Clinical Practice Guideline



Developed for the

Aerospace Medical Association

by their constituent organization

American Society of Aerospace Medicine Specialists


Overview: Ankylosing spondylitis (AS), the most common of the spondyloarthritides, is a chronic inflammatory disease principally involving the hips and axial skeleton.  The name for the disorder is derived from the Greek root "ankylos", which means bent or crooked and "spondylos", which refers to a vertebra.  The term "ankylosis" therefore refers to a fibrous or bony bridging of joints.  In the spine this includes bridging of one or more intervertebral discs.  AS typically has an insidious onset, can have extra-articular manifestations, and is diagnosed based on clinical suspicion supported by imaging techniques and associated human leukocyte antigen HLA-B27.  It also must be differentiated from other types of seronegative spondyloarthropathies, systemic inflammatory arthritis, as well as mechanical and degenerative causes of back pain.


AS commonly affects young adults as evidenced by the peak age of onset being 20 to 30 years.  The male to female ratio is approximately 2 to 3:1.  Among Caucasians, the estimated prevalence rate of AS, as defined by the modified New York criteria, ranges from 68 per 100,000 population older than 20 years in the Netherlands, to 197 per 100,000 in the United States.  In the general population, AS is likely to develop in about 1% to 2% of HLA-B27–positive adults who have a disease-associated B27 subtype, although there may be regional or geographic differences.  For example, in northern Norway, AS may develop in 6.7% of HLA-B27–positive people.  The disease is much more common among HLA-B27–positive, first-degree relatives.  Of HLA-B27–positive AS patients, roughly 10% to 30% of them have signs or symptoms of AS.  The prevalence of AS in working adults with back pain of greater than three weeks duration was 4.6% in one study.  Thus, if the patient has at least one first degree relative with AS and given that the patient is positive for HLA-B27, a presumptive diagnosis of AS is reasonable.


AS can also present with the nonspecific symptoms of low-grade fever, fatigue and weight loss. Non-skeletal involvement frequently occurs, including acute anterior uveitis; neurologic symptoms resulting from fractured spine, atlantoaxial subluxation, cauda equina syndrome and costovertebral rigidity; aortic regurgitation; IgA nephropathy and secondary amyloidosis; ileal and colonic mucosal ulcerations; and osteopenia.


Diagnosis and Treatment:

Because AS has an insidious onset, the diagnosis is based on a high index of clinical suspicion and supported with a judicious use of imaging, laboratory testing along with a therapeutic trial of NSAIDs.  Signs and symptoms suggestive of inflammatory back pain include: onset prior to age 40, insidious onset, symptoms persisting longer than three months, morning stiffness, and improvement with exercise.  The presence of four of the five above has a sensitivity and specificity of up to 75 percent.


Range of Motion (ROM) Measurement:

Assessment of ROM of the lumbar spine is a key clinical finding.  The modified Schober test is one accepted method to assess lumbar spine ROM by measuring the forward flexion of the spine in a patient with suspected AS.  The test is performed with the patient standing erect; a mark is made over the spinous process of the 5th lumbar vertebra or the imaginary line joining the posterior superior iliac spine and another mark is made 10 centimeters above this mark in the midline.  In a patient with no lumbar spine motility abnormalities, the measured distance between the two points should increase by 5 cm when the patient bends forward to touch his toes while keeping the knees locked.  The severity of cervical flexion deformity can be assessed using the Flesche test.  While the patient is standing erect, the heels and buttock are placed against the wall. The patient is instructed to extend his neck in order to touch the wall. The distance between the occiput and the wall is a measure of the degree of cervical flexion deformity.  In addition, assessment of chest wall expansion, loss of cervical lordosis, sacroiliac joint tenderness, hip and peripheral joint involvement are important indicators of range of motion abnormalities.


Serological Testing:

Testing for C-reactive protein and HLA-B27 can help to support the clinical picture, but caution is advised as these tests should not be used as screening tests, that is, the value of either positive or negative results is only realized when the test is applied in the appropriate clinical setting.  A history of chronic, inflammatory low back stiffness, elevated ESR, positive C-reactive protein with a positive HLA-B27 in an otherwise healthy young male with a familial history of inflammatory back stiffness supports a diagnosis of AS.  The finding of a negative HLA-B27 in the same clinical setting reduces the likelihood of AS to 1 in 20 (5%).  Likewise, the indiscriminate use of additional serologic assays (i.e. “the rheumatology lab panel”), in search of alternative diagnoses, is further discouraged.  Serologic studies must be carefully chosen based on the constellation of the presenting history and physical exam features.


Imaging Studies:

A CT of the sacroiliac (SI) joints will visualize bony changes better than plain radiographs; it will not detect early acute inflammatory changes in the bone marrow and it exposes the patient to a relatively high dose of gonadal radiation.  Ultrasound is not currently recommended for the evaluation of AS.  Plain films can be used to follow clinical progression.  Though AS usually manifests as a spinal disease, chronic changes in peripheral joints can occur in about 25 percent of patients.  In the presence of chronic, inflammatory back symptoms and a physical exam consistent with the same, screening plain radiographs of the SI joints and lumbosacral spine are recommended.



The use of NSAIDs and physical therapy are the mainstays of treatment in AS.  This approach is both therapeutic and diagnostic.  The goal of treatment is to provide symptomatic relief, restore function, prevent joint damage and spinal fusion, minimize extra-spinal and extra-articular disease, and prevent complications of spinal disease.  The majority of AS patients using NSAIDs experience relief of symptoms.  Regardless of the NSAID used, the maximum dose is usually required, taken daily for at least two weeks, and the NSAID must be on the list of approved medications for military aviators.  Anti-TNF-alpha agents can also be used in patients with a firm clinical diagnosis of AS with moderate to severe spinal disease who have not responded to NSAIDs.  In advanced cases surgery may be required such as total hip replacement and/or spinal or cervical fusion.  Smoking cessation is recommended due to the detrimental effect COPD can have on the restrictive lung disease secondary to limited costovertebral joint motility.


Aeromedical Concerns: In aviators with AS, cramped cockpit conditions for prolonged periods may be poorly tolerated.  There may be functional limitations in all aircraft, especially in high performance aircraft and flying in typical cockpits may exacerbate eventual disability.  Typical AS symptoms are incompatible with ejection and special duty that would require parachute qualification or other skill sets that may subject a service member to impact forces.  The cervical and lumbosacral limitations of AS may also interfere with emergency ground egress and can limit vision due to restricted neck motion.  Note: the FAA does not take emergency egress as a factor in the consideration for medical certification.  Concomitant uveitis/iritis occurs in up to 25% of cases.  The development of most of the extra-articular manifestations in AS are disqualifying in the military services, and chronic treatment with NSAIDs and tumor necrosis factor alpha antagonists are incompatible with flying duties in the military services.


Medical Work-up: Documentation needs to include a detailed history to include onset of symptoms, time course, joints and/or extra-articular involvement, extra-articular manifestations, medications used and any side-effects and the current activity level.  The exam needs to focus on the affected joints, involved extra-articular tissues, the eyes, kidneys and heart.  Lab testing needs to include a CBC, comprehensive metabolic panel, HLA-B27, serology, urinalysis, ESR, and C-reactive protein.  Radiographs of involved levels of the spine to include SI joints (Ferguson’s views) are also required.  In addition, an echocardiogram and cardiology consult are required if there is involvement of cardiac valves.  All cases will should obtain a rheumatology and ophthalmology report.  If the aviator is military, a medical evaluation board report will be necessary.


Aeromedical Disposition:


Air Force: AS is disqualifying for Flying Classes I, II, and III IAW AFI 48-123, but a waiver is possible with documentation of treatment and resolution of symptoms.


Army: Ankylosing spondylitis, as with other inflammatory spondylopathies, is disqualifying for Army aviation service.  It is discussed primarily in its own Aeromedical Policy Letter but is mentioned in several other connective tissue policy letters.  Waiver, though not usually granted to applicants, will be considered on a case-by case basis for applicants and aircrew for early stage mild or inactive disease who have minimal symptoms, require minimal medications for symptom control, have had no recurrent symptoms or extra-spinal manifestations, who continue to have normal spinal mobility, and whose occupational environmental safety risk remains acceptable.  Disqualification or (discontinuation of waiver) will often be recommended for individuals whose disease involves any of the following: 1) extra-spinal manifestations; 2) use of Class IV medications; 3) symptom or performance issues (such as chronic pain, anxiety, frequent work absences or profiles, issues of potential impact on aviation work performance/safety; or 4) failure to meet retention standards, need for Permanent 3 or 4 profile, or inability to take/perform at least one aerobic AFPT event.


Navy: An established diagnosis with symptoms is CD. Waiver is possible in early cases with normal mobility and no complications


Civilian: See below.


Waiver Experience:


Air Force: Review of AIMWTS revealed a total 13 cases of AS submitted for consideration of a waiver.  There were no 0 FC I/IA cases, seven FC II and six FC III cases.  Of the 13 cases, eight were approved for a waiver.  Five of the cases were disqualified for AS or AS with complications of AS.  In the FC II category, three were disqualified and in the FC III category, two were disqualified.


Army: Since 1990 there have been 123,259 aviators of all types, including applicants enrolled in the Aeromedical Epidemiological Data Repository.   Among them there have been 6 cases of ankylosing spondylitis, 5 in rated aviators and one in an applicant.  All were granted waivers except for one rated aviator.


Navy: Not available at this time.


Civilian: This condition is acceptable in the civilian sector.  See above for consideration concerning medical treatment.  The airman needs to provide statements from the treating physician as to whether there are extra-articular manifestations.  Since the FAA mainly concerns itself with sudden incapacitation in the cockpit, making sure that the airman can remain seated for long periods without experiencing incapacitating pain and extra-articular manifestations should be considered in granting an authorization. Currently the FAA does not maintain statistics on the number of airmen currently certificated with this condition.


Text Box: ICD-9 Code for Ankylosing Spondylitis
720.0	Ankylosing Spondylitis






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Prepared by Drs. Bradford J. Williams and Dan Van Syoc