title: Os naviculare: the multi-ossicle configuration of a normal variant.
abstract: OBJECTIVE
  To describe the multi-ossicle appearance of the os naviculare on MRI and CT examinations and to correlate this appearance with the published classification of this well-known skeletal variant.
  
  
  METHODS
  We retrospectively reviewed 148 patients, examined within a 2-year period (170 CT and MRI studies of the foot-ankle), for the presence of os naviculare. This variant was classified according to a widely used system (type I, II, III). In addition, each navicular variant was further reclassified according to the presence of one or more ossicles. The presence of bone marrow edema was also recorded.
  
  
  RESULTS
  Accessory navicular bone was identified in 34 cases (20%) of the 170 exams. It was detected in 14 male and 14 female patients with the following incidence: 11.15% type I (19 cases), 4.11% type II (7 cases) and 4.74% type III (8 cases). In six cases the location was bilateral. Among patients with os naviculare, a multi-ossicle appearance with a total incidence of 14.7% (8.8% two ossicle configuration and 5.9% three ossicle configuration) was observed. In two type II cases studied with MRI, there was bone marrow edema suggesting a painful pseudarthrosis.
  
  
  CONCLUSIONS
  The presence of multiple accessory navicular bone ossicles, not previously described with cross-sectional imaging, is reported herein. The pathogenesis and clinical relevance of this uncommon variant needs to be elucidated with further studies.
authors.affiliation: Department of Radiology, University Hospital, Heraklion, Greece.
authors.forename: Evangelos
authors.initials: E
authors.lastname: Perdikakis
authors.forename: Eleni
authors.initials: E
authors.lastname: Grigoraki
authors.forename: Apostolos
authors.initials: A
authors.lastname: Karantanas
mesh_terms: D005260:Female; D005528:Foot / Q000000981:diagnostic imaging*; D005532:Foot Deformities, Congenital / Q000000981:diagnostic imaging; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
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