Many Cobb measurements have been reported at various levels for the thoracic kyphosis, but geometric models of the shape of kyphosis are rare. Thoracic vertebral bodies were digitized on 80 normal lateral full-spine radiographs to obtain the mean thoracic kyphosis. Global and segmental angles were determined. Computer iteration processes passed geometric shapes through the posterior body coordinates of the mean thoracic kyphosis to determine the best fit model in the least squares sense. The kyphosis was closely modeled with ellipses. The T1 and T12 areas tended to be flatter in curvature when compared with T2–T11, indicating these are inflection points. Mean global angles were CobbT1–T12 = 44.2°, CobbT2–T11 = 39.9°, and CobbT3–T10 = 33.3°. The T2–T11 kyphotic region was closely modeled with approximately a 70° portion of an ellipse, with minor axis to major axis ratios of 0.6 to 0.72, and with major axis parallel to the posterior body margin of T11.
*Private practice, Elko, Nevada; †CompMath Research Consultant, Huntsville, Alabama; ‡Biomechanics Laboratory, Université du Québec à Trois-Rivières, Canada; §Department of Rehabilitative Medicine, University of Southern California School of Medicine, Pacific Palisades, California; and ∥Marian Medical Center, Santa Maria, California, U.S.A.
Received accepted January 9, 2002.
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