Page 127 - 2020 JSOM Winter

enzymatic activity of blood coagulation factors also occurs, In interpreting Figure 2, several facts should be considered,
further increasing the thrombosis. With rewarming comes a including who is exposed to cold weather and the likelihood of
24
partial thawing of tissue and edema from melting ice. Depend- underreporting. In Figure 2, the denominator for the incidence
ing on the depth of the freezing, skin, nerve, fat, muscle, and calculation is the entire population of the military, not just
bone tissue can be involved. Nerve, cartilage, bone, and endo- those exposed to cold weather. In studies at Fort Wainwright,
thelial cells are injured more rapidly than skin, fat, or connec- Alaska, during three winters (1967–1970), investigators re-
tive tissue. Epiphyseal cartilage (involved in the growth of ported a frostbite incidence of 1,550 cases/100,000 Soldiers,
26
17
long bones) is particularly susceptible to freeze damage. Loss considerably higher than that in Figure 2. In addition, the
of mitochondria can occur in muscle cells. 22,23 frostbite cases in Figure 2 are those clinically diagnosed—that
is, cases in which the Servicemember reported to a medical
care provider, and the provider diagnosed the injury as frost-
Epidemiology
bite. The actual number of frostbite cases is likely under -
Incidence of Frostbite in the Military reported. For example, in an 11-day exercise in the high arctic
Every year since 1995, the Armed Forces Health Surveillance where average temperatures averaged –21°C (–6°F) and wind
Branch of the Defense Health Agency has reported on the in- chills –44°C (–47°F), 17% of Soldiers reporting to the unit
cidence of cold injuries, including frostbite. These reports medical station were diagnosed with frostbite. However, when
are available in the Medical Surveillance Monthly Report at medical personnel actively examined Soldiers at the conclusion
their website (https://www.health.mil/Military-Health-Topics of the exercise, investigators found that an additional 21%
/Combat-Support/Armed-Forces-Health-Surveillance-Branch of the Soldiers experienced frostbite. The underreporting was
/Reports-and-Publications/Medical-Surveillance-Monthly attributed to Soldiers’ not considering the injury sufficiently
- Report). However, these reports generally cover only limited serious, engaging in self-treatment, or ignoring the injury to
periods and do not present the incidence of frostbite over longer accomplish the mission. 27
periods. To determine the frostbite incidence over the longest
possible period, incidence rates for clinically diagnosed frostbite Table 1 shows the anatomic locations of frostbite injuries in
in the military population were obtained from the Defense Med- the active duty US military from 2015 to 2019, where more
ical Epidemiology Database (DMED). From 1997 to 2015, diverse and specific anatomic locations were available using
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frostbite was indicated in the DMED with the International ICD-10 codes. About 41% of frostbite cases occurred in the
Classification of Diseases, Version 9 (ICD-9) code 999.0 (frost- foot/toe region and 38% in the hand/finger region, with all
bite of face), 999.1 (frostbite of the hand), 999.2 (frostbite of the other or unspecified regions accounting for 21%. As shown
foot), and 991.3 (frostbite of other and unspecified sites). Begin- in Table 2, other studies have also found that frostbite is most
ning in 2016, the DMED switched to the International Classi- likely in the foot/toe and hand/finger regions. 28–35 However,
fication of Diseases, Version 10 (ICD-10) codes. In the ICD-10, under some circumstances, the head/face region may have a
frostbite codes include a greater number of more specific an- higher incidence. 26,31,36–39 During outdoor winter activity, the
atomic locations (e.g., head, nose, neck, wrist). These codes face is usually the most exposed region and under conditions
are included in the ICD-10 series T33 (superficial frostbite, 37 of high wind and low temperature may suffer a high frostbite
codes) and T34 (frostbite with tissue necrosis, 37 codes) series. incidence. For example, reindeer herders often ride in snow-
For the analysis reported here, the primary diagnosis and initial mobiles and are exposed to high winds on their faces, and so
occurrence were selected for ICD-9 codes; the primary diagno- experience a high frostbite incidence in this area. Similarly,
36
sis, initial occurrence, and initial encounter (i.e., 7th character A mountaineers often have exposed faces and may experience
code) were selected for ICD-10 codes. Both inpatient and out- very high winds and very low temperatures at altitude, in-
patient cases were included. Incidence rates for each year were creasing risk of frostbite on the face. 39
calculated as [new cases (n)/military population (n)] × 100,000.
Thus, the incidence rate was expressed as cases/100,000 per- Risk Factors for Frostbite
son-years. Figure 2 shows that the overall incidence of clinically The DMED provides data that are useful for examining some
diagnosed frostbite has remained relatively constant from 1997 demographic factors that might be associated with frostbite in
to 2019 at about 17.5 cases/100,000 Service Members, but with military personnel. To examine these, DMED data on the in-
peaks in 1999 and 2014 (both 25 cases/100,000). cidence of frostbite (ICD-9 codes 991.0, 991.1, 991.2, 991.3)

FIGURE 2 Overall incidence of frostbite in the United States TABLE 1 Anatomic Distribution of Frostbite Injuries, Active Duty
Military by year, 1997–2019. US Military, 2016–2019*
Anatomic location N %
Face/head 55 7.2
Neck 4 0.5
Thorax/abdomen/low back/pelvis 7 0.9
Arm/wrist 15 2.0
Hand 101 13.3
Fingers 186 24.6
Hip/thigh/knee/ankle 31 4.1
Foot 131 17.3
Toe 176 23.2
Other/unspecified sites 51 6.7
*Data obtained from the Defense Medical Epidemiology Database.

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