title: Surface Landmarks do not Correspond to Exact Levels of the Cervical Spine: References According to the Sex, Age and Height.
abstract: OBJECTIVE
  A general orientation along the cervical spine could be estimated by external landmarks, and it was useful, quick and less exposable to radiation, but, sometimes it gave reference confusion of target cervical level. The authors reviewed the corresponding between the neck external landmarks and cervical levels.
  
  
  METHODS
  Totally 1,031 cervical lateral radiographs of different patients were reviewed in single university hospital. Its compositions were 534 of males and 497 females; 86 of second decades (10-19 years-old), 169 of third decades, 159 of fourth decades, 209 of fifth decades, 275 of sixth decades, and 133 of more than seventh decades (>60 years-old). Reference external landmarks (mandible, hyoid bone, thyroid cartilage, and cricothyroid membrane) with compounding factors were reviewed.
  
  
  RESULTS
  The reference levels of cervical landmarks were C2.13 with mandible angle, C3.54 with hyoid bone, C5.12 with thyroid cartilage, and C6.01 with cricothyroid membrane. The reference levels of cervical landmarks were differently observed by sex, age, and somatometric measurement (height) accordingly mandible angle from C1 to C3, hyoid bone from disc level of C2 and C3 to C5, thyroid cartilage from disc level of C3 and C4 to C7, and cricothyroid membrane from C4 to disc level of C7 and T1.
  
  
  CONCLUSIONS
  Surface landmarks only provide general reference points, but not correspond to exact levels of the cervical spine. Intraoperative fluoroscopy ensures a more precise placement to the targeted cervical level.
authors.affiliation: Spine and Joint Research Institute, Teun Teun Hospital, Seoul, Korea.
authors.forename: Chang Hyun
authors.initials: CH
authors.lastname: Oh
authors.affiliation: Department of Neurosurgery, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Gyu Yeul
authors.initials: GY
authors.lastname: Ji
authors.affiliation: Department of Neurosurgery, Inha University College of Medicine, Incheon, Korea.
authors.forename: Seung Hwan
authors.initials: SH
authors.lastname: Yoon
authors.affiliation: Department of Neurosurgery, Inha University College of Medicine, Incheon, Korea.
authors.forename: Dongkeun
authors.initials: D
authors.lastname: Hyun
authors.affiliation: Department of Anesthesiology and Pain Medicine, Inha University College of Medicine, Incheon, Korea.
authors.forename: Chun Gil
authors.initials: CG
authors.lastname: Choi
authors.affiliation: Department of Anesthesiology and Pain Medicine, Inha University College of Medicine, Incheon, Korea.
authors.forename: Hyun Kyoung
authors.initials: HK
authors.lastname: Lim
authors.affiliation: Spine and Joint Research Institute, Teun Teun Hospital, Seoul, Korea.
authors.forename: A Reum
authors.initials: AR
authors.lastname: Jang
keywords: Cervical level; Cricothyroid membrane; External landmark; Hyoid bone; Mandible; Thyroid cartilage