title: Logistic regression analysis of factors associated with avascular necrosis of the femoral head following femoral neck fractures in middle-aged and elderly patients.
abstract: BACKGROUND
  Risk factors for femoral neck fracture-induced avascular necrosis of the femoral head have not been elucidated clearly in middle-aged and elderly patients. Moreover, the high incidence of screw removal in China and its effect on the fate of the involved femoral head require statistical methods to reflect their intrinsic relationship.
  
  
  METHODS
  Ninety-nine patients older than 45 years with femoral neck fracture were treated by internal fixation between May 1999 and April 2004. Descriptive analysis, interaction analysis between associated factors, single factor logistic regression, multivariate logistic regression, and detailed interaction analysis were employed to explore potential relationships among associated factors.
  
  
  RESULTS
  Avascular necrosis of the femoral head was found in 15 cases (15.2 %). Age × the status of implants (removal vs. maintenance) and gender × the timing of reduction were interactive according to two-factor interactive analysis. Age, the displacement of fractures, the quality of reduction, and the status of implants were found to be significant factors in single factor logistic regression analysis. Age, age × the status of implants, and the quality of reduction were found to be significant factors in multivariate logistic regression analysis. In fine interaction analysis after multivariate logistic regression analysis, implant removal was the most important risk factor for avascular necrosis in 56-to-85-year-old patients, with a risk ratio of 26.00 (95 % CI = 3.076-219.747).
  
  
  CONCLUSIONS
  The middle-aged and elderly have less incidence of avascular necrosis of the femoral head following femoral neck fractures treated by cannulated screws. The removal of cannulated screws can induce a significantly high incidence of avascular necrosis of the femoral head in elderly patients, while a high-quality reduction is helpful to reduce avascular necrosis.
authors.affiliation: Department of Preventive Medicine, Medical College, Tongji University, Shanghai 200092, China.
authors.forename: Zi-Sheng
authors.initials: ZS
authors.lastname: Ai
authors.forename: You-Shui
authors.initials: YS
authors.lastname: Gao
authors.forename: Yuan
authors.initials: Y
authors.lastname: Sun
authors.forename: Yue
authors.initials: Y
authors.lastname: Liu
authors.forename: Chang-Qing
authors.initials: CQ
authors.lastname: Zhang
authors.forename: Cheng-Hua
authors.initials: CH
authors.lastname: Jiang
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws; D002681:China; D005260:Female; D005265:Femoral Neck Fractures / Q000150:complications* / Q000601:surgery; D005271:Femur Head Necrosis / Q000209:etiology*; D005593:Fracture Fixation, Internal / Q000379:methods*; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D012307:Risk Factors