Injury profiles related to mortality in patients with a low Injury Severity Score: a case-mix issue?
BACKGROUND
Outcome prediction models are widely used to evaluate trauma care. External benchmarking provides individual institutions with a tool to compare survival with a reference dataset. However, these models do have limitations. In this study, the hypothesis was tested whether specific injuries are associated with increased mortality and whether differences in case-mix of these injuries influence outcome comparison.


METHODS
A retrospective study was conducted in a Dutch trauma region. Injury profiles, based on injuries most frequently endured by unexpected death, were determined. The association between these injury profiles and mortality was studied in patients with a low Injury Severity Score by logistic regression. The standardized survival of our population (Ws statistic) was compared with North-American and British reference databases, with and without patients suffering from previously defined injury profiles.


RESULTS
In total, 14,811 patients were included. Hip fractures, minor pelvic fractures, femur fractures, and minor thoracic injuries were significantly associated with mortality corrected for age, sex, and physiologic derangement in patients with a low injury severity. Odds ratios ranged from 2.42 to 2.92. The Ws statistic for comparison with North-American databases significantly improved after exclusion of patients with these injuries. The Ws statistic for comparison with a British reference database remained unchanged.


CONCLUSIONS
Hip fractures, minor pelvic fractures, femur fractures, and minor thoracic wall injuries are associated with increased mortality. Comparative outcome analysis of a population with a reference database that differs in case-mix with respect to these injuries should be interpreted cautiously.


METHODS
Prognostic study, level II.
Department of Surgery, Academic Medical Center, Amsterdam, The Netherlands. p.joosse@amc.nl
Pieter
P
Joosse
Niels W L
NW
Schep
J Carel
JC
Goslings
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D003953:Diagnosis-Related Groups / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D015601:Injury Severity Score; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D016017:Odds Ratio; D011379:Prognosis; D012189:Retrospective Studies; D016896:Treatment Outcome; D014947:Wounds and Injuries / Q000175:diagnosis / Q000453:epidemiology / Q000401:mortality*; D055815:Young Adult