The Presence of Hip Joint Effusion on MRI Is Predictive of a Grade 4 Femoral Neck Stress Injury.

INTRODUCTION: One of the most debilitating types of bone stress injuries is those occurring at the femoral neck. This problem occurs in the military population with much higher incidence than in the normal population and is of great concern to military medical providers. Early detection and accurate diagnosis are key in protecting soldiers and recruits from sustaining a potentially career-ending fracture. In a case study, a 16-year-old elite male distance runner presented with hip pain. MRI found hip joint effusion but was unremarkable for marrow edema and a low-signal fracture line. The initial diagnosis was acute arthritis; however, a follow-up radiograph 1 month later, after the patient had been refraining from running, confirmed a significant non-displaced compression-side Grade 4 femoral neck stress injury (FNSI). In light of the case study and our similar clinical experience, we tested the hypothesis that an MRI study positive for an FNSI, combined with the evidence of a hip joint effusion, is indicative of a Grade 4 FNSI, even without visualization of a low-signal intensity fracture line on T1 or short tau inversion recovery images. MATERIALS AND METHODS: Recruits in Army Basic Combat Training were included in the investigation if 1) diagnosed with a unilateral FNSI, 2) had an initial positive MRI for an FNSI, 3) had a positive bone scan for uptake in the femoral neck area (to validate the diagnosis), 4) had no other hip/pelvis injuries, and 5) had a follow-up MRI within 60 days. Hip joint effusion was defined as 1) ≥2-mm measurable difference in the thickness of fluid along the length of the involved femoral neck when compared to the contralateral uninvolved femoral neck on the initial MRI; 2) visibly assessed as a prominent collection of fluid distending the posterior hip joint capsule on the initial MRI coronal short tau inversion recovery sequence (called the "flash sign"). RESULTS: A total of 162 recruits met the study inclusion criteria. For the detection of a Grade 4 FNSI on the first MRI, the sensitivity, specificity, and positive predictive value of the measured joint effusion criteria were 0.52, 0.94, and 0.89, respectively. or the non-measured flash sign, these values were 0.70, 0.83, and 0.80, respectively. CONCLUSIONS: Both the measured hip joint effusion criteria and the non-measured flash sign were predictive of a Grade 4 FNSI and may be useful in clinical evaluation.

The Subcapital Femoral Neck Stress Fracture: A Novel Subtype of Compression-sided Stress Fracture-A Report of Three Cases.

Femoral neck stress fractures (FNSFs) are increasingly common, particularly in military training. The usual mode of classifying these injuries is based on the involvement of the compression or tension side of the femoral neck; however, this may oversimplify and fail to address factors such as the orientation of the fracture line. We present a novel subtype of a compression-sided FNSF affecting the subcapital femoral neck and report the treatment outcomes in a military trainee population. A retrospective analysis of patients with a subcapital, compression-sided FNSF was identified from a single U.S. Army basic trainee installation. Radiographic evaluation as well as treatment outcomes associated with the ability to complete military training were reported. A total of three patients with a subcapital compression-sided FNSF were identified in a military trainee population, accounting for 10% of all FNSFs that developed over a 3-month period. Of these individuals, one was treated operatively while the other two were treated non-operatively. Overall, one patient was able to return to and successfully complete military training.

Femoral Neck Stress Fractures in Athletes and the Military.

➤: Femoral neck stress fractures (FNSFs) are an infrequent condition in athletic and military populations. ➤: A high index of suspicion with liberal use of magnetic resonance imaging (MRI) is vital for early recognition and treatment initiation. ➤: An associated hip effusion on MRI is a risk factor for an evolving stress injury and requires close assessment and consideration for repeat MRI. ➤: Stress reactions and stable, incomplete FNSFs (<50% of femoral neck width) can be treated nonsurgically. ➤: Surgical intervention is accepted for high-risk, incomplete (≥50% of femoral neck width), and complete FNSFs. ➤: Overall, there is a paucity of high-quality literature on the rates of return to activity following FNSF.

Surgically Treated Femoral Neck Stress Fractures Are Likely to Result in Military Separation During Basic Combat Training.

BACKGROUND: Femoral neck stress fractures are a common condition affecting military service members, most noticeably during basic combat training. Previous studies have investigated the risk factors for femoral neck stress fracture development in basic trainees and outcomes associated with treatment; however, few studies have focused on operatively treated femoral neck stress fracture in the military trainee. Doing so would be important not only for the military, but also providers caring for athletes, such as distance runners, who have a heightened risk for femoral neck stress fracture development. QUESTIONS/PURPOSES: (1) What proportion of US Army trainees completing basic combat training at Fort Jackson, SC, USA, who undergo surgery for femoral neck stress fracture during basic training subsequently leave military service because of the injury? (2) What factors are related to the patient or the fracture are associated with a higher likelihood of military separation? (3) What factors on the initial MRI are associated with progression of the stress fracture extent? METHODS: A retrospective study of a longitudinally maintained database of stress injuries involving basic combat trainees from a single military post was reviewed over a 3-year period. Inclusion criteria included basic trainees undergoing surgery for a femoral neck stress fracture between January 2018 and June 2020 with a minimum of 1-year follow-up. Surgery was indicated for service members with complete and tension-sided femoral neck stress fractures and those with high risk compression-sided stress fractures, generally representing fractures involving more than 50% of the femoral neck width. Over the study period, 57 service members (51% [29 of 57] women with a mean age of 24 years) underwent surgery for a femoral neck stress fracture, and all 57 had a minimum of 1-year follow-up. Identified service members underwent independent data collection including injury and radiographic parameters based on chart and imaging review. Documented fracture line progression on repeat imaging was present in 39% of service members, with a mean fracture line progression of 55% of the femoral neck width. Service members were subdivided based upon the ability to return to military service at 1 year. Univariate analysis was performed using patient and injury variables to identify factors associated with the ability to return to military service. RESULTS: Overall, 58% (33 of 57) of service members who had a femoral neck stress fracture treated surgically underwent military separation. A higher proportion of service members who demonstrated fracture line progression leading to surgical treatment remained in the military (58% [14 of 24] versus 30% [10 of 33]; odds ratio 0.3 [95% confidence interval (CI) 0.1 to 0.9]; p = 0.03). With the numbers available, we found no other patient- or fracture-related variables associated with military separation, although we suspect we may have been underpowered on some of these comparisons, in particular gender (61% [20 of 33] of individuals separated after surgery for this injury were women compared with 38% [9 of 24] who were retained; OR 2.6 [95% CI 0.9 to 7.56]; p = 0.09). The extent of osseous edema on T1-weighted imaging in association with a hip effusion demonstrated a significant positive correlation with final fracture percentage (r = 0.62; p = 0.003). CONCLUSION: Military service members with a femoral neck stress fracture initially managed nonoperatively but with progression of the fracture line requiring surgical intervention were more likely to return to military duties and complete basic combat training, suggesting that early diagnosis of femoral neck stress fractures may be associated with better functional recovery after surgical treatment. Additionally, the extent of the osseous edema on initial MRI T1-weighted imaging sequences may help predict the final extent of femoral neck stress fractures on repeat imaging. Further investigations should incorporate patient-reported outcomes and further explore factors associated with fracture progression and the inability to return to active duty or sport. LEVEL OF EVIDENCE: Level III, therapeutic study.

A multiple intervention strategy for reducing femoral neck stress injuries and other serious overuse injuries in U.S. Army Basic Combat Training.

We hypothesized that the use of evidence based injury prevention strategies would lead to a reduction in the incidence of femoral neck stress injuries (FNSIs) and other serious overuse injuries in U.S. Army Basic Combat Training (BCT). An injury prevention strategy began in late 2008 that included: (1) leadership education, (2) leadership enforcement of proven methods, and (3) injury surveillance and reporting. Data on FNSI and removal from training for injury were analyzed based on the fiscal year 2006 through 2010 (n = 210,002). For men, FNSI were reduced from 13 to 20 cases/10,000 recruits per year (2006-2008) to 8 cases/10,000 recruits in 2010 (p < 0.01); for women, FNSI were reduced from 35 to 41 cases/10,000 recruits per year (2006-2008) to 18 cases/10,000 recruits per year in 2010 (p < 0.01). For men, removals from training for injury were reduced from 0.8 to 1.1 cases/100 recruits per year (2006-2008) to 0.5 cases/100 recruits in 2010 (p < 0.01); for women removal from training for injury was reduced from 2.3 to 2.4 cases/100 recruits (2006-2008) to 1.0 case/100 recruits per years in 2010 (p < 0.01). The time course of the changes suggests that following specific injury prevention methods was effective in reducing injuries.