Wedging of vertebral bodies at the thoracolumbar spine in healthy individuals on whole body MRI screening: correlation with disc degeneration and disc herniation

Abstract

Background

There have been no reports on the relationship between wedging of vertebral bodies at the thoracolumbar spine and disc herniation in healthy individuals on magnetic resonance imaging (MRI).

Purpose

To investigate the degree of wedging of vertebral bodies at the thoracolumbar spine in healthy individuals who underwent whole-body (WB) MRI. We also assessed the correlation between wedging and adjacent disc pathology.

Material and Methods

This retrospective study comprised 200 healthy patients who underwent WB MRI as part of a regular health check from January 2019 to February 2019. We measured anterior and posterior vertical heights of each vertebral body between T10 and L2. The ratio of anterior height to posterior height (APR) was calculated, and we evaluated disc degeneration or disc herniation using WB MRI.

Results

The APR of T10 was significantly higher than at the other levels (P < 0.05), and the APR of L1 was significantly lower (P < 0.05). Men had a significantly smaller APR than women at T12 to L2 (P < 0.05). Regarding the relationship between APR and disc degeneration, the group without disc degeneration had a higher APR, with statistical significance at T12, L1, and L2. Regarding the relationship between APR and disc herniation, the group without disc herniation had a higher APR, with statistical significance at T11, T12, L1, and L2.

Conclusion

Wedging of vertebral bodies is most prominent at L1. Although the values were statistically significant only at some levels, the patients with disc degeneration or herniation had more prominent wedge deformity of thoracolumbar spine.

Keywords

Magnetic resonance imaging vertebral column deformities

Introduction

Wedging is a normal physiological finding of thoracolumbar vertebral bodies (1).

Although every vertebra is slightly wedged, the mid-thoracic and upper lumbar region are commonly involved (1). Wedging of vertebral bodies is frequently accompanied by disc herniation of the upper lumbar spine (2). Upper herniation of the upper lumbar disc is uncommon, clinical manifestations are variable and non-specific, and its etiology is generally unknown (3). This is different from lower lumbar disc herniation (3 –6). Xu et al. (6) reported that the wedge-shaped vertebrae is indicatively correlated with adjacent upper lumbar disc herniation on radiograph, and Wang et al. (2) reported wedge-shaped vertebrae as an independent risk factor for upper lumbar disc herniation in symptomatic patients.

To the best of our knowledge, there have been no reports on the relationship between wedging of vertebral bodies at the thoracolumbar spine and disc herniation in healthy individuals on magnetic resonance imaging (MRI). In our institution, we perform whole-body (WB) MRI as a screening tool in an asymptomatic population for cancer screening and regular health checks. On the basis that asymptomatic patients have “normal” thoracolumbar spine morphology, the incidence of the wedging deformity and disc pathology in the “normal” population is quite interesting.

The aim of the present study was to investigate the degree of wedging of vertebral bodies at the thoracolumbar spine in healthy individuals who underwent WB MRI for cancer screening as well as regular health checks and assess the correlation between wedging of vertebral bodies at the thoracolumbar spine and adjacent disc pathology.

Material and Methods

Case selection

The ethical review board of our hospital approved this study and waived patient consent requirements due to the retrospective design. We retrospectively evaluated 261 consecutive healthy patients who underwent WB MRI as part of a regular health check at our institution from January 2019 to February 2019. Exclusion criteria were previous surgery of the spine (one case), history of cancer (one case, thyroid cancer), incidentally detected spinal tumor (one case), and conditions prohibiting measurement of length (MR artifacts, n = 16 cases; and technical error, i.e. not fully available on the PACS, n = 42 cases). Finally, a total of 200 patients was included in the study, 174 men and 26 women (mean age = 43 ± 7.58 years; age range = 39–75 years).

MRI parameters

We acquired whole spine images from WB MRI scans using a 1.5-T magnet MRI scanner (Signa HDxt; GE Healthcare, Milwaukee, WI, USA). Detailed image sequences and parameters are described in Table 1. Healthy patients were placed in the supine position. We divided the body into four parts: head and neck; trunk; thigh; and leg. All images were synthesized into a single image. The radiofrequency coils utilized were a 12-channeled body array coil, head and neck coil, and the inherent coil of the MRI gentry.

Table 1.

Imaging parameters for magnetic resonance sequences.

Imaging parameter	Coronal T1 fat suppression (3D SPGR)	Coronal T2 STIR	Whole-body sagittal T2 fast spin echo
TR (ms)	6.3/6.1 (abdomen)	7610/2475 (abdomen)	3689
TE (ms)	3.1	35	110
TI (ms)	–	140	–
Flip angle (°)	15	160	160
Matrix size	320 × 256	320 × 224	480 × 256
Field of view (cm)	150 × 46	150 × 46	71 × 40
Slice thickness (mm)	8	8	4
Inter-slice gap (mm)	0	0	0.5
Bandwidth (kHz)	100	41.67	41.67
Echo train length	–	14/24 (abdomen)	26
Signal average	2	1	4.0
Scan time (min:s)	1:29/0:21/2:47/1:34	2:40/1:20/2:44/2:30	2:35/2:35

Image analysis

MRI results were evaluated by consensus of two musculoskeletal radiologists with 16 and nine years of experience. On T2-weighted (T2W) mid-sagittal images, the anterior and posterior vertical heights of each vertebral body between T10 and L2 were measured (Fig. 1). The ratio of anterior height to posterior height (APR) was calculated. A wedged vertebra was defined as a vertebral body with APR < 1.0. The MR images were evaluated with respect to degeneration and posterior disc protrusion of the intervertebral disc in the sagittal images. Degeneration of the disc included any or all of the following: decreased signal on T2W image; narrowing of the disc space; osteophytes of the vertebral apophyses; defects; inflammatory changes; and sclerosis of the end plates (7). Herniation of the disc was defined as a localized or focal displacement of disc material beyond the limits of the intervertebral disc space (7). We evaluated each vertebral body from T10 to L2 and considered them positive when there were previously mentioned abnormalities in the intervertebral disc at the level above or below each spine.

Fig. 1.

Methods of measurement on T2-weighted mid-sagittal MR images. (a) Anterior vertical height: distance between upper and lower corners of the anterior margin of the vertebral body, (b) posterior vertical height: distance between upper and lower corners of the posterior margin of the vertebral body. The APR is calculated as (a)/(b). APR, ratio of anterior height to posterior height; MR, magnetic resonance.

Statistical analysis

We used the paired t test to evaluate the degree of wedging of vertebral bodies between levels. We used the Student’s t test to analyze the association between wedging of the vertebral bodies at the thoracolumbar spines and adjacent disc pathology. We divided the study group into young (aged < 43 years, n = 120 patients) and old (aged ≥43 years, n = 80 patients) according to the mean age of 43 years and compared with Student’s t test. We also divided the study group into male and female and compared them with Student’s t test. Statistical analysis was performed using PASW software version 18.0 (IBM Corp., Armonk, NY, USA). A P value ≤0.05 was considered statistically significant.

Results

The number of wedged vertebrae (i.e. APR < 1.0) was 149 (74.5%) at T10, 189 (94.5%) at T11, 191 (95.5%) at T12, 197 (98.5%) at L1, and 182 (91.0%) at L2. Therefore, most of the vertebrae were wedge-shaped rather than rectangular at the thoracolumbar junction. The mean APRs of each vertebra are described in Table 2 and Fig. 2. The APR was smallest at L1 (0.88 ± 0.06) and largest at T10 (0.96 ± 0.05) (Table 2). The APR of T10 was higher than that of the other levels (P values < 0.05) and the APR of L1 was lower (P values < 0.05). No significant difference was found in APR between T11 and T12 (P = 0.118) or T11 and L2 (P = 0.096) (Table 3).

Table 2.

Ratio of anterior vertical height to posterior vertical height.

Level	Mean
T10	0.96 ± 0.05 (0.84–1.11)
T11	0.90 ± 0.06 (0.72–1.04)
T12	0.89 ± 0.06 (0.71–1.04)
L1	0.88 ± 0.06 (0.68–1.01)
L2	0.91 ± 0.07 (0.61–1.10)

Values are given as mean ± SD (range).

Fig. 2.

Ratio of anterior vertical height to posterior vertical height. APR, anterior height to posterior height.

Table 3.

Comparison of degree of wedging of vertebral bodies between levels.

Vertebrae		P value
T10–T11	0.063 ± 0.062	<0.001
T10–T12	0.070 ± 0.075	<0.001
T10–L1	0.085 ± 0.074	<0.001
T10–L2	0.054 ± 0.086	<0.001
T11–T12	0.007 ± 0.062	0.118
T11–L1	0.022 ± 0.072	<0.001
T11–L2	–0.010 ± 0.081	0.096
T12–L1	0.015 ± 0.060	0.001
T12–L2	–0.016 ± 0.079	0.004
L1–L2	–0.031 ± 0.070	<0.001

Values are given as mean ± SD unless otherwise indicated.

In respect to the APR and its risk factors, the older age group had a smaller APR than the younger age group but there was a significant difference only at L2 (Table 4). The APR of the male group was lower than that of the female group at T11 to L2 and there was a significant difference in the APR at T12 to L2 (P value < 0.05) (Table 4).

Table 4.

APR by age and gender.

	Age			Gender
	Young (<43 years) (n = 120)	Old (≥43 years) (n = 80)	P value	Male (n = 174)	Female (n = 26)	P value
T10	0.966 ± 0.055	0.960 ± 0.048	0.416	0.963 ± 0.054	0.966 ± 0.040	0.798
T11	0.901 ± 0.060	0.900 ± 0.051	0.895	0.897 ± 0.056	0.920 ± 0.055	0.050
T12	0.899 ± 0.058	0.885 ± 0.064	0.098	0.888 ± 0.060	0.930 ± 0.052	0.001
L1	0.882 ± 0.058	0.873 ± 0.067	0.329	0.871 ± 0.060	0.925 ± 0.050	0.000
L2	0.918 ± 0.069	0.898 ± 0.068	0.046	0.904 ± 0.067	0.948 ± 0.074	0.003

Values are given as mean ± SD unless otherwise indicated.

APR, ratio of anterior height to posterior height.

In the relationship between APR and disc degeneration, the group without disc degeneration had a higher APR, with statistical significance at T12, L1, and L2 (Table 5). In the relationship between APR and disc herniation, the group without disc herniation had a higher APR, with statistical significance at T11, T12, L1, and L2 (Table 6).

Table 5.

Disc degeneration and wedging of vertebral bodies.

Level	Disc degeneration	Wedging deformity	APR	P value
T10	–	55 (27.5)	0.968 ± 0.050	0.057
T10	+	145 (72.5)	0.952 ± 0.057	0.057
T11	–	62 (31.0)	0.905 ± 0.057	0.089
T11	+	138 (69.0)	0.890 ± 0.055	0.089
T12	–	62 (31.0)	0.902 ± 0.058	0.003
T12	+	138 (69.0)	0.875 ± 0.064	0.003
L1	–	62 (31.0)	0.889 ± 0.055	0.001
L1	+	138 (69.0)	0.855 ± 0.070	0.001
L2	–	65 (32.5)	0.923 ± 0.062	<0.001
L2	+	135 (67.5)	0.882 ± 0.075	<0.001

Values are given as n (%) or mean ± SD.

APR, ratio of anterior height to posterior height.

Table 6.

Disc herniation and wedging of vertebral bodies.

Level	Disc herniation	Wedging deformity	APR	P value
T10	–	17 (8.5)	0.964 ± 0.052	0.340
T10	+	183 (91.5)	0.952 ± 0.050	0.340
T11	–	21 (10.5)	0.904 ± 0.055	0.011
T11	+	179 (89.5)	0.871 ± 0.064	0.011
T12	–	20 (10.0)	0.898 ± 0.060	<0.001
T12	+	180 (90.0)	0.847 ± 0.050	<0.001
L1	–	29 (14.5)	0.884 ± 0.058	0.008
L1	+	171 (85.5)	0.844 ± 0.074	0.008
L2	–	43 (21.5)	0.921 ± 0.063	<0.001
L2	+	157 (78.5)	0.870 ± 0.078	<0.001

Values are given as n (%) or mean ± SD.

APR, ratio of anterior height to posterior height.

Discussion

Wedging of the vertebral body is one of the hallmarks of compression fracture, but it is non-specific as a normal physiological discovery of the thoracolumbar spine. Thoracolumbar vertebral wedging is directly related to the global spine stance, thoracic kyphosis, and lumbar lordosis and their determinants. In the present study, it was commonly observed in healthy individuals especially at L1 (98.5%), and the degree of vertebral wedging was most prominent at L1 (APR: 0.88 ± 0.06). In addition, vertebral wedging was greater in men than women at T12 to L2. These results correspond to those of previous studies (1,8). It is not yet clear why men have more wedged vertebrae. Matsumoto et al. (8) reported the gender difference exist only in T11 and L2. However, we found such differences are exist in T12, L1, and L2 bodies. We attribute these differences to the fact that the study populations are different countries. In terms of age, the older age group had the smaller APR significantly only at L2 and there was no significant difference at other spine levels. This result is similar but slightly different to a previous study (8). Matsumoto et al. (8) reported that although old age tends to have smaller APR there was no significant difference. There have been several reports about vertebral wedging using X-ray to decide the value of the threshold (1,9 –12). However, there have been few studies in healthy and younger populations. Furthermore, this study is one of the few using MRI. The participants in the present study comprised healthy individuals who underwent WB MRI for cancer screening or regular health checks and without history of surgery.

Therefore, this study suggests the standard of vertebral wedging at the thoracolumbar junction in healthy persons. If other investigators conduct a similar study for individuals who have symptoms, the results might be quite different. However, further studies are needed for establishing an accurate value of reference for diagnosis of compression fracture because degree of wedging may differ due to factors such as smoking, obesity and existence of the endplate changes such as Schmorl nodes (8,13,14).

Although upper lumbar disc herniation may be influenced by several factors, including sex, age, trauma, obesity, and kyphosis, the exact etiology and pathogenesis of upper lumbar disc herniation are unknown (3 –5). Wedging vertebrae are indicatively correlated with adjacent upper lumbar disc herniation by radiograph and are an independent risk factor for upper lumbar disc herniation in symptomatic patients (2,5). In our study of healthy individuals who underwent WB MRI for cancer screening or regular health checks, wedging of vertebral bodies was related to disc degeneration and herniation (Figs. 3 and 4). Although the values were statistically significant only at some spinal levels, results were consistent with previous studies. Wang et al. (2) suggested that the wedging of vertebra can enhance shear and compressive forces of adjacent vertebrae by altering the angle of endplates, and then give rise to the degeneration of adjacent intervertebral discs and eventually result in disc herniation (2). Patients with wedged vertebra might need to be monitored carefully for disc degeneration and disc herniation. However, as variable factors affect disc herniation, further study might be needed, such as a multivariate analysis.

Fig. 3.

A 40-year-old man who underwent a routine health examination. Whole-body sagittal T2 fast spin echo (TR/TE = 4000/110) reveals low signal intensity and decreased disc height suggesting disc degeneration in L1–L2. APR of L1 and L2 is 0.83 and 0.93, respectively. APR, ratio of anterior height to posterior height.

Fig. 4.

A 61-year-old man who underwent a routine health examination. Whole-body sagittal T2 fast spin echo (TR/TE = 4000/110) reveals disc herniation in L1–L2. APR of L1 and 2 is 0.7 and 0.84, respectively. APR, ratio of anterior height to posterior height.

The present study has some limitations. First, because the MR images were whole spinal MRI rather than regular lumbar MRI, the resolution was relatively low and could have decreased measurement accuracy. Second, it was difficult to distinguish subtype (extrusion vs. bulging) of disc herniation because there were no axial images. Third, it was difficult to exclude bias caused by other factors related to disc degeneration and disc herniation. Fourth, some of patients might have suffered compression fractures in the past but have no symptoms and, therefore, this study group may not represent a true “normal” population.

In conclusion, wedging of vertebral bodies is commonly observed in healthy individuals, and the degree of vertebral wedging is most prominent at L1. Although the values were statistically significant only at some levels, the patients with disc degeneration or herniation had more prominent wedge deformity of thoracolumbar spine.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Hee Jin Park

Myung Sub Kim

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