Abstract

Knowledge of injury causes is essential for prevention. To investigate cause coding in service members’ electronic medical records, injury encounters from 2016 to 2019 containing at least one external cause code were analyzed. Approximately 10% of incident injury encounters contained at least one cause code describing the mechanism, activity, or place of occurrence. Less than 2% of overuse injury encounters had a cause code each year, compared to 36.4–44.0% of acute injuries occurring from 2016 to 2019. Cause coding occurred more frequently in records from military facilities compared to outsourced care (p<0.001). Inpatient records were more likely to be cause-coded than outpatient records (p<0.001). More injury encounters in emergency clinics were cause coded (>50%), compared to approximately 7% of primary care and 2% of specialist encounters. In 2019, the leading mechanism was overexertion (19.9%), followed by falls, slips, or trips (18.7%). The primary activity associated with injuries was running (21.1%). Military training ground was the leading place of occurrence (13.0%). Improvements to the quality and quantity of external cause coding in the medical records would provide critical details to inform military injury prevention.

What are the new findings?

From 2016 through 2019, approximately 10% of 1.5 million annual U.S. service member incident injury medical encounters contained external cause codes. Acute injuries were approximately 20 times more likely to receive a cause code than overuse injuries. Causes were less likely to be recorded in outpatient care records and at non-military health care facilities.

What is the impact on readiness and force health protection?

Injuries are the leading reason for service members to seek health care and contribute significantly to military medical non-readiness. Specific and accurate recording of injury cause codes by health care providers establishes and develops a data-informed mechanism for the design, implementation, prioritization, and monitoring of interventions and prevention programs to reduce injury risk among service members.

Background

Injuries have been the leading reason for medical encounters and limited duty among U.S. active duty service members.¹ In 2018, 2 of every 5 medical encounters among service members were due to injury, resulting in over 4.7 million encounters affecting over 675,000 service members.² Military injury surveillance efforts have estimated that injuries annually result in approximately 25 million days of limited duty within the U.S. Army, Navy, Marine Corps, and Air Force.³

U.S. service members receive care for injuries and other health conditions through the Military Health System, which has a dual health care and readiness mission with a focus on promoting and sustaining health.^4,5 As part of a health care encounter, diagnosis and cause codes are entered into electronic medical records by health care providers and, when possible, by medical coders for selected care such as hospitalizations or emergency clinic visits. External cause of injury codes can capture the intent (unintentional or intentional), how the injury occurred (mechanism), the activity at the time of the injury event (activity), and the location where the event occurred (place of occurrence). For injuries, summaries of cause codes from electronic medical records facilitate a data-driven approach and optimize resources by directing efforts to develop relevant injury prevention and treatment plans.^6,7

There is no national requirement to assign external cause of injury codes in medical records,⁸ although the value of injury cause coding to identify intervention opportunities and monitor effects of prevention programs and policies has been noted in International Classification of Diseases, 10th Revision, Clinical Modification coding guidance and previous epidemiological investigations.^8-11 Military leaders recognize that cause information is needed to reduce injuries.^12-14 To date, however, injury cause coding of military medical records remains incomplete.^9,10,15,16

Previous publications have summarized external causes of injury for subsets of U.S. military data.^10,16-18 The purpose of this article is to describe causes of injury for all U.S. service members, from 2016 through 2019, and identify variations in injury cause coding over time and by branch of military service, type of health care visit and facility, and diagnosis category.

Methods

Data consisted of injury medical records maintained in the Defense Medical Surveillance System that were obtained by the authors from the Armed Forces Health Surveillance Division in 2022. Specifically, records were obtained from the Comprehensive Ambulatory/Professional Encounter Record, Standard Inpatient Data Record, and TRICARE Encounter Data Non-Institutional and Institutional files. Prior surveillance analyses indicated that more than 99.5% of incident injury records contained 9 diagnoses or less, therefore 9 diagnosis positions were requested. The records documented ambulatory (outpatient) encounters and hospitalizations (inpatient) that occurred in fixed military medical facilities worldwide and civilian treatment facilities (outsourced care) if reimbursement was sought through the MHS.

The Taxonomy of Injuries¹⁹ was used to identify injuries, from 2016 through 2019, among active component service members in the Army, Navy, Marine Corps, or Air Force. Diagnoses are primarily from ICD-10-CM Chapter 13 (‘M’ codes primarily for micro-traumatic overuse injuries; diseases of the musculoskeletal system and connective tissue) and Chapter 19 (‘S’ and ‘T’ codes for acute injuries; injury, poisoning, and certain other consequences of external causes). Incident injury diagnoses in the primary diagnosis position matching Taxonomy diagnosis codes were included, in accordance with standardized military injury surveillance methodology, excluding codes for subsequent and sequela encounters (i.e., ICD-10-CM codes with D or S suffixes). Incident injuries were the focus of the analysis, given that MHS coding guidance specifies assignment of external cause codes to initial encounters. To identify incident injuries, a 60-day gap-in-care rule was applied by injury type and injured body part, to exclude follow-up visits for the same service members within 60 days.¹⁹

Next, injury medical records containing at least one external cause code in diagnosis positions (1-9) were identified. National Center for Health Statistics categorizations of external cause codes (ICD-10-CM Chapter 20, ‘V’-‘Y’ codes) were adapted for use.²⁰ In alignment with NCHS, a subset of injury diagnosis codes from ICD-10-CM Chapter 19 that describe the injury mechanism were also included as cause codes (T14.91, T15-T19, T36-T65, T71, T73-T76, U07, V00-V99, W00-X58, X71-X83, X92-Y09, Y21-Y33, Y35-Y38). Cause codes of all intentions (unintentional, intentional, assault, legal intervention/war, undetermined) were included. Codes for unspecified mechanisms were identified in accordance with the NCHS-defined ‘Unspecified’ category.²⁰ Given that these codes do not provide actionable information for injury prevention, records that included only these unspecified codes were excluded, but counts are noted in table footnotes. If an unspecified cause code was used in conjunction with a more detailed cause code, the more detailed cause was reported.

Activity codes are ICD-10-CM external cause codes with ‘Y93’ as the first 3 digits in any diagnosis position.^8,21 Similarly, place of occurrence codes are any cause codes with ‘Y92’ as the first 3 digits in any diagnosis position.^8,21 Activity and place of occurrence subsets each have only one Unspecified code, Y93.9 (“Activity, unspecified”) and Y92.9 (“Unspecified place or not applicable”), which were excluded from this analysis in a similar fashion as the unspecified mechanism codes.

The percentage of incident injury records with at least one external cause code are reported by ICD-10-CM chapter, care source (direct or outsourced), visit type (inpatient or outpatient), military treatment facility type (medical center, hospital, or clinic),²² and clinic type (emergency, primary care, specialist). Military treatment facility type for each record was identified by the Defense Medical Information System identifier assigned to the record. For outpatient military treatment facility encounters, Medical Expense and Performance Reporting System codes²³ were also provided and used for categorization into three broad clinical groups: emergency, primary care, and specialist.

Data prior to 2020 are presented in this report, due to the fact that more recent data were affected by pandemic-related changes in service member health care provision and the transition to a new electronic health record, MHS GENESIS.²⁴ Data were not available for four sites—Naval Health Clinic Oak Harbor, Naval Hospital Bremerton, Air Force Medical Services Fairchild, Madigan Army Medical Center—that were the first to transition to GENESIS from 2017 through 2019; these sites were not included in this analysis, due to data completeness concerns related to this initial transition period.

Statistical analyses were conducted in SAS™ version 9.4. Proportions of incident injuries receiving mechanism, activity, or place codes are reported. Chi-square tests were used to evaluate differences in proportions across categories and identify statistically significant temporal trends. This project was reviewed and approved as public health practice by the Defense Centers for Public Health–Aberdeen Public Health Review Board.

Results

From 2016 through 2019, there were 5,973,994 incident medical encounter records for injuries across all services. Only 10.0% of incident injury encounter records (n=594,404) received a cause code (Table 1). Tables 1 and 2 show the numbers and percentages of cause-coded incident injuries.

On average, there were 118,000 total mechanism cause codes assigned to injury records each year (range: 101,281-131,105), including instances in which multiple codes were assigned to the same injury (Table 1). During this period, on average, 7.9% of incident injury records were given a mechanism code, 3.8% received an activity code, and 2.5% received a place of occurrence code annually.

From 2016 through 2019, 9–16% of mechanism cause codes were categorized as Unspecified (e.g., X58.X, “exposure to other specified factors”; Y37.90, “military operations, unspecified”). Likewise, 3–6% of activity codes and 17–22% of place of occurrence codes were Unspecified codes. Unspecified codes are reported in the footnotes of Tables 1 and 2.

Among all services, there were more incident injury records with at least one cause code in later years, increasing from 9.2% in 2016 to 10.3% in 2019 (Table 1, p<0.0001 for all comparisons). Compared to other services, the Army had a higher proportion (range: 10.0-11.7%) of records with at least one cause code (p<0.001).

Incident injury records with ‘S’ and ‘T’ diagnosis codes (predominantly acute injuries) contained at least one cause code over one-third of the time (Table 2) and around 20 times more often than injuries receiving an ‘M’ code (overuse injuries, <2% cause-coded) or other diagnoses (about 1%) (p<0.001). A comparison by care source (Table 2) shows a significantly higher proportion of cause-coded incident injury records at military hospitals and clinics (range: 9.5-10.8%) compared to outsourced care facilities (range: 7.7-8.2%). In addition, inpatient injury records (range: 32.0-40.5%) were more likely to have a cause code compared to outpatient care (range: 9.2-10.3%). Considering treatment facility size, for all services incident injuries treated at military hospitals had the highest proportions of cause-coded records (range: 17.5-19.6%), followed by military medical centers (range: 17.0-19.5%) and clinics (range: 6.1-7.1%). From 2016 through 2019, more than half (range: 53.1-57.1%) of emergency care injury records at military facilities were cause-coded, compared to around 7% from primary care (range: 6.3-7.4%) and less than 3% from specialty care (range: 2.3-2.9%).

After the ICD-10-CM ‘Overexertion’ mechanism cause code was introduced in 2017,¹⁷ the proportion of injury records cause-coded as Overexertion increased significantly (p<0.001), from 16.4% that year to 19.9% in 2019 (Table 3). Overexertion was the leading mechanism of injury in 2018 and 2019. Other frequently coded mechanisms of injury during the 4-year period included “falls/slips/trips” (range: 18.3-23.1%) and “struck by/against” (range: 17.4-21.6%).

Among external cause codes related to activity (Table 4), the most frequently coded activity associated with injury was running (approximately 20% each year), followed by “Other specified” and “Walking/marching/hiking.” The proportion of injuries with activity codes for Walking/marching/hiking increased steadily in the 4-year period, from 7.7% in 2016 to 10.6% in 2019. Frequently coded places of occurrence for injuries (Table 4) were “Military training ground,” “Other specified places,” “Unspecified places in private residences,” and “Other specified sports and athletic areas.”

For all external cause codes, use of ‘Other specified’ codes for mechanism²⁰ (e.g., Other specified child/adult abuse, Other specified foreign body) as well as activity (Y93.83) and place of occurrence (Y92.89) were lower in 2019 compared to 2016 (p<0.001).

Discussion

This is the first comprehensive assessment of ICD-10-CM external cause coding of military electronic injury medical records. Overall, the proportion of injury records with cause coding is small and substantially less than historical military injury hospitalization cause coding rates.²⁵ More frequent and more specific cause coding is needed in outpatient settings, where the majority (99%) of injury treatment occurs.⁹

Cause coding was more common with acute injuries (S and T codes), compared to overuse injuries (M codes). This is not surprising, given that national injury categorization tools focus on acute injuries only.^21,26 Approximately 75% of service member injuries are due to cumulative microtrauma, however, and such injuries are routinely included in injury definitions by sports and occupational medicine experts.²⁷ These overuse injuries, which range from joint pain to Achilles tendonitis and stress fractures, are common in physically active populations and result from often preventable factors such as over-training, over-exertion, repetitive movement, vibration, and prolonged static postures.²⁷ To effectively address military injuries, cause information is needed for both acute and overuse injuries.

Cause coding was also shown to be more common at military treatment facilities, especially hospitals and medical centers. This may be because larger facilities have resources including medical coders who train providers and audit and code records. Emergency care departments, on average, cause coded a much higher proportion of injury records compared to other clinics, with roughly half of injury-related emergency department injury records receiving a cause code. This was consistent across services, suggesting that processes and staffing in emergency care facilitated cause coding.

While assignment of external cause codes is not mandatory in the U.S. or the MHS, annual ICD-10-CM coding guidelines consistently recommend that providers voluntarily report external cause, given its value for injury research and evaluation of prevention strategies.⁸ In addition, the military safety community has recognized the need for injury cause coding to support the systematic identification and mitigation of Department of Defense injuries.^3,13 The small proportion of injury records that are cause-coded, however, represents a challenge for leaders, policy-makers, safety professionals, researchers, public health scientists, and others interested in data-driven injury prevention, since records do not completely reflect the distributions of mechanisms, activities, and places of occurrence for all injuries, in particular overuse injuries. In addition, use of non-specific or ‘Other, specified’ cause codes is high, offering minimal to no value for prevention, monitoring, and treatment.

Limitations of this analysis included use of the first nine diagnoses only, although effects should be minimal, since 99.5% of diagnoses are recorded in the first 9 ‘DX’ fields. An additional limitation was the need to exclude data from four military treatment facilities that were the first to transition the MHS GENESIS records system. Exclusion was necessary to minimize effects of data missingness during the analysis period.

In summary, results indicate that relatively few military injury electronic medical records, overall, receive a cause code of any kind. Next steps for DOD leaders and policy-makers include efforts to improve cause coding, considering suggestions offered by the Centers for Disease Control and Prevention,²⁸ as well as changes to U.S. military medicine policies, procedures, and contracts to increase injury cause coding. CDC recommendations include integration of cause coding into data standards, development of a toolkit on use of cause codes to set priorities and evaluate injury prevention programs, and creation of guidelines and training to instruct health care providers on injury documentation in medical records.28 Providers need support, training, and innovative tools to cause code efficiently and accurately. Ultimately, knowledge of causes is a foundation for the reduction of the burden of injuries on the military medical system and sustainment of military medical readiness.

Author Affiliations

Injury Prevention Branch, Defense Health Agency Public Health–Aberdeen, MD: Dr. Canham-Chervak, Dr. Schuh-Renner, Ms. Rappole; Epidemiology and Analysis Branch, Armed Forces Health Surveillance Division, Public Health Directorate, Defense Health Agency, Silver Spring, MD: Dr. Stahlman; Clinical Public Health and Epidemiology Directorate, Defense Centers for Public Health–Aberdeen: Dr. Jones

Disclaimer

The views expressed in this presentation are those of the authors and do not necessarily reflect the official policy of the Department of Defense, Defense Health Agency, nor the U.S. Government. The mention of any non-federal entity or its products is for informational purposes only, and is not to be construed or interpreted, in any manner, as federal endorsement of that non-federal entity or its products.

References

1. Armed Forces Health Surveillance Division. Absolute and relative morbidity burdens attributable to various illnesses and injuries among active component members, U.S. Armed Forces, 2022. MSMR. 2023;30(6):3-11.
2. Canham-Chervak M, Hauschild V, Schuh-Renner A, Oden K, Jones B. Technical Information Paper, TIP 010-0523: A Standardized Approach to Department of Defense Medical Surveillance of Injuries: Initial Objectives of the Military Injuries Working Group, 2019-2022. Defense Centers for Public Health-Aberdeen, Defense Health Agency, U.S. Dept. of Defense. 2023. Accessed Nov. 2024. https://apps.dtic.mil/sti/trecms/pdf/AD1204754.pdf
3. Ruscio BA, Jones BH, Bullock SH, et al. A process to identify military injury prevention priorities based on injury type and limited duty days. Am J Prev Med. 2010;38(1 suppl):s19-s33. doi:10.1016/j.amepre.2009.10.004
4. Tanielian T, Farmer C. The U.S. Military Health System: promoting readiness and providing healthcare. Health Affairs. 2019;38(8):1259-1267. doi:10.1377/hlthaff.2019.00239
5. Office of the Assistant Secretary of Defense for Health Affairs. Military Health System Strategy, Fiscal Years 2024-2029. Defense Health Agency, U.S. Dept. of Defense. Dec. 12, 2023. Accessed Jan. 15, 2025. https://www.health.mil/referencecenter/publications/2023/12/15/mhs_strategic_plan_fy24_29 
6. Canham-Chervak M, Hooper TI, Brennan FH, et al. A systematic process to prioritize prevention activities sustaining progress toward the reduction of military injuries. Am J Prev Med. 2010;38(1 suppl):s11-s18. doi:10.1016/j.amepre.2009.10.003 
7. Jones BH, Canham-Chervak M, Sleet DA. An evidence-based public health approach to injury priorities and prevention recommendations for the U.S. military. Am J Prev Med. 2010;38(1 suppl):s1-s10. doi:10.1016/j.amepre.2009.10.001 
8. Centers for Medicare and Medicaid Services, National Center for Health Statistics. ICD-10-CM Official Guidelines for Coding and Reporting FY 2023–Updated April 1, 2023 (October 1, 2022-September 30, 2023). U.S. Dept. of Health and Human Services. Updated Apr. 1, 2023. Accessed Nov. 2024. https://www.cms.gov/files/document/fy-2023-icd-10-cm-coding-guidelines-updated-01/11/2023.pdf 
9. Jones BH, Canham-Chervak M, Canada S, Mitchener TA, Moore S. Medical surveillance of injuries in the U.S. military: descriptive epidemiology and recommendations for improvement. Am J Prev Med. 2010;38(1 suppl):s42-s60. doi:10.1016/j.amepre.2009.10.014 
10. Stahlman S, Taubman SB. Incidence of acute injuries, active component, U.S. Armed Forces, 2008-2017. MSMR. 2018;25(7):2-9. 
11. McKenzie K, Fingerhut L, Walker S, Harrison A, Harrison JE. Classifying external causes of injury: history, current approaches, and future directions. Epidemiol Rev. 2012;34:4-16. doi:10.1093/epirev/mxr014 
12. Angello JJ, Smith JW. The military accident and injury prevention challenge: setting a foundation for the future. Am J Prev Med. 2010;38(1 suppl):s212-s213. doi:10.1016/j.amepre.2009.10.019 
13. Gunlicks JB, Patton JT, Miller SF, Atkins MG. Public health and risk management: a hybridized approach to military injury prevention. Am J Prev Med. 2010;38(1 suppl):s214-s216. doi:10.1016/j.amepre.2009.10.017 
14. Schoomaker LE. The U.S. Army medical department commitment to injury reduction. Am J Prev Med. 2010;38(1 suppl):s217. doi:10.1016/j.amepre.2009.10.020 
15. Armed Forces Health Surveillance Center. External causes of traumatic brain injury, 2000-2011. MSMR. 2013;20(3):9-14. 
16. Defense Centers for Public Health–Aberdeen Injury Prevention Branch. U.S. Army Injury Surveillance 2021 Summary. Defense Health Agency, U.S. Dept. of Defense. Feb. 2024. Accessed Jan. 15, 2025. https://ph.health.mil/periodical%20library/cphe-ip-army-injury-surveillance-report-2021.pdf 
17. Canham-Chervak M, Steelman RA, Schuh A, Jones BH. Importance of external cause coding for injury surveillance: lessons from assessment of overexertion injuries among U.S. Army soldiers in 2014. MSMR. 2016;23(11):10-15. 
18. Canham-Chervak M, Rappole C, Grier T, Jones BH. Injury mechanisms, activities, and limited work days in U.S. Army infantry units. US Army Med Dep J. 2018;(2-18):6-13. https://medcoeckapwstorprd01.blob.core.usgovcloudapi.net/pfw-images/dbimages/July-December2018.pdf 
19. Hauschild VD, Schuh-Renner A, McCabe AK, et al, U.S. Army Public Health Center. Public Health Information Paper, PHIP No. 12-01-0717–Fiscal Year 2022 Update: A Taxonomy of Injuries for Public Health Monitoring and Reporting. Defense Centers for Public Health–Aberdeen, Defense Health Agency, U.S. Dept. of Defense. 2021. Accessed Jan. 15, 2025. https://apps.dtic.mil/sti/pdfs/ad1150155.pdf 
20. Hedegaard H, Johnson RL, Garnett MF, Thomas KE. National Health Statistics Reports Number 136: The International Classification Of Diseases, 10th Revision, Clinical Modification (ICD-10-CM) External Cause-of-Injury Framework for Categorizing Mechanism and Intent of Injury. National Center for Health Statistics, Centers for Disease Control and Prevention, U.S. Dept. of Health and Human Services. Dec. 30, 2019. Accessed Jan. 15, 2025. https://www.cdc.gov/nchs/data/nhsr/nhsr136-508.pdf 
21. National Center for Health Statistics. International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM). Centers for Disease Control and Prevention, U.S. Dept. Health and Human Services. Updated Nov. 2022. Accessed Jan. 15, 2025. https://www.cdc.gov/nchs/injury/ice/matrix10.htm 
22. TRICARE. Military Hospitals and Clinics. Defense Health Agency, U.S. Dept. of Defense. Updated Nov. 21, 2024. Accessed Jan. 15, 2025. https://www.tricare.mil/gettingcare/finddoctor/allproviderdirectories/types-of-military-facilities 
23. Defense Health Agency. DHA Procedures Manual: Medical Expense and Performance Reporting System (MEPRS) for Fixed Military Medical and Dental Treatment Facilities. Number 6010.13 (vol 1). U.S. Dept. of Defense. Sept. 27, 2018. Accessed Oct. 2024. https://www.health.mil/reference-center/dha-publications/2018/09/27/dha-pm-6010-13-volume-1 
24. Defense Health Agency. Defense Healthcare Management Systems Fiscal Year 2017 Annual Report. U.S. Department of Defense. Feb. 12, 2018. Accessed Jan. 15, 2025. https://www.health.mil/reference-center/reports/2018/02/12/defensehealthcare-management-systems-fiscal-year-2017-annual-report 
25. Amoroso PJ, Smith GS, Bell NS. Qualitative assessment of cause-of-injury coding in U.S. military hospitals: NATO standardization agreement (STANAG) 2050. Am J Prev Med. 2000;18(3 suppl):174-187. doi:10.1016/s0749-3797(00)00110-0 
26. Hedegaard H, Johnson RL, Garnett MF, Thomas KE. National Health Statistics Report Number 150: The 2020 International Classification of Diseases, 10th Revision, Clinical Modification Injury Diagnosis Framework for Categorizing Injuries by Body Region and Nature of Injury. National Center for Health Statistics, Centers for Disease Control and Prevention, U.S. Dept. of Health and Human Services. Dec. 28, 2020. Accessed Jan. 15, 2025. https://stacks.cdc.gov/view/cdc/100035 
27. Hauret KG, Jones BH, Bullock SH, Canham-Chervak M, Canada S. Musculoskeletal injuries description of an under-recognized injury problem among military personnel. Am J Prev Med. 2010;38(1 suppl):s61-s70. doi:10.1016/j.amepre.2009.10.021 
28. Annest JL, Fingerhut LA, Gallagher SS, et al. Strategies to improve external cause-of-injury coding in state-based hospital discharge and emergency department data systems: recommendations of the CDC Workgroup for Improvement of External Cause-of-Injury Coding. MMWR Recomm Rep. 2008;57(rr-1):1-15. Accessed Nov. 2024. https://www.cdc.gov/mmwr/pdf/rr/rr5701.pdf