The jigsaw sign. A reliable indicator of congenital aetiology in os odontoideum

Fagan, Andrew B., Askin, Geoffrey N. and Earwaker, John W. S. (2004) The jigsaw sign. A reliable indicator of congenital aetiology in os odontoideum. European Spine Journal, 13 4: 295-300. doi:10.1007/s00586-004-0732-2

Author Fagan, Andrew B.
Askin, Geoffrey N.
Earwaker, John W. S.
Title The jigsaw sign. A reliable indicator of congenital aetiology in os odontoideum
Journal name European Spine Journal   Check publisher's open access policy
ISSN 0940-6719
Publication date 2004
Sub-type Article (original research)
DOI 10.1007/s00586-004-0732-2
Volume 13
Issue 4
Start page 295
End page 300
Total pages 6
Editor M. Aebi
Place of publication Germany
Publisher Springer-Verlag
Collection year 2004
Language eng
Subject C1
321017 Orthopaedics
321022 Radiology and Organ Imaging
730114 Skeletal system and disorders (incl. arthritis)
Abstract There is evidence in the literature for both a congenital and a post-traumatic aetiology for os odontoideum. In no series published to date has CT been used to aid in the diagnosis. This is a prospective study of the history of trauma and presence of diagnostic features on CT of 18 consecutive cases with os odontoideum. Our objective was to derive clinically useful radiological features enabling accurate differentiation between congenital and post-traumatic aetiologies. A mid-sagittal CT reconstruction of the atlanto-dens joint was obtained. Hypertrophy of the anterior arch of the atlas was quantified by measurement of the arch-peg-area ratio. The presence of dysplastic features (a positive jigsaw sign) of the atlanto-axial joint were noted. These included narrowing of the cartilage space and interdigitation of the two joint surfaces. A history of a potential traumatic aetiology was only obtained in one of the 18 (6%) in our series. A significant elevation of the arch-peg ratio was found when comparing this series to 85 controls. And a positive jigsaw sign was observed in 75% of cases. These features were not seen in paediatric cases of atlanto-axial instability, including odontoid non-union. In conclusion, an elevated arch-peg ratio and the presence of a jigsaw sign are sensitive and specific diagnostic criteria for os odontoideum. This series supports a congenital aetiology for this condition.
Keyword Clinical Neurology
Os Odontoideum
Computerized Tomography
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collections: 2005 Higher Education Research Data Collection
School of Medicine Publications
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Created: Wed, 15 Aug 2007, 05:15:22 EST