Development of a Novel Cervical Deformity Surgical Invasiveness Index

Peter G. Passias, MD; Samantha R. Horn, BA; Alexandra Soroceanu, MD; Cheongeun Oh, PD; Tamir Ailon, MD; Brian J. Neuman, MD; Virginie Lafage, PhD; Renaud Lafage, MS; Justin S. Smith, MD; Breton Line, BS; Cole A. Bortz, BA; Frank A. Segreto, BS; Avery Brown, BS; Haddy Alas, BS; Katherine E. Pierce, BS; Robert K. Eastlack, MD; Daniel M. Sciubba, MD; Themistocles S. Protopsaltis, MD; Eric O. Klineberg, MD; Douglas C. Burton, MD; Robert A. Hart, MD; Frank J. Schwab, MD; Shay Bess, MD; Christopher I. Shaffrey, MD; Christopher P. Ames, MD

Disclosures

Spine. 2020;45(2):116-123. 

In This Article

Methods

Data Source

This study is a retrospective review of a prospectively-collected database of CD patients enrolled from 13 sites within the United States. Internal Review Board approval was obtained at each participating site before study initiation and informed consent was given by each included patient. Inclusion criteria for the database were patients ages ≥18 years, and radiographic evidence of CD at baseline assessment, defined as the presence of at least one of the following: cervical kyphosis (C2–7 Cobb angle >10°), cervical scoliosis (C2–7 coronal Cobb angle >10°), C2–7 cervical sagittal vertical axis (cSVA) >4 cm, or chin-brow vertical angle (CBVA) >25°. CD patients meeting radiographic inclusion with available baseline and 1-year follow up data were included in this study. Patients with active tumors or infections were excluded from the study.

Data Collection

Demographic and clinical data collected included patient age, sex, body mass index (BMI), previous cervical surgery, and Charlson Comorbidity Index (CCI). Surgical data collected included operative time, EBL, surgical approach, off-label use of bone morphogenetic protein 2, osteotomy use and number of osteotomies, levels fused, and instrumentation used.

Patients were evaluated using full-length free-standing lateral spine radiographs (36" long-cassette) at baseline and 1 year postoperative follow-up visit. Radiographs were analyzed using dedicated and validated software (SpineView; ENSAM, Laboratory of Biomechanics, Paris, France) at a single center with standard techniques.[10–12] Measured cervical spine parameters included cSVA (offset from the C2 plumbline and the postero-superior corner of C7), C2-C7 lordosis (CL: Cobb angle between C2 inferior endplate and C7 inferior endplate), T1 slope minus CL (TS-CL: mismatch between T1 slope and cervical lordosis), and CBVA (angle subtended between the vertical line and the line from the brow to the chin). Measured spinopelvic parameters (Figure 1) included: sagittal vertical axis (SVA: C7 plumb line relative to the posterior-superior corner of S1), pelvic incidence minus lumbar lordosis (PI-LL: mismatch between pelvic incidence and lumbar lordosis), and pelvic tilt (PT: angle between the vertical and the line through the sacral midpoint to the center of the two femoral heads).

Figure 1.

Schematic of the measured sagittal alignment parameters for the cervical (left) and global spinopelvic (right) spinal regions. C2–7 CL indicates cervical lordosis; cSVA, cervical sagittal vertical axis; CBVA, chin-brow vertical angle; TK, thoracic kyphosis; LL, lumbar lordosis; SVA, sagittal vertical axis; PT, pelvic tilt; PI, pelvic incidence.

Invasiveness Index Development

The variables considered for inclusion in the index were developed from a previously published study creating an invasiveness index for adult spinal deformity surgery as well as CD-specific factors.[9] We also calculated the surgical invasiveness index created by Mirza et al for all included patients.[8] Consensus from experienced spine and neurosurgeons selected weightings for each variable that went into the invasiveness index. Linear regression was used to predict operative time, EBL, and length of stay (LOS) using the newly developed CD-specific invasiveness index, controlling for age, sex, and CCI score. Binary logistic regression predicted high operative time, EBL, and LOS based on the medians for each of these outcomes (operative time >338 minutes, EBL >600 mL, LOS >5 days). Multivariable regression modeling was utilized to construct a final model incorporating the strongest combination of factors that would predict operative time, LOS, and EBL. SPSS version 23 was used for all statistical analyses (Armonk, NY). Significance was set at P < 0.05.

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