Epidemiology and risk factors of femoral neck stress fractures in the US military from 2005 to 2016.

INTRODUCTION

Femoral neck stress fractures (FNSFs) are a potentially devastating injury to a service member's livelihood and quality of life if improperly managed. The purpose of this study was to determine the population-level incidence and risk factors associated with FNSF in the US military.

METHODS

The Defence Medical Epidemiology Database was used to identify all distinct FNSF cases in both active and reserve military service members from 2006 to 2015 (International Classification of Diseases, ninth revision, clinical modification code 733.96). The associations of sex and occupation, age, rank and service branch with FNSF outcomes were evaluated. Relative risk (RR) of injury was also calculated based on risk factors of sex, age, rank and branch.

RESULTS

The overall incidence of FNSFs was 0.23/1000 person-years, with rates of 0.27/1000 person-years in enlisted service members (male: 0.18/1000 person-years; female: 0.92/1000 person-years) and 0.07/1000 person-years in officers (male: 0.04/1000 person-years; female: 0.23/1000 person-years). For most occupations, female service members were at significantly greater risk (RR 3.66-11.25). Compared with enlisted infantry members, Special Operations Forces, mechanised/armour, aviation, maintenance and administration were at significantly decreased risk for FNSFs (RR 0.12-0.82). Aviation was the only officer occupation at a significantly decreased risk (RR 0.45) of FNSFs compared with ground and naval gunfire officers. In the multivariable assessment, female sex (RR: 6.02), age <20 years (RR 1.22-2.00), junior enlisted rank (RR 2.63-7.14) and service in the Marine Corps (RR 1.46) were significant risk factors for FNSF outcomes.

CONCLUSIONS

Female sex, younger age and junior enlisted rank were salient risk factors for FNSFs. There were also several occupations that showed an increased risk. Although FNSFs are rare, the likelihood of permanent disability is high when the pathology is not recognised early. Understanding the factors with the greater risk can be used during medical planning and when training clinicians to provide preventive and prompt care.