Pain – Back Pain

Clinical Strategies – Back Pain


A comprehensive review of back pain: the causes, the characteristic clinical presentations, the general approach to management as well as the procedures and imaging studies that are performed.

by Dr. Ashley Davidoff

Back pain is a disturbing and uncomfortable sensation felt in the lower or upper back.  Low back pain may be caused by structural or functional disorders of the lumbar spine, intervertebral discs, nerve roots, spinal cord, muscles or ligaments.  The pain may also originate from the bony pelvis or pelvic organs.   Sometimes disorders in the upper abdomen can present with back pain such as gallbladder disease, kidney and pancreatic disease.  Lastly, the skin of the back can also be the cause of back pain.

The clinical result ranges from fleeting pain to debilitating disease and sometimes to life-threatening disorders.

The diagnosis requires a careful clinical history that focuses on precipitating factors, duration, onset, character, situation, severity, aggravating, relieving, and associated disorders relating to the pain.  Imaging may include plain x-ray films, Computed Tomography (CT) scan, Magnetic Resonance Imaging (MRI) or bone scan.

Treatment depends on the cause of the back pain and ranges from symptomatic relief with bed rest, analgesics and anti-inflammatory medication through physical therapy, to surgery when indicated.

Anatomic Distribution of Back Pain 
Back pain has a wide distribution and includes structures of the thoracolumbar spine, chest and abdominal cavities.
Courtesy of: Ashley Davidoff, M.D


Low back pain is the second most common reason for physician visits in the United States (US).  Up to 84% of adults have low back pain at some point in their lives.  Generalized back pain can have a myriad of etiologies.  For most patients, symptoms are self-limited and resolve without any specific treatment.  However, for other patients, back pain symptoms are chronic and persistent despite non-specific imaging findings and long-term therapy.  Back pain has a substantial impact on lifestyle and quality of life.  One US survey found that 72% of those who sought treatment for back pain gave up on exercising or sports-related activities.  Sixty percent said they were unable to perform some daily activities, and 46% said they had given up sex because of their back condition.  The total costs for the management of low back pain in the United States exceed $100 billion per year.  Seventy-five percent of the total cost is attributable to fewer than 5% of the patients with low back pain.  The problem, therefore, impacts almost all of us in one form or another.

Posterior View

Oblique View
The normal lower thoracic spine, lumbar spine, sacrum, and coccyx with the pelvis are shown here created as a 3D model from a CT scan.  The left image is a posterior view and shows the rod-like structure of the lumbar spine which uses the sacrum and sacroiliac joints to transfer weight and stresses to the bony pelvis, which in turn transfers the weight via the hips to the legs.  The second image is projected obliquely and shows the the normal anterior curvature (lumbar lordosis)  of the lumbar spine which consists of large, solid, rectangular, vertebral bodies that act as support and protection and are separated by the shock-absorbing intervertebral discs (red). Next we will discuss the anatomy and structural principles of the vertebra.
Courtesy of: Ashley Davidoff, M.D.

Structural Principles – The Vertebra

The lumbar vertebra are considered independent building blocks that are connected to vertebra above and below and to the anchoring sacrum that together form a larger unit – the lumbosacral spine.  In the larger sense the lumbar spine connects with the thoracic and cervical spine to form the axial skeleton.  Via the sacrum and sacroiliac joints, the weight of the body is transferred to the lower limbs which help support the weight of the body in the upright position.  The lumbar vertebrae are built for support and for motion.  They support the full weight of the body and have facets oriented to enable flexion and extension and side-to-side motion but they are limited in rotational movement.  Diseases of a degenerative nature are more common in the lumbar spine than the thoracic spine because of the increased motion and weight that affects the lumbar spine.

The vertebra consists of two parts: the anterior portion called the vertebral body and the posterior portion called the vertebral or neural arch.  The vertebral body is the largest part and is characterized by its cylindrical shape. It forms the anterior border of the spinal canal.  The vertebral arch forms the lateral and posterior borders of the spinal canal and consists of two pedicles and two laminae.   Seven further structures arise from the arch including a pair of superior facets, a pair of inferior facets, a pair of transverse processes and a spinous process.

Parts of the Lumbar Vertebra – Lateral Examination
The lateral X-ray examination (a) of the lumbar spine exemplifies the anatomy of one vertebra.  The basic parts that make up a classical vertebra are very similar.  Image (b) shows the anterior portion of the vertebra called the vertebral body (overlaid in bright yellow)  with superior and inferior endplates (dark yellow). The posterior part of the vertebra is called the vertebral arch, or the neural arch.  It consists of the pedicles and the laminae from which the facets, transverse processes and the spinous process arise.  Image (c) shows one of the pedicles in orange, while image (d) shows the superior facet joint in green and the inferior facet joint in teal.  The lamina is shown in (e) (purple) with the spinous process noted in (f) and overlaid in dark pink.
Ashley Davidoff MD
Vertebra in Cross Section
The cross-section of a lumbar vertebral body using CT scan, gives a better view of the anterior component of the vertebral body (yellow) and the posterior arch or neural arch which forms a ring around the spinal cord.  The ring anteriorly is formed by the posterior border of the vertebral body (yellow) the pedicles (salmon) anterolaterally, and the lamina (purple) posterolaterally. The superior (green) and inferior facets (blue) support the ring and create the bonds with vertebra above and below, while the transverse processes (orange) and spinous process (dark pink) enable attachments for muscles and ligaments.
Images courtesy of: Ashley Davidoff, M.D.
Vertebral Body

The vertebral bodies of the lumbar spine are the largest of the vertebral column.  They are wider from side-to-side than they are from anterior-to-posterior.   They are also slightly thicker anteriorly than they are posteriorly.   They usually have concave or straight surfaces superiorly, inferiorly, posteriorly and anteriorly.  They consist of hard cortical bone externally and less dense cancellous bone internally. The superior and inferior parts of the vertebral body are called the superior and inferior endplates, respectively.

The Vertebral Body
The above image is a reconstructed CT scan of the lumbar spine.  In this cross-section of the vertebral body the two bony components are demonstrated as an outer rim of hard compact bone (darker yellow in b) and an inner cancellous component (lighter yellow).  Note, also that the anteroposterior dimension of the vertebral body is shorter than the transverse dimension.  Lastly, note the relationship of the posterior part of the vertebral body to the vertebral canal and to the pedicles.
Courtesy of: Ashley Davidoff, M.D

The pedicles are short, rounded, and strong bony plates made of thick cortical bone.  They connect the posterior aspect of the vertebral body to the lamina, enabling the neural canal to be formed around the spinal cord and the cauda equina.

Pedicle in Lateral Projection
The reconstructed CT scan shows a pedicle (orange overlay) of the lumbar spine.  It is a short, flat, strong, rounded, paired portion that is connected anteriorly to the vertebral body and posteriorly to the lamina forming the bony neural canal for the spinal cord and nerves.
Courtesy Ashley Davidoff MD
Pedicle in Transverse Projection
The laminae are shown joined together in purple in the posterior aspect of the neural arch.
Images courtesy of: Ashley Davidoff, M.D.

The laminae are flattened plates of bone that extend from the pedicles laterally, to join with each other posteriorly and the spinous process forming the posterior components of the neural arch.  Its function is to assist protecting the spinal cord and nerves, create a base for the attachment of other bony components of the posterior arch, and to form a base for the attachment of muscles and ligaments.

Posterior View of the Lamina and its Appendages
This posterior view of the lumbar spine created by reformatting the images of a CT scan, demonstrates parts of the neural or posterior arch.  In the middle is the spinous process (dark pink).  The lamina is shown in purple.  The anterior portion of the ring (pedicles) are hidden by the superior (green) and inferior (light blue) facets which enable a pliable articulation with the vertebra above and below respectively.  The transverse processes are shown in orange.
Courtesy of: Ashley Davidoff, M.D.
Facet Joints

The facet joints are situated posterior to the vertebral body and on either side of the vertebra.   Thus, at the back of the vertebra there are four facet joints that contain both cartilage and a synovial lining.  The joints are almost vertically oriented providing both strength and rotational ability.

Facet Joints
This lateral oblique view of the lumbar spine was created by reformatting the images of a CT scan, and demonstrates the relatively vertical orientation of the facet joint of the lumbar spine (white between the light green superior facet and light blue inferior facet).  This orientation of the joint favors flexion and extension and limits rotation.
Courtesy of: Ashley Davidoff, M.D.
Axial CT of the Facet Joint at the Level of the Disc
The axial CT image shows the superior facet (green) of an inferior lumbar vertebra and the inferior facet of a more superior lumbar vertebra.  Note the orientation of the facets allowing for flexion and extension, but would inhibit twisting motion.
Courtesy of: Ashley Davidoff, M.D. and Philips Medical Systems


The Facet Joint in Transverse View
The transverse view of the lumbar spine was created by reformatting the images of a CT scan and demonstrates the anterior and lateral positioning of the superior facet (light green) with its orientation directed medially and posteriorly.  The inferior facet (light blue) is positioned posteriorly and medially and faces anterolaterally.  This view is also helpful to conceptualize why the joint favors forward and backward flexion and extension, while it limits rotation.
Courtesy of: Ashley Davidoff, M.D.


 Pars Interarticularis

The pars interarticularis is the part of vertebra that links the superior and inferior articular facets.  It is best seen and appreciated in the oblique view of the lumbar spine where the shape of a Scottie dog (Scottish terrier or Aberdeen terrier) can be appreciated.

The pars interarticularis particularly of L5 is frequently the site of a stress fracture in young athletes.  When this injury is suspected, the oblique view of the lumbar spine is extremely helpful and attention to the neck of the Scottie dog is helpful to focus on the anatomical landmark that is affected.

Oblique View of the Lumbar Spine
The left anterior oblique plain X-ray of the lumbar spine shows the Scottie dog with orange nose pointed to the patient’s right side (b).  The neck (light blue) of the Scottie dog represents the pars interarticularis. The eye of the Scottie dog is the pedicle (light orange/salmon), while the transverse process is the nose (bright orange).  The one front leg (teal blue) represents one of the inferior facet joints while the contralateral, inferior facet is represented as a hind leg (teal blue). The ear (lime green) is the superior facet, while the Scottie’s rump (bright pink) is the spinous process.  The body of the animal is overlaid in purple and represents the lamina.
Courtesy of: Ashley Davidoff, M.D.
Intervertebral Disc

The intervertebral disc is a fibrocartilaginous structure that lies between the vertebral bodies.

Structurally, it consists of a soft, inner gelatinous, viscoelastic cushion called the nucleus pulposus which is surrounded by a series of fibrous rings collectively forming a tougher surrounding annulus fibrosis.

The nucleus pulposus is nearly 90% water, but also contains complex proteins. It serves to cushion the stresses between the vertebra as well as enabling the movement of the adjacent vertebral bodies in multiple directions.

Aside from enclosing and protecting the nucleus pulposus, the annulus also connects the vertebral bodies and limits the motion between them. The outer fibers of the annulus blend the anterior and posterior longitudinal ligaments of the spine, and are also attached to the bone at the disk margins via Sharpey’s fibers.

The disc has conceptually been compared to a doughnut with a jelly center.  The intervertebral disc makes up about one-third the length of the spine and represent as a group the largest structure in the body that does not have a direct blood supply.  As the disc expand and contract under duress and motion, they absorb water and nutrients from their direct environment almost like a sponge.

The overall function of the disc is to act as a shock absorber to reduce the loads on the bony axial skeleton.  They compress under stress of weight and spring back when relieved of the stress. The intervertebral disc and facet joints between the vertebra normally allow for a considerable amount of movement including rotation, lateral bending, flexion and extension.

Intervertebral Disc Linking Vertebra Together
The pink intervertebral discs act like gelatinous shock absorbers or cushions between two vertebra.  Note that the discs normally enlarge minimally as they progress from the superior lumbar vertebra to the inferior aspect of the lumbar spine.
Images courtesy of: Ashley Davidoff, M.D.
Intervertebral Disc
The discs in the intervertebral spaces consist of the nucleus pulposus and a more fibrous cartilaginous periphery called the annulus fibrosus.  These are present in all the vertebral spaces except for the upper two cervical intervertebral spaces, the sacrum and the coccyx.
Images courtesy of: Ashley Davidoff, M.D.


The Muscles

In addition to the complex bony and cartilaginous components of the vertebra, the ligaments and muscles play an important role in support and stability.  The thoracic spine has added support in the form of the ribs and the muscles that link the ribs to each other and consequently stabilize the thoracic spine laterally.  The lumbar spine lacks this lateral support and depends solely on the muscles and ligaments for this type of support.

Psoas Muscles
The psoas muscle is overlaid in maroon, runs from the lateral aspect of the lumbar spine, joins the iliacus muscle in the pelvis to form the iliopsoas, and inserts on the greater trochanter.  They provide significant support for the spine and serve to strengthen and anchor the spine to the lower limbs.
Image courtesy of: Ashley Davidoff, M.D.
Muscles of the Back and Abdomen
The lumbar spine is supported by a posterior group of muscles and an anterior group of muscles.  The posterior longitudinal muscles (erector spinae) including the multifidus, longissimus, and the iliocostalis are attached to the spinous processes and the transverse processes of the vertebra.  The quadratus lumborum also has a longitudinal course but runs anteriorly on the transverse processes, while the psoas muscles are attached to the vertebral bodies anteriorly and are inserted with the iliacus muscle onto the greater trochanter of the femur.  The loose connections of the back muscles with the lateral and anterior abdominal musculature, does add minimal support.  The lateral abdominal muscles include the internal oblique, external oblique and transversus abdominis muscle.  The anterior muscle is called the rectus abdominis muscle.
Images courtesy of: Ashley Davidoff, M.D.


The Ligaments

There are five major ligaments that support the spine including the anterior longitudinal ligament, posterior longitudinal ligament, interspinous ligament, supraspinous ligament, and the ligamenta flava. The anterior and posterior longitudinal ligaments run vertically along the anterior and posterior aspects of the vertebral bodies respectively.  The posterior ligament begins to narrow at the lumbar region.  At L4 and L5, the posterior longitudinal ligament is one-half the width of that at L1.  This narrowing produces a weakness in the posterolateral aspect of the intervertebral disk.  This weakness makes the lumbar spine more susceptible to disc herniations.  It is interesting to note that the spinal cord extends only to the L1 vertebra and thus, the typical disc herniations at L4 and L5 are not at risk of impinging on the spinal cord.  However, if there is a severe posterior herniation, this may impinge on the nerves that extend from the base of the spinal cord at L2 (these nerves are also called the cauda equina) which if damaged can cause urine/stool incontinence as well as decreased sensation along the perineum/anus.

Normal Ligaments
The sagittal reconstructed CT scan provides an image that projects some of the ligaments of the thoracolumbar spine.  The anterior longitudinal, (pink) posterior longitudinal (blue) and supraspinous ligaments (bright pink) connect all the thoracolumbar vertebrae together.  The interspinous ligaments (light pink) connect two adjacent vertebra at the level of the spinous processes.
Image courtesy of: Ashley Davidoff, M.D.
Ligaments of the Spine
The cross-section of a single lumbar vertebra using CT scan shows the ligamenta flava (yellow) in addition to the interspinous (bright pink) posterior longitudinal (blue) and anterior longitudinal (dark pink) ligaments.  The ligamenta flava are attached to and connect the laminae of two vertebrae together.
Image courtesy of: Ashley Davidoff, M.D.
Interspinous Ligament of the Spine
The cross-section of a single lumbar vertebra using CT scan shows the interspinous ligament (pink) connecting the adjacent spinous processes together.
Images courtesy of: Ashley Davidoff, M.D.
Ligamentum Flavum

The ligamentum flavum is the strongest of the vertebral ligaments.  The term flavum derives from the Latin word flavum which means yellow and describes the color of the ligament in its natural state.  The ligaments are paired, each lying on the inside of the laminae.

Their function is to connect the vertebra, prevent excessive movement and protect the neural elements and the spinal cord.

The Spinal Cord and Canal

The spinal cord connects the brain with the peripheral nervous system. It is protected by the bony spinal column and its length reaches only to about L1 or L2 where it becomes the conus medullaris; the cone-shaped, tapered end of the spinal cord that has no nerves arising from it.

The nerves for the lumbosacral region hang off the distal spinal cord, like the hairs of a horse’s tail. Hence, the name cauda equina which is the Latin for horse’s tail.   The nerves extend caudally from the end of the spinal cord, lessening in number as they sequentially exit via the neural foramina to their appropriate segments.  At the base of the cauda equina, there are approximately 10 fiber pairs, 3-5 lumbar, 5 sacral, and a single coccygeal nerve.

The CT myelogram shown above, reveals the nerves of the cauda equina as black strands in the bed of white myelographic bed within the thecal sac, surrounded by the bony lumbar spine, and looking very much like the described horse’s tail as seen in the lower image.
Courtesy Ashley Davidoff MD


Cauda Equina in the Thecal Sac
The cauda equina are seen in this cross-section of a CT myelogram.  In the left image they are seen as black dots in the white, myelographic contrast medium and are colored in orange in the right image.  The section is taken at the level of the intervertebral disc (pink) where the lateral aspects of the posterior portion of the bony arch is open forming the neural foramina that allow the nerves to exit.
Images courtesy of: Ashley Davidoff, M.D.
Spinal Canal and its Spaces

The spinal canal is the tubular protective unit that surrounds the spinal cord and nerves.  It is formed by the bony and ligamentous components of the vertebra.  The bones and ligaments of the spinal column are aligned in such a way to create a canal that provides protection and support for the spinal cord and nerve roots.

Looking in on the Spinal Canal
The transverse stacked view of the lumbar spine was created by reformatting the images of a CT scan and demonstrates the bony components of the vertebral column as viewed from above looking in and down.  The protection and support provided by the bony elements appears prohibitive to outside forces, though the column still has to provide sufficient movement to allow flexibility of the spine.
Courtesy of: Ashley Davidoff, M.D.

Between the ligaments and the periosteum of the bones of the spinal canal and the outer membrane (dura mater) of the spinal cord lies the epidural space (also known as the extradural or peri-dural space).  It contains small arterioles, venous plexuses, lymphatics, nerve roots, and loose fatty tissue.  It is in this space that medication is injected for pain relief.

The dura mater (Latin for “hard mother”) is the outermost and toughest layer of the spinal cord and nerves.  Deep to the dura is another membrane called the arachnoid (arachnoid is Greek for cobweb).  It is a thin, avascular membrane which is adherent to the dura.  Deep to the arachnoid and intimately attached to the spinal cord is the pia mater (pia is from the Latin pius meaning tender or gentle) which is a thin delicate and vascular membrane.  The space between the pia and arachnoid is called the subarachnoid space and it contains the cerebrospinal fluid.  It is from this space that fluid is taken for a diagnostic spinal tap, where pressures are measured to evaluate for raised intracranial pressure and where contrast is injected for myelography.

At the level of the distal end of the spinal cord at L1, the subarachnoid space is a ring of about 2-3mm, while below L2 at the level of the cauda equina it expands to form the more capacious lumbar cistern, and is about 9mm in diameter.

Neural Foramen

The neural foramen or intervertebral foramen is an oval shaped space between two vertebra that houses the spinal nerves and vessels.  Each interspace has a pair of foramina.  The foramen is bounded anteriorly by the intervertebral disc and posterior aspects of adjoining vertebral bodies, superiorly by the pedicle of the upper vertebra, and inferiorly by the pedicle of the lower vertebra.  The posterior border is formed by the facets and joints of the two vertebra.  Each neural foramen is thus bounded by three joints.

Neural Foramen
The CT scan of vertebral spine has been reconstructed with volume rendering techniques in the above two images.  In this lateral view, the neural foramen has been outlined in pink and the nerves created in yellow.
Courtesy Ashley Davidoff MD

From the spine, a nerve root will exit the intervertebral foramen below its corresponding segment.  For example, the L4 nerve root will exit the spinal column between L4 and L5.

  • The L1 nerve root supplies motor function to the iliopsoas muscles and sensation on the anterior thigh just below the inguinal ligament.  There are no reflexes associated with the L1 nerve root.
  • The L2 nerve root supplies motor function to the iliopsoas, adductors, and quadriceps.  It also accounts for sensation in the middle of the anterior thigh.  There are no reflexes associated with the L2 nerve root.
  • The L3 nerve root controls the adductor muscles of the hip as well as the quadriceps.  It also accounts for sensation in the anterior thigh just above the knee.   There are no reflexes associated with the L3 nerve root.
  • The L4 nerve root is responsible for the anterior tibialis muscles and sensation over the patella then extending medially to the medial malleolus.  The L4 nerve root is associated with the patella reflex.
  • The L5 nerve root controls the extensor hallucis longus and the hamstring muscles.  It also accounts for sensation over the proximal lateral aspect of the lower leg just as well as the dorsal aspect of the foot and big toe.  There are no reflexes associated with the L5 nerve root.
  • The S1 nerve root accounts for motor function in the peroneus longus and brevis muscles as well as the gastrocnemius.  It supplies sensation over the lateral malleolus.  The S1 nerve root is associated with the Achilles reflex. 

When the relatively small space of the neural foramen is considered in conjunction with its intimate relationship with the posterior aspects of the intervertebral disc and space, and relationship to the facet joints, it is no wonder that a small space occupying event (disc protrusion, herniation or osteophyte presence) could result in a significant clinical event.  The clinical event may be acute or chronic.

Interdependence of the Structures

Interdependence is a fundamental concept throughout the body and the spine is no exception. This concept implies that the combination of vertebra to form a new unit (in this case the lumbosacral spine) that is bigger and more powerful than the individual parts. While the bigger unit is more powerful than the individual parts, the bigger unit is only as strong as its individual parts and continued respect of the role the smaller units play is all important. This concept is typified in the spine when a single slippage of one of the parts, sometimes only by a few mms, can cause devastating and debilitating symptoms.

Unique Features of the Vertebra

Each vertebral body is quite unique and designed with a functional purpose.  For instance, the occipital-atlas joint, where the base of the skull meets the first cervical vertebra—also known as the atlas—is specifically intended for flexion and extension.  The joint below that, the atlantoaxial joint between C1 and C2, is meant for rotation.  The remainder of the upper cervical vertebra motion is rotation, whereas the lower cervical vertebra is designed more for sidebending.

The twelve thoracic vertebrae are unique in the sense that, the facet orientation is backward, upward, and lateral.  Therefore, based on these facet orientations, the thoracic spine is more conductive to rotation around an axial plane.   Whereas, the lumbar vertebra have facets that are orientated in a direction that is backward and medial.  This orientation of the lumbar spine facets favors and optimizes flexion and extension with respect to the sagittal plane.

The five lumbar vertebrae are distinguished by their size, facet orientation and large, almost rectangular, spinous processes.  The normal curvature of the lumbar spine is lordotic.  The large cross-sectional area of the lumbar vertebral body is designed to sustain longitudinal loads.  The L5 vertebra carries the largest amount of weight of any vertebra in the entire spine.  The intervertebral discs enlarge progressively from L1 to L5 respective to the increasing weight each has to bear.

Normal Lordosis of the Lumbar Spine 
The normal forward curve of the lumbar spine is known as a lordotic curve where the convexity of the spine is anterior and the concavity is posterior.  The normal cervical spine is also lordotic.  Lordosis comes from Greek lordōsis, from lordos which means curving forward.
Courtesy of: Ashley Davidoff, M.D.


The wear and tear on the spine as people age is universal and nobody is spared.  We walk, we stand, sit, kneel, and bend over. We move, we jog, we play sports and at each turn we depend on the strength and integrity of the tissues.  The movements around and on the spine are complex and require elasticity, pliability and strength.  Structures age and get worn out.  Elasticity, pliability and strength of tissues is lost; dehydration of the disc occurs and the natural consequences of aging is felt by all the tissues including the back.  However, the shift of structures by only a few mms in the region of the neural canal, as a result of the described degenerating and aging process, can have significant consequences.

The above collection of images represents a collage of photographs taken over a span of 30 years of travel and family life.  They range from workers in a field to family members kicking a soccer ball, all representing the day-to-day activities that take their toll on our backs.
Courtesy of: Ashley Davidoff, M.D.
Normal Young Patient and Elderly Lumbar Spine
The lumbar spine seen in image (a) and (b) are from a young person and are almost normal but for minimal anterior osteophytic change.  The progressive enlargement of the discs from L1 to L5 is normal and their homogeneous appearance is also normal.  In image (c) and (d) the elderly patient shows signs of wear and tear on the lumbar spine.  The discs between L3-4 and L4-5 have degenerated and as a result have absorbed nitrogen seen as a black line between L4 -5.  There has been loss of height of both discs (green) and the excessive forces on the vertebra has resulted in sclerosis seen as whitening of the inferior border of L3 and superior border of L5.  Minor posterior osteophytes (white) serve to buttress the aberrant distribution of the forces as a result of the degeneration.
Courtesy of: Ashley Davidoff, M.D.
Space Limitations

Space is an extremely important aspect of the spinal cord and the nerves.  The exiting nerve roots negotiate the neural canal which is usually quite capacious and measures approximately 15 mm in craniocaudad extent and about 10mm in A-P when viewed in the lateral projection.  The nerves and sheaths are relatively small compared to the neural foramen and so the spatial design seems to have latitude.

Disease processes can affect only one of the structural elements described, so that, for example, isolated disc disease manifest as a herniated disc may result in devastating symptoms.  On the other hand, a multiplicity of structural components may be aberrant, including disc space narrowing, bulging disc, osteophyte formation, facet joint disease and ligamentous weakening without significant symptoms or signs.  The net clinical effect relates to the critical space which the disease occupies together with other factors such as the release of chemical irritants as a result of injury.

Key Elements Relating to Many Causes of Back Pain
The oblique projection of the CT reconstruction of the spine exposes the neural foramen with its pair of nerves (yellow in b) and the intervertebral disc (pink)  The facet joints,  (superior facet = green and inferior facet= light blue)  are seen in image (d).  The intimate relationship between the nerves, disc, and the facet joints is apparent.
Image courtesy of: Ashley Davidoff, M.D.
Neural Foramen
The reformatted CT  images in oblique  lateral  or sagittal projection (a,b) show the neural foramen with nerves (yellow). The reformatted images in oblique projection (c,d) show the neural foramen and nerves in intimate relation with the superior  (blue) and inferior (green) facets and their joint space (c). In (d), facet osteophytes impinge on the nerves and the space occupation and impingement may be the cause of symptoms.  It becomes very clear that minimal changes in the disc or the facets can affect and impinge on the nerves with significant clinical effect.
Image courtesy of: Ashley Davidoff, M.D.

The basic standing position places overall gravitational and longitudinal force on the spine with the greatest weight accommodated by the lumbar spine and more specifically by L5.  The center of gravity of the body is just anterior to the lumbar spine.  The upright posture, therefore, places a continual downward and forward thrust on the lower lumbar spine.  The facet joints are, therefore, under continual stress, with the forces focused on the pars interarticularis. The lordotic shape of the lumbar spine tends to disperse the force so that the other lumbar vertebra assumes responsibility to accommodate a share of the force.  Flexion and extension create variable and changing compressive forces on the discs that from a functional point-of-view, not only serve to disperse pressure, but also create sponge-like negative pressures that help the disc to absorb water and nutrients direct from the immediate environment.  The facet joints have forces exerted on them by flexion and extension, side-to-side motions, and rotational movement.  The ligaments and the orientation of the facet joints limit the extent of movement.  In the healthy spine, the forces are well-balanced  but the spine is only as strong as its weakest link.


There are three major joints between adjacent vertebra: intervertebral disc space and the two facet joints. They act in concert.  When any of these joints is traumatized or degenerates, it puts undue stress on the others and they may respond by creating bony buttresses to aid stability.  These buttresses are called osteophytes. Thus, when the disc loses height, there is consequently much less support for the facet joints at that particular level and the joints become subject to increased stress. In addition, accelerated wear and tear on the joints might occur as a consequence of unbalanced distribution of forces.  The effects of the unbalanced forces puts increased stress on the ligaments and muscles and consequently, pain syndromes result from any one of the consequences of a single weak element in the vertebral chain.  In addition, the natural weakening of the aging bone by osteoporosis diminishes the overall support.

Diseases of the Lumbar Spine

Now that we have a good sense of the structure of the lumbar spine, we will review some of the more common diseases that affect the spine and more specifically those that cause back pain.

The differential diagnosis for back pain can be essentially divided into mechanical versus non-mechanical etiologies.

Mechanical low back pain:

  • Degenerative disc or joint disease
  • Spinal stenosis
  • Herniated nucleus pulposus, annular tears
  • Spondylolysis, spondylolisthesis
  • Osteoporotic compression fracture
  • Severe kyphosis, scoliosis, or transitional vertebrae  
  • Musculoskeletal strain or sprain
  • Cauda equina syndrome

Non-mechanical spinal conditions:

  • Primary vertebral tumors, multiple myeloma, or metastatic cancer to the spine
  • Osteomyelitis, epidural abscess, discitis, or shingles
  • Dissecting aortic aneurysm
  • Nephrolithiasis, pyelonephritis, or perinephric abscess
  • Ankylosing spondylitis, psoriatic spondylitis, Reiter’s syndrome, or Paget’s disease of the bone
Degenerative Disc or Joint Disease

Degenerative joint disease (also known as DJD, osteoarthritis, spondylosis, and spinal arthritis) is a group of disorders that are primarily characterized by changes in the joint cartilage caused by wear and tear on intervertebral discs and/or the cartilage of the facet joints.    As the cartilage changes there are secondary effects on the surrounding tissues that help characterize the disorder including: joint space narrowing, vacuum phenomenon, bony irregularity, sclerosis, eburnation of the opposing joint surfaces, subchondral cyst formation, and osteophytes.

The cause of degenerative disc or joint disease is typically an age-related phenomenon commonly associated with overuse.  Other risk factors include obesity, female sex, family history, and previous back injuries.

The result of the degeneration is a syndrome in which structural changes, compensatory mechanisms, and low-grade inflammation results in pain in the joints or in the surrounding region.  With prolonged DJD, destruction and remodeling of the joint itself will occur.  Often osteophytes or bone spurs will be seen as will an irregularity of the joint surface signaling a chronic inflammatory reaction.  A variety of specific entities including disc bulge, disc herniation, disc rupture, lumbosacral facet syndrome, and spinal stenosis fall under the umbrella of DJD.

Normal Young Patient and Elderly Lumbar Spine
We have shown this image earlier but it is used again to show the normal (a,b) and the common degenerative changes in the lumbar spine seen in image (c) and (d).  In image (c) and (d) the elderly patient shows signs of wear and tear on the lumbar spine.  The discs between L3-4 and L4-5 have degenerated and as a result have absorbed nitrogen seen as a black line between L4 -5.  There has been loss of height of both discs (green) and the excessive forces on the vertebra has resulted in sclerosis seen as whitening of the inferior border of L3 and superior border of L5.  Minor posterior osteophytes (white) serve to buttress the aberrant distribution of the forces as a result of the degeneration.  This is a common appearance of the back seen on lumbar spine X-ray series and on CT scans of the lumbar spine, but as stated the severity of symptoms does not correlate well with the X-ray appearance and it is usually the MRI that has better diagnostic correlation in the patient with acute pain.
Courtesy of: Ashley Davidoff, M.D.

The diagnosis of DJD rests on the combination of the clinical presentation and imaging appearances.  Symptoms associated with osteoarthritis in the lower back include stiffness in the morning that resolves later in the day with more activity, tenderness to palpation of the lumbar spine, and decreased flexibility.

Plain x-rays of the lumbar spine will show evidence of spondylosis, osteophyte formation, and decreased intervertebral space but will not be able to characterize changes in the disc.  MRI is more able to identify structural changes in the soft tissues.

The most common appearance of degenerative joint disease is disc space narrowing with some osteophytic change.  There is often some gas in the joint, usually nitrogen that is sucked into the joint by the vacuum that is caused when the disc loses volume by losing water and shrinks in an airtight space.  This phenomenon is called “vacuum phenomenon”.  Additionally, one usually sees some roughening and sclerosis of the surfaces of the joint.  More commonly than not, the patient with DJD is asymptomatic.  The radiological appearance often does not correlate well with the clinical picture.  Thus, a patient with no symptoms may have significant structural changes and a patient with little structural change on x-ray may have severe symptoms.  The MRI has the most specific correlation with acute symptoms since it reflects the aberrant changes in the disc and abnormal disc position in the patient with acute back pain.  Thus, it is very important to reiterate that it is the combination of the clinical evaluation and the imaging that enables the clinician to make an accurate diagnosis.

Many patients can be treated successfully with weight reduction, core and paraspinal muscle strengthening, NSAIDs, as well as lumbar supportive bracing.  Epidural corticosteroid or facet joint injections may be considered for patients with continued back pain, despite treatment.  Patients that have failed non-operative treatment who continue to have intolerable symptoms of back pain, secondary to degeneration, may require surgical decompression.

Degenerative Disc Disease with Posterior Disc Bulge
 The sagittally reformatted CT scan exemplifies severe degenerative disc disease most obvious as joint space narrowing at L4/5 and L5/S1.  At both these levels vacuum phenomenon is demonstrated as black linear accumulations of gas principally nitrogen, in the interspace.  In addition, there is sclerosis most marked at the L4-L5 level as whitening of increased density at the inferior endplate of L4 and superior endplate of L5 with irregularity of the surface.  The endplate changes are caused by microfractures and attempts at buttressing as a result of loss of protection and support of the disc.
Less obvious is the posterior bulging of the disc at the L2-3 level and at L3-L4 (disc is overlaid in green with impingement on neural foramen noted at L4-5 level).
Courtesy of: Ashley Davidoff, M.D.


Lumbar Spinal Stenosis

Lumbar spinal stenosis is defined as a congenital or acquired narrowing of the spinal canal, nerve root canals, or intervertebral foramina due to spondylosis or degenerative disc disease. It usually affects the middle-aged and older population and affects the cervical or the lumbar spine.  It is uncommon for the thoracic spine to be affected.

The narrowing of the spinal canal is caused by any combination of many degenerative structural changes that affect the spine but the primary process is the degenerative changes in the discs which dehydrate and narrow. This process can cause tilting, slippage, or rotation of vertebral bodies which results in shortening of the spinal column.  The changes in stresses also cause any combination of osteophyte formation, facet hypertrophy, bulging disks, and hypertrophy of the ligamentum flavum.  The ligamentum flavum may also buckle inward as a result of the loss of height and compress the spinal sac and nerve roots.  The ligamentum flavum sometimes also calcify or ossify.  Degenerative spondylolisthesis or slippage of one vertebra on another caused by loss of ligamentous muscular and bony support can further compromise the canal.

The net result is a pressure or impingement of the nerve roots prior to their exit from the foramina due to the narrowing.  Lumbar spinal stenosis rarely causes pressure or impingement on the spinal cord itself because the spinal cord and conus medullaris end at L1.

Normal and Spinal Stenosis Caused by Facet Hypertrophy
Images (a) and (b) are from a normal CT myelogram taken in the axial projection at the level of a lumbar disc and reveal a spinal canal that is capacious.  Since the myelographic contrast is in the thecal sac (orange) the nerve roots of the cauda equina (black dots in (a) can be seen anterior to the contrast which is layering posteriorly (white in (a).  The superior facet (green) and inferior facet (blue) are normal.
The lumbar CT in a patient with spinal stenosis is viewed in the transverse cuts in images (c) and (d).  The thecal sac is narrowed to less than 10mm and hence, spinal stenosis is present.  The thecal sac  (orange in (d)  is narrowed and deformed, and compressed by the enlargement and deformity in this instance, by the facet hypertrophy and deformity of both the superior (green) and inferior facets (blue).  Since this is not a CT myelogram and is from a plain lumbar CT scan, the nerve roots are not seen.
Courtesy of: Ashley Davidoff, M.D.


The diagnosis of spinal stenosis is based on the combination of clinical presentation and imaging.

Clinically, lumbar spinal stenosis may present with classic pseudoclaudication symptoms of leg pain during ambulation that improves with rest. As the name suggests, nerve root entrapment occurs, as there is progressive congenital or acquired narrowing of the spinal canal, nerve root canals, or intervertebral foramen.  Sometimes the pain is relieved when the patient bends forward.  Other symptoms of spinal stenosis include persistent generalized back pain, numbness in the lower extremities with walking, and radicular pain to the feet.

Imaging is essential to make the diagnosis.  Radiographically, the diagnosis is most evident on MRI as one cannot only directly visualize the disc and soft tissues, but also get a relative sense of the bony structural changes.  CT scanning is better for the bony elements but CT myelography is the alternate consideration when MRI is not viable.

Symptoms may be relieved by conservative therapy which includes prolonged sitting and flexion of the lumbar spine.    Non-operative treatment involves analgesics, NSAIDs, physical therapy, cardio aerobic conditioning, and epidural corticosteroid injections.  For patients with persistent severe pain, a decompressive laminectomy can be considered.

MRI – Spinal Stenosis
This T2-weighted MRI image is from a patient with spinal stenosis and is used to explain the changes in the transverse views (b, c).  The narrowing is commonly caused by facet hypertrophy and ligamentous hypertrophy.  On the T2-weighted images the CSF is white and the back of the red arrow points to the normal thecal sac behind the vertebral body seen with the nerves in the sagittal plane, while the red arrowhead points to the normal thecal sac and nerves in the transverse plane.  At the level of the disc at L3-4 and L4-L5, the thecal sac is obliterated since no white CSF can be identified because it has been squeezed out by the facet and ligament hypertrophy.  The base of the green arrow is at the L3-L4 disc space in the sagittal plane and the green arrowhead points to the same level in the axial plane at the level of the spinal stenosis.
Courtesy of: Ashley Davidoff, M.D.


Herniated Nucleus Pulposus

A herniated nucleus pulposus (HNP) is a mechanical disorder that results from a displaced intervertebral disc.  It is commonly referred to as a “slipped disc.”  It is caused by a tear of the annulus fibrosis which allows for a protrusion of the nucleus pulposus.  The resulting mass effect on the nerve roots is responsible for sensory and/or motor deficits and pain.  The disc protrusion is best diagnosed by MRI, which reflects innate changes in the disc and the mass effect on the nerves and epidural space.  CT is an alternate, but less sensitive technique, while plain film can only reflect narrowing of the intervertebral disc space but cannot visualize the disc.

Annulus Fibrosis
Diagram (a) shows the normal annulus fibrosis situated peripherally and circumferentially  in pink and the nucleus pulposus centrally in blue.  The annulus fibrosus can weaken and/or rupture at any point but has the most clinical impact when it weakens posteriorly.  In the diagram above, the normal disc is demonstrated in (a), with early posterior changes from weakening causing disc bulge (b) progressing to further bulge and protrusion in (c), to frank rupture in (d).
Courtesy of: Ashley Davidoff, M.D.


A HNP or annular tear can occur at any age.  There is evidence in the medical literature that suggests that imaging studies may find evidence of a HNP even in patients without lower back symptoms.  Therefore, it is again important to reiterate that clinical correlation is strongly suggested when attributing lower back pain to a HNP.  Symptoms are nonspecific but usually relate to flexion of the lumbar spine and typically occur with prolonged sitting and bending forward.  Patients may also note that symptoms are relieved with laying flat.

At its worse, a HNP may cause radiculopathy; numbness, tingling, and even motor weakness in the lower extremity past the knees.  A frank herniation of the lumbar nucleus pulposus may cause impingement to the cauda equina nerves causing urine or stool incontinence.  This is a surgical emergency and is known as cauda equina syndrome.  HNP causing radiculopathy without symptoms of cauda equina syndrome may be treated initially with narcotic pain medication, prednisone taper, or strong NSAIDs (nonsteroidal anti-inflammatory drugs).

Additionally, an epidural corticosteroid injection can be offered for temporary symptomatic relief in some patients.  After the acute phase of this condition, gradual progression with physical therapy focusing on lumbar spine strengthening and flexibility is advised.  At times, a supportive lumbar brace may be used to help manage the symptoms of a HNP.  The natural history of this condition is gradual clinical improvement and return to regular activities in several weeks to even months.  However, those with persistent symptoms secondary to HNP that is not responsive to non-operative treatment, diskectomy is considered.

Herniated and Ruptured Disc at L5-S1
The T2-weighted MRI in the sagittal plane (a, b) and the axial plane (c, d) show a herniated and ruptured disc with the extruded fragment overlaid in lime green.  (b,d).  The mass effect and effacement on the nerves seen in both the sagittal view where the lime green extruded segment impinges on the string-like nerves (black lines) while in the transverse plane the normal nerves are seen on the right and the effaced nerves are seen on the left.  Additionally, the loss of height of the disc space (dark green in b) is apparent.  The disc space of L5-S1 should be taller than the disc space above, but degeneration and extrusion has reduced the height of the disc.
Courtesy of: Ashley Davidoff, M.D.

Spondylolysis is a non-displaced stress fracture along the pars interarticularis caused by congenital weakness or repetitive trauma to the pars interarticularis.

In the adolescent athletic population, extension-based back pain is especially suspicious for spondylolysis.  With more and more children participating in organized athletics, there appears to be an increase prevalence of this condition.  Sports such as gymnastics, ballet, figure-skating, rowing, and football tend to require repetitive extension of the lumbar spine and thus, may be a source of increase risk for spondylolysis.

The entity may be complicated by spondylolisthesis, which is an anterior slippage or displacement usually of L5 on S1.

The diagnosis is made radiographically using oblique projections of the lumbar spine and is characterized by a break in the “collar” on the Scotty dog.  If this is negative and suspicion remains high, then a SPECT bone scan should be ordered first, followed by a CT scan isolated to the specific area that is positive on the bone scan.

The treatment is initially conservative, using rest, analgesia and temporary cessation from athletic activity. Nonsteroidal anti-inflammatory drugs such as ibuprofen are useful.  In patients who do not respond to this basic therapy, an antilordotic brace for twelve weeks is used, combined with physical therapy emphasizing core and para-spinal musculature strengthening as well as stretching of the hamstring and hip flexor muscles.  The patients are usually transitioned into sports with a supportive brace during activity for four to six more weeks.

Spondylolysis comes from the Greek words spondylos, meaning spine or vertebra, and lysis, which means a break or loosening.

Diagrammatic Fracture through Pars Interarticularis
The oblique plain X-ray of the lumbar spine shows a red line through the pars interarticularis representing the site of a fracture caused by spondylolysis through the neck of the Scottie dog.  In this patient there is no evidence of spondylolysis.
Courtesy of: Ashley Davidoff, M.D.


Spondylolysis of L5
The transverse CT through the pars interarticularis of L5 shows bilateral  fractures of the pars interarticularis as seen by the red lines in the right image.
Courtesy of: Ashley Davidoff, M.D.


Spondylolysis of the Pars Interarticularis
The sagittal reformatted CT of the lower lumbar spine shows a fracture through the pars interarticularis of L5 seen by the red line.
Courtesy of: Ashley Davidoff, M.D.



Spondylolisthesis describes a mechanical abnormality of the vertebral column characterized by slippage of one vertebra on another.

The cause for the slippage or displacement is most commonly spondylolysis and degenerative disease, but also includes congenital isthmic dysplasia, trauma and post-operative iatrogenic causes. The bony defect in the pars interarticularis is responsible for the spondylolisthesis in the group of patients with spondylolysis.  In degenerative disease a combination of ligamentous injury, facet joint disease, and disc thinning lead to the instability and there may be either forward slippage (anterolisthesis ) or retrolisthesis (posterior listhesis).  In the congenital group, bony dysplasia of the vertebral arch and/or the facets at the lumbosacral junction cause the slippage.  Traumatic injury can affect the pars, facets, or ligaments and result in listhesis.

The result of the slippage is anatomical distortion which may cause impingement on the nerves.  The clinical consequence ranges from the asymptomatic patient to one with pain, sensory and/or motor dysfunction.

Diagnosis is based on imaging and a simple lateral examination of the lumbar spine can document the listhesis.  The spondylolysis may be identified on the lateral exam, but oblique views are best for this entity.  CT scan and better still, CT myelography are excellent alternatives and do add more information as to the cause of the slippage.  MRI offers visualization of the soft tissues.

Treatment depends on the cause but the back pain is initially treated with conservative methods of pain relief and rest.

The CT scan of this 86-year-old female shows mild anterolisthesis of L5 on S1.  In this case, degenerative disease is responsible and is characterized by disc space narrowing and vacuum phenomenon.
Image courtesy of: Ashley Davidoff, M.D.
Forward Slippage
In this case, the plain film shows spondylolisthesis of L5 on S1 between 25% and 50% and hence, it is classified as a Grade 2 spondylolisthesis. 73860c04
Image courtesy of: Ashley Davidoff, M.D.


Compression Fractures

Compression fractures of the lumbar spine are mechanical and traumatic disorders of the vertebral body and are characterized by loss of height and shape deformity of the vertebral body.  They are most commonly caused by bone weakening with normal stresses in conditions of osteoporosis or metastatic bone disease,  but in the acute traumatic setting, excessive vertical loading forces on normal bone is the cause of the compression.

The structural result of the osteoporotic compression is a distortion of the vertebral body and change in the distribution of body forces.  Clinically, pain is the most outstanding feature.  It is caused by the bony injury itself but secondary changes in the sacroiliac joints, hips and thoracic spine may cause pain in these areas as well.

Osteoporotic Compression Fractures
The sagittally reconstructed CT scan of the lumbar spine of an 86-year-old with back pain shows three compression fractures of varying severity.  There is mild compression of L3 (teal), moderate of T11, and severe of T12 (green) as a result of osteoporosis.
Images courtesy of: Ashley Davidoff, M.D.
Lytic metastases with Secondary Compression Fractures
Extensive lytic metastatic disease (light green lesions in b) is seen in the thoracolumbar spine.  The weakening of the bone results in a pathological compression fracture of L1 (red arrow).  The compression and the metastases can both be the source of pain.
Images courtesy of: Ashley Davidoff, M.D.
Acute Traumatic Injury

Acute compression fracture of the lumbar spine is caused usually by vertical loading forces on the spine such as a fall from a height.

Comminuted Traumatic Compression Fracture of L3
The axial (a) sagittal reconstruction (b) and coronally reconstructed (c) CT scan of the lumbar spine shows a comminuted fracture of L3.  This image of the lumbar spine is from a young patient who sustained a traumatic burst compression fracture (green) of L1 with retropulsion of the posterior fragment into the thecal sac (white CSF column is obliterated) with impingement on the cauda equina and the conus medullaris.
Courtesy of: Ashley Davidoff, M.D and Philips Medical Systems
Traumatic Compression Fracture of L1
The sagittal T2-weighted image of the lumbar spine is from the patient above. 
Courtesy of: Ashley Davidoff, M.D. and Philips Medical Systems
Musculoskeletal Strain or Sprain

Musculoskeletal strain or sprain is lower back pain without any evidence of systemic, skeletal, joint, or intervertebral disc disease.

The strain is caused when a muscle-tendon unit is stretched or overloaded. A sprain is caused when there is ligamentous or facet capsule injury.  Injury is usually caused by forceful contraction, sudden torsion, direct blows, or forceful straightening.   These injuries are most commonly seen in athletically related injuries, both in professional athletes whose muscles and ligaments are primed and in the weekend athletes.

The diagnosis often is made based on the clinical history where the pain is acute and related to a specific forceful or violent strain on the back muscles or ligaments.

Physical exam findings are non-specific, ranging from extreme lower back pain in all ranges of motion to simply some tenderness to palpation of the para-spinal muscles.  The imaging studies and blood work are often normal, though MRI may show edema of the strains or sprains associated with the injured muscles and ligaments.

Treatment with non steroidal anti-inflammatory drugs (NSAIDs) is effective for symptom pain relief and muscle relaxants for spasm are recommended together with some bed rest and an ice pack.  A common side effect of muscle relaxants is sedation and thus, this class of drug is often given at bedtime to decrease lower back symptoms and aide in sleeping.  Lower back physical therapy and cardio aerobic conditioning is also generally recommended for musculoskeletal strain once the patient has passed through the acute phase of increased pain and discomfort.  There is anecdotal evidence that spinal manipulation by an osteopathic physician, chiropractor, or a masseuse may provide symptomatic relief.


Metastatic disease to bone is a malignant space occupying abnormality caused by seeding from a systemic artery, retrograde extension through a paravertebral vein, or by direct extension of tumor.   Metastases to bone most commonly occur to those bones with residual red marrow and thus, the spine is a relatively common site.  The resulting changes are variable, since the bone responds to the space occupation by osteoblastic, osteoclastic or mixed mechanisms depending on the nature of the malignancy.  The bone, however, is weakened by the process and resulting structural changes such as fractures can occur.  The periosteum is stretched and invaded and this causes pain, though not all metastatic disease is associated with pain.  Continued growth can result in extension into the spinal canal with consequent neurologic involvement.

The diagnosis is considered in patients with a known malignancy who present with new back pain, or a middle-aged or elderly patient who complains of new back pain.  More commonly than not, the pain in the latter instance is related to DJD but it is incumbent on the clinician to exclude metastatic bone disease in this group of patients.

It is reasonable to start with a plain film of the spine that may assist in directing subsequent imaging.  If an obvious metastatic lesion is identified, the diagnostic algorithm is directed to identify the primary lesion.  Depending on the clinical scenario, imaging may be directed to a bone scan, which would identify metastatic pattern of multicentric bone disease or to MRI, which is best able to confirm and characterize metastatic disease.

Treatment depends on the nature of the clinical presentation, disease, and imaging findings but ranges from symptomatic pain relief, to radiation for lesions that have extended into the spinal canal.

Normal versus Blastic Metastatic Disease
In the two sagittal reformatted CT images of the lumbar spine, the normal scan (a) is contrasted with diffuse blastic metastatic disease (b) of the lumbar spine and in fact, all visible bony structures including the sacrum and the sternum.
Courtesy of: Ashley Davidoff, M.D.


Cauda Equina Syndrome

Cauda equina syndrome (CES) is an uncommon emergency clinical syndrome characterized by low back pain, saddle sensory disturbances, usually bilateral sciatica, variable motor disturbance and bladder, bowel and sexual dysfunction.

It is caused by compression of the cauda equina by a variety of disease processes including degenerative disc disease, trauma, inflammatory diseases (ankylosing spondylitis, sarcoidosis) infections (abscesses) neoplastic disease (lymphoma or metastases) and circulatory disease (inferior vena caval thrombosis or hematoma).

The result is motor, sensory, or autonomic nerve dysfunction that tends to be bilateral, but can be unilateral involving nerve roots from L1-5 and S1-5.

The diagnosis is based dominantly on the clinical presentation and the imaging studies confirm structural abnormality but there are no specific findings that will, for example, differentiate cauda equina syndrome and disc herniation.  It is the severity and extent of the clinical presentation that defines the entity.

Treatment is directed to the cause but early decompression is generally indicated.


Osteomyelitis is an infection of bone usually caused by staphylococcus aureus.  Non pyogenic causes include tuberculosis, fungus, parasitic diseases, and yeasts.  The organisms may reach the disc or bone hematogenously with the skin and genitourinary tract often being the primary sources, but bacterial endocarditis, arthritis, and sinusitis also can be primary foci of disease.  Sometimes the infection occurs as a result of direct spread from adjacent septic foci such as an infected aortic graft.

The result includes progressive inflammatory and destructive changes in the anterior elements of the spine characteristically affecting both sides of the disc space.  Less commonly (5%) the posterior elements are affected. The disease is complicated by abscess formation in the disc space, paravertebral abscess, or epidural abscess.  Progressive destruction of the bone can lead to compression.  The latter two complications can lead to neurological compromise.

The diagnosis is based on the clinical presentation and imaging findings.  Pain is commonly insidious in onset, is progressive, until it is incapacitating without responding to conventional analgesics.  Neurological involvement is late.   Only half the patients are febrile, leukocytosis is often absent, though the Erythrocyte sedimentation rate (ESR) is almost always elevated and one of the most reliable lab findings.

The plain film of the lumbar spine is often normal in the early phases, but as bony changes ensue the findings become more apparent.

CT scan is sensitive to the bony changes and will reveal paravertebral soft tissue changes, while MRI is most sensitive to the soft tissue changes and inflammatory exudative changes in the bone and/or soft tissues.  Technetium bone scan shows inflammatory activity but is non specific.

Once the diagnosis is suspected, CT-guided aspiration and/or biopsy is needed to isolate the organism.

Treatment is with antibiotics.  Abscesses require drainage by percutaneous via surgical techniques.

This combination of images from a CT scan of the abdomen are of a middle-aged man who presented with back pain and fever, with a remote history of AAA repair. The lateral scout film shows scalloping of vertebral bodies of L2 and L3 (a) highlighted in green overlay in (b). The CT scan with soft tissue windows (c) and bone windows (d) show a complex fluid collection surrounding the aorta which proved to be a perigraft abscess. The abscess extended and eroded into the anterior portion of the vertebral body (c, d).
Courtesy of: Ashley Davidoff, M.D.


Aneurysmal Disease

Aneurysmal disease of the aorta or iliac arteries may impinge on the vertebral column and uncommonly will cause back pain.  Ruptured aneurysms, however, will result in acute severe back pain associated with hypotension resulting in an acute life-threatening emergency.

Abdominal Aortic Aneurysm
Shown is a CT scan of an 86-year-old female with back pain who was diagnosed with a 5.8cm abdominal aortic aneurysm (red).
Courtesy of: Ashley Davidoff, M.D.


Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a chronic seronegative inflammatory condition of the articular and para-articular joints of the spine that is characterized by its progressive ascending involvement of the spine, starting in the sacroiliac joints and lower lumbar spine and progressing to the cervical spine.   The inflammatory changes also characteristically involve sites where the joint capsules, ligaments and tendons are attached to the bone and bony ankylosis of the spine results.  Associated diseases include peripheral arthritis, iritis, and pulmonary disease.

The cause of the disease is mostly unknown but 95% of patients with the disease exhibit the HLA B27 marker suggesting a genetic factor.  However, all patients with HLA B27 do not develop ankylosing spondylitis and not all patients with AS have a positive HLA B27.  The disease does run in families, strengthening the genetic and familial involvement in the etiology of the disease.

The diagnosis is usually made by a combination of clinical, blood tests and imaging studies.

Clinically, the patient is usually a young male who presents with low back pain centered over the sacrum and which may radiate to the buttocks and legs.  As the upper spine becomes involved pain ascends into the thoracolumbar area.  Flexion becomes difficult.

During the acute phases, the ESR is elevated and 95% of patients exhibit the HLA B27 antigen.

Radiologically, the appearance of the spine is pathognomonic characterized by bony ankylosis. In the early stages, bilateral sacroiliitis characterized by indistinctness of the joint, with subchondral erosions on the iliac side.  The early changes in the spine are characterized by anterior corner erosions on the vertebral bodies, (Romano lesions) with subsequent bridging between the vertebra, followed by bony ankylosis.

Treatment is usually aimed at pain control and decreasing inflammation, with nonsteroidal anti-inflammatory drugs (NSAIDs) most commonly used. Steroids and immunosuppressive agents are sometimes used to reduce the inflammation.

The word ankylosing comes from the Greek word ankylos, meaning anchoring, or stiffening, while spondylos means vertebra. Spondylitis refers to inflammation of one or more vertebrae.

Ankylosing Spondylitis
In this sagittal reconstruction of a CT scan of the lumbar spine, the bony ankylosis of the anterior longitudinal ligament and supraspinous ligament is characteristic of ankylosing spondylitis.
Courtesy of: Ashley Davidoff, M.D.


Causes and Predisposing Factors

Risk factors for back pain include smoking, obesity, older age, female gender, physically strenuous work, sedentary work, anxiety, and depression.  Rarely, acute back pain is a harbinger for a serious systemic illness such as a neoplastic malignancy, aortic aneurysm, abscess formation, or rheumatologic disease.

Lastly, some possible etiologies of generalized back pain can be broadly categorized as:

  • Spinal nerve injuries
  • Vertebral fractures
  • Discogenic pain
  • Degenerative joint disease
  • Developmental defects
  • General contusions and strains
  • Neoplasm
  • Infection or abscess formation
  • Rheumatologic disease
  • Referred pain (i.e. from an aortic aneurysm, renal stones, hip pathology, etc)

The differential diagnosis for back pain can be essentially divided into mechanical versus non-mechanical etiologies.

 Mechanical low back pain:

  • Musculoskeletal strain or sprain
  • Degenerative disc or joint disease
  • Herniated nucleus pulposus, annular tears
  • Cauda equine syndrome
  • Spinal stenosis
  • Osteoporotic compression fracture
  • Spondylolysis, spondylolisthesis
  • Severe kyphosis, scoliosis, or transitional vertebrae

Non-mechanical spinal conditions:

  • Primary vertebral tumors, multiple myeloma, or metastatic cancer to the spine
  • Osteomyelitis, epidural abscess, discitis, or shingles
  • Dissecting aortic aneurysm
  • Nephrolithiasis, pyelonephritis, or perinephric abscess
  •  Ankylosing spondylitis, psoriatic spondylitis, Reiter’s syndrome, or Paget’s disease of the bone
Clinical Approach to Back Pain

The clinical approach to the diagnosis of back pain requires careful and insightful questioning.  Since back pain is a common problem, it is incumbent to start out with a history that elucidates the character of the pain and defines associated symptoms and diseases.  It is all too easy to get an MRI to help with the diagnosis, but the imaging findings, as pointed out, frequently have no correlation with the actual disease process, and so it is incumbent to progress with history, clinical examination and lab tests before proceeding to imaging techniques.

As pointed out in the introduction to the pain module series, there are elements of pain that need to be elucidated including precipitating factors, duration, onset, character, severity, situation, aggravating, relieving factors and radiation of the pain.

Precipitating Factors

There are a few factors that precipitate injury to the back including the severity of the force, frequency, and direction of the precipitating force that puts strain on the back.

Severity of precipitating force is logically an important factor, so that all severe forces in the primed and non-primed back, or in the young or old back, will play a precipitating role.  Thus, in a motor vehicle accident (MVA) or violent athletic injury any part of the complex is subject to injury including muscle, disc, ligament, capsule, or bone. It is also logical that a person who presents with back pain after this type of injury needs urgent diagnostic and therapeutic attention.  In the elderly patient or the unprimed non-athletic back, even minor injury, twist or turn, or unaccustomed back position, can be sufficient to change the balance of structures by just a few mms to cause pressure on the nerves or even disc herniation.  The spring or summer time with renewal of physical activity in the form of gardening or exercise, for example,  can result in the clinical syndrome of back pain.    The lifting of heavy objects using the back, rather than the legs, to take the force are definite precipitating factors that are associated with back injury.

The direction of the force sometimes plays an important role.  Prolonged bending over or sitting forward such as might occur in gardening or prolonged journey where the patient may sit for a long time are often precipitating factors.  Flexion of the back puts frontward force on the disc and opens the posterior aspect of the intervertebral space and predisposes to herniation, particularly in the weakened disc.  Repetitive extension of the back such as occurs in gymnastics, dance, or figure skating is the usual cause of stress fractures of the pars interarticularis of L5 causing spondylolysis and spondylolisthesis.

Duration and Onset

Pain may be hyperacute, (reaching a peak measured in seconds, minutes, to hours), acute (less than 6 weeks), and chronic (greater than 6 weeks.)  The hyperacute unrelenting pain that has no precipitating factors, that lasts for hours, heralds an urgent situation and requires immediate referral to the emergency room.  Renal colic with characteristic loin-to-groin distribution and hematuria is a less urgent example.  Confirmation of the diagnosis requires a CT scan without intravenous contrast.  The hyperacute pain of a ruptured aneurysm is the real emergency and the clue is the presence of hypotension in the elderly patient.  In this clinical setting the vascular surgeons should be on board as soon as this diagnosis is suspected clinically and an emergency CT scan without contrast would quickly establish the diagnosis.  An aortic dissection with back pain is also a hyperacute presentation, but the back pain tends to be higher and the blood pressure is usually elevated.  It is also an emergency but there usually is more time available between diagnosis and treatment as long as there is no clinical suggestion of pericardial involvement.  The other examples of relatively spontaneous hyperacute back pain include an acute herniated disc, or an acute compression fracture.

Most of the pain syndromes are more insidious and advance over days or a week.  DJD, HNP tend to build up over a few days and then last for longer; days to weeks.  Spondylolysis, spondylolisthesis, spinal stenosis, and osteomyelitis are also insidious and may last for months.

In general, back pain lasts for 3-6 weeks and more than 80% will resolve by 12 weeks.

The onset of back pain has been discussed to some extent in the paragraph above.  There are those diseases that present with severe back pain without any provocation.  Often these are concerning situations and include diseases such as renal colic, ruptured aneurysms and aortic dissection.  There are those that are precipitated acutely by minimal provocation with relatively acute onset and these usually are caused by discogenic diseases.   Lastly, there are back pain syndromes that have an insidious onset and include slowly progressive DJD, spinal stenosis and osteomyelitis, for example.

Pain Characteristics

In most instances the acute pain tends to be sharp and severe, while chronic pain tends to be dull and deep.  Renal colic tends to come in waves of severity.  The neuromuscular mechanical pains tend to be continuous and unrelenting.  The pain of a ruptured aneurysm is lancinating and severe.   The radicular pain has a correlative distribution of a nerve root.

The pain may be felt in the low back, buttocks or down the legs.  It may be unilateral or bilateral, localized or diffuse.  Once there is a radicular component, flags are raised as to neurological involvement raising the level of clinical concern.

Patient positioning often makes the pain worse and sometimes the pain is relieved by position.  So flexion in the patient with HNP may make the pain worse.  Sometimes lying down, or lying down in a specific position makes the pain worse.  The relationship to minor changes in position suggests how tenuous the involved space is where by virtue of a few mms, pain is either aggravated or relieved.

In DJD, the pain is worst in the morning and is relieved as the day wears on.   In spinal stenosis, the pain is aggravated by walking and relieved by rest.  Since this simulates claudication it is called pseudoclaudication.  Spinal stenosis is often also relieved when the patient flexes.  HNP on the other hand is often relieved by lying flat where there is relative hyperextension of the spine and hence closing of the posterior space of the intervertebral disc.

The pain is termed radicular pain when it radiates down the legs and usually implies nerve root involvement.  This can occur in any of the diseases described and in all cases raises the clinical concern.

The presence of other sensory or motor disturbance such as paresthesias, tingling, muscle weakness, urinary or fecal incontinence, have similar implications of nerve root involvement and create concern for cauda equina syndrome.  Symptoms or signs that suggest a systemic illness such as malaise, weight loss, or fevers are also concerning, and raise concern for malignancy, or osteomyelitis.

In patients over the age of 65, malignancy, compression fractures, spinal stenosis, and aortic aneurysms become more prevalent.  Disease specific imaging studies should be ordered without delay.

Lumbar spinal stenosis may present with classic pseudoclaudication symptoms of leg pain during ambulation that improves with rest.  Other symptoms of pseudoclaudication include numbness in the lower extremities with walking and radicular pain to the feet.

Physical Examination

First, a general inspection of the back must be performed with the examiner being cognizant for any evidence of scoliosis, abnormal kyphosis of the thoracic spine, or increased lordosis of the lumbar spine.

Palpate the entire spine to isolate any areas of point tenderness.  Then test the lumbar spine range of motion in flexion, extension, sidebending, and rotation to see if any of these movements elicits any discomfort or pain.  Unilateral spondylolysis can be isolated by having the patient stand on one leg with extension of the lumbar spine.  A positive test is where there is pain ipsilateral to the weight-bearing leg.

In addition, a straight leg test can be used to help confirm any radicular symptoms.  This test is performed with the patient lying supine as the examiner raises one leg as far as possible with the knee in extension and the ankle in dorsiflexion.  If there are any radicular symptoms down the leg, then the test is considered positive.  Furthermore, the examiner needs to check the flexibility of the hip flexor muscles to isolate any hip flexion contractures that may be causing hyperlordosis.  Hip joint range of motion should also be examined to determine if the patient’s back symptoms are actually referred pain from any hip pathology.

Finally, a thorough neurological exam should be performed focusing on the L5 and S1 nerve roots, since 98% of clinically relevant disc herniations occur at L4-5 and L5-S1.  The L5 nerve root innervates the muscles that dorsiflex the great toe and foot.  Thus, it can be tested by having the patient walk on his heels.  Similarly, the S1 nerve root innervates the muscles that plantar flex the great toe and foot.  Hence, walking on the toes will test for this.  There’s also a diminished ankle jerk associated with a S1 nerve compression.  The L4 nerve root innervates the quadriceps and can be tested by having the patient do a squat and rise.  Patella reflex tend to be diminished with L4 nerve impingement.  Lastly, if there is a clinical suspicion for cauda equina syndrome, which is a surgical emergency, a rectal exam to check for rectal tone and post void residuals should be obtained.


Typically, if a mechanical cause of low back pain is suspected, then no blood work needs to be collected.  However, if there is multiple joint involvement and other systemic symptoms, then a rheumatological and infectious cause should be in the differential diagnosis.  An initial rheumatological and infectious work-up includes an erythrocyte sedimentation rate (ESR) and a complete blood count (CBC).  If there is a clinical suspicion for ankylosing spondylitis, then a HLA B27 should also be added.


Up to 90% of patients with back pain in the absence of sciatica or systemic symptoms improve over time and without intervention.

Given the favorable prognosis, imaging studies are infrequently required.  Imaging is not necessary during the first 4 to 6 weeks, unless the patient fits any of the following criteria:

  • Recent trauma
  • Focal progressive neurological deficit
  • Unexplained weight loss, fever, or a history of cancer
  • History of intravenous drug use
  • Age less than 18 or greater than 50 years old
  • Osteoporosis or a history of prolonged corticosteroid use

If there are persistent symptoms for greater than 6 weeks without any neurological deficits, then an initial AP and lateral plain radiograph should be obtained targeting the area of discomfort.

Early use of magnetic resonance imaging (MRI) and computerized tomography (CT) scans that do not fit the above criteria is strongly discouraged.  The medical literature has clearly shown that disk herniations, spinal stenosis, or facet arthropathy can occur in asymptomatic patients.  Hence, when the patient presents clinically with lower back pain, there is a good chance that the spine pathology seen on MRI or CT have already been there for some time prior to the patient developing symptoms.

In general, MRI is the modality of choice when evaluating any disc, nerve, and ligamentous injury.  CT scans are generally better for analyzing any bony pathology.  Moreover, MRI and CT scans are more sensitive than plain x-rays at detecting early spinal malignancy and infection.  Therefore, MRI and CT scans should be reserved for patients in whom there is a strong clinical suspicion of underlying infection, malignancy, or persistent neurological deficits.

Additionally, nuclear medicine (SPECT) bone scans can be used to isolate the area where a suspected stress fracture, malignancy, infection, or inflammatory arthritis may occur.


Once non-mechanical spinal conditions have been ruled out by a thorough history, physical examination, and diagnostic imaging, then the clinician can safely proceed to treat mechanical low back pain.  Non-operative treatment of general musculoskeletal strain, degenerative disc/joint disease, herniated discs, and spinal stenosis without neurological deficits are essentially equivalent.  Up to 90% of patients with back pain in the absence of sciatica or systemic symptoms improve over time and without intervention.

Initial treatment involves non-steroidal anti-inflammatory drugs (NSAIDs) for acute symptomatic relief and activity modification with gradual progression to physical therapy for abdominal and erector spinae muscle strengthening.  Bed rest does not increase the speed of recovery from acute low back pain and may sometimes delay recovery.

For a herniated nucleus pulposus with radicular symptoms, a quick 6-7 day tapering course of an oral corticosteroid may be used to temper severe lower back pain.  Narcotic medication may also be occasionally needed for acute severe pain but should be used for only a short period of time.  Moreover, epidural corticosteroid injections offer symptomatic relief for selected patients.  Incidentally, a corticosteroid epidural injection can also be used for persistent back pain with spinal stenosis.  Moreover, persistent back pain associated with degenerative joint disease in the spine may also benefit from a corticosteroid facet joint injection.

Diskectomy is the surgical option for a persistently symptomatic herniated nucleus pulposus that does not respond to non-operative management.  Diskectomy produced better pain relief than non-operative management over a period of four years, but it is unclear whether there is any advantage after 10 years.  Surgery should only be considered if pain symptoms do not improve after six weeks of treatment as the natural history of herniated disks is often favorable.  For spinal stenosis associated with persistent severe pain, a decompressive laminectomy may be necessary.

Interestingly, some patients with chronic low back pain have no radiculopathy or anatomical abnormalities that clearly explain their symptoms.  The current medical literature supports aerobic conditioning to reduce pain and improve function in these patients with chronic low back pain.

If the patient has been diagnosed with spondylolysis, treatment involves initial restriction of activities as well as a Boston overlapping bracing which is a hard plastic shell custom molded brace.  Patients will also be started on physical therapy emphasizing core strengthening.

Lastly, non-operative treatment of lumbar compression fractures includes pain management, bracing with a thoracic-lumbar-sacral orthosis, and physical therapy.  Surgical treatment is needed if there is neurological compromise associated with the compression fracture.

Red Flags

Factors that raise concern include:

  • Age less than 18 or greater than 50:  In the younger patient, athletically related injury such as spondylolisthesis is considered, whereas in the older patient metastases and osteomyelitis are considered.
  • Unexplained weight loss or fever:  When patients have systemic symptoms, they are often accompanied with systemic diseases.  With weight loss, a primary malignancy with metastases to the spine is a consideration, while the patient with fever, osteomyelitis must be considered.  In this same category are those patients with a history of IV drug abuse or alcohol abuse.
  • Steroid use:  In those patients on steroids, both infections and compression fracture must be considered.
  • Unremitting pain:  Osteomyelitis and metastases are a cause of unremitting pain.  If the patient presents with saddle distribution of pain with incontinence, then cauda equina syndrome is considered and an urgent MRI should be performed along with a surgical consultation.  Cauda equina syndrome is a surgical emergency and it is caused by acute mechanical compression of nerves supplying the lower extremities, bowel, and bladder.  If the patient has symptoms of urine or stool incontinence, decreased sensation in the perineum and anus, then cauda equine syndrome must be considered.

Low back pain is a very common symptom and is the second most common reason for a physician visit in the United States.  In fact, it has been estimated that up to 84% of adults have lower back pain at some point in their lives.  For most patients, symptoms are self-limited and resolve without any specific radiographic imaging or treatment.  Imaging is not necessary during the first 4-6 weeks, unless the patient fits any of the following criteria:

  • Recent trauma
  • Focal progressive neurological deficit
  • Unexplained weight loss, fever, or a history of cancer
  • History of intravenous drug use
  • Osteoporosis or a history of prolonged corticosteroid use
  • Age less than 18 or greater than 50 years old
  • Emergencies related to lower back pain are rare, but if symptoms of urine/stool incontinence or decreased sensation in the perineum/anus manifest, then an immediate referral to the emergency department is necessary. 

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Cassidy JD, Carroll LJ, Cote P. The Saskatchewan health and back pain survey. The prevalence of low back pain and related disability in Saskatchewan adults. Spine. 1998; 23:1860.

d’Hemecourt PA, Gerbino PG, Micheli LJ. Back injuries in the young athlete. Clin Sports Med. 2000; 19(4):663.

Katz JN. Lumbar disc disorders and low-back pain: socioeconomic factors and consequences. J Bone Joint Surg Am. 2006; 88 suppl 2:21

American Academy of Orthopedic Surgeons. Press Release. 2006

Deyo RA, Loeser JD, Bigos SJ. Herniated lumbar intervertebral disk. Ann Intern Med. 1990; 112:598.

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Jarvik JG, Deyo RA. Diagnostic evaluation of low back pain with emphasis on imaging. Ann Intern Med. 2002; 137:5

Web References

Ankylosing Spondylitis eMedicine Peh CG Wilfred MD MBBS FRCP FRCR MHSM

Back Pain – Mechanical e Medicine Perina Debra MD

Back Pain eMedicine Pathophysiology of Chronic Back Pain   Wheeler Anthony H MD

Back Pain Lumbar Vertebral Compression  Mark King

Back Pain Imaging Medscape Finch Philip Technology Insight

Cauda Equina Syndrome eMedicine Beeson Michal S MD MBA FACP

Compression Fractures (Lumbar) eMedicine Sherman Andrew L

Facet Joint Disease eMedicine Lumbosacral facet syndrome Gerard Malanga MD

Herniated Nucleus Pulposus eMedicine  Foster Mark MD

Intervertebral Disc degeneration Medscape

Osteomyelitis EMedicine  Spinal Infections Vinas Federico C MD

Spinal Stenosis eMedicine Hsiang John NK MD PhD

Spinal Stenosis Alexander JT

Spondylolisthesis eMedicine Irani Zubin MD MBBS

Sprain and Strain eMedicine  Lumbosacral Spine Sprain Strain Injuries Radebold Andrea MD  Kinesiology