Prevalence and Predictive Factors of Concurrent Cervical Spinal Cord Compression in Adult Spinal Deformity

Takayoshi Shimizu, MD, PhD; Ronald A. Lehman Jr, MD; Suthipas Pongmanee, MD; J. Alex Sielatycki, MD; Eric Leung, BA; K. Daniel Riew, MD; Lawrence G. Lenke, MD

Disclosures

Spine. 2019;44(15):1049-1056. 

In This Article

Materials and Methods

Patient Population

This study was conducted at a single institution and approved by the institutional review board prior to data collection. A review of the medical records of patients with ASD who were indicated for major thoracolumbar realignment surgery at our institution between September 2015 and September 2017 was carried out. All ASD patients routinely undergo preoperative cervical MRI evaluation at our institution. Preoperative assessment consisted of routine neurological examination, including thorough motor/sensory, deep tendon reflex, Hoffman reflex, and gait testing. Overall, 121 patients during this period met the inclusion and exclusion criteria. Inclusion criteria were patients (1) aged > 20, (2) indicated for >5 level arthrodesis surgery, and (3) who underwent full-body stereoradiography (EOS imaging system; EOS Imaging SA, Paris, France) evaluation. Exclusion criteria were (1) cervical fusion surgery prior to cervical MRI evaluation and (2) neuromuscular or connective tissue disorders; four patients were excluded from the analysis because of prior cervical surgery to decompress the spinal cord.

Data Collection

Patient demographics including age, gender, diagnosis, and body mass index (BMI) were recorded. Radiographic evaluation was performed based on the full-body stereoradipgraph. Spinopelvic parameters were measured using the validated software (KEOPS, SMAIO, Lyon, France), including pelvic incidence (PI), lumbar lordosis (LL), PI-LL mismatch, thoracic kyphosis (T2-T2, T5-12, and T5-12 Cobb's angles), thoracolumbar kyphosis (T10-L2 Cobb's angle), pelvic tilt (PT), and sacral slope (SS). The interobserver reproducibility and intraobserver repeatability of the software have been previously shown as intraclass correlation coefficients (ICCs) of 0.9960 and rc = 0.9872, respectively.[4] Parameters that could not be measured with the software were measured on the picture archiving and communication system (PACS) by two independent spine surgeons (TS and SP), and the interrater reliability (ICCs) was assessed. These included the cervical spine and sagittal balance parameters. Cervical parameters were C0-C2 angle (C0-2, occiput to C2 Cobb's angle), C2-C7 lordosis (C2-7L: C2-C7 Cobb's angle), C2-C7 SVA (cSVA: horizontal distance between a plumb line dropped from C2 to the posterosuperior corner of C7), and T1 slope (T1S: angle between the superior endplate of T1 and a horizontal reference line). The spinopelvic balance was evaluated using C7 sagittal vertical axis (C7SVA) and T1 pelvic angle[5] (TPA: angle between the line from the femoral head axis to the center of the T1 vertebra and the line from the femoral head axis to the middle of the S1 superior endplate). The global balance parameters included the global sagittal axis[6] (GSA: a global alignment angle measured from the line from the midpoint of the two distal femoral condyles to the center of the C7 vertebra and the line from the center of the two distal femoral condyles to the posterosuperior corner of the S1 endplate). The Torg-Pavlov ratio[7] at the narrowest cervical segment was measured in each patient according to the previously published method. The presence of ossification of the posterior longitudinal ligament (OPLL) was also evaluated based on computed tomography (CT) if available or cervical radiography in cases in which CT was not performed.

CSCC was diagnosed based on the sagittal and axial views of 1.5T T2-weighted MRI and also graded according to its severity by two independent spine surgeons. CSCC grade was determined using the modified Cord Compression Index[8] (CCI, Table 1): the sum of the anterior 0 to 3 points and the posterior 0 to 3 points at each segment (C2/3, C3/4, C4/5, C5/6, C6/7, and C7/T1) according to the compressed intervertebral disc or ligamentum flavum. The CCI has three grades: Grade 1 (compression of 0–2 points), Grade 2 (3–4 points), and Grade 3 (5–6 points). Significant CSCC was defined as Grade >2. The presence of cord signal change on T2-weighted imaging was also noted.

Data Analysis

In the study cohort, the prevalence of CSCC was calculated according to the CCI. Patients with significant CSCC (Grade >2) were further analyzed in terms of (1) the distribution of cord compression level, (2) the number of compressed spinal cord segments, and (3) prevalence according to age by decade. A multivariate linear regression analysis was performed to identify the predictive factors for CSCC (CCI score). Patients with OPLL and Torg-Pavlov ratio < 0.8 were excluded in the regression analysis as these are different etiologies from degenerative diseases.

Statistical Analysis

Data are presented as mean ± standard deviation, unless specified otherwise. The interobserver reliability was calculated according to the ICC and Cohen's κ value for continuous variables and categorical variables (CCI), respectively, and classified as poor (0–0.39), moderate (0.4–0.74), or excellent (0.75–1). A multivariate regression analysis was performed with variables that were selected using a stepwise method from all the demographic and radiographic variables. JMP version 13 (SAS, Cary, NC) was used for all analyses. The statistical significance was set at P < 0.05.

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