Clinical Practice
Guideline
For
ABNORMAL SPINAL
CURVATURE
________________________________________________________________________
Developed for the
Aerospace Medical Association
by their constituent organization
American Society of
Aerospace Medicine Specialists
________________________________________________________________________
Overview: Abnormal spinal curvature, also
known as kyphoscoliosis, has an incidence approximating 0.1% in the U.S.
population (12) while the USAF Aeromedical Consult Service recorded an
incidence of approximately 3% in their active duty referral population (19). Scoliosis curves measured by the Cobb method
(6) are classified mild (<30°) or severe (>100°;
12). Reported errors of measurement
include ± 2-3° (15, 18), with standard deviations
of ± 2.4° for orthopedists and ± 7.2° for
radiologists (24). Mild curves <30° tend
not to progress over 40-year follow-up (23), and are unlikely to be associated
with symptoms (2). Additionally, there
is no evidence that adults with normal pulmonary function experience
deterioration due to curve progression (5).
Similarly, kyphotic curves <60° have a benign prognosis (8).
The highest
rate of scoliosis progression appears to be the 50-75° category, where about 30° of progression was noted in 40 year
follow-up (23). This finding is
consistent with reported curve progression of adult idiopathic scoliosis
approximating 10° per decade and stature reduction of
about 1.5 cm per decade (14). Advancing
age has been associated with increasing rigidity, increasing likelihood of
pain, and reduced pulmonary function (14).
While back pain is the most frequent problem of adult scoliosis (3),
there is no clear evidence that the incidence of back pain in scoliosis
patients exceeds age-matched controls (5).
Severe
scoliosis (>100°) has been associated with reduced
vital capacity which could produce lower arterial oxygen content, predisposing
to pulmonary hypertension or cor pulmonale (5, 12). Cardiology consultation to exclude pulmonary
hypertension when right axis deviation is seen on ECG has been previously
recommended (16). In fact, cardiology
referral in the context of aeromedical evaluation is unnecessary due to the
unlikely presentation of curves >100°, well above the maximum waiverable
limit.
No surgical
or non-surgical treatment options were identified with the capability of
correcting disqualifying kyphoscoliosis to meet aeromedical standards.
Biomechanics
of spinal curvature may predispose to an increased risk of spine fracture or
other injuries during high G exposures such as those associated with the use of
ejection seats or hard landings in rotary wing aircraft (9). Vertebral fractures frequently occur at loads
exceeding the set ejection seat exposure limit of 20G (9, 11), but can occur
with forces as low as 10-12Gs when the spine is not entirely vertical (9). The upper body center of gravity lies
anterior to the spine and increasing kyphoscoliosis shifts the center of
gravity further forward or out of vertical alignment. This deviation increases the potential for
flexion compression fracture (22).
Consequently, entrance exam restrictions for aircrew previously proposed
have ranged from a scoliosis curve maximum of 10° in 1971 (10), to the USAF standard
of 20°, which increased to 25° in 1993 (17, 24). Finally, the current anatomically specific
USAF restrictions are described in the Aeromedical Disposition section
below. Two studies of USAF
ejection-related vertebral fractures have shown: (a) 6 USAF crewmen
experiencing 2 ejections within a 2-month to 8-year interval, in whom no
vertebral column injury was found after the 2nd ejection, despite the fact that
all 6 suffered vertebral fractures with the 1st ejection (20, 21); (b) a
10-year follow-up of 70 crewmen with normal vertebral spine x-rays just after
ejection, wherein 30 developed radiologic evidence of compression fractures on
follow-up (7, 20).
Aeromedical Concerns: Primary aeromedical concerns
relative to kyphoscoliosis involve the increased risk of fracture or other
spinal injuries with increasing deviation of the spinal axis from the vertical
position. Additional risks of sudden
incapacitation, critically distracting symptoms, or functional limitations
during flight may accompany clinically significant or progressive spinal
curvatures.
Medical Work-up: Clinical suspicion of abnormal
spinal curvature should be evaluated with plain film radiographs and orthopedic
consultation to include orthopedist measurement of kyphosis, lordosis, and
scoliosis curves by the Cobb method (24).
Although aeromedically acceptable spinal curvature is not likely to affect
pulmonary function, normal baseline PFTs would suggest a good prognosis,
particularly for borderline cases where a waiver is being considered (5). Since kyphoscoliosis-related pulmonary
hypertension or cor pulmonale is unlikely to occur with scoliosis curves
<100°, well above the maximum acceptable limits for military
entrance, military continuation, or air crew standards, ECG or cardiology
consultation will not likely be required in these populations (4, 12).
Aeromedical Disposition (military): The United States Air Force (USAF)
disqualifies (DQ) for continued service: Spinal deviation or curvature
more than moderate, interfering with function or causing unmilitary
appearance. DQ for entrance:
Spinal deviation or curvature that prevents a physically active vocation in
civilian life, interferes with proper wear of a uniform or military equipment,
is symptomatic, or involves lumbar scoliosis >20°,
thoracic scoliosis >30°, or kyphosis and lordosis greater
than 55 degrees. DQ for Flying (all classes): Lumbar scoliosis >20°,
thoracic scoliosis >25°, any abnormal curvature producing
noticeable deformity when dressed, pain, interference with function, or which
is progressive. Finally, DQ for survival
training instructor duty selection or retention: Scoliosis >25°, any
abnormal spine curvature with noticeable deformity, pain, interference with
function, or which is progressive (4).
The United
States Navy DQ scoliosis >20° without waiver for applicants,
but can be waived in designated personnel.
DQ kyphosis >40°, may be waived to 45° in
designated personnel. Waiver is not
normally considered when pain, interference with function, or progression are
present (2).
The United
States Army DQ for initial flight applicants: Any degree of lumbar or
thoracic scoliosis. DQ for flying
personnel: Scoliosis >20°, but routinely waived to 25° if
asymptomatic; kyphosis or lordosis >55°.
Waivers not normally granted when pain, interference with function, or
when condition is progressive (1).
Aeromedical Disposition (civilian): The Civil Aeromedical Institute
branch of the FAA does not list specific kyphoscoliosis guidelines, but notes
that any significant restriction of range of motion or motor deficit being
considered for medical certification may require a Medical Flight Test to
determine eligibility for a Statement of Demonstrated Ability, to be
coordinated through the Regional Flight Surgeon. Follow-up status reports are recommended
annually for any deficit that may be slowly progressive. If chronic back pain is present, a complete
orthopedic or neurosurgical evaluation is recommended and a medical certificate
should not be issued if pain is sufficient to prevent prolonged sitting, or if
severe radiculopathy or motor dysfunction are present (13).
Waiver Experience (military): A large
military waiver database lists 33 waiver requests for abnormal spinal curvature
with 18 approved and 15 disapproved from May 2002 to Oct 2007. Factors associated with approval included
continuation aircrew in positions limited to low G, non-ejection seat,
non-rotary aircraft, e.g., experienced military pilots, boom operators,
airborne linguists, and flight surgeons.
Factors associated with disapproval included initial applicants for
pilot, navigator, and para-rescue positions, in addition to those with higher
spinal curvatures, e.g., >27%.
Waiver Experience (civilian): FAA Special Issuance medical
certificates granted for spinal column deformity over the past 3 years totaled
1,914, including 629 First Class, 440 Second Class, and 845 Third Class
certificates, as of Oct 2007. Although
the number of special issuances denied for spinal column deformity is not
available, only 9.4% (2,663) of the total 28,235 SI applications received in
2006 were deferred or denied.
References:
1. Abnormal Spinal Curvature.
2. Abnormal Spinal Curvature.
3. Aebi M. The adult scoliosis. Eur Spine
J. 2005;
14:925-948.
4. Air Force Instruction 48-123v2-3, 5 Jun
2006. Retrieved on 1 Oct 2007 from http://www.e-publishing.af.mil/forms-pubs/?txtSearchWord=afi48-123&btnSearch.x=7&btnSearch.y=9&rdoFormPub=rdoPub
5. Bradford DS, Lonstein
JE, Ogilvie JW, Winter RB (eds). Moe’s
Textbook of Scoliosis and Other Spinal Deformities. WB Saunders,
Philadelphia. 1995;
17:369-370.
6. Cobb JR.
Outline for the study of scoliosis in instructional course
lectures. The
7. Crooks M.
Long term effects of ejecting from aircraft. Aerospace Medicine.
1970; 41(7):803-804. As cited in Rayman
RB, Hastings JD, Kruyer WB, Levy RA, Pickard JS. Clinical Aviation Medicine,
4th ed. Professional Publishing Group, Ltd,
8. Dee R.
Principles of Orthopedic Practice. McGraw Hill,
9. DeHart RL, Davis JR. Fundamentals of Aerospace Medicine, 3rd ed. Lippincott
Williams and Wilkins, Philadelphia. 2002; 23:503.
10. DelaHaye RP, Gueffier G, Metges PJ. Radiologic examination of the spine and the combat pilot’s
capability for duty (Radiologic spinal examination of combat pilots and
limiting angle for scoliosis). Improved
and simplified methods for the clinical evaluation of aircrew; papers presented
at the Aerospace Medical Panel specialist meeting held in Luchon,
France, 29-30 September 1971. Conference proceedings no. 95, part 2,
Advisory Group for Aerospace Research and Development, Paris, France. 1972.
11. Ernsting F, King P. Aviation Medicine,
4th ed.
Butterworths, Boston. 2006; 24:379.
12. Fishman AP.
Fishman’s Pulmonary Diseases and Disorders, 3rd ed. McGraw-Hill
Companies, New York. 1998;
97:1542-1547.
13. Guide for Aviation Medical Examiners, Decision
Considerations. Federal
Aviation Administration. Updated 30 May 2006.
Retrieved on 2 Oct 2007 from http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/app_process/exam_tech/item43/amd/spine/
14. Hawes MC, O’Brien JP. The transformation of spinal curvature into
spinal deformity: Pathological processes
and implications for treatment. Scoliosis.
2006. Retrieved on 1 Oct 2007 from http://www.scoliosisjournal.com/content/1/1/3
15. Jeffries BF, Tarlton
J, DeSmet AA, Dwyer SJ, Brower AC. Computerized measurements
and analysis of scoliosis. Radiology. 1980; 134:381-385. As cited in Wilson MS, Stockwell
J, Leedy MG. Measurement of scoliosis by orthopedic
surgeons and radiologists. Aviation, Space, and Environmental Medicine. 1983;
Jan:69-71.
16. Kapp E.
Abnormal Spinal Curvature, Updated Jun 1998. USAF Aeromedical Waiver Guide. Retrieved on 1 Oct 2007 from https://kx.afms.mil/kxweb/dotmil/file/web/ctb_070921.pdf
17. Morris CE, Briggs J, Popper SE. Human subject
research at Armstrong Laboratory, 1973-93:
Medical and musculoskeletal disqualifications. Aviation, Space, and
Environmental Medicine. 1997; 68(5):378-383.
18. Nordwall A. Studies in idiopathic
scoliosis relevant to etiology, conservative and operative treatment. Acta Orthop Scand.
1973; (Supp):1-178. As cited in Wilson
MS, Stockwell J, Leedy MG.
Measurement of scoliosis by orthopedic surgeons and radiologists. Aviation, Space, and
Environmental Medicine. 1983; Jan:69-71.
19. Popper SE, Morris CE. Are human subject
volunteers still players in aeromedical research as we enter the 21st
century? Aviation,
Space, and Environmental Medicine.
1997; 68(8):746-750.
20. Rayman RB, Hastings JD, Kruyer WB, Levy RA,
Pickard JS. Clinical
Aviation Medicine, 4th ed. Professional Publishing Group, Ltd,
21. Smelsey SO. Study of pilots who have made multiple ejections. Aerospace Medicine.
1970; 41(5):563-566. As cited in Rayman
RB, Hastings JD, Kruyer WB, Levy RA, Pickard JS. Clinical Aviation
Medicine, 4th ed. Professional Publishing Group, Ltd,
22. Vasishta
VG, Pinto LJ. Aviation Radiology: Teaching series. Ind
J Aerospace Med. 2003; 47(2):42-44.
23. Weinstein SL, Ponstei
IV. Curve progression in idiopathic
scoliosis. J Bone
Joint Surg. 1983; 65:447-455.
24. Wilson MS, Stockwell
J, Leedy MG. Measurement of scoliosis by orthopedic
surgeons and radiologists. Aviation, Space, and Environmental Medicine. 1983;
Jan:69-71.
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