Question 1816
{"accessible":false,"alternatives":[{"id":9021,"text":"one third of the canal is occupied by cerebrospinal fluid"},{"id":9022,"text":"one third of the canal is occupied by epidural fat"},{"id":9023,"text":"one third of the canal is occupied by the dens"},{"id":9024,"text":"one third of the canal is occupied by the cord"}],"archived":false,"correctAlternativeId":9022,"explanation":"\u003cp\u003eThe spinal canal at C1 in adults measures around 3 cm in AP dimension with the dens taking up 1 cm, the cord 1 cm and the remaining 1 cm filled with CSF, most of which is found posterior to the cord. This means that the canal is quite capacious at this level and you need to narrow it by at least one third in order for the cord to become compressed.\u0026nbsp;\u003c/p\u003e","id":1816,"imageUrl":null,"imageAttribution":null,"imageAttributionCaseInfo":null,"firstQuestionPath":"/questions/1816","nextQuestionPath":"/articles/cervical-spine/questions/1811","relatedArticles":[{"id":57340,"title":"Cervical spine alignment","link":"/articles/cervical-spine-alignment?lang=gb"}],"alsoUsedIn":[{"id":804,"kind":"Course","title":"X-ray Interpretation: Cervical Spine - page 804","link":"https://radiopaedia.org/courses/x-ray-interpretation-cervical-spine/pages/804"},{"id":804,"kind":"Course","title":"Emergency Radiology Course - Melbourne - page 804","link":"https://radiopaedia.org/courses/emergency-radiology-course-melbourne-2022/pages/804"},{"id":804,"kind":"Course","title":"Emergency Radiology Course - Brisbane - page 804","link":"https://radiopaedia.org/courses/emergency-radiology-course-brisbane-2022/pages/804"}],"stem":"\u003cp\u003eWhich is\u003cstrong\u003e NOT\u003c/strong\u003e part of Steele’s rule of thirds for the normal dimensions of the upper cervical canal at C1?\u003c/p\u003e","menuLinks":[{"text":"Report problem with question","url":"https://docs.google.com/forms/d/e/1FAIpQLSfO3soWYhOjJ7yErSysyCe5V4A1CqW7WK3rDA7MtAkecMGqNw/viewform?entry.1624461248\u0026entry.553583435=https://radiopaedia.org/questions/1816"}],"attemptsPercentages":[{"alternativeId":"9021","percentage":8},{"alternativeId":"9023","percentage":9},{"alternativeId":"9024","percentage":4},{"alternativeId":"9022","percentage":80}],"promptToLogin":false,"questionManager":false,"articleId":"cervical-spine"}