title: Concomitant septic arthritis and osteomyelitis of the hip in young children; a new pathophysiological hypothesis suggested by MRI enhancement pattern.
abstract: BACKGROUND
  In children, septic arthritis (SA) of the hip is either primary or concomitant with acute haematogenous osteomyelitis (AHO). However, seldom, patients with isolated SA at presentation, may later show osteomyelitis in the metaphysis. The aim of this study was to elaborate a physiopathological hypothesis based on the peculiar MRI findings to explain the onset of AHO after SA.
  
  
  METHODS
  Cases of acute infection of the hip admitted between January 2010 and December 2013 were retrospectively reviewed to assess radiographic and MRI features, as well as bacteriological findings. Only children with isolated SA were included in this study, whereas cases of concomitant SA and AHO at presentation were excluded.
  
  
  RESULTS
  Ten patients met the inclusion criteria. Six (1-11 months) demonstrated, on the initial MRI, decreased perfusion on gadolinium enhanced fat-suppressed T1-weighted sequence of the femoral epiphysis and developed one month later metaphyseal AHO. Four (5-14 years) did not show decreased perfusion and did not develop AHO on follow-up. The type of germ involved influenced neither the type of enhancement pattern nor the outcome.
  
  
  CONCLUSIONS
  Age under one year and decreased perfusion of the affected femoral epiphysis increases the risk of secondary AHO. Our study is the first report in human medicine supporting the physiopathological hypothesis described by Alderson et al. in an animal model: primary infection can originally affect the joint, then penetrate the epiphyseal cartilage, and finally spread into the metaphyseal region through transphyseal vessels present only in the first 12/18 months of life.
authors.affiliation: Unit of Pediatric Radiology Geneva University Hospital HUG, 6 Willy-Donzé, Geneva, 1205, Switzerland. laura.merlini@hcuge.ch.
authors.forename: Laura
authors.initials: L
authors.lastname: Merlini
authors.affiliation: Unit of Pediatric Radiology Geneva University Hospital HUG, 6 Willy-Donzé, Geneva, 1205, Switzerland. mehrak.dumont@hcuge.ch.
authors.forename: Mehrak
authors.initials: M
authors.lastname: Anooshiravani
authors.affiliation: Unit of Pediatric Orthopedics, University Hospital, Geneva, Switzerland. dimitri.ceroni@hcuge.ch.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Ceroni
mesh_terms: D000293:Adolescent; D001170:Arthritis, Infectious / Q000150:complications* / Q000473:pathology*; D002648:Child; D002675:Child, Preschool; D006621:Hip Joint / Q000473:pathology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010019:Osteomyelitis / Q000209:etiology* / Q000473:pathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity