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Original Article
21 (); 512-516
doi:
10.1016/j.jor.2020.09.006

Poor spinal alignment in females with obesity: The Yakumo study

, , , , , , , ,
a Department of Orthopaedic Surgery, Nagoya University Graduate School of Medicine, 65,Tsurumai,Showa-ku, Nagoya, Aichi, 466-8550, Japan
b Department of Orthopaedic Surgery, Kansai University of Welfare Sciences, 3-11-1, Asahigaoka, Kashihara, Osaka, 5820026, Japan

∗Corresponding author: Kei Ando. andokei@med.nagoya-u.ac.jp

Received: , Accepted: ,
Professor P K Surendran Memorial Education Foundation
Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Abstract

The goal of this prospective study was prospectively to investigate the relationship between obesity and spinal sagittal alignment.

286 were referred for orthopedic evaluation. Differences in spinal parameters among these groups and between males and females were evaluated.

Obese subjects had significantly higher C2S, CPA, CTPA, PI-LL, and lower cervical lordosis, L4S1, lumbar lordosis, and sacral slope. In multivariate logistic regression analysis adjusted for age in females, CTPA was identified as the only independent and significant factor associated with obesity.

Obesity in females has significant relationships with spinal sagittal alignment and results in poorer physical QOL.

Keywords

Obesity
Sex
Spinal alignment
Yakumo study
Healthy volunteer
CTPA
1

1 Introduction

In modern affluent societies, obesity has unfavorable effects on cardiovascular disease, diabetes mellitus, and hypertension.1–4 Moreover, obesity is recognized as an important factor in spinal disorders such as low back pain, reduced disc height in the lumbar spine, and perioperative complications during spinal surgery.5–8 The ideal posture involves positioning of the body against gravity in an efficient manner. Postural deviations occur when misaligned body parts generate increased muscular stress that may make it difficult to maintain proper balance.9 Obese people often display protruding abdomens that promote anterior displacement of the center of gravity, anteversion of the pelvis, and an associated increase in lumbar lordosis.10

Sagittal imbalance in middle-aged and elderly subjects is related to physical ability.11,12 There also may be sex-related differences in whole sagittal alignment,13,14 and obesity-related differences in sagittal alignment may also be specific to each sex. However, to the best of our knowledge, there is a lack of radiographic data for Japanese obese adults, and no information on sex differences for relationships among cervical regional alignment, thoracolumbar regional alignment, and whole spine alignment, in obese adults. Therefore, the aim of this study was firstly to examine sagittal alignment of the regional spine, whole spine, and spinopelvic region in Japanese obese adults, and to examine differences between males and females.

2

2 Materials and methods

2.1

2.1 Patient population

The subjects were healthy volunteers who participated in a health checkup that has been held annually for 32 years in the town of Yakumo in Hokkaido, Japan, and is supported by the local government (the Yakumo study).15,16 This study included 286 participants (109 men, 177 women) aged 50–86 years (mean 64.5 years) for whom whole spine lateral radiographs were recorded (Table 1). The participants met the following criteria: (1) age ≥50 years, (2) consented to participate after being fully informed of the study, and (3) underwent whole spine X-ray.

Table 1 Summary of demographic data in 286 subjects.
Item Value
Age (y) 64.5 ± 10.2
Male (N) 109 (38.1)
Female (N) 177 (61.9)
Height (cm) 158.0 ± 8.3
Weight (kg) 58.9 ± 11.5
Body mass index (kg/m2) 23.5 ± 3.5
Body fat percentage (%) 29.2 ± 7.0
Back muscle strength (kg) 79.1 ± 31.5
C2S: C2 Slope 9.9 ± 8.5
CL: C2-7 lordosis 11.3 ± 12.2
cSVA: C2-7 SVA 24.3 ± 14.5
CPA: C2-pelvic angle 14.6 ± 8.4
CTPA: C2-T1 pelvic angle 2.5 ± 1.3
T1S: T1 Slope 22.3 ± 9.1
TK: Thoracic kyphosis 22.6 ± 10.3
TLK: Thoracolumbar kyphosis 8.4 ± 11.3
TPA: T1 pelvic angle 12.1 ± 8.2
L4S1: L4-S1 lordosis 39.8 ± 9.7
LL: Lumbar lordosis 43.5 ± 12.2
PI: Pelvic incidence 47.8 ± 11.5
PT: Pelvic tilt 17.8 ± 8.7
SS: Sacral Slope 30.0 ± 8.1
PI-LL: Pelvic incidence-Lumbar lordosis 4.3 ± 11.2
SVA (C7S1): Sagittal vertical axis 2.9 ± 34.3
PCS (SF-36) 50.4 ± 10.2
MCS (SF-36) 49.7 ± 8.7
2.2

2.2 Radiological assessment

Radiographs were obtained under standard conditions of (1) the patient standing and staring straight ahead with hands on the clavicles, (2) acquisition of two views (lateral craniopelvic, and lateral pelvic), and (3) a distance of 1.5 m between the X-ray tube and radiograph. Digitized radiographs were transferred to a computer as Digital Imaging and Communications in Medicine (DICOM) data and evaluated using imaging software (Surgimap Spine; Nemaris Inc., New York City, NY).

2.3

2.3 Measured parameters

The parameters measured in radiographs were as follows: C2 slope (C2S, angle between the horizontal plane and C2 inferior endplate), cervical lordosis (CL, Cobb angle between the C2 and C7 inferior endplates), C2–C7 SVA (cSVA, distance between a plumb line from the center of the C2 vertebral body and posterior superior corner of C7), T1 slope (T1S, angle between the horizontal plane and T1 superior endplate), thoracic kyphosis (Cobb angle between the T4 superior endplate and T12 inferior endplate), thoracolumbar kyphosis (TLK, Cobb angle between T10 and the L2 superior endplate), L4-S1 lordosis (L4S, Cobb angle between L4 and the S1 superior endplate, Lordosis written as plus), lumbar lordosis (LL, Cobb angle between L1 and the S1 superior endplate, Lordosis written as plus), pelvic tilt (PT), sacral slope (SS), pelvic incidence (PI), and PI−LL. Global parameters measured radiographically (Fig. 1) included the sagittal vertical axis (SVA), cervicothoracic pelvic angle (CTPA), C2 pelvic angle (CPA), and T1 pelvic angle (TPA).

Global radiographic parameters. CTPA, the angle between a line from the center of C2 to the femoral heads (FH) and a line from FH to the center of T1, is a global angular measure of cervical sagittal balance and is correlated with the C2–C7 plumbline. TPA is a measure of global sagittal alignment that correlates with C7 SVA and is defined as the angle between a line from the center of T1 to the FH and a line from the FH to the center of the S1 endplate. CPA (C2 pelvic angle) is the angle between a line from the C2 centroid to the FH and a line from the FH to the middle of the S1 endplate. CTPA is obtained by subtracting TPA from CPA (CTPA = CPA - TPA). CTPA; continuous line, CPA; broken line, TPA; dotted line.
Fig. 1 Global radiographic parameters. CTPA, the angle between a line from the center of C2 to the femoral heads (FH) and a line from FH to the center of T1, is a global angular measure of cervical sagittal balance and is correlated with the C2–C7 plumbline. TPA is a measure of global sagittal alignment that correlates with C7 SVA and is defined as the angle between a line from the center of T1 to the FH and a line from the FH to the center of the S1 endplate. CPA (C2 pelvic angle) is the angle between a line from the C2 centroid to the FH and a line from the FH to the middle of the S1 endplate. CTPA is obtained by subtracting TPA from CPA (CTPA = CPA - TPA). CTPA; continuous line, CPA; broken line, TPA; dotted line.

The participants were classified into two groups using obesity criteria proposed by the Japanese Society for the Study of Obesity (JASSO) for evaluation of individuals of Japanese descent. The JASSO criteria define body mass index (BMI) ≥25 kg/m2 as obesity. QOL was evaluated using SF-36 (Japanese ver. 2.0).17 Two summary measures of the SF-36, the Physical Component Summary (PCS) and Mental Component Summary (MCS), were evaluated. Subjects answered questions by themselves, but with support if required.16

2.4

2.4 Statistical analysis

SPSS v.26 (IBM-SPSS, Inc., Chicago, IL) was used for statistical analyses. An unpaired t-test was used to analyze differences between obese and non-obese subjects and between males and females. Multivariate logistic regression analysis with an odds ratio (OR) was performed to evaluate age-adjusted factors associated with obesity. P < 0.05 was considered to be significant in all analyses.

3

3 Results

Background data and radiographical parameters are shown in Table 1. The average BMI was 23.5 kg/m2 and the % body fat was 29.2%. There were 193 (67.5%) non-obese patients and 93 (32.5%) obese patients (Table 2). Age did not differ significantly between these groups.

Table 2 Characteristics of subjects with and without obesity.
Item Non-obese BMI <25 kg/m2 Obese BMI ≧25 kg/m2 P value
Number subjects (n) 193 93
Age (y) 65.1 ± 10.1 64.1 ± 10.4 NS
Male (N) 63 (57.8) 46 (42.2) NS
Female (N) 130 (73.4) 47 (26.6) NS
Back muscle strength/weight (kg) 1.4 ± 0.4 1.3 ± 0.4 NS
C2S: C2 Slope 9.0 ± 8.8 11.7 ± 7.5 <.05*
CL: C2-7 lordosis 12.3 ± 12.7 9.2 ± 10.7 <.05*
cSVA: C2-7 SVA 21.8 ± 14.1 29.4 ± 14.0 <.01*
CPA: C2-pelvic angle 13.4 ± 8.9 16.0 ± 7.3 <.05*
CTPA: C2-T1 pelvic angle 2.4 ± 1.3 2.9 ± 1.3 <.01*
T1S: T1 Slope 22.6 ± 9.2 21.7 ± 8.9 NS
TK: Thoracic kyphosis 22.9 ± 10.1 22.0 ± 10.6 NS
TLK: Thoracolumbar kyphosis 7.6 ± 11.3 10.1 ± 11.4 NS
TPA: T1 pelvic angle 11.6 ± 8.7 13.1 ± 7.2 NS
L4S1: L4-S1 lordosis 40.8 ± 9.9 37.9 ± 9.2 <.05*
LL: Lumbar lordosis 45.5 ± 12.7 39.4 ± 10.0 <.01*
PI: Pelvic incidence 48.8 ± 12.4 45.8 ± 9.1 <.05*
PT: Pelvic tilt 17.4 ± 9.3 18.7 ± 7.3 NS
SS: Sacral Slope 31.4 ± 8.3 27.1 ± 6.7 <.01*
PI-LL: Pelvic incidence-Lumbar lordosis 3.3 ± 11.8 6.4 ± 9.7 <.05*
SVA (C7S1): Sagittal vertical axis 4.3 ± 35.2 0.0 ± 32.2 NS
PCS (SF-36) 51.4 ± 9.1 48.5 ± 11.8 <.05*
MCS (SF-36) 49.4 ± 8.6 50.4 ± 8.9 NS

Among radiographic parameters, obese patients had significantly higher C2S, CPA, CTPA, C2-7 SVA, and PI-LL; and significantly lower CL, L4S, LL, PI, and SS. However, none of these parameters differed significantly between obese and non-obese males. In contrast, in females, obese subjects had significantly higher C2S, cSVA, CPA, and CTPA, and significantly lower CL, L4S, LL, and SS (Table 3). In multivariate logistic regression analysis adjusted for age in females, CTPA (OR: 2.355, P < 0.05) was the only independent significant factor associated with obesity (Table 4, Fig. 2). PCS in SF36 was significantly poorer in all obese subjects (Table 2). There was no significant difference in PCS between obese and non-obese males, but obese females tended to have a poorer PCS than non-obese females (p = 0.08) (Table 3).

Table 3 Characteristics of male and female subjects with and without obesity.
Item Non-obese BMI <25 kg/m2 Obese BMI ≥25 kg/m2 Unpaired t-test P value Non-obese BMI <25 kg/m2 Obese BMI ≥25 kg/m2 Unpaired t-test P value
Male Female
Number 63 46 130 47
Age (y) 66.9 ± 9.8 66.1 ± 9.5 NS 63.2 ± 9.7 61.1 ± 11.7 NS
Sex 63 (57.8) 46 (42.2) NS 130 (73.4) 47 (26.6) NS
Height (cm) 165.2 ± 6.4 165.1 ± 5.7 NS 153.4 ± 5.9 154.2 ± 6.7 NS
Weight (kg) 60.9 ± 6.2 74.5 ± 7.8 <.01* 49.9 ± 5.9 65.6 ± 9.1 <.01*
Body mass index (kg/m2) 22.3 ± 1.9 27.3 ± 2.2 <.01* 21.2 ± 2.2 27.5 ± 2.5 <.01*
Body fat percentage (%) 21.1 ± 3.5 27.5 ± 2.6 <.01* 30.2 ± 4.7 38.8 ± 5.2 <.01*
Back muscle strength (kg) 104.1 ± 26.2 112.1 ± 28.5 NS 60.2 ± 16.6 62.2 ± 17.9 NS
Back muscle strength/weight (kg) 1.7 ± 0.4 1.5 ± 0.4 <.05* 1.2 ± 0.3 1.0 ± 0.3 <.01*
C2S: C2 Slope 9.8 ± 9.2 11.2 ± 7.6 NS 8.6 ± 8.7 12.2 ± 7.5 <.05*
CL: C2-7 lordosis 13.0 ± 11.4 10.2 ± 10.2 NS 11.9 ± 13.3 8.2 ± 11.2 <.05*
cSVA: C2-7 SVA 27.4 ± 15.9 30.8 ± 15.8 NS 19.1 ± 12.3 28.1 ± 12.0 <.01*
CPA: C2-pelvic angle 14.0 ± 9.1 16.9 ± 7.1 NS 14.0 ± 8.8 15.1 ± 7.5 <.05*
CTPA: C2-T1 pelvic angle 2.7 ± 1.4 2.9 ± 1.4 NS 2.2 ± 1.2 2.9 ± 1.1 <.01*
T1S: T1 Slope 24.2 ± 9.5 22.3 ± 8.4 NS 21.8 ± 8.9 21.1 ± 9.5 NS
TK: Thoracic kyphosis 21.9 ± 9.9 23.3 ± 10.5 NS 23.4 ± 10.3 20.7 ± 10.6 NS
TLK: Thoracolumbar kyphosis 10.0 ± 11.9 13.8 ± 11.6 NS 6.5 ± 10.8 6.6 ± 10.2 NS
TPA: T1 pelvic angle 11.3 ± 8.7 14.0 ± 6.8 NS 11.8 ± 8.7 12.2 ± 7.5 NS
L4S1: L4-S1 lordosis 41.5 ± 10.6 39.9 ± 9.5 NS 40.4 ± 9.5 35.9 ± 8.7 <.05*
LL: Lumbar lordosis 41.9 ± 13.0 38.9 ± 8.8 NS 47.2 ± 12.2 40.0 ± 11.0 <.01*
PI: Pelvic incidence 46.6 ± 13.6 46.1 ± 8.8 NS 49.9 ± 11.6 45.5 ± 9.4 NS
PT: Pelvic tilt 16.6 ± 9.6 19.5 ± 7.3 NS 17.8 ± 9.1 17.9 ± 7.3 NS
SS: Sacral Slope 30.0 ± 9.2 26.7 ± 6.4 NS 32.1 ± 7.8 27.6 ± 7.0 <.01*
PI-LL: Pelvic incidence-Lumbar lordosis 4.7 ± 11.0 7.2 ± 8.6 NS 2.7 ± 12.2 5.5 ± 10.7 NS
SVA (C7S1): Sagittal vertical axis (−)1.0 ± 35.5 2.0 ± 33.6 NS (−)5.9 ± 35.2 (−)2.0 ± 31.1 NS
PCS (SF-36) 50.5 ± 10.7 47.8 ± 13.2 NS 51.8 ± 8.3 49.1 ± 10.4 0.08
MCS (SF-36) 50.0 ± 8.7 49.1 ± 8.8 NS 49.1 ± 8.6 51.6 ± 8.9 NS
Table 4 Results of multivariate logistic regression analysis for obesity in females.
Variable Adjusted OR P value 95% CI
C2slope .961 .328 0.887–1.041
CL 1.047 .082 0.994–1.14
CPA .969 .276 0.916–1.025
CTPA 2.355 .000 1.527–3.633
L4S1 1.046 .116 0.989–1.105
LL 1.051 .127 0.986–1.121
SS 0.998 .976 0.898–1.11
Obese females had significantly higher C2S, cSVA, CPA, and CTPA; and significantly lower CL, L4S, LL, and SS compared to non-obese females.
Fig. 2 Obese females had significantly higher C2S, cSVA, CPA, and CTPA; and significantly lower CL, L4S, LL, and SS compared to non-obese females.

A comparison of two cases is shown in Fig. 3. A radiograph of a non-obese case with BMI 17.9 kg/m2 gave values of C2S 8°, CL 26°, CPA 16°, CPTA 3°, LL 44°, L4S 37°, and SS 28°; whereas these values from a radiograph of an obese case with BMI 28.4 kg/m2 were C2S 14°, CL 6°, CPA 30°, CPTA 6°, LL 4°, L4S 9°, and SS 8°.

Comparison of two female subjects. Left: radiograph in a non-obese case with BMI 17.9 kg/m2, showing C2S 8°, CL 26°, CPA 16°, CPTA 3°, LL 44°, L4S 37°, and SS 28°. Right: radiograph in an obese case with BMI 28.4 kg/m2, showing C2S 14°, CL 6°, CPA 30°, CPTA 6°, LL 4°, L4S 9°, and SS 8°.
Fig. 3 Comparison of two female subjects. Left: radiograph in a non-obese case with BMI 17.9 kg/m2, showing C2S 8°, CL 26°, CPA 16°, CPTA 3°, LL 44°, L4S 37°, and SS 28°. Right: radiograph in an obese case with BMI 28.4 kg/m2, showing C2S 14°, CL 6°, CPA 30°, CPTA 6°, LL 4°, L4S 9°, and SS 8°.
4

4 Discussion

In this study of relationships between obesity and spinal parameters, subjects with obesity had significantly higher C2 slope, CPA, CTPA, and PI-LL; and significantly lower cervical lordosis, L4S1, lumbar lordosis, and sacral slope. Several previous studies have examined relationships between obesity and the spine.5,10,18,19 A study in Brazil showed that spinal malalignment, and notably increased thoracic kyphosis and lumbar lordosis, led to anteversion of the head in obese individuals.10 A study in the US found no significant difference in lumbopelvic parameters in obese and non-obese patients, but SVA was significantly greater in obese patients.19 Obesity has also been associated with reduced disc height in the lumbar spine, but not at the lumbosacral junction.5 In the current study, lower LL, SS, and CL, and higher CPA and CTPA in obese subjects caused the trunk to lean forward. There may also be racial differences in sagittal spinopelvic parameters,20–22 and interestingly, the participants in these studies were not of Asian descent, a factor that we believe might have a significant impact on findings related to spinal alignment.

Regarding sex-related differences in spinal parameters, the C2–C7 SVA is greater in males than in females,13,23 Vialle et al. found significant differences in LL and PI between males and females,24 and Zhu et al. showed that females have significantly higher LL than males.21 After lumbar kyphotic changes, compensatory changes such as decreased thoracic kyphosis prevent bending forward and maintenance of spinal sagittal alignment.25 However, in some elderly people, spinal flexibility is lost, and positive spinal inclination (a bent forward posture) occurs due to lumbar kyphosis.25 Boden et al. found age-related changes in the cervical spine in at least 90% of healthy males aged ≥50 years and in 90% of healthy females aged ≥60 years.26 The current study also revealed significantly lower cSVA and higher LL in females.

Regarding the effect of obesity, we found no difference in radiographic parameters between obese and non-obese males, but significant differences in females. To our knowledge, this is the first study to examine the effects of obesity on spinal sagittal alignment in each sex. All muscle volumes were higher in men than women, whereas the fat fraction was higher in the multifidus and erector spinae in women. Rafael et al. found correlations of the multifidus volume with PT, PI, LL and CPA, erectors spinae volume with CPA, and psoas volume with TK, TL and SVA.27 We speculate that spinal alignment in females may be influenced by a change in BMI due to weaker back strength, whereas the stronger back strength of males eliminates this effect.

In logistic regression analysis, only CTPA was significantly related to obesity among the spinal parameters examined. The CTPA defines the relative proportion of cervical deformity, and is used as an angular measure of cervical sagittal alignment.28 Angular measures have an advantage over linear measures in that they do not require calibration of the radiograph, which can add error to the measurement. Obesity influences cervical alignment, and in this study, obese females with a large CTPA tended to have a poorer PCS. This is consistent with a previous report that a forward stooped posture was an important indicator of lower QOL.29

The limitations of the study include most of the subjects working in agriculture or fishing, which differs from elderly people in urban areas. A second limitation is that no radiographic evaluations of the knee joints were performed. Examinations of the whole spine using radiography would be useful for complete evaluation of sagittal alignment, notably because alignment of the lower limbs on standing has an impact on total sagittal alignment.

5

5 Conclusion

In this study, relationships of obesity with sagittal alignment of the regional spine, whole spine, and spinopelvic region were evaluated in Japanese adults, and sex differences in these parameters were examined. There were no differences in radiographic parameters between obese and non-obese males, but obese females had significantly higher C2S, cSVA, CPA, CTPA, and significantly lower CL, L4S, LL, and SS compared to non-obese females. We suggest that rehabilitation therapy for obesity and a bent forward posture may improve QOL in middle-aged and elderly people. This is the first report of radiographic data for Japanese obese adults, and information on sex differences for relationships among cervical regional alignment, thoracolumbar regional alignment, and whole spine alignment, in obese adults.

Source of funding

This study was supported by a Japanese Ministry of Health, Labor, and Welfare Grant-in-Aid for Scientific Research (C) (18K09102). No other funds were received in support of this work.

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