To prioritize the cervical parameter targets for alignment.
Included: cervical deformity (CD) patients (C2–7 Cobb angle > 10°, cervical lordosis > 10°, cervical sagittal vertical axis [cSVA] > 4 cm, or chin-brow vertical angle > 25°) with full baseline (BL) and 1-year (1Y) radiographic parameters and Neck Disability Index (NDI) scores; patients with cervical [C] or cervicothoracic [CT] Primary Driver Ames type. Patients with BL Ames classified as low CD for both parameters of cSVA (< 4 cm) and T1 slope minus cervical lordosis (TS–CL) (< 15°) were excluded. Patients assessed: meeting minimum clinically important differences (MCID) for NDI (< -15 ΔNDI). Ratios of correction were found for regional parameters categorized by primary Ames driver (C or CT). Decision tree analysis assessed cutoffs for differences associated with meeting NDI MCID at 1Y.
Seventy-seven CD patients (mean age, 62.1 years; 64% female; body mass index, 28.8 kg/m2). Forty-one point six percent of patients met MCID for NDI. A backwards linear regression model including radiographic differences as predictors from BL to 1Y for meeting MCID for NDI demonstrated an R2 of 0.820 (p=0.032) included TS–CL, cSVA, McGregor’s slope (MGS), C2 sacral slope, C2–T3 angle, C2–T3 SVA, cervical lordosis. By primary Ames driver, 67.5% of patients were C, and 32.5% CT. Ratios of change in predictors for MCID NDI patients for C and CT were not significant between the 2 groups (p>0.050). Decision tree analysis determined cutoffs for radiographic change, prioritizing in the following order: ≥ 42.5° C2–T3 angle, > 35.4° cervical lordosis, < -31.76° C2 slope, < -11.57-mm cSVA, < -2.16° MGS, > -30.8-mm C2–T3 SVA, and ≤ -33.6° TS–CL.
Certain ratios of correction of cervical parameters contribute to improving neck disability. Prioritizing these radiographic alignment parameters may help optimize patient-reported outcomes for patients undergoing CD surgery.
Incidence of adult cervical deformity (CD) as a distinct clinical diagnosis is rising, along with the literature concentrating on methodology for appropriately assessing the disease [
Restoration of cervical sagittal alignment involves neural element decompression and/or fusion of the cervical and caudal spinal regions, often invasive in nature and poses risks for major complications and poor patient-reported outcomes [
Explicitly, when assessing deformity specific to the cervical spine, a standardized classification system of deformity severity is in its preliminary stages. The most well-known classification was created by Ames and the International Spine Study Group, but it has yet to be formally validated with connection to HRQoL outcomes [
This was a retrospective cohorts study of a prospective, multicenter International Spine Study Group (ISSG) database of CD patients enrolled from 2013–2018 at 13 participating centers around the United States. Institutional Review Board approval was required protocol by each site and informed patient consent was obtained. Patients enrolled in the database were greater than 18 years with evidence of one of the following CD baseline radiographic parameters: cervical kyphosis (C2–7 Cobb angle > 10°), cervical scoliosis (C2–7 coronal Cobb angle > 10°), C2–7 sagittal vertical axis (SVA) > 40 mm, or chin-brow vertical angle (CBVA) > 25°. Database exclusion criteria comprised of patients with spinal deformity of neuromuscular etiology, presence of active infection, or malignancy. The study inclusion criteria required complete baseline (BL) and 1-year (1Y) radiographic measurements and the HRQoL measure, Neck Disability Index (NDI), as well as demonstrated cervical or cervicothoracic Ames sagittal deformity driver descriptor. The Ames deformity driver consists of 5 categories, detailing the primary driver of cervical deformity as follows: C, a primary sagittal deformity apex in cervical spine; CT, a primary sagittal deformity apex at the cervicothoracic junction; T, primary sagittal deformity apex in the thoracic spine; S, a primary coronal deformity (C2–7 Cobb angle greater than or equal to 15); and CVJ, a primary craniovertebral junction deformity. In order to analyze a more homogenous CD population, patients were excluded if they were categorized with another Ames driver (thoracic [T], coronal [S]) or were classified as a low Ames CD modifier for both the parameters of cervical SVA (cSVA) (< 4 cm) and T1 slope minus cervical lordosis (TS–CL) (< 15°).
Patient demographic and clinical data assessed patient age, sex, BMI, and CCI. Operative factors assessed: surgical approach, levels fused, operative time, and estimated blood loss (EBL). Full-length free-standing lateral spine radiographs were used to assess the patient population at BL and 1Y. Radiographs were analyzed with SpineView (ENSAM, Laboratory of Biomechanics, Paris, France) software according to the literature [
Descriptive analyses determined demographic, clinical, and surgical data. Frequency analysis evaluated categorical variables with chi-square analysis determining significant variance of expected versus observed values. Patients were assessed based on meeting the minimal clinically important difference (MCID) for NDI scores at 1nyear (< -15 ΔNDI) [
Seventy-seven CD patients with complete radiographic and HRQoL data met inclusion criteria for Ames driver descriptors of C or CT. Twelve patients with S or T Ames driver descriptors were excluded. Mean patient age was 62.1 years, mean BMI of 28.8 kg/m2, with 64% of the cohort as female. The average CCI score was 0.94. By approach, these CD patients underwent majorly posterior surgeries (41.6%), while 39% had combined approaches and 19.4% anterior. Forty-four point two percent of patients underwent osteotomies and 53.2% decompression. Average levels fused was 7.5 (posterior, 8.3; anterior, 3.5). The mean total operative time was 553.1 minutes, with an EBL of 1,128.1 mL. Thirty-two patients (41.6%) met MCID for NDI. Ten patients (13%) had a revision procedure.
Between C and CT groups, there were significant differences for both baseline and 1-year cohort means of cSVA, T1 Slope, C2–T3 SVA, and C2 slope. CT patients exhibited significantly greater malalignment at baseline for cSVA (66.6 mm vs. 35.7 mm, p<0.001), T1 slope (41.4° vs. 20.6°, p<0.001), C2–T3 SVA (110.2 mm vs. 57.2 mm, p<0.001), as well as MGS (p=0.042) and C2 slope (p=0.008). C driver patients had greater CL malalignment preoperatively (-17.5° vs. -4.5°). At 1-year CT patients remained significantly more malaligned in cSVA, T1 slope, C2–T3 SVA, and C2 slope (all p<0.001) (
A backwards linear regression model found the following radiographic differences as predictors of meeting MCID for NDI from baseline to 1 year: TS–CL, cSVA, MGS, C2 slope, C2–T3 angle, C2–T3 SVA and CL demonstrated the greatest variation contributing to MCID for NDI with an R2 of 0.820 (p=0.032). When assessing individual Ames driver type cohorts, C driver patients demonstrated an R2 value of 0.844 (p=0.029) without inclusion of the TS–CL or C2–T3 SVA parameter. CT patients had an R2 value of 0.778 (p=0.025), without the TS–CL angle.
Ratios of change in predictors for MCID NDI patients (BL-1Y) for C driver patients: 260.8% MGS, 140.3% CL, 121.2% C2–T3 angle, 49.6% C2 slope, 41.1% cSVA, 20.5% TS–CL, 3.1% C2–T3 SVA. Correction in CT driver patients included: 168.7% CL, 93% MGS, 70.8% C2–T3 angle, 31.1% cSVA, 27.5% C2 slope, 24.9% TS–CL, 13.7% C2–T3 SVA. The ratios of radiographic differences were not significant between the C and CT driver groups (p>0.050) (
Decision tree analysis determined cutoffs for radiographic change, prioritizing in the following order (based upon ordinal regression values): a correction ≥ 42.5° C2–T3 angle (odds ratio [OR], 5.667; 95% confidence interval [CI], 1.074–29.891; p=0.041), > 35.4° CL (OR, 4.636; 95% CI, 0.857–25.071; p=0.075), < -31.76° C2 slope (OR, 3.2; 95% CI, 0.852–12.026; p=0.085), <-11.57-mm cSVA (OR, 3.185; 95% CI, 1.137–8.917; p=0.027), < -2.16° MGS (OR, 2.724; 95% CI, 0.971–7.636; p=0.057), > -30.8-mm C2–T3 SVA (OR, 0.462), and ≤ -33.6° TS–CL (OR, 0.271) (
Patients who met thresholds for recommended cervical parameter prioritization trended toward improvement in both NDI and modified Japanese Orthopedic Association (mJOA) scale for all measurements at 1 year (
High-risk cohorts undergoing treatment of adult CD include patients with advanced age, obesity, greater comorbidity burden, and severe frailty status. While classification systems, such as the one created by Ames and the ISSG, provide correction guidelines for the representative majority of CD patients, operating on patients with preoperative presentation of increased risk for poor outcomes has facilitated the need for a prioritization of alignment scheme for CD surgery [
Utilizing a CD prospective multicenter database and biplanar stereoradiography, allowing for the acquisition of full-body imaging in the weight-bearing position, our analysis determined that prioritizing regional cervical radiographic alignment parameters in a certain order to a specific degree optimized reaching the MCID in a patient’s self-reported neck disability. Despite regional driver of CD (cervical or cervicothoracic), radiographic correction for patients who reached MCID for NDI were similar. The prioritization of parameters are as follows: C2–T3 angle, C2–7 lordosis, C2 slope, cSVA, MGS, C2–T3 SVA, and, lastly, TS–CL.
First, we found that the C2–T3 angle should be corrected. This angle connects each of the regions of the spine, by incorporating the unequivocal relationship between the cervical and thoracolumbar spine morphology [
The third parameter to prioritize in correction of CD is the C2 slope. We found that correction of this radiographic measurement, led to increased neck disability improvement [
Then, the cSVA was found to be prioritized. The restoration of this parameter has been correlated with improved postoperative outcomes and prevention of disability [
Lastly, the mismatch between T1 slope and CL parameter was prioritized. This relationship accounts for the intrinsic compensation of T1 slope on the CL to balance the head over the thoracic inlet and maintain the physiological neck tilting [
Through the combination of regional cervical radiographic factors, we found that prioritizing the lordosis of the cervical spine (through C2–C7 and C2–T2), followed by occipitocervical incorporation (C2 slope) global assessment (cSVA, C2–T3 SVA, TS–CL), and horizontal improvement (MGS). This proposed prioritization involves the innate interdependence of the spine: cervical lordosis depends on both thoracic kyphosis and lumbar lordosis. With the distinct diagnosis of CD, cervical lordosis adaptation is due to the cervical spinal segment changes relative to the global spine to attempt to maintain the head over the pelvis and horizontal gaze [
Our study is not without limitations, including the retrospective nature of this study and the small number of patients. While the multicenter methodology used for database construction increases the generalizability of our findings, the data analyzed for the purposes of this study may be skewed toward more complex cases. Another limitation lies in the heterogeneous nature of the patient population in regards to cervical procedure and complexity, which may have been accounted for by removing thoracic and coronal Ames type CD drivers. The method of radiographic measurement is also not without limitation. Although the measurements were standardized to be taken with the patient standing in a relaxed position looking forward, these images remain as a representation of a point in time and are not reflective of force plate of dynamic motion studies. However, the horizontal gaze tends to stay stable and lower extremities ted to affect lumbo-pelvic alignment the most. Future studies should investigate the proposed prioritization and thresholds on a prospective trial with a larger, homogenous population of patients undergoing CD corrective surgery.
Certain ratios of correction of cervical parameters contribute to improving neck disability. Specific cutoffs of radiographic differences from baseline to 1 year were found prioritizing C2–T3 angle, followed by cervical lordosis, C2 slope, C2–7 plumb line, MGS, C2–T3 SVA, and TS–CL all strongly associated with meeting the MCID for the NDI score. Prioritizing these radiographic alignment parameters may help optimize patient-reported outcomes for patients undergoing CD surgery.
The authors have nothing to disclose.
The International Spine Study Group (ISSG) is funded through research grants from DePuy Synthes and individual donations.
Baseline (BL) and 1-year (1Y) cervical and whole spine radiographs of a 72-year-old female who did not meet proposed radiographic prioritization of alignment.
Baseline (BL) and 1-year (1Y) cervical and whole spine radiographs for a 61-year-old male who met proposed radiographic prioritization of alignment.
Demographic and surgical characteristics of the cohort
Demographic | Value |
---|---|
Mean age (yr) | 62.1 |
Female sex (%) | 64 |
Body mass index (kg/m2) | 28.8 |
Race (%) | |
White | 91.6 |
Black | 5.6 |
Other | 2.8 |
Charlson Comorbidity Index | 0.94 |
Smoker (%), yes | 6.5 |
Approach (%) | |
Anterior only approach | 19.4 |
Posterior only approach | 41.6 |
Combined approach | 39 |
Total levels fused | 7.5 |
Osteotomy (%) | 44.2 |
Decompression (%) | 53.2 |
Operative time (min) | 553.1 |
Estimated blood loss (mL) | 1,128.1 |
Revision (%) | 13 |
Radiographic parameters at baseline and 1 year, as well as the difference between baseline and 1 year for cervical (C) and cervicothoracic(CT) Ames driver types
Radiographic parameter | C | CT | p-value |
---|---|---|---|
Baseline | |||
cSVA (mm) | 35.7 ± 24.4 | 66.6 ± 14.5 | < 0.001 |
CL (°) | -17.5 ± 18.4 | -4.5 ± 20.5 | 0.009 |
T1 slope (°) | 20.6 ± 12.6 | 41.4 ± 12.6 | < 0.001 |
TS–CL (°) | 37.7 ± 18.2 | 45.5 ± 16.4 | 0.086 |
CBVA (°) | 0.41 ± 2.0 | 0.48 ± 2.3 | 0.893 |
MGS (°) | 2.9 ± 10.6 | 8.6 ± 12.6 | 0.042 |
C2–T3 angle (°) | -18.6 ± 20.5 | -27.0 ± 20.8 | 0.113 |
C2–T3 SVA (mm) | 57.2 ± 34 | 110.2 ± 22.4 | < 0.001 |
C2 slope (°) | 35.9 ± 19.1 | 49.2 ± 18.7 | 0.008 |
At 1-year | |||
cSVA (mm) | 33.4 ± 18.4 | 49.3 ± 12.2 | < 0.001 |
CL (°) | 4.4 ± 12.2 | 10.9 ± 16.9 | 0.064 |
T1 slope (°) | 28.3 ± 11.4 | 44.7 ± 10.1 | < 0.001 |
TS–CL (°) | 23.9 ± 10.7 | 33.8 ± 13.5 | 0.001 |
CBVA (°) | 0.81 ± 6.5 | 3.3 ± 6.5 | 0.558 |
MGS (°) | -2.2 ± 8.8 | 1.2 ± 9.2 | 0.150 |
C2–T3 angle (°) | -0.29 ± 20.5 | -2.3 ± 20.8 | 0.580 |
C2–T3 SVA (mm) | 63.2 ± 34.0 | 92.7 ± 22.4 | < 0.001 |
C2 slope (°) | 21.9 ± 11.0 | 33.3 ± 14.3 | < 0.001 |
% of Correction baseline to 1 year | |||
cSVA | 41.1 | 31.1 | 0.904 |
CL | 140.3 | 168.7 | 0.753 |
TS–CL | 20.5 | 24.9 | 0.775 |
MGS | 260.8 | 93.0 | 0.209 |
C2–T3 angle | 121.2 | 70.8 | 0.193 |
C2–T3 SVA | 3.1 | 13.7 | 0.052 |
C2 slope | 49.6 | 27.5 | 0.830 |
SVA, sagittal vertical axis; cSVA, cervical SVA; CL, cervical lordosis; TS–CL, T1 slope minus CL; CBVA, chin-brow vertical angle; MGS, McGregor’s slope.
p<0.05, statistically significant difference.
Order of prioritization based off of binary logistic ordinal regression values of radiographic parameters and cutoff values for correction
Radiographic parameter | OR | 95% CI | p-value | Cutoffs of correction prioritized in order |
---|---|---|---|---|
C2–T3 angle | 5.667 | 1.074–29.871 | 0.041 |
C2–T3 angle Δ ≥ 42.5° |
C2–C7 lordosis | 4.636 | 0.857–25.071 | 0.075 | CL Δ > 35.4° |
C2 slope | 3.200 | 0.852–12.026 | 0.085 | C2 slope Δ < -31.76° |
cSVA | 3.185 | 1.137–8.917 | 0.027 |
cSVA Δ < -11.57 mm |
MGS | 2.724 | 0.971–7.636 | 0.057 | MGS Δ < -2.16° |
C2–T3 SVA | 0.462 | 0.116–1.849 | 0.275 | C2–T3 SVA Δ > -30.8 mm |
TS–CL | 0.271 | 0.048–1.1516 | 0.137 | TS–CL Δ ≤ -33.6° |
OR, odds ratio; CI, confidence interval; SVA, sagittal vertical axis; cSVA, cervical SVA; CL, cervical lordosis; TS–CL, T1 slope minus CL; MGS, McGregor’s slope.
p<0.05, statistically significant difference.
NDI and mJOA scores at 1 year between patients who met proposed prioritization cutoff values and those who did not
Variable | Met improvement threshold | Did not meet improvement threshold | p-value |
---|---|---|---|
NDI scores at 1 year | |||
C2–T3 angle | 23.8 | 38 | 0.035 |
CL | 24.7 | 37.6 | 0.071 |
C2 slope | 31.8 | 37 | 0.398 |
cSVA | 32.6 | 39.3 | 0.158 |
MGS | 32.9 | 42.4 | 0.055 |
C2–T3 SVA | 34.7 | 45.5 | 0.130 |
TS–CL | 28.2 | 37 | 0.253 |
mJOA scores at 1 year | |||
C2–T3 angle | 15.78 | 14 | 0.087 |
CL | 15 | 14.15 | 0.442 |
C2 slope | 14.58 | 14.19 | 0.673 |
cSVA | 14.8 | 13.73 | 0.152 |
MGS | 14.58 | 13.61 | 0.197 |
C2–T3 SVA | 14.38 | 13.5 | 0.422 |
TS–CL | 15 | 14.17 | 0.477 |
NDI, Neck Disability Index; mJOA, modified Japanese Orthopaedic Association; SVA, sagittal vertical axis; cSVA, cervical SVA; CL, cervical lordosis; TS–CL, T1 slope minus CL; MGS, McGregor’s slope.
p<0.05, statistically significant difference.