What is the risk associated with being a qualified military parachutist?

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1 Occup. Mod. Vol. 49, 3, pp , 1999 Copyright O 1999 Upptncott WBDams & WHOns for SOM Printed In Great Britain. All rights reserved /99 What is the risk associated with being a qualified military parachutist? INTRODUCTION Major M. C. M. Bricknell,* Lieutenant Colonel P. J. Amoroso* and M. M. Yore* *23 Parachute Field Ambulance, Montgomery Lines, Aldershot, Hants GUI3 9PU, UK; * US Army Research Institute of Environmental Medicine, Natick, MA , USA Military parachuting has been recognized as a hazardous activity since it was first introduced In World War II. Other risks associated with military service include actual war-fighting, training with weapons and explosives, operating with armoured vehicles or deployment to climatic extremes. These other hazards should be considered in any assessment of the additional risk associated with military parachuting. The aim of this study was to identify the risk attributable to parachuting amongst US Army enlisted soldiers. This study identified a cohort of infantry soldiers who served between They were separated by receipt of parachute hazardous duty pay. There was a total of 329,794 person-years (PY) available for study of which 18% were in the exposed group. The rate of hospitalization was very similar in both groups [123.9 per 1,000 PYs for the exposed group, 127 in the non-exposed group: relative risk (RR) = 0.98, 95% confidence interval (Cl) = ). The exposed group was 1.49 times (Cl = ) more Ilkety to be admitted as a result of an injury as compared with the non-exposed group. Military parachuting was times (Cl = ) more likely to be the cause of an injury. This study has shown that receipt of hazardous duty pay for military parachuting can be used as a marker in identifying significant additional risks to the health of infantry soldiers associated with military parachuting. This was reflected in an increased incidence of admission for acute injury and musculoskeletal trauma (particularly a trauma pattern associated with parachuting) as a result of military parachuting. Other risks, which are associated with parachute pay, are admission for the effects of heat, battle injury and helicopter accidents. Key words: Military; occupational health; parachuting. Occup. Med. Vol. 49, , 1999 Reaivtd 26 January 1998; accepud in final form 18 June 1998 The views expressed in this paper are those of the authors and do not necesjarily represent UK Ministry of Defence or US Department of Defense policy. Military parachuting has been recognized as a hazardous activity since it was first introduced in World War II. It has not been possible, however, to determine the risk to an individual soldier associated with serving with airborne forces and make a comparison with the risk associated with other military service because the majority of reports available in the medical literature measure risk per descent rather than using individual soldiers or duration of exposure to parachuting as a denominator. Recent injury rates for US parachutists have been Correspondence and reprint requests to: Dr M. C. M. Bricknell, 53 Albany Road, Fleet, Hants GU13 9PU, UK. Tel: (+44) reported as approximately 8.0 injuries per 1,000 aircraft exits. 1 There are many other risks associated with military service that are less well-characterized than military parachuting. Such risks include actual war-fighting, training with weapons and explosives, operating with armoured vehicles or deployment to climatic extremes. These other hazards should be considered in the assessment of the additional risk associated with military parachuting. The armed forces provide free medical care and rehabilitation for soldiers who may be injured during the course of their duties. Furthermore injured soldiers usually remain on full pay until the long-term prognosis is clear. Permanent injury may unfortunately lead to a

2 140 Occup. Med. Vol. 49, 1999 soldier being discharged, though the consequences of this are offset by some degree of disability pension. The consequences to the Army are also important because an injury may result in time away from duty or the loss of a trained soldier. There is no consistent system for grading the severity of injuries and therefore a surrogate is required. Suitable surrogates include primary care consultation, time off work, hospital consultation, hospital admission, medical discharge or death. Each of these has its own methodological shortcomings but in practice the main limitation is the availability and reliability of records. A recent study has been done using records of hospital admissions and medical discharges in the British Army. 2 This study found that there was no difference in hospital admission rates between parachute infantry soldiers as compared with non-parachute infantry. However parachute infantry had a significantly increased risk of medical discharge. This study could only assess risk by means of a comparison of annual rates of admission or discharge rather than duration of exposure. It was considered that a worthwhile international comparison would be a similar study looking at parachute trained soldiers in the US Army to determine whether being trained as a parachute soldier led to an increased overall risk of injury. There are many differences between the US Army and the British Army but a principal difference is the absence of a 'Regimental' system. Thus, in the US Army, an infantry soldier may volunteer to become parachute trained at any point in their career and they are not subsequently tied to this duty (although many do remain in airborne forces). Like the British Army, service with airborne forces is recognized with additional hazardous duty pay. The US Army has recently developed an integrated system of databases, the Total Army Injury and Health Outcomes Database (TAIHOD), 3 which links information from the Defence Manpower Data Centre (DMDC), the Individual Patient Data System (TPDS), the Army Safety Management Information System, the Army Physical Disability Case Processing System, the Army Casualty Information Processing System and the Health Risk Assessment dataset. This system is based at the United States Army Institute of Environmental Medicine. Cohorts of individuals can be defined within each of these datasets by social security number (SSN) and cross-referenced to any other dataset. The actual SSN is encrypted to ensure anonymity. Thus it is possible to create a study population based on a demographic characteristic and then compare rates of events such as hospital admission. This methodology can be further refined to duration of exposure if there is a demographic record to determine presence or absence of exposure. The DMDC records soldiers' employment in accordance with the Military Occupational Classification and Structure (MOS). 4 This defines the exact skills and capabilities required for each job. Each soldier is similarly graded on completion of basic and advanced training. This enables personnel to be matched to employment. The coding system has separate categories for commissioned officers, warrant officers and enlisted soldiers. An individual's MOS may be revised during the course of their career after further training or promotion. This system enables a population with particular skills to be identified. Individuals' records are also annotated if they are in receipt of additional pay for hazardous duty (including parachute pay). All hospitalizations including day-case admissions for Army personnel are recorded in the IPDS. This records demographic data that enables these records to be linked to the DMDC database. The diagnosis is coded in accordance with the International Classification of Diseases, Revision 9 (ICD-9) 5 system. The cause of all admissions for injury is also coded using the NATO coding system STANAG The aim of this study was to identify the risk attributable to parachuting amongst US Army enlisted infantry soldiers. MATERIALS AND METHODS Defining the study population The study was based on a series of searches from the TAIHOD database for the period It was necessary to define a group of comparable soldiers with similar employment and pay scale in whom the principal difference in exposure to risk was military parachuting. It was considered that this cohort should have been exposed to the full range of combat operations and environments (heat, cold, temperate, armour, dismounted, builtup areas) but should have had an equal opportunity of volunteering to undertake training as military parachutists. The most consistent military employment category is infantry soldiers. These are coded by the MOS 1 IB, C, H or M. The definitions for each code are shown in Table 1. These areas of employment were closed to women. All soldiers who volunteer to undertake military parachuting are eligible to receive parachute pay. This is awarded on completion of the course at the Basic Airborne Training School and continues to be paid if the soldier remains on the strength of an airborne unit and performs a minimum number of parachute descents. This was used as a surrogate to record exposure to military parachuting. Thus the study cohort was all soldiers recorded in the DMDC with MOS B, C, H or M during the period This cohort was divided into those in receipt of parachuting hazardous duty pay (exposed) and those not in receipt of this additional pay (non-exposed) according to pay records. The period in each group for each individual was counted by month and then summarized into person-years (PY) of exposure. Defining outcome Outcomes were defined as a record in the IPDS. These were then subdivided by ICD code for principal diagnosis. The hospitalization records for acute injuries and

3 M. C. M. Bricknelt et a/.: Risk associated with being a miitary parachutist 141 Table 1. Definition of MOS codes for Infantry soldiers Code Definition B C H M Infantryman (supervises, leads, or serves as a member of an infantry activity that employs Individual or crew served weapons in support of offensive and defensive combat operations) Indirect fire infantryman (supervises, leads, or serves as a member of a mortar squad, section, platoon. Employs crew and Individual weapons in offensive, defensive and retrograde ground combat tactical operations) Heavy anti-armour weapons Infantryman (supervises, leads, or serves as a member of a crew-served weapon squad, section, or platoon employing heavy arrti-armour crew-served weapons In offensive and defensive combat operations) Fighting vehicle infantryman (supervises, leads, or serves as a member of a fighting vehicle unit or activity employing vehicular and dismounted weapons in combat operations) poisonings (ICD code ) were further separated by STANAG 50 code. RESULTS Table 2 shows comparisons of the demographic data for the exposed and non-exposed groups. All differences between the groups were statistically significant using Chi-squared testing. Infantry soldiers in the exposed group were more likely to be White, ranked E4-E6 and younger than in the non-exposed group. Inevitably there were many more soldiers with MOS M in the non- Table 2. Comparisons between study populations by person/year Characteristic MOS B C H M Ethnic group White Black Hispanic American Indian/Alaskan Asian/Pacific Islandan Other Unknown Rank E1-E3 E4-E6 E7-E9 Unknown Age (yrs) Miscoded Unknown Totals Parachutists' 49, , , , , , , , , , , ,507 30,681 13,262 6,759 3, ,548 % 82.3% 8.2% 8.1% 1.3% 80.8% 9.7% 4.5% 0.6% 1.7% 2.7% 25.6% 65.3% 9.2% 7.6% 51.5% 22.3%.4% 5.5% 1.4% 0.3% 0.1% Non-parachutists" 145, , , , , , , , , , , , , , ,956 55,066 33,746 24,534 10,327 2, , ,246 * Parachutists o soldiers in receipt of parachute pay. b Non-parachuttsts = 3oWlef3 not In receipt of parachute pay. p < 01 for all differences. % 53.8%.4% 8.5% 26.3% 67.9% 21.1% 5.7% 0.7% 1.9% 2.7% 28.3% 60.9% 10.8% 6.8% 45.9%.4% 12.5% 9.1% 3.8% 0.8% 0.2% 0.5% 0.1% exposed group which reflects the lack of armoured vehicles in airborne units. Figure 1 shows the summary flow chart for the analyses. There was a total of 329,794 PYs for study of which 18% were in the exposed group (denned by receipt of parachute pay) and 82% in the non-exposed group. The rate of hospitalization was very similar in both groups [123.9 per 1,000 PYs for the exposed group, 127 in the non-exposed group; relative risk (RR) = 0.98, 95% confidence interval (CI) = ]. Infantry soldiers, in receipt of parachute pay, were 1.49 times (CI = ) more likely to be admitted as a result of an injury as compared with those not receiving parachute pay. Military parachuting was times (CI = ) more likely to be the cause of an injury in the exposed group as compared with the non-exposed group. Table 3 shows a breakdown of hospital admission events by ICD code group and the rate per 1,000 years of exposure. Admission for injury represented 29% of all admissions for the exposed group as compared with 19.2% in the non-exposed group. Parachute infantry overall were less likely to be admitted for conditions other than injuries than the non-exposed group but the difference in relative risk for each ICD group was minimal except for mental disorders (RR = 0.5, CI = ). There were 633 individual ICD-9 diagnoses for hospital admission for the whole study population. Table 4 shows the top diagnoses for hospital admission in the exposed group as compared with the non-exposed group. There is a noticeable difference in the ranking of diagnosis for the non-exposed group though the top 10 diagnoses appear in the top diagnoses for the exposed group except for 'streptococcal sore throat' which is ranked 33 in the exposed group. The most significant differences in risk are for intracranial injury, fracture of ankle, fracture of vertebral column and effect of heat and light. Table 5 shows the STANAG 50 codes for cause of acute hospital admission. Military parachuting was the cause of admission for 26.6% of injuries in the exposed group. Other causes with marked increased relative risks were 'instrumentalities of war enemy', 'excessive heat' and 'rotary wing aircraft other'. The relative effect of parachuting can be determined by subtracting the injuries caused by parachuting from the acute admission rates and then comparing the risk of acute admission

4 142 Occup. Med. vol. 49, 1999 Figure 1. Summary flow chart of analyses (rates per 1000 person years of exposure). Military Occupational Specialty B, C, HorM person years Parachute Pay person years 18.1% Not parachute pay person years 81.9% HospHalisation cases 7378 (123.9) (RR % Cl ) Injury (ICD ) 2165 (36.3) (RR % Q ) Military Parachuting 576 (9.67) (RR.1 95% a ) Not hospftaosation cases (876) Table 3. Analysis of hospital admissions by diagnostic group ICD code group _L HospHalisation cases (126.5) Parachutists* Rate per 1,000 person years Injury (ICD ) 6580 (24.3) Military parachuting 130 (0.48) Non-parBchutlsts b 1 Not hospmafisation cases (873) Rate per 1,000 person years Relative risk 95% confidence limits Injury and poisoning 2, , Diseases of the musculoskeletal system and connective tissue , Diseases of the digestive system , Diseases of the respiratory system , Supplementary classification , Mental disorders , O.58 Infectious and parasitic diseases , Diseases of the genitourinary system , Diseases of the skin and subcutaneous tissue Symptoms, signs and Ill-defined conditions , Diseases of the circulatory system Diseases of the nervous system and 3ense organs , Neoplasms Endocrine, nutritional, metabolic diseases, Immunity disorders Congenital anomalies Diseases of the blood and blood forming organs Miscodings Totals 7, , * Parachutists soldiers In receipt of parachute pay. b Non-parachutists = soldiers not In receipt of parachute pay. 0 Supplementary classification conditions include non-spectflc fottow-up examinations, vasectomy and 'other orthopaedic aftercare'. between the two groups. This reduced the relative risk of acute admission from 1.49 to 1.12 (CI = ). In the exposed group, 54% of the injuries caused by military parachuting were intracranial injuries, fractures of the ankle and fractures of the vertebral column. In the non-exposed group there were 130 acute admissions attributed to military parachuting and the same three diagnoses caused 51% of these admissions. It was also

5 M. C. M. BrickneD et a/.: Risk associated wtth being a mffiary parachutist 143 Table 4. Analysis of hospital admissions by the top diagnoses Parachutists' Non-parachutists b Diagnosis Rate per 1,000 person years Rank Rate per 1,000 person years Rank Relative risk 95% Confidence limits Internal derangement of the knee Other derangment of joint Intracranlal Injury Inguinal hernia Fracture of ankle Adjustment reaction Disorder of tooth development and eruption Alcohol dependence syndrome Other cellulitis and abscess Other disorders of synovium, tendon and bursa Pneumonia unspecified Other disorders of bone and cartilage Other non-infectious gastroenteritis and colitis Fracture of vertebral column without mention of spinal cord injury Other and unspecified disorders of joint Effect of heat and light Fracture of face bones Deviated nasal septum Intervertebral disc disorders Injury, other and unspecified * Parachutists = soldiers In receipt of parachute pay. b Non-parachutists = soldiers not in receipt of parachute pay found that all of this subset of the non-exposed group except four cases had been admitted to hospitals that had reported admissions from military parachuting in the exposed group. DISCUSSION This study demonstrates the utility of TAIHOD for examination of a research question using previously collected data. It is a unique system that allowed a retrospective cohort study to be created from routine military demographic data and then enabled outcomes to be observed using another 'outcomes-based' data set. It was possible to use the entire military population for the sample in this study thus generating a very large sample size. This study relied on accurate capture and coding of routine information but previous experience with this dataset suggests this is reliable. 7 There were many more armoured infantry soldiers (MOS M) in the non-exposed group than the exposed group. This was to be expected as the principal airborne unit, 82nd Airborne Division, has very few armoured vehicles. Soldiers who work with armoured vehicles may be in a hazardous work environment as compared with soldiers who do not, but these vehicles also offer some protection from external hazards. It was felt that infantry soldiers in this environment are not a uniquely selected group and therefore this risk should be included in the comparison. There was a higher proportion of White soldiers in the exposed group as compared with the nonexposed group. This is consistent with results from other studies on ethnic distribution in the US Army (Amoroso , , , PJ, et al. Analysis of military occupational specialities and hospitalisation. 1997, unpublished). Although admission for acute injuries were a significant cause of hospital admissions it should be noted that approximately 70% of admissions in the exposed group and 80% of admissions in the non-exposed group were for other conditions. This would suggest that overall, infantry in receipt of parachute pay are relatively more healthy than other soldiers. Table 3 shows a significant differences in RR for many specific ICD-9 groups including mental disorders. Table 4 shows that parachute trained infantry are significantly less likely to be admitted to hospital for 'adjustment reaction' or 'alcohol dependence syndrome'. Soldiers in receipt of parachute pay will all have attended the Basic Airborne Training School. All soldiers attending this school are medically assessed prior to attendance. This training is physically demanding and thereby introduces a degree of selection based on physical fitness. These factors may explain the increased mean health of the exposed population. In the exposed group, military parachuting was responsible for 26% of acute admissions. The effect is most noticeable in Table 4, which shows the excess preponderance of musculoskeletal injuries as a cause of admission. The relative risk of admission for 'intracranial injury', 'fracture of the ankle' and 'fracture of the vertebral column without mention of spinal cord injury' in the exposed group is substantially higher than in the nonexposed group and this is reflected in the relative rankings. Military parachuting was the reported cause for approximately 50% of these cases in the exposed group, whereas the principal cause in the non-exposed group

6 144 Occup. Med. Vol. 49, 1999 Table 5. Analysis of acute hospitalisations by cause Cause Parachutists* Rate per 1,000 person years Non-parachutists'' Rate per 1,000 person years Relative risk 95% Confidence limits Parachute military aircraft Driver, passenger non military vehicle Athletics and sports Other specified agents Fall/jump different level Guns, explosives Instrumentalities of war enemy Excessive heat Cutting/piercing Instrument Complications medical Fighting Fall/Jump same level Twist, turn, slip (no fall) Driver, passenger military vehicle Sting of venomous arthropod Fire, explosion Ingest toxic substance Incident to military aircraft Falling/projected object/missile Animals Static objects Fall/]ump stairs or ladder Marching/drilling Ill-fitting shoes, clothes Rotary-wing aircraft, other Excessive cold Motor vehicle non-traffic Foreign object body orifice Ughtning/cataclysm Inhale toxic substance Unspecified agent/unknown Lift, push, pull Hot liquids/steam Other Total ,165 Parachutists = soldiers in receipt of parachute pay. b Non-parachutists = soldiers not In receipt of parachute pay. was being involved in a traffic accident in a non-military vehicle or athletics and sports. The associations of the other risks attributable with being in receipt of parachute pay are indirect. US Airborne Forces are the lead element in the US strategic deployment capability that has seen soldiers deployed to the Persian Gulf, Haiti and Somalia during the study period. This is the probable explanation for the increased RR of'instrumentalities of war enemy'. The increased risk of admission due to excessive heat (shown in both Table 4 and Table 5) may be the result of the location of units in hot areas of the USA and the high levels of physical training undertaken by airborne units. The increased risk due to 'rotary wing aircraft' is probably the result of the relative increased use of helicopters in airborne operations as compared with other types of military operations. There were 130 records of soldiers in the non-exposed group being injured as a result of military parachuting. The distribution of injury and the location from which these admissions were reported suggests that these were , truly the result of military parachuting. Therefore there must have been a subset of infantry soldiers who are not recorded as being in receipt of parachute pay but who undertook military parachuting. These represented a very small proportion of the total admissions in the nonexposed group and thus were not a significant source of bias in the study. This study relied on a retrospective analysis of previously collected data. There were inevitably some records that had been mis-coded. Approximately 0.5% of records had illogical or missing ages. There were 0.3% of records mis-coded in the exposed group and 0.7% in the unexposed group. There was one hospital admission in the non-exposed group for a complication of pregnancy, childbirth or the puerperium from a cohort of soldiers who were exclusively male! Overall the substantial majority of the records were internally consistent and there was no evidence of a systematic bias in the data. There is considerable variation in the individual exposure to parachuting ranging from soldiers who perform the minimum number of descents to remain

7 M. C. M. Bricknell et a/.: Risk associated with being a military parachutist 145 eligible for additional pay to jumpmasters whose primary activity is parachuting. It was not possible to examine this issue by use of pay records as a marker. CONCLUSIONS This study has shown that being in receipt of hazardous duty pay for military parachuting is associated with a significant additional risk of injury to infantry soldiers. This risk is reflected in an increased incidence of admission for acute injury, musculoskeletal trauma (particularly a trauma pattern associated with parachuting) and as a result of military parachuting. Other risks which are associated with parachute pay, are admission for the effects of heat, batde injury and helicopter accidents. The US Army has already investigated an outsidethe-boot ankle brace to reduce ankle injuries 8 and has commissioned a research and development project to procure a parachute with a substantially reduced landing velocity as compared with the in-service version. 9 However, until changes in drills and equipment have reduced the additional risk associated with military parachuting to zero, it is appropriate that the risk associated with military parachuting should be recognized. The US Army already has detailed health and safety instructions to reduce the risk of heat injury and helicopter accidents. It is possible that the excess association with these as a cause of admission may be the result of increased exposure rather than failure of protective measures per se. The increased risk of battle injury is almost certainly die result of increased exposure which is one reason why soldiers volunteer for airborne forces. This study did not make complete use of thetaihod facilities. Further work could compare these populations for duration of hospital stay, lost working time, medical disability and death. It would also be possible to set up a case-control comparison of health status using data from individually completed health risk appraisals. This might enable a comparison of risk-taking behaviour to be undertaken on the two groups to see if this might explain the excess risk that remains after removing the effect on military parachuting. TAIHOD provided an ideal mechanism for examination of the occupational risk associated with military parachuting. The ability to link records by a unique, encrypted identifier to outcome databases and the size of the study population make this an exceptional resource for the study of military occupational health. The methodology described in this can be repeated for many other military occupational groups and it is certain to save money in the long term by providing answers to questions that otherwise would have required much greater resources to study. ACKNOWLEDGEMENTS MB was supported in this study by the Drummond Foundation of the Royal Army Medical Corps and the Golden Jubilee Travelling Fellowship from the Society of Occupational Medicine. REFERENCES 1. Craig SC, Morgan J. Parachuting injury surveillance, Fort Bragg, North Carolina, May 1993 to December Milii Med 1997; 162: Bricknell MCM. Is service with the Parachute Regiment bad for your health? Occup Med 1998; 49: Amoroso PJ, Swartz WG, Hoin FA, Yore MM. Total Army Injury and Health Outcomes Database. Natick, MA (USA): US Army Research Institute of Environmental Medicine, Technical Report NoTN97-2, 21 Feb Army Regulation 6-1 Military occupational classification and structure. Washington DC: Headquarters, Department of the Army, 1 July International Classification of Disease, 9th Revision, Clinical Modification. Los Angeles, CA (USA): Practice Management Information Corp, Statistical Classification of Diseases, Injuries and Causes of Death. STANAG 50 MED (Edition 5) (Amendment 2). Belgium: NATO, Amoroso PJ, Bell NS, Jones BH. Injury among female and male army parachutists. Aviat Space Environ Med 1997; 68: Amoroso PJ, Ryan JB, Bickley BT, Leitschuh P, Taylor DC, Jones BH. Impact of an outside-the-boot ankle brace associated with military airborne training. Natick, MA (USA): US Army Research Institute of Environmental Medicine. Technical Report T-95-1, 13 Oct Wallace P. Faster Jump, Lighter Landing. TheWbrrior. Natick, MA (USA): US Army Soldier Systems Command, Sept 1997.

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