Clinical Practice Guideline
for
HERNIATED NUCLEUS PULPOSUS
Developed for the
Aerospace Medical Association
by their constituent
organization
American Society of Aerospace Medicine Specialists
Overview: The intervertebral
disc is comprised of three parts. The
nucleus pulposis (NP) is a mucoprotein
gel located in the posterocentral portion of the
disc. Surrounding the NP is the annulus
fibrosis (AF), concentric laminated bands of fibrous tissue. And finally, cartilaginous end-plates
separate the disc from the vertebral body.
HNP occurs when the NP herniates through the
AF, usually in a posterior or posterolateral
fashion. This can only occur when the AF
is disrupted either by violent trauma or recurrent microtrauma. A history of trauma has been elicited in over
50% of those with lumbar HNP.
Approximately
80% of HNPs occur in the lumbar region. The age-incidence curve for lumbar HNP peaks
in the second through fourth decades of life and the incidence is higher in
males than females. Other pathologic
lesions (i.e. spondylosis and spinal stenosis) have
been noted in 50% of the cases with lumbar HNP.
Approximately 20% of HNPs occur in the
cervical region and 20-33% of these have concurrent lumbar disc
involvement. The age-incidence curve for
cervical HNP peaks in the fifth through sixth decades of life and the incidence
is higher in males than females. Less
than 1% of the HNPs occur in the thoracic
region. The age-incidence curve for
thoracic HNP peaks in the fifth through sixth decades of life and the incidence
is equal for both sexes.
Symptoms
from HNP vary from asymptomatic to paraplegia.
Herniated disc matter may compress nerve roots, vascular structures, and
even the spinal cord (above L-2).
Symptoms such as pain, numbness, paresthesias,
weakness and muscle wasting are usually the presenting findings. However, progression of disease may lead to quadriparesis, paraplegia, and emergent conditions such as cauda equina syndrome and conus syndrome.
Aeromedical Concerns: Inability to
perform flying duties may be a result of baseline symptoms (pain,
weakness). Sudden incapacitation and
permanent disability are significant concerns, particularly in a high-G
environment or during ejection. And
finally, the forces applied to the intervertebral
disc under high-G stress may lead to accelerated progression of disease. Following surgical treatment of HNP, concerns
are raised regarding vertebral joint stability and subsequent catastrophic
failure of the vertebral column, depending on the type and nature of the
procedure. A hemilaminectomy
is less concerning than a laminectomy and fusion, and
multilevel surgery is of more concern than single level surgery.
Recurrences
and frequent removal from aviation duties may have adverse effects on aviation
missions, particularly in the military.
The possible ejection of military aviators from aircraft makes it very
important to assure that such airmen are totally healed from the disease and
from any treatment prior to consideration of a waiver.
Medical Work-up: Diagnosis of HNP is based on
characteristic symptomatology, confirmed by radiologic studies.
The predominant studies used to document HNP are myelography,
CT and MR imaging. HNP is confirmed by
the demonstration of herniation of disc material
(size and direction) and distortion/displacement of the thecal
sac, epidural fat, and/or nerve root.
However, repeated studies have failed to delineate a direct relationship
between the degree of herniation and the amount of
symptoms. In fact, 35% of individual
over the age of 40 years have been noted to have various anomalies of intervertebral discs while remaining asymptomatic.
Standard
treatment for HNP consists of conservative therapy, surgery, and chemonucleolysis.
Conservative therapy (i.e., bedrest, pain
medication, and physical therapy) has resulted in symptomatic improvement in
30-95% of HNPs.
Several studies have documented regression and even complete resolution
in up to 50% of HNPs within 6 months. Surgical resection of HNP is effective in 90%
of carefully selected HNPs but up to 30% of those who
undergo surgery have unsatisfactory results (extradural
fibrosis/scarring, recurrent HNP, and spinal stenosis secondary to bone
overgrowth). Surgery should be limited
to: 1) severe intractable pain not responding to conservative therapy, 2)
significant neurologic deficit (most notably weakness) that is at risk for
becoming permanent, and 3) frequently recurring episodes of radiculopathy
that causes significant functional impairment.
In addition, operative complications such as nerve root or cord injury
and postoperative joint instability may occur.
Chymopapain injected into the HNP results in
enzymatic hydrolysis of the chondromucoprotein
portion of the HNP. Although this
procedure has been in use for twenty years, long-term effects from chemonucleolysis are unknown; this treatment modality has
fallen into disfavor in the past few years.
Several studies have documented a 20-30% failure rate with this
procedure and complication rates similar to surgery.
Aeromedical Disposition (military): Waiver can be considered following the
successful treatment of HNP. As noted
above, the treatment may be conservative and/or surgical. Initial evaluation should include history and
physical examination to ensure that the examinee is asymptomatic and able to
perform duties without limitations. If
history or physical elicits findings, further studies (such as nerve conduction
study and electromyelogram) may be needed for further
evaluation. Also, a consultation from an
orthopedic surgeon should clear the examinee for flying duties and delineate
prognosis. Finally, imaging studies (CT
or MRI) should document structural resolution of the HNP. The type of aircraft flown is very important
in an aeromedical disposition for HNP patients.
Aeromedical Disposition
(civilian):
In the civilian environment
aeromedical certification is more likely than for the military. For consideration, an individual must provide
a complete orthopedic or neurosurgical evaluation. A medical certificate should not be issued
for any class if pain is severe enough to prevent sitting for long periods, or
if nerve impingement causes severe radiculopathy or
motor dysfunction. Obviously, the use of
narcotic analgesics or muscle relaxants is contraindicated in the aerospace
environment. A medical certificate may
be issued if symptoms have resolved with treatment (conservative or surgical),
and appropriate written medical documentation has been provided. Select cases may be forwarded for to a
FAA-selected consultant for review and recommendations.
Waiver Experience (military): A military waiver file lists 343 members with the diagnosis of
HNP. Of those evaluated, over 95%
received waivers for flying duties, two thirds of whom were corrected with
surgery or chemonucleolysis. Occasionally, categorical waivers are issued
in order to preclude flying in high-G performance or ejection seat
aircraft. Waivers are considered usually
3 to 6 months after successful treatment.
(A thorough history and physical exam should be performed to assure no
persistent neurologic or range of motion deficits). Recurrent symptoms after treatment would
preclude waiver consideration.
Waiver Experience
(civilian): As of January 2001 there were 3,329 First-class,
2,627 Second-class, and 5,888 Third-class airmen with issued medical
certificates in the FAA for all variety of HNP, laminectomy,
and cervical disk surgery. It should be
noted that 5-20% of individuals undergoing surgery will have significant
recurrent pain, and these aviators will most likely pose risks in the aviation
environment. Mild HNP will most likely
not create aviation problems after conservative therapy has concluded.
References:
Dee
R. Degenerative Diseases and Disc Disorders of the Lumbar Spine. Dee R, Mango E, Hurst LC (eds). Principles of Orthopedic Practice. 1989;
2:997-1034.
Ellenberg
MR, Ross ML, Honet JC, Schwartz M, Chodoroff G, Enochs S.
Prospective evaluation of the course of disc herniations
in patients with proven radiculopathy. Arch Phys Med Rehabil 1993;
74:3-8.
Gentry LR, Turski PA, Strother CM, Javid MJ, Sackett JF. Chymopapain chemonucleolysis: CT changes after treatment. American Journal of Radiology 1989; 145:361-9.
Manelfe C, Chevrot A, Arrue P, Mark AS. Disc Herniations. Manelfe C (ed). Imaging of the Spine and Spinal Cord. 1992; 269-72.
Rayman RB. Clinical
Aviation Medicine, Third edition,
Teplick JG, Haskin
ME. Computed tomography of the postoperative lumbar spine.
American Journal of Radiology 1983; 141:865-84.
White
AA, Panjabi MM. Clinical Biomechanics of the Spine. 1990;
2:3-5.
October
9, 2001