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

Results

The study population had a mean age of 24.4 ± SD 5.26 years and a predominance of men (88.0%). Most patients (73.0%) do not have a lordotic C2-C7 alignment during standing, although C4-C7 angular alignment was lordotic in 53.8% of the patients. Key radiographic parameters in the standing posture are shown in Table 1. Of note, the mean angular alignment of the cervical spine is approximately neutral at −0.6° ± SD 11.1°. The mean SVA is −8.8 ± SD 24.2 mm and the T1-slope is 17.4° ± SD 8.7°. Spinopelvic indices showed a mean PI of 51.0° ± SD 10.4° and a mean PT of 13.7° ± SD 9.2°.

Significant differences exist between standing, erect sitting, and natural sitting postures. In terms of angular alignment, more lordosis is observed during sitting as compared to standing (P < 0.001). This is even more pronounced in the natural sitting posture (P < 0.001), as shown in Table 2, in which all patients assumed a lordotic cervical profile regardless of alignment during standing (mean C2-C7 Cobb −17.2° ± SD 12.1°).

In terms of translation of the cervical spine, C0 SVA, C2 SVA, and C7 SVA shifted forward during erect sitting and yet further during natural sitting (P < 0.05). Values of the forward translation with respect to the posterosuperior corner of the S1 and hip center are shown in Table 2. T1 slope increased from 17.4° ± SD 8.7° during standing to 30.2° ± SD 7.4° during natural sitting (P < 0.001).

Analysis of various cervical spine angular and horizontal alignments in standing posture (Table 3) showed that both T1 slope and SVA measured upon standing are predictors of cervical sagittal alignment (P < 0.05). In particular, SVA < 10 mm is highly significant in predicting C4-C7 kyphosis (P < 0.001), and to a lesser extent, C2-C7 kyphosis (P = 0.02). T1 slope of <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 appears to be a more significant predictor of kyphosis than SVA (OR 17.33, P = 0.001 vs OR 11.67, P = 0.02, respectively).

No patients had cervical kyphosis during natural sitting and therefore radiographic parameters in this position were not evaluated for predictors of cervical kyphosis upon standing.

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