Risk Factors for Injuries During Military Static-Line Airborne Operations: A Systematic Review and Meta-Analysis

Multi-joint protective effects of lumbar brace on lumbar, hip, knee, and ankle in parachute landing with backpack load

There were high injury risks on lumbar and lower limb joints in parachuting landing, and the lumbar brace could protect lumbar. Besides, a backpack load was necessary in parachute landing and increased the injury risk. This study aimed to evaluate multi-joints protective effects of the lumbar brace on lumbar and lower limb joints in parachuting landing with the backpack load. Seven participants landed from a 120 cm height platform without and with a lumbar brace and without and with a 5-kg backpack load, respectively. Infrared makers were pasted on trunk, pelvis, and lower limb in order to build a multi-rigid-body model for calculating kinematic and kinetic parameters. The joint angular displacements of lumbar and ankle and the peak vertical ground reaction force were significantly decreased from 29.2 ± 9.2°, 45.2 ± 7.8°, and 14.7 ± 2.0 bodyweight to 21.6 ± 4.9° (p < 0.05), 39.0 ± 10.1° (p < 0.05) and 10.7 ± 1.3 bodyweight (p < 0.05) respectively by the lumbar brace with no backpack load, and the joint angular displacement of hip was significantly increased from 52.6 ± 7.2° to 68.3 ± 12.5° (p < 0.05). The joint angular displacement of lumbar and ankle were significantly decreased from 29.0 ± 5.0° and 53.8 ± 5.1° to 25.1 ± 5.2° (p < 0.05) and 48.5 ± 2.5° (p < 0.05) respectively by the lumbar brace with the backpack load, and the joint angular displacement of hip and knee were significantly increased from 60.1 ± 8.2° and 110.1 ± 9.3° to 69.7 ± 13.2° (p < 0.05) and 116.8 ± 5.8° (p < 0.05), respectively. The lumbar brace could provide the multi-joint protective effect by decreasing injuries of lumbar and ankle in landing both without and with the backpack load.

The risk factors for injuries in parachuting and load exposure in the training of Chinese paratroopers

BACKGROUND

Parachutists are generally recognized as a "high-risk" group among military personnel. However, the findings came mostly from data analysis without soldiers as subjects.

OBJECTIVE

This study aimed to investigate the injury prevalence in Chinese paratroopers on-site and determine the relationship between injury and risk factors encountered during parachuting and land-based training.

METHODS

This study consisted of a field study with questionnaire and an experiment on muscle load during the simulated training exercise of platform jumping with surface electromyography (EMG), in which 7230 paratroopers and 38 soldiers were involved respectively. Chi-square test was used for the injury rate analysis, ANOVA and t-test for comparison of EMG data, and logistic regression for the analysis of multiple factors. Taking both intensity and time into consideration, jump-years (J-yrs) was used as a complex indicator for exposure to parachuting. Either injury per 1000 jumps or injured persons per 100 soldiers were calculated as injury prevalence.

RESULTS

The overall injury rate among Chinese parachutists was found to be 13.9 injuries per 1000 parachute jumps and 24.5% based on personnel. The person-based injury rate increased with the exposure level significantly (χ2 = 142.06, 2-sided, P < 0.05; trend test also significantly). Among the identified risk factors the uneven terrain was ranked as the most important one by logistic analysis. The EMG amplitude in MVE% increased with the platform height of all the 8 measured muscles and even reached 100% in 4 muscles, showing a high impact at landing. In addition, some characteristics of parachuting injury were also revealed by the injury type and site analysis.

CONCLUSION

A dose-response relationship between parachuting and injury was observed significantly in the survey of Chinese paratroopers. Their injury rate was found to be relatively higher than the reported internationally. Landing impact as a critical point for injury seemed to be proved by the investigation and also the experiment with EMG measurement. It is suggested for future studies, to use the person-based injury rate, landing studied in work physiology and with consideration of different landing skills.

Finite element analysis of shank and ankle with different boot collar heights in parachuting landing on inversion ground surface

This study aimed to the biomechanics of the foot-ankle-shank complex with different boots collar heights in parachuting landing on inversion ground surface. A finite element model including tibia, fibula, ankle, foot and parachuting boot was developed. Three collar heights (low, medium, high) of the parachuting boot were simulated. Von-Mises stress, ankle inversion angle, ligament force and bone displacement were analyzed. Compared with that of the high and low collar heights, boots with medium collar height produced the lowest peak stress on the tibia and the articular cartilage of the subtalar joint. In addition, the medium collar height can better control the ankle inversion and minimize the tensile forces on the lateral ankle ligaments.

Protection by Ankle Brace for Lower-Extremity Joints in Half-Squat Parachuting Landing With a Backpack

Half-squat parachuting landing is a kind of activity with high impact force. Injuries on lower-extremity joints are common in half-squat parachuting landing and would be increased with a backpack. An ankle brace was used to prevent ankle injuries in landing. However, few quantitative studies reported about the protection of an ankle brace for lower-extremity joints in half-squat parachuting landing with a backpack. This study focused on evaluating the protective effects of an ankle brace in half-squat parachuting landing with a backpack. Seven male participants landed from 120 cm with a backpack and an ankle brace. Each participant performed three landing trials on every experimental condition. Kinetics and kinematics of the hip, knee, and ankle were analyzed. It was found that the ankle brace did not significantly affect the ground reaction force with backpack but increased the ground reaction force from 14.7 ± 2.0 bodyweight to 16.2 ± 1.9 bodyweight (p = 0.017) without the backpack. The ankle brace significantly (p < 0.05) decreased the angular displacement, angular velocity, and angular acceleration of the ankle both without and with the backpack. In conclusion, the ankle brace could restrict ankle motion and significantly increase ground reaction force without the backpack. However, the ankle brace did not significantly influence ground reaction force and still restricted ankle motion with the backpack. Therefore, the ankle brace was more effective in half-squat parachuting landing with the backpack than no-backpack landing.

Association Between Self-Reported Sleep Quality and Musculoskeletal Injury in Male Army Rangers

INTRODUCTION

Musculoskeletal injuries and insufficient sleep are common among U.S. Army Rangers. There has been limited research into whether indices of sleep differ between injured and uninjured Rangers. The purpose of this study was to investigate the association between self-reported sleep and musculoskeletal injury in Rangers.

MATERIALS AND METHODS

A total of 82 Army Rangers (male, 25.4 ± 4.0 years) were asked if they currently have any musculoskeletal injuries; completed the Pittsburgh Sleep Quality Index (PSQI), the Insomnia Severity Index (ISI), and the Stanford Sleepiness Scale; and were asked about their average sleep quality/sleep duration over the preceding week. Rangers were then dichotomized into groups, one that reported a current musculoskeletal injury and another that did not.

RESULTS

The reported musculoskeletal injury prevalence was 15.9% (n = 13). The Rangers that reported an injury, compared to those that did not, had a significantly higher Global PSQI score (6.7 ± 3.7 versus 4.5 ± 2.7, P = .012) and ISI score (10.9 ± 3.7 versus 7.2 ± 4.1, P = .003), both indicative of poorer sleep. The group reporting an injury rated their average sleep quality over the preceding week significantly lower compared to those that did not report an injury (50.8 ± 17.5 versus 68.9 ± 18.3, P = .001). There was no significant group difference in the average nightly sleep duration (6.1 ± 1.0 hours versus 6.5 ± 0.9 hours, P = .099).

CONCLUSION

In this cohort of male Army Rangers, In this cohort of male Army Rangers, those with a musculoskeletal injury reported poorer sleep quality than uninjured Rangers. Sleep duration was not associated with reported injuries; however, both the injured group and uninjured group averaged less than the recommended amounts of sleep. Further investigation into the relationship between musculoskeletal injury and sleep in military personnel is warranted.

Risk factors for musculoskeletal injuries in the military: a qualitative systematic review of the literature from the past two decades and a new prioritizing injury model

BACKGROUND

Musculoskeletal injuries (MSkIs) are a leading cause of health care utilization, as well as limited duty and disability in the US military and other armed forces. MSkIs affect members of the military during initial training, operational training, and deployment and have a direct negative impact on overall troop readiness. Currently, a systematic overview of all risk factors for MSkIs in the military is not available.

METHODS

A systematic literature search was carried out using the PubMed, Ovid/Medline, and Web of Science databases from January 1, 2000 to September 10, 2019. Additionally, a reference list scan was performed (using the "snowball method"). Thereafter, an international, multidisciplinary expert panel scored the level of evidence per risk factor, and a classification of modifiable/non-modifiable was made.

RESULTS

In total, 176 original papers and 3 meta-analyses were included in the review. A list of 57 reported potential risk factors was formed. For 21 risk factors, the level of evidence was considered moderate or strong. Based on this literature review and an in-depth analysis, the expert panel developed a model to display the most relevant risk factors identified, introducing the idea of the "order of importance" and including concepts that are modifiable/non-modifiable, as well as extrinsic/intrinsic risk factors.

CONCLUSIONS

This is the qualitative systematic review of studies on risk factors for MSkIs in the military that has attempted to be all-inclusive. A total of 57 different potential risk factors were identified, and a new, prioritizing injury model was developed. This model may help us to understand risk factors that can be addressed, and in which order they should be prioritized when planning intervention strategies within military groups.

Evaluation of Head and Body Kinematics Experienced During Parachute Opening Shock

INTRODUCTION

The U.S. Army conducts airborne operations in order to insert soldiers into combat. Military airborne operations are physically demanding activities with a unique loading environment compared with normal duties. A significant amount of research surrounding airborne operations has focused on assessing the incidence and type of associated injuries as well as the potential risk factors for injuries. During parachute opening shock and other high-acceleration events (e.g., fixed wing flight or vehicle crashes), the neck may be vulnerable to injury if inertial loads overcome the voluntary muscular control of the cervical spine and soft tissue structures. A recent epidemiological survey of sport skydivers showed that the neck, shoulders, and back were the most frequently reported sites of musculoskeletal pain. In addition, the survey indicated that wing loading (a measure of the jumper's weight divided by the size of the parachute canopy) was a potential contributing factor for developing musculoskeletal pain. Recently, there have been efforts to measure the severity of parachute opening shock as an additional potential risk factor for injury; however, no studies have measured both head and body accelerations and no studies have measured head or body angular rate during parachute opening shock. The purpose of this study was to measure and characterize the accelerations and angular rates of both the head and body during parachute opening shock as well as investigate potential factors contributing to higher severity opening shock, which may link to the development of musculoskeletal pain or injury.

MATERIALS AND METHODS

Data were collected from the U.S. Army Parachute Team, The Golden Knights, under an approved Medical Research and Material Command Institutional Review Board protocol. Subjects were instrumented with a helmet- and body-mounted sensor package, which included three angular rate sensors and three single-axis accelerometers each. Data were collected at 2,500 samples per second. Kruskal-Wallis tests were used to determine if helmet-mounted equipment (e.g., cameras), neck length, neck circumference, or wing loading (the ratio of jump weight to the size of the main parachute canopy) affected the accelerations or angular rates of the head or body.

RESULTS

A total of 54 jumps conducted by 19 experienced free-fall jumpers were analyzed. For the head, the mean (± SD) resultant accelerations and angular rates were 5.8 (± 1.6) g and 255.9 (± 74.2) degrees per second (deg/s), respectively. For the body, the resultant accelerations and angular rates were 4.3 (± 1.5) g and 181.3 (± 61.2) deg/s, respectively. A wing loading above 1.4 pounds per square foot (lb/ft2) was found to have a significant effect on head (P = .001) and body (P = .001) resultant acceleration as well as body angular rate about the Y-axis (P = .001).

CONCLUSIONS

There is evidence to suggest that wing loading has an influence on individual head and body resultant accelerations. However, no significant effects were found for the other variables (e.g., neck length and circumference, helmet-mounted equipment, etc.). Future research should focus on identifying additional factors that result in changes in accelerations and angular rates of the head and body during parachute opening shock events.

A Reporting Quality Assessment of Systematic Reviews and Meta-Analyses in Sports Physical Therapy: A Review of Reviews

This review of reviews aimed to evaluate the reporting quality of published systematic reviews and meta-analyses in the field of sports physical therapy using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. This review of reviews included a literature search; in total, 2047 studies published between January 2015 and December 2020 in the top three journals related to sports physical therapy were screened. Among the 125 identified articles, 47 studies on sports physical therapy were included in the analysis (2 systematic reviews and 45 meta-analyses). There were several problems areas, including a lack of reporting for key components of the structured summary (10/47, 21.3%), protocol and registration (18/47, 38.3%), risk of bias in individual studies (28/47, 59.6%), risk of bias across studies (24/47, 51.1%), effect size and variance calculations (5/47, 10.6%), additional analyses (25/47, 53.2%), and funding (10/47, 21.3%). The quality of the reporting of systematic reviews and meta-analyses of studies on sports physical therapy was low to moderate. For better evidence-based practice in sports physical therapy, both authors and readers should examine assumptions in more detail, and report valid and adequate results. The PRISMA guideline should be used more extensively to improve reporting practices in sports physical therapy.

Parachute-Induced Pectoralis Major Tears in Military Servicemembers: What Is the Functional Recovery?

Background

Although the most common injury mechanism for pectoralis major (PM) tears is an eccentric loading mechanism typically caused by bench pressing, within the military, there is a unique injury mechanism associated with airborne operations. The results of operative repair for these parachute-induced PM tears have not been previously reported.

Purpose/Hypothesis

To assess the functional outcomes in military servicemembers undergoing operative repair of parachute-induced PM tears. We hypothesized that functional recovery would be impaired with delayed surgical intervention.

Study Design

Cohort study; Level of evidence, 3.

Methods

Included were active duty military servicemembers who underwent operative repair for PM tears caused by a parachute-induced mechanism. Charts were reviewed to identify characteristic, injury, and surgical variables. Patients completed the functional outcome assessment with the Disabilities of the Arm, Shoulder and Hand (DASH) and the American Shoulder and Elbow Surgeons (ASES) questionnaires. Outcomes were compared between patients treated within 6 weeks of injury and those treated beyond 6 weeks.

Results

Of the 68 identified PM tears, 25 were the result of parachute-induced mechanisms. A total of 13 patients consented and completed the functional outcome assessment. The mean patient age was 30.6 ± 6.4 years, and the mean follow-up period was 5.46 ± 1.26 years. Ten patients underwent repair within 6 weeks of injury, and the remaining 3 patients underwent repair at a mean of 338 days after injury (95% CI, -42.8 to 718.8 days), a significant difference between groups (P = .006). All 13 patients were able to return to military duties at a mean of 6 months from injury. Patients treated within 6 weeks of injury had significantly higher functional outcomes (DASH score, 6.17 vs 26.67; P = .018; ASES score, 85.97 vs 49.5; P = .008), with greater strength performance compared with preinjury (bench press, 90.58% vs 38.95%; P = .0057; push-ups, 81.9% vs 23.8%; P = .023) compared with patients treated beyond 6 weeks of injury.

Conclusion

Operative repair of parachute-induced PM tears within 6 weeks of injury provided a superior functional and strength recovery when compared with delayed surgical repair. Acute repair should be recommended for military servicemembers who experience this unique injury mechanism.

Finite element analysis of lumbar spine with different backpack positions in parachuting landing

The purpose of this study was to investigate the lumbar spine stress with different backpack positions in parachuting landing using a finite element model of lumbar vertebra 1-5. The backpack gravity center was set at three positions (posterior-high (case PH), posterior-low (case PL), and anterior-low (case AL)) respectively. In results, the peak Von-Mises stresses of the matrix, nucleus, fibers, endplate and ligament in case AL were 2.765 MPa, 0.534 MPa, 6.561 MPa, 4.045 MPa and 1.790 MPa respectively, lower than those in case PL (6.913 MPa, 1.316 MPa, 20.716 MPa, 10.917 MPa and 5.147 MPa respectively) and case PH (7.328 MPa, 1.394 MPa, 22.147 MPa, 11.617 MPa and 5.464 MPa respectively). In conclusion, setting the gravity center of backpack at anterior-low position would reduce lumbar spine stress and reduce lumbar spine injuries.

A novel prophylactic Chinese parachute ankle brace

Background

The objective is to compare the effects of a self-designed and self-manufactured novel prophylactic ankle brace [Chinese parachute ankle brace (CPAB)] and two ordinary ankle braces on the ankle joint during a half-squat parachute landing (HSPL) via biomechanical assessment.

Methods

Twenty elite paratroopers were in four different conditions: no brace, elastic brace, semi-rigid brace, and CPAB. Each participant was instructed to jump off a platform with three different heights, 40, 80, and 120 cm, and land on the force plate in a half-squat posture. The vertical ground reaction forces (vGRFs), joint angles, moments, powers, and works were calculated. After the experiment, every participant completed the questionnaires designed for this study.

Results

Increasing the dropping height increased all of the parameters significantly (P<0.01), except for time to peak vGRF (T-PvGRF). Applying three braces can all slightly increase vGRF (P=0.237) and reduce T-PvGRF by 6–10 ms, as well as decrease the joint angles, velocities, and moments on the sagittal and coronal planes. Wearing CPAB and a semi-rigid brace more efficiently restricted dorsiflexion and inversion (P<0.05), and they both significantly reduced ankle work (t=5.107, P<0.01; t=3.331, P<0.01) and peak power (t=7.237, P<0.01; t=6.711, P<0.01) at 120 cm. The total scores from low-to-high were semi-rigid brace (19.20±2.99), elastic brace (21.91±3.25), and CPAB (23.37±3.08).

Conclusions

The CPAB was more effective at restricting ankle joint motion on the coronal and sagittal planes than the other two prophylactic ankle braces. Therefore, the CPAB had the advantages of a novel appearance, high efficiency, and superior comfort, providing a reliable choice for parachute jumping and training in China.

Spinal cord injury in the United States Army Special Forces

OBJECTIVE

Spinal cord injury (SCI) is an area of key interest in military medicine but has not been studied among the US Army Special Forces (SF), the most elite group of US soldiers. SF soldiers make up a disproportionate 60% of all Special Operations casualties. The objective of this study was to better understand SCI incidence in the SF, its mechanisms of acquisition, and potential areas for intervention by addressing key issues pertaining to protective equipment and body armor use.

METHODS

An electronic survey questionnaire was formulated with the close collaboration of US board-certified neurosurgeons from the Mount Sinai Hospital and Cleveland Clinic Departments of Neurosurgery, retired military personnel of the SF, and operational staff of the Green Beret Foundation. The survey was sent to approximately 6000 SF soldiers to understand SCI diagnosis and its associations with various health and military variables.

RESULTS

The response rate was 8.2%. Among the 492 respondents, 94 (19.1%) self-reported an SCI diagnosis. An airborne operation was the most commonly attributed cause (54.8%). Moreover, 87.1% of SF soldiers reported wearing headgear at the time of injury, but only 36.6% reported wearing body armor, even though body armor use has significantly increased in post-9/11 SF soldiers compared with that in their pre-9/11 counterparts. SCI was significantly associated with traumatic brain injury, arthritis, low sperm count, low testosterone, erectile dysfunction, tinnitus, hyperacusis, sleep apnea, posttraumatic stress disorder, major depressive disorder, and generalized anxiety disorder. Only 16.5% of SF soldiers diagnosed with SCI had been rescued via medical evacuation (medevac) for treatment.

CONCLUSIONS

A high number of SF soldiers self-reported an SCI diagnosis. Airborne operations landings were the leading cause of SCI, which coincided with warfare tactics employed during the Persian Gulf War, Operation Iraqi Freedom, and other conflicts. A majority of SCIs occurred while wearing headgear and no body armor, suggesting the need for improvements in protective equipment use and design. The low rate of medevac rescue for these injuries may suggest that medical rescue was not attainable at the time or that certain SCIs were deemed minor at the time of injury.

A descriptive study of orthopaedic injuries due to parachute jumping in soldiers

Background

While parachute jumping, soldiers may suffer minor or life-threatening injuries in various parts of the body. Several trauma scoring systems assess the severity of such injuries. The primary goal of this study was to assess clinical characteristics and the severity of orthopaedic, musculoskeletal, and other injuries from military training-related parachute jumping using two trauma scoring systems (AIS and ISS). Our secondary goal was to assess whether there was an increase in injury rates with age.

Methods

In total, 185 military personnel between 19 and 51 years old who were injured as a result of daytime static parachute jumping during 44 months between January 2016 and August 2019 were included in the study. Demographic data; vital signs; the level of consciousness; the Glasgow Coma Scale; ISS trauma region classifications; anatomical injury sites; AIS and ISS scores; diagnoses; treatment methods; hospitalization status; and duration of hospital stay were examined descriptively.

Results

There were 184 male and one female participant. The most commonly injured body site was the foot (33.5%), and the most common diagnosis was soft tissue trauma (64.3%). The most commonly injured body site was the foot (33.5%), and the most common diagnosis was soft tissue trauma (64.3%). Regarding treatment methods, 51.4% received analgesic pills and cold pack application, 42.7% received a plaster splint, and 5.9% had orthopaedic surgery. The mean ISS score was 5.16 ± 3.92. The hospitalization rate was significantly higher for patients with a critical AIS score than those with a severe AIS score (p < 0.001).

Conclusions

The use of trauma scoring systems to assess injury severity among patients admitted to an ED due to a parachute jumping injury may facilitate treatment selection. We found that AIS and ISS were useful in determining injury severity. Therefore, we recommend the use of trauma scoring systems for assessing the injury severity and the therapeutic approach, and we advocate for the use of the 17 anatomical regions we used in this study. We also found that with increasing age, the severity of injury could increase.

Incidence and risk factors associated with injuries during static line parachute training in Royal Thai Army

BACKGROUND

Incidence and risk factors of parachute injuries has been studied in developed countries, but not in trainees of the airborne forces in the Royal Thailand Army.

METHODS

A prospective cohort study was conducted among 992 military personnel who attended the basic airborne training program from February to July 2018. Information sheets were used to collect data about (a) personal demographics; (b) environmental conditions surrounding the parachute practice; and (c) parachute-related injuries. The incidence rate of injury was then calculated. Risk factors were examined using multilevel Poisson regression analysis and presented as incidence rate ratio (IRR) and 95% confidence interval (95% CI).

RESULTS

A total of 166 parachute-related injuries occurred in 4677 jumps. The incidence rate of injury was 35.50 per 1000 jumps (95%CI: 30.04-41.21). Factors significantly related to parachute injury included: jumping with equipment versus without equipment [adjusted IRR (95% CI): 1.28 (0.88-1.87)], higher wind speed [1.54 (1.27-1.87) per knot], airplane versus helicopter exit [1.75(0.68-4.55)], side versus rear exit [2.13 (1.43-3.23)], night versus day jumping [2.19 (0.81-5.90)], and presence of motion sickness [3.43 (1.93-6.92)].

CONCLUSIONS

To prevent military static line parachute injuries, the following factors should be taken into consideration: type of aircraft, aircraft exit, time of the day, equipment, motion sickness and wind speed.

TRIAL REGISTRATION

The project was certified by the Research Ethics Committee, Faculty of Medicine, Chulalongkorn University (IRB No. 697/60).

RETURNING A SPECIAL OPERATIONS CANDIDATE TO DUTY FOLLOWING AN AIRBORNE OPERATION INJURY: A CASE REPORT

BACKGROUND

Musculoskeletal injuries are recognized as the leading health problem and primary source of injury, disability, and financial burden across the military.^1-5 Special Operations Forces are at an increased risk of musculoskeletal injury due to increased physical demands, precipitous deployments, and continual training and deployment cycles.^6,4 Multiple injury screening tools exist, yet decisions to return to duty are frequently deferred to individual institutional protocol or provider clinical decision making, with no accepted gold standard.^2,3,4,5.

PURPOSE

The purpose of this case report is to describe the application of a system to return a Special Operations Forces candidate to duty following an ankle injury sustained during a military static line airborne operation while in the Special Forces Qualification Course.

CASE DESCRIPTION

The subject was a 34-year-old male with surgical fixation of a left distal fibular fracture with syndesmotic tear after landing from a static line airborne jump during the Special Forces Qualification Course. This case report provides a system to determine return to duty following an ankle fracture and provides a guide to returning a subject to participation, duty, and tactical performance training.

OUTCOMES

Outcome measures recorded were vast, as the use of multiple measures are more indicative of overall function than any single measure. Impairment based measures included Global Rating of Change Scale (GROC), Numeric Pain Rating Scale (NPRS), lateral step down and Closed Chain Dorsiflexion (CCDF). Functional outcome measures included: the Functional Movement Screen™ (FMS™), Lower Quarter Y-Balance (LQYB), three hop tests for distance, and physical performance metrics.

DISCUSSION

The most substantial challenge to this process was the lack of standardized and validated military return to duty testing and guidelines in the literature. Ideally, pre-injury assessment would provide a baseline; however, compared to peers, the subject was well within acceptable ranges for all physical performance metrics at final Return to Duty testing. The subject was returned to duty 10 months after initial injury being physically comparable to his cohorts and being able to complete all military requirements.

LEVELS OF EVIDENCE

5.

Parachute use to prevent death and major trauma when jumping from aircraft: randomized controlled trial

OBJECTIVE

To determine if using a parachute prevents death or major traumatic injury when jumping from an aircraft.

DESIGN

Randomized controlled trial.

SETTING

Private or commercial aircraft between September 2017 and August 2018.

PARTICIPANTS

92 aircraft passengers aged 18 and over were screened for participation. 23 agreed to be enrolled and were randomized.

INTERVENTION

Jumping from an aircraft (airplane or helicopter) with a parachute versus an empty backpack (unblinded).

MAIN OUTCOME MEASURES

Composite of death or major traumatic injury (defined by an Injury Severity Score over 15) upon impact with the ground measured immediately after landing.

RESULTS

Parachute use did not significantly reduce death or major injury (0% for parachute v 0% for control; P>0.9). This finding was consistent across multiple subgroups. Compared with individuals screened but not enrolled, participants included in the study were on aircraft at significantly lower altitude (mean of 0.6 m for participants v mean of 9146 m for non-participants; P<0.001) and lower velocity (mean of 0 km/h v mean of 800 km/h; P<0.001).

CONCLUSIONS

Parachute use did not reduce death or major traumatic injury when jumping from aircraft in the first randomized evaluation of this intervention. However, the trial was only able to enroll participants on small stationary aircraft on the ground, suggesting cautious extrapolation to high altitude jumps. When beliefs regarding the effectiveness of an intervention exist in the community, randomized trials might selectively enroll individuals with a lower perceived likelihood of benefit, thus diminishing the applicability of the results to clinical practice.