Analysis of Incidence and Outcome Predictors for Patients Admitted to US Hospitals with Acetabular Fractures from 1990 to 2010

PATIENT SELECTION

All patients admitted to hospitals in the US with a fracture of the acetabulum between 1990 and 2010 were identified using ICD-9-CM codes. Discharges with a diagnosis code (ICD-9-CM) of closed fracture of the acetabulum (808.0) or open fracture of the acetabulum (808.1) were identified using previously described techniques.²² The database was subsequently queried to identify patients treated using open reduction and internal fixation (ORIF) (ICD-9-CM, 79.30/79.39), closed reduction and internal fixation (CRIF) (ICD-9-CM, 79.10/79.19), or external (ICD-9-CM, 78.10/78.19) or internal (ICD-9-CM, 78.50/78.59) fixation without reduction. Demographic variables were then collected, including age, sex, primary diagnosis, associated diagnoses, type of fracture (open vs closed), prevalence of comorbidities, length of stay, and discharge destination. The complication screening package²³ was used to determine the incidence of complications. The variable adverse event was created on the basis of the variables postoperative bleeding (998.1), acute postoperative infection (998.5), acute postoperative anemia (285.1), acute renal failure (584), acute myocardial infarction (410), pulmonary embolism (415.1), induced mental disorder (293), pneumonia (480-486), pulmonary insufficiency (518.5), deep venous thrombosis (453.4), intubation (96.xx), and blood transfusion (99.x).

STATISTICAL ANALYSIS

Because of the large sample size, a normal distribution of the data was assumed. Differences between categorical variables were compared using the Pearson chi square test, while the independent-samples t test was used to compare differences between continuous variables. To determine independent predictors of in-hospital outcomes (death, adverse events, requirement for blood transfusion, or treatment with ORIF), all variables present in at least 2% of the population²⁴ were included in a multivariable binary logistic regression model. For in-hospital adverse events, a 1% cutoff was used due to their lower rates of occurrence, as previously described.²⁵The dichotomous variables were death, presence of adverse events, receipt of blood transfusion, and treatment with ORIF. A multivariable regression model allows for the control of potential confounders, isolating the effect of individual variables on inpatient outcomes. Covariates accounted for in the regression model included gender, age, region of the country, and preexisting comorbidities (diabetes mellitus, hypertension, congestive heart failure, coronary artery disease, atrial fibrillation). To assess the association between individual variables and inpatient outcomes, odds ratios and confidence intervals were calculated. A P value of <.001 was used to define statistical significance, correcting for multiple comparisons, as previously described.²⁵ US census data were used to obtain national population estimates for each year of the study from 1990 to 2010.²⁶ Rates were presented as the number of acetabular fractures per 100,000 standard population. All data were analyzed using the software Statistical Package for the Social Sciences [SPSS] version 20.

RESULTS

INCIDENCE AND DEMOGRAPHICS

A cohort representative of 497,389 patients with a diagnosis of acetabular fracture was identified between 1990 and 2010 (Table 1). In 1990, 19,560 cases (7.84 per 100,000 capita) of acetabular fractures were recoded, while in 2010, the number of cases increased to 29,373 or 9.5 per 100,000 capita (P < .001) (Table 2). The mean age of patients with an acetabular fracture was 52.6 years (standard deviation [SD], 23.7) and 60.6% were male (Table 1). The most frequently associated diagnosis was closed fracture of the pelvis (29.8%) followed by fracture of the femur (13.1%) and closed fracture of the ilium (3.8%) (Table 1). Of the total cohort, 23.2% underwent ORIF (Table 1). In 1990, 12.6% of patients with a diagnosis of acetabular fracture underwent ORIF, whereas 20.4% of patients underwent ORIF in 2010 (P < .001) (Table 2). Average length of hospital stay was 8.3 days (SD, 17.9) overall (Table 1). In 1990 the average length of stay was 17.0 days (SD, 14.9), decreasing to 10.3 days (SD, 9.3) in 2010 (P < .001) (Table 2).

Table 1. Patient Characteristics for Patients with Acetabular Fractures in the United States from 1990 to 2007

Abbreviation: SD, standard deviation.

Table 2. Patient Characteristics in 1990, 1995, 1999, 2003, and 2007 Among Patients with Acetabular Fractures

Abbreviations: DOC, days of care; ORIF, open reduction internal fixation.

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