title: Seasonal Variation in Hip Fracture Mortality.
abstract: OBJECTIVE
  This study aims to identify if wintertime surgery increases the mortality of the patients after hip fracture operations.
  
  
  METHODS
  Retrospective observational cohort study.
  
  
  METHODS
  The data for this citywide retrospective observational cohort study came from Clinical Data Analysis Reporting System.
  
  
  METHODS
  This study included 35 409 patients with hip fracture operations from July 2005 to December 2013.
  
  
  METHODS
  Cox regression hazard model was used to estimate the independent effect of operation being performed in winter on the hazard of mortality. The hazard model included covariates found to be independent predictors of mortality: age, sex, surgical delay, and Charlson Comorbidity Index (CCI).
  
  
  RESULTS
  There was a seasonal variation with more hip fracture operations happening in the winter months. The 1-month, 6-month, 1-year, and 5-year mortality were 3%, 11%, 17%, and 47%, respectively. Operation performed in winter was associated with a higher hazard of mortality (hazard ratio [HR] 1.040; 95% confidence interval: 1.010-1.072;P= .009). The HR was greater with male sex (HR 1.786;P= .000), advanced age (≥85 years old: HR 2.819;P= .000), the longer surgical delay (HR 1.018;P= .000), and higher CCI (severe CCI group: HR 2.963;P= .000).
  
  
  CONCLUSIONS
  Wintertime hip fracture surgery was associated with an increased hazard of mortality after adjusting for other known risk factors affecting mortality post hip fracture operations.
authors.affiliation: Queen Mary Hospital, Pok Fu Lam, Hong Kong.
authors.forename: Dennis K H
authors.initials: DK
authors.lastname: Yee
authors.affiliation: The University of Hong Kong, Pok Fu Lam, Hong Kong.
authors.forename: Christian
authors.initials: C
authors.lastname: Fang
authors.affiliation: Queen Mary Hospital, Pok Fu Lam, Hong Kong.
authors.forename: T W
authors.initials: TW
authors.lastname: Lau
authors.affiliation: Queen Mary Hospital, Pok Fu Lam, Hong Kong.
authors.forename: Terence
authors.initials: T
authors.lastname: Pun
authors.affiliation: The University of Hong Kong, Pok Fu Lam, Hong Kong.
authors.forename: T M
authors.initials: TM
authors.lastname: Wong
authors.affiliation: The University of Hong Kong, Pok Fu Lam, Hong Kong.
authors.forename: Frankie
authors.initials: F
authors.lastname: Leung
keywords: anesthesia; fragility fractures; geriatric trauma; osteoporosis; trauma surgery