Clinical Practice Guideline
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.
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