Numerous studies have attempted to delineate the normative value for T1S−CL (T1 slope minus cervical lordosis) as a marker for both cervical deformity and a goal for correction similar to how PI-LL (pelvic incidence–lumbar lordosis) mismatch informs decision making in thoracolumbar adult spinal deformity (ASD). The goal of this study was to define the relationship between T1 slope (T1S) and cervical lordosis (CL).
This is a retrospective review of a prospective database. Surgical ASD cases were initially analyzed. Analysis across the sagittal parameters was performed. Linear regression analysis based on T1S was used to provide a clinically applicable equation to predict CL. Findings were validated using the postoperative alignment of the ASD patients. Further validation was then performed using a second, normative database. The range of normal alignment associated with horizontal gaze was derived from a multilinear regression on data from asymptomatic patients.
A total of 103 patients (mean age 54.7 years) were included. 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 no significant correlation between T1S and T1S−CL. Linear regression analysis revealed that T1S−CL assumed a constant value of 16.5° (R2 = 0.664, standard error 2°). These findings were validated on the postoperative imaging (mean absolute error [MAE] 5.9°). The equation was then applied to the normative database (MAE 6.7° controlling for McGregor slope [MGS] between −5° and 15°). 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.
Normative CL can be predicted via the formula CL = T1S − 16.5° ± 2°. This implies a threshold of deformity and aids in providing a goal for surgical correction. Just as pelvic incidence (PI) can be used to determine the ideal LL, T1S can be used to predict ideal CL. This formula also implies that a kyphotic cervical alignment is to be expected for individuals with a T1S < 16.5°.
ABBREVIATIONSASD = adult spinal deformity; CBVA = chin-brow vertical angle; CL = cervical lordosis (C2–7 lordosis); C0 = occiput; cSVA = cervical SVA; HRQOL = health-related quality of life; LL = lumbar lordosis; MAE = mean absolute error; MGS = McGregor slope; PI = pelvic incidence; PT = pelvic tilt; RMSE = root mean square error; SVA = sagittal vertical axis; TIA = thoracic inlet angle; TK = thoracic kyphosis; T1S = T1 slope; T1S−CL = T1S minus CL.
Correspondence Virginie Lafage: Hospital for Special Surgery, New York, NY. email@example.com.
INCLUDE WHEN CITING Published online October 5, 2018; DOI: 10.3171/2018.5.SPINE171232.
Disclosures Dr. Shaffrey reports consultant relationships with Medtronic, NuVasive, Zimmer Biomet; direct stock ownership in NuVasive; and a patent-holder relationship with and receipt of royalties from Medtronic, NuVasive, and Zimmer Biomet. Dr. Mundis reports consultant relationships with NuVasive, K2M, and Allosource, and patent-holder relationships with NuVasive and K2M. Dr. Hostin reports a consultant relationship with DePuy Spine. Dr. Burton reports a consultant relationship with Allosource, receipt of clinical or research support for the present study from DePuy, and receipt of royalties from DePuy. Dr. Lenke reports a consultant relationship with Medtronic; prior consultant relationships with K2M and DePuy-Synthes Spine; receipt of royalties from K2M and Medtronic; receipt of grant support from DePuy-Synthes Spine, the Scoliosis Research Society (SRS), EOS, Setting Scoliosis Straight Foundation, and AOSpine; an expert witness relationship with Fox Rothschild, LLC (patent infringement case); receipt of royalties from Quality Medical Publishing; philanthropic research funding from Evans Family Donation and Fox Family Foundation; fellowship support from AOSpine; and reimbursement for airfare/hotel from Broadwater, Seattle Science Foundation, SRS, Stryker Spine, The Spinal Research Foundation, and AOSpine. Dr. Gupta reports a consultant relationship with, being on the Surgeon Advisory Board of, travel, and receipt of royalties from DePuy; being a personal stockholder with J&J and P&G; and payments from OMeGA and AOSpine to institution for fellowship support. Dr. Ames reports receipt of royalties from Stryker, Biomet Zimmer Spine, DePuy Synthes, NuVasive, Next Orthosurgical, K2M, and Medicrea; consulting relationships with DePuy Synthes, Medtronic, Stryker, Medicrea, K2M, and Biomet Zimmer; receipt of research support from Titan Spine, DePuy Synthes, and ISSG; receipt of grant funding from SRS; being on the executive committee of ISSG; and being director of Global Spinal Analytics. Dr. Klineberg reports consultant relationships with DePuy Synthes, Stryker, Springer, Trevena, and Allosource; receipt of honoraria from K2M; and receipt of honoraria and a fellowship grant from AOSpine. Dr. Bess reports a consultant relationship and patent-holder relationship with K2, receipt of clinical or research support for the present study from DePuy Spine, and receipt of support for non–study-related clinical or research efforts from K2, Medtronic, NuVasive, and Orthofix. Dr. Schwab reports direct stock ownership in Nemaris Inc.; consultant relationships with Zimmer Biomet, Medicrea, MSD, and K2M; speaking/teaching arrangements with Zimmer Biomet, MSD, and K2M; and support of non–study-related clinical or research efforts from DePuy, NuVasive, K2M, and Stryker (paid through ISSGF). Dr. V. Lafage reports direct stock ownership in Nemaris Inc.; speaking/teaching arrangements with AO and DePuy Spine; and support of non–study-related clinical or research efforts from NASS, SRS (grants), DePuy, Stryker, K2M, and NuVasive (grants paid by ISSGF).
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