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

A New Understanding

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

Disclosures

Spine. 2017;42(21):1614-1621. 

In This Article

Methodology

Study Design

This is a comparative study, which analyses whole-spine radiographs taken during standing, erect sitting, and natural sitting prospectively. This study has been approved by the local ethics board committee and was conducted over a 6-month period at a single tertiary healthcare centre with a dedicated spine surgery service.

Patients younger than 30 years presenting with first episodes of isolated mechanical, low back pain, which had lasted for less than 3 months were recruited. In order to rule-out potentially confounding pre-existing spinal problems, all patients underwent a detailed history taking and physical examination before enrolment.

Exclusion criteria included the following:

  1. Patients with neck pain, upper limb radiculopathy, or myelopathy.

  2. Previous spinal conditions including those listed in (1) or surgical intervention to the spine.

  3. Presence of red flag symptoms including constant pain, night pain, fever, loss of weight, and loss of appetite.

  4. Significant previous or recent trauma to the spine.

  5. Significant history of malignancy or family history of malignancy.

  6. Presence of spinal deformity on forward bending test.

  7. Contraindications to radiographs (e.g., existing or suspected pregnancy).

Radiographic Examination

Following clinical assessment by the attending spine specialist, all patients underwent three sets of whole-spine lateral radiographs using EOS technology (EOS Imaging, Paris, France).[16] The sequence of radiographs was randomized through drawing lots.

Pictorial charts demonstrating how to stand and sit in an erect manner were displayed beside the EOS machine for better standardization. The uniformity of these postures was further reinforced through standardized verbal instructions given by the radiographer. All images were taken by trained radiographers with more than 2 years of experience in using EOS technology.

For the standing radiograph, patients were instructed to "keep [their] eyes horizontal and look straight ahead, stand as straight as possible without leaning forwards or backwards, and touch [their] collar bones with [their] fingers." For the erect sitting radiograph, the patients were instructed to "keep [their] eyes horizontal and look straight ahead, sit as straight as possible without leaning forwards or backwards, and touch [their] collar bones with [their] fingers." Finally, for the natural sitting radiograph, patients were instructed to "keep [their] eyes horizontal and look straight ahead, sit as naturally as [they] would on a chair." Once this posture had been assumed, the patients were then told to "hold on to [their] current posture and bring [their] fingers to touch [their] collarbones."

Radiographic Measurements

The EOS radiographs obtained were stored on the secured hospital server and accessed using Centricity Enterprise Web (General Electric) for measurements of spinal parameters. Measurements were conducted by two blinded orthopedic specialists and an average reading was recorded.

Key cervical parameters measured include global cervical lordosis (CL), lower cervical alignment (LCA) taken from C4 to T1, C0-C2 angle, T1-slope, C0-C7 SVA, and C2-7SVA. C4 was taken for C4-T1 angular measurements based on pilot data, which showed that S-shaped and inverted S-shaped curves had end vertebra at C4.

CL was measured using the Harrison posterior tangent method[17] on the C2 and C7 vertebrae. LCA was measured using the Cobb method from superior endplate of C4 to inferior endplate of C7.

C0-C2 angle was measured using angle McRae line and the line tangential to the inferior aspect of the axis, T1 slope was measured using the angle subtended by the superior endplate and the horizontal line, and C0-C7, C2-C7 SVA were measured based on horizontal offsets dropped by a vertical line from the external auditory meatus and mid-C2 vertebral body with respect to the mid-C7 vertebral body.

Other spinal measurements performed include the SVA, thoracic kyphosis, thoracolumbar junctional angle, lumbar lordosis, SS, pelvic tilt (PT), and pelvic incidence (PI).

SVA was measured as the offset between the sagittal C7 plumb line and the posterosuperior corner of the sacrum. Thoracic and lumbar spinal curvatures were measured using the Cobb method. Thoracic kyphosis was taken as the angle between the inferior endplate of C7 and the inferior endplate of T12. Thoracolumbar junctional angle was taken as the angle between the superior endplate of T11 and the inferior endplate of L2. Lumbar lordosis was taken as the inferior endplate of T12 and the superior endplate of S1. For the spinopelvic parameters, including PI, PT, and SS, standard measurement techniques as described in the literature were used.

The sagittal spinal profile for all three postures were also described using apical and end vertebrae taken as the most horizontally displaced and most tilted vertebra on the sagittal profile of the cervical spine, respectively.[18]

Statistical Analysis

A power analysis conducted using pilot data with α set at 0.05 and β at 80 estimated that a sample size of 25 patients was required to detect a clinically significant difference of 5° change in cervical alignment between standing and sitting postures. This calculation was performed with reference to a similar study by the same authors when comparing standing and sitting cervical spinal alignments.[3]

The data were compiled in Microsoft Excel 2011 Version 14.2.4, and the statistical analysis was performed using Statistical Package for the Social Sciences Version 22.0. Categorical variables are described in percentages and continuous variables as means with standard deviations (SDs).

Univariate analysis was performed to evaluate differences between standing, erect sitting, and natural sitting postures in terms of cervical angular alignments C0-C2, C2-C7, and C4-C7, as well as sagittal translations of C0, C2, and C7 horizontal offsets from the posterosuperior sacrum and the hip center. Multivariate analysis with assessment of odds ratio (OR) was specifically performed to identify the role of low T1 slope and negative SVA on the cervical spine profile upon standing.

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