title: Is the timing of surgery associated with avascular necrosis after unstable slipped capital femoral epiphysis? A multicenter study.
abstract: BACKGROUND
  An unstable slipped capital femoral epiphysis (SCFE) is associated with a high rate of avascular necrosis (AVN). The etiology of AVN seems to be multifactorial, although it is not thoroughly known. The aims of our study were to determine the rate of AVN after an unstable SCFE and to investigate the risk factors for AVN, specifically evaluating the notion of an "unsafe window", during which medical interventions would increase the risk for AVN.
  
  
  METHODS
  This retrospective multicenter study included 60 patients with an unstable SCFE diagnosed between 1985 and 2014. Timing of surgery was evaluated for three time periods, from acute onset of symptoms to surgery: period I, <24 h; period II, between 24 h and 7 days; and period III, >7 days. Multivariate logistic regression analysis was used to identify risk factors for AVN.
  
  
  RESULTS
  Closed reduction and pinning was performed in 43 patients and in situ pinning in 17. Among these cases, 16 patients (27%) developed AVN. The rate of AVN was significantly higher in patients treated by closed reduction and pinning (15/43, 35%) than in those treated by in situ pinning (1/17, 5.9%) (p = 0.022). In patients treated by closed reduction and pinning, the incidence of AVN was 2/11 (18%) in period I, 10/13 (77%) in period II and 3/15 (20%) in period III, showing the significantly higher rate in period II (p = 0.002). The surgery provided in period II was identified as an independent risk factor for the development of AVN.
  
  
  CONCLUSIONS
  Our rate of AVN was 27% using two classical treatment methods. Time-to-surgery, between 24 h and 7 days, was independently associated with AVN, supporting the possible existence of an "unsafe window" in patients with unstable SCFE treated by closed reduction and pinning.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kohno
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. Electronic address: yasunaka@ortho.med.kyushu-u.ac.jp.
authors.forename: Yasuharu
authors.initials: Y
authors.lastname: Nakashima
authors.affiliation: Department of Pediatric Orthopaedic Surgery, Osaka City General Hospital, Osaka, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Kitano
authors.affiliation: Department of Orthopaedic Surgery, Sendai City Hospital, Sendai, Japan.
authors.forename: Taichi
authors.initials: T
authors.lastname: Irie
authors.affiliation: Department of Orthopaedic Surgery, Japanese Red Cross Sendai Hospital, Sendai, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kita
authors.affiliation: Department of Orthopaedic Surgery, Fukuoka Children's Hospital, Fukuoka, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Nakamura
authors.affiliation: Department of Orthopaedic Surgery, Okayama University, Okayama, Japan.
authors.forename: Hirosuke
authors.initials: H
authors.lastname: Endo
authors.affiliation: Department of Orthopaedic Surgery, Okayama University, Okayama, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Fujii
authors.affiliation: Department of Bone and Joint Surgery, Kawasaki Medical School, Kurashiki, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kuroda
authors.affiliation: Department of Bone and Joint Surgery, Kawasaki Medical School, Kurashiki, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Mitani
authors.affiliation: Department of Orthopaedic Surgery, Nagoya University, Nagoya, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kitoh
authors.affiliation: Department of Orthopaedic Surgery, Nagoya University, Nagoya, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Matsushita
authors.affiliation: Department of Orthopaedic Surgery, Aichi Children's Health and Medical Center, Obu, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Hattori
authors.affiliation: Department of Orthopaedic Surgery, Aichi Children's Health and Medical Center, Obu, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Iwata
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Iwamoto
mesh_terms: D001858:Bone Nails; D002648:Child; D015331:Cohort Studies; D005260:Female; D005271:Femur Head Necrosis / Q000000981:diagnostic imaging / Q000209:etiology* / Q000601:surgery*; D005500:Follow-Up Studies; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000601:surgery; D016015:Logistic Models; D008297:Male; D019060:Minimally Invasive Surgical Procedures / Q000295:instrumentation / Q000379:methods; D015999:Multivariate Analysis; D019637:Orthopedic Procedures / Q000295:instrumentation / Q000379:methods*; D012189:Retrospective Studies; D018570:Risk Assessment; D012720:Severity of Illness Index; D060048:Slipped Capital Femoral Epiphyses / Q000150:complications* / Q000000981:diagnostic imaging / Q000601:surgery*; D013997:Time Factors; D016896:Treatment Outcome