Medical textbooks present the pelvis and the spine as distinct entities—an unfortunate practice that does not reflect the crucial and critical role that the pelvis plays in regulating spino-pelvic alignment. Researchers are working to delineate this role. Dubousset proposed the concept of the 3-dimensional pelvic vertebra, which suggested that the pelvis is just another caudal vertebra of the spine, and that analysis of the spine requires simultaneous analysis of pelvic morphology.1 To quantify pelvic morphology, Legaye introduced the pelvic incidence angle (PI) and espoused the theory that this angle regulates sagittal curvature of the spine.2 The PI is formed from 2 lines: line 1, perpendicular to the sacrum from the midline of the sacral plate, aims to quantify spatial orientation and dictate the lumbar curve; line 2, extending from the midline of the sacrum to the midpoint between femoral heads, illustrates the importance of sacral position inside the pelvis (SDC Figure 1, http://links.lww.com/BRS/B99).
*Spine Service, Hospital for Special Surgery, New York, NY
†NYU Hospital for Joint Diseases, New York, NY.
Address correspondence and reprint requests to Bassel G. Diebo, MD, Spine Service, Hospital for Special Surgery, 535 E. 70th Street, New York City, NY 10021; E-mail: Diebob@hss.edu
Received 4 January, 2016
Revised 5 January, 2016
Accepted 5 January, 2016
The manuscript submitted does not contain information about medical device(s)/drug(s).
No funds were received in support of this work.
No relevant financial activities outside the submitted work.
Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Website (www.spinejournal.com).