Non-modifiable Risk Factors Associated with Sternoclavicular Joint Dislocations in the U.S. Military
Authors: Gun Baris , Dean Robert , Go Beatrice , Richardson Catherine , Waterman Brian R 
Published: February 2018

Abstract

INTRODUCTION
Sternoclavicular joint (SCJ) dislocations, although uncommon, are observed in patients with ligamentous laxity as well as those who experience traumatic injuries. The incidence and epidemiology of this costly and debilitating injury to our relatively young and active military population have not previously been reported. The purpose of this study is to consider and quantify the non-modifiable risk factors associated with this injury.

METHODS
Using Defense Medical Epidemiological Database, first-time occurrences, from 2006 to 2015 for the ICD-9-CM code 839.61 (closed dislocation of the SCJ), were obtained and further categorized by gender, race, age, rank, and branch of service. Race was classified based on self-reporting of patients into White, Black, or other categories. Age was divided into the categories of less than 20 yr, 20–24 yr, 25–29 yr, 30–34 yr, 35–39 yr, and greater than 40 yr. Rank was categorized as junior enlisted (E-1 to E-4), senior enlisted (E-5 to E-9), junior officer (O-1 to O-3), and senior officer (O-4 to O-10). Branch of service includes Army, Navy, Air Force, and Marines. Multivariate data analysis was performed to obtain rate per 1,000 person-years as well as adjusted rate (adjusted for age group, gender, race, rank, and service) to isolate risk factors.

RESULTS
Between 2006 and 2015, 427 cases of closed SCJ dislocations occurred among an at-risk population of 13,772,342 person-years for an unadjusted incidence rate (IR) of 0.031 per 1,000 person-years. The annual unadjusted IR ranged from 0.017 in 2006 to 0.059 in 2014 with the greatest increase occurring between 2006 and 2007 representing 61% increase in the rate of injuries. Males were almost twice as likely to sustain these injuries compared with females (adjusted rate ratio 1.73; 95% confidence interval [CI] 1.23, 2.43). Age was not found to be a risk factor for the development of these injuries with IRs for each age group overlapping with 95% CI for all other age groups. Similarly, the other category for race was also not found to be a statistically significant risk factor. Junior Officers (adjusted rate 0.017; 95% CI 0.011, 0.025) were found least likely to suffer from these injuries with Junior Enlisted (0.034; 95% CI 0.030, 0.040) and Senior Enlisted (0.032; 95% CI 0.028, 0.037) most at risk. Being in the Navy (0.019; 95% CI 0.015, 0.025) was found to be most protective compared with Air Force (0.032; 95% CI 0.026, 0.039), Army (0.036; 95% CI 0.031, 0.041), and Marines (0.036; 95% CI 0.028, 0.045).

DISCUSSION and CONCLUSION
Annual unadjusted IR of SCJ dislocations readily increased from 2006 to 2014. Statistically significant risk factors, for suffering a closed SCJ dislocation, identified by our study, were male sex, enlisted rank, and branch of service other than Navy. Age and race were not found to have a statistically significant risk. These results can shed light on non-modifiable risk factors for dislocations of the SCJ and can be used in other studies to aid in reducing injury burden on the U.S. Military.