Reliability assessment of a novel cervical spine deformity classification system.
OBJECTIVE
Despite the complexity of cervical spine deformity (CSD) and its significant impact on patient quality of life, there exists no comprehensive classification system. The objective of this study was to develop a novel classification system based on a modified Delphi approach and to characterize the intra- and interobserver reliability of this classification.


METHODS
Based on an extensive literature review and a modified Delphi approach with an expert panel, a CSD classification system was generated. The classification system included a deformity descriptor and 5 modifiers that incorporated sagittal, regional, and global spinopelvic alignment and neurological status. The descriptors included: "C," "CT," and "T" for primary cervical kyphotic deformities with an apex in the cervical spine, cervicothoracic junction, or thoracic spine, respectively; "S" for primary coronal deformity with a coronal Cobb angle ≥ 15°; and "CVJ" for primary craniovertebral junction deformity. The modifiers included C2-7 sagittal vertical axis (SVA), horizontal gaze (chin-brow to vertical angle [CBVA]), T1 slope (TS) minus C2-7 lordosis (TS-CL), myelopathy (modified Japanese Orthopaedic Association [mJOA] scale score), and the Scoliosis Research Society (SRS)-Schwab classification for thoracolumbar deformity. Application of the classification system requires the following: 1) full-length standing posteroanterior (PA) and lateral spine radiographs that include the cervical spine and femoral heads; 2) standing PA and lateral cervical spine radiographs; 3) completed and scored mJOA questionnaire; and 4) a clinical photograph or radiograph that includes the skull for measurement of the CBVA. A series of 10 CSD cases, broadly representative of the classification system, were selected and sufficient radiographic and clinical history to enable classification were assembled. A panel of spinal deformity surgeons was queried to classify each case twice, with a minimum of 1 intervening week. Inter- and intrarater reliability measures were based on calculations of Fleiss k coefficient values.


RESULTS
Twenty spinal deformity surgeons participated in this study. Interrater reliability (Fleiss k coefficients) for the deformity descriptor rounds 1 and 2 were 0.489 and 0.280, respectively, and mean intrarater reliability was 0.584. For the modifiers, including the SRS-Schwab components, the interrater (round 1/round 2) and intrarater reliabilities (Fleiss k coefficients) were: C2-7 SVA (0.338/0.412, 0.584), horizontal gaze (0.779/0.430, 0.768), TS-CL (0.721/0.567, 0.720), myelopathy (0.602/0.477, 0.746), SRS-Schwab curve type (0.590/0.433, 0.564), pelvic incidence-lumbar lordosis (0.554/0.386, 0.826), pelvic tilt (0.714/0.627, 0.633), and C7-S1 SVA (0.071/0.064, 0.233), respectively. The parameter with the poorest reliability was the C7-S1 SVA, which may have resulted from differences in interpretation of positive and negative measurements.


CONCLUSIONS
The proposed classification provides a mechanism to assess CSD within the framework of global spinopelvic malalignment and clinically relevant parameters. The intra- and interobserver reliabilities suggest moderate agreement and serve as the basis for subsequent improvement and study of the proposed classification.
Department of Neurosurgery, University of California, San Francisco, California;
Christopher P
CP
Ames
Department of Neurosurgery, University of Virginia Medical Center, Charlottesville, Virginia;
Justin S
JS
Smith
San Diego Center for Spinal Disorders, San Diego, California;
Robert
R
Eastlack
San Diego Center for Spinal Disorders, San Diego, California;
Donald J
DJ
Blaskiewicz
Department of Neurosurgery, University of Virginia Medical Center, Charlottesville, Virginia;
Christopher I
CI
Shaffrey
Department of Orthopedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
Frank
F
Schwab
Department of Orthopedic Surgery, Rocky Mountain Hospital for Children, Denver, Colorado;
Shay
S
Bess
Department of Orthopedic Surgery, Hospital for Special Surgery, New York, New York;
Han Jo
HJ
Kim
San Diego Center for Spinal Disorders, San Diego, California;
Gregory M
GM
Mundis
Department of Orthopedic Surgery, University of California, Davis, Sacramento, California;
Eric
E
Klineberg
Department of Orthopedic Surgery, University of California, Davis, Sacramento, California;
Munish
M
Gupta
Department of Orthopedic Surgery, Baylor Scoliosis Center, Plano, Texas;
Michael
M
O'Brien
Department of Orthopedic Surgery, Baylor Scoliosis Center, Plano, Texas;
Richard
R
Hostin
Department of Neurosurgery, Northwestern University Feinberg School of Medicine, Chicago, Illinois;
Justin K
JK
Scheer
Department of Orthopedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
Themistocles S
TS
Protopsaltis
Department of Neurosurgery, Weill Cornell Medical College, New York, New York;
Kai-Ming G
KM
Fu
Department of Orthopedic Surgery, Oregon Health Sciences University, Portland, Oregon;
Robert
R
Hart
Department of Orthopedic Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania;
Todd J
TJ
Albert
Department of Orthopedic Surgery, Washington University, St Louis, Missouri;
K Daniel
KD
Riew
Department of Neurosurgery, University of Toronto, Ontario, Canada; and.
Michael G
MG
Fehlings
Department of Orthopaedic Surgery, University of California, San Francisco, California.
Vedat
V
Deviren
Department of Orthopedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
Virginie
V
Lafage
D002574:Cervical Vertebrae; D003697:Delphi Technique; D006801:Humans; D015588:Observer Variation; D011859:Radiography; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D013121:Spinal Curvatures / Q000145:classification* / Q000000981:diagnostic imaging; D013904:Thoracic Vertebrae
CBVA = chin-brow to vertical angle; CL = cervical lordosis; CSD = cervical spine deformity; CVJ = craniovertebral junction; HRQOL = health-related quality of life; LL = lumbar lordosis; NDI = Neck Disability Index; PA = posteroanterior; PI = pelvic incidence; PT = pelvic tilt; SF-36 = 36-Item Short Form Health Survey; SRS = Scoliosis Research Society; SVA = sagittal vertical axis; TS = T-1 slope; cervical spine deformity; classification; horizontal gaze; kyphosis; mJOA = modified Japanese Orthopaedic Association Scale; myelopathy; sagittal alignment; validation