitivity and high specificity. It can
help to provide information as to which anatomic lesions found in
imaging studies are
truly physiologically significant.181 See Chapters 9 through 11
for further details.
Laboratory StudiesBlood tests are rarely used in isolation as a
diagnostic strat-egy for low back pain. Some blood tests are
helpful as an adjunct in diagnosing inflammatory disease of the
spine (with such markers of inflammation as sedimentation rates and
C-reactive proteins), as well as some neoplastic disorders, such as
multiple myeloma with a serum protein electrophoresis and urine
protein electrophoresis.
Differential Diagnosis and Treatment: The Prototype of Back Pain
Greater Than Leg Pain
Mechanical Low Back PainNearly 85% of those who seek medical
care for low back pain do not receive a specific diagnosis.50 The
majority of these patients most probably have a multifactorial
cause for back pain, which includes deconditioning; poor muscle
A
B C
D EFIGURE 40-18 Abdominal strength grading. A, The patient lies
supine with the knees bent (supine crook lying). The physician cues
the patient to activate the transversus abdominis (Pull your belly
button toward your backbone), and a very slight lumbar lordosis is
maintained in a neutral position in which the spine is neither
flexed nor extended. The ability to maintain the neutral spine is
progressively challenged by loading the spine via lower extremity
movements. Grading is as follows. B, Grade 1: The patient is able
to maintain a neutral spine while extending one leg by dragging the
heel along the table; the other leg remains in the starting
position. C, Grade 2: The patient is able to maintain a neutral
spine while holding both legs flexed 90 degrees at the hip and 90
degrees at the knee, and touching one foot to the mat and then the
other. D, Grade 3: The patient is able to maintain a neutral spine
while extending one leg by dragging the heel along the table. The
other leg is off the mat and flexed 90 degrees at the hip and 90
degrees at the knee. E, Grade 4: The patient is able to maintain a
neutral spine while extending one leg hovered an inch or two above
the table, while the other leg is off the mat and flexed 90 degrees
at the hip and 90 degrees at the knee. Grade 5: The patient is able
to extend both legs a few inches off the mat and back again while
maintaining the spine in neutral.
Superior articular process(ear of Scottie dog)
Transverse process(nose)
Pedicle(eye)
Defect at pars interarticularis(collar or broken neck)
Inferior articular process(foot)
FIGURE 40-19 Oblique drawing of the lumbosacral junction,
outlining the Scottie dog and the area of spondylolysis.
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887CHAPTER 40 Low Back Pain
recruitment; emotional stress; and changes associated with aging
and injury such as disk degeneration, arthritis, and ligamentous
hypertrophy. This type of back pain can be given many names; simple
backache, nonspecific low back pain, lumbar strain, and spinal
degeneration are a few of the common names for this condition. The
name given to a condition sends certain messages to the patient who
receives the diagnosis. The term simple backache might cause a
patient to think that the physician misunderstands because, from
the patients perspective, the pain is not simple if it has not
resolved in a few days. The label non-specific low back pain can
cause the patient to continue to seek care from multiple providers
to receive a specific diag-nosis. Lumbar strain suggests that the
condition was caused by overactivity, which is often not the case,
and that further physical activity would cause it to recur, which
is not true. Spinal degeneration sends the message that the changes
are permanent and will probably worsen.235 The term mechani-cal low
back pain is perhaps the best term for this multifac-torial axial
backache. It suggests the mechanism of injury better than terms
such as strain or sprain, and it does not imply permanence.
The biomechanics of the spine are not unlike the bio-mechanics
of other systems, in that longevity of the com-ponents and
efficiency of the system depend on precise
movements of each segment. In the spine, this means both an
alignment in sustained postures and movement pat-terns that reduce
tissue strain and allow for efficient muscle action without trauma
to the joints or soft tissue.189 Clini-cians and researchers alike
theorize that when alignment and movement patterns deviate from the
ideal, degenera-tion and tissue overload is more likely. This is
analogous to the abnormal tire wear that occurs on a car when the
wheels are out of alignment. Unlike machinery, the body can adapt
over the course of time to stress on the segments. This adaptation
can be the healthy response of tissue to loading (as is seen with
exercise), such as muscle hypertrophy or increased bone density. It
can also, however, begin a cycle of microtrauma that can lead to
macrotrauma.125,140,189 The theoretic model for this approach is
strong, and research is beginning to validate many of these
concepts, although this is not easy given the complex nature of the
system.
History, Physical Examination, and Diagnostic Tests in
Mechanical Low Back Pain
The history and physical examination in mechanical low back pain
are variable. No specific diagnostic tests exist for mechanical low
back pain. Tests and imaging are used to exclude other
diagnoses.
Treatment of Low Back Pain
Most studies of the various treatments for low back pain,
particularly chronic low back pain, unfortunately have shown
limited efficacy. Even the most commonly pre-scribed treatments,
such as medications, exercise, and manipulation, in large trials
tend to show improvements of only 10 to 20 points on a 100-point
pain visual ana-logue scale. For this reason, most clinicians use
multiple treatments on a particular patient in the hope that their
cumulative effect will provide sufficient pain relief and an
improvement in symptoms. The most common treatments for low back
pain are discussed below.
Reassurance and Patient Education. Education should include
providing as much of an explanation as patients need in terms they
can understand. The physician should also provide empathy and
support and impart a positive
A B CFIGURE 40-20 Disk extrusion in a 48-year-old woman with
back and left leg pain. A and B, Sagittal T2- and T1-weighted
magnetic resonance image (MRI) showing L5S1 disk extrusion with
caudal extension. C, Axial T2-weighted MRI showing the extrusion is
left paracentral in the lateral recess, occupying the space where
the S1 root resides.
A B
FIGURE 40-21 Anteroposterior (A) and lateral (B) myelograms of a
59-year-old woman with severe L4L5 central stenosis caused by a
large left L4L5 zygapophyseal joint synovial cyst. Note the obvious
filling defect at the L4L5 level. She had symptoms of cauda equina
syndrome and regained full neurologic function after decompression
surgery.
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888 SECTION 4 Issues in Specific Diagnoses
message. Reassurance that there is no serious underlying
pathology, that the prognosis is good, and that the patient can
stay active and get on with life despite the pain can help counter
negative thoughts and misinformation that the patient might have
about back pain.235
Strong evidence from systematic reviews indicates that the
advice to continue ordinary activity as normally as pos-sible
fosters faster recovery and can lead to less disability than the
advice to rest and let pain be your guide.236 It is controversial
whether patients with low back pain fare bet-ter with a specific
diagnosis or not. Education and explana-tions, however, should be
adequate. As Waddell states in his book The Back Pain Revolution,
Simply saying that I cant find anything wrong might imply that you
are not sure and make patients worry more!235 On the other hand,
some diagnoses carry negative messages to patients that suggest
permanent damage and the need to get fixed, such as degenerative
disk disease or arthritis.235 Mechanical low back pain is a useful
diagnostic term because it implies the mechanism of the pain and
the way it is best treated without suggesting permanence.
Beyond a diagnosis, there is other information that patients
want about low back pain. In a study of patients who presented with
low back pain to their primary care doctors in a health maintenance
organization setting, the information that patients wanted from
their doctor included the likely course of their back pain, how to
man-age their pain, how to return to usual activity quickly, and
how to minimize the frequency and severity of recurrences. They
ranked each of these areas of education a higher pri-ority than
finding a cause or receiving a diagnosis for their pain.235
Providing this information in an amount and in a way that patients
can understand helps build a therapeutic doctorpatient relationship
and, it is hoped, helps reduce anxiety and speed recovery.
Back Schools. The term back school is generally used for group
classes that provide education about back pain. The content and
length of these classes varies a great deal, but generally they
include information about the anatomy and function of the spine,
common sources of low back pain, proper lifting technique and
ergonomic training, and sometimes advice about exercise and
remaining active. Studies have generally found back schools to be
effective in reducing disability and pain for those with chronic
low back pain.224
Exercise. No well-controlled studies show that exercise is
effective for the treatment of acute low back pain. Many
practitioners believe that exercise for patients with acute low
back pain is appropriate to prevent deconditioning, to reduce the
chance of recurrence of symptoms, and to reduce the risk of the
development of chronic pain and dis-ability. This is consistent
with rehabilitation principles for other acute injuries, such as
sports-related injuries or reha-bilitation after joint replacement
surgery.239 This principle is not yet supported by scientific
research, perhaps because of problems with long-term exercise
compliance, the over-all favorable prognosis for each episode of
acute back pain, or the outcome measures used.
Multiple high-quality studies have found, however, that exercise
results in positive outcomes in the treatment of
chronic low back pain.226 This includes pain relief (although
this relief is modest, with a recent metaanalysis of 43 tri-als
showing a mean difference of 10 points on a 100-point scale),
improvement in function, and slightly reduced sick leave.43,87 It
appears that the most effective exercise for low back pain includes
an individualized regimen learned and performed under supervision
that includes stretching and strengthening.87 This is not
surprising because it is gener-ally believed that the purpose of
exercises for the treatment of low back pain is to strengthen and
increase endurance of muscles that support the spine and improve
flexibility in areas where this is lacking. This is combined with
motor retraining to establish normal patterns of muscle activity,
and treatment of deficits of the kinetic chain that interfere with
biomechanical efficiency. One reason that studies have not been
able to determine what exercises are best for patients with low
back pain could be that multiple forms of exercise can achieve the
goal of restoring function and regaining physical
fitness.116,225,239
The exact dose of exercise, how much exercises should be
advanced, and the ideal length of supervised treatment is not
known. Because endurance is a significant problem with many
patients with persistent back pain, activity lev-els should be
increased in planned, fixed increments based on realistic goals
rather than on symptoms. This is because it is normal in the course
of low back pain that there will be temporary exacerbations of pain
along the way. Beyond the physiologic benefits of exercise,
increasing activity has positive effects on beliefs and behaviors
about pain. Small doses of exercise that are not sufficient to
cause physi-ologic change have been found to increase function and
decrease pain. When specifically studied, this appeared to be from
decreased fear-avoidance beliefs and reduced anxiety. By exposing
fearful patients to physical activity through gradually increasing
activity levels despite pain, they receive positive reinforcement
by meeting goals, and personal experience can reduce fear of
movement, reinjury, and catastrophizing.22 Adverse effects of
exercise for low back pain are rarely reported, so it is generally
a very safe form of treatment.
Specific Exercise Treatment for Low Back Pain. Exercise
prescriptions for mechanical low back pain generally begin with the
goal of improving alignment and posture. Although researchers have
not been able to consistently identify which specific postural
faults are associated with chronic low back pain,56 the correction
of posture could be important for at least two reasons. One is that
exercises are more effective if they are done from a position of
proper alignment that promotes optimal joint function and move-ment
patterns. The second is that, for virtually all patients, much more
time will be spent in habitual postures such as sitting and
standing than will ever be spent exercising. If these habitual
postures can reduce abnormal tissue strains, there is a better
chance of reducing pain and promoting healing.188
Research on measuring posture, especially in regard to what is
normal posture and whether exercise can influ-ence posture, is
difficult to conduct, and there are few stud-ies to guide us in
this area. In general, posture is evaluated in both sitting and
standing positions, and an attempt to correct faulty posture is
made. Some of these postural faults
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889CHAPTER 40 Low Back Pain
are habitual and can be improved with education, cuing, and
practice. Some postural faults are structural problems that do not
change with exercise, such as the kyphosis of Scheuermann disease
or idiopathic scoliosis, and should be addressed with aids such as
higher armrests or a chair with increased lumbar support. Many
postural faults begin as habitual, and then become structural as
tight muscles and tendons do not allow immediate correction with
cuing, and weak muscles cannot maintain the proper posi-tion even
if it can be reached. This is what is seen with typi-cal postural
faults such as long-standing lordosis, in which hip flexors and
lumbar paraspinals become tight from pro-longed positioning in
lordosis, and abdominal muscles become long and weak from disuse
and their prolonged lengthened position.
These types of faults can be addressed with the proper exercises
to stretch tight areas and strengthen weak areas. This is harder,
however, to achieve in patients with persis-tent back pain.
Multiple studies have shown that subjects with chronic low back
pain have deficits in spinal proprio-ception and make repositioning
errors. For example, in a study in which asymptomatic patients were
compared with patients with chronic low back pain in an activity in
which participants were assisted into neutral spine posture and
then asked to reproduce this position after periods of relaxed full
lumbar flexion, the group with back pain had significantly more
repositioning errors.157 This has impor-tant implications for
treatment because those with back pain might need extensive
training by a physical therapist to change their posture, rather
than just education regard-ing posture or a few simple
demonstrations.
Lumbar stabilization and core strengthening exercises that
strengthen the muscles that support the spine are the most common
exercises used to treat low back pain. A wide range of exercises
can be used to strengthen these tissues. Because of research that
shows that the deep stabi-lizers, such as the multifidi and
transversus abdominus, do not function as well in those with low
back pain, some pro-grams emphasize beginning training of these
muscles in the treatment of low back pain. Typically the exercise
pro-gram is then progressed to include more complex dynamic and
functional tasks. These are sometimes called motor control
exercises because of the emphasis on precision of movement, rather
than simply gaining global strength or flexibility. Multiple
randomized controlled trials have shown that lumbar stabilization
exercises, core strengthen-ing, and motor control exercises are
beneficial in reducing pain and improving function in patients with
persistent low back pain. It is not clear whether these types of
exer-cises are superior to other types.121
Modifications for Those in Whom Exercises Aggravate Pain.
McGill138 has done extensive research evaluating spi-nal forces
generated during exercise. For example, sit-ups cause more than
3000 N of compressive loads on the spine because of psoas activity,
about the same as moderately heavy lifting. Leg raises also cause
relatively high compres-sive forces. Curl-ups cause lower forces on
the spine, so they are a better choice for anterior abdominal
strengthening in the early stages of rehabilitation, or in those
who have increased pain and cannot tolerate exercises with
increased spinal loading. Lying prone and extending the spine
while
extending the arms and legs causes more than 6000 N of
compression to the spine and might be much too intense for those
with back injuries. The quadruped position with the leg extended,
however, also activates spinal extensors but causes less than half
the amount of spinal compression if done properly with the
abdominal muscles engaged and the spine in neutral.138 These
examples show how modi-fication of exercises can reduce spinal
forces and increase exercise tolerance.
Some patients, especially those with persistent pain, can have
high fear-avoidant behavior and develop kinesopho-bia (a fear of
movement and a belief that movement will increase pain or cause
them to be injured). This fear of pain, rather than forces on the
spine or spinal pathology, leads to poor exercise tolerance. If
this is the reason for poor exer-cise tolerance, it can be
addressed by graded reactivation and gradual increases in activity.
A positive experience with this might decrease fears. For more
severe cases, a multidis-ciplinary approach that includes
psychologic counseling to explore these dysfunctional thought
processes might be needed. The physician should emphasize to
patients that exercise needs to become a daily habit. Lack of
compliance is one of the main reasons why exercise treatments fail.
The health benefits of the exercise program beyond pain relief
should be discussed, and patients should be reminded that
exercising needs to continue even after symptoms decrease or
resolve.
Flexion Exercises for Low Back Pain. Once popular for the
treatment of acute low back pain, using a series of flex-ion
exercises has not been found to be more helpful for acute low back
pain than other interventions, such as spi-nal manipulation, in
several studies. No research has been done on the effectiveness of
flexion exercises for chronic low back pain.223
Extension Exercises for Low Back Pain. Still commonly used by
therapists in the treatment of low back pain, and in particular
back pain accompanied by radicular leg pain, extension-based
exercises are often done using the prin-ciples of the McKenzie
method of physical therapy. This therapy approach divides the
diagnosis for back pain into three categories: derangement,
dysfunction, and postural syndrome. The most common of these are
derangements, and exercises are chosen that centralize the pain,
that is, move the pain from the leg or buttock into the low back.
Although early studies were very promising, later studies have
found this type of physical therapy to be helpful for low back pain
but no more effective than other types of exercise.40,223
Aerobic Activity. Increasing aerobic activity is a corner-stone
of most exercise programs for low back pain. Studies in this area
are often difficult to interpret because, both in the clinical and
research settings, aerobic activity is usually combined with
strengthening and flexibility exercise. Stud-ies have shown that
group classes that combine low-impact aerobics with strengthening
and stretching floor exercises can be as effective in reducing pain
and decreasing dis-ability as individualized physical therapy and
strengthen-ing with weight machines.128 Many clinicians have found
that patients with chronic low back pain tend to have very
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890 SECTION 4 Issues in Specific Diagnoses
low fitness levels, but research in this area has had
conflict-ing results. For example, in one study in which prediction
equations to estimated VO2max (a measure of aerobic fit-ness) in
patients with chronic low back pain were com-pared with normal
values, the values for chronic low back pain patients did not
differ from age-matched normal values for sedentary men and
women.250,251 This could be because those who agreed to participate
in the study were not representative of all patients with chronic
low back pain, or it might simply demonstrate the poor aerobic
fit-ness of sedentary people in general. Perhaps this poor fit-ness
level is related more to lifestyle than to back pain.