Cervicalgia amongst helicopter pilots using helmet mounted devices

Material and Methods

This study is based on the available data of a recent questionnaire survey on backache [3]. This was based on an earlier validated questionnaire [8]. The questionnaire included demographic, flying and lifestyle related inputs, besides focussing on different aspects of backache, including the incidence, frequency, location, severity and measures sought for relief from the pain.

The questionnaire was posted to the Medical authorities of the helicopter base operating Mi-8 and Mi-17 helicopter. The structured questionnaire was, in turn, given to the available pilots of the helicopter units and was posted back to the authors within a period of 45 to 60 days.

The analysis in the present survey is limited to descriptive statistics to plan prospective studies on spinal strain amongst NVG using helicopter pilots.

Results

The results of this study are based on the questionnaire feedback from a total of 55 helicopter pilots currently flying Mi-8 (n = 31 ; 56.36%.) or Mi-17 (n = 24; 43.63%). The mean age of the respondents was 32.35 years (SD 8.58) and 29.0 years (SD 3.57) for Mi-8 and Mi-17, respectively. The respective mean flying hours were 2223.0 hours (SD 2071.28) and 3500.0 hours (SD 1141.24) for Mi-8 and Mi-17 helicopter, respectively.

The overall incidence of back pain in Mi-8 and Mi-17 operating pilots was 67.74% (n = 21) and 75.0% (n = 18), respectively (Figure 1). The remaining pilots who did not report backache (n = 16) did not respond to the remaining questionnaire. Hence the results hereafter are based on the feedback of the pilots (n = 39) reportedly having complaints of backache.

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Figure 1:

Incidence of backache among Mi-8 and Mi-17 Pilots (Percent)

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On one hand, 33.33% Mi-8 pilots reportedly had pain almost every day and 23.8% had it once a week and 19.04% occasionally; on the other, 27.77% of Mi-17 pilots only had occasional complaint of back pain and 22.22% each had pain only once in a week or even once in a quarter (Figure 2).

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Figure 2:

Frequency of backache among Mi-8 and Mi-17 Pilots (Percent)

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The commonest activity precipitating back pain was flying (Mi-8, n = 19, 90.47%; Mi-17, n = 14, 77.77%) (Figure 3). The type of sorties most notorious to precipitate back pain were the ferry or cross-country sorties (Mi-8, 84.03%; Mi-17, 88.88%) (Table I). Majority of Mi-17 pilots (61.11%) reported that the pain was likely to be precipitated after flying for more than two hours, as also reported by Mi-8 pilots (42.85%) but an equal percentage of Mi-8 pilots reported onset of pain after flying for an hour.

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Figure 3:

Activity precipitation backache in Mi-8 and Mi-17 Pilots (Number)

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The commonest location of the pain was the lower back (Mi-8, 85.71%; Mi-17, 66.66%) with neck being the second common location ((Mi-8, 19.04%; Mi-17, 22.22%), as also the buttocks for Mi-17 pilots (22.22%) (Table III). Majority of Mi-8 pilots (57.14%) complained of pain being moderate in severity, whereas 50.0% Mi-17 pilots reported only discomfort and another 44.44% had pain of moderate severity (Table IV).

Majority of the respondents (Mi-8, 42.85%; Mi-17, 38.88%) reported relief from the pain between 2 to 6 hours after the sortie; and others (Mi-8, 38.09%; Mi-17, 33.33%) found relief within 2 hours of landing (Table V). Measure to obtain relief from the pain included either taking rest on hard bed (Mi-17, 61.11%) or some spinal stretching exercise after the sortie (Mi-8. 47.16%). Despite many of the pilots complaining of back pain, their response to a pointed question about seeking medical attention in the past 12 months revealed that only 5 (Mi-8, 23.80%) and 1 (Mi-17, 5.55%) sought medical attention only once, whereas 15 (Mi-8, 71.42%) and 12 (Mi-17, 66.66%) each affirmed that they never sought any medical help.

Discussion

This study purports to specifically analyse the data of a questionnaire survey on the incidence of backache pertaining to pilots flying Mi-8 and Mi-17 helicopters. The analysis focussed on the nature of back pain reported by the pilots. This is required to define the likely pattern of strain on the back while using HMD during flight. This shall help plan and propose prospective studies on altered biomechanical strain and resulting stress on the spine while using NVG during flight and to define the preventive measures.

An overall incidence of back pain among Mi-8 and Mi-17 pilots was 67.74% and 75.0%, respectively (Figure 1). The frequency of pain varied from almost every day (Mi-8, 33.33%) to only occasional complaints (Mi-17, 27.77%) (Figure 2). Flying was reportedly the commonest activity precipitating back pain (Mi-8, 90.47%; Mi-17, 77.77%) (Figure 3). Sorties like ferry or cross¬ country were most notorious to precipitate back pain (Mi-8, 84.03%; Mi-17, 88.88%) (Table I); thus the prolonged duration of sortie was likely to cause back pain (Table II).

Lower back (Mi-8, 85.71%; Mi-17, 66.66%), neck (Mi-8, 19.04%; Mi-17, 22.22%) and buttocks (Mi-17, 22.22%) were the common locations for the pain (Table III). The severity of pain was between discomfort (Mi-17, 50.0%) to moderate (Mi-8, 57.14%) in severity (Table IV). The pain was relieved 2 to 6 hours after the sortie (Mi-8, 42.85%; Mi-17, 38.88%) (Table V) and required rest on hard bed (Mi-17, 61.11%) or some stretching exercise (Mi-8. 47.16%). Majority ofthe respondents did not seek any medical consultation for their malady (Mi-8, 71.42%, Mi-17, 66.66%).

While the the results of this study confirm to the existing body of work on back pain among helicopter pilots [4-8], an incisive look keeping the likely changes in the load bearing on the spine while using HMD to accomplish missions at night, with undefined hours on duty and resulting altered circadian rhythm for the pilots, shall definitely affect the performance capabilities and mission preparedness of the pilots. Therefore, there is a need to study each of the factors affecting mental workload and performance to keep the pilots mentally agile and fit for mission accomplishment. This paper shall hereafter focus only on the need to study biomechanics of the back, especially the neck, to define strain and stress pattern while using HMD.

Delahaye et al reported that helicopter pilots complain of aching at the nape of the neck, due to extreme movements of the head, which could worsen with the protective helmet [4]. It has been widely accepted that the back pain among helicopter pilots is classically caused by combination of twisted seated posture due to cockpit control layout, especially the collective; and the vibrations resulting from the main rotor of the frequency range between 3 to 7 Hz, which matches with that of the upper torso of principal resonance frequency of 5 Hz.

de Olivieara and Nadal suggested that the most important factor in the spine related disability could be due to the cyclic mechanical load imposed by the vibration [9]. They quoted an earlier study about the correlation between neck and shoulder muscle load with increased susceptibility to problems on exposure to whole-body vibration. The load and problems aggravate further while working in twisted position compared from the neutral, as is the predicament of the helicopter pilots.

A higher incidence of spine related disorders among helicopter pilots may therefore be because of the vibration leading to cumulative load on the spine. The altered load conditions due to increased weight of HMD and the whole-body vibration transmissibility must be correlated with the spinal degenerative changes and its location amongst helicopter pilots. A study of musculoskeletal disabilities among aircrew (n = 232) at an Indian evaluation centre reported that 58.5% of helicopter aircrew had spinal musculoskeletal disability, compared to 53.2% and 46.9% in fighter and transport aircrew, respectively [10]. The majority of aircrew (38%, n = 46) had MRI confirmed degenerative disease of the disk. 80.4% had degenerative disease of the lumbo-sacral disk (50% each at L4/L5 and L5/S1 level) and 19.5% had cervical disk degeneration (maximum 78% at C5/ C6 level). The percentage of cervical degeneration must be viewed with concern with HMD likely to affect the load on the spine causing chronic strain.

Therefore there is a need to undertake extensive whole-body vibration studies with different HMD used by Indian helicopter pilots. This shall help define the stress loading at different levels of spine. In addition, the Spatial Disorientation simulator at the Institute of Aerospace Medicine can be utilised for simulated long duration cross-country sorties with HMD to study the musculo-skeletal fatigue of neck and upper torso. The same studies can, then, be extended to actual operations to study the strain effects of combination of in-flight stresses on the spine. The resulting body of work can finally help define the preventive strategy for safe operations with HMD. This includes work-rest and physical exercise schedule of the squadron pilots. Physical exercise shall aim at toning up ofthe spinal especially neck muscles, as part of the pilots' daily routine to prevent long term adverse effects of the helicopter flying with HMD. It is suggested that mandatory MRI scan at regular intervals must be planned for helicopter pilots based on cumulative flying hours. This shall help visualise early non-symptomatic spinal degenerative changes, before it compromises pilots' physical well-being and flying efficiency.

Conclusion

An analysis focussing on the nature of back pain reported by the pilots flying Mi-8 and Mi-17 helicopters was undertaken to define the likely pattern of strain on the back while using HMD during flight. The findings suggest that neck remains a potential area of concern in view of the flight conditions and the altered weight on the head with HMD. Recommendations for prospective studies on altered biomechanical stress and resulting strain of spine while using NVG during flying and the preventive measures have been made.