Evaluation of the association between postural control and sagittal curvature of the spine.

INTRODUCTION: Balance is key to controlling body posture. Balance is typically assessed by measures of the body's vertical orientation, obtained by balancing out the forces acting on different body segments. The ability to maintain balance is assessed by evaluating centre of pressure (CoP) displacement; such assessments are typically used to evaluate responses to a treatment process. PURPOSE OF STUDY: This study evaluated the efficiency of compensatory reactions in children according to the extent of thoracic kyphosis and lumbar lordosis. MATERIALS AND
METHOD: The study enrolled 312 children aged 8‒12 years, including 211 patients with postural disorders: thoracic kyphosis outside the 47‒50-degree range and lordosis outside the 38‒42-degree range (study group). A control group was also recruited and comprised 101 children without postural disorders. The DIERS formetric 4D system was used to assess posture and CoP displacement.
RESULTS: Children in the study group showed a significantly greater range of CoP displacement than children in the control group. The kyphosis angle correlated with the maximum CoP displacement in the coronal plane and the maximum CoP displacement in the sagittal plane during gait. The kyphosis angle also correlated with the maximum CoP displacement back in the static test. The size of the lordosis angle correlated with the maximum displacement of CoP in the coronary plane during gait, and with the maximum displacement of CoP toward the left, forward, and backward in the static test. The correlation coefficient of the lordosis angle with displacement of the CoP in the sagittal plane was 0.999.
CONCLUSIONS: We found an association between kyphosis and lordosis and the amplitude of CoP displacement, which may reflect the postural control system's response to biomechanical destabilisation caused by changes in kyphosis and lordosis.The lordosis angle correlation strength for displacement of CoP in sagittal plane is 0.999 and adopts a linear value.

Introduction

Posture defines the individual placement of the body’s limbs in relation to one another under dynamic and static conditions while in an upright position. It corresponds to the typical biomechanical conditions for the functioning of the human body [1]. Correct body posture allows one to retain a vertical position and limits movement of the centre of mass in relation to the support plane [2, 3], ensuring maximum stability with the minimum muscle involvement [4]. The amplitude of thoracic kyphosis and lumbar lordosis, which stabilize the spine, preventing curvature in other planes, are important for maintaining a correct posture [5].

A faulty posture comprises a set of irregularities, defined as small, individual deviations from the correct posture, which can be corrected using appropriate therapy [6, 7]. There are many causes for posture disorders, including limb-length disturbances, which change the position of the pelvis and thus affects the shape of the spine [8-11]. In such cases, limb length equalization is sufficient intervention [8, 12]. Asymmetrical shoulder loading also affects the shape of the spine [13]. Posterior and pelvic muscle insufficiency is another source of posture disorders, and in these cases therapy improving the strength of these muscles is effective for correcting the disorders [14, 15]. Many studies have shown that spinopelvic alignment and sagittal balance are major contributors to an energy-efficient posture of the individual in the healthy and diseased states [16-18].

Body posture disorders are common among the paediatric population and are increasingly becoming a serious epidemiological concern in this age group [6, 7, 19, 20]. The literature indicates that determining the angle of healthy curvature of the spine in the sagittal plane is challenging, with discrepant findings across studies. In radiological studies, in a population of individuals aged 20‒63 years, the mean angle of thoracic kyphosis was 28.9° ± 12.1° in women and 31.2° ± 7.9° in men, while the average angle of lumbar lordosis was 45.7° ± 12.9° in woman and 43.9° ± 10.8° in men [21]. The range of a healthy thoracic kyphosis angle should be 20‒40° in growing teenagers, based on data from 1960 provided by the Scoliosis Research Society [22]. Using radiological examination, Lin et al. determined the angle of lumbar lordosis at an average age of 50 years to be 33.2° ± 12.1°; they did not observe significant differences between women and men [23]. Radiological examinations of 350 healthy people aged 18‒50 years showed average values of 45° for lumbar lordosis [24]. In radiological studies of children aged 3‒10 years, the average thoracic kyphosis angle was 42.0° ± 10.6° and the average lumbar lordosis angle was 53.8° ± 12.0° [25]. In the same study, the mean thoracic kyphosis angle was 45.8° ± 10.4° and lumbar lordosis angle was 57.7° ± 11.1° for the age range 10‒18 years [25]. Further radiological examinations in children aged 8‒19 years reported an average thoracic kyphosis angle of 47.47° ± 12.7° and average lumbar lordosis angle of 39.6° ± 12.4° [26]. A study of people aged between 2 and 27 years, conducted by Wenger and Frick, reported that the average angle of thoracic kyphosis increased with age, from 20° in childhood, to 25° in adolescence, to 40° in adulthood, which makes it challenging to establish uniform norms concerning changes occurring during puberty [22]. The DIERS system provides norms for certain parameters that are considered physiological: a kyphotic angle of 48° ± 9° and a lordosis angle of 43° ± 8° for women and 36° ± 7° for men [27]. Thus, the lack of consistent values in the literature that define a healthy spinal curve in the sagittal plane impedes the comparison of studies, and may be ascribed to varying inclusion criteria, which makes the distinction between the upper boundary of standard thoracic kyphosis and severe juvenile deformation almost impossible [5].

Kyphosis and lordosis influence balance in the upright individual. Balance allows one to regain a previous state of equilibrium in the body while performing or after the completion of motor tasks [28]. The determinant used to define the ability to maintain balance is the centre of pressure (CoP) displacement; evaluating CoP displacement is used to reflect responses to treatment. An accurate definition of the parameters used to describe balance allows one to choose appropriate actions to improve balance via therapy, and knowledge of changes occurring within the parameters describing balance dysfunction allows appropriate selection of treatment methods to optimize the therapeutic process. Spontaneous CoP displacement consist of two-dimensional information (observation of individual elements of the route on a statokinesiogram), i.e., analysing postural shifts in the sagittal and coronal plane separately allows one to determine postural stability [28-30]. Additionally, gait analysis in relation to body posture also yields useful information. Changes in the body shape cause an asymmetrical load on the legs, which generates a postural muscle imbalance as well as a displacement in the CoP [31]. CoP displacement during quiet standing reflects the net contribution of the central nervous system (CNS) to control the movement of the Centre of Mass (CoM). Where the horizontal acceleration of the CoM is proportional to the difference between the CoP-CoM [32]. During quiet stance it is the hip abductors/adductors that generate torque to control ML movement, and it is the ankle plantar flexors/dorsiflexors that control A/P movement. During walking, the movement of the CoP moves from posterior to anterior under the foot, and M/L. Although the above concept holds true (ie., CoP reflects net output of CNS control), how it does this is more complex given the multiple degrees of freedom, and joint motions.

With the increase in postural dysfunction, the path covered by the CoP in a given unit of time is extended, indicating that compensatory reactions are weakened [32]. When the CNS senses that this shift in the centre of gravity (CoG) requires correction, the CoP changes until it lies posterior to the CoG, allowing the body to return to it’s original condition. Assessment of the changes in the CoG and CoP conditions has demonstrated that the plantar flexors-dorsiflexors that control the net ankle moment can regulate the body’s CoG [32]. The CNS attempts to counteract gravitational forces on the body by adjusting the alignment of body segments, so that any disorder in this biomechanical system will reduce the efficiency of equivalent reactions. The net muscle moment is the sum of the balance and postural components [32]. There is a significant relationship between body posture, the efficiency of compensatory reactions, and the gait quality [33]. In cases of minor deformations this may mainly apply to the sagittal plane, but with pronounced abnormal curvatures of the spine, dysfunctions may also involve movement of the CoP in the coronal plane [34].

Purpose of study

This study investigated the influence of thoracic kyphosis and lumbar lordosis on compensatory reactions in children without posture disorders and in those with pathological thoracic kyphosis and lumbar lordosis angles.

Materials and method

Study participants

The study involved 312 children aged 8‒12 years. Study participants were recruited consecutively from among patients who came to our outpatient clinic and included children who met the inclusion criteria.

The study group consisted of 211 patients with postural disorders, in terms of the degree of thoracic kyphosis and lumbar lordosis: kyphosis outside the 35‒59° range and lordosis outside the 27‒51° range [26]. This group comprised 112 girls (53.1%) and 99 boys (46.9%). The control group consisted of 101 children in whom no postural disorders were found in a clinical trial. Children in this group were recruited consecutively from among those who came for a preventive body posture examination. The children included in the control group did not show any signs of body posture disorder in physiotherapeutic assessment. The group comprised 51 girls (50.5%) and 50 boys (49.5%). The morphological parameters of children from both groups are presented in Table 1.

Table 1

Morphological parameters of children from the study group and the control group.

Parameter	Study group		Control group
	Average	SD	Average	SD
Age	10.7	1.3	10.7	1.4
Body height	1.4	0.2	1.4	0.1
Body mass	34.7	11.9	38.7	8.0
BMI	20.2	2.4	20.0	2.5

The research was conducted from 2016 to 2018. The study was approved by the Bioethics Committee of the Faculty of Medicine and Health Sciences, Jan Kochanowski University, Kielce (consent no. 1/2016 issued on 15 January 2016). Informed consent for participation in the study was obtained from each child and their parents/guardians. Participation in the research was voluntary, combined with ensuring anonymity regarding the Personal Data Protection Act of 29.08.1997 (Journal of Laws No. 133, item 883. Republic of Poland).

Inclusion criteria

The inclusion criteria were as follows: age 8‒12 years; good overall condition (Eastern Cooperative Oncology Group performance status scale ≤ 2); ability to perform at least personal activities; consent from the legal guardian/parent to participate in the research. Additionally, the study group participants were included if they had a body posture defect: on the DIERS system, a posture defect was defined as a pelvic inclination > 5 mm, lateral deviation < 5 mm, and surface rotation < 5 degrees. If the lateral deviation was > 5 mm and the surface rotation was > 5 degrees, with a pelvic inclination of < 5 mm, scoliosis was diagnosed [35]. Furthermore, control group participants were included if there was no postural defect.

Exclusion criteria

Children were excluded from participation if there were any co-morbidities that may affect the body axis, e.g., Sheuerman disease, genetic diseases, such as Beckwith‒Wiedemann syndrome, or metabolic diseases, or if they had a body mass index below 16.99 or above 29.99.

Research methodology

Body posture was assessed under static conditions in a habitual standing position, with the back to the camera and facing straight ahead. Body posture assessment was accompanied by simultaneous measurement of ground reaction force to the feet, and the CoP movement in a static position.

The DIERS formetric 4D system (DIERS International Gmbh, Schlangenbad, Germany) was used to assess posture [36-37]. Using rasterstereography, the DIERS formetric 4D device allows for photogrammetric video recording of the subject’s back surface. By analysing the surface of the back, the data collected allow analysis of the spinal axis [38]. The digital recording lasted about 3 seconds and comprised 12 photos; data analysis was performed using the built-in computer software.

Measurements of ground reaction forces on the feet and the CoP movement in a static position were conducted using the DIERS pedoscan device in combination with the DIERS formetric system [39]. The subject stood in the centre of a measuring platform of 80 × 100 cm. The feet were positioned straight ahead in their natural, relaxed position. The maximum peak in four directions (left, right, forward, and backward) was evaluated. The measurement was carried out for 3 seconds at the same time as the shape of spine was assessed with the DIERS formetric system.

The analyses of ground reaction forces and equivalent reactions under dynamic conditions were conducted using a DIERS pedogait device consisting of a treadmill and a built-in pedobarographic platform, measuring 80 × 100 cm, with 5376 built-in sensors. The measurement was made during a calm walk at a speed of 2 km/h, over a distance of 16 m. The maximum peak in the sagittal and frontal planes was evaluated.

The following parameters were assessed:

Kyphosis angle

This is the kyphotic angle measured between Vertebra Prominens and the estimated position of T12.

Lordosis angle

This is the lordotic angle, measured between the estimated position of T12 –DM (Centre between Dimple L and Dimple R

Maximum displacement of centre of pressure in coronal plane during gait

The parameter is calculated in millimetres [mm], which is the greatest displacement (maximum peak) of the projection of the center of pressure in the coronal plane during gait at a distance of 16 m.

Maximum displacement of centre of pressure in sagittal plane during gait

The parameter is calculated in millimetres [mm], which is the greatest displacement (maximum peak) of the projection of the center of pressure in the sagittal plane during gait at a distance of 16 m.

Maximum displacement of the CoP in the coronal plane under static conditions

This parameter is calculated in millimetres [mm] and shows the distance (maximum peak) covered by the projection of the center of pressure on to the ground in 3 seconds in the coronal plane (body to the left and right).

Maximum displacement of the CoP in the sagittal plane under static conditions

This parameter is calculated in millimetres [mm] and shows the distance (maximum peak) covered by the projection of the center of pressure on to the ground in 3 seconds in the sagittal plane (forward and backward).

Statistical analysis

Statistical analysis was conducted using IBM SPSS Statistics v23 software (IMB SPSS Inc, Chicago, IL, USA). Basic descriptive statistics analysis was performed. To assess the normality of the distribution of variables, we used the Kolmogorov‒Smirnov test [40]. To establish the relationship between the studied variables, we used the Spearman rank correlation test [41]. The level of significance was set at p < 0.05.

Results

Basic descriptive statistics of the examined quantitative variables were calculated. Analyses were performed separately for the study group and the control group.

Most of the examined variables had a non-normal distribution. Hence, we conducted statistical analyses using nonparametric tests. As our inclusion criteria did not allow inclusion of individuals with kyphosis and lordosis below and above the reference values, there was no significant difference between the groups. All parameters describing CoP movement were significantly different between the study and control groups. Details are presented in Table 2.

Table 2

Comparison of values of examined variables in the study and control groups.

	study group (n = 211)		control group (n = 101)
	M	SD	M	SD	U	Z	p	r
Angle of thoracic kyphosis VP-ITL [°]	41,37	9,60	39,45	8,28	9695,0	-1,288	0,198	0,07
Angle of lumbar lordosis ITL-DM [°]	37,05	9,55	38,33	8,59	9593,0	-1,425	0,154	0,08
Maximum displacement of centre of pressure in coronal plane during gait [mm]	104,63	25,08	98,73	19,22	9126,5	-2,051	0,040	0,12
Maximum displacement of centre of pressure in sagittal plane during in gait [mm]	202,07	58,32	160,39	32,37	5542,5	-6,858	<0,001	0,39
Maximum displacement of the CoP in the coronal plane under static conditions [mm] (to the left)	1,03	1,55	0,56	0,33	6846,5	-5,109	<0,001	0,29
Maximum displacement of the CoP in the coronal plane under static conditions [mm] (to the right)	0,80	0,64	0,55	0,35	7445,0	-4,307	<0,001	0,24
Maximum displacement of the CoP in the sagittal plane under static conditions [mm] (forward)	1,18	1,01	0,83	0,41	7108,5	-4,758	<0,001	0,27
Maximum displacement of the CoP in the sagittal plane under static conditions [mm] (backward)	0,69	0,97	0,43	0,28	8145,5	-3,367	0,001	0,19

We then investigated the relationship between body posture and CoP movements under static and dynamic conditions. A series of Spearman’s ρ rank correlation analyses were performed separately for the study group and the control group. As the angle of kyphosis increased, the maximum displacement of the CoP in the coronal as well as in the sagittal plane increased (Table 3). The increase in the maximum CoP displacement in the sagittal plane relative to the angle of kyphosis was markedly faster than in the frontal plane. As the angle of kyphosis increased, the maximum backward displacement of the CoP also increased (Table 3).

Table 3

Significant relationships between the angle of thoracic kyphosis and other variables tested in the study group and in the control group.

		Angle of thoracic kyphosis VP-ITL [°]
		study group	control group
Maximum displacement of centre of pressure in coronal plane during gait [mm]	Spearman ρ	0.182	-0.043
	relevance	0.008	0.672
Maximum displacement of centre of pressure in sagittal plane during gait [mm]	Spearman ρ	0.438	0.155
	relevance	<0.001	0.121
Maximum displacement of the CoP in the coronal plane under static conditions [mm] (to the left)	Spearman ρ	0.126	-0.029
	relevance	0.068	0.770
Maximum displacement of the CoP in the coronal plane under static conditions [mm] (to the right)	Spearman ρ	0.118	-0.140
	relevance	0.089	0.164
Maximum displacement of the CoP in the sagittal plane under static conditions [mm] (forward)	Spearman ρ	-0,066	-0,062
	relevance	0,341	0,541
Maximum displacement of the CoP in the sagittal plane under static conditions [mm] (backward)	Spearman ρ	0.177	0.040
	relevance	0.010	0.688

Along with the increase in the angle of lordosis, an increase in CoP displacement were observed. There was an increase in the maximum displacement of the CoP in the coronal plane, maximum displacement of the CoP in the coronal plane (static conditions, body to the left). Moreover, there was a reduction in the forward as well as in the backward displacement of the maximum CoP in the static test with an increased lordosis angle (Table 4).

Table 4

Significant relationships between the angle of lumbar lordosis and other variables tested in the study group and in the control group.

		Angle of lumbar lordosis ITL-DM [°]
		study group	control group
Maximum displacement of centre of pressure in coronal plane during gait [mm]	Spearman ρ	0.265	-0.031
	relevance	<0.001	0.762
Maximum displacement of centre of pressure in sagittal plane during gait [mm]	Spearman ρ	0.999	0.129
	relevance	<0.001	0.199
Maximum displacement of the CoP in the coronal plane under static conditions [mm] (to the left)	Spearman ρ	0.154	-0.021
	relevance	0.025	0.836
Maximum displacement of the CoP in the coronal plane under static conditions [mm] (to the right)	Spearman ρ	0.133	-0.032
	relevance	0.054	0.748
Maximum displacement of the CoP in the sagittal plane under static conditions [mm] (forward)	Spearman ρ	-0.172	-0.005
	relevance	0.012	0.964
Maximum displacement of the CoP in the sagittal plane under static conditions [mm] (backward)	Spearman ρ	0.381	0.037
	relevance	<0.001	0.715

The displacement of the CoP in the sagittal plane increased with an increment in the lordosis angle. Interestingly, the results of the tests form a straight trend line (Fig 1).

Fig 1

Relationship of angle of lordosis to maximum displacement of centre of pressure in sagittal plane during gait.

Discussion

This study investigated whether the magnitude of thoracic kyphosis and lumbar lordosis has an impact on compensatory reactions in children. We found that the kyphosis angle correlated with the maximum CoP displacement during gait (Table 3), and the lordosis angle correlated with the maximum CoP displacement during gait and with the maximum C0P displacement under static conditions (Table 4). Children with impaired body posture were characterized by significantly higher maximum CoP displacement than children with a physiologically normal spine shape (Table 2), which indicated a reduced ability to control vertical posture.

Our results indicated a relationship between the shape of the spine and the maximum displacement of CoP under static conditions. The kyphosis angle correlated weakly with the maximum backward displacement of the CoP (r = 0.177 p = 0.01). The lordosis angle correlated with the maximum leftward, forward, and backward COP displacement; these correlations were also weak (r = 0.154, -0.17, and 0.381, respectively), although statistically significant (p < 0.05).

Nalut et al. [42] made similar observations, although their research showed a clearly stronger effect on the path-length in the coronal plane (increased by 50%) than in the sagittal plane (increased by 25%). Wilczyński et al. [43] showed both an increase in the CoG path-length in both planes, as well as an increase in the maximum displacement in all four directions, with the increase in thoracic kyphosis; these findings agreed with the results obtained in the present study. Subsequently, they emphasized that the impact of thoracic kyphosis disorders on the quality of equivalent reactions is independent of the co-occurrence of spinal axis disorders in the coronal plane [44]; this allows us to distinguish this element as independent of postural dysfunction as a whole.

Changing the angle of kyphosis affects the dorsal and calf muscle tension, contributing to the weakening of equivalent reactions [31] Therefore, a change in the angle of kyphosis can start a chain of biokinematic changes. However, these relationships should be verified in future studies involving the simultaneous measurement of kyphosis, lordosis, postural muscle tone, and CoG displacement.

The curvature of the spine had a markeldy larger impact on the maximum displacement of the CoP during gait. The angular kyphosis angle correlated with the maximum displacement of the CoP in the coronal plane during gait with an effect force of 0.182 (p = 0.008), and in the sagital plane with an effect force of 0.438 (p < 0.001). The lumbar lordosis angle correlated with the maximum displacement of the CoP during gait in the coronal plane with an effect force of 0.265 (p < 0.001), and in the sagittal plane with an effect force of 0.999 (p < 0.001). Therefore, these correlations were of moderate strength, except for the relationship between the lumbar lordosis angle and the maximum displacement of the CoP in the sagittal plane, which was very strong. This may also be due to an increase in the rear-foot load with the increase in the lumbar lordosis angle, as reported by Suoza et al. [45] who observed this phenomenon in patients with temporomandibular joint dysfunction.

Comparison of the magnitude of the maximum CoP displacement in a group of children with a physiologically normal spine and a group with impaired posture revealed statistically significant differences between the groups in all directions of CoP displacement, both in standing position and while walking, with smaller shifts in children with a physiologically normal spine (Table 2). Particularly interesting observations relate to the strength of the effect of these differences, which is definitely greater than the correlation of individual shifts with the size of thoracic kyphosis and lumbar lordosis. This disproportion may indicate that spine disorder also affects other mechanisms related to the control of CoP displacement and suggests that further analyses of a larger number of variables and their interrelationships are warranted in future.

The clear relationship between the reduction in the kyphosis angle and the shortening of the CoG displacement path arises may be due to the fact that postural dysfunction determines the extent of postural reaction disorders, as described by Nault et al. [42]. Rougier et al. [46] explains this phenomenon by the fact that CoG displacement during gait is changed by the forces transmitted to the feet and are partly reduced by compensations occurring in the hip and ankle.

Winter et al. [32] also points out that, with the restoration of the physiological value of thoracic kyphosis, an improvement in balance can be expected, due to shifts in the center of mass in the upper torso, which is then transferred to the ground by the hip and ankle. In contrast, Carlsöö improved dynamic balance by restoration of the physiological size of thoracic kyphosis, which was attributed to the reduction of tensions flowing through the sacro-dorsal and calf muscles to the feet [31].

Our study showed a significant relationship between the angle of kyphosis and the displacement of the CoP in the sagittal plane (r = 0.438, p < 0.001) and in the coronal plane (r = 0.182, p = 0.008) (Table 3). With the increase of this curvature, the deviations in the CoP displacement in both planes increased. In their report, Nault et al. presented similar observations, although their research showed a markedly greater effect on the CoP path-length in the coronal plane (increased by 50%) than in the sagittal plane (increased by 25%) [42]. Another report demonstrated that changes in balance parameters correlated with the change in the angle of lumbar lordosis, negating the effect of the angle of thoracic kyphosis [47]. Drzal-Grabiec et al., who conducted research using the formetric system, obtained a significant correlation between both the total CoP path-length and its maximum deviations, depending on the angles of thoracic kyphosis and lumbar lordosis [48], confirming the results obtained in our study.

Maintaining body balance is due to coordinated interaction of the balance organs with the cerebellar and spinal cord centers. Body control in space also requires the interaction of the motor apparatus, eyeballs, and the reticular formation in the brainstem. Adjustment reactions consist of the coordination of tonic-reflex, striving to maintain the body in a vertical position [49]. Atrial-spinal reflexes are the foundation of appropriate postural reactions of the muscles responsible for the position of the neck, torso, and lower limbs. The sensorimotor performance of the musculoskeletal system in this way determines the appropriate equivalent reactions [32].

As the dysfunction increases, postural lengthening is observed in the given CoG, indicating that equivalent reactions are weakened [32]. There is a significant relationship between body posture, efficiency of equivalent reactions, and gait quality [33]. In the case of minor spinal deformations, this may mainly affect the sagittal plane, but with pronounced curvatures of the spine, the dysfunctions also include movement of the CoG in the frontal plane [42].

Body posture is inextricably linked to the ergonomics of gait, and its symmetry is necessary for the proper movement of the CoG during human movement [32]. Movement of the CoG is registered by pressure receptors in the feet, and related reactions aimed at maintaining balance occur by reflex [50].

Our findings confirmed the relationship between body posture disorders and equivalent reactions. Abnormalities in the sagittal plane, i.e., the extent of thoracic kyphosis and lumbar lordosis (Tables 3 and 4) have a particularly marked impact on the increase in the CoP deflection. It is known that disorders in the sagittal plane most commonly underlie dysfunctions in the coronal and transverse planes [51].

The key element of the present study is the method used for assessing spinal curvature and length of CoP displacement. We showed that, when assessing the curvature of the spine in an anatomical manner, the compensatory reactions were clearly dependent on the extent of spinal curvature [47, 48], while no relationship was found when assessing the spinal curvature using the Spinal Maus [52], a device guided manually along the spine on the skin to assess the curvatures of the vertebral column. The method used for spinal examination appears to be of great importance, as mentioned by Kluszczyński et al. [53]. It is possible that another way of assessing spinal curvature and the displacement of the CoP may lead to other conclusions, which should be evaluated in future research.

In this study, we demonstrated that the extent of kyphosis and lordosis is related to the amplitude of CoP displacement. This association may reflect the postural control system’s response to biomechanical destabilisation resulting from altered kyphosis and lordosis.

The lordosis angle correlation strength for displacement of COP in sagittal plane is 0.999 and adopts a linear value.

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19 May 2020

PONE-D-20-08811

Evaluation of the Efficiency of Compensation Reactions in Children by the Extent of Thoracic Kyphosis and Lumbar Lordosis.

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Reviewer #1: The authors present a manuscript about compensation reactions in children related to the amount of thoracic kyphosis and lumbar lordosis. While their manuscript contained interesting information, it could not be approved as submitted. If the authors choose to revise their manuscript, please address the following comments. As a general advice, please have a native English speaker revise your manuscript in order to enhance its readability:

Page 2, Abstract: “The study group consists of 211 patients with postural disorders with respect to the degree of thoracic kyphosis and lumbar lordosis…” Please define what you mean by postural disorders: hyperkyphosis, hypokyphosis, hyperlordosis etc.?

Page 2, Abstract: “Along with the increase in the angle of lordosis, an increase in indicators was observed: maximum movement of the CoP in the coronal plane, maximum movement of the CoP to the side (statically body to the left); and a reduction in the forward movement of the maximum CoP in the static test and the backward movement of the maximum CoP in the static test.” Please clarify.

Introduction I suggest that you group together the results of the different studies you mentioned. The Wenger and Frick study should be put apart as it points to the fundamental fact that sagittal spinal alignment is age dependent, which is important for your study

Page 4 “The main element in controlling body posture is balance. Its typical parameters are constituted of measures of the body’s vertical orientation, obtained by balancing out the forces acting on different body segments [17]. This phenomenon is related to inertia forces and inertia characteristics of individual body segments [18].” This information is considered common knowledge. For the sake of concision, I suggest omitting these phrases.

Page 4 “The determinant used to define the ability to maintain balance are the center of pressure (CoP) movements, the establishing of which allows controlling the treatment process…” What do you mean by “allows controlling the treatment process”? Please clarify

Page 4 “With the increase in postural dysfunction, an extension of the path covered by the centre of pressure in a given unit of time is observed, which means that compensating reactions are weakened [18].” Please be more explicit. As this is mean subject of your research project, this deserves more explanations

Page 4 “postural muscle disbalance” consider muscle imbalance

Page 4 “unnormal” = abnormal

Purpose of the study “This study aims to evaluate the efficiency of compensating reactions in children by the extent of thoracic kyphosis and lumbar lordosis…” my proposal: Our project is to study the influence of thoracic kyphosis and lumbar lordosis on compensating reactions in children?

Page 5 “body posture defect observed in clinical trial related to abnormalities in thoracic kyphosis and lumbar lordosis” Please give us the threshold above or below which the thoracic kyphosis and lumbar lordosis were considered abnormal

Page 6 Please provide the references of the “DIERS formetric 4D system”

Discussion

Page 10 “The inspirational aspect lies in the fact that body posture disorders make up one of the factors that can affect various systems of the human body [31], starting with pain accompanying postural dysfunctions [32-35], through pulmonary ventilation disorders [36], intestinal motility disorders to malocclusion [35]…” Those comments are controversial and stray away from the main subject of this work. It will induce some readers to question the seriousness of this work and might induce them to stop reading this article before apprehending the full extent of your work. My advice: omit this phrase…

Page 11 “while no relationship was found when assessing the figure using Spinal Maus [40]…” The average reader might not be aware about the signification of the “Spinal Maus” ? Please explain

Clinical Significance This chapter contains some general comments which don’t provide significant information. I would suggest repeating with simple words the result of your research: “Increased sagittal curves of the spine provoke increased movements of the center of gravity.” How this relates to clinical problems should be the subject of another study.

Conclusions You mention conclusion number 3 and 4: what are the other conclusions (number 1 and 2)?

Reviewer #2: The following revisions are recommended:

General: overall the manuscript presents interesting findings. However, it is recommended that the authors review the manuscript, and incorporate significant revisions. The major revisions that are required are:

1) Analysis: include more detail in the results, and also statistical analysis between groups.

2) Re-write the objectives to more directly reflect the analysis.

3) Re-vise/re-organize/re-write some sections in the introduction/discussion: This is important, as the strength of the data set is lost in it's current form, as the message is difficult to follow. (see below)

1. Abstract:

- please clarify 'The determinant used to define the ability to maintain balance are the center of pressure (CoP) movements, the establishing of which allows controlling the treatment process.' What do you mean by controlling the treatment process. Recommend separating this sentence into two parts, so that the 'treatment' implication is more clearly described.

Objective: please see above.

Methods:please consider being more specific in relation to the term postural disorder and spinal curvature. The context of the study is postural disorders, but the measurements obtained are specific to spinal curvature which are one component of a postural disorder. (see comments below for introduction)

- results: rather than using the term 'equilibrium reactions', suggest using the term COP displacement.

Conclusion:

conclusion 1: suggest reporting on what was observed statistically, I don't agree that the size of the curve alone resulted in large equilibrium reaction. Rather there is a positive association between kyphosis, lordosis and amplitude of COP displacement. This association is a potential reflection of the postural control's system response to the structural/mechanical destabilisation that is caused by increased kyphosis/lordosis.

conclusion 2: is this not included in conclusion 1? suggest revising this 2nd conclusion, and being more specific in relation to the strength of the association, and not just the linearity.

2. Introduction:

1st paragraph: this is an important paragraph to provide the overall context of the present study. It is suggested that the author's include a more specific description of what is involved with a postural disorder. For example, the sentence 'A faulty posture comprises a set of irregularities, defined as small, individual deviations from the correct posture, which can be corrected using a properly selected therapy'.... can be further described by including reference to the underlying skeletal structures that impact a correct alignment: (ie., lower limb alignment, pelvis position/orientation, spine/thoracic cage, scapular position etc.....' from this, then indicate that there is an interest in further understanding how a spinal alignment (thorcic, lumbar) is assessed and treated.

2nd paragraph: In consideration above, then be more specific in the first sentence, and introduce kyphosis and lordosis within the context of spinal alignment.

3rd paragraph: suggest revising this paragraph.

Sentence 1: 'The main element in controlling body posture is balance.' This is to general of a statement. It is recommended to be more specific in this paragraph to draw upon the link between postural alignment and the CNS driven mechanisms that the body utilises to control upright posture. The next two sentences are clearer, and more specific, thus it is suggested to start this paragraph with these two sentences, and introduce the idea that the CNS attempts to counteract the gravitational forces that are acting on the body by adjusting alignment of body segments (compensation), and secondly generating postural responses to control this alignment. A measure that reflects these postural responses is the centre of pressure, which is a reflection of the net torque generated about each body segment.

3. Purpose: see above comment, it is suggested to be more specific and state 2 objectives that better link with the statistical anlaysis. (ie., 1: compare between groups; 2: explore associations.

4. Methods:

- general comment: revise the decimal precision to be consistent (ie., to 1 decimal point).

- Inclusion/exclusion criteria: it is not clear what the threshold was for defining a postural defect, please define what is ECOG/WHO.

- how was movement of the COP quantified, and what was the actual measure? Was it standard deviation, root mean square, peak max, min, range. This has to be more clearly specified.

5. Results:

General: multiple correlations are performed. Did the authors adjust the p value for multiple comparisons?

Paragraph 5: what is the statistical comparison between the groups.

Discussion: It is suggested to re-organize the discussion with a specific focus on the following:

Current Paragraphs:

Paragraph 1: this interpretation should be moved later in the discussion, and move content/ideas to suggested paragraph 5 (see below)

Paragraph 2: this interpretation should be moved later in the discussion, and move content/ideas to suggested paragraph 5(see below)

Paragraph 3: integrate this into the suggested new paragraph 4 (see below).

Paragraph 4: include this in recommended paragraph 2 (see below)

Paragraph 5: include this in recommended paragraph 6 (see below). Mainly, this is a methodological discussion, which relates to the different techniques that are used to predict spinal curvature from the surface of the skin. Thus, the validity of the current technique should be discussed in relation to other techniques.

Paragraph 6: remove, or integrate into paragraph 5 below.

Paragraph 7: remove, or integrate into paragraph 5 below.

Paragraph 8: clinical significance: integrate into paragraph 5 below

New organization

Paragraph 1: Restate the primary objectives, and the main findings.

Paragraph 2 and 3: Compare the findings obtained in the present study with those of previous literature. This comparison is made in the current 3rd paragraph. It is recommended to move this up to 2nd paragraph, and expand upon this comparison. First, compare the findings to previous work with respect to 1:static posture; 2) walking. Also include specific comments related to 1) differences between the clinical population and the non-clinical population; 2) the strength of the association between kyphosis/lordosis and the COP displacement (in static, and dynamic).

Paragraph 4: Interpret your findings in relation to the population differences, and also the relationships between measures. This should specifically focus on the relationship between COP excursion and kyphosis/lordosis. Bring into consideration what the COP reflects from a CNS/musculoskeletal/torque perspective, and how structural alignment of the spine affects the mechanical stability of the body. For example, this reviewer suggests the following lines of thought/interpretation:

CNS compensates for structural alignment of the body segments. IN this case, there seems to be a relationship between COP and amplitude of kyphosis or lordosis. Is this increase in COP excursion a reflection of 1) mechanical detabilisation of the trunk caused by greater kyphosis/lordosis; 2) response of CNS to modulate the torques at the ankle,hips (during standing), and ankle, knee, hips during walking. This greater modulation of torque is then reflected through increased COP excursion in static/dynamic tasks.

Paragraph 5: interpretation within the broader context: what do these findings imply with respect to clinical assessment and management of patients.

Paragraph 6: limitations:

- consider methodological aspects that you brought into the discussion in paragraph 5(see above). this relates to the validity/reliability of the surface model to predict kyphosis/lordosis.

- consider the internal and external threats to validity.

Conclusion: revise conclusion.

- there is not a cause-effect shown in this study, rather there is an association that is demonstrated.

- see comments above for conclusion in the abstract.

**********

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Reviewer #1: No

Reviewer #2: No

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8 Jul 2020

Dear Editor and dear reviewers,

Thank you for your thorough assessment and valuable tips on the complex work, entitled: "Efficiency of Compensation Reactions in Children by the Extent of Thoracic Kyphosis and Lumbar Lordosis ".

We are of the opinion that all suggestions given are correct and their application will positively influence the comprehensibility of the text and clarity of the message. Therefore, during changes in the text, we tried to apply as closely as possible all the comments provided.

In the remainder of the letter I will try to answer in detail how the individual suggestions were responded, in the order in which they were submitted.

Answers to editor's comments:

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming.

Answer: The professional editing company took care of adjusting the text corrected by the reviewers, so the style of the corrected text sent is in line with PLOS ONE requirements.

2. Please include in your methods section a brief description of how participants were recruited.

Answer: The paragraph describing the recruitment process of participants was expanded.

3. Have manuscript read by native English speaker and use terms that have specific meaning in bio mechanical literature.

Answer: The language edition was commissioned to a professional company, which takes into account the specificity of the thematic area and the language requirements of PLOS ONE during the correction.

Answers to Reviewer #1

The authors present a manuscript about compensation reactions in children related to the amount of thoracic kyphosis and lumbar lordosis. While their manuscript contained interesting information, it could not be approved as submitted. If the authors choose to revise their manuscript, please address the following comments. As a general advice, please have a native English speaker revise your manuscript in order to enhance its readability.

Answer: Thank you to the reviewer for your time and valuable comments. We appreciate that he noticed the value of the sent manuscript. We apologize for any language errors. We commissioned the language correction of the corrected text to a professional company and we hope that the language of the corrected version does not raise any objections.

Page 2, Abstract: “The study group consists of 211 patients with postural disorders with respect to the degree of thoracic kyphosis and lumbar lordosis…” Please define what you mean by postural disorders: hyperkyphosis, hypokyphosis, hyperlordosis etc.?

Answer: The reviewer rightly noted that the term used was not precise. We have improved it both in the summary and in the part describing the material and the research method.

Page 2, Abstract: “Along with the increase in the angle of lordosis, an increase in indicators was observed: maximum movement of the CoP in the coronal plane, maximum movement of the CoP to the side (statically body to the left); and a reduction in the forward movement of the maximum CoP in the static test and the backward movement of the maximum CoP in the static test.” Please clarify.

Introduction I suggest that you group together the results of the different studies you mentioned. The Wenger and Frick study should be put apart as it points to the fundamental fact that sagittal spinal alignment is age dependent, which is important for your study

Answer: The results described in the summary have been described more clearly

Page 4 “The main element in controlling body posture is balance. Its typical parameters are constituted of measures of the body’s vertical orientation, obtained by balancing out the forces acting on different body segments [17]. This phenomenon is related to inertia forces and inertia characteristics of individual body segments [18].” This information is considered common knowledge. For the sake of concision, I suggest omitting these phrases.

Answer: As suggested, this part has been removed.

Page 4 “The determinant used to define the ability to maintain balance are the center of pressure (CoP) movements, the establishing of which allows controlling the treatment process…” What do you mean by “allows controlling the treatment process”? Please clarify

Answer: We apologize for too vague returns. We have expanded this sentence.

Page 4 “With the increase in postural dysfunction, an extension of the path covered by the centre of pressure in a given unit of time is observed, which means that compensating reactions are weakened [18].” Please be more explicit. As this is mean subject of your research project, this deserves more explanations

Answer: Thank you for your valuable attention. We changed this part. Page 4 “postural muscle disbalance” consider muscle imbalance

Page 4 “unnormal” = abnormal

Answer: Thank you for the suggestion. As a suggestion, both phrases have been replaced with those proposed throughout the text.

Purpose of the study “This study aims to evaluate the efficiency of compensating reactions in children by the extent of thoracic kyphosis and lumbar lordosis…” my proposal: Our project is to study the influence of thoracic kyphosis and lumbar lordosis on compensating reactions in children?

Answer: Thank you for the suggestion. Reviewer 2 also commented on this part, so taking both suggestions into account the sentence " This study evaluated the efficiency of compensatory reactions in children according to the extent of thoracic kyphosis and lumbar lordosis.".

Page 5 “body posture defect observed in clinical trial related to abnormalities in thoracic kyphosis and lumbar lordosis” Please give us the threshold above or below which the thoracic kyphosis and lumbar lordosis were considered abnormal.

Answer: The reference ranges for the size of thoracic kyphosis and lumbar lordosis were determined on the basis of the work suggested by the device manufacturer describing large screening tests. This information was included in the text.

Page 6 Please provide the references of the “DIERS formetric 4D system”

Answer: The paper was supplemented with suggested references for research on the DIERS system. Publications cited in the manuscript are numbered: 7,35,36,37,38,39,40 in the literature.

Page 10 “The inspirational aspect lies in the fact that body posture disorders make up one of the factors that can affect various systems of the human body [31], starting with pain accompanying postural dysfunctions [32-35], through pulmonary ventilation disorders [36], intestinal motility disorders to malocclusion [35]…” Those comments are controversial and stray away from the main subject of this work. It will induce some readers to question the seriousness of this work and might induce them to stop reading this article before apprehending the full extent of your work. My advice: omit this phrase…

Answer: As suggested, this part has been removed.

Page 11 “while no relationship was found when assessing the figure using Spinal Maus [40]…” The average reader might not be aware about the signification of the “Spinal Maus” ? Please explain.

Answer: This sentence indicates a difference in measurements that take place automatically and when manual participation of the researcher is needed. The text added the sentence: " This device is guided manually on the skin along the spine to assesses the curvatures of the vertebral column".

Clinical Significance This chapter contains some general comments which don’t provide significant information. I would suggest repeating with simple words the result of your research: “Increased sagittal curves of the spine provoke increased movements of the center of gravity.” How this relates to clinical problems should be the subject of another study.

Answer: This part of the text has been changed as suggested and linked to the discussion.

Conclusions You mention conclusion number 3 and 4: what are the other conclusions (number 1 and 2)?

Answer: The conclusions in the manuscript sent were incorrectly numbered. Currently, after the suggestions of Reviewer 2, this part of the manuscript looks as follows:

"1. We found an association between kyphosis and lordosis and the amplitude of CoP displacement, which may reflect the postural control system’s response to biomechanical destabilisation caused by changes in kyphosis and lordosis.

2. The lordosis angle correlation strength for displacement of COP in sagittal plane is 0.999 and adopts a linear value.".

Answers for Reviewer 2.

Thank you for the extremely detailed analysis of the manuscript submitted. We are grateful for the enormity of our time manuscript. In the process of improving the manuscript, we followed all comments, which resulted in a complete rebuilding of the manuscript. I will refer in turn to all suggested and introduced changes.

General: overall the manuscript presents interesting findings. However, it is recommended that the authors review the manuscript, and incorporate significant revisions. The major revisions that are required are:

1) Analysis: include more detail in the results, and also statistical analysis between groups.

2) Re-write the objectives to more directly reflect the analysis.

3) Re-vise/re-organize/re-write some sections in the introduction/discussion: This is important, as the strength of the data set is lost in it's current form, as the message is difficult to follow. (see below)

Answer:

Ad.1 A table was added comparing the results of the parameters obtained for both groups.

Ad2. According to the reviewer's recommendations, the following was used: „This study evaluated the efficiency of compensatory reactions in children according to the extent of thoracic kyphosis and lumbar lordosis.”.

Ad.3 In principle, the entire manuscript is reorganized to stick to the suggestions.

1. Abstract:

- please clarify 'The determinant used to define the ability to maintain balance are the center of pressure (CoP) movements, the establishing of which allows controlling the treatment process.' What do you mean by controlling the treatment process. Recommend separating this sentence into two parts, so that the 'treatment' implication is more clearly described.

Answer: The following explanatory note has been added.

Objective: please see above.

Answer: Changed as suggested by the reviewer to: " This study evaluated the efficiency of compensatory reactions in children according to the extent of thoracic kyphosis and lumbar lordosis.".

Methods:please consider being more specific in relation to the term postural disorder and spinal curvature. The context of the study is postural disorders, but the measurements obtained are specific to spinal curvature which are one component of a postural disorder. (see comments below for introduction)

Answer: The reference ranges for the size of thoracic kyphosis and lumbar lordosis were determined on the basis of the work suggested by the device manufacturer describing large screening tests. This information was included in the text

Results: rather than using the term 'equilibrium reactions', suggest using the term COP displacement.

Answer: Changed as directed

Conclusion:

conclusion 1: suggest reporting on what was observed statistically, I don't agree that the size of the curve alone resulted in large equilibrium reaction. Rather there is a positive association between kyphosis, lordosis and amplitude of COP displacement. This association is a potential reflection of the postural control's system response to the structural/mechanical destabilisation that is caused by increased kyphosis/lordosis.

conclusion 2: is this not included in conclusion 1? suggest revising this 2nd conclusion, and being more specific in relation to the strength of the association, and not just the linearity.

Answer: As suggested, the applications were reworded.

2.Introduction:

1st paragraph: this is an important paragraph to provide the overall context of the present study. It is suggested that the author's include a more specific description of what is involved with a postural disorder. For example, the sentence 'A faulty posture comprises a set of irregularities, defined as small, individual deviations from the correct posture, which can be corrected using a properly selected therapy'.... can be further described by including reference to the underlying skeletal structures that impact a correct alignment: (ie., lower limb alignment, pelvis position/orientation, spine/thoracic cage, scapular position etc.....' from this, then indicate that there is an interest in further understanding how a spinal alignment (thorcic, lumbar) is assessed and treated.

Answer: As suggested, the following information has been added.

2nd paragraph: In consideration above, then be more specific in the first sentence, and introduce kyphosis and lordosis within the context of spinal alignment.

Answer: As suggested, the following information has been added.

3rd paragraph: suggest revising this paragraph.

Sentence 1: 'The main element in controlling body posture is balance.' This is to general of a statement. It is recommended to be more specific in this paragraph to draw upon the link between postural alignment and the CNS driven mechanisms that the body utilises to control upright posture. The next two sentences are clearer, and more specific, thus it is suggested to start this paragraph with these two sentences, and introduce the idea that the CNS attempts to counteract the gravitational forces that are acting on the body by adjusting alignment of body segments (compensation), and secondly generating postural responses to control this alignment. A measure that reflects these postural responses is the centre of pressure, which is a reflection of the net torque generated about each body segment.

Answer: As suggested, this paragraph was rebuilt.

3. Purpose: see above comment, it is suggested to be more specific and state 2 objectives that better link with the statistical anlaysis. (ie., 1: compare between groups; 2: explore associations.

Answer: Taking into account your suggestion as well as the suggestion of the first reviewer, the purpose is described as follows: „This study evaluated the efficiency of compensatory reactions in children according to the extent of thoracic kyphosis and lumbar lordosis.”.

4. Methods:

- general comment: revise the decimal precision to be consistent (ie., to 1 decimal point).

- Inclusion/exclusion criteria: it is not clear what the threshold was for defining a postural defect, please define what is ECOG/WHO.

- how was movement of the COP quantified, and what was the actual measure? Was it standard deviation, root mean square, peak max, min, range. This has to be more clearly specified.

Answer: As suggested, this part has been corrected.

5. Results:

General: multiple correlations are performed. Did the authors adjust the p value for multiple comparisons?

Paragraph 5: what is the statistical comparison between the groups.

Answer: Tables were added comparing the size of parameters in the control and study groups. This is the current version of the manuscript table number 3. During statistical analysis, no protocol was used to adjust the p-value for many comparisons (such as the Dunn test). This is due to the fact that 6 correlations were generally tested in the study group. The same correlations were tested in the control group, and the parameters in the control group were compared. We realize that this can be understood as testing 12 correlations and then the use of p-value adjustment may be justified. However, low-strength correlations have only been signaled, and the work mainly focuses on very strong correlations that take linear values.

Discussion: It is suggested to re-organize the discussion with a specific focus on the following:

Current Paragraphs:

Paragraph 1: this interpretation should be moved later in the discussion, and move content/ideas to suggested paragraph 5 (see below)

Paragraph 2: this interpretation should be moved later in the discussion, and move content/ideas to suggested paragraph 5(see below)

Paragraph 3: integrate this into the suggested new paragraph 4 (see below).

Paragraph 4: include this in recommended paragraph 2 (see below)

Paragraph 5: include this in recommended paragraph 6 (see below). Mainly, this is a methodological discussion, which relates to the different techniques that are used to predict spinal curvature from the surface of the skin. Thus, the validity of the current technique should be discussed in relation to other techniques.

Paragraph 6: remove, or integrate into paragraph 5 below.

Paragraph 7: remove, or integrate into paragraph 5 below.

Paragraph 8: clinical significance: integrate into paragraph 5 below

New organization

Paragraph 1: Restate the primary objectives, and the main findings.

Paragraph 2 and 3: Compare the findings obtained in the present study with those of previous literature. This comparison is made in the current 3rd paragraph. It is recommended to move this up to 2nd paragraph, and expand upon this comparison. First, compare the findings to previous work with respect to 1:static posture; 2) walking. Also include specific comments related to 1) differences between the clinical population and the non-clinical population; 2) the strength of the association between kyphosis/lordosis and the COP displacement (in static, and dynamic).

Paragraph 4: Interpret your findings in relation to the population differences, and also the relationships between measures. This should specifically focus on the relationship between COP excursion and kyphosis/lordosis. Bring into consideration what the COP reflects from a CNS/musculoskeletal/torque perspective, and how structural alignment of the spine affects the mechanical stability of the body. For example, this reviewer suggests the following lines of thought/interpretation:

CNS compensates for structural alignment of the body segments. IN this case, there seems to be a relationship between COP and amplitude of kyphosis or lordosis. Is this increase in COP excursion a reflection of 1) mechanical detabilisation of the trunk caused by greater kyphosis/lordosis; 2) response of CNS to modulate the torques at the ankle,hips (during standing), and ankle, knee, hips during walking. This greater modulation of torque is then reflected through increased COP excursion in static/dynamic tasks.

Paragraph 5: interpretation within the broader context: what do these findings imply with respect to clinical assessment and management of patients.

Paragraph 6: limitations:

- consider methodological aspects that you brought into the discussion in paragraph 5(see above). this relates to the validity/reliability of the surface model to predict kyphosis/lordosis.

- consider the internal and external threats to validity.

Answer: The entire discussion was reorganized according to the detailed guidelines.

Conclusion: revise conclusion.

- there is not a cause-effect shown in this study, rather there is an association that is demonstrated.

- see comments above for conclusion in the abstract.

Answer: As suggested, the conclusions have been improved in both the summary and the main part. The conclusions now read as follows:

„1. We found an association between kyphosis and lordosis and the amplitude of CoP displacement, which may reflect the postural control system’s response to biomechanical destabilisation caused by changes in kyphosis and lordosis.

2. The lordosis angle correlation strength for displacement of COP in sagittal plane is 0.999 and adopts a linear value”.

Thank you for the opportunity to make changes in our manuscript. We have referred to all your comments and suggestions. We believe, that in current form, our manuscript meets the standards of PLOS ONE.

Sincerely,

the Authors.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

29 Sep 2020

PONE-D-20-08811R1

Evaluation of the Efficiency of Compensation Reactions in Children by the Extent of Thoracic Kyphosis and Lumbar Lordosis.

PLOS ONE

Dear Dr. Żurawski,

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Academic Editor

PLOS ONE

Additional Editor Comments (if provided):

Considerable improvement in response to first review, further explanations are requested

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Partly

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: No

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors undertook a comprehensive review of their article and addressed my comments in a satisfactory way. Their manuscript is now better structured and easier to read. It contains valuable information and therefore I recommend this manuscript for publication.

However, there still remains a minor critical comment. I would still suggest omitting the following phrases as they stray away from the main theme and contain controversial statements:

Page 16: Body posture disorders can affect various systems of the human body [52], from the

pain accompanying postural dysfunctions [53-56], through pulmonary ventilation disorders

[57] and intestinal motility disorders, to malocclusion [54]. The relationship between spinal

curvature and balance disorders has been confirmed in numerous studies [29, 30, 54, 58, 59].

Page 17: Most authors use the Romberg test to assess body balance. However, the ability to use vision to improve motor skills in children during development is only emerging and both values can be aligned closely [61].

Reviewer #2: Thank you for revising the manuscript and incorporating the suggested revisions. The following revisions are further recommended:

1. Title: Revise the title, as it is not clear. It is suggested that the revised title more closely reflect the analysis. For example'Evaluation of the association between postural control and sagittal curvature of the spine'.

2. Abstract: revise the text:

‘worse’ with ‘smaller’

‘coronary’ with coronal

3. Introduction:

1. Revise: ‘ The physiological values…’ to ‘ The amplitude of ‘

2. Combine 2nd and 3rd paragraphs. ‘ Body posture disorders…..’ with the next paragraph starting with ‘The literature’….

3. It is important to better distinguish the displacement of the COP under both feet during upright quiet standing, with that of the COP displacement under 1 foot during walking. Although this is described in paragraph 4, it is recommended to revise this paragraph to be more clear.

For example:

1. COP displacement during quiet standing reflects the net contribution of the CNS to control the movement of the Centre of Mass. Where the horizontal acceleration of the COM is proportional to the difference between the COP-COM. (Winter et al., ) during quiet stance it is the hip abductors/adductors that generate torque to control ML movement, and it is the ankle plantar flexors/dorsiflexors that control A/P movement

2. During walking, the movement of the COP moves from posterior to anterior under the foot, and ML. Although the above concept holds true (ie., COP reflects net output of CNS control), how it does this is more complex given the multiple degrees of freedom, and joint motions.

In light of this, it is suggested to revise this paragraph to further strengthen the rational as to why the investigators chose the COP as the primary outcome variable to measure standing stability, and also stability during walking.

Methods:

1. Clarify for how long the centre of pressure was recorded. Was it 3 seconds, the same as the rastersterography, or a different length of time.

2. Research methodology: It is recommended to define each parameter that was included in the analysis. For example, Table 2 contains variables such as ‘Maximum displacement of centre of gravity in coronal plane in pressure gait’. This is very difficult to understand what this variable is in the table. Therefore, each measure described in Table 2 should be defined in the methods.

a. Angle of Thoracic Kyphsosi, Angle of lumbar Lordosis

b. Displacement of centre of gravity in coronal/sagittal planes in pressure gait

c. Maximum displacement of centre of pressure to side [mm].

Results:

1. Table 2, 3 and 4 are redundant. It is recommended to include primarily Table 4.

2. Revise the variable names to be consistent with the definition in the methods, and also how COP displacement is referred to throughout the manuscript. For example:

a. ‘Maximum displacement of center of gravity in coronal plane in pressure gait’. Suggest revising to ‘Maximum displacement of centre of pressure in coronal plane during gait’.

b. ‘Maximum displacement of center of gravity in sagittal plane in pressure gait’. Suggest revising to ‘Maximum displacement of centre of pressure in sagittal plane during gait’.

Discussion

- It is suggested to use consistent terminology with respect to COP displacement. Rather than using terms such as ‘swing’, ‘deflections’, it is suggested to consistently the word ‘displacement’ throughout the text.

- Revise – Nalut, and Naulut to correct reference ‘ Nault’.

- Revise statement ‘ Rougier et al., explains this phenomenon by the fact that swing during walking is changed by the forces tramsitted to the feet and are partly reduced by compensations occurring in the hip and ankle’. It is not clear what ‘swing’ means. Is this the swing phase of gait?

**********

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Reviewer #1: Yes: Reinhard Zeller

Reviewer #2: No

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3 Oct 2020

Dear Editor and dear Reviewers,

Thank you for your thorough assessment and valuable tips on the complex work, entitled: "Efficiency of Compensation Reactions in Children by the Extent of Thoracic Kyphosis and Lumbar Lordosis ".

We are of the opinion that all suggestions given are correct and their application will positively influence the comprehensibility of the text and clarity of the message. Therefore, during changes in the text, we tried to apply as closely as possible all the comments provided.

In the remainder of the letter I will try to answer in detail how the individual suggestions were responded, in the order in which they were submitted.

Answers to Reviewer #1

The authors undertook a comprehensive review of their article and addressed my comments in a satisfactory way. Their manuscript is now better structured and easier to read. It contains valuable information and therefore I recommend this manuscript for publication.

However, there still remains a minor critical comment. I would still suggest omitting the following phrases as they stray away from the main theme and contain controversial statements:

Page 16: Body posture disorders can affect various systems of the human body [52], from the

pain accompanying postural dysfunctions [53-56], through pulmonary ventilation disorders

[57] and intestinal motility disorders, to malocclusion [54]. The relationship between spinal

curvature and balance disorders has been confirmed in numerous studies [29, 30, 54, 58, 59].

Page 17: Most authors use the Romberg test to assess body balance. However, the ability to use vision to improve motor skills in children during development is only emerging and both values can be aligned closely [61].

Answer: Thank you for this suggestion. As suggested, this part has been removed.

Answers for Reviewer 2.

Thank you for revising the manuscript and incorporating the suggested revisions. The following revisions are further recommended:

1. Title: Revise the title, as it is not clear. It is suggested that the revised title more closely reflect the analysis. For example' Evaluation of the association between postural control and sagittal curvature of the spine '.

Answer: Thanks for the suggestion. The title has been changed as proposed.

2. Abstract: revise the text:

‘worse’ with ‘smaller’

‘coronary’ with coronal

Answer: Thanks for the suggestion. Words changed: 'worse' with 'greater', 'coronary' with coronal '. Worse in this case meant a longer diplacement in all directions, so instead of 'worse' we put 'greater'.

3. Introduction:

1. Revise: ‘ The physiological values…’ to ‘ The amplitude of ‘

Thanks for the suggestion. The text has been changed as proposed.

2. Combine 2nd and 3rd paragraphs. ‘ Body posture disorders…..’ with the next paragraph starting with ‘The literature’….

Answer: Thanks for the suggestion. The text has been changed as proposed.

3. It is important to better distinguish the displacement of the COP under both feet during upright quiet standing, with that of the COP displacement under 1 foot during walking. Although this is described in paragraph 4, it is recommended to revise this paragraph to be more clear.

For example:

1. COP displacement during quiet standing reflects the net contribution of the CNS to control the movement of the Centre of Mass. Where the horizontal acceleration of the COM is proportional to the difference between the COP-COM. (Winter et al., ) during quiet stance it is the hip abductors/adductors that generate torque to control ML movement, and it is the ankle plantar flexors/dorsiflexors that control A/P movement

2. During walking, the movement of the COP moves from posterior to anterior under the foot, and ML. Although the above concept holds true (ie., COP reflects net output of CNS control), how it does this is more complex given the multiple degrees of freedom, and joint motions.

In light of this, it is suggested to revise this paragraph to further strengthen the rational as to why the investigators chose the COP as the primary outcome variable to measure standing stability, and also stability during walking.

Answer: Thank you for this suggestion. Section 4 has been supplemented with the proposed content.

Methods:

1. Clarify for how long the centre of pressure was recorded. Was it 3 seconds, the same as the rastersterography, or a different length of time.

Answer: Thank you for this suggestion. the text was supplemented with the sentence 'The measurement was carried out for 3 seconds at the same time as the shape of spine was assessed with the DIERS formetric system.'

2. Research methodology: It is recommended to define each parameter that was included in the analysis. For example, Table 2 contains variables such as ‘Maximum displacement of centre of gravity in coronal plane in pressure gait’. This is very difficult to understand what this variable is in the table. Therefore, each measure described in Table 2 should be defined in the methods.

a. Angle of Thoracic Kyphsosi, Angle of lumbar Lordosis

b. Displacement of centre of gravity in coronal/sagittal planes in pressure gait

c. Maximum displacement of centre of pressure to side [mm].

Answer: Thank you for this valuable suggestion. The parameters were described and their nomenclature arranged throughout the manuscript.

Results:

1. Table 2, 3 and 4 are redundant. It is recommended to include primarily Table 4.

Answer: Thank you for the suggestion. Tables removed as recommended.

2. Revise the variable names to be consistent with the definition in the methods, and also how COP displacement is referred to throughout the manuscript. For example:

a. ‘Maximum displacement of center of gravity in coronal plane in pressure gait’. Suggest revising to ‘Maximum displacement of centre of pressure in coronal plane during gait’.

b. ‘Maximum displacement of center of gravity in sagittal plane in pressure gait’. Suggest revising to ‘Maximum displacement of centre of pressure in sagittal plane during gait’.

Answer: Thank you for these suggestions. The text was corrected as recommended.

Discussion

- It is suggested to use consistent terminology with respect to COP displacement. Rather than using terms such as ‘swing’, ‘deflections’, it is suggested to consistently the word ‘displacement’ throughout the text.

Thank you for these suggestions. The text was corrected as recommended.

- Revise – Nalut, and Naulut to correct reference ‘ Nault’.

Answer: Thank you for these suggestions. The text was corrected as recommended.

- Revise statement ‘ Rougier et al., explains this phenomenon by the fact that swing during walking is changed by the forces tramsitted to the feet and are partly reduced by compensations occurring in the hip and ankle’. It is not clear what ‘swing’ means. Is this the swing phase of gait?

Answer: Thank you for these suggestions. The text was corrected as recommended. The statement 'Rougier et al., Explains this phenomenon by the fact that swing during walking is changed by the forces tramsitted to the feet and are partly reduced by compensations occurring in the hip and ankle ’changed to' Rougier et al. this phenomenon by the fact that CoG displacement during walking is changed by the forces transmitted to explain the feet and are partly reduced by compensations occurring in the hip and ankle '.

Thank you for the opportunity to make changes in our manuscript. We have referred to all your comments and suggestions. We believe, that in current form, our manuscript meets the standards of PLOS ONE.

Sincerely,

the Authors.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

12 Oct 2020

Evaluation of the association between postural control and sagittal curvature of the spine

PONE-D-20-08811R2

Dear Dr. Żurawski,

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James G. Wright

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

14 Oct 2020

PONE-D-20-08811R2

Evaluation of the association between postural control and sagittal curvature of the spine

Dear Dr. Żurawski:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

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on behalf of

Professor James G. Wright

Academic Editor

PLOS ONE