The Prevalence and Body Site Distribution of Stress Fractures Among Female Combat Soldiers in the Israeli Defense Forces: A Cross-Sectional Study

Introduction

Israel is one of only three countries over the world (Israel, North Korea and Norway) in which compulsory military service for females is mandated. Before 2015, only a few selected combat duties were open for women; most women performed noncombat duties in rear units. All combat duties are now open for both genders. Female gender is considered to be a major risk factor for injuries, and there are substantial physiological differences between males and females that may have deleterious effect on a unit's readiness and performance.^1–6 Thus, the full integration of women into combat units may have far-reaching consequences on female soldiers' health, on the resources of military medical services, and on unit's readiness and performance, all of which were described in the experience of the British army. ⁷

After full integration of females into the British army, British military commanders mandated identical training programs for males and females. The immediate result of this measure was a dramatic increase of injury rates and lost training days among females.^7–9

One of the most troublesome overuse injury is stress fractures, which are characterized by significant loss of training days and pose a diagnostic challenge for the combat unit's physicians.^2,10 The rates of these fractures also serve as a sensitive indicator for overall overuse injury rates in these units.

The most common site for the occurrence of stress fracture is the distal tibia followed by metatarsal bones, the shaft of the femur, the neck of the femur, and the pelvis.^2,11–14 Stress fractures of the femoral neck should draw special attention and treatment since these fractures may be complicated by avascular necrosis of the femoral head, leading to severe disability and the need for hip arthroplasty at a relatively young age.^15,16

Materials and Methods

Results

In this study, 2223 female soldiers were included. A total of 1384 (62%) were trained in the noninfantry combat training track and 839 (38%) were trained in the infantry combat training track. In the noninfantry group, mean weight, height, and BMI were 59.66 ± 10.7 kg, 162.81 + 5.97 cm, and 22.5 ± 3.54 kg/m², respectively. The mean weight, height, and BMI in the infantry group were 60.67 ± 9.7 kg, 162.82 ± 5.95 cm, and 22.88 ± 3.39 kg/m², respectively. The differences of weight and BMI between groups were statistically significant (p = 0.0202, p = 0.0118, respectively). The height difference between the groups was not statistically significant (p = 0.9679). For detailed anthropometric data by training track, see Table 1.

Out of 2223 female soldiers, 258 (11.6%) were diagnosed with a stress fracture. Two hundred fifteen fractures (83%) were clinically diagnosed. Sixty-four bone scans were performed, of these, 43 (67%) demonstrated stress fractures and confirmed the clinical suspicion of a stress fracture, 6 (10%) were negative for stress fractures, and for 15 (23%) of the results of bone scanning were missing.

The most frequent stress fracture site was the distal tibia (215 cases, 83%). For detailed distribution of stress fractures by site of fracture, see Figure 1.

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FIG. 1.

Stress fractures distribution by site of injury.

The average lost training days due to a stress fracture were 26.6 days. The averages lost training days for metatarsal, distal tibia, femur, and pelvis stress fractures were 16, 29, 40, and 42 days, respectively. Five percent of soldiers diagnosed with a stress fracture lost <11 training days, 62% lost 11–30 training days, 33.5% lost >30 training days, and 13.5% lost >50 training days. For detailed distribution of soldiers diagnosed with stress fractures by amount of lost training days, see Figure 2.

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FIG. 2.

Detailed distribution of soldiers diagnosed with stress fractures by amount of lost training days.

After adjusting for age and BMI, the risk for developing a stress fracture was 2.15 (215%) times higher in the noninfantry group than in the infantry group. This result was statistically significant (p = 0.0232, 95% confidence interval 1.346, 4.536). For detailed logistic regression results for the adjusted association between training type and stress fracture development, see Table 2.

Discussion

The purpose of this study was to characterize and evaluate the frequency of stress fractures among females in the IDF.

The mean BMI was 22.6 kg/m² with a standard deviation of ±3.5 kg/m², which demonstrates that most female soldiers were in the normal category of weight (category II, normal weight 18–25 kg/m²) or slightly overweight (category III, overweight 25–30 kg/m²). Although statistically significant differences in weight and BMI were found, we consider these small differences clinically insignificant.

The rate of stress fractures observed in this study was 11.6% and is similar to rates in other armies around the world. ¹⁷ Most stress fractures (83%) occurred in the calf and ankle region, most of these (90%) in the distal tibia. These numbers are similar to the numbers reported in other studies performed on military^14,17 and nonmilitary^2,11–13 populations. The quoted studies on military populations included male and female recruits during combat training who were trained following the same training program.

In the Australian army, an intervention plan for reduction of stress fractures was conducted and resulted in a vast reduction in pelvic stress fracture rates from 11.2% to 0.6%. ¹⁷ In light of the fact that bone scan data results were missing in 23% of women, we propose a comprehensive study to define the precise sensitivity and specificity of clinical and imaging diagnosis to establish an IDF diagnosis protocol. Such a protocol should include guidelines for the use of clinical diagnosis, diagnosis by imaging, or both modalities.

The rate of femoral stress fractures was 6%. Unlike stress fractures of the distal tibia, femoral stress fractures have the potential for severe complications with the result of permanent disabilities. We urge a dedicated effort to ascertain the risk factors for these fractures and the implementation of plans for intervention to reduce the high rate of these fractures.

The risk of developing a stress fracture among female soldiers who performed noninfantry combat basic training was 2.15 times higher than that of female soldiers who performed infantry basic combat training (odds ratio = 2.15, p = 0.0232). This result is surprising and counter intuitive, since the infantry combat training is twice as long and requires higher physical effort and fitness demands. The main reasons for this surprising finding in our opinion may be the higher professional level of the training team and the basic physical fitness of the soldiers in the infantry combat training units as compared with the noninfantry units.

Another reason that may explain this finding may be related to nutrition issues such as low vitamin D levels and lack of adequate sleep duration in the noninfantry units. Again, these data suggest the need for a study to delineate the reasons for this unexpected finding.

Sixty-two percent of those who suffered a stress fracture lost >21 days of training and 21% lost >40 days of training. These numbers are very high and emphasize the need to consider stress fractures prevention among female soldiers as a high priority military public health issue.

Conclusions and Recommendations