Risk factors and foot biomechanical characteristics of idiopathic scoliosis: a cross-sectional study

Abstract

Idiopathic scoliosis (IS) caused by an unknown etiology is prevalent in primary and secondary school students. Early detection and prevention are challenging because of the limited knowledge about controllable risk factors and imbalances in body mechanics. In this study, we examined the potential causative factors of IS and its correlation with foot mechanics among 7–14 year-old students in northern Jiangsu Province, China. Based on a stratified whole cluster sampling, 4387 students were examined, of whom of whom 165 were diagnosed with scoliosis. Through logistic regression analysis, the following risk factors were identified: age group, female gender, thinness, unsuitable desk and chair heights, heavy schoolbags, backpack carried on one shoulder, daily sedentary time ≥ 10 h, daily playing electronic products time ≥ 2 h, daily physical activity time < 1 h, sports programs with unilateral limb power, lumbar and back fatigue, unequal thickness of worn soles on both feet and flat foot. When compared to healthy people, IS patients exhibit foot biomechanics characterized by a diagonal distribution of bilateral weight-bearing and walking instability, as well as poor balance function if they have an abnormal foot type, as in the case of flat foot. Our study revealed that the detection rate of scoliosis in primary and secondary school students in northern Jiangsu Province, China, is relatively is on the high side, so it is necessary to strengthen education and screening, concentrate on female students, and provide guidance on how to develop a healthy lifestyle and learning habits. Assessment of plantar pressure distribution and postural symmetry is an effective means of predicting scoliosis. Plantar pressure analysis can serve as an additional tool for assessing the risk of scoliosis.

Introduction

Scoliosis is a complex three-dimensional structural deformity of the spine, with idiopathic scoliosis (IS) being the most common type¹. The global prevalence of IS ranges between 0.47% and 5.20%, and there are significant differences in incidence across different regions^2,3. At present, numerous studies have discussed the prevalence and risk factors for scoliosis in different regions of China, but most of these studies are concentrated in economically developed regions^4–6. In contrast, in northern Jiangsu Province, China, where the level of economic and social development is relatively low, there are almost no epidemiological investigations or related research on scoliosis among primary and secondary school students. The socioeconomic conditions, living habits and distribution of medical resources in this region are different from those in other regions. These factors may affect the incidence and progression of scoliosis.

In recent years, researchers have reported that alterations in lower limb biomechanics may affect the development of scoliosis. For instance, some studies have suggested that structural and functional abnormalities of the foot may lead to misalignment of the lower limb mechanical axis, thereby affecting spinal stability^7,8. Currently, research on the relationship between lower limb biomechanics and scoliosis is still in its exploratory stages, with particularly limited studies focusing on foot biomechanics in patients with idiopathic scoliosis.

In addition to lower limb biomechanics, lifestyle habits, ergonomics, physical activities, and sleep periods also play crucial roles in the development of idiopathic scoliosis^9–12. Therefore, we investigated and evaluated the prevalence and risk factors of idiopathic scoliosis in northern Jiangsu, through scoliosis screening combined with questionnaire surveys. Additionally, foot biomechanical parameters were collected using the gait analysis system to analyse the lower limb mechanical factors that may affect spinal stability. This study aims to provide a new perspective and reference for the early detection, timely diagnosis, and targeted intervention of idiopathic scoliosis.

Materials and methods

Study design and participants

Patients with a previous history of spinal surgery, foot dysfunction or neurological disorders were excluded from this study.

This study is divided into two phases. The first phase is an epidemiological study of scoliosis. In 2024, we used a stratified cluster sampling method to survey primary and secondary school students from 5 cities and 24 counties in northern Jiangsu Province. The sample size was determined based on the urban population and gender ratio, and survey participants were stratified according to grade level and sampled by class to conduct scoliosis screening and questionnaire surveys. The second phase is a plantar pressure study. On one hand, students diagnosed with scoliosis formed the study population (IS group). On the other hand, healthy participants, matched 1:1 by gender and within ± 0.5 years of age during the same screening period, formed the healthy group. The foot mechanics parameters of the two groups were then compared. On the other hand, scoliosis patients were categorized into flat foot, high-arched foot, and normal foot groups based on foot type, and the Cobb angle and foot mechanical parameters were compared among the three groups.

This study followed the ethical standards outlined in the Declaration of Helsinki and was approved by the ethics committee of the Affiliated Hospital of Nanjing University of Traditional Chinese Medicine (NO.2024NL-038-02). Before participation, we informed all participants about the study’s objectives and ensured the protection of their privacy and confidentiality. Written informed consent was obtained from all students and their guardians. All methods were conducted in accordance with relevant guidelines and regulations.

Scoliosis screening methods

The screening program was conducted by our team of professionally trained doctors in accordance with the standards outlined in the 'Screening for Spinal Curvature Abnormalities in Children and Adolescents’ (GB/T 16133-2014). The specific methods are as follows: (1) The subject stands naturally, and the examiner observes whether the shoulders, bilateral subscapular angles, and bilateral iliac crests are symmetrical, and whether the spinous processes deviate from the central axis or are tilted. (2) Adams forward bending test (FBT): The subject’s feet are close together, the knee joint is straight, the head is bowed down, the waist is bent forward slowly to approximately 90°, the hands are put between the knees gradually (to avoid false deviation of the subject’s torso and shoulder), and whether the two sides of the spine are uneven is observed. Patients with positive forward bending tests were suspected of having scoliosis. (3) Trunk rotation measurement: The subject maintained the Adam’s forward bend test posture, and the angle of trunk rotation (ATR) was measured using a scoliometer. An ATR greater than or equal to 5° (ATR ≥ 5°) is highly suggestive of scoliosis. (4) Whole-spine X-ray examination: The initial screening indicated a high suspicion of scoliosis in the student. Further evaluation through whole-spine X-ray examination is required to measure the Cobb angle of the spine. A Cobb angle greater than or equal to 10° (≥ 10°) confirms the diagnosis of scoliosis.

Questionnaire design

The survey questionnaire was designed based on the "2021 National Student Common Disease Surveillance and Intervention Project Plan". The questionnaire covers topics such as students’ basic information, study and lifestyle habits, frequency of seat rotation, desk and chair heights, weight of schoolbags, habits of carrying backpacks, duration of sedentary behavior, sleep duration, time spent on electronic products, physical activity, lumbar and back fatigue, and wearing soles on both feet. When students completed the questionnaire, schoolteachers were not involved in the process. Doctors from our team provided uniform instructions on how to complete the questionnaire and subsequently collected and verified the responses. Questionnaires with more than 20% missing data were considered invalid.

Definitions of relevant indicators

The height of the desks and chairs (when seated, with both hands placed on the desk and the angle between the upper arm and the forearm being close to 90° and with the back and waist relaxed and straight, the height of the desk and chair is considered suitable. Otherwise, the height is considered unsuitable); the schoolbag weight (the schoolbag weighing less than 10% of a student’s body weight is considered light or moderate; if it exceeds 10%, it is considered heavy); the type of force generation in sports (bilateral limb synergistic force type of sports, such as pull-ups, swimming, etc.; unilateral limb force type of sports, such as table tennis, badminton, etc.; lumbar and back fatigue (lumbar and back fatigue refers to a subjective feeling of discomfort, pain, or fatigue in the lower back and back region^13,14); worn soles (using standardized calipers, the thickness of the soles in the heel and midfoot areas of both shoes was measured. If the thickness difference between the two shoes at the same location exceeded 2 mm, it was defined as unequal wear on both shoes); foot type: the plantar imprints of both feet were scanned using the gait analysis system (Force Distribution Measurement, FDM) (Cordewener, Germany), which automatically calculates the arch index (%). Based on the arch index, the feet were categorized as normal foot (18–30%), flat foot (> 30%), or high-arched foot (< 18%)¹⁵. The BMI grading was determined according to the standards of 'Screening for Malnutrition in School-aged Children and Adolescents’ (WS/T 456-2014)¹⁶ and 'Screening for Overweight and Obesity in School-aged Children and Adolescents’ (WS/T 586-2018)¹⁷. Individuals were classified into three categories—thin, normal, and overweight or obese—based on whether their BMI was below, within, or above the corresponding gender- and age-specific thresholds.

Detection of plantar pressure and gait parameters

The gait analysis system was used to collect plantar pressure-related parameters. All participants underwent plantar pressure and gait measurements. First, the participants stood barefoot on the sensor surface of the plantar pressure plate in a natural posture, with their eyes looking straight ahead, feet shoulder-width apart, and hands resting naturally at their sides. After standing steadily, plantar weight-bearing pressure data were collected, and the average of three measurements was recorded. Subsequently, participants walked back and forth on the pressure plate five times at their usual natural speed to collect gait data.

The plantar pressure and gait parameters included the following: percentage of weight-bearing on the right and left feet; percentage of weight-bearing on the forefoot and rearfoot; percentage of gait cycles occupied by the stance phase; plantar impulse; foot progression angle; step width; step length; step speed; stride length; and body center of gravity offset distance (Fig. 1).

Fig. 1.

The butterfly diagram formed by the movement of the body center of gravity during walking. (a) Butterfly diagram of a healthy subject with a regular butterfly pattern and smooth gait, with the body center of gravity centered at the center of the butterfly. (b) Butterfly diagram of an IS patient (the patient’s spine curves to the left); the butterfly pattern tends to be disordered, gait is severely imbalanced, and the body center of gravity is concentrated on the left front side.

Centre of pressure (COP): The gait analysis system divides the dynamic process of foot‒ground contact into four temporal phases (Fig. 2), which are the initial contact phase (ICP), the forefoot contact phase (FFCP), the foot flat phase (FFP) and the forefoot push-off phase (FFPOP), which constitute a complete stance cycle. In accordance with Min-Chi Chiu et al., the center of pressure (COP) trajectory is represented as a curve on a Cartesian coordinate system, as depicted in Fig. 2f¹⁸. In this coordinate system, the vertical Y-axis is defined as the line connecting the center of the heel and the head of the second metatarsal, whereas the horizontal X-axis is defined as the line perpendicular to the Y-axis and passing through the center of the heel. The X-axis scale represents the displacement of the COP relative to the Y-axis (mm), denoted as COPx. The maximum (COPx max) and minimum (COPx min) values of COPx are collected for each phase, and then the displacement of the COP for each phase is calculated by subtracting the minimum value from the maximum value (COPx max-COPx min).

Fig. 2.

Schematic diagram of the COP trajectory (white line). (a–e) The four temporal phases of the stance period: ICP, initial contact phase; FFCP, forefoot contact phase; FFP, foot flat phase; FFPOP, forefoot push off phase. (f) Schematic diagram of the Cartesian coordinate system.

Due to the variability in the direction of the main curve of the spine in IS patients, the bilateral foot data for the IS group are described based on the convex side and concave side of the main curve. For the healthy group, the detection indicators were calculated as the average values of the bilateral foot data. The detection data were processed and exported by the device system.

Statistical analysis

SPSS 25.0 statistical software was used to analyze the data after the database was created. Count data were expressed as frequencies and percentages and compared using the chi-square (X²) test. A binary logistic regression model was used to analyze the risk factors for scoliosis. Based on the results of the normality test, if the data followed a normal distribution, one-way ANOVA combined with the least significant difference (LSD) post hoc test or independent samples t-test was used for intergroup comparisons; if the data did not follow a normal distribution, the Kruskal–Wallis H test or Mann–Whitney U test was used for intergroup comparisons. A p-value < 0.05 was considered statistically significant.

Results

Scoliosis detection rate in participants

A total of 4,387 primary and secondary school students, including 2,341 males and 2,046 females aged 7–14 years (male-to-female ratio: 1.14: 1), were surveyed. During the initial screening, 268 students (6.11%) were identified as highly suspected of having scoliosis. Among these suspected scoliosis students, 254 (5.79%) underwent whole spine X-ray examination, and a total of 165 students were finally diagnosed with scoliosis, for an overall detection rate of 3.76% (165/4387); all of them had single curve scoliosis. The detection rate was 2.69% (63/2341) in the male group and 4.98% (102/2046) in the female group. The screening process for idiopathic scoliosis is shown in Fig. 3, and the detection rate of each age group is shown in Fig. 4.

Fig. 3.

Flow diagram showing the screening process for idiopathic scoliosis.

Fig. 4.

Line diagram showing the detection rates for the male group and the female group and the total detection rate for each age group.

Analysis of factors influencing scoliosis

A total of 4,387 questionnaires were collected, of which 4,326 were valid, 2,315 for male students and 2,011 for female students, with a valid questionnaire rate of 98.6%. Univariate and multivariate logistic regression analyses were performed with scoliosis (yes = 1, no = 0) as the dependent variable and variables with statistically significant differences according to the X² test as independent variables (Table 1). The results revealed that age group 11–14 years (OR = 2.392), female (OR = 2.008), thinness (OR = 1.762), unsuitable desk and chair heights (OR = 1.491), heavy schoolbags (OR = 1.818), backpack carried on one shoulder (OR = 1.657), daily sedentary time ≥ 10 h (OR = 2.147), daily playing electronic products time ≥ 2 h (OR = 1.505), daily physical activity time < 1 h (OR = 1.450), sports programs with unilateral limb power (OR = 1.582), lumbar and back fatigue (OR = 2.147), unequal thickness of worn soles on both feet (OR = 2.696) and flat foot (OR = 1.515) were risk factors for scoliosis in primary and secondary school students (Table 2).

Table 1.

Sociodemographic characteristics and detection of scoliosis in primary and secondary school students aged 7–14 years in northern Jiangsu Province, China. Categorical variables were tested via the chi-square test. BMI, body mass index.

Variable	Overall	IS		P value
	n = 4387	n = 165	Detection rate (%)
Age group				< 0.001
7–10 years old	1844	41	2.22
11–14 years old	2543	124	4.87
Gender				< 0.001
Male	2341	63	2.69
Female	2046	102	4.98
BMI				< 0.001
Thin	692	43	6.21
Normal	2374	95	4.00
Overweight or obese	1321	27	2.04
Seat rotation (times/month)				0.848
≤ 1	2574	98	3.80
> 1	1813	67	3.69
Whether the height of the desks and chairs is suitable for the student’s height				0.007
Yes	2363	72	3.04
No	2024	93	4.59
The habit of eating				0.818
Picky about food	1258	46	3.65
Not picky about food	3129	119	3.80
Daily breakfast with milk or calcium tablets				0.178
Yes	2246	76	3.38
No	2141	89	4.16
Weight of schoolbag				0.001
Light or moderate	3713	124	3.33
Heavy	674	41	6.08
The habit of carrying backpack				< 0.001
On both shoulder	3437	111	3.22
On one shoulder	950	54	5.68
Daily sedentary time				0.003
< 10 h	2515	76	3.02
≥ 10 h	1872	89	4.75
Sleep time				0.816
< 8 h	2033	75	3.68
≥ 8 h	2354	90	3.82
Daily playing electronic products time				< 0.001
< 2 h	3166	99	3.12
≥ 2 h	1221	66	5.41
Daily physical activity time				0.021
< 1 h	2461	107	4.34
≥ 1 h	1926	58	3.01
Types of sports programs				0.001
Bilateral limb synergistic power	3253	104	3.19
Unilateral limb power	1134	61	5.37
Lumbar and back fatigue				< 0.001
Yes	635	43	6.77
No	3752	122	3.25
Thickness of worn soles on both feet				< 0.001
Bipedal equality	3751	117	3.12
Bipedal inequality	636	48	7.55
Foot type				< 0.001
Flat foot	642	58	9.03
Normal foot	3640	103	2.83
High-arched foot	105	4	3.81

Table 2.

Univariate and multivariate analyses of risks associated with idiopathic scoliosis in primary and secondary school students.

Variable	Univariate analyses		Multivariate analyses
	OR (95% CI)	P value	OR (95% CI)	P value
Age group
7–10 years old	1		1
11–14 years old	2.254 (1.575–3.226)	< 0.001	2.392 (1.616–3.541)	< 0.001
Gender
Male	1		1
Female	1.897 (1.378–2.612)	< 0.001	2.008 (1.434–2.812)	< 0.001
BMI
Normal	1		1
Thin	1.589 (1.097–2.303)	0.014	1.762 (1.198–2.592)	0.004
Overweight or obese	0.501 (0.325–0.772)	0.002	0.509 (0.327–0.793)	0.003
Whether the height of the desks and chairs is suitable for the student’s height
Yes	1		1
No	1.532 (1.120–2.097)	0.008	1.491 (1.075–2.067)	0.017
Weight of schoolbag
Light or moderate	1		1
Heavy	1.875 (1.164–2.539)	0.001	1.818 (1.244–2.657)	0.002
The habit of carrying backpack
On both shoulder	1		1
On one shoulder	1.806 (1.294–2.521)	0.001	1.657 (1.170–2.346)	0.004
Daily sedentary time
< 10 h	1		1
≥ 10 h	1.602 (1.172–2.189)	0.003	2.147 (1.538–2.996)	< 0.001
Daily playing electronic products time
< 2 h	1		1
≥ 2 h	1.770 (1.287–2.435)	< 0.001	1.505 (1.073–2.109)	0.018
Daily physical activity time
≥ 1 h	1		1
< 1 h	1.464 (1.057–2.027)	0.022	1.450 (1.033–2.035)	0.032
Types of sports programs
Bilateral limb synergistic power	1		1
Unilateral limb power	2.000 (1.245–2.379)	0.001	1.582 (1.128–2.218)	0.008
Lumbar and back fatigue
Yes	1		1
No	2.161 (1.510–3.092)	< 0.001	2.147 (1.473–3.130)	< 0.001
Thickness of worn soles on both feet
Bipedal equality	1		1
Bipedal inequality	2.535 (1.792–3.587)	< 0.001	2.696 (1.740–4.176)	< 0.001
Foot type
Normal foot	1		1
Flat foot	1.799 (1.238–2.614)	0.002	1.515 (1.245–2.781)	0.029
High-arched foot	1.132 (0.410–3.126)	0.041	1.038 (0.709–1.801)	0.038

BMI, body mass index; OR, odds ratio; CI, confidence interval.

Analysis of plantar pressure and gait

There was no significant difference in the baseline data between the IS group and the healthy group (P > 0.05) (Table 3).

Table 3.

Baseline characteristics of the IS group and the healthy group.

	n	Gender		Age(years)	Height(m)	Weight(kg)	BMI(kg/m2)
		Male	Female	Median(IQR)	Median(IQR)	Median(IQR)	Mean ± SD
IS group	165	63	102	11.89(10.50–14.00)	1.54(1.44–1.65)	43.39(34.75–51.80)	17.91 ± 3.27
Healthy group	165	63	102	11.93(10.50–14.00)	1.55(1.45–1.65)	44.4(34.80–53.85)	18.12 ± 3.04
P value				0.649*	0.48*	0.256*	0.542†

Age, height, and weight do not conform to a normal distribution and are represented by the median (IQR); BMI conforms to a normal distribution and is expressed as the mean ± SD. IQR, interquartile range; SD, standard deviation.

* P value from the Mann‒Whitney U test.

^† P value from independent samples T test.

Plantar pressure: In terms of full-foot weight-bearing, the full plantar pressure of the main curve concave side foot was significantly greater than that of the main curve convex side foot and the healthy group (P < 0.001). In terms of the weight-bearing ratio of the rearfoot to the forefoot, the weight-bearing ratio of the main curved concave side foot was significantly lower than that of the healthy group, whereas the weight-bearing ratio of the main curved convex side foot was significantly greater than that of the healthy group, with both differences being statistically significant (P < 0.001) (Table 4).

Table 4.

Comparison of the proportion of plantar pressure distribution between the IS group and the healthy group.

		n	Whole foot (%)	Forefoot (%)	Rearfoot (%)	R/F
			Mean ± SD	Mean ± SD	Mean ± SD	Median(IQR)
IS group	Main curve concave side foot	165	53.64 ± 3.02‡§	25.14 ± 3.17‡§	28.50 ± 4.38§	1.16(0.91–1.37)‡§
	Main curved convex side foot	165	46.37 ± 3.01‡	15.26 ± 2.33‡	31.10 ± 3.59‡	2.11(1.73–2.42)‡
Healthy group		165	50.00 ± 3.34	20.63 ± 1.15	29.37 ± 3.51	1.43(1.27–1.59)
P value			< 0.001*	< 0.001*	< 0.001*	< 0.001†

R/F, rearfoot/forefoot, rearfoot pressure divided by forefoot pressure. IQR, interquartile range; SD, standard deviation.

*P value from one-way analysis of variance (ANOVA).

^†P value from the Kruskal‒Wallis H test.

^‡Compared with the healthy group, P < 0.05.

^§Compared with the main curved convex side foot, P < 0.05.

Gait: The plantar impulse of the main curved concave side foot was significantly greater than that of the main curved convex side foot and the healthy group (P < 0.001). The offset distance of the body center of gravity in the IS group was significantly greater than that in the healthy group (P < 0.001) (Table 5). In terms of COP displacement in the four temporal phases of the stance phase. The COP displacement of the main curved concave side foot significantly increased during FFCP and FFPOP (P < 0.05). However, there was no significant difference between ICP and FFP (P > 0.05) (Table 6).

Table 5.

Comparison of gait parameters between the IS group and the healthy group. SD, standard deviation.

		n	Stance phase proportion (%)	Plantar impulse (N*s)	Foot progression angle (°)	Step width (cm)	Step length (cm)	Step speed (m/s)	Stride length (cm)	Body center of gravity offset distance (mm)
			Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD
IS group	Main curve concave side foot	165	61.32 ± 4.53	187.32 ± 10.39‡§	6.61 ± 1.68	12.16 ± 2.56	48.66 ± 4.73	0.81 ± 0.10	95.92 ± 8.34	9.62 ± 2.31‡
	Main curved convex side foot	165	60.37 ± 4.37	158.71 ± 5.71‡	7.04 ± 1.39
Healthy group		165	61.16 ± 3.05	162.30 ± 6.73	6.86 ± 2.05	12.70 ± 2.41	49.5 ± 3.55	0.79 ± 0.04	97.18 ± 5.15	5.47 ± 1.05
P value			0.095*	< 0.001*	0.078*	0.051†	0.06†	0.091†	0.100†	< 0.001†

*P value from one-way analysis of variance (ANOVA).

^†P value from independent samples T test.

^‡Compared with the healthy group, P < 0.05.

^§Compared with the main curved convex side foot, P < 0.05.

Table 6.

Comparison of COP displacement (Mean ± SD, mm) in the four temporal phases of the stance phase between the IS group and the healthy group.

		n	ICP	FFCP	FFP	FFPOP
IS group	Main curve concave side foot	165	3.86 ± 1.86	2.64 ± 0.93‡§	4.63 ± 2.61	11.09 ± 4.81‡§
	Main curved convex side foot	165	3.67 ± 1.28	1.89 ± 0.71	4.87 ± 2.13	8.12 ± 3.65
Healthy group		165	3.77 ± 1.71	1.73 ± 0.67	4.38 ± 1.66	7.84 ± 2.31
P value			0.540*	< 0.001*	0.113*	< 0.001*

COP Centre of pressure, SD standard deviation.

*P value from one-way analysis of variance (ANOVA).

^‡Compared with the healthy group, P < 0.05.

^§Compared with the main curved convex side foot, P < 0.05.

Effects of foot type on scoliosis

Upon examination, among the patients with scoliosis, 58 had flat foot, 4 had high-arched foot, and 103 had normal foot. Among the 58 patients with flat foot, 43 had bilateral flat foot and 15 had unilateral flat foot. All four cases of high-arched foot were bilateral. The measurement of the Cobb angle in patients with these three foot types revealed that the angle was 19.95 ± 2.45° in patients with flat foot, 16.97 ± 1.27° in patients with high- arched foot, and 15.27 ± 1.18° in patients with normal foot. The results clearly revealed that patients with flat foot had the greatest degree of scoliosis (P < 0.05) (Fig. 5A). When comparing the body center of gravity offset distance and COP displacement distance, 15 patients with unilateral flat foot were excluded to eliminate the potential interference of asymmetrical foot morphology on the comparison results. In terms of the body center of gravity offset distance, the distances of the scoliosis patients with flat foot, high-arched foot and normal foot were 12.45 ± 2.92 mm, 10.73 ± 0.97 mm and 7.91 ± 1.96 mm, respectively, and the body center of gravity offset distance of the flat foot and high-arch foot was significantly greater than that of the normal foot (P < 0.05) (Fig. 5B). In the comparison of the COP displacement distances among the three foot types during the stance phase, the flat foot on the concave side of the main curve had the greatest COP displacement distance (P < 0.05), as shown in Fig. 5C, whereas on the convex side of the main curve, there was no significant difference in the COP displacement distance among the three foot types (P > 0.05), as shown in Fig. 5D.

Fig. 5.

Effects of foot type on scoliosis. (A) Cobb’s angle of scoliosis patients with different foot types. (B) The body center of gravity offset distance of scoliosis patients with different foot types. (C) COP displacement distance of different foot types in the main curve concave side foot. (D) COP displacement distance of different foot types in the main curve convex side foot. COP, Centre of pressure. The same letter (a or b) indicates that the difference between two comparisons is not significant (P < 0.05); different letters indicate that the difference between two comparisons is significant (P > 0.05).

Discussion

The subjects selected in this study are primary and secondary school students. This group is in a period of rapid development and is at a high risk of developing scoliosis. If preventive measures can be taken before the onset of the disease, early warning or correction of the disease can be achieved, which can provide a guarantee for the normal subsequent development of the spine. The results of this study revealed that the prevalence of scoliosis among primary and secondary school students aged 7–14 years in northern Jiangsu Province was 3.76%, significantly higher than the overall prevalence rate of 1.2% of scoliosis among Chinese adolescents¹⁹. This indicates that the prevalence of scoliosis in northern Jiangsu Province is at a relatively high level, but of course, this result cannot fully represent the prevalence of adolescent idiopathic scoliosis in this region, as some of the students are under 10 years old. The detection rate of scoliosis among students aged 11–14 years was higher than that among students aged 7–10 years. These findings suggest that parents should pay closer attention to their children’s spinal growth and development after the age of 11, particularly for girls. The incidence of IS exhibits such characteristics, and we speculate that possible reasons include rapid physical development and accelerated spinal growth during adolescence, while the intrinsic muscular stabilizing structures of the spine are not yet fully developed and thus fail to maintain normal spinal alignment²⁰. Another reason might be the increasing academic burden associated with higher grade levels, requiring students to sit at desks for prolonged periods, which results in the spine being maintained in poor posture for extended durations and ultimately affects its normal morphology²¹. The gender difference in the incidence of scoliosis may be related to higher leptin levels in girls, which can influence bone metabolism and contribute to dysregulation of spinal growth²². Additionally, spinal ligaments and muscle strength are generally weaker in girls than in boys, making girls more susceptible to scoliosis²³.

Our study also revealed that nutritional status (thinness and obesity) was closely associated with scoliosis. Thinness and obesity are risk factors and protective factors for scoliosis, respectively. From a mechanical stability perspective, individuals who are physically thin tend to have relatively weaker spinal paravertebral muscle strength, which reduces the ability to support and stabilize the spine. Additionally, most thin individuals have insufficient nutrient intake, which may also impair normal bone development and density, thereby increasing the risk of scoliosis²⁴.

The multifactorial logistic regression analysis in this study revealed that scoliosis is associated with several factors, including unsuitable desk and chair height, carrying a backpack on one shoulder, daily sedentary time ≥ 10 h, daily use of electronic products for ≥ 2 h, daily physical activity for < 1 h, and participation in sports involving unilateral limb power. The height of desks and chairs has a significant impact on students’ spinal development²⁵. Too high or too low desks and chairs lead to incorrect sitting postures in students, causing their spines to remain in a twisted state while listening, reading, or writing. This results in uneven force distribution on the muscles on both sides of the spine, leading to continuous fatigue and soreness in the lumbar and back regions. Over time, this destabilizes the lumbar spine and may eventually contribute to the development of scoliosis. We advocate for individualized adjustments to the heights of desks and chairs to accommodate students’ physical growth and development. Currently, children and adolescents face heavy academic workloads. Some students need to complete their coursework using electronic devices, which can easily lead to poor learning postures. These postures can alter the biomechanical structure of the spine, affecting its morphology and function. Tegtmeier et al. conducted a scoping review and reported that prolonged use of electronic products, such as smartphones and tablets, increases the abnormal biomechanical risk to the spine²⁶. Many daily life habits can potentially impact spinal health and should be emphasized. Carrying a backpack on one shoulder or using heavy schoolbags can cause uneven stress on the spine and shift the center of gravity, leading to asymmetric bone growth, spinal imbalance, and ultimately abnormal spinal development²⁷. Therefore, we recommend that the weight of schoolbags carried by primary and secondary school students should not exceed 10% of their body weight, and they should develop the habit of wearing backpacks on both shoulders.

The survey revealed that primary and secondary school students in northern Jiangsu Province have limited time for physical activities. A lack of exercise can lead to weakening and relaxation of the muscles surrounding the spine, making it difficult to maintain the spine’s normal physiological curvature²⁸. The World Health Organization’s 2020 'Guidelines on Physical Activity and Sedentary Behaviour’ recommend that students engage in at least 1 h of moderate- to high-intensity aerobic exercise daily²⁹. We also found that students who frequently engaged in sports activities requiring unilateral limb strength (e.g., table tennis, badminton) had a higher prevalence of scoliosis. This may be related to the imbalance in the development of muscle strength on both sides of the spine caused by long-term unilateral limb use³⁰. Therefore, it is important to diversify daily physical activity programs, such as incorporating broadcast gymnastics, swimming, and pull-ups, to comprehensively and evenly strengthen the muscle groups surrounding the spine.

The lumbodorsal muscle system plays a crucial role in maintaining spinal stability³¹. Lumbar and back fatigue is an important indicator that the lumbodorsal muscles are in a prolonged state of tension and spasm without relaxation or relief³². Under such conditions, the function of the muscle groups begins to decline, making them unable to withstand the physiological load required to stabilize the spine, which increases the likelihood of spinal deformation. In our study, lumbar and back fatigue increased the risk of scoliosis by 2.147 times. The condition of shoe sole wear can provide important information about upright postural stability and walking balance. Our survey revealed that the detection rate of scoliosis in students with unequal sole wear thickness on both feet was 2.696 times higher than that in students with equal sole wear thickness on both feet. This may result from the interaction between the spine and the foot. On the one hand, gait imbalance increases the risk of scoliosis. On the other hand, scoliosis also leads to an asymmetric load distribution in the lower limbs³³. Parents should pay close attention to their children’s lumbar and back fatigue during the growth phase and monitor their children’s sole wear, as these could be early signs of scoliosis.

The plantar surface is the area in contact with external surfaces during standing. Foot biomechanics can reflect the body’s weight-bearing balance, spinal symmetry, and the ability to maintain a stable posture and prevent falls during movement^34,35. The foot transmits sensory information to the central nervous system, providing feedback to regulate body posture. Abnormal foot structure and mechanical distribution can lead to compensatory spinal deformities or changes in curvature, potentially resulting in functional scoliosis³⁶. A study has shown that the musculoskeletal structure around the spine functions as both an effector and a receptor, playing a critical role in maintaining static and dynamic balance. If the physiological structure of the spine is altered, it can lead to abnormal posture control during walking, resulting in asymmetrical changes in gait mechanics³⁷. In severe cases, this may manifest as balance disorders or even falls.

According to our results, flat foot is a risk factor for IS. Among patients with scoliosis, those with flat foot exhibited a tendency towards more severe spinal curvature compared to other two foot types. We determined that the subtalar joints in flatfoot exhibit valgus deformity, and the tibias and femurs on the same side of the lower limb are internally rotated, leading to pelvic tilt.The central axis of the human torso compensates for pelvic tilt, leading to physiological lateral flexion or rotation of the spine. This long-term asymmetric mechanical imbalance ultimately results in the spine’s loss of compensatory ability, causing fixed lateral flexion and rotation of the spine, which contributes to the development of scoliosis.

In this study, there was a significant difference in plantar pressure distribution between the two feet of patients with scoliosis. The total plantar pressure on the concave side of the main curve was significantly greater than that on the convex side, indicating that the patient’s center of gravity tends toward the concave side. This finding is consistent with the results reported by Jin-Xu Wen et al.³⁸. Compared with the plantar pressure distribution of healthy individuals, patients with scoliosis exhibit an imbalance between the forefoot and rearfoot pressure distribution. Specifically, the loading increases on the anterior part of the concave side and on the posterior part of the convex side. This occurs because patients with scoliosis experience trunk lateral deviation and pelvic rotation, leading to a shift in the body’s center of gravity and resulting in a diagonal distribution of foot load.

Regarding gait, this study revealed that the plantar impulse of the main curved concave side foot was significantly greater than that of the main curved convex side foot and healthy individuals during walking. High-intensity plantar impulses can lead to fatigue and damage to the bones, muscles, and joints of the lower limbs, and long-term accumulation of such impulses increases the risk of injury³⁹. It is suggested that plantar pressure distribution should be adjusted in conjunction with scoliosis treatment. Compared with healthy individuals, patients with scoliosis showed no significant differences in the stance phase period, foot progression angle, step width, step length, step speed, or stride length. This may be because patients compensate through somatic motor control during walking, resulting in these indices failing to demonstrate sufficient sensitivity. In terms of the body center of gravity offset distance, the distance traveled by scoliosis patients was significantly greater than that of healthy individuals. Furthermore, if patients have abnormal foot types, the amplitude of body center of gravity oscillation increases even further, indicating a greater degree of imbalance during walking and an elevated risk of falling.

COP displacement can reflect the body’s balance function in the coronal plane⁴⁰. In this study, the COP displacement of the main curve concave side foot in patients with scoliosis was greater than that of the main curve convex side foot and healthy individuals during both the FFCP and FFPOP phases. However, the difference was not significant during the ICP and FFP phases.

During the stance phase of human gait, the foot and ankle sequentially roll through the heel, forefoot, and toes to absorb impact and propel the body forward. During the ICP phase, the heel absorbs impact and facilitates the transition to forefoot and full-foot support. In the FFCP and FFP phases, the ankle roll gradually shifts the center of gravity forward to prepare for the subsequent push-off and propulsion. In the FFPOP phase, the forefoot and toes act as the fulcrum of the lower limb’s rigid lever, completing the transition from the stance phase to the swing phase. Patients with scoliosis, due to trunk inclination and pelvic rotation, tend to bear more weight on the concave side, resulting in increased load on the anterior half of the concave side foot. Consequently, during the FFCP and FFPOP, the concave side foot bears more load than normal muscular strength can handle during forward center of gravity shifts and push-off actions. This leads to increased instability, manifested as greater displacement of the COP. We also found that abnormal foot types, such as flat foot, can exacerbate coronal plane imbalance during walking. This suggests that in the treatment of idiopathic scoliosis, targeted interventions—such as corrective exercises and the use of orthopedic insoles to improve balance and gait mechanics—should also be implemented for patients with abnormal foot types.

Limitations

This study has several limitations. First, although stratified cluster sampling was used to conduct scoliosis screening and questionnaire surveys among primary and secondary school students, potential sample selection bias may exist. For instance, some students did not participate due to absenteeism or other reasons, which may affect the completeness and representativeness of the sample. Future plans include expanding the sample size, conducting multicenter studies, and improving the participation rate. Second, the questionnaire survey relied on a questionnaire designed by the Common Disease Surveillance and Intervention Program for Students, which has limitations such as incomplete entries and responses potentially influenced by memory bias and subjective bias. In the future, multiple data collection methods, such as diary entries and field investigations, will be employed. Finally, our findings reveal distinct foot biomechanical patterns in IS patients, characterized by asymmetric weight bearing and gait instability. Notably, the bilateral foot data in this study were analyzed based on the convex and concave sides of the main spinal curve. However, this approach, while applicable to single-curve scoliosis, may not fully capture the biomechanical complexity of double-curve patterns. In future studies, we plan to expand the sample size and stratify patients by curve type (e.g., single vs. double curves) to assess whether significant differences in foot biomechanical characteristics exist between these subgroups.

Conclusions

In summary, the detection rate of scoliosis among primary and secondary school students aged 7–14 years in northern Jiangsu Province, China, is relatively high. This is closely associated with factors such as age group, gender, BMI, and learning and lifestyle habits. It is essential to strengthen education, publicity, and screening efforts; guide students in developing healthy learning and lifestyle habits; and ensure adequate nutrition. Scoliosis patients exhibit poor weight-bearing symmetry in both feet and increased walking instability. Therefore, the treatment of scoliosis should not only address structural deformities of the spine but also consider abnormal foot biomechanics. Plantar pressure analysis can serve as an additional tool for assessing the risk of idiopathic scoliosis and can aid in developing targeted interventions.

Author contributions

S.P.F. contributed the central idea, and X.Y.M., C.S., B.G.M., W.Y.H., S.L.S., C.L. and L.Z.Y. analysed most of the data. S.P.F. and Z.Y.Q. wrote the initial draft of the paper, M.W. guided the theory and design of the research, and revised the article. All authors contributed to refining the ideas, carrying out additional analyses, and finalizing this paper. All the authors read and approved the final manuscript.

Funding

This study was supported by the construction project of Inheritance Studio for National Famous and Veteran TCM Experts (National TCM Education Letter [2022] No. 75) and the Technology Project of Jiangsu Provincial Administration of Traditional Chinese Medicine (No. ZD202202) and Jiangsu Provincial Civil-Military Integration Innovation Platform (Su Cai Gong Mao [2023] No. 63) and Jiangsu Provincial Hospital of Traditional Chinese Medicine Innovation and Development Fund Project (No. Y2023CX25).

Data availability

The datasets generated and analysed during this study are not publicly available to protect the privacy of the participants. The data are available from the Affiliated Hospital of Nanjing University of Chinese Medicine and can be obtained from the corresponding author (email: wenge1977@126.com) upon reasonable request.

Declarations

Competing interests

The authors declare no competing interests.

Ethics committee approval

This study was approved by the ethics committee of the Affiliated Hospital of Nanjing University of Traditional Chinese Medicine (NO. 2024NL-038-02).

Consent for publication

Informed consent was obtained from all the participants.