Article Text
PDF
Abstract
Introduction Non-battle injuries have been the leading cause of medical evacuation in the recent wars in Afghanistan and Iraq. This study investigates the hypothesis, that the occurrence of knee problems could be associated with mounted patrolling in armoured vehicles independent of other risk factors.
Method Retrospective questionnaire-based cohort study of Danish soldiers deployed to Afghanistan during 1 February–31 July 2013.
Results 307 soldiers included. Response rate 70%. 33% reported knee pain. Main finding: Significant association between knee pain and time spent weekly on mounted patrols (OR 1.23, CI 1.07 to 1.41, p=0.003). Controlled for confounders age, body mass index and duration of military employment (OR 1.22, CI 1.06 to 1.41, p=0.006). Adjusted for confounders and all other risk factors (OR 1.25, CI 1.07 to 1.48, p=0.007). The main finding in a subset of the 33% with knee pain: Significant association between more severe knee problems with Knee injury and Osteoarthritis Outcome Score below 400 and time spent weekly on mounted patrols (OR 1.49, CI 1.17 to 1.56, p=0.002).
Conclusions A major concern regarding knee problems among Danish deployed military personnel is identified. The risk of suffering from knee problems and the severity of symptoms increase with the amount of time spent inside a vehicle on mounted patrols.
- ORTHOPAEDIC & TRAUMA SURGERY
- PAIN MANAGEMENT
Statistics from Altmetric.com
Key messages
A major concern regarding knee problems among Danish deployed military personnel is identified.
The risk of suffering from knee problems and the severity of symptoms increase with the amount of time spent inside a vehicle on mounted patrols.
Prevention training programmes or other modalities to prevent knee injuries and other musculoskeletal disorder caused by prolonged mounted patrolling should be developed.
Further knowledge and potential prevention programmes, if successful, will be beneficial to military personnel and to the civilian population.
Introduction
The leading cause of medical evacuation of US military service members during the operations in Iraq and Afghanistan were not injuries sustained in combat but rather disease and non-battle injuries (DNBI) with evacuations attributed to musculoskeletal disorders (MSDs) as the most prevalent.1
Correspondingly, MSDs and musculoskeletal injuries (MSI) were found to be the most common types of casualty (50.4% of DNBI) in a study of a US Army Brigade Combat Team (BCT) deployed to Iraq. Knee injuries or disorders accounted for 13.5% when the MSD and MSI in the study were classified by body location.2
The results of another study of a US Army BCT indicate that non-emergent orthopaedic injuries including knee problems arising in personnel, who complete their deployments, are also a major problem.3
The research done so far documents that MSD and MSI among deployed troops are of concern, but there are few studies which have examined the risk factors for these conditions. One study of patient encounters at the BCT physical therapist revealed that different military occupational specialities (MOS) are preferentially susceptible to different diagnoses and injury mechanisms. Infantry MOS was found to be associated with knee problems. The infantry units operated off the bases wearing individual body armour in mountainous terrain. Many of the soldiers reported a loss of footing during patrols or an exacerbation of a pre-existing condition as a cause of knee pain.4
A similar pattern has been observed in the Danish Battle Group (DBG) deployed to the Helmand Province in southern Afghanistan during the period between 2008 and 2012, where activities comprised of counterinsurgency operations and primarily dismounted patrolling.5
When the operational pattern of the DBG by the spring of 2013 changed towards more mounted patrolling, it was noticed by healthcare personnel at the DBG Medical Centre that soldiers with complaints of knee problems primarily participated in mounted patrols and not in dismounted foot patrols. The senior medical officer, the junior medical officers and the physiotherapist in the DBG observed this independently. Motivated by this unexpected clinical observation, it was decided to conduct a study of risk factors for knee problems among Danish soldiers deployed to Afghanistan, and in particular to investigate the hypothesis that the occurrence of knee problems could be associated with mounted patrolling in armoured vehicles independent of other risk factors.
Participants and methods
This was an epidemiological cohort study of Danish soldiers deployed to Afghanistan from 1 February to 31 July 2013. Eligible for inclusion in the study (study cohort) were soldiers in subunits with tasks mainly outside the bases thus exposed to long hours of mounted patrolling. The units in the DBG selected for participation in the study were the infantry companies, the engineer platoon, the main battle tank (MBT) platoon, the medical platoon, the escort platoon and the special operation platoon. There were no exclusion criteria. The study was designed as a retrospective questionnaire-based investigation, where participants filled in a questionnaire at the end of their tour. The questionnaire consisted of the following sections:
Questions concerning demographic information: Age, rank, body mass index (BMI), gender, unit affiliation, duration of employment in the armed forces, information of deployed job function, weight of equipment and body armour, time spent weekly on dismounted patrols, time spent weekly on mounted patrols, time spent weekly on sport/fitness/weight lifting, running more than 5 h/week (yes/no), doing crossfit more than 5 h/week (yes/no), knee pain in one or both knees within the last 4 weeks (yes/no).
Information on knee problems: Time since the occurrence of knee problem, suspected mechanism of injury, previous surgery, physiotherapeutic care, use of painkillers, number of days with limited duty caused by knee problems.
For subjects reporting knee problems the Knee injury and Osteoarthritis Outcome Score (KOOS) was used. This is a self-administered instrument measuring knee outcome at five levels: pain, symptoms, activities of daily living, function in sport and recreation and knee-related quality of life.6–8 A lower score is associated with a more severe knee injury/problem.
As the study was based only on participants answering questionnaires, evaluation by the Research Ethics Committee was not required according to Danish law. The study protocol was approved by the Danish Data Protection Agency and by the Danish Armed Forces Health Service Institutional Review Board, and participation in the study was voluntary. Before eventually entering the study, participants were given a letter with an invitation to participate, including information on the study and the questionnaire, a proforma for informed consent and a return envelope. Both filling in the questionnaire and signing of the informed consent were required for participation in the study. The questionnaire was anonymous.
Statistical analysis was performed using the open-source R language and environment for data analysis and graphics (R V.2.15.0 (2012-03-30) Copyright 2012 The R Foundation for Statistical Computing). Two outcome measures were analysed in two sets of logistic regression models. The first set included all participants. The outcome measure was the binary variable knee pain (yes/no). The data were analysed in three logistic regression models, an unadjusted model (1.a.) including the independent variables (risk factors): time spent in vehicle, job function, the weight of body armour and equipment, running more than 5 h weekly (yes/no) and doing crossfit more than 5 h weekly (yes/no). A model (1.b.) with same independent variables, but adjusted for the baseline confounders age, BMI and duration of military employment. A model (1.c.) with independent variables as in (2), but adjusted for all other risk factors including time spent weekly on sport/fitness/weight lifting and time spent weekly on dismounted patrols. The second set of models included the subset of participants reporting knee problems. The outcome measure in this part of the analyses was the binary variable KOOS <400, identifying the group with the most severe knee problems. The subgroup data were analysed in two models, (2.a.) an unadjusted model with independent variables as in model 1.a. and an adjusted model (2.b.) with independent variables similar to model 1.b. A significance level of 0.05 was chosen. All models were tested for goodness-of-fit.
Results
The questionnaire was handed out to 307 soldiers in the selected units. Of those, 240 responded, but 25 of the returned questionnaires could not be included in the data analysis because of insufficient completion, giving a final response rate of 70% (215 participants). Demographically, responders were mainly men (97%) and enlisted personnel (76%). The average age of participants was 26 years, and the total service time in the military was on average 4 years. Of the 215 participants, 70 (33%) reported having had knee pain within the last 4 weeks (Table 1).
Demographic data and distribution of risk factors
The main finding in the total population was a significant association between knee pain and time spent weekly on mounted patrols (OR 1.23, CI 1.07 to 1.41, p=0.003) in a logistic regression model with job function in armoured vehicle, weight of equipment, weekly running and weekly crossfit included as independent variables, but otherwise unadjusted. This association remained significant when analysed in a model controlled for the confounders age, BMI and duration of military employment (OR 1.22, CI 1.06 to 1.41, p=0.006) and in a model adjusted for confounders and all other risk factors (OR 1.25, CI 1.07 to 1.48, p=0.007). No associations were found between reporting of knee pain and job function as armoured vehicle commander or driver versus other functions in the vehicle; likewise no association was found to other risk factors such as weight of equipment and body armour, running, doing crossfit or other kind of sports and participating in mounted patrols (Table 2).
ORs for reported knee problems in overall cohort (N=215) by selected risk factors; unadjusted and adjusted regression results
The main finding in the subset of 70 participants with knee pain was the association between more severe knee problems with KOOS score below 400 and time spent weekly in vehicle (OR 1.49, CI 1.17 to 1.56, p=0.002) in a logistic regression model with other risk factors of interest included. Neither associations were found between job function in a vehicle, weight of equipment, running or crossfit, nor were associations found with previous knee injury or surgery. In a model with the confounders age, BMI and duration of employment in the military included, the association between low KOOS score and time spent weekly in vehicle remained significant (OR 1.59, CI 1.21 to 2.20, p=0.002) (Table 3).
ORs for KOOS <400 in KPG (N=70) by selected risk factors
The group with the KOOS below 400 had more treatments by the physical therapist, and used more drugs against pain. There was no difference between the groups with regards to release from duty (Table 4).
Descriptives of knee injured
Discussion
To our knowledge, the association between knee pain and long driving times in a military population has not previously been reported. Our study indicates a likely association between long periods spent inside a vehicle on mounted patrols and increased prevalence of knee pain, both in crude analysis and after adjustment for a large set of potential confounders and risk factors for knee problems.
In 2000, a survey on Danish MBT personnel found that the prevalence of knee pain was increased in the MBT group (41%) compared with other personnel groups, but the association did not remain significant after adjustment for demographic and other variables;9 the MBT personnel included in this study were not subjected to any particular analysis. Our findings suggest that it is not the type of mounted vehicle but how long spent inside that vehicle that could play a role in the development of knee problems. Furthermore, there was no consistent association between knee problems and specific placements/functions inside the vehicles, indicating that in addition to repetitive motions of the lower extremities (as when driving the vehicle), the contribution of other physical factors associated with prolonged driving such as non-neutral/awkward body postures, relative immobilisation of the knees and exposure to local or whole-body vibrations is likely to cause knee pain. Our findings are in accordance with the findings of the previous studies of civilian populations such as truck drivers and taxi drivers.9–11
Theoretically, another reason for knee pain could be that soldiers who spent most of their active working hours inside a vehicle are more likely to over exercise during free hours, but the total hours of exercise were controlled for in this analysis with no correlation, suggesting this is not a contributory factor. The overall 33% prevalence of knee problems among the respondents was high compared with what has been detected previously in Danish deployed personnel (6.8% in Afghanistan and 17% in KFOR in 2010).5 This difference is so large that we believe a real increase has occurred which could be caused by the change in operation patterns towards mounted patrols. However, this result should be interpreted with caution since the risk of selection bias in our study is considerable due to the presumption that knee injured soldiers would be more interested in participating in a knee investigation. The soldiers might feel more encouraged to report knee problems compared with surveys addressing MSIs in general.
The likely association between mounted patrolling/other activities inside vehicles is further strengthened by the fact that we also found a significant association between the severity of knee problems (low KOOS scores) and time spent inside the vehicle.
Although 33% reported knee problems and 11% reported having severe knee problems only 1% were released from duty because of these knee problems during deployment, implying a high working morale among soldiers; alternatively it could represent difficulties in obtaining leave during deployment.
The soldiers with KOOS <400 use more painkillers and consulted a physiotherapist more than the rest of the knee pain group suggesting a potential benefit in preventing severe knee problems by the use of analgesia and resources spent on physiotherapists.
The reported response rate of 78% and the completion rate of 70% are sufficient for this type of study, given that participation was voluntary and uncompensated but the population size was small and the study may have been limited by the shortcomings of a cross-sectional design. There is the possibility of selection bias and we are unable to determine bias regarding the non-responders, suggesting that the findings of this study should be interpreted with caution. The use of a validated questionnaire (KOOS) to evaluate the severity of knee problem, however, has strengthened the strength of the study's conclusions.
Conclusions
This study identifies a major concern regarding knee problems among Danish deployed military personnel though it does not seem to affect the individual soldier's willingness to work during deployment. The risk of suffering from knee problems and the severity of symptoms increases with the amount of time spent inside a vehicle on mounted patrols. In combat environments protection against improvised explosive devices and other actions of war comes first, but it is the responsibility of Danish Armed Forces (DAF) to take all precautions to make sure the health and fitness of deployed soldiers is as good as possible. CPT has developed training programmes for soldiers during predeployment drilling to prevent the non-battle injury. These programmes focus primarily on preventing overuse/fatigue injuries during dismounting patrols with emphasis on functional lower limb exercises and core stability exercise. Since the pattern of fighting in wars for Danish troops is more likely to be mounted than dismounted in the future, and it should be a prioritised task for the DAF and Danish military Centre for Physical Training (CPT) to investigate the findings of this study to develop training programmes or other modalities to prevent knee injuries and other MSD caused by prolonged stay in vehicle.
Since MSD is a major concern in the general population and is widespread in many countries, with substantial costs and impact on the quality of life,11 such knowledge and potential prevention programmes, if successful, will be beneficial to military personnel and to the civilian population.
Footnotes
Contributors CRL is the guarantor of this paper. CRL: substantial contributions to the conception, design of the work, the acquisition and interpretation of data; drafting the work; final approval of the version published. TH: contributions to the design of the work and interpretation of data; revising the work critically for important intellectual content; final approval of the version published. AS: substantial contributions to the analysis and interpretation of data; revising the work critically for important intellectual content; final approval of the version published. LN: substantial contributions to the conception and design of the work and interpretation of data; revising the work critically for important intellectual content; final approval of the version published. All: agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Funding Partly funded by the Danish Armed Forces Health Service.
Competing interests CRL was employed as a reservist in The Danish Armed Forces Health Service at the time this work was conducted. LN was employed in The Danish Army Operative Command at the time this work was conducted.
Provenance and peer review Not commissioned; externally peer reviewed.