The morphology of cervical deformities: a two-step cluster analysis to identify cervical deformity patterns

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OBJECTIVE

Cervical deformity (CD) is difficult to define due to the high variability in normal cervical alignment based on postural- and thoracolumbar-driven changes to cervical alignment. The purpose of this study was to identify whether patterns of sagittal deformity could be established based on neutral and dynamic alignment, as shown on radiographs.

METHODS

This study is a retrospective review of a prospective, multicenter database of CD patients who underwent surgery from 2013 to 2015. Their radiographs were reviewed by 12 individuals using a consensus-based method to identify severe sagittal CD. Radiographic parameters correlating with health-related quality of life were introduced in a two-step cluster analysis (a combination of hierarchical cluster and k-means cluster) to identify patterns of sagittal deformity. A comparison of lateral and lateral extension radiographs between clusters was performed using an ANOVA in a post hoc analysis.

RESULTS

Overall, 75 patients were identified as having severe CD due to sagittal malalignment, and they formed the basis of this study. Their mean age was 64 years, their body mass index was 29 kg/m2, and 66% were female. There were significant correlations between focal alignment/flexibility of maximum kyphosis, cervical lordosis, and thoracic slope minus cervical lordosis (TS-CL) flexibility (r = 0.27, 0.31, and −0.36, respectively). Cluster analysis revealed 3 distinct groups based on alignment and flexibility. Group 1 (a pattern involving a flat neck with lack of compensation) had a large TS-CL mismatch despite flexibility in cervical lordosis; group 2 (a pattern involving focal deformity) had focal kyphosis between 2 adjacent levels but no large regional cervical kyphosis under the setting of a low T1 slope (T1S); and group 3 (a pattern involving a cervicothoracic deformity) had a very large T1S with a compensatory hyperlordosis of the cervical spine.

CONCLUSIONS

Three distinct patterns of CD were identified in this cohort: flat neck, focal deformity, and cervicothoracic deformity. One key element to understanding the difference between these groups was the alignment seen on extension radiographs. This information is a first step in developing a classification system that can guide the surgical treatment for CD and the choice of fusion level.

ABBREVIATIONS CD = cervical deformity; cSVA= cervical sagittal vertical axis; HRQOL = health-related quality of life; mJOA = modified Japanese Orthopaedic Association; NDI = Neck Disability Index; NRS = numeric rating scale; TS-CL = thoracic slope minus cervical lordosis; T1S = T1 slope.
Article Information

Contributor Notes

Correspondence Renaud Lafage: Hospital for Special Surgery, New York, NY. renaud.lafage@gmail.com.INCLUDE WHEN CITING Published online November 15, 2019; DOI: 10.3171/2019.9.SPINE19730.Disclosures Dr. Passias reports being a paid presenter or speaker for AlloSource, the Cervical Scoliosis Research Society, Globus Medical, Medicrea, SpineWave, and Zimmer Biomet. Dr. Ames reports he is an employee of the University of California, San Francisco; he is a consultant for DePuy Synthes, Medtronic, Stryker, Medicrea, K2M, and Zimmer Biomet; he receives royalties from Stryker, Zimmer Biomet, DePuy Synthes, NuVasive, Next Orthosurgical, K2M, and Medicrea; he does research for Titan Spine, DePuy Synthes, and the International Spine Study Group (ISSG); he is on the editorial board of Operative Neurosurgery; he has received grant funding from the Scoliosis Research Society; he is on the executive committee of ISSG; and he is the director of Global Spine Analytics. Dr. Shaffrey reports he owns stock in NuVasive; he is a consultant for Medtronic, NuVasive, SI-Bone, and Siemens; and he holds patents with Medtronic, NuVasive, Zimmer Biomet, and SI-Bone. Dr. Mundis reports being a consultant for NuVasive, K2M, Viseon, and SeaSpine; and he owns stock in NuVasive and Viseon. Dr. Gutpa reports being a consultant for Medtronic and DePuy Synthes; he owns stock in J&J and P&G; he receives royalties from Innomed; he has received funds for travel expenses from Medicrea; and his institution receives grant funding for a fellowship from AOSpine and OMeGA. Dr. Klineberg reports being a consultant for DePuy Synthes, Stryker, and Medicrea; and he has received fellowship grant funding and honoraria from AOSpine. Dr. Smith reports being a consultant for Zimmer Biomet, NuVasive, Stryker, AlloSource, and Cerapedics; he received clinical or research support for the present study from DePuy Synthes and ISSG, which also provided funding for non–study-related clinical or research efforts that he oversees; he has received fellowship support from NREF and AOSpine; he receives royalties from Zimmer Biomet and NuVasive; and he owns stock in Alphatec. Dr. Burton reports receiving clinical or research support for the present study from DePuy Synthes; he is a consultant for Bioventus; he has received funding of non–study-related clinical or research efforts that he oversees from Pfizer; and he holds a patent with DePuy Synthes. Dr. Schwab reports being a consultant for Globus Medical, Zimmer Biomet, K2M, and MSD; he has received funding for non–study-related clinical or research efforts that he oversees from DePuy Synthes, K2M, NuVasive, Medtronic, AlloSource, Orthofix, and SI-Bone through ISSG; and he has paid speaking/teaching arrangements with Globus Medical, Zimmer Biomet, K2M, and MSD. Dr. V. LaFage reports she has received funding for non–study-related clinical or research efforts that she oversees from DePuy Synthes, K2M, NuVasive, Medtronic, AlloSource, Orthofix, and SI-Bone through ISSG; she is a consultant for Globus Medical; and she has paid teaching/speaking arrangements with DePuy Synthes. Mr. R. LaFage reports owning stock in Nemaris.
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