INCREASING HOSPITAL ADMISSIONS FOR PATELLAR INSTABILITY: A NATIONAL DATABASE STUDY FROM 2004-2017
Authors: Poorman Matthew , Talwar Divya , SanJuan Justin , Baldwin Keith , Sutliff Nikki , Franklin Corinna C. 
Published: March 2019

Background: Patellar instability refers to subluxation or dislocation of the patella out of the trochlear groove of the femur. Patellar instability is classically thought to be most common in adolescent girls. Risk factors for patellar instability described in the literature include female sex, race, sports participation, personal or family history of patellar instability, ligamentous laxity, trochlear dysplasia, and other anatomic factors. However, the epidemiology of patellar instability is not fully characterized, as some studies have produced conflicting information or been drawn from limited populations. In this study, we used the Pediatric Health Information System (PHIS) database to examine trends in admissions for patellar instability throughout the United States. We believe that a national pediatric hospital database will help to illustrate trends in the epidemiology of patellar instability. We hypothesized that there would be an increasing rate of patellar instability admissions in recent years. Secondarily, we examined how demographic factors and insurance status relate to admissions for patellar instability. Methods: This study used Pediatric Health Information System (PHIS) which is a comprehensive administrative database in which more than 45 pediatric hospitals participate, including not-for-profit, freestanding, and tertiary care pediatric centers associated with the Children’s Hospital Association. Patients with ICD 9 & 10 codes 8363, 8364, 71785, M221.0, S83.001, S83.002, S83.003, S83.004, S83.005, and S83.006, were abstracted from PHIS. We abstracted patient characteristics such as age, sex, race, primary source of payment, and discharge year, as well as hospital characteristics such as hospital city. We included all patients admitted with patellofemoral dislocations that were reported in the PHIS database between January 1, 2004 and April 30, 2017. A Shapiro-Wilk test was conducted to determine normality of the dataset, along with a subsequent Pearson correlation to examine the relationship between number of patellar dislocation admissions over the years studied, adjusted for number of hospitals in the study. The relationship between age at admission and sex was examined using a two sample T-test and a linear regression analysis. All statistical analyses were performed using IBM SPSS Statistics Software Version 23.0 (IBM Corp, Armonk, NY, USA). Statistical significance was set at p < 0.05. Results: An estimated total of 25,413 admissions for patellar instability were identified by the search of the PHIS database; 15,444 (60.8%) were female patients and 9,966 (39.2%) were male. The adjusted number of admissions per reporting hospital significantly increased over the years studied (r=0.775, p<0.001), from 14.5 admissions per reporting hospital in 2004 to 86.0 admissions per reporting hospital in 2016. Males were admitted for patellar instability at a significantly older age than females in the data extracted from the PHIS database (14.36 ± 0.23 vs. 13.58 ± 0.20 years, p<0.001). Of all patellar instability admissions, 55.0% were white, 20.4% were black, 1.7% were Asian, and 22.9% were unknown race. A larger number of patellar instability admissions occurred in patients with insurance status other than Medicaid in every year that data was collected. Conclusions/Significance: Based on a PHIS database search, pediatric hospital admissions for patellar instability are steadily increasing. The majority of patients admitted for patellar instability are female, white, and have insurance other than Medicaid. Males admitted for patellar instability tended to be older than females admitted for the same. [Table: see text][Figure: see text][Figure: see text][Figure: see text][Figure: see text]