Journal
JOURNAL OF BIOMECHANICS
Volume 40, Issue 9, Pages 1953-1959Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.jbiomech.2006.09.007
Keywords
occipital condyles; bending; upper cervical spine; kinematics; centers of rotation; condyle Double
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The center of rotation (COR) of the upper cervical spine (UCS) is an important biomechanical landmark that is used to determine upper neck moment, particularly when evaluating injury risk in the automotive environment. However, neither the location of the UCS CORs nor the occipital condyles (OCs), which are frequently the referenced landmark for UCS CORs, have been measured with respect to known cranial landmarks. This study determines the CORs using pure bending (+/- 3.5Nm), 3D digitization, and image analysis. Landmarks digitized included the OCs, external auditory meatus (EAM), infraorbital foramen, zygion, nasion, and the foramen magnum. The centroid of each occipital condylar surface (area 301 +/- 29.8 mm(2); length 25.4 +/- 3.2 min) was located 18.4 min posterior, 54.4 mm medial, and 3 1.0 mrn inferior of the EAM. The UCS CORs were distinct: On average, OC-C1 CORs (22.5 mm posterior and 22.6 mm inferior to the left EAM) were superior and more posterior of OCs; C1-C2 CORs (7.4 mm posterior and 46.7 turn inferior to the left EAM) were inferior and more anterior of OC; and OC-C2 CORs (17.0 mm posterior and 33.1 mm inferior to the left EAM) were aligned with OC. There was a statistically significant difference between the percentage of UCS rotation in C1-C2 and OC-Cl; 45% of the flexion and 71 % of the extension occurred in OC-C1. Details of an anatomical variant with two pairs of distinct condylar surfaces are also presented. (C) 2006 Elsevier Ltd. All rights reserved.
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