A unique geometrical representation of the cervical spine based on meta-analysis-derived descriptors

This study was aimed at developing a unique geometrical model of the cervical spine, representative of a global population, for use in designing spinal fixation instrumentation. The purpose of the work is to (i) develop a geometrical model of the cervical spine representing a global population of subjects and (ii) demonstrate the utility of the model for design and manufacture of spinal fixation instrumentation. Several methods for quantifying the cervical lordosis exist such as Jackson’s physiological stress line method, Harrison’s posterior tangent method and Ishihara’s cervical curvature index method. While these methods are adequate for clinical use, they do not yield any engineering metric, needed for designing spinal instrumentation. A meta analysis of 28 published studies, representing a global population was conducted, geometrical construction method was devised to model the cervical spine uniquely. The pooled mean estimates of the Cobb angle, T1 slope, cSVA, and cervical arc length were 14.72°, 24.75°, 19.56 mm and 96.2 mm respectively. The cervical spine was precisely located as an arc of the unique ellipse with major and minor axes of 752 mm and 492.5 mm respectively. The T1 slope and Cobb angle primarily determine the position of the spine on the ellipse. A unique geometrical representation of the cervical spine was demonstrated and its applicability for the design and manufacture of spinal fixation instrumentation was shown for the various 2- level spinal segments.