• Renaud Lafage, Vincent Challier, Barthelemy Liabaud, Shaleen Vira, Emmanuelle Ferrero, Bassel G Diebo, Shian Liu, Jean-Marc Vital, Keyvan Mazda, Themistocles S Protopsaltis, Thomas J Errico, Frank J Schwab, and Virginie Lafage.
• *Department of Orthopaedic Surgery, Hospital for Special Surgery, Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, New York; ‡Spine Unit 1, CHU Pellegrin, Bordeaux, France; §Orthopaedic Surgery, Robert Debre Hospital, Paris, France.
• Neurosurgery. 2016 Jul 1; 79 (1): 108-15.

BackgroundThe maintenance of horizontal gaze is an essential function of upright posture and global sagittal spinal alignment. Horizontal gaze is classically measured by the chin-brow vertical angle (CBVA), which is not readily measured on most lateral spine radiographs.ObjectiveTo evaluate relations between CBVA and the slope of the line of sight, the slope of McGregor's line (McGS), and Oswestry Disability Index.MethodsPatients were identified from a single center database of 531 spine patients who underwent full-body EOS x-rays. Correlations between CBVA, the slope of the line of sight, and McGS were assessed. Using a quadratic regression with Oswestry Disability Index and CBVA, windows of low disability were identified. Comparison of sagittal spinopelvic parameters was carried out between patients with "ascending gaze" and "neutral position."ResultsThree hundred three patients were included (74% female, mean age 54.8 years, body mass index 26.6 ± 6.0 kg/m). CBVA strongly correlated with the slope of the line of sight (r = 0.996) and McGS (r = 0.862). Regression studies between Oswestry Disability Index and CBVA yielded a range of values corresponding to low disability (-4.7 degrees to 17.7 degrees). Similarly, a low disability range for the slope of the line of sight (-5.1 degrees to 18.5 degrees) and McGS (-5.7 degrees to 14.3 degrees) was computed. Patients with "ascending gaze" had a worse spinopelvic alignment than "neutral position" patients.ConclusionThe slope of the line of sight and McGS correlated strongly with CBVA and can be used as surrogate measures. The range of values for these measures corresponding to low disability was identified. These values can be used as a general guideline to assess alignment for diagnostic purposes. Cervical compensatory mechanism may modify the natural head position in sagittally misaligned patients.AbbreviationsCBVA, chin-brow vertical angleHRQoL, health-related quality of lifeMcGS, slope of McGregor's lineODI, Oswestry Disability IndexSLs, slope of the line of sight.

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