The increased use of improvised explosive devices (IEDs) by terrorists and insurgent activities in Iraq and Afghanistan has yielded an unprecedented proportion of blast-related casualties compared with previous wars , with recent estimates indicating blasts are responsible for approximately 75 percent of U.S. combat casualties in Operations Iraqi and Enduring Freedom . The ear is the most vulnerable and typically the first organ to incur injury from a blast (or pressure) wave [5-7]. Although hearing protection devices are available in the combat theater, recent anecdotal reports indicate some troops decline to wear hearing protection for fear of reduced situational awareness on the battlefield [8-10]. Not surprisingly, blast injury to the ear has emerged among deployed military personnel [11-12].
Blast-related ear injuries often present as damage to the sensitive structures of the inner and middle ear, such as the cochlea, ossicular chain, tympanic membrane (TM), and vestibular system [5,13-14]. Damage to these components of the auditory system may result in transient or permanent impairment, such as hearing loss and tinnitus (ringing in the ears) [15-17]. In 2010, hearing loss and tinnitus were the top two service-connected disabilities among veterans receiving compensation , and they are increasing at a dramatic rate [18-20]. From fiscal years 2006 to 2010, the number of veterans who received new compensation awards for "impairment of auditory acuity" grew by more than 72 percent . The total annual expense to deliver hearing healthcare services and compensate veterans for hearing impairment has been estimated to exceed $1 billion .
Blast-related ear injuries are a primary concern during deployment because they can compromise an individual's hearing acuity and, as a result, may reduce situational awareness and adversely affect operational readiness . In a communication-dependent environment, such as the battlefield, where listening can be critical for combat effectiveness and survival, a hearing-impaired servicemember may become "more of a liability than an asset" . As such, the prevention, identification, and treatment of blast-related ear injuries are critical to the overall mission and health of the force. The objectives of this study were to (1) assess the prevalence and types of blast-related ear injuries among servicemembers wounded in Operation Iraqi Freedom; (2) examine the effect of hearing protection worn during the blast injury event; and (3) identify the association between specific ear injuries, new-onset hearing loss, and tinnitus outcomes within 1 yr after injury.
The study population was obtained from the Expeditionary Medical Encounter Database (EMED), which is maintained by the Naval Health Research Center in San Diego, California. The EMED contains information abstracted from medical records of U.S. military personnel completed by providers at forward-deployed Navy-Marine Corps treatment facilities in the combat zone (i.e., nearest to the point of injury) and throughout the continuum of care . Records from each level of care are reviewed by certified nurse coders at the Naval Health Research Center and assigned codes from the International Classification of Diseases-9th Revision-Clinical Modification (ICD-9-CM), Abbreviated Injury Scale (AIS) 2005, and Injury Severity Score (ISS) coding systems [24-26].
At the time of this analysis, there were 13,226 military personnel in the EMED with an injury event that occurred during Operation Iraqi Freedom. Of these, 4,817 were injured in a blast during the study period between March 1, 2004, and August 31, 2008 (Figure). A blast injury event was defined as the presence of a blast-related mechanism of injury and/or ICD-9-CM external cause of injury code (E code) in the EMED clinical record. The blast mechanisms of injury included aerial bomb, grenade, IED, vehicle-borne IED, landmine, mortar, rocket-propelled grenade, rocket, and unexploded ordinance. …