Bone Stress Injuries in the Military: Diagnosis, Management, and Prevention

Pelvis

Pelvic stress fractures are rare and represent only 1.6% to 7.1% of all stress fractures.^13,27,28 Given the low frequency, physicians must have a high index of suspicion to make the correct diagnosis. These fractures typically occur in marathon runners and other patients who present with persistent pain and a history of high levels of activity. As pelvic stress fractures typically involve the superior or inferior pubic rami, or sacrum, and are at low risk for nonunion,¹³ most are managed with nonoperative treatment and activity modification for 8 to 12 weeks.²⁷

Femur

Femoral stress fractures are also relatively uncommon, accounting for about 10% of all stress fractures. Depending on their location, these fractures can be at high risk for progression, nonunion, and significant morbidity.²⁹ Especially concerning are femoral neck stress fractures, which can involve either the tension side (lateral cortex) or the compression side (medial cortex) of the bone. Suspicion of a femoral neck stress fracture should prompt immediate NWB.⁵ Early recognition of these injuries is crucial because once displacement occurs, their complication and morbidity rates become high.¹³ Patients with compression-side fractures should undergo NWB treatment for 4 to 6 weeks and then slow progression to WB activity. Most return to light-impact activity by 3 to 4 months. By contrast, tension-side fractures are less likely to heal without operative intervention.¹¹ All tension-side fractures (and any compression-side fractures >50% of the width of the femoral neck) should be treated with percutaneous placement of cannulated screws (Figure 3).

Stress fractures of the femoral shaft are less common than those of the femoral neck and represent as little as 3% of all stress fractures.³² However, femoral shaft stress fractures are more common in military populations. In French military recruits, Niva and colleagues³³ found an 18% incidence. Similar to femoral neck fractures, femoral shaft fractures typically are diagnosed with advanced imaging, though the fulcrum test and pain on WB can aid in the diagnosis.¹⁹ These injuries are often managed nonoperatively with NWB for a period. Weishaar and colleagues³⁴ described US military cadets treated with progressive rehabilitation who returned to full activity within 12 weeks. Displaced femoral shaft fractures associated with bone stress injury are even less common, and should be managed operatively. Salminen and colleagues³⁵ found an incidence of 1.5 fractures per 100,000 years of military service. Over a 20-year period, they surgically treated 10 of these fractures. Average time from intramedullary nailing to union was 3.5 months.

Tibia

The tibia is one of the more common locations for stress injury and fracture. In a prospective study with members of the military, Giladi and colleagues³⁶ found that 71% of stress fractures were tibia fractures. In addition, a large study of 320 athletes with stress fractures found 49.1% in the tibia.³⁷ Fractures typically are diaphyseal and transverse, usually occurring along the posteromedial cortex, where the bone experiences maximal compressive forces (Figure 4).^5,13

Compression-side fractures often heal with nonoperative management, though healing may take several months. Swenson and colleagues⁴⁰ studied the effects of pneumatic bracing on conservative management and return to play in athletes with tibial stress fractures. Patients with bracing returned to light activity within 7 days and full activity within 21 days, whereas those without bracing returned to light activity within 21 days and full activity within 77 days. Pulsed electromagnetic therapy is of controversial benefit in the management of these injuries. Rettig and colleagues⁴¹ conducted a prospective randomized trial in the treatment of US Navy midshipmen and found no reduction in healing time in those who underwent electromagnetic therapy. Stress fractures with displacement and fractures that have failed nonoperative treatment should undergo surgery. Reamed intramedullary nailing is the gold standard of operative management of these injuries.⁵ Varner and colleagues⁴² reported the outcomes of treating 11 tibial stress fractures with intramedullary nailing after nonoperative management (4 months minimum) had failed. With surgery, the union rate was 100%, and patients returned to full activity by a mean of 4 months.

Metatarsals

Stress fractures were first discovered by Briethaupt¹ in the painful swollen feet of Prussian army members in 1855 and were initially named march fractures. Waterman and colleagues⁶ reported that metatarsal stress fractures accounted for 16% of all stress fractures in the US military between 2009 and 2012. The second metatarsal neck is the most common location for stress fractures, followed by the third and fourth metatarsals, with the fifth metatarsal being the least common.⁵ The second metatarsal is thought to sustain these injuries more often than the other metatarsals because of its relative lack of immobility. Donahue and Sharkey⁴³ found that the dorsal aspect of the second metatarsal experiences twice the amount of strain experienced by the fifth metatarsal during gait, and that peak strain in the second metatarsal was further increased by simulated muscle fatigue. The risk of stress fracture can be additionally increased with use of minimalist footwear, as shown by Giuliani and colleagues,⁴⁴ particularly in the absence of a progressive transition in gait and training volume with a change toward minimalist footwear. In patients with a suspected or confirmed fracture of the second, third, or fourth metatarsal, treatment typically is NWB and immobilization for at least 4 weeks.⁵ Fifth metatarsal stress injuries (Figure 2) typically are treated differently because of their higher risk of nonunion. Patients with a fifth metatarsal stress fracture complain of lateral midfoot pain with running and jumping. For those who present with this fracture early, acceptable treatment consists of 6 weeks of casting and NWB.⁵ In cases of failed nonoperative therapy, or presentation with radiographic evidence of nonunion, treatment should be intramedullary screw fixation, with bone graft supplementation based on surgeon preference. DeLee and colleagues⁴⁵ reported on the results of 10 athletes with fifth metatarsal stress fractures treated with intramedullary screw fixation without bone grafting. All 10 experienced fracture union, at a mean of 7.5 weeks, and returned to sport within 8.5 weeks. One complication with this procedure is pain at the screw insertion site, but this can be successfully managed with footwear modification.⁴⁵

Prevention

Proper identification of patients at high risk for stress injuries has the potential of reducing the incidence of these injuries. Lappe and colleagues⁴⁶ prospectively examined female army recruits before and after 8 weeks of basic training and found that those who developed a stress fracture were more likely to have a smoking history, to drink more than 10 alcoholic beverages a week, to have a history of corticosteroid or depot medroxyprogesterone use, and to have lower body weight. In addition, the authors found that a history of prolonged exercise before enrollment was protective against fracture. This finding identifies the importance of having new recruits undergo risk factor screening, which could result in adjusting training regimens to try to reduce injury. The RED-S consensus statement¹⁴ offers a comprehensive description of the physiologic factors that can contribute to such injury. Similar to proper risk factor identification, implementation of proper exercise progression programs is a simple, modifiable method of limiting stress injuries. For new recruits or athletes who are resuming activity, injury can be effectively prevented by adjusting the frequency, duration, and intensity of training and the training loads used.⁴⁷

Vitamin D and calcium supplementation is a simple intervention that can be helpful in injury prevention, and its use has very little downside. A double-blind study found a 20% lower incidence of stress fracture in female navy recruits who took 2000 mg of calcium and 800 IU of vitamin D as daily supplemention.⁴⁸ Of importance, a meta-analysis of more than 65,000 patients found vitamin D supplementation was effective in reducing fracture risk only when combined with calcium, irrespective of age, sex, or prior fracture.⁴⁹ In female patients with the female athlete triad, psychological counseling and nutritional consultation are essential in bone health maintenance and long-term prevention.⁵⁰ Other therapies have been evaluated as well. Use of bisphosphonates is controversial for both treatment and prevention of stress fractures. In a randomized, double-blind study of the potential prophylactic effects of risedronate in 324 new infantry recruits, Milgrom and colleagues⁵¹ found no statistically significant differences in tibial, femoral, metatarsal, or total stress fracture incidence between the treatment and placebo groups. Therefore, bisphosphonates are seldom recommended as prevention or in primary management of stress fracture.

In addition to nutritional and pharmacologic therapy, activity modification may have a role in injury prevention. Gait retraining has been identified as a potential intervention for reducing stress fractures in patients with poor biomechanics.⁴⁷ Crowell and Davis⁵² investigated the effect of gait retraining on the forces operating in the tibia in runners. After 1 month of gait retraining, tibial acceleration while running decreased by 50%, vertical force loading rate by 30%, and peak vertical force impact by 20%. Such studies indicate the importance of proper mechanics during repetitive activity, especially in patients not as accustomed to the rigorous training methods used with new military recruits. However, whether these reduced loads translate into reduced risk of stress fracture remains unclear. In addition, biomechanical shoe orthoses may lower the stress fracture risk in military recruits by reducing peak tibial strain.⁵³ Warden and colleagues⁵⁴ found a mechanical loading program was effective in enchaining the structural properties of bone in rats, leading the authors to hypothesize that a similar program aimed at modifying bone structure in humans could help prevent stress fracture. Although there have been no studies of such a strategy in humans, pretraining may be an area for future research, especially for military recruits.

Conclusion

Compared with the general population, members of the military (new recruits in particular) are at increased risk for bone stress injuries. Most of these injuries occur during basic training, when recruits significantly increase their repetitive physical activity. Although the exact pathophysiology of stress injury is debated, nutritional and metabolic abnormalities are contributors. The indolent nature of these injuries, and their high rate of false-negative plain radiographs, may result in a significant delay in diagnosis in the absence of advanced imaging studies. Although a majority of injuries heal with nonoperative management and NWB, several patterns, especially those on the tension side of the bone, are at high risk for progression to fracture and nonunion. These include lateral femoral cortex stress injuries and anterior tibial cortex fractures. There should be a low threshold for operative management in the setting of delayed union or failed nonoperative therapy. Of equal importance to orthopedic management of these injuries is the management of underlying systemic deficits, which may have subjected the patient to injury in the first place. Supplementation with vitamin D and calcium can be an important prophylaxis against stress injury. In addition, military recruits and athletes with underlying metabolic or hormonal deficiencies should receive proper attention with a focus on balancing energy intake and energy expenditure. Stress injury leading to fracture—increasingly common in military populations—often requires a multimodal approach for treatment and subsequent prevention.

Am J Orthop. 2017;46(4):176-183. Copyright Frontline Medical Communications Inc. 2017. All rights reserved.