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Journal of Craniovertebral Junction and Spine
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Year : 2021  |  Volume : 12  |  Issue : 4  |  Page : 401-405  

What are the major drivers of outcomes in cervical deformity surgery?

1 Departments of Orthopaedic and Neurologic Surgery, NYU Langone Orthopedic Hospital, New York Spine Institute, New York, NY, USA
2 Department of Orthopedics, SUNY Downstate, New York, NY, USA

Date of Submission26-Jul-2021
Date of Acceptance06-Nov-2021
Date of Web Publication11-Dec-2021

Correspondence Address:
Peter Gust Passias
Departments of Orthopaedic and Neurological Surgery, Division of Spinal Surgery, NYU Langone Medical Center, Orthopaedic Hospital – NYU School of Medicine, New York Spine Institute, 301 East 17th St, New York 10003, NY
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jcvjs.jcvjs_106_21

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Background Context: Cervical deformity (CD) correction is becoming more challenging and complex. Understanding the factors that drive optimal outcomes has been understudied in CD corrective surgery.
Purpose: The purpose of the study was to weight baseline (BL) factors on impact upon outcomes following CD surgery.
Study Design/Setting: This was a retrospective review of a single-center database.
Patient Sample: The sample size of the study was 61 cervical patients.
Outcome Measures: Two outcomes were measured: “Improved outcome (IO)”: (1) radiographic improvement: “nondeformed” Schwab pelvic tilt (PT)/sagittal vertical axis (SVA) and Ames cervical sagittal vertical axis (cSVA)/T1 Slope – cervical lordosis (TSCL); (2) clinical: MCID Euro-QOL 5 Dimension (EQ5D), Neck Disability Index (NDI), or improvement in modified Japanese Orthopedic Association (mJOA) scale modifier; and (3) complications/reoperation: no reoperation or major complications and “poor outcome” (PO): (1) radiographic deterioration: “moderate” or “severely” deformed Schwab SVA/PT and Ames cSVA/TS-CL; (2) clinical: not meeting MCID EQ5D and NDI worsening in mJOA modifier; and (3) complications/reoperation: reoperation or complications.
Materials and Methods: CD patients included full BL and 1-year (1Y) radiographic measures and Health related quality of life (HRQLs) questionnaires. Patients who underwent a reoperation for infection were excluded. Patients were categorized by IO, PO, or not. Random forest assessed ratios of predictors for IO and PO. Categorical regression models predicted how BL regional deformity (Ames cSVA, TS-CL, and horizontal gaze), BL global deformity (Schwab PI-LL, SVA, and PT), regional/global change (BL to 1Y), BL disability (mJOA score), and BL pain/function impact outcomes.
Results: Sixty-one patients were included in the study (55.8 years, 54.1% of females). Surgical approach included 18.3% anterior, 51.7% posterior, and 30% combined. The average number of levels fused for the cohort was 7.7. Mean operative time was 823 min, and estimated blood loss (EBL): 1037ccs. At 1Y, 24.6% had an IO and 9.8% had PO. Random forest analysis showed the top five individual factors associated with an IO: BL maximum kyphosis, maximum lordosis, C0–C2, L4 pelvic angle, and NSR back pain (80% radiographic, 20% clinical). Categorical IO regression model (R2 = 0.328, P = 0.007) showed low BL regional deformity (β = ‒0.082), low BL global deformity (β = ‒0.099), global improvement (β = ‒0.532), regional improvement (β = ‒0.230), low BL disability (β = ‒0.100), and low BL NDI (β = ‒0.024). Random forest demonstrated the top five individual BL factors associated with PO, 80% were radiographic: BL CL apex, DJK angle, cervical lordosis, T1 slope, and NSR neck pain. Categorical PO regression model (R2 = 0.306, P = 0.012) showed high BL regional deformity (β = ‒0.108), high BL global deformity (β = ‒0.255), global decline (β = ‒0.272), regional decline (β = 0.443), BL disability (β = −‒0.164), BL and severe NDI (>69) (β = ‒0.181).
Conclusions: Categorical weight demonstrated radiographic as the strongest predictor of both improved (global alignment) and PO (regional deformity/deterioration). Radiographic factors carry the most weight in determining an improved or PO, and can be ultimately utilized in preoperative planning and surgical decision-making to optimize outcomes.

Keywords: Cervical deformity, patient reported outcomes, radiographic outcomes

How to cite this article:
Passias PG, Pierce KE, Imbo B, Krol O, Passfall L, Tretiakov P, Moattari K, Williamson T, Joujon-Roche R, Passano B, Ahmad W, Naessig S, Diebo B. What are the major drivers of outcomes in cervical deformity surgery?. J Craniovert Jun Spine 2021;12:401-5

How to cite this URL:
Passias PG, Pierce KE, Imbo B, Krol O, Passfall L, Tretiakov P, Moattari K, Williamson T, Joujon-Roche R, Passano B, Ahmad W, Naessig S, Diebo B. What are the major drivers of outcomes in cervical deformity surgery?. J Craniovert Jun Spine [serial online] 2021 [cited 2023 May 30];12:401-5. Available from: https://www.jcvjs.com/text.asp?2021/12/4/401/332206

   Introduction Top

Cervical deformity (CD) refers to malalignment of the normal lordotic curve of the cervical spine, with the most common CD being cervical kyphosis.[1] Ramchandran et al. attempt to define CD as at least one of the following: cervical kyphosis, cervical scoliosis, C2–C7 cervical sagittal vertical axis (cSVA) >4 cm, or chin-brow vertical angle (CBVA) >25°.[2] There are multiple etiologies of CD which can result in pain or possibly neurologic or physical impairment.[3]

The indications for surgical correction of cervical deformity include progressive myelopathy, severe radiculopathy, other severe neurologic deficit, and severe functional impairment (i.e., dysphagia), severe mechanical pain, and progressive kyphotic deformity.[4],[5],[6] Surgical management attempts to relieve pain, decompress neurologic elements, realign the cervical spine, improve horizontal gaze, and improve function. Outcomes of CD correction are poorly defined. Greater degree of surgical CD correction has been associated with improved patient-reported outcomes.[7] Radiographic cervical parameters have been previously correlated with HRQL. One study found a significant correlation between baseline (BL) C2–C7 sagittal vertical axis (SVA) values of 5 cm or more and worse outcomes on HRQL assessments.[8] In addition, positive sagittal malalignment has been linked to poor Neck Disability Index (NDI) scores.[9]

A recent study showed myelopathy to be a strong independent driver of patient-oriented outcome measures.[10] This retrospective study attempts to use full BL and 1-year (1Y) radiographic measures as well as HRQL measures to predict if a patient will have an “improved outcome (IO),” “poor outcome (PO),” or “null outcome.”

   Materials and Methods Top

Data overview

Patients with a clinical diagnosis of cervical spine deformity, greater or equal to 18 years of age, and undergoing cervical fusion procedures by a single spine surgeon were included in the dataset. The database required radiographic evidence of CD, defined as cervical kyphosis (C2–C7 sagittal Cobb angle >10°), cervical scoliosis (C2–C7 coronal Cobb angle >10°), C2–C7 sagittal vertical axis (C2–C7 SVA) >4 cm, or CBVA >25°, measured with preoperative radiographs. Institutional Review Board approval was obtained prior to enrollment, and every patient gave consent before data collection.

Study inclusion criteria

Patients included underwent a cervical osteotomy and had full BL and 1Y radiographic and health-related quality of life (HRQL) data. Those who underwent reoperation for an infection were excluded.

Data collection

Basic BL data were collected prior to operative intervention, including age, gender, body mass index, and comorbidity burden, otherwise described as the Charlson Comorbidity Index.

Surgical data were also collected for analysis, such as total number of levels fused, surgical approach, decompression type, and osteotomy type: three column osteotomy, Ponte osteotomy, and facet osteotomy. Patient-reported outcomes were collected and recorded in the dataset, including the NDI, modified Japanese Orthopedic Association (mJOA) scale, and Euro-QOL 5-Dimension (EQ5D) questionnaire, but these health-related quality of life questionnaires (HRQLs) were not utilized in the present study.

BL up to 1Y postoperative radiographs were measured using validated software programming (SpineView; ENSAM Laboratory of Biomechanics, Paris, France) at a single academic center. Cervical sagittal alignment and balance was evaluated using C2–C7 Cobb angle for cervical lordosis (CL: angle between the lower endplates of C2 and C7), cSVA (C2 plumb line offset from the posterosuperior corner of C7), and the mismatch between T1 slope and CL (TS-CL). Global sagittal alignment measures assessed included thoracic kyphosis (TK: angle between the lower endplates of T4 and T12) and lumbar lordosis (LL: angle between the lower endplates of L1 and S1).

Outcome measures

Patients were classified as having a postoperative IO, PO, or null outcome. To define these outcome measures, patients were required to have three categories fulfilled of radiographic outcome, clinical outcome, and complication/reoperation outcome. The radiographic outcomes were classified as the software requirements specification (SRS)–Schwab adult spinal deformity severity modifiers and the Ames-ISSG CD modifiers. The clinical outcomes were derived from the HRQLs of NDI, mJOA, and EQ5D. Finally, the complication/reoperation outcome depended on the presence or absence of a postoperative complication or reoperation.

An IO was defined as improved in all three outcomes: radiographic, clinical, and complication/reoperation. The radiographic outcome for the IO patients included having a 1Y postoperative “0” SRS–Schwab modifier category for pelvic tilt (PT <20°) and sagittal vertical axis (SVA <4 cm), along with a “0” Ames-ISSG (cSVA <4 cm) and T1 slope minus CL (TS-CL <15°). Their clinical outcome required having met the minimal clinically important difference for EQ5D (a BL to 1Y difference of >0.09) and NDI (a BL to 1Y difference of <15), as well as improvement in the patient's Ames-ISSG mJOA modifier. For the last category, these patients did not have a postoperative complication or reoperation.

For the PO, the opposite of every category was utilized for definition. The radiographic outcome had + or ++ SRS– Schwab PT and SVA modifier severity (>20° and > 4 cm, respectively), as well as “1” or “2” 1Y Ames ISSG cSVA and TS CL modifier severity (>4 cm and 15°, respectively). The clinical outcome for PO had no patients meeting MCID for either EQ5D or NDI, as well as worsening in their Ames-ISSG mJOA modifier. Meanwhile, these patients did experience a complication or reoperation after their procedure.

Statistical analysis

Descriptive statistics provided basic means and characteristics of our patient cohort. Chi-square analyses assessed significance of categorical variables. Random forest assessment generated 10,000 conditional inference trees to determine the top five preoperative factors associated with an outcome (IO and PO).

Categorical linear regression model predicted the following impact on our IO and PO: BL regional deformity, BL global deformity, regional change, global change, BL disability, and BL pain function. BL regional deformity was defined via the Ames-ISSG CD modifiers, where preoperative low deformity was a “0” in cSVA, TS-CL, and CBVA modifiers, while high was “2” Ames-ISSG severity in cSVA and TS-CL modifiers. BL global deformity was defined as the SRS–Schwab modifiers of “0” SVA, PI-LL, and PT at BL for low, and high for “++” in those radiographic parameters. Regional change was defined as BL to 1Y improvement (”1” or “2” to a respective “0” or “1”) or decline (”0” or “1” to a respective “1” or “2”) in Ames-ISSG modifier severity. Global change included BL to 1Y improvement (+ or ++ to a respective “0” or +) or decline (”0” or + to a respective + or ++) in SRS–Schwab modifier severity. BL disability was defined via mJOA scores, where low as a “0” and high as “1” or “2” in Ames-ISSG modifier severity. Finally, the BL pain/function category was defined via the BL NDI scores, where low included those who had preoperative scores from 0 to 28 and severe as >50.

All statistic tests were run on the Statistical analysis was performed using SPSS software (version 21.0, IBM, Armonk, New York) software, with P < 0.05 noted as statistically significant.

   Results Top

Cohort overview

Overall, there were 61 patients included in our study. The mean age for the cohort was 55.8 years, with 54.1% as female. The surgical approach breakdown included 18.3% as anterior approach, 51.7% posterior approach, and 30% who underwent combined anterior–posterior approach. The average total levels fused was 7.7, with a mean operative time of 823 min. Estimated blood loss for the cohort averaged around 1037 ccs.

Radiographic overview

Patients presented radiographically at BL with an average PT of 16.2 ± 8.02, PI-LL of −3.46 ± 11.9, SVA: −5.05 ± 59.8, TS-CL: 23.0 ± 14.1, and cSVA: 26.8 ± 15.7. At 1Y postoperatively, patients presented with an average PT of 13.4 ± 7.34, PI-LL of − 5.47 ± 13.6, SVA: −4.70 ± 40.8, TS-CL: 21.0 ± 8.26, and cSVA: 25.7 ± 10.7.

Breakdown of outcome groups

At 1Y, 24.6% were classified with an IO and 9.8% of the cohort had a PO.

Random forest variables

Our random forest with conditional inference tree analysis showed the top five individual factors associated with those that were classified with an IO which were BL maximum kyphosis, BL maximum lordosis, C0–C2 angle, L4 pelvic angle, and NRS back pain. This amounted to 80% radiographic factors and 20% clinical.

The random forest for the PO demonstrated of the top five individual BL factors, 80% were radiographic, with 20% as clinical. These factors included BL CL apex, the DJK angle, CL, T1 slope, and BL NRS neck pain.

Categorical regression models

The IO categorical regression model had an R2 value of 0.328 (P = 0.007), including low BL regional deformity (β = −0.082), low BL global deformity (β = −0.099), global improvement (β = 0.532), regional improvement (β = 0.230), low BL disability (β = 0.100), and low BL NDI (β = 0.024).

Categorical PO regression model demonstrated an R2 value of 0.306 (P = 0.012), comprised of high BL regional deformity (β = −0.108), high BL global deformity (β = −0.255), global decline (β = 0.272), regional decline (β = 0.443), high BL disability (β = −0.164), and BL severe NDI (>69) (β = 0.181).

   Discussion Top

Restoration of cervical sagittal alignment is challenging, complex, and poses risk for major complications as well as poor patient-reported outcomes. Although outcomes can range widely, CD corrective surgery results in overall high patient satisfaction and appears to be an effective option when conservative measures fail.[1],[2] Understanding the factors that drive optimal outcomes has been understudied in CD corrective surgery. Previous research has revealed that determinants of patient outcomes are multifactorial and include a combination of patient, surgical, and radiographic parameters.[2] The present cohort of 61 patients who underwent CD correction was analyzed to determine factors which predict “improved operative outcomes” (IO) versus “poor operative outcomes” (PO). Categorical weight demonstrated that radiographic factors carry the most weight in determining an IO or PO, which can ultimately be utilized in preoperative planning and surgical decision-making to optimize outcomes.

In the present study, random forest demonstrated the top five individual factors associated with IO to be BL maximum kyphosis, BL maximum lordosis, C0–C2, L4 pelvic angle, and NSR back pain. Furthermore, random forest demonstrated the top five individual factors associated with PO to be BL CL Apex, DJK angle, CL, T1 slope, and NSR neck pain.

Few studies have attempted to characterize determinants of outcomes following CD corrective surgery. A study by Tang et al. found that disability of the neck increases with progressive cervical malalignment. Specifically, they found a correlation between cSVA >40 mm and worse outcomes on health-related quality of life (HRQL) measures.[3] It has been found that postoperative improvements in cervical regional alignment positively correlate with improved HRQL measures.[4] Smith et al. found that residual global sagittal malalignment (C7-S1 SVA) was associated with worse outcomes based on NDI2. Furthermore, a study by Passias et al. demonstrated relationships between myelopathy, global sagittal realignment, and HRQL measures following CD correction. They concluded that improvement in myelopathy symptoms, as assessed by mJOA, is a key driver of patient-reported outcomes following corrective surgery and demonstrates the importance of correcting sagittal alignment in these patients.[5] However, Kato et al. found no significant differences in postoperative outcomes regardless of achievement of deformity correction in patients with myelopathy, and concluded that aggressive realignment in these patients may not be necessary.[6] One contributing factor to this inconsistency may be related to current HRQL metrics not being deformity specific. Current metrics can fail to fully assess a patient's deformity and outcomes, making analysis of CD patients challenging and unreliable.[7]

Researchers have previously explored determinants of poor operative outcomes. One such study by Protopsaltis et al. prospectively attempted to characterize factors leading relating to failure to radiographically correct cervical alignment. Failure to correct cSVA was associated with revision surgery, worse preoperative C2 PT angle, concurrent thoracolumbar deformity, and failure to correct secondary, thoracolumbar drivers of deformity. Early postoperative DJK was also a major determinant of these radiographic failures.[8] Further studies have similarly determined that the location and subsequent correction of the primary driver of the deformity is an important determinant for clinical and radiographic outcomes.[9] Furthermore, a recent study by Bortz et al. determined that severe preoperative malalignments were the strongest indicators of nonroutine discharge following corrective surgery. These preoperative alignments included C1 slope >14, TS-CL ≥57, and cSVA ≥40 mm.[10]

In the present study, categorical regression models found that radiographic factors carry the most weight in determining an improved or PO. In both IO and PO groups, change in global (SRS–Schwab modifier severity) and regional (Ames modifier severity) radiographic measures from BL to 1Y following surgery most strongly correlated with operative outcome. This was more strongly correlated than BL radiographic measures and clinical HRQL measures. Therefore, it is believed that these radiographic measures are the key drivers of outcomes.

The relationship between cervical radiographic measures and outcomes has been studied in the past. Villavicencio et al. found that, following ACDF, maintaining or improving segmental sagittal alignment had significant effect on improvement in outcome measures.[11] This is contrasted by studies which have failed to find a relationship between regional alignment and functional status.[12],[13],[14] Guérin et al. found no relationship between C2–C7 alignment and HRQL measures.[13] Aykac et al. were unable to find a correlation between HRQL measures and cervical-specific radiographic parameters (C0–C2 and C2–C7 lordosis) in patients with adolescent idiopathic scoliosis.[14]

   Conclcusion Top

In this context, we sought to identify factors that may drive outcomes following adult CD surgery. In order to support this work, we used a prospective single center database of consecutively enrolled cervical deformity patients. This dataset has been used to study patient outcomes and associated risk factors following surgical correction of CD


This study has accompanying limitations due to its retrospective nature. In addition, there is not currently a CD-specific outcome measure; therefore, more general measures needed to be used to assess patient outcomes. Clinical research in this area is sparse and further studies are needed to fully characterize the determinants of outcomes in CD corrective surgery.

Financial support and sponsorship


Conflicts of interest

Peter G Passias MD reports personal consulting fees for Spine Wave, Zimmer Biomet, DePuy Synthes, and Medicrea outside the submitted work.

   References Top

Etame AB, Wang AC, Than KD, La Marca F, Park P. Outcomes after surgery for cervical spine deformity: Review of the literature. Neurosurg Focus 2010;28:E14.  Back to cited text no. 1
Ramchandran S, Protopsaltis TS, Sciubba D, Scheer JK. Prospective multi-centric evaluation of upper cervical and infra-cervical sagittal compensatory alignment in patients with adult cervical deformity. Eur Spine J 2018;27:416-25.  Back to cited text no. 2
Tang JA, Scheer JK, Smith JS, Deviren V, Bess S, Hart RA, et al. The impact of standing regional cervical sagittal alignment on outcomes in posterior cervical fusion surgery. Neurosurgery 2015;76 Suppl 1:S14-21.  Back to cited text no. 3
Protopsaltis TS, Scheer JK, Terran JS, Smith JS, Hamilton DK, Kim HJ, et al. How the neck affects the back: Changes in regional cervical sagittal alignment correlate to HRQOL improvement in adult thoracolumbar deformity patients at 2-year follow-up. J Neurosurg Spine 2015;23:153-8.  Back to cited text no. 4
Passias PG, Horn SR, Bortz CA, Ramachandran S, Burton DC, Protopsaltis T, et al. The relationship between improvements in myelopathy and sagittal realignment in cervical deformity surgery outcomes. Spine (Phila Pa 1976) 2018;43:1117-24.  Back to cited text no. 5
Kato S, Nouri A, Wu D, Nori S, Tetreault L, Fehlings MG. Impact of cervical spine deformity on preoperative disease severity and postoperative outcomes following fusion surgery for degenerative cervical myelopathy: Sub-analysis of AOSpine North America and International Studies. Spine (Phila Pa 1976) 2018;43:248-54.  Back to cited text no. 6
Passias PG, Horn SR, Oh C, Ramchandran S, Burton DC, Lafage V, et al. Evaluating cervical deformity corrective surgery outcomes at 1-year using current patient-derived and functional measures: Are they adequate? J Spine Surg 2018;4:295-303.  Back to cited text no. 7
Protopsaltis TS, Ramchandran S, Hamilton DK, Sciubba D, Passias PG, Lafage V, et al. Analysis of successful versus failed radiographic outcomes after cervical deformity surgery. Spine (Phila Pa 1976) 2018;43:E773-81.  Back to cited text no. 8
Passias PG, Bortz C, Horn S, Segreto F, Poorman G, Jalai C, et al. Drivers of cervical deformity have a strong influence on achieving optimal radiographic and clinical outcomes at 1 year after cervical deformity surgery. World Neurosurg 2018;112:e61-8.  Back to cited text no. 9
Bortz CA, Passias PG, Segreto F, Horn SR, Lafage V, Smith JS, et al. Indicators for nonroutine discharge following cervical deformity-corrective surgery: Radiographic, surgical, and patient-related factors. Neurosurgery 2019;85:E509-19.  Back to cited text no. 10
Villavicencio AT, Babuska JM, Ashton A, Busch E, Roeca C, Nelson EL, et al. Prospective, randomized, double-blind clinical study evaluating the correlation of clinical outcomes and cervical sagittal alignment. Neurosurgery 2011;68:1309-16.  Back to cited text no. 11
Jagannathan J, Shaffrey CI, Oskouian RJ, Dumont AS, Herrold C, Sansur CA, et al. Radiographic and clinical outcomes following single-level anterior cervical discectomy and allograft fusion without plate placement or cervical collar. J Neurosurg Spine 2008;8:420-8.  Back to cited text no. 12
Guérin P, Obeid I, Gille O, Bourghli A, Luc S, Pointillart V, et al. Sagittal alignment after single cervical disc arthroplasty. J Spinal Disord Tech 2012;25:10-6.  Back to cited text no. 13
Aykac B, Ayhan S, Yuksel S, Guler UO, Pellise F, Alanay A, et al. Sagittal alignment of cervical spine in adult idiopathic scoliosis. Eur Spine J 2015;24:1175-82.  Back to cited text no. 14


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