RESEARCH ARTICLE
Demographic and Occupational Predictors of Neck Pain in Pilots: Analysis and Multinational Comparison Bryan K. Lawson, Owen Scott, Fortune J. Egbulefu, Rosemarie Ramos, Joel W. Jenne, and Edward R. Anderson LAWSON BK, SCOTT O, EGBULEFU FJ, RAMOS R, JENNE JW, ANDERSON Our aim is to elucidate the demographic and occupaER. Demographic and occupational predictors of neck pain in pilots: tional predictors of acute neck pain among a comprehenanalysis and multinational comparison. Aviat Space Environ Med sive group of pilots. Furthermore, our objective is to 2014; 85:1185–9. compare these results with respect to pilot nationalities, Objective: This study aimed to elucidate the overall risk and demographic/ occupational predictors of neck pain among professional pilot gender, and pilot age. We postulate Delivered aviators. by Ingentaairframe to: jacobtype, busch Methods: There were 413 surveys characterizing the severity and charIP: 185.14.195.104 On: Sat,that 16 the Jul 2016 07:19:02 increased prevalence of acute occupational neck acter of neck pain symptoms that were administered to a multinational Copyright: Aerospace Medical Association pain is not specifi c to high performance aircraft, but rather cohort of pilots representing 3 separate airframe types. All results were that these trends will be realized throughout the pilot compared to a nonaviator control group. Univariate and multivariate regression analyses were performed to elucidate independent predictors community. Our comparisons were performed on a broad of occupationally related neck pain. Results: Of the surveys, 92% were group of aviators, including small airframe/trainer picompleted and returned. Multivariate analysis reveals that the pilot prolots, high-performance/high 1G pilots, and transport/ fession is independently predictive of increased occupational neck pain passenger aircraft pilots, with international and nonaviasymptoms (OR 1.94, 95% CI 3.72, 1.01). High performance airframes, cargo/passenger airframes, and increasing age were also independent tor control groups to assist in normalizing our results. We predictors of increased neck pain scores (OR 5 3.91, 95% CI 7.10, 2.15; hypothesized that our analysis would establish all airOR 5 3.22, 95% CI 5.83, 1.77; OR 5 4.00, 95% CI 7.43, 2.15, respecframe types and increasing age as independent predictors tively). Conclusions: Our broad, multinational/multi-airframe analysis reof increased occupationally induced neck pain symptoms veals that the pilot profession, most notably high performance and long-haul cargo/passenger airframes, display an increased risk of affecting the individual’s activities of daily living. neck pain symptoms. Keywords: aviators, occupational neck pain, predictors, 1G.
METHODS
T
HE STUDY OF occupational health in aviators presents very specific challenges for military and civilian health professionals. Specifically, trends of acute neck pain have been increasing with the higher performance characteristics of modern era aircraft (5,8,16). These populations have been particularly reticent to fully disclose occupational neck pain symptoms in order to maintain their active flying status. As a result, most scientific evaluations of this target cohort are designed as anonymous questionnaires (2,4,18). The 3-mo period prevalence of occupational acute neck injury has been reported as high as 97% in high performance airframes (8,11). Given the increasingly high prevalence of these symptoms, and their associated impact on the pilots’ mission readiness and ability to perform standard inflight procedures, the majority of these screening studies have focused on this high-performance population (1,3,5). As a result very few analyses have evaluated the prevalence and predictors of these symptoms across a generalizable pilot sample, including larger transport/ passenger aircraft pilots and small personal/trainer aircraft pilots (10).
Institutional Research Review Board (IRB) approval was given at all participating sites prior to proceeding with this survey-based comparative study. Participating sites were screened to ensure a broad cross section of the aviation population would be able to participate in this study. The chosen sites serve as operational and training locations for large cargo/passenger type aircraft, highperformance high positive G-load aircraft, and small trainer/recreational aircraft, thus allowing evaluation of varying degrees of occupational cervical spine stress.
From the Department of Orthopaedics and Rehabilitation, San Antonio Military Medical Center, Ft. Sam Houston, TX; the Department of Flight Medicine, Sheppard Air Force Base, TX; and the Department of Epidemiology and Biostatistics, Wilford Hall USAF Medical Center, Lackland AFB, TX. This manuscript was received for review in June 2014. It was accepted for publication in September 2014. Address correspondence and reprint requests to: Bryan K. Lawson, M.D., Department of Orthopaedics and Rehabilitation, San Antonio Military Medical Center, 3551 Roger Brooke Dr., Ft. Sam Houston, TX; [email protected]. Reprint & Copyright © by the Aerospace Medical Association, Alexandria, VA. DOI: 10.3357/ASEM.4077.2014
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NECK PAIN PREDICTORS IN PILOTS—LAWSON ET AL. Furthermore, these sites serve as concomitant training facilities for all NATO forces, thus allowing comparison between U.S. and International aviator groups. All surveys for the study group were completed during a unit training briefing after adequate instruction on the completion process. All surveys for the control group were completed in a similar manner. Subjects There were 413 surveys administered to the study group (consisting of a multinational cohort of highperformance/high 1G-load aircraft pilots, cargo/ passenger aircraft pilots, and trainer aircraft pilots). For the control group, 57 surveys were administered (nonaviator military officers of similar age and time in service). Survey
TABLE I. POPULATION DEMOGRAPHICS. Study Group Demographic Group Male Female Unknown Gender U.S. Pilot NATO International Pilot Unknown Nationality Trainer/Small Airframe Pilots High-Performance/High 1G Load Airframe Pilots Large Cargo/Passenger Airframe Pilots Unknown Primary Airframe Age 18-24 Age 25-30 Age 31-40 Age 41-50 Age 501 Unknown Age
N
Control Group %
N
%
390 11 12 333 68 12 275 97
94% 3% 3% 81% 16% 3% 67% 23%
48 9 0 -
84% 16% 0% -
29
7%
-
-
0 27 18 10 2 0
0% 47% 32% 18% 3% 0%
12 136 116 111 37 1 12
3% 33% 28% 27% 9% 0.20% 2.8%
Questions on the degree, severity, quality, and character of occupationally related neck pain were based on the Neck Disability Index Questionnaire (NDI) (17). Study group, N 5 413; Control group, N 5 57. Additional inquiries were used in order to assist in demographic characterization of our study and control Delivered by Ingenta to: jacob busch populations. Given the dogmaticIP:assumption that the 185.14.195.104 On: Sat, 16 Jul 2016 07:19:02 The neck disability index scores, stratified by specific Copyright: Aerospace Medical Association aviation population is averse to participation in longitupopulation demographics, are demonstrated in Table II. dinal clinical research for fear of negative professional Analysis with respect to pilot nationality (U.S. versus repercussions, questions were also added to assess the International cohort) and gender did not reveal any stapopulation’s willingness to participate in studies to tistically signifi cant difference in neck pain scores. Howevaluate their chronic musculoskeletal neck pain. Neck ever, our analysis of variance did reveal statistically pain scores greater than 8 were considered clinically sigsignifi cant mean neck pain scores when comparing the nificant symptom profiles for each participant (12,13,17). three differing airframe types, and in our comparison of the four age groups (P , 0.001 for both comparisons) Statistical Analysis (Table II). Three primary statistical analyses were used to charOur logistical regression model was used to further acterize the trends in occupational neck pain present in assess the trends shown in the neck pain scores among our study group. Stata Data Analyses and Statistical our study population. Our multivariate analysis was Software was used for all comparisons and analyses able to determine which of our demographic parame(Stata Corp LP, College Station, TX). In this study ters were independently predictive of higher neck pain P-values less than 0.05 were considered statistically sigscores (Table III). Our overall analysis revealed that the nificant for all analyses and comparisons. pilot profession, regardless of airframe, was independently predictive of increased neck pain scores when 1) Differences in neck pain scores were compared across all demographic parameters (Nationality, Airframe Type, Gender, and Age). compared to a nonaviator control group, as detailed These results were evaluated using Analysis of Variance (ANOVA) below. Only two patient demographics, airframe type to determine statistical significance in these comparisons. and pilot age, were predictive of clinically significant 2) Logistical regression analyses with j option were performed to neck pain without any two-way interactions with determine which demographic characteristics represented independent predictors of clinically significant occupational neck other variables. pain. Regression analysis groups were defined by a cut point As described above, our multivariate analysis was exabove and below a neck pain score of 8 (17). panded to include a comparison of our control group. 3) Cross-tabulation with Chi-squared analysis was used to deterThis comparison displayed an odds ratio of 1.94 when mine which neck pain characteristics and lifestyle limitations were consistently associated with specific demographic groups. For this comparing the clinical risk of increased neck pain in analysis, individual questionnaire inquiries were compared for all aviators in comparison to their matched control group demographic subgroups (Nationality, Airframe, Gender, Age). (P 5 0.04, 95% CI 3.72, 1.01). High-performance/high 1G and large cargo/passenger type primary airframes RESULTS were independently predictive of increased occupational neck pain (OR 5 3.91, 95% CI 7.10, 2.15; P , 0.001 A total of 413 surveys were administered to the study and OR 5 3.22, 95% CI 5.83, 1.77; P 5 0.004, respecgroup with 382 surveys being returned, yielding a 92% tively). In addition, increasing age was determined to participation rate. All surveys administered to the conrepresent an independent predictor per our multivariate trol group were completed and returned. The populaanalysis. Statistically significant increases in aviationtion characteristics of the study and control populations induced neck pain were noted in the 31-40 yr group are demonstrated in Table I. 1186
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NECK PAIN PREDICTORS IN PILOTS—LAWSON ET AL. TABLE II. NECK DISABILITY INDEX SCORE COMPARISONS BY DEMOGRAPHIC CHARACTERISTICS. Mean
Median
SD
50th percentile
75th percentile
U.S. pilots International pilots
4 4
6.2 6.6
6.6 6.8
4 4
10 10
F statistic 5 0.14; P 5 0.71; r2 5 0.0004
Male pilots Female pilots
6.2 7.4
4 6
6.6 6
4 6
10 10
F statistic 5 0.37; P 5 0.54; r2 5 0.0010
5 9.2 7.8 4.2 5 8.6 10.4
2 8 8 2 3 8 8
6 7.2 6.2 4.8 5.6 7.2 9.2
2 8 8 2 3 8 8
8 12 11 6 8 12 16
F statistic 5 15.24; P , 0.001; r2 5 0.008
Trainer/small airframe pilots High performance/high 1G load airframe pilots Large cargo/passenger airframe pilots Age 18-24 Age 25-30 Age 31-40 Age 41-50
F statistic 5 12; P , 0.001; r2 5 0.11
trainer/small airframe cohort). Increasing age was in(OR 5 3.49, 95% CI 6.48, 1.88; P , 0.001) and in the dicative of an increased rate of self-limited participation 41-50 yr group (OR 5 4.00, 95% CI 7.43, 2.15; P , 0.001). in preferred recreational activities (Table IV, P , 0.001). Multivariate analysis of pilot nationality and gender did not show that these demographic characteristics were Finally, of all pilots surveyed, 82% stated that they independent predictors of increased neck pain. would be willing to participate in longitudinal health Comparison of positive survey response rates restudies to evaluate the occupational risks inherent to Delivered by to: jacobcareers. busch This question was phrased to include vealed many statistically significant variations in Ingenta the aviation IP: 185.14.195.104 On: Sat, 16 Jul 2016 07:19:02 lifestyle effects of occupational neck pain within the Medical the possibility of multiple visits and the possible incluCopyright: Aerospace Association various demographic subgroups (Table IV). Regarding sion of laboratory and imaging studies. the intensity of reported cervical pain symptoms, sigDISCUSSION nificantly more international aviators, high performance pilots, and cargo pilots reported moderate to severe This study was conducted to determine the risk and baseline neck pain symptoms (P 5 0.02, P , 0.001, and overall lifestyle effect of occupation-related neck pain P , 0.001, respectively). Furthermore, pilots’ of age 30 inherent to professional aviation career fields. Our primary and greater reported a higher rate of moderate to severe aim was to elucidate the demographic and occupational symptoms at baseline (P , 0.001). predictors of acute neck pain among a comprehensive When compared within their respective demographic group of pilots while comparing these results with resubgroups, the international aviator cohort, high perforspect to pilot nationality, airframe type, gender, and a mance aircraft group, and older age groups (greater ge. We have detailed an increased overall risk of octhan 30 yr of age) reported more difficulty performing cupational neck pain for all aviators regardless of dedaily grooming or self-care tasks secondary to their neck mographic subgroup when compared to nonaviators. pain symptoms (P 5 0.006, P 5 0.049, and P , 0.001, respectively). More women (45% vs. 8% of men) reported moderate intensity headaches directly attributed TABLE III. MULTIVARIATE REGRESSION ANALYSIS TO DETERMINE to their baseline neck pain issues (P , 0.001 for this INDEPENDENT PREDICTORS OF NECK PAIN IN AVIATORS. comparison). Female aviators, high performance pilots, Demographic Characteristic Odds Ratio 95% CI P-Value large airframe/cargo pilots, and older pilots reported exacerbation of their neck pain symptoms with standard All Aviators driving maneuvers (P 5 0.001, P 5 0.001, and P 5 0.003, Non-Aviator Control Group 1.00 respectively). No significant difference in drivingAll Pilots 1.94 (3.72,1.01) 0.04 Pilot Nationality related symptomatic exacerbation was noted between U.S. Aviator Cohort 1.00 the U.S. and international aviator cohorts. International Aviator Cohort 1.00 (1.78,0.56) 0.98 Regarding sleep loss secondary to neck pain sympPilot Gender Male 1.00 toms, 62.5% of high performance pilots and 46.3% of Female 1.47 (2.59,0.83) 0.53 cargo pilots reported at least 1-3 h of sleep lost per night Primary Airframe (P 5 0.003 when compared to the trainer/small airframe Trainer/Small Airframe Pilots 1.00 cohort). Increasing pilot age displayed a higher rate of 3.91 (7.10,2.15) High Performance/High 1G ,0.001 Load Airframe Pilots consistent sleep loss due to cervical pain symptoms (TaLarge Cargo/Passenger 3.22 (5.83,1.77) 0.004 ble IV, P 5 0.002). Airframe Pilots More high performance pilots (54.2%) and large Pilot Age airframe/cargo pilots (32.1%) reported limiting partici18-24 1.00 25-30 1.38 (2.62,0.73) 0.16 pation in their preferred recreational activities due to a 31-40 3.49 (6.48,1.88) ,0.001 frequent exacerbation of neck pain symptoms while per41-50 4.00 (7.43,2.15) ,0.001 forming these tasks (P , 0.001 when compared to the Aviation, Space, and Environmental Medicine x Vol. 85, No. 12 x December 2014
1187
1188
,0.001
10.3 18.8 45.8 55.6
32.1
32.8 36.6 58.5 63.9
0.002
46.3
15.1 18.8 35.5 41.7
0.003
1.6 4.5 0.9 2.8 6.4 8.1 12.1 13.9
n.s., 0.70
0.8 0.7 6.3 15.2
,0.001
0.5
n.s. 5 not significant.
2.4 1.8 11.1 14.0
,0.001
10.7
0.049
28.6
n.s., 0.50
n.s., 0.37
3.1 0.0
n.s., 0.2
7.3 12.5 2.3 5.3
,0.001
3.6
0.003
36.7 62.5 18.6 39.5
0.001
43.7 54.6 0.001 24.5 27.3 n.s., 0.76 2.4 0.0 ,0.001 8.0 45.5 n.s., 0.60 4.5 0.0 n.s., 0.41 6.0 0.0
14.2
,0.001
16.2 54.2
27.5 9.1 n.s., 0.91
n.s., 0.80 42.6 51.0 n.s., 0.06 26.6 14.3 n.s., 0.90 2.5 1.6 n.s., 0.97 9.4 7.8 0.006 4.7 11.5 0.02
Pilot Nationality U.S. Aviator Cohort International Aviator Cohort Pilot Gender Male Female Primary Airframe Trainer/Small Airframe Pilots High-Performance/High 1G Load Airframe Pilots Large Cargo/Passenger Airframe Pilots Pilot Age 18-24 25-30 31-40 41-50
5.0 9.3
Furthermore, large cargo/passenger primary airframes, high-performance/ high 1G load primary airframes, and increasing pilot age are all demonstrated as independent predictors of clinically significant neck pain within the pilot population. High performance aircraft and passenger/cargo aircraft have significantly higher scores likely resulting from increased 1G exposure and time in cockpit/sortie length, respectively. Neck pain has been previously shown as one of the most significant causes of morbidity and time out of work among pilots. These trends of increasing neck pain and its sequelae have tended to affect mission readiness among military and civilian aviators. As also demonstrated in our analysis, age and overall flight hours have been previously associated with aviation-related occupational neck pain (14–16). Our data revealed that most aviators reporting positive symptoms were experiencing mild to moderate disability as a result of their neck pain symptoms (17). Unlike previous analyses, which have primarily focused on evaluation of in-flight symptoms, our analysis is based on the effects of occupational neck pain on the Delivered by Ingentaaviator to: jacob busch and ability to perform standard activi’s lifestyle IP: 185.14.195.104 On: Sat, 16 Jul 2016 07:19:02 ties of daily living. We did not observe a gender differCopyright: Aerospace Medical Association ence among all reported symptom categories; however, women did report more headaches and difficulty with basic driving maneuvers resulting from their neck pain symptoms. Furthermore, pilots of age 30 or greater demonstrated significantly higher morbity in all but two of the symptom categories. Increased pain intensity, decreased sleep quality, and difficulty with driving maneuvers as a result of neck pain were correlated with airframe type (with a higher prevalence in high performance aircraft). Our review of the current literature reveals that previous studies evaluating occupational neck pain in pilots have been primarily focused on in-cockpit symptoms and provocative in-flight maneuvers. These studies have been able to effectively isolate newly implemented flight equipment, such as the joint helmet mounted cuing system and in-flight night vision goggles, that are responsible for increased episodes of debilitating inflight neck pain (11). Furthermore, these studies have elucidated which common in-flight maneuvers (i.e., an over the shoulder “check six” or “forward bend” maneuvers during a 1G load) are associated with in-flight and immediate postflight neck pain (8,9,18). These studies' designs have been instrumental in assisting ergonomic flight equipment design and in targeting the in-cockpit behaviors responsible for pilot morbidity. However, the scope of symptomatic evaluation is limited to in-flight and immediate postflight neck pain. In contrast to these previous evaluations we have attempted to characterize the effect and prevalence of aviation-induced neck pain as it pertains to activities of daily living and general life quality. In 2012, Tucker et al. attempted to determine the predictors of neck pain in fighter pilots (14). This analysis was performed on Australian fighter pilots, similar to our high-performance/high 1G cohort. The results of 4.3 8.3
n.s., 0.91
0.005 27.9 22.3
P-Value Demographic Characteristic
%
P-Value
%
P-Value
%
P-Value
%
P-Value
%
P-Value
%
P-Value
%
Pain or Self Limiting with Recreational Activities 1-3 h of Nightly Sleep Loss Due to Neck Pain Neck Pain with Standard Driving Maneuvers Difficulty Concentrating on Tasks Moderate Intensity Headaches Neck Pain with Daily Grooming or Self-Care Moderate to Severe Baseline Neck Pain
TABLE IV. COMPARISON OF POSITIVE SURVEY RESPONSE RATES BY DEMOGRAPHIC GROUP (RESPONSES IN RELATION TO THE SUBJECTS NECK PAIN SYMPTOMS ONLY).
NECK PAIN PREDICTORS IN PILOTS—LAWSON ET AL.
Aviation, Space, and Environmental Medicine x Vol. 85, No. 12 x December 2014
NECK PAIN PREDICTORS IN PILOTS—LAWSON ET AL. the U.S. Air Force Medical Corps, the U.S. Air Force Office of the this survey-based analysis revealed in-flight neck pain Surgeon General, the Department of the Air Force, the Department of to be positively associated with overall flight hours only. Defense, or the U.S. Government No other demographic parameters were included in the No financial or other conflicts of interest are declared by the authors. No grants or corporate support were used in conducting logistical regression analysis. Notably, of all the studies in this study. This study was approved by the Wilford Hall Medical our literature search that attempted to characterize demoCenter IRB. graphic predictors of neck pain in aviators, no compariAuthors and affiliations: Bryan K. Lawson, M.D., Fortune J. Egbulefu, sons were made to a nonaviator control group and all M.D., Joel W. Jenne, M.D., and Edward R. Anderson, M.D., Department of Orthopaedics and Rehabilitation, San Antonio Military Medical studies were limited to high 1G load fighter pilots. These Center, Ft. Sam Houston, TX; Owen Scott, M.D., Department of Flight analyses fail to provide a broad normalization of neck Medicine, Sheppard Air Force Base, TX; and Rosemarie Ramos, Ph.D., pain prevalence to the nonflying population (6,14,18). M.P.H., Department of Epidemiology and Biostatistics, Wilford Hall Additionally, the majority of aviator types (small aircraft USAF Medical Center, Lackland AFB, TX. and large cargo/passenger airline type) are left out of these analyses, thus limiting their generalizability. Our REFERENCES analysis results have been normalized to determine prev1. Andersen HT. Neck injury sustained during exposure to high-G alence with respect to a nonexposed (nonaviator) control forces in the F16B. Aviat Space Environ Med 1988; 59:356–8. 2. Ang B, Harms-Ringdahl K. Neck pain and related disability in group while including all primary airframes. helicopter pilots: A survey of prevalence and risk factors. Aviat In order to further increase the generalizability of our Space Environ Med 2006; 77:713–9. regression analysis, a broad spectrum of nationalities 3. De Loose V, Van den Oord M, Burnotte F, Van Tiggelen D, Stevens were included in our study. Previous studies have inV, et al. Functional assessment of the cervical spine in F-16 pilots with and without neck pain. Aviat Space Environ Med variably included one specific nationality (i.e., U.S., 2009; 80:477–81. Australian, Dutch, Japanese, and Scandinavian avia4. De Loose V, Van den Oord M, Burnotte F, Van Tiggelen D, Stevens tors) (7,9,14). Attempts to use this data broadly in aviaV, et al. Individual, work-, and flight-related issues in F-16 Delivered by to: jacob pilotsbusch reporting neck pain. Aviat Space Environ Med 2008; tion medicine can be subject to error secondary to Ingenta the IP: 185.14.195.104 On: Sat, 16 Jul 79:2016 779–83.07:19:02 different training requirements, hour restrictions, and Copyright: Aerospace Medical 5. DrewAssociation WE Sr. Spinal symptoms in aviators and their relationship equipment available to these populations. Our group of to G-exposure and aircraft seating angle. Aviat Space Environ multinational pilots were all participating in the same Med 2000; 71:22–30. 6. Hämäläinen O, Vanharanta H, Bloigu R. Determinants of 1Gztraining regimen and using similar operational flying related neck pain: a preliminary survey. Aviat Space Environ systems during our analysis. Med 1993; 64:651–2. This survey-based study did not include any func7. Hämäläinen O, Vanharanta H, Bloigu R. 1Gz-related neck pain: a follow-up study. Aviat Space Environ Med 1994; 65:16–8. tional analyses to detail the degree of impairment sec8. Jones JA, Hart SF, Baskin DS, Effenhauser R, Johnson SL, et al. ondary to the studied occupational exposures. These Human and behavioral factors contributing to spine-based data points are useful when quantifying specific occuneurological cockpit injuries in pilots of high-performance pational limitations related to neck pain in our aviator aircraft: recommendations for management and prevention. Mil Med 2000; 165:6–12. cohort. Future research efforts will include these analy9. Kikukawa A, Tachibana S, Yagura S. G-related musculoskeletal ses to determine the effects of targeted muscle strengthspine symptoms in Japan Air Self Defense Force F-15 pilots. ening exercises, strain-reducing neck and head mounted Aviat Space Environ Med 1995; 66:269–72. equipment, and increased neck support during 1G ma10. Landau DA, Chapnick L, Yoffe N, Azaria B, Goldstein L, Atar E. Cervical and lumbar MRI findings in aviators as a function of neuvers on aviation-related occupational neck pain. aircraft type. Aviat Space Environ Med 2006; 77:1158–61. In conclusion, the results of our study reveal pilot age 11. Lange B, Torp-Svendsen J, Toft P. Neck pain among fighter pilots and primary airframe are independent predictors of after the introduction of the JHMCS helmet and NVG in their environment. Aviat Space Environ Med 2011; 82:559–63. clinically significant neck pain within the professional 12. MacDermid JC, Walton DM, Avery S, Blanchard A, Etruw E, aviation population. Moreover, the results of our multiet al. Measurement properties of the neck disability index: a variate analysis show that the pilot profession regardsystematic review. J Orthop Sports Phys Ther 2009; 39:400–17. less of age, time in cockpit, or airframe has an increased 13. McCarthy MJ, Grevitt MP, Silcocks P, Hobbs G. The reliability of the Vernon and Mior neck disability index, and its validity risk of significant neck pain in comparison to nonaviacompared with the short form-36 health survey questionnaire. tors. These predictors are useful in the evaluation of proEur Spine J 2007; 16:2111–7. fessional aviators by occupational health specialists. The 14. Tucker B, Netto K, Hampson G, Oppermann B, Aisbett B. Predicting neck pain in Royal Australian Air Force fighter results of this analysis will allow clinical stratification of pilots. Mil Med 2012; 177:444–50. professional aviators in order to predict and possibly 15. van den Oord MH, De Loose V, Meeuwsen T, Sluiter JK, Fringsmitigate time out of cockpit and limit overall morbidly. Dresen MH. Neck pain in military helicopter pilots: prevalence Future analyses will be conducted to determine the efand associated factors. Mil Med 2010; 175:55–60. 16. Vanderbeek RD. Period prevalence of acute neck injury in U.S. fectiveness of cervical musculature strengthening, headAir Force pilots exposed to high G forces. Aviat Space Environ gear modification, and lifestyle modifications on neck Med 1988; 59:1176–80. pain in our same pilot cohort. 17. Vernon H, Mior S. The Neck Disability Index: a study of reliability ACKNOWLEDGMENTS The views expressed herein are those of the authors and do not reflect the official policy or position of Wilford Hall Medical Center,
and validity. J Manipulative Physiol Ther 1991; 14:409–15. 18. Wagstaff AS, Jahr KI, Rodskier S. 1Gz-induced spinal symptoms in fighter pilots: operational and individual associated factors. Aviat Space Environ Med 2012; 83:1092–6.
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Demographic and Occupational Predictors of Neck Pain in Pilots: Analysis and Multinational Comparison Bryan K. Lawson, Owen Scott, Fortune J. Egbulefu, Rosemarie Ramos, Joel W. Jenne, and Edward R. Anderson LAWSON BK, SCOTT O, EGBULEFU FJ, RAMOS R, JENNE JW, ANDERSON Our aim is to elucidate the demographic and occupaER. Demographic and occupational predictors of neck pain in pilots: tional predictors of acute neck pain among a comprehenanalysis and multinational comparison. Aviat Space Environ Med sive group of pilots. Furthermore, our objective is to 2014; 85:1185–9. compare these results with respect to pilot nationalities, Objective: This study aimed to elucidate the overall risk and demographic/ occupational predictors of neck pain among professional pilot gender, and pilot age. We postulate Delivered aviators. by Ingentaairframe to: jacobtype, busch Methods: There were 413 surveys characterizing the severity and charIP: 185.14.195.104 On: Sat,that 16 the Jul 2016 07:19:02 increased prevalence of acute occupational neck acter of neck pain symptoms that were administered to a multinational Copyright: Aerospace Medical Association pain is not specifi c to high performance aircraft, but rather cohort of pilots representing 3 separate airframe types. All results were that these trends will be realized throughout the pilot compared to a nonaviator control group. Univariate and multivariate regression analyses were performed to elucidate independent predictors community. Our comparisons were performed on a broad of occupationally related neck pain. Results: Of the surveys, 92% were group of aviators, including small airframe/trainer picompleted and returned. Multivariate analysis reveals that the pilot prolots, high-performance/high 1G pilots, and transport/ fession is independently predictive of increased occupational neck pain passenger aircraft pilots, with international and nonaviasymptoms (OR 1.94, 95% CI 3.72, 1.01). High performance airframes, cargo/passenger airframes, and increasing age were also independent tor control groups to assist in normalizing our results. We predictors of increased neck pain scores (OR 5 3.91, 95% CI 7.10, 2.15; hypothesized that our analysis would establish all airOR 5 3.22, 95% CI 5.83, 1.77; OR 5 4.00, 95% CI 7.43, 2.15, respecframe types and increasing age as independent predictors tively). Conclusions: Our broad, multinational/multi-airframe analysis reof increased occupationally induced neck pain symptoms veals that the pilot profession, most notably high performance and long-haul cargo/passenger airframes, display an increased risk of affecting the individual’s activities of daily living. neck pain symptoms. Keywords: aviators, occupational neck pain, predictors, 1G.
METHODS
T
HE STUDY OF occupational health in aviators presents very specific challenges for military and civilian health professionals. Specifically, trends of acute neck pain have been increasing with the higher performance characteristics of modern era aircraft (5,8,16). These populations have been particularly reticent to fully disclose occupational neck pain symptoms in order to maintain their active flying status. As a result, most scientific evaluations of this target cohort are designed as anonymous questionnaires (2,4,18). The 3-mo period prevalence of occupational acute neck injury has been reported as high as 97% in high performance airframes (8,11). Given the increasingly high prevalence of these symptoms, and their associated impact on the pilots’ mission readiness and ability to perform standard inflight procedures, the majority of these screening studies have focused on this high-performance population (1,3,5). As a result very few analyses have evaluated the prevalence and predictors of these symptoms across a generalizable pilot sample, including larger transport/ passenger aircraft pilots and small personal/trainer aircraft pilots (10).
Institutional Research Review Board (IRB) approval was given at all participating sites prior to proceeding with this survey-based comparative study. Participating sites were screened to ensure a broad cross section of the aviation population would be able to participate in this study. The chosen sites serve as operational and training locations for large cargo/passenger type aircraft, highperformance high positive G-load aircraft, and small trainer/recreational aircraft, thus allowing evaluation of varying degrees of occupational cervical spine stress.
From the Department of Orthopaedics and Rehabilitation, San Antonio Military Medical Center, Ft. Sam Houston, TX; the Department of Flight Medicine, Sheppard Air Force Base, TX; and the Department of Epidemiology and Biostatistics, Wilford Hall USAF Medical Center, Lackland AFB, TX. This manuscript was received for review in June 2014. It was accepted for publication in September 2014. Address correspondence and reprint requests to: Bryan K. Lawson, M.D., Department of Orthopaedics and Rehabilitation, San Antonio Military Medical Center, 3551 Roger Brooke Dr., Ft. Sam Houston, TX; [email protected]. Reprint & Copyright © by the Aerospace Medical Association, Alexandria, VA. DOI: 10.3357/ASEM.4077.2014
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NECK PAIN PREDICTORS IN PILOTS—LAWSON ET AL. Furthermore, these sites serve as concomitant training facilities for all NATO forces, thus allowing comparison between U.S. and International aviator groups. All surveys for the study group were completed during a unit training briefing after adequate instruction on the completion process. All surveys for the control group were completed in a similar manner. Subjects There were 413 surveys administered to the study group (consisting of a multinational cohort of highperformance/high 1G-load aircraft pilots, cargo/ passenger aircraft pilots, and trainer aircraft pilots). For the control group, 57 surveys were administered (nonaviator military officers of similar age and time in service). Survey
TABLE I. POPULATION DEMOGRAPHICS. Study Group Demographic Group Male Female Unknown Gender U.S. Pilot NATO International Pilot Unknown Nationality Trainer/Small Airframe Pilots High-Performance/High 1G Load Airframe Pilots Large Cargo/Passenger Airframe Pilots Unknown Primary Airframe Age 18-24 Age 25-30 Age 31-40 Age 41-50 Age 501 Unknown Age
N
Control Group %
N
%
390 11 12 333 68 12 275 97
94% 3% 3% 81% 16% 3% 67% 23%
48 9 0 -
84% 16% 0% -
29
7%
-
-
0 27 18 10 2 0
0% 47% 32% 18% 3% 0%
12 136 116 111 37 1 12
3% 33% 28% 27% 9% 0.20% 2.8%
Questions on the degree, severity, quality, and character of occupationally related neck pain were based on the Neck Disability Index Questionnaire (NDI) (17). Study group, N 5 413; Control group, N 5 57. Additional inquiries were used in order to assist in demographic characterization of our study and control Delivered by Ingenta to: jacob busch populations. Given the dogmaticIP:assumption that the 185.14.195.104 On: Sat, 16 Jul 2016 07:19:02 The neck disability index scores, stratified by specific Copyright: Aerospace Medical Association aviation population is averse to participation in longitupopulation demographics, are demonstrated in Table II. dinal clinical research for fear of negative professional Analysis with respect to pilot nationality (U.S. versus repercussions, questions were also added to assess the International cohort) and gender did not reveal any stapopulation’s willingness to participate in studies to tistically signifi cant difference in neck pain scores. Howevaluate their chronic musculoskeletal neck pain. Neck ever, our analysis of variance did reveal statistically pain scores greater than 8 were considered clinically sigsignifi cant mean neck pain scores when comparing the nificant symptom profiles for each participant (12,13,17). three differing airframe types, and in our comparison of the four age groups (P , 0.001 for both comparisons) Statistical Analysis (Table II). Three primary statistical analyses were used to charOur logistical regression model was used to further acterize the trends in occupational neck pain present in assess the trends shown in the neck pain scores among our study group. Stata Data Analyses and Statistical our study population. Our multivariate analysis was Software was used for all comparisons and analyses able to determine which of our demographic parame(Stata Corp LP, College Station, TX). In this study ters were independently predictive of higher neck pain P-values less than 0.05 were considered statistically sigscores (Table III). Our overall analysis revealed that the nificant for all analyses and comparisons. pilot profession, regardless of airframe, was independently predictive of increased neck pain scores when 1) Differences in neck pain scores were compared across all demographic parameters (Nationality, Airframe Type, Gender, and Age). compared to a nonaviator control group, as detailed These results were evaluated using Analysis of Variance (ANOVA) below. Only two patient demographics, airframe type to determine statistical significance in these comparisons. and pilot age, were predictive of clinically significant 2) Logistical regression analyses with j option were performed to neck pain without any two-way interactions with determine which demographic characteristics represented independent predictors of clinically significant occupational neck other variables. pain. Regression analysis groups were defined by a cut point As described above, our multivariate analysis was exabove and below a neck pain score of 8 (17). panded to include a comparison of our control group. 3) Cross-tabulation with Chi-squared analysis was used to deterThis comparison displayed an odds ratio of 1.94 when mine which neck pain characteristics and lifestyle limitations were consistently associated with specific demographic groups. For this comparing the clinical risk of increased neck pain in analysis, individual questionnaire inquiries were compared for all aviators in comparison to their matched control group demographic subgroups (Nationality, Airframe, Gender, Age). (P 5 0.04, 95% CI 3.72, 1.01). High-performance/high 1G and large cargo/passenger type primary airframes RESULTS were independently predictive of increased occupational neck pain (OR 5 3.91, 95% CI 7.10, 2.15; P , 0.001 A total of 413 surveys were administered to the study and OR 5 3.22, 95% CI 5.83, 1.77; P 5 0.004, respecgroup with 382 surveys being returned, yielding a 92% tively). In addition, increasing age was determined to participation rate. All surveys administered to the conrepresent an independent predictor per our multivariate trol group were completed and returned. The populaanalysis. Statistically significant increases in aviationtion characteristics of the study and control populations induced neck pain were noted in the 31-40 yr group are demonstrated in Table I. 1186
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NECK PAIN PREDICTORS IN PILOTS—LAWSON ET AL. TABLE II. NECK DISABILITY INDEX SCORE COMPARISONS BY DEMOGRAPHIC CHARACTERISTICS. Mean
Median
SD
50th percentile
75th percentile
U.S. pilots International pilots
4 4
6.2 6.6
6.6 6.8
4 4
10 10
F statistic 5 0.14; P 5 0.71; r2 5 0.0004
Male pilots Female pilots
6.2 7.4
4 6
6.6 6
4 6
10 10
F statistic 5 0.37; P 5 0.54; r2 5 0.0010
5 9.2 7.8 4.2 5 8.6 10.4
2 8 8 2 3 8 8
6 7.2 6.2 4.8 5.6 7.2 9.2
2 8 8 2 3 8 8
8 12 11 6 8 12 16
F statistic 5 15.24; P , 0.001; r2 5 0.008
Trainer/small airframe pilots High performance/high 1G load airframe pilots Large cargo/passenger airframe pilots Age 18-24 Age 25-30 Age 31-40 Age 41-50
F statistic 5 12; P , 0.001; r2 5 0.11
trainer/small airframe cohort). Increasing age was in(OR 5 3.49, 95% CI 6.48, 1.88; P , 0.001) and in the dicative of an increased rate of self-limited participation 41-50 yr group (OR 5 4.00, 95% CI 7.43, 2.15; P , 0.001). in preferred recreational activities (Table IV, P , 0.001). Multivariate analysis of pilot nationality and gender did not show that these demographic characteristics were Finally, of all pilots surveyed, 82% stated that they independent predictors of increased neck pain. would be willing to participate in longitudinal health Comparison of positive survey response rates restudies to evaluate the occupational risks inherent to Delivered by to: jacobcareers. busch This question was phrased to include vealed many statistically significant variations in Ingenta the aviation IP: 185.14.195.104 On: Sat, 16 Jul 2016 07:19:02 lifestyle effects of occupational neck pain within the Medical the possibility of multiple visits and the possible incluCopyright: Aerospace Association various demographic subgroups (Table IV). Regarding sion of laboratory and imaging studies. the intensity of reported cervical pain symptoms, sigDISCUSSION nificantly more international aviators, high performance pilots, and cargo pilots reported moderate to severe This study was conducted to determine the risk and baseline neck pain symptoms (P 5 0.02, P , 0.001, and overall lifestyle effect of occupation-related neck pain P , 0.001, respectively). Furthermore, pilots’ of age 30 inherent to professional aviation career fields. Our primary and greater reported a higher rate of moderate to severe aim was to elucidate the demographic and occupational symptoms at baseline (P , 0.001). predictors of acute neck pain among a comprehensive When compared within their respective demographic group of pilots while comparing these results with resubgroups, the international aviator cohort, high perforspect to pilot nationality, airframe type, gender, and a mance aircraft group, and older age groups (greater ge. We have detailed an increased overall risk of octhan 30 yr of age) reported more difficulty performing cupational neck pain for all aviators regardless of dedaily grooming or self-care tasks secondary to their neck mographic subgroup when compared to nonaviators. pain symptoms (P 5 0.006, P 5 0.049, and P , 0.001, respectively). More women (45% vs. 8% of men) reported moderate intensity headaches directly attributed TABLE III. MULTIVARIATE REGRESSION ANALYSIS TO DETERMINE to their baseline neck pain issues (P , 0.001 for this INDEPENDENT PREDICTORS OF NECK PAIN IN AVIATORS. comparison). Female aviators, high performance pilots, Demographic Characteristic Odds Ratio 95% CI P-Value large airframe/cargo pilots, and older pilots reported exacerbation of their neck pain symptoms with standard All Aviators driving maneuvers (P 5 0.001, P 5 0.001, and P 5 0.003, Non-Aviator Control Group 1.00 respectively). No significant difference in drivingAll Pilots 1.94 (3.72,1.01) 0.04 Pilot Nationality related symptomatic exacerbation was noted between U.S. Aviator Cohort 1.00 the U.S. and international aviator cohorts. International Aviator Cohort 1.00 (1.78,0.56) 0.98 Regarding sleep loss secondary to neck pain sympPilot Gender Male 1.00 toms, 62.5% of high performance pilots and 46.3% of Female 1.47 (2.59,0.83) 0.53 cargo pilots reported at least 1-3 h of sleep lost per night Primary Airframe (P 5 0.003 when compared to the trainer/small airframe Trainer/Small Airframe Pilots 1.00 cohort). Increasing pilot age displayed a higher rate of 3.91 (7.10,2.15) High Performance/High 1G ,0.001 Load Airframe Pilots consistent sleep loss due to cervical pain symptoms (TaLarge Cargo/Passenger 3.22 (5.83,1.77) 0.004 ble IV, P 5 0.002). Airframe Pilots More high performance pilots (54.2%) and large Pilot Age airframe/cargo pilots (32.1%) reported limiting partici18-24 1.00 25-30 1.38 (2.62,0.73) 0.16 pation in their preferred recreational activities due to a 31-40 3.49 (6.48,1.88) ,0.001 frequent exacerbation of neck pain symptoms while per41-50 4.00 (7.43,2.15) ,0.001 forming these tasks (P , 0.001 when compared to the Aviation, Space, and Environmental Medicine x Vol. 85, No. 12 x December 2014
1187
1188
,0.001
10.3 18.8 45.8 55.6
32.1
32.8 36.6 58.5 63.9
0.002
46.3
15.1 18.8 35.5 41.7
0.003
1.6 4.5 0.9 2.8 6.4 8.1 12.1 13.9
n.s., 0.70
0.8 0.7 6.3 15.2
,0.001
0.5
n.s. 5 not significant.
2.4 1.8 11.1 14.0
,0.001
10.7
0.049
28.6
n.s., 0.50
n.s., 0.37
3.1 0.0
n.s., 0.2
7.3 12.5 2.3 5.3
,0.001
3.6
0.003
36.7 62.5 18.6 39.5
0.001
43.7 54.6 0.001 24.5 27.3 n.s., 0.76 2.4 0.0 ,0.001 8.0 45.5 n.s., 0.60 4.5 0.0 n.s., 0.41 6.0 0.0
14.2
,0.001
16.2 54.2
27.5 9.1 n.s., 0.91
n.s., 0.80 42.6 51.0 n.s., 0.06 26.6 14.3 n.s., 0.90 2.5 1.6 n.s., 0.97 9.4 7.8 0.006 4.7 11.5 0.02
Pilot Nationality U.S. Aviator Cohort International Aviator Cohort Pilot Gender Male Female Primary Airframe Trainer/Small Airframe Pilots High-Performance/High 1G Load Airframe Pilots Large Cargo/Passenger Airframe Pilots Pilot Age 18-24 25-30 31-40 41-50
5.0 9.3
Furthermore, large cargo/passenger primary airframes, high-performance/ high 1G load primary airframes, and increasing pilot age are all demonstrated as independent predictors of clinically significant neck pain within the pilot population. High performance aircraft and passenger/cargo aircraft have significantly higher scores likely resulting from increased 1G exposure and time in cockpit/sortie length, respectively. Neck pain has been previously shown as one of the most significant causes of morbidity and time out of work among pilots. These trends of increasing neck pain and its sequelae have tended to affect mission readiness among military and civilian aviators. As also demonstrated in our analysis, age and overall flight hours have been previously associated with aviation-related occupational neck pain (14–16). Our data revealed that most aviators reporting positive symptoms were experiencing mild to moderate disability as a result of their neck pain symptoms (17). Unlike previous analyses, which have primarily focused on evaluation of in-flight symptoms, our analysis is based on the effects of occupational neck pain on the Delivered by Ingentaaviator to: jacob busch and ability to perform standard activi’s lifestyle IP: 185.14.195.104 On: Sat, 16 Jul 2016 07:19:02 ties of daily living. We did not observe a gender differCopyright: Aerospace Medical Association ence among all reported symptom categories; however, women did report more headaches and difficulty with basic driving maneuvers resulting from their neck pain symptoms. Furthermore, pilots of age 30 or greater demonstrated significantly higher morbity in all but two of the symptom categories. Increased pain intensity, decreased sleep quality, and difficulty with driving maneuvers as a result of neck pain were correlated with airframe type (with a higher prevalence in high performance aircraft). Our review of the current literature reveals that previous studies evaluating occupational neck pain in pilots have been primarily focused on in-cockpit symptoms and provocative in-flight maneuvers. These studies have been able to effectively isolate newly implemented flight equipment, such as the joint helmet mounted cuing system and in-flight night vision goggles, that are responsible for increased episodes of debilitating inflight neck pain (11). Furthermore, these studies have elucidated which common in-flight maneuvers (i.e., an over the shoulder “check six” or “forward bend” maneuvers during a 1G load) are associated with in-flight and immediate postflight neck pain (8,9,18). These studies' designs have been instrumental in assisting ergonomic flight equipment design and in targeting the in-cockpit behaviors responsible for pilot morbidity. However, the scope of symptomatic evaluation is limited to in-flight and immediate postflight neck pain. In contrast to these previous evaluations we have attempted to characterize the effect and prevalence of aviation-induced neck pain as it pertains to activities of daily living and general life quality. In 2012, Tucker et al. attempted to determine the predictors of neck pain in fighter pilots (14). This analysis was performed on Australian fighter pilots, similar to our high-performance/high 1G cohort. The results of 4.3 8.3
n.s., 0.91
0.005 27.9 22.3
P-Value Demographic Characteristic
%
P-Value
%
P-Value
%
P-Value
%
P-Value
%
P-Value
%
P-Value
%
Pain or Self Limiting with Recreational Activities 1-3 h of Nightly Sleep Loss Due to Neck Pain Neck Pain with Standard Driving Maneuvers Difficulty Concentrating on Tasks Moderate Intensity Headaches Neck Pain with Daily Grooming or Self-Care Moderate to Severe Baseline Neck Pain
TABLE IV. COMPARISON OF POSITIVE SURVEY RESPONSE RATES BY DEMOGRAPHIC GROUP (RESPONSES IN RELATION TO THE SUBJECTS NECK PAIN SYMPTOMS ONLY).
NECK PAIN PREDICTORS IN PILOTS—LAWSON ET AL.
Aviation, Space, and Environmental Medicine x Vol. 85, No. 12 x December 2014
NECK PAIN PREDICTORS IN PILOTS—LAWSON ET AL. the U.S. Air Force Medical Corps, the U.S. Air Force Office of the this survey-based analysis revealed in-flight neck pain Surgeon General, the Department of the Air Force, the Department of to be positively associated with overall flight hours only. Defense, or the U.S. Government No other demographic parameters were included in the No financial or other conflicts of interest are declared by the authors. No grants or corporate support were used in conducting logistical regression analysis. Notably, of all the studies in this study. This study was approved by the Wilford Hall Medical our literature search that attempted to characterize demoCenter IRB. graphic predictors of neck pain in aviators, no compariAuthors and affiliations: Bryan K. Lawson, M.D., Fortune J. Egbulefu, sons were made to a nonaviator control group and all M.D., Joel W. Jenne, M.D., and Edward R. Anderson, M.D., Department of Orthopaedics and Rehabilitation, San Antonio Military Medical studies were limited to high 1G load fighter pilots. These Center, Ft. Sam Houston, TX; Owen Scott, M.D., Department of Flight analyses fail to provide a broad normalization of neck Medicine, Sheppard Air Force Base, TX; and Rosemarie Ramos, Ph.D., pain prevalence to the nonflying population (6,14,18). M.P.H., Department of Epidemiology and Biostatistics, Wilford Hall Additionally, the majority of aviator types (small aircraft USAF Medical Center, Lackland AFB, TX. and large cargo/passenger airline type) are left out of these analyses, thus limiting their generalizability. Our REFERENCES analysis results have been normalized to determine prev1. Andersen HT. Neck injury sustained during exposure to high-G alence with respect to a nonexposed (nonaviator) control forces in the F16B. Aviat Space Environ Med 1988; 59:356–8. 2. Ang B, Harms-Ringdahl K. 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