DOI: https://doi.org/10.21203/rs.2.20879/v1
Background: Spine health is a significant aspect of adolescent health, but few studies have focused on adolescent sagittal plane health. This study aimed to investigate the current status of sagittal spine morphology and function in adolescents.
Method: This cross-sectional study analysed 1152 effective samples obtained from junior and senior high school students (543 boys and 609 girls) from demonstration, middle-level, and general schools in Beijing. Spinal sagittal morphology and function were measured by Spinal Mouse, a spine measuring instrument. The sacrum angle (SA), thoracic kyphosis angle (TKA), lumbar lordosis angle (LLA), inclination angle (INA), sacral range of motion (SROM), thoracic range of motion (TROM), lumbar range of motion (LROM), and inclination range of motion (IROM) were measured. The Matthiass test was used to measure the change in angle after external load placement on the adolescent spine. Sacral angle change (SAc), thoracic angle change (TKAc), lumbar lordosis angle change (LLAc), and inclination angle change (INAc) were also analysed.
Result ： Abnormal TKA rate was 48.2% and 44.7% in the junior and senior high school. Abnormal LLA rate was 44.6% and 55.4%. In the spinal mobility test of the junior high school , SROM, TROM, LROM, and IROM were 60.6°±19.1°, 23.0°±16.6°, 23.0°±16.6°, and 136.1°±16.9°, respectively, for boys and 66.0°±34.4°, 14.0°±17.3°, 66.3°±18.6°, and 127.4°±26.8°, for girls. There were significant differences found between boys and girls (P<0.05 or P<0.01). In the Matthiass test, INAc of the junior high school was 5.7°±5.0° and 2.6°±3.7° for boys and girls, whereas INAc of the senior high school was 2.8°±3.3 and 1.6°±3.0, showing significant differences (P<0.01). The canonical correlation coefficient of SA, SROM, LROM, and IROM was 1.3877, -2.5384, -0.6625, and 1.6336. SROM and LROM were found to be negatively correlated with spinal function, whereas IROM was positively correlated with spinal function.
Conclusion: Adolescents have a high incidence of thoracic kyphosis. During flexion and extension, the thoracic and lumbar vertebral activity and overall activity are better in boys. However, girls are better at maintaining the strength quality of stable muscle groups with a normal spine shape. Sacral obliquity and pelvic position greatly influence the spinal morphology of adolescents.
Spine health is important for both adults and adolescents. Evidence shows that neck and back pains, which are related to the global burden of disease, are key factors. A healthy spine is the basis for maintaining good posture and health living conditions. Teenagers’ postures are vulnerable to external influences. The spine is the backbone of the human body, and poor living habits, lack of exercise, imbalanced nutrition, and so on may cause the decline of spine health, leading to nonspecific back pain, abnormal spinal physiological curvature, and so on [1, 2]. The popularity of sedentary lifestyles in recent years [3, 4] has increased the prevalence of obesity [5, 6], which also has effects on adolescents' body posture and spine health[7]. One study showed that the incidence of low back pain is high among Chinese adolescents, and the incidence of nonspecific low back pain is > 20% among junior and senior high school students, which deserves attention [8]. Relevant studies have shown that spinal morphology (such as thoracic kyphosis) and spinal function (lumbar mobility) are correlated with nonspecific low back pain[8]. In addition, the sagittal morphology of the spine affects the development of pulmonary function in growing children and adolescents [9]. More seriously, there is a correlation between the sagittal morphology of the spine and coronal scoliosis [10]. Anomalies in the sagittal plane are likely to lead to more severe spinal diseases, for instance, changes in the morphology of the thoracic sagittal plane, which may trigger the occurrence of idiopathic scoliosis [11, 12]. Thus, the shape and function of the spine will affect the health of the adolescent spine to a certain extent.
At present, there are many studies on adolescent scoliosis. Quantitative studies on the sagittal shape and function of the adolescent spine are rare. Therefore, this study sampled and quantitatively measured the physiological curvature of the spine and its basic functions in adolescents to determine the status of adolescent spine health among Chinese students.
The complete protocol of this cross-sectional study (Registration # ChiCTR1900021700). was approved by the academic board of the China Institute of Sports Science (No. 201818-21). All methods were performed in accordance with the guidelines and regulations of the institution. Before the study, written informed consent was obtained from each study subject and their parents. We excluded all students who refused to participate in the study. During the analysis, all participants' names and other identifiers have been removed from all sections of the manuscript.
From September 2014 to September 2016, the middle schools in Xicheng District of Beijing were divided into demonstration, ordinary, and general schools. Three schools were selected by random sampling at each level. At each school, three classes (Junior 2, Senior 1, and Senior 2) were selected by simple random sampling. A cluster survey was conducted in the selected classes to test spine morphology and function.
Before the test, all students and parents were given an informed consent form and questionnaires (the main contents of the questionnaires included whether the student had a definite diagnosis of spinal diseases, whether there had been back or lumbar pain in the past month, whether there had been an acute back injury in the past month, whether there had been sports-related injuries to other body parts in the past month, and so on).
In the pre experiment, which was 34 males and 28 females were included, the mean value of TKA in boys is 37.3°and 35.4°, respectively. And the standard deviation is 10.2 for the whole subjects. With he type I error rate was setting at 0.05 and power at 80%, the study used the following formulas to compute sample size :
As a result, each group should have at least 450 subjects. Considering the 10% of rejection rate. We design to include at least 500 subjects in male and female.
The subjects were given screening questionnaires and were examined by physical therapists. The exclusion criteria were as follows: a. history of spine fracture, spine-related surgery, shoulder joint motion injury, pelvis-related injury, or definitive diagnosis of spine-related diseases (such as cauda equina syndrome, lumbar disc herniation, spinal stenosis, congenital scoliosis, idiopathic scoliosis, and so on); b. pain in the spine in the past month; c. acute spine-related injuries in the past month; d. limb fracture, joint trauma, and other phenomena in the past month; e. structural kyphosis with obvious structural abnormalities; f. positive Adams flexion test (to exclude possible scoliosis); and g. anomalous kyphosis with thoracic deformity
The gold standard of spinal morphology testing is X-ray irradiation, but the radiation produced is contrary to the ethical requirements. In this study, a non-invasive device (Spinal Mouse) was used to test the spine morphology and function; this device has good reliability and validity for replacing X-ray use to some extent[13-15].
The test methods were as follows: the subjects were asked to take off their shoes and their jackets and expose the entire back from the seventh cervical vertebra (C7) to the third sacral vertebra (S3). The surface localization of all spinous processes from C7 to S3 was marked with a fluorescent pen. The test protocol included standing sagittal plane, maximum flexion, maximum extension, and Matthiass test[16, 17]. All body position tests first determined all the spinous process markers on the body surface and then used the receiver to test the spine based on the spine markers. The specific testing methods for each body position were as follows: 1. upright position, the study participants were instructed to stand upright in a casual position with feet shoulder-width apart bearing equal weight, arms by their sides, and looking straight ahead; 2. forward bending position, the study participants were instructed to stand with their feet shoulder width apart and to bend the torso forward while keeping the legs straight and allowing the arms to fall naturally; 3. extended position, the study participants were instructed to stand with their feet shoulder-width apart bearing equal weight, arms by their sides or supported by the hips, looking straight ahead, with the jaw close to the chest. the participants were asked to stretch the torso backwards as far as possible; 4. Matthiass test, the study participants were instructed to stand with their feet shoulder-width apart, looking straight ahead. When asked, the subjects pushed their arms forward horizontally while holding a certain amount of weight until their arms created a 90° angle with the shoulders. Spinal curvature and pelvic tilt were measured. The participant was instructed to retain this posture for 30 seconds; then, the second spinal curvature and pelvic tilt measurements were taken.
The test indexes included the thoracic kyphosis angle (TKA), lumbar lordosis angle (LLA), sacral/hip angle (SA), and incline (INA) of the sagittal plane while the participants were in the standing and sitting positions.
The TKA is the Cobb angle from T1 to T12, and the LLA is the Cobb angle from L1 to S1. SA reflects pelvic positioning (the angle between the surface contour line and the vertical line of the sacrum) and pelvic mobility as a result of the limited movement of the sacroiliac (SI) joint. The incline line is the line between T1 and S1. The angle between the incline line and the vertical line is called the INA. The ROMs of the left and right thoracic and lumbar spine in the frontal plane were recorded. The ROMs of the sacrum, thoracic spine, and lumbar spine from the fully flexed position to the fully extended position in the sagittal plane, which can reflect the overall mobility of the spine, were also recorded. The Matthiass test was used to measure the changes in the TKA, LLA, SA, and INA upon loading.
Research agrees that the normal range for the TKA should be 20°–40° [18, 19].
However, few studies have reported the normal range of LLA among adolescents. Jean et al. reported a normal LLA range of 48.0° ±11.7° [20]. In this study, the normal range for the LLA was considered to be 48.0° ± 11.7°. We used the mean value ± 2 standard deviations based on the results of Jean et al.’s study.
We make groups by sex and grade. Because gender difference and the fact that the students in different grades have great diversities on pressure and life schedule among Chinese students. Using the SPSS 19.0 statistical software, an independent sample t test was carried out on the basic indicators of height, weight, and age among the groups to test whether there were significant differences among the groups. An independent samples t-test was used for all indicators of the same sex and age groups. The likelihood ratio chi-square test was used to analyse whether there were differences in the incidence of abnormal thoracic kyphosis and lumbar lordosis among the different groups. Simple correlation analysis was used to analyse the correlation between age and spinal morphology and function. The difference was statistically significant with P<0.05.
SAS 9.4 was used for data cleaning and analysis. The CANCORR process was used to analyse 4 indexes (sacral INA, thoracic kyphosis angle, lumbar lordosis angle, INA) reflecting spinal morphology and 8 indexes (sacral activity, thoracic activity, lumbar activity, INA activity, sacral inclination load, thoracic kyphosis load, and lumbar lordosis load) reflecting spinal function. Canonical correlation analysis was carried out to further explore the internal relationship between the two variables of the adolescent spine, with P < 0.05 indicating statistical significance.
Students who met the test criteria and agreed to participate in the test underwent spinal morphology and function tests. A total of 502 junior and 670 senior high school students were tested; 490 junior (244 boys, 246 girls) and 662 senior high school students (299 boys and 363 girls) were effectively sampled. 20 samples didn’t finish the test, which were excluded from the analysing.
The basic information of the subjects is shown in Table 1. There was no significant difference in height, weight, or BMI between the groups.
| age(year) | height(cm) | weight(kg) | BMI(kg/m2) | |
|---|---|---|---|---|
| Middle school(n = 490) | ||||
| male(n = 244) | 12.9 ± 0.74 | 165.3 ± 7.8 | 55.4 ± 12.8 | 20.1 ± 3.8 |
| female(n = 246) | 12.8 ± 0.72 | 160.6 ± 6.2 | 51.9 ± 10.5 | 20.0 ± 3.7 |
| High school(n = 662) | ||||
| male(n = 299) | 15.5 ± 0.72 | 175.8 ± 5.8 | 67.9 ± 12.7 | 22.0 ± 3.8 |
| female(n = 363) | 15.4 ± 0.66 | 164.7 ± 6.5 | 56.9 ± 9.9 | 20.6 ± 3.2 |
The results of the spine morphology test in the upright position are shown in Table 2. In the junior high school group, the INA of the girls was smaller than that of boys, with significant difference (P < 0.01). The INA of the high school group was smaller than that of the junior high school group, and the difference was significant (P < 0.05 for boys, P < 0.01 for girls).
| sex | Middle school | High school | ||||||
|---|---|---|---|---|---|---|---|---|
| SA(°) | TKA(°) | LLA(°) | INA(°) | SA(°) | TKA(°) | LLA(°) | INA(°) | |
| Male | 14.7 ± 6.6 | 39.5 ± 9.3 | 22.8 ± 8.1 | 5.2 ± 3.4 | 13.7 ± 5.9# | 40.6 ± 10.0 | 22.9 ± 7.8 | 4.5 ± 2.9# |
| female | 14.3 ± 8.0 | 38.5 ± 10.3 | 23.5 ± 9.9 | 4.2 ± 2.7** | 14.2 ± 8.3 | 38.0 ± 9.0* | 23.7 ± 11.2 | 3.6 ± 2.5**## |
| In the same grade, compared with girls, * means P < 0.05, ** means P < 0.01; | ||||||||
| In the same sex, middle school and high school, # means P < 0.05 and ## means P < 0.01. | ||||||||
The incidence of the abnormal thoracic kyphosis and lumbar lordosis is shown in Table 3. In the high school group, the abnormal thoracic kyphosis angle rate of the girls was lower than that of the boys. Additionally, among the girls, the abnormal thoracic kyphosis angle rate in the high school group was lower than that in the junior high school group (P < 0.01).
| TKA | LLA | |||
|---|---|---|---|---|
| Normal (%) | Abnormal(%) | Normal(%) | Abnormal(%) | |
| Middle school(n = 490) | ||||
| male(n = 244) | 49.6 | 50.4 | 37.7 | 62.3 |
| female(n = 246) | 54.1 | 45.9 | 43.1 | 56.9 |
| Total | 51.8 | 48.2 | 40.4 | 59.6 |
| High school(n = 662) | ||||
| male(n = 299) | 46.8 | 53.2 | 43.1 | 56.9 |
| Female(n = 363) | 62.6 | 37.4** ## | 45.8 | 54.2 |
| Total | 55.3 | 44.7 | 44.6 | 55.4 |
| In the same grade, compared male and female, * means P < 0.05, ** means P < 0.01; | ||||
| In the same sex, compared middle school and high school, # means P < 0.05 and ## means P < 0.01. | ||||
The spinal function of the adolescents was evaluated using the spine mobility test and t Matthiass strength test. The results of the spine mobility test are shown in Table 4. The sacral mobility of the male students was less than that of the female students, whereas the range of thoracic, lumbar, and INAs of male students was larger than those of the female students, and the difference was significant (P < 0.05 or P < 0.01). The sacral mobility of the high school group was greater than that of the middle school group, whereas the lumbar mobility of the high school group was smaller than that of the middle school group, and the difference was significant (P < 0.01). Among the girls, the sacral mobility and INA of the high school group were greater than those of the middle school group, and the difference was significant (P < 0.05 or P < 0.01).
| sex | Middle school | High School | ||||||
|---|---|---|---|---|---|---|---|---|
| SROM(°) | TROM (°) | LROM(°) | IROM (°) | SROM(°) | TROM(°) | LROM(°) | IROM (°) | |
| boy | 60.6 ± 19.1 | 23.0 ± 16.6 | 81.3 ± 15.4 | 136.1 ± 16.9 | 66.0 ± 17.6## | 21.6 ± 16.0 | 77.9 ± 15.1## | 138.4 ± 16.0 |
| girl | 66.0 ± 34.4* | 14.0 ± 17.3** | 66.3 ± 18.6** | 127.4 ± 26.8** | 72.2 ± 26.9#** | 15.7 ± 17.2** | 65.8 ± 18.2** | 133.4 ± 21.7##** |
| In the same grade, compared male and female, * means P < 0.05, ** means P < 0.01; | ||||||||
| In the same sex, compared junior high school and senior high school, # means P < 0.05 and | ||||||||
| ## means P < 0.01 | ||||||||
The Matthiass test results are shown in Table 5. The changes in the sacral INA, thoracic kyphosis angle, and INA of the girls in the junior high school group were smaller than those of the boys, showing a significant difference (P < 0.01). In the senior high school group, only the changes in the sacral INA were smaller in the girls than in the boys, showing a significant difference (P < 0.01). The spinal motion change value of the high school group was smaller than that of the middle school group among boys, whereas INA in the high school group was smaller than that of the middle school group among girls.
| sex | Middle school | High school | ||||||
|---|---|---|---|---|---|---|---|---|
| SAc(°) | TKAc(°) | LLAc(°) | INAc(°) | SAc(°) | TKAc(°) | LLAc(°) | INAc(°) | |
| male | 2.2 ± 4.1 | 2.5 ± 6.1 | 3.1 ± 4.5 | 5.7 ± 5.0 | 1.0 ± 3.3## | 1.3 ± 4.9# | 1.6 ± 4.1## | 2.8 ± 3.3## |
| female | 0.5 ± 5.0** | 0.3 ± 6.5** | 2.3 ± 6.0 | 2.6 ± 3.7** | 0.4 ± 5.2 | 0.6 ± 5.1 | 1.4 ± 5.6 | 1.6 ± 3.0**## |
| In the same grade, compared male and female, * means P < 0.05, ** means P < 0.01; | ||||||||
| In the same sex, compared middle school and high school, # means P < 0.05 and ## means P < 0.01 | ||||||||
Table 6 shows that for the four pairs of typical variables, the likelihood ratio method was used to test whether the difference between the canonical correlation coefficient and zero was significant. The first three pairs of canonical correlation coefficient had statistical significance. Therefore, the study of the correlation between the two groups of variables could be transformed into the correlations among the first three pairs of canonical correlation variables. The correlation coefficient of the first typical variable was 0.442, the correction value was 0.432, the eigenvalue was 0.243, and the contribution rate was 0.626. This shows that the first typical variable provides 62.6% of the relevant information. The variation explained by the first pair of typical variables accounts for 62.6% of the total variation (variance), indicating a dominant role. Therefore, the first pair of typical variables was further analysed. The specific results are shown in Tables 7 and 8.
| 1st canonical variables. | 2ed canonical variables. | 3rd canonical variables. | 4th canonical variables. | |
|---|---|---|---|---|
| Canonical correlation coefficient | 0.442 | 0.303 | 0.191 | 0.075 |
| Adjustment | 0.432 | 0.293 | 0.181 | 0.054 |
| standard error | 0.024 | 0.027 | 0.029 | 0.03 |
| Canonical correlation squares | 0.195 | 0.092 | 0.037 | 0.006 |
| characteristic value | 0.243 | 0.101 | 0.038 | 0.006 |
| ratio | 0.626 | 0.262 | 0.098 | 0.015 |
| cumulative proportion | 0.626 | 0.887 | 0.985 | 1 |
| likelihood ratio | 0.7 | 0.87 | 0.958 | 0.994 |
| F | 13.06 | 7.6 | 4.05 | 1.26 |
| P | < 0.0001 | < 0.0001 | < 0.0001 | 0.278 |
| Morphology 1 | Morphology 2 | Morphology 3 | Morphology 4 | ||
|---|---|---|---|---|---|
| sacrum angle | 1.3877 | 0.0361 | -0.0597 | 3.8689 | |
| thoracic kyphosis angle | 0.4332 | -0.3184 | -1.0234 | 1.2982 | |
| lumbar lordosis angle | 0.4683 | -0.3840 | -0.2542 | 4.1538 | |
| inclination angle | -0.1544 | -0.8451 | 0.3673 | -1.8263 | |
| Function1 | Function 2 | Function 3 | Function 4 | |
|---|---|---|---|---|
| SROM | -2.5384 | -0.7195 | 0.8828 | -6.6192 |
| TROM | -0.3198 | -0.1053 | 0.9499 | -0.9484 |
| LROM | -0.6625 | 0.0358 | 0.4695 | -4.2631 |
| INA ROM | 1.6336 | 1.129 | -0.2675 | 5.4665 |
| SAc | -0.4797 | 0.6182 | 0.0957 | -1.3402 |
| TKAc | -0.2094 | 0.4173 | 0.4544 | -0.3354 |
| LLAc | -0.5157 | 0.5563 | 0.0176 | -1.6812 |
| INAc | 0.3377 | 0.1619 | -0.4192 | 1.3019 |
As shown in Tables 7 and 8, the first typical variable (Form1) of the spinal morphological index is Form1 = 1.3877*sacral inclination*+ 0.4332*thoracic kyphosis*+ 0.4683*lumbar lordosis*- 0.1544*inclination*(the upper right corner of the original variable * represents a standardized variable). The results show that in Form1, the typical coefficient of sacral inclination was larger, indicating that it played a larger role in the first typical variable. Form1 mainly represented the sacral inclination index, and its value was positively correlated with the spinal morphology.
The first typical variable of spine function index (Function1) is Function1=-2.5384*sacral ROM*-0.3198*thoracic ROM*-0.6625*lumbar ROM*+1.6336*INA ROM*-0.4797*sacral change*-0.2094*thoracic vertebral change*-0.5157*lumbar vertebral change*+0.3377*INAc* (the upper right corner band * of the original variable represents the standardized variable). The results show that the typical coefficients of sacral ROM, INA ROM, and lumbar ROM in Function1 were larger, which indicated that Function1 played a larger role. Function1 mainly represents sacral ROM, INA ROM, lumbar ROM, and other indicators. However, because the coefficients of sacral ROM and lumbar ROM were negative, they were negatively correlated with spinal function, whereas the INA ROM was positively correlated with spinal function.
The canonical correlation coefficient of Form1 and Function1 is 0.442 (P < 0.0001), which indicates a positive correlation between the sacral INA of spinal morphology and the ROM of spinal function but a negative correlation with sacral ROM and lumbar ROM.
At present, there are a few studies on the morphology of the sagittal and brachial spine in adolescents, and there are no corresponding quantitative screening criteria for sagittal and brachial spine curvature abnormalities. The data in this study show that the incidence of abnormal thoracic kyphosis and lumbar lordosis is high, except for girls in the junior high school group, who have an abnormal rate of > 45%. The LLA of the junior high school group was 22.8 + 8.1 and 23.5 + 9.9 (boys and girls, respectively), whereas that of the senior high school group was 22.9 + 7.8 and 23.7 + 11.2,. There was a certain gap between these values and the standard values reported by foreign scholars. Although this study did not use X-rays for testing, the test method used has a certain degree of reliability and validity and can basically reflect the status of adolescent spinal morphology in the sagittal plane.
The high incidence of sagittal morphological abnormalities may be related to the prevalence of sedentary hypokinesia and screen time. Long sitting times are likely to have adverse effects on the spinal development of adolescents, who are in the growth stage. If the correct sitting posture is not guaranteed, the normal S-shaped state of the spine will probably be changed, thereby destroying the normal biomechanical structure of the human spine. Kamac studied the difference in spine shape between a sitting posture and a standing posture during the growth and development of children and adolescents. The results showed significant differences in different segments of the spine in the sagittal plane between the sitting and standing postures during the growth and development of children and adolescents [21]. The adolescent skeleton is susceptible to bad posture, which may lead to excessive kyphosis of the thoracic spine and the reduction of lumbar curvature. Abnormality of the thoracic kyphosis angle is a common phenomenon of sagittal and strong surface abnormalities. Scholars have found that the incidence of adolescent kyphosis is between 1% and 8%, and the incidence in boys and girls is roughly equal. The formation of excessive kyphosis of the thoracic spine is closely related to poor daily posture [22].
Muscle strength is closely related to human health, and strength has a certain impact on adolescent spine health. For example, studies have shown that better back muscle endurance can protect against back pain to some extent [23]. In this study, the Matthiass strength test results show that female students are better than male students at maintaining the correct shape of the spine against external force. This phenomenon may indicate that the female students have stronger small muscle groups than the male students. In China's physical education syllabus and students' fitness monitoring, the main emphasis is on the maximum strength and explosive power of large muscle groups, as demonstrated in sit-ups, standing long jump, and so on. There is a lack of effective exercise methods for maintaining the strength and quality of the small muscle groups that contribute to the correct shape of the spine. Compared with large muscle groups, the small muscle groups, especially the stable muscle groups in the core area of the body, are closely related to adolescent spine health. The data of this study suggest that the coordinated development of small and large muscles should be emphasized in future sports teaching reform and adolescent health intervention.
This study explored the relationship between spinal morphology and function in adolescents through a canonical correlation analysis. In the most important first typical relationship, sacral inclination is positively correlated with spinal morphology; that is, within a certain range, the larger the sacral inclination, the better the spinal morphology. Sacral obliquity is the angle between the upper end plate and the horizontal line of S1 [24, 25]; studies have shown that it may be associated with low back pain [26]. At the same time, on the Spinal Mouse test, sacral inclination was highly correlated with the pelvic position, and sacral inclination was more often present than absent when the pelvis was excessively retroverted. It can be inferred from the experimental results that there may be a small sacral inclination, i.e., pelvic retroversion, in the spines of adolescents. The phenomenon of pelvic retroversion may also affect the curvature of the lumbar spine in adolescents, thus affecting the shape of the entire spine. Sacral obliquity is seldom involved in the study of the sagittal and stiff surface morphology of the spine, but Barrey et al. found that the decrease in sacral obliquity and the increase in pelvic obliquity in the adolescents were significantly different from those of normal adults [27]. At the same time, sacral obliquity is recognized to be highly correlated with lumbar lordosis[28]. Whether sacral inclination affects the shape and function of lumbar lordosis in adolescents deserves further study. Based on the results of this study, spine health intervention efforts should consider increasing the attention to sacral inclination and pelvic position to correct the abnormal spinal morphology caused by the sacrum and pelvis.
In the first canonical correlation of spinal function, the greater the sacral mobility and lumbar mobility, the worse the spinal function. In the theory of rehabilitation medicine, the stability of the lumbar spine should be maintained as much as possible in sports. The stability of the lumbar spine is closely related to the function of the spine and the prevention of back pain [29]. The results of this study are consistent with this view. As the spine progresses from full flexion to full extension, the sacrum and lumbar spine should remain as stable as possible; the greater the activity, the worse the spinal function. In this study, the degree of tilt activity represents the change in the tilt line and reflects the overall degree of activity. Given that the cervical spine, lumbar spine, and lumbosacral joints compensate for one another (in part), the change in tilt angle cannot be simply understood as the sum of all joint activities; rather, it basically reflects the activity of the thoracic, lumbar, and lumbosacral joints (sac/hip j.) as the spine moves from flexion to extension. According to the assumption that sacral mobility is negatively correlated with lumbar mobility and spinal function, there may be a lack of thoracic mobility in adolescents. In Gary Cook's Selective Functional Movements Assessment System (SFMA), spinal motion requires the participation of all segments. The absence of any segment’s function will inevitably have an impact on the overall spinal function [31, 32]. For example, the results of this study suggest that adolescents who perform flexion-extension exercises use excessive lumbar spine compensation due to inadequate activity of the thoracic spine, thus affecting the overall function of the spine to a certain extent. In recent years, insufficient activity of the thoracic vertebrae has attracted the attention of scholars. Studies have shown that increased activity of the thoracic spine plays an important role in improving spine-related problems, such as nonspecific low back and neck pains [30, 31]. Therefore, insufficient thoracic spine activity is likely to be prevalent among adolescents. In future spinal-related interventions, thoracic spine mobility should be fully considered to achieve better prevention and treatment.
The canonical correlation analysis of spine morphology and function also showed that, within a certain range, the greater the sacral INA of spine morphology, the greater the degree of motion of the INA. This suggests that sacral inclination is a factor that restricts the overall ROM of the spine in adolescents. In this study, sacral obliquity can be considered to be approximately related to pelvic position, and the smaller the sacral obliquity, the smaller the pelvic retroversion. Whether long-term sedentary behaviour or other unhealthy lifestyle factors result in the pelvic retroversion in adolescents that restricts the overall ROM of the spine during movement deserves further consideration and research. Each segment of the spine interacts with the others during daily activities. The results of this study support this view. The mobility of lumbar lordosis and sacral inclination (which represents pelvic mobility to a certain extent) are mutually constrained. The mobility of the pelvis increases, whereas the mobility of the lumbar spine decreases, and vice versa. As mentioned above, the lumbar spine should be mainly stable, whereas the pelvis and hip joints should be more flexible. If the pelvic mobility of adolescents is limited, the adjacent lumbar spine is likely to compensate for the increased mobility to maintain motor ability. This adaptive change may lead to nonspecific low back pain and even other spine-related diseases[29, 32]. Therefore, in adolescent spine health intervention efforts, attention should be paid to improve the pelvic mobility during exercise to reduce the pressure of lumbar spine.
When the data of the junior and senior high school groups were compared in terms of spinal physiological curvature, the INA index of the boys and girls in the senior high school group was significantly smaller than that of the junior high school group. The tilt angle represents the degree of forward and backward tilt of the body’s centre of gravity to a certain extent. The smaller the tilt angle, the greater the range of backward tilt of the body’s centre of gravity. This shows that with increasing age, adolescents tend to have a tendency toward retroverted centres of gravity, which may be related to their abnormal body posture. For example, the long periods spent in a lying-down posture may cause upper and lower crossing syndrome, which may affect the body’s centre of gravity [33]. At present, there are a few studies on the standard value of the correct body posture and tilt angle for the whole population. It is of positive significance to determine the standard angle of the adolescent centre of gravity to promote spine health. In terms of the strength index, the high school group was better than the junior high school group at maintaining the basic form of the spine; this was especially true for the boys. The degree of spinal deformations of each spinal segment in 30 seconds was lower in the high school group than in the junior high school group. Although the female students have lower scores, the difference was not statistically significant. The results suggest that with increasing age, the boys’ strength for maintaining the physiological curvature of the spine increases, whereas the girls remain relatively deficient. Previous studies have shown that the paravertebral muscles may be associated with low back pain and adolescent idiopathic scoliosis [34–36]. In recent years, the prevalence of scoliosis in adolescents has shown an obvious sex bias, with women showing a higher prevalence [37]. The paravertebral muscle hypothesis has been confirmed by some studies[38, 39]. The results of this study suggest that women may have deficiencies in the small muscle groups that maintain the spinal morphology. Whether this may lead to further postural abnormalities and spinal-related diseases in women deserves further study.
There are some limitations to this study. Although the reliability and validity of the Spinal Mouse tests have been recognized by scholars, there is a gap between this method and the gold standard X-ray. It is of far-reaching significance to find a more reliable evaluation scheme that can effectively replace the use of X-rays for the future study of adolescent spinal morphology and function. At the same time, the sample of this study included middle school students in the Xicheng District of Beijing. The Xicheng District is an area with a higher educational level and leads in terms of quality education promotion in China. In other areas of China, students face greater learning pressure and schoolwork burden. Whether the sagittal shape and function of their spines will be affected is uncertain. Therefore, more scientific sampling should be carried out in the future to identify the morphological and functional characteristics of the sagittal spine of Chinese students to provide reliable data for promoting adolescent spine health.
Compared with the standards for thoracic kyphosis and lumbar lordosis, the incidence of abnormal thoracic kyphosis and lordosis in adolescents is high in this study. Moreover, in the weight-bearing test, girls are better than boys at maintaining the strength of stable muscle groups with normal spine morphology. In the motion from flexion to extension, the ROM of the thoracic and lumbar spine and the total ROM are better in boys than in girls, and the decrease in ROM of the thoracic spine may have a greater impact on the function of the adolescent spine. In the upright posture, girls in junior and senior high schools showed a tendency toward a more forward body centre of gravity. The sacral angle, which reflects the pelvic position, had a great impact on adolescent spinal morphology. Our data provide a reference value for the development of postural spine health screening among adolescent students and provide a direction for preventing serious adolescent spine-related diseases and for reducing the risk of spine-related problems in adulthood.
sacrum angle SA
thoracic kyphosis angle TKA
lumbar lordosis angle LLA
inclination angle INA
sacral range of motion SROM
thoracic range of motion TROM
lumbar range of motion LROM
inclination range of motion IROM
Sacral angle change Sac
thoracic angle change TKAc
lumbar lordosis angle change LLAc
inclination angle change INAc
Ethics approval and consent to participate
The complete protocol of this cross-sectional study was approved by the academic board of the China Institute of Sports Science (No. 201818-21). The written Informed consent was sent to students and parents, which indicating the purpose and methods of this study. We include the subjects who signed the consent into our study.
Consent for publication
Data of this study, which do not contain any personal information, were analysed and showed in group.
Availability of data and materials
The datasets analysed during the current study available from the corresponding author on reasonable request.
Competing interests
The authors declare that they have no competing interests.
Funding
The study was funded by China Institute of Sport Science (19-14,19-21). The funding institute didn’t intervene the design of the study and collection, analysis, and interpretation of data and in writing the manuscript.
Authors' contributions
QF designed the whole study, QF and YZ analysed and interpreted the patient data r. FW and MW contributor in writing and revising the manuscript. All authors read and approved the final manuscript.
Acknowledgements
Thanks for the funding from China Institute of Sport Science. Thank all the subjects for participating in this study. Thanks for all co-author’s contribution in this manuscript.