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Cervical Alignment Variations in Different Postures and Predictors of Normal Cervical Kyphosis

A New Understanding

Hey, Hwee Weng Dennis, MBBS (Sing), MRCS (Ire), MMED (Orth), MCI (Sing), FRCSEd (Orth), FAMS (Orth); Lau, Eugene Tze-Chun, MB BChir (Cantab); Wong, Gordon Chengyuan, MBBS (Sing); Tan, Kimberly-Anne, MBBS (Aus), BSc (Med) Hons; Liu, Gabriel Ka-Po, MBBCh (Ire), MSc (Ire), FRCS (Ire), FRCSEd (Orth); Wong, Hee-Kit, MBBS (Sing), MMED (Surg), FRCS (Glas), MCh (Orth) Liv, FAMS (Orth)

doi: 10.1097/BRS.0000000000002160
CERVICAL SPINE
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Study Design. Comparative study of prospectively collected radiographic data.

Objective. To predict physiological alignment of the cervical spine and study its morphology in different postures.

Summary of Background Data. There is increasing evidence that normal cervical spinal alignment may vary from lordosis to neutral to kyphosis, or form S-shaped or reverse S-shaped curves.

Methods. Standing, erect sitting, and natural sitting whole-spine radiographs were obtained from 26 consecutive patients without cervical spine pathology. Sagittal vertical axis (SVA), global cervical lordosis, lower cervical alignment C4-T1, C0-C2 angle, T1 slope, C0-C7 SVA and C2-7SVA, SVA, thoracic kyphosis, thoracolumbar junctional angle, lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence were measured. Statistical analysis was performed to elucidate differences in cervical alignment for all postures. Predictive values of T1 slope and SVA for cervical kyphosis were evaluated.

Results. Most patients (73.0%) do not have lordotic cervical alignment (C2-C7) upon standing (mean −0.6, standard deviation 11.1°). Lordosis increases significantly when transitioning from standing to erect sitting, as well as from erect to natural sitting (mean −17.2, standard deviation 12.1°). Transition from standing to natural sitting also produces concomitant increases in SVA (−8.8–65.2 mm) and T1-slope (17.4°–30.2°). T1 slope and SVA measured during standing significantly predicts angular cervical spine alignment in the same position. SVA < 10 mm significantly predicts C4-C7 kyphosis (P < 0.001), and to a lesser extent, C2-C7 kyphosis (P = 0.02). T1 slope <20° is both predictive of C2-C7 and C4-7 kyphosis (P = 0.001 and P = 0.023, respectively). For global cervical Cobb angle, T1 slope seems to be a more significant predictor of kyphosis than SVA (odds ratio 17.33, P = 0.001 vs odds ratio 11.67, P = 0.02, respectively).

Conclusion. The cervical spine has variable normal morphology. Key determinants of its alignment include SVA and T1 slope. Lordotic correction of the cervical spine is not always physiological and thus correction targets should be individualized.

Level of Evidence: 3

University Orthopaedics, Hand and Reconstructive Microsurgery Cluster (UOHC), National University Health System, Singapore.

Address correspondence and reprint requests to Hwee Weng Dennis Hey, MBBS (Sing), MRCS (Ire), MMED (Orth), MCI (Sing), FRCSEd (Orth), FAMS (Orth), University Orthopaedics, Hand and Reconstructive Microsurgery Cluster (UOHC), National University Health System, 1E Kent Ridge Rd, NUHS Tower Block Level 11, Singapore 119228; E-mail: dennis_hey@nuhs.edu.sg

Received 7 November, 2016

Revised 28 January, 2017

Accepted 23 February, 2017

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

No relevant financial activities outside the submitted work.

Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.