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Effectiveness of an external ankle brace in reducing parachuting-related ankle injuries
  1. Rose S Luippold1,
  2. Sandra I Sulsky1,
  3. Paul J Amoroso2
  1. 1ENVIRON International Corporation, Amherst, Massachusetts, USA
  2. 2Department of Clinical Investigation, Madigan Army Medical Center, Tacoma, Washington, USA
  1. Correspondence to Rose S Luippold, Senior Associate, ENVIRON International Corporation, 28 Amity St, Suite 2A, Amherst, MA 01002, USA; rluippold{at}environcorp.com

Abstract

Outside-the-boot parachute ankle braces (PABs) worn during US Army paratrooper training have been shown to reduce the risk of severe ankle injuries. In spite of evidence to the contrary, anecdotal reports continue to suggest increases in risk of other types of injury, and the cost of obtaining and periodically replacing the PAB has been used to justify its discontinued use. The authors identified inpatient and outpatient treatment for injuries during US Army paratrooper training. Those undergoing training during two periods when PAB use was mandated had 40% lower risks of ankle injury (brace I, RR=0.60 (95% CI 0.47 to 0.75); brace II, RR=0.62 (95% CI 0.49 to 0.78)), with no difference in risks of other types of injury. There were no differences in risk of ankle injury during periods when brace use was not mandated. The PAB is safe, effective and cost effective.

  • Epidemiology
  • risk factors
  • injury
  • military personnel
  • aviation
  • evaluation
  • occupational

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Introduction

Ankle injuries account for 30–60% of parachuting-related injuries in the military, with the estimated incidence from 1 to 4.5 per 1000 jumps.1–6 They result in substantial direct and indirect medical costs and have a negative impact on soldiers' well-being, and possibly on their career progression. An outside-the-boot parachute ankle brace (PAB) was developed to reduce risk of ankle injuries. It was tested in a small, randomised trial, conducted at the US Army Airborne School (Fort Benning, Georgia, USA) in October 1993.7 The trial demonstrated that the PAB reduced ankle sprains among 745 trainees by 85%. By 1994 all trainees at the school were required to use the PAB.

In October 2000, financial concerns and anecdotal reports of increases in complicated entanglements, as well as injuries to other parts of the lower body led to discontinuation of PAB use.3 Concerns about increases in non-ankle injuries were allayed by a study of hospitalisations among US Army Airborne trainees.8 Use of the PAB appeared to reduce risk of severe ankle injuries without increasing risk of other types of traumatic injury, and medical costs avoided far exceeded the cost of acquiring the braces. These results contributed to the decision to reintroduce the PAB in July 2005; they were used until late 2006, then again discontinued for reasons of cost and renewed suspicion that risk of other injuries was increased with PAB use. Subsequent reports by Knapik et al3 9 corroborated previous observations that PAB wearers were at reduced risk of ankle injury. A recent review10 concludes that the PAB (at a cost of US$28.50 each) is effective in reducing both ankle injuries and medical and personnel costs.

This study improves the Knapik et al investigations3 9 by extending the risk period, and is an extension of the Schmidt et al8 investigation that additionally evaluates injuries treated in outpatient settings. It includes all US Army Airborne trainees who commenced Jump School on or after 1 October 1998, covering 8.5 months of brace use after their reintroduction in 2005. The aims of this study are to determine if previous observations that the brace protects against severe ankle injuries would be repeated and to investigate possible differences in the value of the PAB as a protective device for less severe injuries than previously considered.

Methods

Outcome and covariate data were from the Total Army Injury and Health Outcomes Database, which includes biannual updates to demographic and occupational information from the Defense Manpower Data Center, and annual updates of hospital records from the Individual Patient Data System, and ambulatory care records from military (Standard Ambulatory Data Record: SADR) and non-military (Health Care Service Record and Tricare Encounter Data – Institutional: TED NI) treatment facilities.11 Electronic rosters provided Airborne training start date, student class/company assignment, graduation, reason for not graduating (if applicable), and interruptions in training, including those that ended in a return to the programme within 6 months (ie, a ‘turn back’). Roster records were routinely modified for students experiencing interruption(s) in training, with relevant data fields edited to reflect the most recent status. Because earlier roster data were overwritten, we ascertained the latest jump week attended. Trainees in classes beginning 1 October 1998 through 27 November 2006 who progressed to ‘jump week’, the third and final week of training, were eligible for inclusion. Women comprise only 3% of the trainees, and preliminary analysis showed that study-eligible women had a higher rate of ankle injury than men (3.4% vs 1.5%, respectively, data not shown), with no apparent association between injury and PAB use. Because this suggests the need for separate investigation of brace use for women, including mechanical factors outside the scope of this paper, women were excluded from this analysis (figure 1).

Figure 1

Outside-the-boot parachute ankle brace (PAB) extension cohort: eligibility and exclusion criteria. DMDC, Defense Manpower Data Center.

Individual use or non-use of PABs was not recorded, but Army procedures specified assignment to PAB use on the basis of class/company and time period. The PAB was used by all classes/companies starting jump week between 1 October 1998 and 30 September 2000 (‘brace I’) and was not used between 1 October 2000 and 4 July 2005 (‘no brace I’). ‘brace II’ and ‘no brace II’ were concurrent, 5 July 2005 to 11 December 2006: A and B Companies used the PAB, while C and D Companies did not (specific companies assigned to PAB use identified by F Manning, personal communication, 2007). Compliance is expected to be nearly 100% for those assigned to PAB use. Correctness of brace use was not documented.

Anecdotal reports suggest students may delay treatment for injuries until after completion of Airborne training, but preliminary data suggest most seek care no later than the week after training.8 The period at risk for detecting parachuting-related injuries was therefore defined as 2 weeks, from the first day of the latest jump week through the end of the week after scheduled completion of training.

Ambulatory care records between 1 October 1997 (the earliest electronic records available) and 30 September 2007 included date of care, up to eight diagnoses coded according to International Classification of Diseases 9th Revision, Clinical Modification (ICD-9-CM), and up to four procedures coded according to the Current Procedural Terminology system. Records for all hospital admissions for the same time period provided admission and discharge dates, and up to eight diagnoses and procedures coded according to ICD-9-CM. We counted unique episodes of care based on calendar date, combining inpatient and outpatient records for each trainee to identify the earliest date of care. The Barell injury diagnosis matrix classified traumatic injuries into 20 body regions12; we modified these to incorporate relevant ICD-9-CM codes not typically used in the inpatient setting (V-codes, and codes in the 700s or 900s). For this report, we summarised ankle, non-ankle and vertebral column injuries (VCIs), the latter because Schmidt et al, on the basis of a small number of injuries, suggested increased risk of VCIs among brace users.8 A trainee could have more than one type of injury during the same time period, but each type of injury was counted only once. All injuries during the 2-week risk period were considered parachute-related. We additionally identified ankle and non-ankle injuries treated during one calendar year preceding jump week, because previous injury may predict future injury risk. Other covariates examined in this analysis are found in table 1. Ethnicity was considered because studies of US Army personnel reported that African-American men have lower rates of injury than Caucasian men.13

Table 1

Descriptive characteristics of US Army Airborne School male trainees* by parachute ankle brace (PAB) protocol, 1998–2006 (n=68 418)

Statistical methods

SAS V.9.1 was used for data management and analysis. We compared injury rates for each protocol period (number of injuries/ total number of trainees during the period) and for each study year. RRs and 95% CIs from Poisson regression models quantified the adjusted RR of injury relative to the first ‘no brace’ period.

Results

Trainees during the brace II and no brace II periods tended to be older, had been in service longer, and were more likely to have delays during training compared with those entering training earlier. Non-graduation rates were slightly higher during periods of no PAB use (table 1). There were 325 hospitalisations and 7905 ambulatory care visits during the 2-week risk period. Ankle injuries comprised 29% (1036/3550) of injury-related episodes of care, and 35% (361/1036) of ankle injuries were fractures (data not shown).

After adjustment for age at the start of training, pay grade, duration of service, ankle injury during the previous year, non-ankle injury during the previous year, and turn back status, risk of ankle injury was lower during both periods when PAB was used (brace I, RR=0.60 (95% CI 0.47 to 0.75); brace II, RR=0.62 (95% CI 0.49 to 0.78)) compared with the no brace I period (table 2). Risk of ankle injury was similar during the two periods of no PAB use (RR=0.94, 95% CI 0.78 to 1.14). Risk of non-ankle injuries were lower during the brace I than the no brace I period (RR=0.77, 95% CI 0.68 to 0.88), but similar to the referent during brace II (RR=0.92, 95% CI 0.81 to 1.05) and no brace II (RR=0.86, 95% CI 0.75 to 0.97). Likewise, risk of VCIs was lower during the brace I than the no brace I period (RR=0.42, 95% CI 0.19 to 0.90), but risks during brace II (RR=0.95, 95% CI 0.55 to 1.65) and no brace II (RR=1.08, 95% CI 0.65 to 1.79) were similar to VCI risk during no brace I.

Table 2

Multivariable models for the prediction of selected injuries* among US Army Airborne School male trainees,† 1998–2006 (n=68 418)

Discussion

This study corroborates results from previous investigations that identified reduced risk of ankle injury when the PAB was used during Airborne training3 8 with no accompanying increase in the risk of other injuries,3 6 7 including VCIs. The inclusion of a period of concurrent brace use and non-use by alternating training companies in the latest study period provides support for the hypothesis that differences in injury rates are due to brace use rather than to differences among soldiers trained at different times.

The main limitations of this analysis stem from the use of time rather than number of training jumps as the measure of exposure, selected because the student roster did not supply the actual number of jumps completed, or dates on which jumps were scheduled. Injuries occurring during jump week were designated as parachuting-related, but could have occurred during any type of activity. Although the primary activities during jump week were the required five jumps, information about other activities was unavailable, and cause of injury coding in inpatient and outpatient records were absent and unreliable, respectively. As a result, the denominators of the rates were not necessarily comparable, because the total number of jumps completed by individual trainees could not be known. The five-jump requirement was consistent, except for an 18 month period (approximately 2005–2006) when turn back students were required to repeat all five jumps (B Morway, personal communication, 2008), increasing the chances of a parachuting-related injury being experienced versus trainees without turn backs. The actual number of these instances is unknown, but is probably small: 115 of the 2270 trainees turned back (for any reason) during jump week had ankle injuries designated as jump-related.

Despite shortcomings of the student rosters, this study features several improvements over previous investigations of the PAB. Use of medical records more accurately captures injury diagnoses than self-reports.9 The case definition includes inpatient and outpatient care, allowing assessment of the effectiveness of PABs in preventing less severe injuries than previously investigated,3 8 expanding the scope of the investigation and suggesting an even more favourable ratio of equipment costs versus medical costs avoided than that reported by Schmidt et al.8 The consistency of results with previous investigations emphasises the need for objective analysis over a reliance on anecdotes when developing safety programmes, and clearly indicates that the PAB can reduce individual soldier morbidity and financial costs to the US Army.

What is already known on this subject

  • The PAB is effective at reducing the risk of severe ankle injury among Paratrooper trainees;

  • The low economic cost of obtaining the PAB is far outweighed by avoided treatment costs and individual Soldier morbidity.

What this study adds

  • Inclusion of injuries treated in the outpatient setting expands the case definition and evaluation of benefits to include less severe injuries than previously considered;

  • Including another period of PAB use and non-use corroborates previous findings of PAB effectiveness in reducing risk of ankle injury and not increasing risk of other types of injury.

Acknowledgments

We are grateful to Mr Jeffrey Williams and Ms Lauren Komp for producing the analytical datasets and for their able management of the TAIHOD, and Major Owen Hill and Ms Monika Wahi of USARIEM for their willingness to review this work. Ms Betsy Morway provided invaluable assistance in understanding the Airborne School data files. Mr Fred Manning provided important practical information about the Airborne School and PAB use.

References

View Abstract

Footnotes

  • Funding Funding was provided by the US Department of the Army, contract number W911QY-09-P-0316.

  • Competing interests None.

  • Ethics approval This research was reviewed and found to be exempt by the following ethics review boards: the Human Use Review Committee, US Army Research Institute of Environmental Medicine, September 2006; the US Army Medical Research and Material Command's Office of Research Protections, Human Research Protection Office, November 2009; and ENVIRON International Corporation's Institutional Review Board, September 2006.

  • Provenance and peer review Commissioned; externally peer reviewed.

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