1. Background
In a recent review article, the burden of spinal pain in military was outlined (1). A common, painful condition affecting the lower portion of the spine is known as low back pain (LBP). Spinal pain is the most common complaint among soldiers in both operational and nonoperational environments. LBP is the primary condition, accounting for approximately 75% of spinal pain syndromes in military personnel (1). There is evidence of increased risk for spinal pain in an operational setting (2) and LBP is one of the principal reasons for soldiers seeking medical attention, including physical therapy in theaters of operations (3, 4). Furthermore, spinal pain was the fifth leading cause of medical evacuation out of theater in one operation, accounting for 2445 of a total of 34 006 evacuations (7%), and notably, the condition was associated with a low rate of return to duty (5). Therefore, spinal pain contributes considerably to difficulties in keeping the fighting force intact during deployments. The knowledge about risk factors for LBP among the deployed forces is lesser compared to the knowledge about the consequences of spinal pain and LBP during deployments. Soldiers working in some military occupations are more at risk of incurring LBP than others during deployment. A recent study found the highest occurrence of LBP among deployed noninfantry occupations such as service/supply and repair/maintenance (6). These occupations often require driving vehicles or continuous heavy lifting of supplies and the personnel are at risk of workplace accidents and prone to remain in awkward positions for extended periods. A survey of 263 soldiers in a Brigade Maneuver Team during their third month of deployment identified lifting tasks and wearing heavy loads as risk factors for musculoskeletal injuries, including LBP (7). A very recent prospective cohort study of demographic and physical risk factors for new-onset LBP among deployed forces identified the following risk factors for LBP: age, wearing body armor, the time spent on walking patrol, and the weight of equipment worn (8). Studies conducted in nonmilitary cohorts have found that psychosocial factors at work might contribute to the occurrence of LBP, but the evidence is still incomplete (9). High rates of psychiatric comorbidity found in veterans and service members with persistent back pain suggest a related etiology, (1) but there is no other research investigating the effect of psychosocial factors on LBP among deployed soldiers. This study was based on data obtained from an occupational medical health surveillance program, initiated by the Iranian Armed Forces Health Service in 2004. The background population for the study consisted of soldiers; they were asked to fill in questionnaires focused on exposures in the deployment area and health outcomes during deployment. This study added to the current knowledge by assessing not only self-reported work-related physical exposures, but also psychosocial exposures and their impacts on LBP complaints during the year in which the deployment took place.
2. Objectives
The purpose of the study was to identify any deployment-related explanatory variables associated with LBP.
3. Patients and Methods
3.1. Study Design and Study Population
The study was designed as a retrospective cohort study and data came from responses to postdeployment questionnaires with emphasis placed on using standardized and validated questions. A total of 3862 military service personnel (study population) were involved in this study. The deployments took place in the period between June 2004 and February 2006. From the defense personnel management system, age, gender, and military rank data for the total study population could be obtained. A questionnaire and a letter providing information about the study were given to all the personnel in the study population. All the participants were asked to give informed consents and answer the questionnaire according to the health surveillance program for the military deployments. Among those eligible for participation, 1506 soldiers filled the questionnaires, giving an average response rate of 37.7%. Because of insufficient completion or missing personal information, 66 questionnaires were excluded. In addition, 30 participants were excluded because of self-disinterest, leaving 1360 participants in the study.
3.2. Covariate Measures
The questionnaire used in the study was based on a questionnaire previously employed in one study (10). It consisted of several sections with questions; the parts pertinent to this study were (1) demographic and personal characteristics (confounders) including age, gender, military rank, partner status (single vs. married), time spent in deployment and self-reported height, and weight; (2) predeployment lifestyle and health; (3) unit affiliation, work-related factors, and factors concerning social support from leaders and colleagues during deployment; (4) exposures potentially associated with LBP during deployment; and (5) health outcomes. The self-reported exposures were assessed on a four-level categorical scale, from “No exposure” to “exposed more than 30 days during the deployment”; the social support variables were assessed on a four-level scale ranging from “never” to “often.” The four-level scale used for assessing exposures was transformed to a binary variable by merging the two lowest values to the value of "exposure < six days" and the two highest to the value “exposure” 6 days. A similar transformation was applied in the case of social support variables.
3.3. Case Definition
The health outcomes part included the standardized Nordic questionnaire (SNQ) for the analysis of musculoskeletal symptoms (11) and this was used to assess the presence of LBP in this study. The outcome LBP was constructed as a categorical variable with an ordered three-value scale based on the following four questions from the SNQ:
(1) What is the total time that you have had LBP during the last 12 months?
(2) Has LBP caused you to reduce your activity during the last 12 months?
(3) What is the total time that LBP has prevented you from doing your normal work during the last 12 months?
(4) Have you been visited by a doctor, physiotherapist, or other such persons because of LBP during the last 12 months? Answer possibilities for (1) and (3) were “0 days”, “1 - 7 days”, “8 - 30 days”, and “more than 30 days”, and for (2) and (4) they were “No” and “Yes”. The scores for the outcome variable LBPs were 0, 1, and 2. The value 0 was assigned if the answers to questions 1 to 4 were either “0 days” or “No”. The value 1 was assigned if the answer to question 1 was “1 - 7 days”, “8 - 30 days” or “more than 30 days”, and the answers to question 2 to 4 were either “0 days” or “No”. The value 2 was assigned if the answer to question 1 was “1 - 7 days”, “8 - 30 days” or “more than 30 days”, and at least 1 of the answers to question 2 to 4 were not “0 days” or “No”. The ordinal scale was constructed to indicate severity, the value 0 meant “no LBP”, 1 meant “LBP with no consequences”, and 2 meant “LBP with consequences”. The consequences were defined as reduced physical activity, reduced capacity for work, or need for treatment.
3.4. Statistical Analysis
As the composition of the study population in terms of age, gender, and military rank was known from the defense personnel management system, it was possible to adjust the population of respondents for potential nonresponse bias by post-stratification (12). The study group was younger with lower ranks compared to the background population of all the soldiers (Table 1). Using age categories and rank as post-stratification variables, a nonresponsive weighting scheme was constructed. In case of a missing value for either age or rank in the study group, only the non-missing variable was applied. In case the participants had filled in neither age nor rank, they were assigned the weight (1). The resulting sampling weights were included in all the statistical models thereby adjusting these for no response. The statistical analyses were performed using odds (ologit command in STATA). Potential confounders and covariates were identified in a priori c2 tests of contingency tables with the explanatory variables in the rows and LBP in the columns. In these initial c2 analyses of associations of covariates with LBP, a binary (not three-valued) categorical LBP variable was used, indicating the presence of LBP (case values 1 or 2) or not (noncase value 0) during the past year. The method of selecting variables for further analysis in OLR models was an adjusted manual strategy based on the method described by Janwantanakul et al. (13) with a cutoff value of P = 0.2 in the c2 tests. All the selected covariates were subsequently analyzed in univariate OLR models adjusted for significant confounders. Finally, all the covariates with P values = 0.2 in the univariate models were analyzed in a multivariate OLS model, where backward elimination was performed until every covariate still in the model had a Wald test P value = 0.2. The level of significance was chosen to be P = 0.05.
Table 1. Demographic Characteristics of the Study Group Compared With the Background Population
aValues are presented as No. (%).
bMissing values are not included in the calculation of percentage.
4. Results
Among the 1360 participants, 350 reported LBP during the past 12 months and were defined as cases; 200 (57.1%) reported LBP for 1 - 7 days, 100 (28.6%) for 8 - 30 days, and 50 (14.3%) for more than 30 days. Of the cases, 112 (32%) reported reduced physical activity, 104 (29.7%) reported sick leave, and 88 (25.1%) reported treatment by doctor or physiotherapist during the past 12 months because of LBP. On the severity scale, 218 (62.3%) were assigned the value 1 (LBP without consequences) and 132 (37.7%) were assigned the value 2 (LBP with consequences). Table 2 shows LBP associations with demographic and individual confounders, i.e. age, rank, marriage, weight, height and body mass index (BMI), and predeployment covariates, i.e. total time spent in previous deployments, back pain in the past (more than one year ago), and smoking history. The following variables were most strongly associated with LBP (cutoff P = 0.20): Age, marriage, height, weight, and BMI. These were included in the subsequent regression models. Table 3 is similar to Table 2, but shows the associations of recorded deployment-related covariates and exposures with LBP. The following deployment-related variables were most associated with LBP (P = 0.20): the duration of deployment, unit affiliation, support from leaders, job satisfaction, psychological stress, poor psychosocial working environment, average length of sleep during the deployment, and change of exercise habits. The following exposures during deployment were most associated with LBP (P = 0.20): whole-body vibrations, heavy lifting, awkward working postures, driving in wheeled armored personnel carrier vehicles, office work, working in depots and storage facilities, and maneuver. There were neither associations between LBP and time spent on physical exercise in the deployment, nor between LBP and accidents because of sport, traffic, or work. Table 4 shows the results of univariate and multivariate analyses. As mentioned above, the outcome variable LBP in these analyses was an ordinal variable, constructed of four central questions on LBP in the SNQ. Cronbach’s alpha for the LBP variable was calculated as 0.76, which was sufficient evidence for the internal consistency of the measure. In the univariate analyses, the following covariates were found to be significantly associated with LBP: age, support from leaders, psychological stress, poor psychosocial working environment, whole-body vibrations, heavy lifting, awkward working positions, working in depots or storehouses, and maneuver exposure. In a final multivariate model, after back-ward elimination, only age, support from leaders, psychological stress, exposure for awkward working positions, and working in depots or storehouses remained significantly associated with LBP.
Table 2. Demographic and Individual Confounders and Predeployment Covariates to Low Back Pain Stratified by Outcomea
| Covariate | No LBP | LBP | P Value |
|---|---|---|---|
| Age group, y b | 0.017 | ||
| < 25 | 420 (79.6) | 108 (20.4) | |
| 25 - 29 | 268 (72.4) | 102 (27.6) | |
| 30 - 39 | 172 (69.9) | 74 (30.1) | |
| > 39 | 100 (63.3) | 58 (36.7) | |
| Military rank b | 0.269 | ||
| Private | 400 (74.9) | 134 (25.1) | |
| NCO/officer | 184 (69.7) | 80 (30.3) | |
| Cohabitation b | 0.061 | ||
| Married | 400 (69.7) | 174 (30.3) | |
| Single | 540 (76.3) | 168 (23.7) | |
| Total time deployed, y b | 0.321 | ||
| < 5 | 544 (75.1) | 180 (24.9) | |
| 5 ≤ 10 | 252 (73.6) | 126 (26.4) | |
| 10 ≤ 15 | 72 (65.5) | 38 (34.5) | |
| 15 ≤ 20 | 42 (87.5) | 6 (12.5) | |
| Back pain in the past b | 0.805 | ||
| No | 608 (74.3) | 210 (25.7) | |
| Yes | 334 (75.2) | 110 (24.8) | |
| History of smoking b | 0.570 | ||
| Never smoked | 356 (74.2) | 124 (25.8) | |
| Ex-smoker | 82 (68.3) | 38 (31.7) | |
| Smoker | 150 (70.6) | 104 (29.4) | |
| Weight, kg c | 82.5 ± 12.7 | 83.4 ± 11.8 | 0.420 |
| Height, cm c | 181.7 ± 7.4 | 180.5 ± 7.6 | 0.060 |
| BMI, kg/m2 c | 25.0 ± 3.2 | 25.6 ± 3.1 | 0.030 |
aAbbreviations: OLR = ordinal logistic regression.
bValues are presented as No. (%).
cValues are presented as mean ± SD.
Table 3. Deployment-Related Covariates of Low Back Pain (LBP) Stratified by Outcome Including Administrative, Psychosocial and Physical Activity and Work-Associated Exposure Variablesa
| Covariate | No LBP | LBP | P Value |
|---|---|---|---|
| Duration of deployment, y b | 10 ± 0.15 | 11 ± 0.15 | 0.100 |
| Unit affiliation c | 0.128 | ||
| Infantry | 464 (76.6) | 142 (23.4) | |
| Engineer/CIS | 84 (71.2) | 34 (28.8) | |
| Logistics/medical | 144 (75.8) | 46 (24.2) | |
| Staff/administration | 66 (60.0) | 44 (40.0) | |
| Supply/maintenance | 252 (75.0) | 84 (25.0) | |
| Social support from colleagues c | 0.798 | ||
| Often/sometimes | 796 (73.0) | 294 (27.0) | |
| Rarely/never | 144 (74.2) | 50 (25.8) | |
| Colleagues willing to listen to your problems c | 0.902 | ||
| Often/sometimes | 846 (73.3) | 308 (26.7) | |
| Rarely/never | 90 (72.6) | 34 (27.4) | |
| Social support from leaders c | 0.023 | ||
| Often/sometimes | 692 (75.9) | 220 (24.1) | |
| Rarely/never | 244 (67.0) | 120 (33.0) | |
| Leaders willing to listen to your problems c | 0.027 | ||
| Often/sometimes | 796 (75.2) | 254 (24.8) | |
| Rarely/never | 162 (65.3) | 86 (34.7) | |
| Job satisfaction c | 0.146 | ||
| Very satisfied | 250 (74.0) | 88 (26.0) | |
| Satisfied | 640 (74.3) | 222 (25.7) | |
| Unsatisfied/very unsatisfied | 48 (60.0) | 32 (40.0) | |
| Exposure for psychological stress c | 0.000 | ||
| No | 602 (79.2) | 158 (20.8) | |
| Yes | 334 (64.2) | 186 (35.8) | |
| Exposure for poor psychosocial working environment c | 0.005 | ||
| No | 828 (75.4) | 270 (24.6) | |
| Yes | 98 (60.5) | 64 (39.5) | |
| Average length of sleep per night during the deployment, h c | 0.090 | ||
| 6 | 336 (69.4) | 148 (30.6) | |
| > 6 | 576 (75.6) | 186 (24.4) | |
| Change of exercise habits during the deployment c | 0.188 | ||
| Same as before deployment | 380 (74.2) | 132 (25.8) | |
| Less exercise | 210 (67.3) | 102 (32.7) | |
| More exercise | 324 (75.4) | 106 (24.6) | |
| Hours spent on exercise per week during deployment, h c | 0.346 | ||
| 1 - 2 | 322 (70.9) | 132 (29.1) | |
| None | 74 (74.0) | 26 (26.0) | |
| 3 - 4 | 214 (68.6) | 98 (31.4) | |
| > 4 | 286 (76.9) | 86 (23.1) | |
| Accidents because of sport during the deployment c | 0.747 | ||
| None | 910 (74.0) | 320 (26.0) | |
| 1 accident | 88 (75.9) | 28 (24.1) | |
| > 1 accident | 12 (85.7) | 2 (14.3) | |
| Accidents because of work during the deployment c | 0.493 | ||
| None | 888 (75.0) | 296 (25.0) | |
| 1 accident | 90 (70.3) | 38 (29.7) | |
| > 1 accident | 32 (66.7) | 16 (33.3) | |
| Accidents because of traffic during the deployment c | 0.690 | ||
| None | 950 (74.1) | 332 (25.9) | |
| 1 accident | 46 (74.2) | 16 (25.8) | |
| > 1 accident | 14 (87.5) | 2 (12.5) | |
| Exposure for whole-body vibrations c | 0.018 | ||
| No | 550 (77.0) | 164 (23.0) | |
| Yes | 396 (68.8) | 180 (31.2) | |
| Exposure for heavy lifting c | 0.090 | ||
| No | 568 (76.1) | 188 (23.9) | |
| Yes | 376 (70.2) | 160 (29.8) | |
| Exposure for awkward working positions c | 0.001 | ||
| No | 632 (77.8) | 180 (22.2) | |
| Yes | 312 (65.8) | 162 (34.2) | |
| Exposure for driving tracked armored personnel carrier vehicles c | 0.656 | ||
| No | 548 (72.7) | 206 (27.3) | |
| Yes | 198 (74.2) | 138 (25.8) | |
| Exposure for driving wheeled armored personnel carrier vehicles c | 0.007 | ||
| No | 136 (86.1) | 22 (13.9) | |
| Yes | 808 (71.9) | 316 (28.1) | |
| Exposure for office work in staffs c | 0.003 | ||
| No | 630 (77.0) | 188 (23.0) | |
| Yes | 296 (66.2) | 150 (33.8) | |
| Exposure for working in depots or storehouses c | 0.003 | ||
| No | 886 (74.0) | 312 (26.0) | |
| Yes | 26 (48.1) | 28 (51.9) | |
| Exposure for repair/maintenance in garage c | 0.531 | ||
| No | 628 (73.9) | 222 (26.1) | |
| Yes | 286 (71.5) | 114 (28.5) | |
| Exposure for maneuver c | 0.014 | ||
| No | 692 (75.7) | 222 (24.3) | |
| Yes | 220 (65.9) | 114 (34.1) |
aAbbreviation: LBP, low back pain.
bValues are presented as median ± SD.
cValues are presented as No. (%).
Table 4. Univariate and Multivariate Ordinal Logistic Regression (OLR) Models With Low Back Pain as a Dependent Variable
| Covariate a | Univariate Models Where Covariates Are Adjusted for Confounders | Multivariate Model With All Selected Covariates From the Univariate Analysis | Final Multivariate Model | ||
|---|---|---|---|---|---|
| OR (CI)b | P Value | OR (CI) | P Value | OR (CI) | |
| Age group, y c | 0.033 d | 0.164d | |||
| < 25 | 1 (base) | 1 (base) | 1 (base) | ||
| 25 – 29 | 1.40 (0.88 – 2.22) | 0.156 | 1.19 (0.69 – 2.05) | 0.529 | 1.33 (0.80 – 2.25) |
| 30 – 39 | 1.72e (1.05-2.82) | 0.032 | 1.30 (0.68 – 2.47) | 0.425 | 1.56 (0.88 – 2.78) |
| > 39 | 2.11e (1.18 - 3.78) | 0.011 | 1.87 (0.82 – 4.24) | 0.135 | 2.36e (1.19 - 4.67) |
| Cohabitation | |||||
| Married | 1 (base) | 1 (base) | 1 (base) | ||
| Single | 0.73 (0.51 – 1.06) | 0.097 | 1.03 (0.65 – 1.64) | 0.879 | 1.03 (0.67 – 1.60) |
| Height | 0.98 (0.96 – 1.00) | 0.099 | 0.99 (0.96 – 1.01) | 0.224 | 0.99 (0.96 – 1.01) |
| Duration of deployment | 1.48 (0.45 – 4.85) | 0.517 | Not included | Not included | Not included |
| Unit affiliation | 0.999d | Not included | Not Included | Not included | |
| Infantry | 1 (base) | ||||
| Engineer/CIS | 1.14 (0.56 – 2.33) | 0.710 | |||
| Logistics/medical | 0.83 (0.46 – 1.51) | 0.541 | |||
| Staff/administration | 1.41 (0.68 – 2.91) | 0.353 | |||
| Supply/maintenance | 0.97 (0.59 – 1.60) | 0.905 | |||
| BMI | 1.04 (0.98 – 1.11) | 0.147 | 1.04 (0.98 – 1.11) | 0.213 | 1.04 (0.98 – 1.11) |
| Social support from leaders c | |||||
| Often/sometimes | 1 (base) | 1 (base) | 1 (base) | ||
| Rarely/never | 1.70e (1.12 – 2.57) | 0.013 | 1.70 (0.87 – 3.33) | 0.120 | 1.69e (1.09 – 2.63) |
| Leaders willing to listen to your problems | Not included | ||||
| Often/sometimes | 1 (base) | 1 (base) | |||
| Rarely/sever | 1.84e (1.13 – 2.98) | 0.014 | 0.97 (0.44 – 2.15) | 0.935 | |
| Job satisfaction | 0.334d | Not included | Not included | Not included | |
| Very satisfied | 1 (base) | ||||
| Satisfied | 1.09 (0.69 – 1.71) | 0.711 | |||
| Unsatisfied/very unsatisfied | 1.69 (0.72 – 3.94) | 0.224 | |||
| Exposure for psychological stress c | |||||
| No | 1 (base) | 1 (base) | 1 (base) | ||
| Yes | 2.11f (1.44 - 3.10) | 0.000 | 1.44 (0.90 – 2.31) | 0.127 | 1.71g (1.14 - 2.56) |
| Exposure for poor psychosocial working environment | Not included | ||||
| No | 1 (base) | 1 (base) | |||
| Yes | 2.08g (1.25 - 3.47) | 0.005 | 1.15 (0.63 – 2.11) | 0.648 | |
| Average length of sleep Per night, h | Not included | Not included | Not included | ||
| 6 | 1 (base) | ||||
| > 6 | 0.87 (0.59 – 1.30) | 0.507 | |||
| Change of exercise habits | 0.268d | Not included | Not included | ||
| Same as before deployment | 1 (base) | ||||
| Less exercise | 1.51 (0.94 – 2.42) | 0.089 | |||
| More exercise | 0.75 (0.47 – 1.19) | 0.221 | |||
| Exposure for whole-body vibrations | Not included | ||||
| No | 1 (base) | 1 (base) | |||
| Yes | 1.77 g (1.20-2.61) | 0.004 | 1.26 (0.76 – 2.09) | 0.361 | |
| Exposure for heavy lifting | Not included | ||||
| Yes | 1 (base) | 1 (base) | |||
| No | 1.70g (1.15 - 2.52) | 0.008 | 0.84 (0.51 – 1.41) | 0.515 | |
| Exposure for awkward working positions c | |||||
| No | 1 (base) | 1 (base) | 1 (base) | ||
| Yes | 2.42f (1.63 - 3.59) | 0.000 | 1.97g (1.19 - 3.26) | 0.008 | 1.98g (1.31 - 2.99) |
| Exposure for driving wheeled armored personnel carrier vehicles | Not included | ||||
| No | 1 (base) | 1 (base) | |||
| Yes | 2.05 (0.94 – 4.48) | 0.071 | 1.50 (0.59 – 3.83) | 0.395 | |
| Exposure for office work | Not included | ||||
| No | 1 (base) | 1 (base) | |||
| Yes | 1.40 (0.90 – 2.19) | 0.137 | 1.27 (0.77 – 2.07) | 0.351 | |
| Exposure for working in depots or storehouses c | |||||
| No | 1 (base) | 1 (base) | 1 (base) | ||
| Yes | 3.53g (1.48 - 8.41) | 0.004 | 2.79e (1.02 - 7.61) | 0.045 | 2.60e (1.04 - 6.53) |
| Exposure for maneuver | Not included | ||||
| No | 1 (base) | 1 (base) | |||
| Yes | 1.60e (1.06 - 2.40) | 0.025 | 1.13 (0.71 – 1.77) | 0.611 | |
aConfounders: age group, cohabitation, height, BMI, and gap time.
bCI, confidence interval.
cCovariates that are significant in the final model are marked with bold types.
dP value for the variable as a whole (all categories).
e0.01 = P < 0.05.
fP < 0.001.
g0.001 = P < 0.01.
5. Discussion
One of the main findings of this study was that risk factors for LBP in a civilian occupational environment were also important in a military operational setting. However, it turned out that a history of LBP was not a risk factor for the condition. It should be stressed that this finding is contradicted by other researches including military and civilian cohorts (14, 15). The increased risk of maneuver and no maneuver injuries in a theater of maneuver did not seem to contribute essentially to the occurrence of LBP in this cohort, i.e. there were no associations with exposure to accidents during the deployment. Exposure to maneuver was associated with LBP in the initial screening of explanatory variables, but after the adjustment for other variables, the association disappeared. The pattern of operations of the Iranian maneuver group was characterized by mounted patrols and not so much strenuous duty involving dismounted maneuver activities, walking patrols, and load carriage. This could explain the stronger influence of no maneuver exposures on LBP. The main physical factors univariate associated with LBP in the study group were whole body vibrations, heavy lifting, awkward working positions, and working in depots or storehouses, with only the two latter variables remaining in the final multivariate model. The findings are in concordance with the findings of MacGregor et al. who demonstrated a higher risk of post-deployment LBP in service supply and maintenance military occupational specialties (MOS) than in infantry in a large cohort of US marines (6). Evidence of the LBP risk of working in an awkward posture was summarized in a systematic review, reporting conflicting evidence for an association with LBP (16). A more recent longitudinal study supported the hypothesis that exposure to awkward positions of the body during work or leisure time was a causal factor of LBP (17). In spite of MOS, soldiers often work with the body bent, twisted or in other awkward postures. It was found that those reporting doing that most and those working in depots had the highest risks of LBP. These findings indicate a role of ergonomics in prevention measures.
In a general population cohort, a positive association between age and LBP was established, but only in males (18). This corresponds well with the results of this study and the study by Roy et al. (8) where older age was found to be a risk factor. The majority of study participants in both studies were males. The psychosocial risk factors of LBP have been studied intensely in civilian cohorts. There are a variety of methodological issues making it difficult to compare results and conclusions from these studies, e.g. the definition of psychosocial variables, reliability, and reproducibility of measurements as well as the definition of outcome. Another study (19) found an effect of low job satisfaction and low workplace social support after reviewing 11 cohort and case-control studies. However, the authors noted that slight chances in the rating system they used could have resulted in a different conclusion. Sterud and Tynes (20) concluded that studies of better quality appeared to associate with low job satisfaction and job stress more consistently with the development of LBP. In this study, low job satisfaction was not a risk factor. A later review study assessing both level of evidence and strength of associations came to the conclusion that there was moderate evidence for no association between social support at work and LBP (9). In this study, there was no effect of social support from colleagues, but perceived lack of support by leaders increased the risk of LBP (adjusted OR = 1.69). In a very recent large prospective study, a low level of supportive leadership was not a significant predictor of LBP (21). The study cohort consisted of a general working population with many different civilian occupations. The results of this study indicated that military leaders could have a role in prevention of LBP. A moderate association between reporting of psychological stress during deployment and LBP was found (adjusted OR = 1.71). In many studies in civilian cohorts, there has been a strong association between self-reported stress and LBP, but in general, the evidence for a causal association has been deemed insufficient (9). In civilian studies, the association between LBP and contaminated drinking water has been documented very well, prolonged consumption of water with 4 ppm fluoride ion and above associated with LBP (22). In another study, drinking excessive black tea and green tea containing significant amounts of fluoride was recognized as a risk factor for LBP (23). Unfortunately, there have been no other military studies directly evaluating this issue. However, there is evidence indicating that mood and anxiety disorders and other psychiatric comorbidity increases the risk of spine pain in military populations (1).
The study group was a self-selected cohort that volunteered to participate in the health surveillance program and the response rate was low. This implied the risk of selection bias. To compensate for this, nonresponse weights were used in the statistical analyses (post-stratification). Because of the low response rate, the study did not try to estimate the incidence or prevalence of LBP in the study group, but with the pos-stratification adjustments, the analyses of associations were found to be valid. Recall bias was possible. The study design did not allow detailed assessment of all the activities of the deployed soldiers. As exposures were evaluated by analyzing the responses to selected questions, there may be risk factors that could have been overlooked. Examples were wearing body armor and weight of equipment worn, which have been identified as risk factors (8). If these factors had been registered and included in the statistical calculations, it would probably have influenced the results. Some limitations of using pain as an outcome must be mentioned. The lack of a standardized approach to measuring severity and frequency of LBP made it difficult to compare studies on the subject. Subjective measures as pain tend to be less reliable in distinguishing between categories such as cases and non-cases. The SNQ instrument is acknowledged as one of the best for evaluating musculoskeletal pain. By using SNQ in this study, it was possible to define cases explicitly and examine associations with risk factors, including psychosocial factors potentially affecting the perception of pain. Another issue pertinent to the case definition was the time of exposures. A participant reported one or more episodes of LBP in the past 12 months (recorded when filling in the questionnaire). Exposures, though, were only registered for the actual deployment time, implying the possibility that relevant exposures in the immediate pre- and post-deployment periods could be missed. To be deployed, the soldiers had to be medically fit and would not go to the theater with significant back pain, and the period after the end of deployment was characterized by vacation and light duties. Therefore, it was assumed that the influences of exposures before and after deployment were limited, but it cannot be ignored.
Risk factors known to be associated with LBP in a civilian occupational environment are also important factors associated with LBP in a military operational setting. In the studied cohort of Iranian soldiers, older age, lack of support from leaders, psychological stress, awkward working positions, and working in depots or storehouses were significantly associated with LBP after adjustment of all other variables. Maneuver and exposure to work, sport, or traffic accidents were not associated with LBP in this study, which was attributed to the characteristics of the actual deployment. Preventive measures should include pre-deployment preparation of leaders to cope with LBP and other musculoskeletal troubles among their subordinates and involve medical personnel, especially deployed physiotherapists, by giving advice to soldiers of different MOS on how to optimize ergonomics at work. Other measures to be considered are pre-habilitation, i.e. strength training, aiming to prevent injuries before the actual occurrence, and physiotherapist-guided, pre-deployment low back training, mimicking the demands of deployment in a given functional role.
