Background: In children, septic arthritis (SA) of the hip is either primary or concomitant with acute haematogenous\nosteomyelitis (AHO). However, seldom, patients with isolated SA at presentation, may later show osteomyelitis in the\nmetaphysis. The aim of this study was to elaborate a physiopathological hypothesis based on the peculiar MRI findings\nto explain the onset of AHO after SA.\nMethods: Cases of acute infection of the hip admitted between January 2010 and December 2013 were retrospectively\nreviewed to assess radiographic and MRI features, as well as bacteriological findings. Only children with isolated SA were\nincluded in this study, whereas cases of concomitant SA and AHO at presentation were excluded.\nResults: Ten patients met the inclusion criteria. Six (1ââ?¬â??11 months) demonstrated, on the initial MRI, decreased perfusion\non gadolinium enhanced fat-suppressed T1-weighted sequence of the femoral epiphysis and developed one month\nlater metaphyseal AHO. Four (5ââ?¬â??14 years) did not show decreased perfusion and did not develop AHO on follow-up.\nThe type of germ involved influenced neither the type of enhancement pattern nor the outcome.\nConclusions: Age under one year and decreased perfusion of the affected femoral epiphysis increases the risk of\nsecondary AHO. Our study is the first report in human medicine supporting the physiopathological hypothesis\ndescribed by Alderson et al. in an animal model: primary infection can originally affect the joint, then penetrate\nthe epiphyseal cartilage, and finally spread into the metaphyseal region through transphyseal vessels present only\nin the first 12/18 months of life.
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