General Session: Cervical Degenerative - Hall F
Presented by: D. Stein
B. Staub(1), R. Lafage(1), D. Stein(1), H.J. Kim(1), C. Shaffrey(2), G. Mundis(3), R. Hostin(4), D. Burton(5), L. Lenke(6), M. Gupta(7), C. Ames(8), E. Klineberg(9), F. Schwab(1), V. Lafage(1), International Spine Study Group (ISSG)
(1) Hospital for Special Surgery, New York, NY, United States
(2) University of Virginia, Charlottesville, VA, United States
(3) San Diego Center for Spinal Disorders, La Jolla, CA, United States
(4) Baylor Scoliosis Center, Plano, TX, United States
(5) University of Kansas Medical Center, Kansas City, KS, United States
(6) Columbia University Medical Center, New York, NY, United States
(7) Washington University, Saint Louis, MO, United States
(8) University of California, San Francisco, San Francisco, CA, United States
(9) University of California, Davis, Sacramento, CA, United States
Introduction: Past studies have postulated that the T1 slope (T1S) is possibly the key to understanding cervical sagittal alignment. Furthermore, they have shown that cervical lordosis (CL), T1S, and T1S minus CL (T1S-CL) all correlate with HRQOL measures in patients with cervical deformity. Borrowing concepts validated in thoracolumbar adult spinal deformity (ASD) correction, has led to the belief that T1S is analogous to PI in terms of driving lordosis. This current study attempts to define cervical curvature in terms of T1s, and delineate the normative value for the T1S-CL as a marker for both cervical deformity and as a goal for correction.
Purpose: To evaluate T1S-CL as an independent variable that can be used to determine the ideal CL Design: Retrospective review of a prospective multicenter database
Methods: A prospective multicenter database of surgical ASD patients served to identify subjects with the following criteria: no cervical fusion, MGS between -5 and 15° pre and post-op, and a change in T1S and CL proportional to each other between preop and postop to prove normal compensatory cervical motion. Correlation analysis across the sagittal parameters was performed. Linear regression analysis was based on T1S. Findings were validated using the post-op alignment and a separate cohort of normative subjects. The range of normal alignment associated with horizontal gaze was derived from a multilinear regression on asymptomatic patients.
Results: 103 patients (mean age = 54.7yo) met the inclusion criteria from 837 in the database. Analysis revealed a strong correlation between T1S and C0-7 lordosis (r = 0.886), C2-7 lordosis (r = 0.815), and C0-2 lordosis (r = 0.732). There was a moderate correlation between T1S and cSVA (R = 0.470). There was no significant correlation between T1S and T1S-CL. Linear regression analysis revealed that T1S-CL assumed a constant value of 16.5° (R-square=0.664, Std Error=2°). These findings were validated on post-op imaging, resulting in a mean absolute error of 5.9°. On a normative population, when controlling for MGS between -5 and 15°, the mean absolute error was 6.7°. A multilinear regression between C2-7, T1S, and MGS demonstrated a range of T1S-CL between 14.5 and 26.5 was necessary to maintain horizontal gaze.
Conclusion: There is no significant correlation between T1S and the mismatch between T1S and CL. This suggests that cervical mismatch is independent of thoracic input and is thus constant. Normative CL can be predicted via the formula CL = TS - 16.5 ± 2. This implies a threshold of deformity and aids in providing a goal for surgical correction. This formula also implies that a kyphotic cervical alignment is to be expected for subject with a T1 slope < 16.5.