A Retrospective analysis of Five Years Musculoskeletal Injury Data in British Infantry Recruits

The Infantry Training Centre (ITC), Catterick delivers both Phase 1 and Phase 2 training to a maximum of 4,000 recruits per year [1-2]. Combat Infantryman’s Course (CIC) which consist of both phase 1 and phase 2 training. Phase 1, consist of an initial military training lasting for 13 weeks whilst phase 2 consist of infantry specifi c military training lasting a minimum of 14 weeks [3]. CIC is the framework upon which all regular infantry recruit training is based and is the entry point for the British Army Infantry Regiments [2,4-6]. The CIC course is designed to develop soldering skills, army values and lifestyle and turn civilian recruit into a fully qualifi ed infantry soldier prepared for combat operations. The course is both physically and mentally demanding, arduous and stressful in order to prepare the recruits to work effectively in various situations. The completion of CIC training is mandatory for all infantry recruit to progress their infantry career [6].


Introduction
The Infantry Training Centre (ITC), Catterick delivers both Phase 1 and Phase 2 training to a maximum of 4,000 recruits per year [1][2]. Combat Infantryman's Course (CIC) which consist of both phase 1 and phase 2 training. Phase 1, consist of an initial military training lasting for 13 weeks whilst phase 2 consist of infantry specifi c military training lasting a minimum of 14 weeks [3]. CIC is the framework upon which all regular infantry recruit training is based and is the entry point for the British Army Infantry Regiments [2,[4][5][6]. The CIC course is designed to develop soldering skills, army values and lifestyle and turn civilian recruit into a fully qualifi ed infantry soldier prepared for combat operations. The course is both physically and mentally demanding, arduous and stressful in order to prepare the recruits to work effectively in various situations.
The completion of CIC training is mandatory for all infantry recruit to progress their infantry career [6]. Delivered over a minimum of twenty eight weeks, the CIC is considered the most physically arduous and demanding of all initial military training courses in the British Army [1][2][3][4][5][6]. The intensity, volume and frequency of physical activity is greater than that which the majority of recruits have previously been exposed to [1][2][3][4]. Training is designed to develop aerobic fi tness, muscular strength and physical endurance through the progressive delivery of running, resistance training and occupational military tasks [1,2,5,6]. However, it is widely considered that the inability to adapt to rapid increases in high impact physical activity is a key contributory factor in the subsequent development of musculoskeletal injuries (MSKI) [1,7,8].
A study by Sharma et al. [2,6], observed an overall MSKI incidence of 48.6% MSKI in British Infantry recruits at the ITC whilst Robinson et al. [16], later reported an overall incidence as high as 58% for recruits within the same institution. Recently, Heagerty and colleagues [1], observed as many as 39.1% of infantry recruits, undergoing basic training, to report at least one MSKI in the same institution.
Largely attributable to the incidence of MSKI, the medical discharge rate at the ITC has been reported as high as 8% [5], with as many as 33% of recruits discharged prior to completion of the training due to a variety of reasons. These include medical discharge, voluntarily release or professional training failures [6]. The far reaching challenges to organisational effectiveness presented by MSKI are not unique to the British Army but are found to occur across military training establishments globally [1,9,14,22]. Musculoskeletal military training injuries are considered to contribute to morbidity, loss of training time, impaired performance, a strain on resources, reduced manning and in some cases, medical discharge [1,2,5,6,[22][23][24].
Furthermore, the increased burden on the medical chain, temporary downgrade, placement on light duties and potential risk of subsequent medical discharge all impacts upon the supply of trained personnel to the wider British Army [1,2,5,[25][26][27][28][29]. Consequently these injuries have been identifi ed as a threat to organisational effectiveness and productivity and ultimately compromising operational capability [1,2,5,7,22,24].
As potentially career and therefore life changing events, in the physical domain but seen increasingly form a psychological perspective, MSKI can have signifi cant impact on the individuals affected [1][2][3][4][5][6][7][10][11]. The associated costs represent a signifi cant fi nancial consideration and therefore ultimately impact upon military budgets [1,2,5,6,[27][28][29][30]. Although there is a strong global appetite to identify and implement injury prevention strategies, population specifi c data is limited and there fi rmly remains the need to identify effective interventions [7,14]. The accumulation of accurate and meaningful injury data is a prerequisite for identifying injury patterns and prior to determining the direction of subsequent interventions [1,2,5,7,21,[24][25][26][27][28][29][30]. Injury surveillance data is fundamental to evaluation and refi nement of service delivery which in turn underpins a continual commitment to health care governance whilst on-going service evaluation and quality improvement is an imperative refl ected in the Infantry Training Centers' Mission statement [25].

Methods
This is a retrospective study in which injury data were

Data Analysis
All MSKI referred to the PCRF were entered into the password protected database by the Departmental Clinical Administrator. The data were analysed descriptively, with 95% confi dence interval (CI) by site, type, cause, rate and time of presentation. All data were checked independently by the Clinical Administrator as well as three senior members of the physiotherapy management team as to its accuracy prior to analysis. All MSKI data were considered relative to the total annual recruit infl ow to ITC. All recruits entering

Results
4777 MSKI were referred to the PCRF from a total infl ow of 12,501 recruit trainees over fi ve consecutive training years at ITC. The incidence of all reported MSKI sustained by recruits undertaking the CIC varied annually, ranging from 32.5 (95% CI: 30.7-34.4%) to 52.4% (95% CI: 47.9-52.4%) representing a cumulative fi ve year incidence of 38.2 (95% CI: 37.4-39.1%) ( Table 2). Table 2 presents the sub-classifi cation of MSKI as a percentage of the annual MSKI incidence rate, considered as a percentage of recruit infl ow over fi ve consecutive training years at the ITC. Overuse excluding (non-stress fracture) MSKI represent a fi ve year incidence rate of 23.9% (95% CI: 23.1-24.6%) of total recruit infl ow. Traumatic injuries represent 8.8% (95% CI: 8.3-9.3%) whilst stress fractures alone represent 5.5% of infl ow (95% CI: 5.14-5.9%). Pre-enlistment injuries equate to a fi ve year cumulative incidence rate of 11.3% (95% CI: 10.7-11.8%). The pathophysiology of stress fractures is such that they may be considered as overuse in causation. Consequently, it may be considered appropriate to combine the incidence of stress fractures with overuse (non-fracture) MSKI. This combined sub-classifi cation of overuse injuries represents a fi ve year cumulative incidence of 29.4%, which equates in practical terms to nearly one in every three recruits sustaining an overuse injury.

Site of injury
The most common reported site for training injuries was the lower limb. The specifi c hierarchical distribution of injury site for the last fi ve training years are shown, with a 95% confi dence interval, in fi gure 1. The fi gure illustrates that MSKI to the ankle and foot (25.1-35.3%) are the most prevalent followed by injuries to the knee (21.0-25.8%) during four consecutive training years, 2012 and 2016. However, in the 2016/17 training year, this was reversed. Notably, injuries to the hip increased (13.1%) whilst MSKI to the calf and shin were seen to reduce (12.0%) as compared to the previous four training years.    Figure 2 describes reported injury causation. Notably, for the four consecutive training years (2012-2016) the MSKI presenting to the PCRF were attributed to a high impact fast pace marching with external load (backpack) called Tabbing. However, conversely traumatic injuries were observed to be the most prevalent identifi able cause of MSKI presented at the PCRF for the 2016/17 training year.

MSKI resulting in Medical Discharge
Annual medical discharge due to MSKI is presented by sub-classifi cation as a percentage of annual and cumulative fi ve year infl ow (  Similarly, a higher injury incidence (60%) was reported in a study of American recruits over a12 week training period.

Discussion
However, professional accountability to meet both internal and external drivers of governance insists that opportunities to drive down injury incidence and enhance service delivery are constantly sought [1,17].
There is some variation in the pattern of annual injury incidence over the last fi ve training years. It is recognized that MSKI are multi-factorial in origin and as such it may be tenuous to attribute a single intervention to either increments or reductions in incidence. However, it may be suggested that targeted injury prevention strategies may have   Insidious in onset, generic, formulaic approaches to address the multi-factorial cause of these injuries have rarely been effective, whilst strategies specifi cally addressing the cause and mechanism of injury have shown to be the most effective [1,10].
Traditionally, a reduction in the total volume of exercising mileage has been the fi rst considered response. A study of US Marine recruits showed that a 40% (22 mile) reduction in running distance was associated with a 54% reduction in stress fracture incidence with no signifi cant change in run times [10].
Similar outcomes were obtained with Australian Army recruits, where running was replaced with a graduated programme of loaded foot marches resulting in a reduction of all lower limb injuries by 43% and more specifi cally a reduction in knee injuries by 53% [10].
Stress fractures, a pathological consequence of the body's inability to dissipate load are considered as a sub-classifi cation of overuse injury. Lower limb stress fracture rates are reported to range globally from 0.8 to 6.9% across initial entry military training populations [1,2,6,17,27,28]. Although it is encouraging that a reduction in annual incidence from a peak of 8.9% down to 4.4% (of total recruit infl ow) has been observed at ITC, focus must be maintained on addressing all sub-classifi cations of overuse MSKI. The incidence of traumatic injuries may be mitigated through education and sound risk assessment.
However, although perhaps considered an unavoidable biproduct of arduous physical activity every effort must also be made to reduce their occurrence. A fi ve year cumulative incidence of 8.8% (95% CI: 8.3-9.3%) of the total recruit infl ow for traumatic injuries was observed in comparison to 23.9% (95% CI: 23.1-24.6%) for all overuse injuries.
As shown in table 3, as much as 21.5% of total infl ow presented with an MSKI by week eight of training. This is similar to observations made in previous studies in which the initial weeks of training were identifi ed as an important area in term of injury prevention [1,2,15,16]. The potential for variation and inconsistency in volume, type, intensity, frequency and consistency of physical activity conducted by recruits prior to enlistment is likely to have considerable bearing on physical conditioning, fi tness and robustness [2,6,7]. Notably, a lack of exposure to physical activity, associated poor baseline fi tness levels as well as inadequate preparation prior to commencing military training have all been identifi ed as risk factors for development of MSKI [1][2][3][4][5][6][7][8].
In addition, to the physical challenges previous studies have suggested that recruits are additionally susceptible to mental stresses due to the impact of re-locating from their previous civilian domestic environment, undergoing arduous training within an unfamiliar environment, a sudden restriction in social freedom as well as periods of sleep deprivation [2,6,31].
These stresses to the new recruit are believed to signifi cantly contribute to the incidence of MSKI within the early part of infantry training [6,31].  This re-distribution of injury incidence in the 2016/17 training year may be, in part, attributed to the introduction of a revised approach to training which in turn might have had a favourable impact on the matching of applied training load to the physical capacity of the recruit. Essentially, the recruits remained in training longer before sustaining an MSKI and consequently had a longer opportunity to develop physically without being distracted by injury. This is particular important for a young adult population who are subject to increased exposure to arduous physical activity whist still physiologically maturing.
As per table 2, an incidence of 23.9% of total infl ow presented with an overuse MSKI. This equated to 77% of all injuries presenting to the Physiotherapy Department, described as either overuse fracture or non-fracture in nature. As mentioned above, in spite of limited knowledge regarding recruits pre-enlistment fi tness, as well as the quality, quantity and nature of their previous physical activity levels, let alone their genetic profi le it is reasonable to suggest that, from a purely physiological perspective, those individuals reporting overuse MSKI found diffi culty coping with the content, type, intensity and volume of the training.
Ultimately, this indicates a mismatch in physical capacity versus applied tissue loading and suggests a requirement to address this balance throughout the course but particularly during the fi rst half of training. Stress fractures and all other (non-stress fracture) overuse injuries are the subclassifi cation of MSKI which have the highest attributable incidence of subsequent medical discharge (Table 4). This further re-iterates the impact that overuse MSKI has had not just on the medical services and training teams but also on the wastage of injured infantry recruits at ITC. Progressive physical loading is recognised as a key component of effective programming from the perspective of both injury mitigation as well as overall development of optimal physical performance. Effective strategies designed to address the prevention of these MSKI would therefore have far reaching effect.
It has been reported that careful modifi cation of risk factors can reduce the incidence of all injuries. Specifi c consideration of the environment (terrain and climate) along with progressive increments in distance, intensity and frequency accompanied by adequate periods for rest and recovery have been advised [8,[18][19][20]23]. This is particularly relevant to those recruits who sustain overuse injuries and serves as a recommended area for consideration in future reviews of the content of infantry training at ITC.
In addition, the fi ve year cumulative incidence of preenlistment injuries (11.3%: 95% CI: 10.7-11.8%) represents a 5 year cumulative incidence of 29.5% among all injuries presenting to the PCRF. This suggests the need for further data analysis in order to investigate the relationship between previous injury, performance and training outcomes. The results of a follow up investigation may have implications on pre-enlistment medical screening criteria.
The prevalence of training injuries observed at ITC is not unique to the British Army. The observations made from this fi ve year analysis are consistent with those reported across other NATO military populations [1][2]10,17,18,20].
The responsibility to investigate and address the cause is fi rmly recognised. Indeed, a sense of urgency is reported, with strong recommendations that proportional attention should be therefore dedicated to the prevention of these potentially reducible injuries [1][2][3][4][5][6][7][8][9][10]22,26,30]. This data has served as a basis for the introduction of a comprehensive service evaluation which in turn provided justifi cation for the introduction of an integrated injury prevention strategy-Project OMEGA [7]. If successful, this initiative could have a favorable impact on injury incidence rates and the associated wastage not least the time lost to training, the accompanying fi nancial implications and ultimately the impact on operational effectiveness. Furthermore, it may represent a mechanism to identify areas for potential improvement to the content and delivery of physical development training within infantry training environments.

Conclusion
This retrospective study highlights the magnitude and impact of MSKI injuries and subsequent attrition on the British Army. It is imperative that meaningful interpretation of data surveillance is used to guide the application of evidence based interventions in order to reduce the incidence of potentially avoidable MSKI. Retrospective analysis of fi ve years of injury data provided baseline data from which a better understanding of injury patterns may be made. The data reported for the 2016/17 training year, represents the lowest injury incidence.
The fi ndings in this paper suggest that Project OMEGA may have positively contributed to the reduction of all MSKI incurred during infantry recruit training. In order to assess the impact of Project OMEGA further data analysis is recommended.