Frequency of Coexistent Spinal Segment Variants: Retrospective Analysis in Asymptomatic Young Adults

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FIG 1.
Allocation of spinal segment distribution variants in thoracic (rib-bearing) vertebrae.
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FIG 2.
Allocation of spinal segment distribution variants in lumbar vertebrae.
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FIG 3.
Frequency and distribution of the cervical rib.
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FIG 4.
Frequency and distribution of the TLTV. AOC indicates accessory ossification center.
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FIG 5.
Frequency and distribution of the LSTV.
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FIG 6.
Correlation between spinal segment variants. The asterisk indicates an atypical number of presacral segments or an atypical distribution of thoracolumbar vertebrae; dagger, the inability to visualize the ILL.
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FIG 7.
Example of thoracolumbar and lumbosacral transitional anatomy. Coronal MIP CT image of the lumbar spine demonstrates thoracolumbar and lumbosacral anatomy with an accessory ossification center on the right at T12 (open arrow) as well as a partially sacralized L5 vertebral body with an unfused left transverse process (closed arrow).

Table 1:

The Castellvi classification for LSTV

Classification	Laterality	Description
I	Unilateral (a) Bilateral (b)	Dysplastic transverse process with a ≥19-mm width on the craniocaudal dimension
II		Lumbarization or sacralization with an enlarged transverse process that has a diarthrodial joint with the sacrum
III		Lumbarization or sacralization with complete osseous fusion of the transverse process to the sacrum
IV	–	Unilateral IIa transition with a IIIa transition on the contralateral side

Table 2:

Comparative distribution of spinal segment variants

Spinal Segment Variant	Overall (n = 450)	Women (n = 279)	Men (n = 171)	P Value^{^a}
Spinal segment distribution variant^{^b}	107 (23.8%)	71 (25.4%)	36 (21.1%)	.343
Cervical rib	19 (4.2%)	13 (4.7%)	6 (3.5%)	.728
TLTV	69 (15.3%)	36 (12.9%)	33 (19.3%)	.091
LSTV	119 (26.4%)	60 (21.5%)	59 (34.5%)	.003

↵a Result of the χ² test for the difference between frequencies of spinal segment variants by sex.
↵b An atypical number of presacral segments or an atypical distribution of thoracolumbar vertebrae.

Table 3:

Association among spinal segment variants

	Cervical Rib	TLTV	ILL^{^a}	LSTV
	OR (95% CI), P Value	OR (95% CI), P Value	OR (95% CI), P Value	OR (95% CI), P Value
ILL^{^a}	–	–	–	2.10 (0.79–5.31), .121
TLTV	–	–	1.50 (0.42–4.29), .482	1.87 (1.08–3.20), .023
Cervical rib	–	2.70 (0.92–7.09), .053	4.86 (1.06–16.54), .020	3.28 (1.29–8.47), .012
Spinal segment distribution variant^{^b}	2.44 (0.92–6.19), .062	66.13 (30.34–166.85), <.001	3.06 (1.18–7.80), .018	5.47 (3.43–8.80), <.001

Note:—The en dash indicates duplicate entries.
↵a Inability to visualize iliolumbar ligament.
↵b An atypical number of presacral segments or an atypical distribution of thoracolumbar vertebrae.