Validity of radiological screening as part of initial medical examination of aircrew.

Material and methods

The present study was conducted at Air Force Central Medical Establishment, New Delhi, a premier institute carrying out evaluation of both civil and military aircrew. This study involved retrospective analysis of radiological investigations conducted on the aircrew. A search of our database yielded a total of 1786 aircrew who underwent radiological evaluation between Jan 2004 and Dec 2006. Study population consisted of asymptomatic, active individuals undergoing flight medical examinations for the cockpit and non-cockpit aircrew duties. All the aircrew after detailed medical examination were subjected to following radiological evaluation

1. Chest radiograph,

2. X-ray cervical spine (standing) frontal view and lateral view

3. Thoracic spine (lying down) frontal view and lateral view

4. Lumbar spine (lying down) frontal view and lateral view

All radiographs were interpreted by board-certified radiologist, and a written report was generated for each examination. The result of each radiograph was reviewed and classified as normal or abnormal. Depending on the abnormality noted on the initial radiological investigation further evaluation was carried out as per the existing protocol ofthe center. Individuals with an abnormal chest X-ray were evaluated with digital radiography, followed by computed tomography (CT) chest and pulmonary function test where indicated. Those with spinal abnormalities were evaluated further by functional films in flexion and extension. Findings that were considered normal variants or inconsequential (such as healed fractured rib or clavicle or extra ribs) were categorized as normal. Patients with major abnormalities were assigned to one of two groups: true-positive results (abnormal radiograph in the presence of disease) and false-positive results (abnormal radiograph in the absence of disease). Final disposal of the aircrew was done as per the laid down protocol in Manual of Medical Examination and Medical Boards (IAP 4303).

Results

A total of 1786 healthy aircrew underwent screening radiological investigations, 88.2% (1575) of these were for cockpit aircrew duties and 11.8% (211) for non-cockpit aircrew duties. The mean age of the study population was a 20.3±2.1 year (range 18 - 23 years) with majority of aircrew being male (80.1%).

Summary of the abnormal findings noted in various radiological investigations is as given in figure 1. Abnormalities were initially detected in 10.5% (188) of the screening chest radiographs, 4.4% (78) of the cervical radiographs and 14.4% (258) of the lumbosacral spine radiographs. Radiological investigations resulted in the permanent disqualification of 6.2% (111) aircrew.

Close

Figure 1:

Summary of radiological abnormalities noted in the aircrew

Export to PPT

Abnormalities noted in the initial chest radiograph are as given in table I. Prominent vascular markings and hilar prominence was the commonest abnormality noted in (116 ), and all these aircrew were further evaluated with digital radiographs, chest CT scans and pulmonary function test as per the laid protocol. Final result of these investigations is as given in table II. Of the total 116 aircrew who were noted to have radiological abnormality on the conventional X-ray only 8 were finally confirmed to have significant abnormality. In the rest it was either superimposition of normal structures or variants of normal findings. This eventually resulted in an additional 116 digital X rays, 20 chest CT scans and 20 pulmonary function tests.

Pulmonary fibrosis and fibrocavitatory lesions were noted in 1.3% (23) aircrew. All these candidates were declared unfit and were advised evaluation to establish the aetiology of the radiologic abnormality. In addition chest radiograph also revealed scoliosis in 2.2% (41) aircrew. However it measured less than 14 degrees (Cobb's method) in all the cases and therefore did not merit disqualification for flying duties. Other miscellaneous abnormalities identified were blunting of costophrenic angle, pleural tags, mediastinal shift and loss of thoracic kyphosis.

Salient findings of the radiological investigations of the spine are as given in table III. Partial loss of the cervical lordosis was the commonest abnormality noted in 68 (3.8%) aircrew; none of these aircrew had restriction of the neck movements and were hence declared fit. Cervical rib was noted in 4 (0.2 %) aircrew, all were declared fit as none of them had any associated neurovascular compromise.

Lumbar spine X-ray showed abnormalities in 14.4% of aircrew. Spina bifida of LV5 and SV1 was noted in total of 94 (5.2 %) aircrew (88 in the cockpit and 6 in the non-cockpit aircrew) and they were all declared fit for aviation duties. Incomplete sacralisation was noted in total of 76 (4.2%) aircrew (68 in the cockpit and 8 in the non-cockpit aircrew). All of these aircrew except for the 8 candidates for non cockpit aircrew duties were declared unfit for aviation duties. Partial loss ofthe lumbar lordosis was noted in 32 (1.8%) aircrew; none of them had restriction of the back movements and were hence declared fit. Bilateral lumbarisation and sacralisation was noted in 17 (0.9%) and 15 (0.8 %) aircrew and all of them were awarded full flying medical category.

Discussion

The feasibility and success of screening examinations for flight duties are dependent on several principles. The conditions being sought should be important to assess the fitness for aviation duties. The screening test should be sufficiently accurate and have the least possibility of harm to the person. In addition, the costs of evaluation, treatment, disqualification, or retaining the pilot on active duty with the disorder should also be estimated and risk benefit analyzed.

The World Health Organization has recommended that chest radiographic screening is not required for aviators except in those exposed to occupational lung hazards [7, 8]. Cox et al [4] reviewed 3500 chest radiographs in healthy persons screened for flight duty, and found abnormality in 107 (3%). Fifty-five of these were subsequently found to be false positive. In the study by Schenk et al [9] 2000 aircrew were screened by chest radiography and only five (0.26%) were abnormal, none of abnormalities resulted in disqualification for flying duties . These figures from studies in western population are in contrast with the high incidence of radiological abnormalities in our study .These may be due to difference in the disease pattern in our country compared to the West. High incidence of pulmonary fibrosis and fibrocavitory lesions noted in the current study lend support to the continued usage of this modality for screening. Therefore, chest radiograph is still a mandatory requirement in initial medical examination of aircrew especially in countries where there is high prevalence of pulmonary tuberculosis.

High rate of false positivity was noted on the conventional chest radiographs in the present study, as compared to the published literature [9]. Majority of these abnormalities were not found on repeat digital chest radiographs. There is need to replace the conventional radiograph with the digital radiography at institutions carrying out initial medical examination of aircrew, to prevent wastage oftime and resources.

The clinico-radiological correlation is not definite in spinal disorders. This problem is further compounded when we extrapolate the clinical significance of radiological abnormalities from patients to a population of healthy, asymptomatic adults in order to predict their future functional status. Most common spinal abnormality noted in the present study was scoliosis and straightening of the spinal curvature which did not lead to disqualification of any candidate from flying duties. This is akin to what has been noted in other studies done in the young asymptomatic adults [8, 10, 11].

Even though, neck pain in high performance fighter aircraft pilots receives much attention, spinal disorders leading to low back pain are reported to be twice more common in fighter aviators [12]. Association of lumbar spine abnormalities with low back ache has been controversial. In a study from Israel done in young army recruits (more applicable to the present study) spina bifida, left-sided scoliosis, hemi-lumbarization, sacralization and hemisacralization, Schmorl's nodules or mild degenerative changes were not associated with low back ache [11]. Iwamoto et al found spondylolysis to be a significant risk factor for low back pain in rugby players, there was no direct relation between sacralization( partial or complete) and low back pain [13, 14]. Unilateral asymmetrical lumbar sacralization was the commonest abnormality leading to disqualification of the aircrew in the present study. This disorder has been shown to increase the torque forces leading to disc herniation of lumbosacral spine [15].

Conclusion

Radiographic screening is definitely useful for detecting asymptomatic spinal and pulmonary abnormalities which place the aviator at high risk for adverse consequences during flying duties. Digital radiographic screening with its better resolution is a superior tool and leads to optimal utilization of resources.