In the previous section, we discussed the historical impact of DNBIs during military deployments and how trends related to the impact of disease and NBIs have shifted during recent military conflicts. During contemporary military operations, we have observed that musculoskeletal injuries and conditions have emerged as leading causes for hospitalization and medical evacuation due to DNBIs [2, 14, 15]. An increased emphasis on injury surveillance during and following recent military operations and deployments [12, 14] has resulted in a much clearer picture of the total burden that these NBIs place on military service members and the Military Health System and Veterans Administration as well as the impact they have on military readiness. This section will review the recent literature related to NBI, including data from ODS and other military and humanitarian operations through OIF and OEF.

Writer et al. [14] reported on NBI casualties within the US Army during ODS and other military and humanitarian deployments during the early 1990s . Improved medical surveillance made these data available sooner than they had been during previous military operations; however, in the case of ODS they were still not available for analysis until 3 years following the operation. NBIs were the leading cause of death during ODS with 183 fatalities compared to only 147 due to combat injuries [14, 16]. This may have been due, in part, to the long buildup phase, and relatively short combat phase, during the first Gulf War. During ODS, NBIs and musculoskeletal injuries and conditions were the leading causes of hospitalization, accounting for 25 and 13 % of all hospitalizations, respectively. The most common types of NBIs treated during ODS were primarily acute orthopedic injuries, including fractures, sprains and strains, and joint dislocations among the top four types of injuries treated. The three most common causes of NBI hospitalization during ODS were motor vehicle accidents (4.0/1000 person-years), falls (4.0/1000 person-years), and sports and athletics (3.6/1000 person-years), which accounted for 56 % of all NBI hospitalizations [14]. The authors also reported that injury was also among the leading causes for hospitalization and outpatient visits during deployments to Somalia and Haiti and military exercises in Egypt, where 70 % of all cases were sprains and strains with three quarters being acute injuries and the remaining one quarter being due to chronic conditions or aggravation of a prior injury [14]. Overall, NBIs primarily affecting the musculoskeletal system were a leading cause of both inpatient and outpatient visits during all of these operations .

In contrast to prior military operations, a number of publications documenting the impact of DNBIs during OIF and OEF across the various branches of military service have appeared in the literature [1, 2, 8–12, 15, 17–19]. Additional advances to injury and illness surveillance infrastructure [17, 18] as well as individual efforts by military medical providers have provided more robust data on DNBIs than have been available for previous military deployments. These data have also been available sooner, which has enabled early and ongoing assessments of the impact of NBIs during OIF and OEF. This has also been possible due to the long duration of sustained military operations in Iraq and Afghanistan compared to previous military engagements.

Several studies have examined the frequency and causes of NBIs significant enough to require medical evacuation from Iraq and Afghanistan [9–11, 15, 17, 19]. Most of these studies have relied on data from the US Transportation Command’s (TRANSCOM) Regulating and Command and Control Evacuation System (TRAC²ES), which is used for tracking aeromedical evacuations from theater [17]. The TRAC²ES was developed as an administrative tool to track the movement of military service members requiring medical air evacuation [18]. The system integrates logistical and transportation information as well as clinical decision-support elements in support of the Department of Defense’s medical transportation mission [17]. Data elements from TRAC²ES are now routinely provided for medical surveillance purposes to the Armed Forces Health Surveillance Center via the Assistant Secretary of Defense for Health Affairs, and these data are integrated with data from the Defense Medical Surveillance System [15, 17].

The potential utility of TRAC²ES for medical surveillance among troops deployed in support of OEF and OIF was initially described by Hauret et al. in 2004 [18]. Their preliminary analysis examined medical evacuation data from TRAC²ES for all military personnel that were evacuated from the US Central Command Area of Responsibility (OEF and OIF) between 1 January 2003 and 22 November 2003. The majority of service members medically evacuated during the study period were less than 30 years of age, were in the junior enlisted ranks (E1–E4), and were deployed in support of OIF. Furthermore, nearly half of all medical evacuations during the study period were due to injuries, and over 75 % of those injuries were classified as NBIs. Injuries and musculoskeletal conditions were the leading diagnoses requiring medical evacuation from theater during the study period, accounting for nearly 40 % of all evacuations. In a 10 % random sample (n = 954), the ICD-9-CM codes and patient history text fields in TRAC²ES were reviewed to validate the data in the system and determine causes of injury codes. Overall, there was a high degree of consistency between the data in TRAC²ES and the results from the random sample that was reviewed. Similar to data reported for ODS, the most common causes of NBIs during the study period were (1) falls, (2) motor vehicle accidents, (3) sports and physical training, (4) crushing and blunt trauma, and (5) lifting, pushing, and/or pulling.

A more detailed analysis of medical evacuation data from TRAC²ES among military service members deployed in support of OIF between 1 January 2003 and 31 December 2003, combined with data elements from the Defense Medical Surveillance System, was subsequently published [17]. The results of this study essentially confirmed and extended the preliminary findings reported by Hauret et al. [18]. Nearly 75 % of all medical evacuations from OIF during 2003 occurred during the second and third quarters of the year [17]. The most common reason for medical evacuation was DNBI, which was responsible for 86.5 % of all evacuations from OIF during the study period. Nearly all medical evacuations (94 %) during the study period were classified as routine, suggesting that the patient could safely be evacuated within 72 h of their initial medical encounter [17]. The remaining medical evacuations were classified as priority (4.6 %) requiring transportation with 24 h with minimal delays, or urgent (1.4 %) requiring immediate transport to save life or limb or to prevent serious complications. The leading diagnoses requiring medical evacuation during the study period were injuries and musculoskeletal conditions (40.8 %), similar to the findings reported by Hauret et al. [18] In addition, orthopedic surgical care was the leading specialty care category required to treat the medical conditions of evacuees, when the need for specialty care was evaluated among those requiring medical evacuation from OIF during the study period.

Another study examined combat and DNBI casualties among US Army and marine corps personnel that were significant enough to require hospitalization during the Major Combat Phase, and the subsequent Support and Stability Phase, of OIF [9]. Similar to previous studies, the authors utilized medical evacuation and hospitalization data from TRAC²ES for the Major Combat Phase of OIF (March 21–April 30, 2003); however, they relied on data from the Joint Patient Tracking Application to document casualties during the subsequent Support and Stability Phase of OIF (March 1, 2004–April 30, 2005). While both systems are part of the Theater Medical Information Program-Joint, it is unclear whether data from these two administrative systems are comparable and equally effective for surveillance purposes. Regardless, the study reported some interesting findings. Notably, the phase of OIF was significantly associated with the type of casualties requiring hospitalization during the study period. Specifically, a significantly greater proportion of DNBI casualties were reported during the Support and Stability Phase of OIF (76.4 %) when compared to the Major Combat Phase (63.4 %). Overall, DNBIs accounted for 75 % of all hospitalizations during both phases combined. As reported previously in other studies, the majority of casualties were males (90 %) and serving in the Army (83.5 %); however, those serving in the Marine Corps were more likely to sustain combat-related injuries. Among the DNBIs reported, injury and musculoskeletal conditions were again reported as the leading reasons for hospitalization regardless of phase, and the distributions were similar among males and females.

In a series of follow-up studies [2, 3, 19] to their preliminary work [18], Hauret and colleagues examined the distribution and causes of NBIs significant enough to require medical evacuation from OEF and OIF. They conducted an analysis of medical evacuation data from TRAC²ES among military service members deployed in support of OIF between March 2003 and December 2006 and among service members deployed in support of OEF between October 2001 and December 2006 [2]. They also supplemented the air evacuation data with information obtained from accident investigations and casualty reports. Overall, they reported that 83 % of medical evacuations from OIF and OEF during the study period were due to DNBIs and that 34.8 % of these were due to NBIs compared with 48.2 % that were due to disease. When only examining medical evacuations due to DNBIs, 58 % were due to disease while the remaining 42 % were due to NBIs, with the majority of these injuries impacting the musculoskeletal system. Similar to previous reports, over 90 % of soldiers evacuated for NBIs were males, over half were less than 30 years of age, and most were in the junior-enlisted (OIF) and senior-enlisted (OEF) ranks. The top five diagnostic categories for injuries significant enough to require medical evacuation were (1) fractures, (2) inflammation and pain due to overuse, (3) joint dislocations, (4) sprains and strains, and (5) internal joint derangement [2]. Fractures, joint dislocations, and sprains and strains accounted for over 71 % of all NBIs requiring medical evacuation from OIF and OEF. Notably, all of these diagnoses represent orthopedic injuries affecting the musculoskeletal system. The top five anatomic locations of NBIs significant enough to require medical evacuation from OIF or OEF included the low back and upper and lower extremities, specifically the (1) back, (2) knee, (3) wrist and hand, (4) foot and ankle, and (5) shoulder [2]. Overall, 75 % of all NBIs requiring medical evacuation impacted the upper or lower extremities. Approximately 53 % of all NBIs were documented as acute traumatic injuries, and 28 % were classified as injury-related musculoskeletal conditions. By and large, more than 80 % of all NBIs requiring medical evacuation from theater fell into these two major diagnostic subgroups. The four leading categories for cause of injury requiring medical evacuation for NBIs from OIF and OEF in rank order included: (1) sports and physical training, (2) falls and/or jumps, (3) motor-vehicle-related accidents, and (4) crushing or blunt trauma. It is noteworthy that sports and physical-training-related injuries were the leading causes of medical evacuation for NBIs from both Iraq and Afghanistan during the study period. A follow-up study reported that sports and physical-training-related injuries remained the leading cause of NBIs significant enough to require medical evacuation through 2011 in Iraq and 2012 in Afghanistan [19]. When sports and physical-training-related injuries were examined in this follow-up study, basketball (24 %), physical training (19 %), weightlifting (17 %), and American football (16 %) resulted in the highest proportion of injuries in this category. The most common types of sports-related NBIs requiring medical evacuation were sprains and strains (29 %), fractures (22 %), and joint dislocations (16 %) [19]. Finally, the most commonly affected body parts were the knee (26 %), ankle and foot (15 %), hand and wrist (14 %), and shoulder (14 %) [19]. Another follow-up study [1] reporting on medical evacuation data from Iraq between 2003 through 2011 confirmed and extended many of the findings initially reported by Hauret et al. [2].

Cohen et al. [10] examined medical evacuation data from OIF and OEF and factors associated with return to duty within 2 weeks between January 2004 and December 2007. The authors reviewed medical evacuation data contained in a database maintained by the Deployed Warrior Medical Management Center in Landstuhl, Germany. Similar to previous studies, approximately 75 % of all medical evacuations were due to DNBIs. In each of the 4 years examined during the study period, NBIs affecting the musculoskeletal system were the leading causes for medical evacuation. Approximately 33 % of those medically evacuated from OEF returned to their unit in Afghanistan within 2 weeks of evacuation, and only 21 % of those medically evacuated from OIF returned to their unit within 2 weeks in Iraq [4]. The majority of those returning to duty were medically evacuated for DNBIs, with only 4 % of those sustaining combat injuries returning to duty within 2 weeks. Musculoskeletal injuries and injury-related musculoskeletal conditions were among the leading diagnostic categories that prevented military service members with NBIs from returning to duty within 2 weeks of medical evacuation. Specifically, 87 % of those with musculoskeletal injuries or conditions and 86 % of those with back injuries or pain were unable to return to duty following medical evacuation for NBIs. Overall, military service members who were evacuated due to a NBI that affected the musculoskeletal system were 54 % less likely to return to duty, and those evacuated with back injuries or pain were 59 % less likely to return to duty within 2 weeks of evacuation in multivariable statistical models [10]. The authors noted that the most common NBIs requiring medical evacuation from theater were also the same injuries that were less likely to permit a service member to return to duty following evacuation (e.g., musculoskeletal injuries and conditions, back injuries, and pain). This noteworthy finding has important implications for injury prevention and force health protection among deployed troops.