title: Cricoid cartilage and esophagus: CT scan study of the dynamic variability of their relative positions.
abstract: BACKGROUND
  Cricoid pressure occludes the esophagus (E) by compressing it between the cricoid cartilage (CC) and the body of the sixth cervical vertebra (C6). This technique is used to prevent passive regurgitation during the induction of anesthesia in patients at high risk for regurgitation. Failures of this technique had been described and a possible displacement of the E relative to the CC had been reported, but there is no study about displacement during antero-posterior movements of the head.
  
  
  OBJECTIVE
  The aim of our study was to evaluate the displacement of the CC relative to the cervical E, during flexion and extension movements of the head.
  
  
  METHODS
  We retrospectively studied X-ray computed tomography (CT) images of 21 patients with suspected cervical trauma. Patients were in the supine position. In the first series of images, the head was positioned at maximal flexion by means of a support placed under the external occipital protuberance. In the second series of images, the head was maintained in extension by means of a support placed under the shoulders. Each position was obtained as far as possible within the limits of pain and restricted movement. In flexion and extension, we used the lowest slice from the cricoid cartilage. The variables measured were: diameters of CC (CD) and E (OD), left and right lateral displacements of E.
  
  
  RESULTS
  A total of 13 CT were analyzed. CD and OD as well as OD/OC ratios did not vary significantly in flexion and extension. We noticed 61.5 and 92.3% (respectively in flexion and in extension) of left or right displacement: 23% of patients presented right displacement in both flexion and extension; 38.5% of patients did not present any right displacement in flexion or in extension; 61.5% of patients presented left displacement in both flexion and extension. More generally, almost 92% of patients presented displacement either in flexion or extension, or both.
  
  
  CONCLUSIONS
  In our study, it can be seen that the E is clearly displaced with regard to the CC, that this displacement is favored by extension. Only 2/13 patients have an "over than 3 mm" displacement in extension whereas 5/13 in flexion. So, even if there are more displacements in extension, they are inferior to 3 mm and may not be considered as significant considering the occlusion of E. According to our results, the extension position of the head produces more displacement of the E but should preserve the containment of the cricoid pressure if we consider the thickness of the E wall.
authors.affiliation: Laboratory of Anatomy-INSERM U887, Faculté de Médecine, University of Burgundy, 7 Boulevard Jeanne d'Arc, Dijon, France. m.benkhadra@wanadoo.fr
authors.forename: Mehdi
authors.initials: M
authors.lastname: Benkhadra
authors.forename: F
authors.initials: F
authors.lastname: Lenfant
authors.forename: J
authors.initials: J
authors.lastname: Bry
authors.forename: K
authors.initials: K
authors.lastname: Astruc
authors.forename: O
authors.initials: O
authors.lastname: Trost
authors.forename: F
authors.initials: F
authors.lastname: Ricolfi
authors.forename: C
authors.initials: C
authors.lastname: Girard
authors.forename: P
authors.initials: P
authors.lastname: Trouilloud
authors.forename: G
authors.initials: G
authors.lastname: Feigl
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D003413:Cricoid Cartilage / Q000000981:diagnostic imaging* / Q000502:physiology; D004947:Esophagus / Q000000981:diagnostic imaging* / Q000502:physiology; D005260:Female; D019416:Head Movements; D006801:Humans; D008297:Male; D008875:Middle Aged; D009333:Neck / Q000000981:diagnostic imaging; D019838:Neck Injuries / Q000000981:diagnostic imaging / Q000503:physiopathology; D011312:Pressure; D014057:Tomography, X-Ray Computed; D055815:Young Adult