The
Epidemiology of Neck Pain
Donald
R. Gore, MD, Medical College of Wisconsin, Milwaukee, Wis. Abstract Neck pain is
a common problem in our society and, at any given time, affects about 10% of the
general population. The sources of pain are caused by conditions that compress,
destroy, or irritate pain-sensitive structures such as the annulus fibrosus,
posterior longitudinal ligament, and the capsule of the zygapophyseal joints.
Involvement of the cervical nerve roots usually results in pain and neurologic
findings in the distribution of the nerve. Referred pain from visceral disease
may cause neck pain and may also be confused with primary shoulder disease and
peripheral nerve entrapments. Common conditions thought to cause neck pain are
degenerative disc disease, with or without disc herniation, and degenerative
arthritis of the zygapophyseal joints. Aside from patients with disc herniations
demonstrated on imaging studies and pain in a specific nerve root distribution,
the relationship with degenerative changes is not always clear. This is because
degenerative conditions are common with aging and many times are incidental
findings in asymptomatic people. Specific conditions that have been studied but
also are not well understood are post-traumatic neck pain syndrome, commonly
known as whiplash injuries, and pain following repetitive activities in an
occupational setting. Although causes of neck pain are not well understood,
outcome studies have shown that it frequently is not a self-limiting condition
and can be a long-term problem. [© 1998 Medscape, Inc.]
Introduction
Epidemiology is the branch of medical science that studies the causes,
incidence, prevalence, and control of a disease in a defined population.
Although there are numerous epidemiologic studies of low-back pain, relatively
few investigations of neck pain have been conducted. There are several reasons
for this, the most important being that neck pain is not as common as low-back
pain and, when present, is not as disabling; therefore, it doesn't have the same
economic impact on society as does low-back pain. Neck pain is a symptom of a
disease process. Knowing the etiology of neck pain aids in understanding its
epidemiology.
Sources
of Neck Pain
The
human neck is a complex structure that contains the extension of a number of
vital visceral structures, including the trachea, esophagus, and the carotid and
vertebral arteries, and a musculoskeletal system that provides for support and
motion of the head. The cervical spine itself is a series of seven separate bone
elements, all with intricate articulations and an elaborate system of ligaments
and associated muscles. The first and second cervical vertebrae are different in
size and shape from each other and the remaining five vertebrae. However, all of
the segments have true synovial joints. The anterior articulations of the
vertebrae below C2 occur via intervertebral discs. Both the anterior and
posterior joints are surrounded by a fibrous capsule and supported by ligaments
and muscles. These joints both allow and limit neck motion. The capsule,
ligament, and muscles all contain an abundance of free nerve endings which are
capable of transmitting pain impulses. Irritation or damage to these structures
causes primary neck pain.
The
cervical vertebrae also protect and allow passage of the spinal cord and
cervical nerve roots. Pathologic processes such as compression, especially of
the nerve roots, are a frequent source of neck pain and referred pain from the
neck. Cervical nerves are both sensory and motor so that damage, in addition to
pain, may cause numbness, tingling, muscle weakness, and reflex deficits in a
specific location. Signs and symptoms along the distribution of a cervical nerve
root are called cervical radiculopathy.
The
cervical nerve roots C5, C6, and C7 are the most commonly involved and result in
characteristic signs and symptoms in the upper extremities. Because the
distal-most innervation of C4 is to the top of the shoulder, compression of the
C4 nerve root does not produce symptoms below the level of the shoulder, and
usually there is no demonstrable muscle weakness or any reflex abnormalities.
Damage or irritation of C1, C2, and C3 does not result in reflex or motor
deficits but can result in pain in the back of the neck extending along the back
of the head. Pain from neck sources other than cervical nerve roots does not
result in sensory, motor, or reflex deficits and the pain patterns are not as
well defined. Pain reproduction studies have investigated patients with neck
pain but without evidence of specific nerve root involvement. Discography and
zygapophyseal joint injections[1] were used, indicating that there are a variety
of etiologies for neck pain. Other possible sources of neck pain, whose
importance has not been established, are the cervical sympathetic nerves and the
innervation present in the anterior surface of the dura.
Causes
of Neck Pain
Pain
originating in and confined to the neck may arise from infections, tumors, and
degenerative changes of the zygapophyseal joints and intervertebral discs.
Cervical radicular pain is pain in the distribution of a cervical nerve root.
This can be caused by any process that compresses or irritates the nerve, the
most common being herniated intervertebral discs (Figure 1a,b) and osteophytes
which narrow the neuroforamen (Figure 2a,b,c). Disc protrusion and osteophytes
can also narrow the spinal canal, causing pressure on the cervical cord and
resulting in a myelopathy (Figure 3).
Referred
neck pain is generated by disease in an anatomic structure other than the neck.
Examples of this are visceral diseases such as angina, apical lung tumors, and
subdiaphragmatic irritation as in a subdiaphragmatic abscess. The most common
conditions that may be confused with neck problems are intrinsic shoulder
diseases such as impingement, rotator cuff tears, and adhesive capsulitis.
Peripheral nerve entrapment occurring in thoracic outlet syndrome, ulnar cubital
tunnel syndrome, and carpal tunnel syndrome can simulate cervical nerve root
compression. Systemic diseases such as rheumatoid arthritis,
spondyloarthropathies, fibromyalgia, and herpes zoster may also cause neck pain.
However, in these conditions it is unusual for the only symptom to be in the
neck.
Incidence
and Prevalence of Neck Pain
Neck
pain has most frequently been studied in five different populations
Incidence
is the number of new cases of a disease which occur during a specified period of
time, whereas prevalence is the number of cases present at any one time. Most
reports in the medical literature are crude prevalence studies. Since neck pain
has many causes, and a number of factors such as age, sex, occupation, and
cigarette smoking effect its occurrence,[2] it is difficult to compare the
results obtained from research done on differing study populations. In addition,
most reports are based on questionnaires, so the cause of the pain cannot be
validated; also, neck, shoulder, and upper-extremity pain are frequently
considered together.
General
Population Even with the limitations mentioned above, some information -- mostly
from Scandinavian countries -- is available. Neck pain occurs half as often as
low-back pain[3] and is slightly more common in women. In Norway, Bovim and
colleagues,[4] in a random sample of 10,000 persons ages 18-67 years, found a
prevalence of 13.8%. In a similar study in Finland, Makela and associates[2]
discovered neck pain in 9.5% of males and 13.5% of females. The United States'
National Center for Health Statistics reported 7.0% of men and 9.4% of women had
neck pain in the period between 1976-1980.[3] In addition to neck pain being
more common in women, Makela[2] also found that older patients, those involved
in both mentally and physically stressful jobs, and current smokers were more
likely to have neck pain.
Auto
Accident
Post-Traumatic
Pain
The
most common post-traumatic neck pain syndrome is a whiplash injury and follows
an automobile accident. The term was first used by Crowe[5] in 1928 in an
unpublished report, then in an article by Davis[6] in 1945, and later by Gay and
Abbott[7] in 1953. The original descriptions were of a mechanism of injury
rather than a disease process. Although many now object to its use, the term
"whiplash" is routinely used by laymen, lawyers, and medical
professionals in reference to a patient with neck pain after an automobile
accident in which a more specific diagnosis cannot be made.
The
most frequent scenario is a patient whose vehicle is struck from behind causing
a hyperextension motion of the neck. The combination of seat belts and properly
adjusted head restraints reduces the likelihood of neck injuries.[8]
Recently
Grauer and colleagues[9] have shown with cadaver studies that in a simulated
whiplash injury the neck forms an S-shaped curve with initial hyperextension of
the lower cervical spine and upper-level flexion, followed by extension of the
entire cervical spine. It would be expected that if physiologic limits of motion
are exceeded, than injury would occur. This physiologic limit of motion was
reached in the lower cervical spine in their studies.
Hyperextension
injuries of the neck can damage a number of structures, including the anterior
muscles and ligaments, the disc, and zygapophyseal joints. These injuries have
been demonstrated on cadavers and experimental animals and found in human
autopsy studies of victims of motor vehicle accidents.[10]
Recently
Jonsson and coworkers[11] reported on 50 consecutive patients with whiplash-type
cervical spine distortions in automobile accidents. At 6 weeks, 24 had
persistent neck pain and underwent MRI imaging. Of these, 8 were found to have
large cervical disc protrusions and had surgery. Two patients had posterior
fusions for instability based on lateral flexion and extension films. This
report is in contrast to our own experience and that of others' where, despite
careful evaluation of whiplash patients, conclusive objective pathology is
rarely found.
Borchgrevink
and associates[12] studied 201 patients with neck pain following automobile
accidents. The patients were randomly divided into two treatment groups. In one
group, immobilization by means of a cervical collar and sick leave from work was
provided. In the other, no immobilization was used, no sick leave was given, and
the patients were instructed to act as usual. At 6 months, the
"act-as-usual" group showed more overall progress, as measured by
subjective symptoms ratings. The researchers found, however, that 10% of this
group still had severe symptoms at 6 months, which emphasizes that neck pain
following an automobile accident in many patients is not a self-limited
condition.
The
symptom complex most frequently seen is neck pain that may not be present
immediately after the accident but begins in most patients within 24 hours.[13]
Other frequent complaints are headache, dizziness, paresthesia, and cognitive
somatic and psychological sequelae.
This
unrelated constellation of symptoms without objective evidence of structural
injury has led to speculation that the condition is an emotional rather than a
physical problem. Since the neck pain patient's vehicle has been struck from
behind, causation and therefore liability usually rest with the other driver.
Our current tort system favors documentation which encourages frequent physician
visits, exaggeration of complaints, expensive testing, and extensive symptomatic
treatment, most of which have no proven value in altering the natural history of
the patient's symptoms.
Occupational
Neck Pain
Occupational
neck pain can be divided into two categories -- those patients who have had
specific injuries and those in whom the onset of neck pain seems to be related
to normal work activity.
Specific
injuries that may occur in the workplace include motor vehicle accidents,
falling from a height, and being struck on the head. In these instances,
causation is not hard to determine; neck pain that begins during normal work
activities, however, is more difficult to assess.
Employees
in occupations which require repetitive use of the upper extremities such as
machine operators, carpenters, and office workers are more likely to have neck
complaints.[14] If work activity is truly the cause the of the patient's
complaints then a strong relationship with the activity and the onset and
persistence of the symptoms should be evident. For instance, it must be
established that the symptoms began after performing the activity and the
complaints improve or completely subside if that activity is eliminated. Usually
the distinction between work causation and other factors is not clear because
preexisting disease and activities that are not involved with work cloud the
picture. In addition, there is no conclusive evidence in the medical literature
that overuse results in structural damage. There is, however, a segment of the
population with permanent symptoms after a period of overactivity at a specific
task. In these situations, evaluation and treatment proceeds as with any other
group of patients but causation usually cannot be established.
Herniated
Intervertebral Cervical Discs
In
contrast to studies of patients with neck pain as a syndrome, a herniated
cervical disc is a specific diagnosis. The only published study that provides an
incidence rate was done by Kondo and colleagues.[15] They analyzed residents of
Rochester, Minn, from 1950 to 1974 and found an annual herniated disc incidence
of 5.5/100,000 people. The most frequent level involved was C5-6, followed by
C4-5 and C6-7. In reviews of surgically-treated patients, these are also the
most frequent levels involved.
Kelsey
and associates[16] reported on 88 people with cervical disc protrusions living
in New Haven and Hartford, Conn. Forty were surgically treated after the
diagnosis of herniated cervical disc was made. Based on their clinical
appearance, 20 were listed as probable and 28 as possible disc protrusions.
Fifty-two patients were men and 36 were women, and most patients were in their
40s and 50s. The researchers compared cervical disc protrusion patients with
age- and sex-matched controls. A strong association was found between protrusion
and recurrent lifting of heavy objects on the job, cigarette smoking, and
frequent diving from a board. Driving vibrating equipment and time spent in
motor vehicles were weakly associated. Frequent twisting of the neck on the job
and sitting on the job were not associated with the clinical diagnosis of
herniated disc.
The
association of lifting heavy objects and driving vibrating equipment with
prolapsed disc is not surprising, but the relationship with smoking is not as
easily explained. Cigarette smoking has been implicated in impeding bone
metabolism and in interfering with fracture repair, in nonunions in fractures,
in arthrodesing procedures, and in increasing the rate of postoperative wound
infections.[17] A number of studies have identified smoking as a risk factor for
low-back pain, and although several explanations have been proposed, the
mechanism has not been elucidated.
Degenerative
Changes
Degenerative
changes of the intervertebral discs cause disc-space narrowing, osteophyte
formation, and sclerosis of the vertebral body end plates (Figure 4). These
changes are easily seen on lateral roentgenograms but are the response of the
vertebrae to disc degeneration and so appear after the process is well
developed. Therefore, any study based on plain roentgenograms underestimates the
prevalence of disc degeneration. Degenerative changes in the zygapophyseal
joints include joint-space narrowing, sclerosis, and osteophyte formation; but
the changes are not as easily seen or quantified on plain roentgenograms (Figure
5). The joints are paired and located behind the vertebral bodies, so they can
only be isolated by oblique views; and even then, one oblique view usually does
not show all the joints. For these reasons, little information is available on
the frequency of degenerative changes in these joints.
Plain
lateral roentgenogram showing end-plate sclerosis, narrowing of the
intervertebral disc space, and anterior osteophyte formation.
5.
(click image to zoom) Plain lateral roentgenogram showing sclerosis, narrowing,
and osteophyte formation in the C3-4 zygapophyseal joint.
Degenerative
changes of the cervical spine, as seen on plain roentgenograms and more
sophisticated imaging studies, are common in both symptomatic and asymptomatic
people and are thought to be part of the normal aging process (Figure 6).
Degenerative findings are considered to be pathologic when they produce
symptoms. However, with the exception of patients with radicular pain,
localizing neurologic deficits, and nerve root compression as seen on MRI or CT
myelogram studies, the relationship with the patient's neck pain is unclear.
Figure
6. (click image to zoom) A. Normal, plain lateral roentgenogram of 44-year-old,
asymptomatic female. B. Plain lateral roentgenogram of 54-year-old female,
indicating degenerative changes of zygapophyseal joints most severe at C4-5 and
intervertebral disc degenerative changes at C6-7.
One
of the most perplexing clinical challenges is to distinguish the source of a
patient's pain when degenerative changes are present. In a review of 200
asymptomatic women, we found that by age 60 to 65, 95% and 70% of women had
degenerative changes as seen on plain roentgenograms.[18] Boden found MRI
abnormalities of the cervical spine in 19% of 63 asymptomatic volunteers.
Fourteen percent occurred in subjects under the age of 40, and 28% in those over
40.[19] Zapletal and colleagues[20] evaluated the atlanto-odontoid joint in 500
consecutive patients who underwent computed tomography of the brain or paranasal
sinuses. They found no abnormalities before the fourth decade but thereafter the
prevalence increased steadily with age, so that by the ninth decade over 60% had
degenerative changes. In a separate article, Zapletal and associates[21]
evaluated 355 occipital frontal radiographs of the paranasal sinuses for
evidence of osteoarthritis of the lateral C1-C2 joints. Degenerative changes
were found ranging from 5.4% in the sixth decade to 18.2% in the ninth. They
emphasize that these degenerative changes could be a source of upper neck pain
and occipital headaches (Figure 7).
Plain
open-mouth roentgenogram showing unilateral degenerative changes at C1-2.
Outcome
In
1982, Rothman[22] stated, "It does not appear that cervical disc
degeneration is a brief self-limited disorder but rather a chronic disease
productive of significant pain and incapacity over an extended period of
time."
As
discussed in the previous sections, degenerative disease of the cervical spine
and neck pain are not synonymous. Degenerative changes are often present in
asymptomatic people, and in some people with neck pain no structural abnormality
can be demonstrated. However, in our experience, Rothman's statement holds true
for patients with neck pain with or without degenerative changes.
In
1987, we reported on a review of 205 patients initially seen for neck pain in an
office setting.[23] Patients with previous neck surgery, objective neurologic
deficits, malignancies, or rheumatoid arthritis were excluded. The patients were
re-examined and interviewed an average of 15 years (10 to 25 years) after the
onset of their neck problems. In all patients, lateral roentgenograms were
available for comparison between the initial visit and the final evaluation.
At
follow-up, 79% had a decrease in pain, and of these, 43% were pain-free; however
32% had moderate or severe residual pain. Patients who had been injured and
initially had severe pain were most likely to have an unsatisfactory outcome;
however, no other clinical features were of value in predicting the final
result. Initially, 121 patients had injuries, of which 76 were due to motor
vehicle accidents. Sixty-eight were involved in litigation, 58 in personal
injury claims, and 10 in workman's compensation claims. At final evaluation, all
but 4 claims had been settled, and all of these patients stated their initial
pain had decreased in severity. Interestingly, 23 patients were dissatisfied
with the outcome of their litigation. However, there was no statistical
relationship between their level of satisfaction and the amount of pain or pain
relief reported at final interview.
The
roentgenographic features measured were degenerative changes at each
intervertebral disc space, sagittal diameters of the spinal canal at each disc
space, and cervical lordosis. None of the roentgenographic findings present
initially or developed in the follow-up period correlated with pain or had any
predictive value for pain relief.
Most
important, this study emphasizes that neck pain is frequently not a self-limited
problem, and that many patients will have long-term symptoms that may be
moderately disabling.
Summary
Neck pain is a common problem in our society and at any given time affects about
10% of the general population. The actual cause of the problem is frequently
difficult to determine. Neck pain in as many as one-third of patients is not
self-limiting and may produce moderate long-term disabilities.
DISCUSSION:
It
is important to note that extensive research has been performed on low impact
accidents, and how injuries result to occupants from these accidents. One such
research project was performed by The National Highway Traffic Safety
Administration, published by E. Horton, "Why Don't We Buckle Up,"
Science Digest, Feb. 1985, in which they state, "a ten-mile an hour
collision is equivalent to catching a two-hundred pound bag of cement dropped
from a second story window. People don't understand the dynamics of
crashes!" Extrapolate this evidence to a non low impact collision and the
potential effects become even more dramatic.
Another
research study done by The Engineering Society For Advancing Mobility Land Sea
Air and Space, at the University of Texas Health Science Center, page 28,
concluded that in rear-end accidents of 2.5 mph, "Despite having
experienced no neck excursions beyond their voluntary range limits, three of our
four subjects transiently had very mild, but clinical neck discomfort
symptoms." This occurred in healthy individuals that were prepared for a
read-end collision of 2.5 mph! The research was completed in 1993 and published
in the SAE Technical Paper Series in March 1-5, 1993 issue.
Historically,
insurance company claims adjusters have assumed that collision injuries
correlate to the vehicle external structural damage and the cost of repair of
the vehicle. The assumption that injuries relate to the amount of external
vehicle damage is in all types of crashes has no scientific basis. (Nordhoff and
Emori 1996).
The
absence or presence of vehicle damage is not a reliable indicator of injury
potential in rear end impacts. Based upon the principle of conservation of
energy, any energy, which does not go into damaging the vehicle, must be
converted into kinetic energy, which is the source of patient/occupant injury
(Smith)
Because
of the very large mass of motor vehicles, even the smallest speed collisions
generate significant kinetic energy. The kinetic energy is transferred into the
struck vehicle. (Kinetic Energy of the striking vehicle is equal to the Kinetic
Energy after impact plus the vehicle damage- Newton's 3-rd law of mechanics) The
physical facts dictate that the magnitude of passenger injury can not be totally
correlated with vehicle damage. In fact, the smaller the vehicle damage the
greater the kinetic energy available to cause and injury! This effect is
especially relevant in low speed, rear impact collisions (Navin and Romilly,
Smith, Nordhoff and Emori).
The
development of safety or "no damage" bumpers has been the standard for
the last few decades. They are designed specifically to minimize vehicle damage
in low impact collisions, and there is clear evidence that insurance property
losses have decreased dramatically as a result (Smith). Unfortunately, when
vehicle damage energy is reduced, the energy is transferred into kinetic energy
that causes patient injury. Current bumper standards have the effect of reducing
property damage while subjecting the occupants to a more violent ride and
increasing the probability occupant injury. (Navin, Smith). Published experts (Navin
and Rommily) in motor vehicle accidents have completed experiments and made
observations that degree of patient/passenger injury is not related to the size,
speed, or magnitude of damage of the involved vehicles.
The
cervical spine is especially vulnerable to trauma because of the physical
dynamics involved in the actual force, as well as the inherent weakness of the
cervical spine or manner in which the injury occurred. Even a slight impact can
produce a large number of pounds of force on the head and neck. For example, a
3500 lb. automobile traveling a mere 10 miles per hour would strike an immovable
car with some 25 tons of force. This force on the patients cervical spine is
magnified because the base of the neck acts as a fulcrum and the actual neck
itself is a lever which propels the head and neck backwards, forwards and side
to side.
The
cervical spine is the weakest area of the spine and also the most mobile. The
bones of the neck are the smallest in the spine, and comprised of over 30 small
joints. Each joint about the size of an adult human's smallest finger. Because
of the small size and greater mobility, there is greater potential for injury.
Adding to the neck's weakness is the fact that the cervical spine is perched on
top of a relatively immobile thoracic spine. This situation makes the base of
the neck a fulcrum. Much like a bamboo stick, stuck in the ground. If the stick
is forced backward, forward, left or right, it will break where it is inserted
in the ground. The cervical spine also contains the smallest shock-absorbing
disk in the spine, especially between the second and third vertebrae. The
cervical spine serves as a support and foundation to the head, which weights
from 8-12 lbs. The head is therefore supported on an unstable platform, much
like a house being built on quicksand.
In
summary:
Motor
vehicle collision patient/passenger injury and clinical prognosis for recovery,
is not related to the damage of their vehicle. Rather, injury and prognosis are
coupled with direction of impact (rear end, awareness, and head/neck rotation or
inclination).