This article was downloaded by: [University Of Pittsburgh] On: 25 March 2015, At: 15:21 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Motor Behavior Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/vjmb20
Measuring Postural Sway in Sitting: A New Segmental Approach ae
b
b
b
c
Derek John Curtis , Lisbeth Hansen , Malene Luun , Ragnhild Løberg , Marjorie Woollacott , d
e
b
e
Sandy Saavedra , Stig Sonne-Holm , Steen Berggreen & Jesper Bencke a
Department of Physical and Occupational Therapy, Hvidovre University Hospital, Denmark
b
Metropolitan University College, Faculty of Healthcare and Rehabilitation, Copenhagen, Denmark c
Institute of Neuroscience, University of Oregon, Eugene
d
Department of Rehabilitation Sciences College of Education, Nursing & Health Professions, University of Hartford, Connecticut
Click for updates
e
Gait Analysis Laboratory, Department of Orthopedic Surgery, Hvidovre University Hospital, Denmark Published online: 02 Mar 2015.
To cite this article: Derek John Curtis, Lisbeth Hansen, Malene Luun, Ragnhild Løberg, Marjorie Woollacott, Sandy Saavedra, Stig Sonne-Holm, Steen Berggreen & Jesper Bencke (2015): Measuring Postural Sway in Sitting: A New Segmental Approach, Journal of Motor Behavior, DOI: 10.1080/00222895.2014.1003782 To link to this article: http://dx.doi.org/10.1080/00222895.2014.1003782
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Journal of Motor Behavior, Vol. 0, No. 0, 2015 Copyright © Taylor & Francis Group, LLC
RESEARCH ARTICLE
Measuring Postural Sway in Sitting: A New Segmental Approach Derek John Curtis1,5, Lisbeth Hansen2, Malene Luun2, Ragnhild Løberg2, Marjorie Woollacott3, Sandy Saavedra4, Stig Sonne-Holm5, Steen Berggreen2, Jesper Bencke5 Department of Physical and Occupational Therapy, Hvidovre University Hospital, Denmark. 2Metropolitan University College, Faculty of Healthcare and Rehabilitation, Copenhagen, Denmark. 3Institute of Neuroscience, University of Oregon, Eugene. 4 Department of Rehabilitation Sciences College of Education, Nursing & Health Professions, University of Hartford, Connecticut. 5Gait Analysis Laboratory, Department of Orthopedic Surgery, Hvidovre University Hospital, Denmark.
Downloaded by [University Of Pittsburgh] at 15:21 25 March 2015
1
ABSTRACT. Global measures of trunk sway are traditionally used even though the trunk comprises a multiple number of segments. The authors’ aim was to measure the seated sway of typically developing children using a multisegment approach. Twenty typically developing children divided into 2 groups, older and younger than 10 years old, participated in this study. The children sat unsupported for 30 s while their posture and sway were quantified using stereophotogrammetry. The tendency in both age groups was to sit with a backward tilted pelvis and a kyphotic trunk. The sitting position was most varied in the younger group. Marker sway amplitude and velocity in sitting were age dependent, with reduced sway amplitude and velocity with increased age for all segments. Anteroposterior intersegmental angular sway was not age dependent. The difference in marker sway in the anteroposterior direction for the younger group appeared to result from an equally stable trunk supported on a less stable pelvis. Mediolateral marker sway and intersegmental angular sway showed a clearer age dependency. Trunk postural control does not appear to differ between children older and younger than 10 years old, but sagittal plane pelvic stability can explain the increased sway reported in younger children. Keywords: kinematics
postural
sway,
children,
adolescents,
developing children. Static postural control has also been shown to be related to functional abilities in children with cerebral palsy (CP; Pavao, Nunes, Santos, & Rocha, 2014). While the concept of disparate postural control abilities in the different segments of the trunk in typically developing infants is widely accepted, varying degrees of control in different trunk segments in children and adolescents with neuromotor disability is less widely described. A recent review of clinical tools assessing balance in children and adults with cerebral palsy (Saether, Helbostad, Riphagen, & Vik, 2013) identified four tools that measure trunk control. Three of these four clinical tools, the Trunk Control Measurement Scale (Heyrman et al., 2011), the Sitting Assessment for Children with Neuromotor Dysfunction (Reid, 1995), and the Trunk Impairment Scale (Saether et al., 2013) assess the trunk as a single segment and measure trunk control through functional ability. The fourth clinical tool that this study identifies is the Segmental Assessment of Trunk Control (SATCo; Butler, 1998). The SATCo is used to assess trunk control on a segmental basis and to determine the trunk level at which static, active and reactive trunk control are absent in a top-down manner. The purpose of this multisegment approach is to determine the trunk level at which specific therapy is to be aimed. Specific training at this trunk level may produce improved trunk control and increased motor function, as the segmental level of trunk postural control has been shown to be closely related to gross motor function in children with cerebral palsy (Curtis et al., 2014). We reasoned that this segmental approach, if used in sway measurement of steady-state sitting could be useful in identifying specific segmental postural control deficits in children with reduced trunk control in steady-state sitting. Previously, steady-state seated postural control has been quantified in research using various measures of head sway with kinematic markers placed on the head and tracked over time to quantify stability in trunk and head control (Brogren, Forssberg, & Hadders-Algra, 2001; Heyrman et al., 2013; Hedberg, Forssberg, & Hadders-Algra, 2004; Rachwani et al., 2013; Saavedra, van Donkelaar, & Woollacott, 2012). Other studies have used kinetics to quantify
sitting,
F
or children with a motor disability, the ability to stand and walk can be challenging making sitting skills an important focus for improving their function and quality of life. Independent sitting is a significant motor milestone and is the basis of many activities of daily living. Despite the relatively large base of support in comparison with standing, independent sitting requires adequate postural control of the trunk and head to keep the body’s centre of mass over the base of support. This postural control is not present at birth, but is generally considered to develop in a cephalocaudal sequence. During this development, postural control of the trunk is different for different trunk segments. Progression in trunk control is mirrored in an infant’s functional development. Infants can hold up their head and upper trunk typically at an age of 4–5.5 months, sit independently briefly or prop-sit at 5–6.5 months and sit independently at an age of 6–8 months (Harbourne & Stergiou, 2003). The importance of trunk control in activities such as reaching has been investigated in a number of studies (de Graaf-Peters, Bakker, van Eykern, Otten, & Hadders-Algra, 2007; Hopkins & Ronnqvist, 2002; Rachwani et al., 2013; Samsom & de Groot, 2000). Postural control appears to be an important determinant of motor function in typically
Correspondence address: Derek John Curtis, Department of Physical and Occupational Therapy, Hvidovre University Hospital, Kettegard All e 30 DK-2650, Hvidovre, Denmark. e-mail: [email protected] 1
Downloaded by [University Of Pittsburgh] at 15:21 25 March 2015
D. J. Curtis et al.
postural sway in sitting either using instrumented benches or directly sitting the child on a force plate and quantifying sway through parameters related to change in centre of pressure over time (Brogren et al., 2001; Ju, Hwang, & Cherng, 2012; Kyvelidou, Harbourne, & Stergiou, 2010; Kyvelidou, Harbourne, Stuberg, Sun, & Stergiou, 2009). These established sway measures quantify either the ability of the individual to stabilize their head or trunk in space or their ability to stabilize their centre of mass over their base of support. This information is extremely informative of the individual’s global postural control function, and can give important information concerning the subject’s ability to control their postural alignment and stability. These measurement methods do not, however, give any specific information to assist the physician or therapist to plan a targeted therapy. The trunk and head are in reality a multiple number of spinal segments, the alignment and movement of which determine the sway measurement. Increased trunk and head sway or center of pressure excursions do not help in the identification of the specific segments that have reduced postural control. Similarly, subjects could potentially achieve a normal sway measurement by using strategies to reduce the degrees of freedom in the intervertebral joints for example by adopting a lumbar lordotic or kyphotic posture when in fact they have reduced postural control in these segments. There are at the present time no studies that report the unsupported static seated posture of typically developing children on a segmental level in the spine. We reasoned that a description of the normal values for segmental sway would be of value as a reference when measuring sway in unsupported sitting in children with neuromotor disability by providing information concerning the normal segmental distribution of sway in the trunk and head. Variations from this pattern could help in localizing reduced segmental postural control. The aim of this study, therefore, was to measure both posture and segmental trunk and head sway in unsupported steady state sitting of typically developing children. Method We recruited 20 typically developing children through posters and announcements on the mailing system at a college educating health personnel in Copenhagen. Eleven children under 10 years old, mean (range) age 6.6 (4–9) years, height 123 (105–141) cm, weight 22.7 (16–30.4) kg, five girls and six boys; and nine children 10 years old and over, mean (range) age 13.2 (10–16) years, height 132 (132–178) cm, weight 46.3 (27.4–59.9) kg, three girls and six boys, were included in the study. The included children were tested at a movement laboratory using a Vicon 612 eight camera system (Vicon Motion Systems Ltd., Oxford, England). Procedures followed were in accordance with the Helsinki Declaration of 1975, as revised in 2013. The 2
procedures followed protocol and the study was approved by the local responsible ethics committee. The marker protocol for the trunk was based upon the spinal levels described in SATCo (Butler, Saavedra, Sofranac, Jarvis, & Woollacott, 2010) The SATCo test defines the following trunk segments: cervical, upper thoracic, midthoracic, lower thoracic, upper lumbar, lower lumbar, and pelvis. The boundaries between the trunk segments described in the SATCo test are the shoulder girdle, the axillae, inferior scapula, lower ribs, below ribs, and the top of the sacrum. The location of the markers was agreed at a Skype meeting with Dr. Butler (December 16, 2013). The markers were attached to the following bony landmarks to define the boundaries between the trunk segments: cervical-upper thoracic C7, upper thoracic-lower thoracic T3, lower thoracic-upper lumbar T11, upper lumbar-lower lumbar L3, and lower lumbar-pelvis midpoint between spina iliaca posterior superior (Figure 1a). The Frankfurt plane (see Figure 1b) was used as the transverse plane of the head coordinate system. The sagittal axis was defined as a line from the midpoint of a line joining the tragi auricularis on both sides of the head and the midpoint of a line joining the inferior margins of the orbits. The transverse axis was defined as a line passing through the two tragi auricularis. The vertical axis was defined as an axis orthogonal to the sagittal and transverse axes. To measure head movements using this coordinate system, markers were placed on the tragi auricularis (EAR) bilaterally and the middle of the forehead (FOHD) with a virtual marker aligned with the inferior margin of the left orbit (IMLO). The pelvis was defined using the Helen Hayes protocol with markers on the two spina iliaca anterior superior (ASIS) together with the sacrum marker (SACR). The sagittal axis of the pelvis was defined as a line from the sacrum marker through the midpoint of a line joining the two ASIS markers and the transverse axis as a line through the two ASIS markers. The vertical axis was defined as an axis orthogonal to the sagittal and transverse axes. Following attachment of the markers, a calibration frame was recorded to allow calculation of the positions of the virtual marker IMLO in the dynamic trials. Children were seated on a height-adjustable stool without a back support. The stool’s height was adjusted so that their feet were flat on the floor, their thighs were parallel to the floor and their lower leg vertical. A small screen was placed at a height corresponding to their eye height if they sat in an upright sitting posture. The screen was positioned at each child’s midline 1 m in front of the bench. The children were instructed to watch a film on the screen with their hands hanging by their sides and while they watched the film their kinematics were captured. A film was used to focus the child’s attention as the intended clinical use of this test is with children with cognitive deficits who would possibly have difficulties in focusing their attention on a fixed point or following instructions. The screen was very small and the distance sufficient that the area of focus was Journal of Motor Behavior
Downloaded by [University Of Pittsburgh] at 15:21 25 March 2015
Measuring Postural Sway in Sitting
FIGURE 1. (a) Position of the markers on the head, trunk and pelvis and (b) the Frankfurt plane.
small. All children saw the same film, which was chosen to capture their attention but not change their arousal level. It was hoped that this method of focusing the child’s attention would minimize the effect of the visual and audio stimulation on the postural sway of the child. The children were instructed to sit still and watch the film but received no instruction to sit as still as possible as we did not want to measure a stiff sitting posture with muscular cocontraction but a natural relaxed quiet sitting posture. The children did not receive any postural instructions either, for example, “sit as tall as possible.” The first continuous 30-s period of the trial in which all of the markers were visible and the child did not make any voluntary postural movements was selected for the data analysis. A period of 30 s was adopted as this has been reported to be a reasonable duration with respect to reliability and validity for sway measures (Le & Riach, 1996). Two methods of quantifying sway were used and these are illustrated in Figure 2. The first method used the more established sway measures, in which the amplitude and mean velocity of the markers in the anteroposterior (AP) and mediolateral (ML) directions in the transverse plane were quantified (Figure 2b). The AP and ML amplitudes for each marker were calculated as the standard deviation of the marker in the AP and ML directions from its mean position in the global transverse plane. The mean AP and ML velocities were calculated as the total distance travelled by the marker in the AP and ML directions of the 2015, Vol. 0, No. 0
global transverse plane, divided by the length of the trial in seconds. The second method involved the calculation of intersegmental angles between sections of the spinal column (trunk segments). The orientation of a trunk segment was defined from the positions of the markers on the boundary of the segment. A line through these two markers was assumed to be the vertical axis of the segment. The vertical axis of the lower thoracic segment is, for example, defined as being a line through the T11 and the T7 markers and the vertical axis for the upper thoracic segment is defined as being a line through the T7 and the T3 markers. Relative angles between the vertical axes of adjacent segments (intersegmental angles) were calculated in the frontal and sagittal planes of the global coordinate system. The approach to the calculation of the sagittal plane upper thoracic-lower thoracic intersegmental angle is illustrated in Figure 2a and the calculation of sagittal and frontal plane intersegmental angles are shown in Figure 3. Intersegmental angles for curves to the right in the frontal plane and kyphosis in the sagittal plane were assigned a negative value. Angles for the pelvis and head were calculated as global angles. Positive values were assigned to tilting the head backwards (pitch) and tipping the right ear to the right shoulder (roll). For the pelvis, positive values were assigned to anterior tilt in the sagittal plane and tilting of the pelvis to the right in the frontal plane. The mean intersegmental angles were calculated as an expression of the posture adopted by the child and the standard deviation of these angles calculated to 3
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D. J. Curtis et al.
FIGURE 2. Calculation of sway parameters: (a) representative intersegmental angle and (b) representative marker sway.
reflect the intersegmental angular sway. Calculations were performed using inherent models (Plug-in-Gait, Vicon Motion Systems Ltd.), or a custom-written software model (BodyBuilder, Vicon Motion Systems Ltd.). Kolmogorov-Smirnov tests were used to check for normal distribution. Data were analyzed in two groups, children under and over 10 years old, as age-related aspects of
sway have been reported in children in other studies (Hong, James, & Newell, 2008; Monteiro Ferronato & Barela, 2011; Riach & Hayes, 1987). Independent samples t tests were used to determine differences between the two age groups for data with normal distribution. For intersegmental angular sway a total of 12 t tests were used and for marker amplitude and velocity measures of sway a total of 14 t
FIGURE 3. Worked example of the calculation of a representative intersegmental angle from marker coordinates (upper thoraciclower thoracic).
4
Journal of Motor Behavior
Measuring Postural Sway in Sitting
the older group and increased in a consistent bottom-up manner for both groups with marker amplitude increasing from 1.21 mm (SACR) to 7.38mm (midhead) in the younger group and from 0.27 (SACR) to 2.72 mm (midhead) in the older group. These differences were significant for the SACR, T7, T3, and C7 markers (p D .016, .011, .018, and .023, respectively) and highly significant for the L3, T11, and midhead markers (p D .009, .005, and .009, respectively). Mean ML direction marker velocities were approximately four times larger for the younger group in comparison with the older group and increased in a consistent bottom-up manner for both groups with marker velocity increasing from 0.55 (SACR) to 5.18 mm/s (midhead) in the younger group and from 0.11 (SACR) to 1.69 mm/s (midhead) in the older group. These differences were significant for the L3, T11, and T7 markers (p D .015, .012, and .010, respectively) and highly significant for the T3, C7, and midhead markers (p D .007, .005, and .003, respectively). We performed post hoc two-way analyses of variance using marker and age group as independent variables to investigate whether the increase cranially in AP and ML marker sway amplitude and velocity for both age groups were significant. The analyses showed a significant main effect of marker level on AP marker sway, F(6, 126) D 8.335, p < .001; on ML marker sway, F(6, 126) D 6.854, p < .001; on AP marker velocity, F(6, 126) D 6.590, p < .001; and ML marker velocity, F(6, 126) D 8.626, p < .001. Sitting position and intersegmental angular sway are shown in Table 2.
tests. Statistical analysis was performed using IBM SPSS Statistics Version 19. A p value of
Journal of Motor Behavior Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/vjmb20
Measuring Postural Sway in Sitting: A New Segmental Approach ae
b
b
b
c
Derek John Curtis , Lisbeth Hansen , Malene Luun , Ragnhild Løberg , Marjorie Woollacott , d
e
b
e
Sandy Saavedra , Stig Sonne-Holm , Steen Berggreen & Jesper Bencke a
Department of Physical and Occupational Therapy, Hvidovre University Hospital, Denmark
b
Metropolitan University College, Faculty of Healthcare and Rehabilitation, Copenhagen, Denmark c
Institute of Neuroscience, University of Oregon, Eugene
d
Department of Rehabilitation Sciences College of Education, Nursing & Health Professions, University of Hartford, Connecticut
Click for updates
e
Gait Analysis Laboratory, Department of Orthopedic Surgery, Hvidovre University Hospital, Denmark Published online: 02 Mar 2015.
To cite this article: Derek John Curtis, Lisbeth Hansen, Malene Luun, Ragnhild Løberg, Marjorie Woollacott, Sandy Saavedra, Stig Sonne-Holm, Steen Berggreen & Jesper Bencke (2015): Measuring Postural Sway in Sitting: A New Segmental Approach, Journal of Motor Behavior, DOI: 10.1080/00222895.2014.1003782 To link to this article: http://dx.doi.org/10.1080/00222895.2014.1003782
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Journal of Motor Behavior, Vol. 0, No. 0, 2015 Copyright © Taylor & Francis Group, LLC
RESEARCH ARTICLE
Measuring Postural Sway in Sitting: A New Segmental Approach Derek John Curtis1,5, Lisbeth Hansen2, Malene Luun2, Ragnhild Løberg2, Marjorie Woollacott3, Sandy Saavedra4, Stig Sonne-Holm5, Steen Berggreen2, Jesper Bencke5 Department of Physical and Occupational Therapy, Hvidovre University Hospital, Denmark. 2Metropolitan University College, Faculty of Healthcare and Rehabilitation, Copenhagen, Denmark. 3Institute of Neuroscience, University of Oregon, Eugene. 4 Department of Rehabilitation Sciences College of Education, Nursing & Health Professions, University of Hartford, Connecticut. 5Gait Analysis Laboratory, Department of Orthopedic Surgery, Hvidovre University Hospital, Denmark.
Downloaded by [University Of Pittsburgh] at 15:21 25 March 2015
1
ABSTRACT. Global measures of trunk sway are traditionally used even though the trunk comprises a multiple number of segments. The authors’ aim was to measure the seated sway of typically developing children using a multisegment approach. Twenty typically developing children divided into 2 groups, older and younger than 10 years old, participated in this study. The children sat unsupported for 30 s while their posture and sway were quantified using stereophotogrammetry. The tendency in both age groups was to sit with a backward tilted pelvis and a kyphotic trunk. The sitting position was most varied in the younger group. Marker sway amplitude and velocity in sitting were age dependent, with reduced sway amplitude and velocity with increased age for all segments. Anteroposterior intersegmental angular sway was not age dependent. The difference in marker sway in the anteroposterior direction for the younger group appeared to result from an equally stable trunk supported on a less stable pelvis. Mediolateral marker sway and intersegmental angular sway showed a clearer age dependency. Trunk postural control does not appear to differ between children older and younger than 10 years old, but sagittal plane pelvic stability can explain the increased sway reported in younger children. Keywords: kinematics
postural
sway,
children,
adolescents,
developing children. Static postural control has also been shown to be related to functional abilities in children with cerebral palsy (CP; Pavao, Nunes, Santos, & Rocha, 2014). While the concept of disparate postural control abilities in the different segments of the trunk in typically developing infants is widely accepted, varying degrees of control in different trunk segments in children and adolescents with neuromotor disability is less widely described. A recent review of clinical tools assessing balance in children and adults with cerebral palsy (Saether, Helbostad, Riphagen, & Vik, 2013) identified four tools that measure trunk control. Three of these four clinical tools, the Trunk Control Measurement Scale (Heyrman et al., 2011), the Sitting Assessment for Children with Neuromotor Dysfunction (Reid, 1995), and the Trunk Impairment Scale (Saether et al., 2013) assess the trunk as a single segment and measure trunk control through functional ability. The fourth clinical tool that this study identifies is the Segmental Assessment of Trunk Control (SATCo; Butler, 1998). The SATCo is used to assess trunk control on a segmental basis and to determine the trunk level at which static, active and reactive trunk control are absent in a top-down manner. The purpose of this multisegment approach is to determine the trunk level at which specific therapy is to be aimed. Specific training at this trunk level may produce improved trunk control and increased motor function, as the segmental level of trunk postural control has been shown to be closely related to gross motor function in children with cerebral palsy (Curtis et al., 2014). We reasoned that this segmental approach, if used in sway measurement of steady-state sitting could be useful in identifying specific segmental postural control deficits in children with reduced trunk control in steady-state sitting. Previously, steady-state seated postural control has been quantified in research using various measures of head sway with kinematic markers placed on the head and tracked over time to quantify stability in trunk and head control (Brogren, Forssberg, & Hadders-Algra, 2001; Heyrman et al., 2013; Hedberg, Forssberg, & Hadders-Algra, 2004; Rachwani et al., 2013; Saavedra, van Donkelaar, & Woollacott, 2012). Other studies have used kinetics to quantify
sitting,
F
or children with a motor disability, the ability to stand and walk can be challenging making sitting skills an important focus for improving their function and quality of life. Independent sitting is a significant motor milestone and is the basis of many activities of daily living. Despite the relatively large base of support in comparison with standing, independent sitting requires adequate postural control of the trunk and head to keep the body’s centre of mass over the base of support. This postural control is not present at birth, but is generally considered to develop in a cephalocaudal sequence. During this development, postural control of the trunk is different for different trunk segments. Progression in trunk control is mirrored in an infant’s functional development. Infants can hold up their head and upper trunk typically at an age of 4–5.5 months, sit independently briefly or prop-sit at 5–6.5 months and sit independently at an age of 6–8 months (Harbourne & Stergiou, 2003). The importance of trunk control in activities such as reaching has been investigated in a number of studies (de Graaf-Peters, Bakker, van Eykern, Otten, & Hadders-Algra, 2007; Hopkins & Ronnqvist, 2002; Rachwani et al., 2013; Samsom & de Groot, 2000). Postural control appears to be an important determinant of motor function in typically
Correspondence address: Derek John Curtis, Department of Physical and Occupational Therapy, Hvidovre University Hospital, Kettegard All e 30 DK-2650, Hvidovre, Denmark. e-mail: [email protected] 1
Downloaded by [University Of Pittsburgh] at 15:21 25 March 2015
D. J. Curtis et al.
postural sway in sitting either using instrumented benches or directly sitting the child on a force plate and quantifying sway through parameters related to change in centre of pressure over time (Brogren et al., 2001; Ju, Hwang, & Cherng, 2012; Kyvelidou, Harbourne, & Stergiou, 2010; Kyvelidou, Harbourne, Stuberg, Sun, & Stergiou, 2009). These established sway measures quantify either the ability of the individual to stabilize their head or trunk in space or their ability to stabilize their centre of mass over their base of support. This information is extremely informative of the individual’s global postural control function, and can give important information concerning the subject’s ability to control their postural alignment and stability. These measurement methods do not, however, give any specific information to assist the physician or therapist to plan a targeted therapy. The trunk and head are in reality a multiple number of spinal segments, the alignment and movement of which determine the sway measurement. Increased trunk and head sway or center of pressure excursions do not help in the identification of the specific segments that have reduced postural control. Similarly, subjects could potentially achieve a normal sway measurement by using strategies to reduce the degrees of freedom in the intervertebral joints for example by adopting a lumbar lordotic or kyphotic posture when in fact they have reduced postural control in these segments. There are at the present time no studies that report the unsupported static seated posture of typically developing children on a segmental level in the spine. We reasoned that a description of the normal values for segmental sway would be of value as a reference when measuring sway in unsupported sitting in children with neuromotor disability by providing information concerning the normal segmental distribution of sway in the trunk and head. Variations from this pattern could help in localizing reduced segmental postural control. The aim of this study, therefore, was to measure both posture and segmental trunk and head sway in unsupported steady state sitting of typically developing children. Method We recruited 20 typically developing children through posters and announcements on the mailing system at a college educating health personnel in Copenhagen. Eleven children under 10 years old, mean (range) age 6.6 (4–9) years, height 123 (105–141) cm, weight 22.7 (16–30.4) kg, five girls and six boys; and nine children 10 years old and over, mean (range) age 13.2 (10–16) years, height 132 (132–178) cm, weight 46.3 (27.4–59.9) kg, three girls and six boys, were included in the study. The included children were tested at a movement laboratory using a Vicon 612 eight camera system (Vicon Motion Systems Ltd., Oxford, England). Procedures followed were in accordance with the Helsinki Declaration of 1975, as revised in 2013. The 2
procedures followed protocol and the study was approved by the local responsible ethics committee. The marker protocol for the trunk was based upon the spinal levels described in SATCo (Butler, Saavedra, Sofranac, Jarvis, & Woollacott, 2010) The SATCo test defines the following trunk segments: cervical, upper thoracic, midthoracic, lower thoracic, upper lumbar, lower lumbar, and pelvis. The boundaries between the trunk segments described in the SATCo test are the shoulder girdle, the axillae, inferior scapula, lower ribs, below ribs, and the top of the sacrum. The location of the markers was agreed at a Skype meeting with Dr. Butler (December 16, 2013). The markers were attached to the following bony landmarks to define the boundaries between the trunk segments: cervical-upper thoracic C7, upper thoracic-lower thoracic T3, lower thoracic-upper lumbar T11, upper lumbar-lower lumbar L3, and lower lumbar-pelvis midpoint between spina iliaca posterior superior (Figure 1a). The Frankfurt plane (see Figure 1b) was used as the transverse plane of the head coordinate system. The sagittal axis was defined as a line from the midpoint of a line joining the tragi auricularis on both sides of the head and the midpoint of a line joining the inferior margins of the orbits. The transverse axis was defined as a line passing through the two tragi auricularis. The vertical axis was defined as an axis orthogonal to the sagittal and transverse axes. To measure head movements using this coordinate system, markers were placed on the tragi auricularis (EAR) bilaterally and the middle of the forehead (FOHD) with a virtual marker aligned with the inferior margin of the left orbit (IMLO). The pelvis was defined using the Helen Hayes protocol with markers on the two spina iliaca anterior superior (ASIS) together with the sacrum marker (SACR). The sagittal axis of the pelvis was defined as a line from the sacrum marker through the midpoint of a line joining the two ASIS markers and the transverse axis as a line through the two ASIS markers. The vertical axis was defined as an axis orthogonal to the sagittal and transverse axes. Following attachment of the markers, a calibration frame was recorded to allow calculation of the positions of the virtual marker IMLO in the dynamic trials. Children were seated on a height-adjustable stool without a back support. The stool’s height was adjusted so that their feet were flat on the floor, their thighs were parallel to the floor and their lower leg vertical. A small screen was placed at a height corresponding to their eye height if they sat in an upright sitting posture. The screen was positioned at each child’s midline 1 m in front of the bench. The children were instructed to watch a film on the screen with their hands hanging by their sides and while they watched the film their kinematics were captured. A film was used to focus the child’s attention as the intended clinical use of this test is with children with cognitive deficits who would possibly have difficulties in focusing their attention on a fixed point or following instructions. The screen was very small and the distance sufficient that the area of focus was Journal of Motor Behavior
Downloaded by [University Of Pittsburgh] at 15:21 25 March 2015
Measuring Postural Sway in Sitting
FIGURE 1. (a) Position of the markers on the head, trunk and pelvis and (b) the Frankfurt plane.
small. All children saw the same film, which was chosen to capture their attention but not change their arousal level. It was hoped that this method of focusing the child’s attention would minimize the effect of the visual and audio stimulation on the postural sway of the child. The children were instructed to sit still and watch the film but received no instruction to sit as still as possible as we did not want to measure a stiff sitting posture with muscular cocontraction but a natural relaxed quiet sitting posture. The children did not receive any postural instructions either, for example, “sit as tall as possible.” The first continuous 30-s period of the trial in which all of the markers were visible and the child did not make any voluntary postural movements was selected for the data analysis. A period of 30 s was adopted as this has been reported to be a reasonable duration with respect to reliability and validity for sway measures (Le & Riach, 1996). Two methods of quantifying sway were used and these are illustrated in Figure 2. The first method used the more established sway measures, in which the amplitude and mean velocity of the markers in the anteroposterior (AP) and mediolateral (ML) directions in the transverse plane were quantified (Figure 2b). The AP and ML amplitudes for each marker were calculated as the standard deviation of the marker in the AP and ML directions from its mean position in the global transverse plane. The mean AP and ML velocities were calculated as the total distance travelled by the marker in the AP and ML directions of the 2015, Vol. 0, No. 0
global transverse plane, divided by the length of the trial in seconds. The second method involved the calculation of intersegmental angles between sections of the spinal column (trunk segments). The orientation of a trunk segment was defined from the positions of the markers on the boundary of the segment. A line through these two markers was assumed to be the vertical axis of the segment. The vertical axis of the lower thoracic segment is, for example, defined as being a line through the T11 and the T7 markers and the vertical axis for the upper thoracic segment is defined as being a line through the T7 and the T3 markers. Relative angles between the vertical axes of adjacent segments (intersegmental angles) were calculated in the frontal and sagittal planes of the global coordinate system. The approach to the calculation of the sagittal plane upper thoracic-lower thoracic intersegmental angle is illustrated in Figure 2a and the calculation of sagittal and frontal plane intersegmental angles are shown in Figure 3. Intersegmental angles for curves to the right in the frontal plane and kyphosis in the sagittal plane were assigned a negative value. Angles for the pelvis and head were calculated as global angles. Positive values were assigned to tilting the head backwards (pitch) and tipping the right ear to the right shoulder (roll). For the pelvis, positive values were assigned to anterior tilt in the sagittal plane and tilting of the pelvis to the right in the frontal plane. The mean intersegmental angles were calculated as an expression of the posture adopted by the child and the standard deviation of these angles calculated to 3
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D. J. Curtis et al.
FIGURE 2. Calculation of sway parameters: (a) representative intersegmental angle and (b) representative marker sway.
reflect the intersegmental angular sway. Calculations were performed using inherent models (Plug-in-Gait, Vicon Motion Systems Ltd.), or a custom-written software model (BodyBuilder, Vicon Motion Systems Ltd.). Kolmogorov-Smirnov tests were used to check for normal distribution. Data were analyzed in two groups, children under and over 10 years old, as age-related aspects of
sway have been reported in children in other studies (Hong, James, & Newell, 2008; Monteiro Ferronato & Barela, 2011; Riach & Hayes, 1987). Independent samples t tests were used to determine differences between the two age groups for data with normal distribution. For intersegmental angular sway a total of 12 t tests were used and for marker amplitude and velocity measures of sway a total of 14 t
FIGURE 3. Worked example of the calculation of a representative intersegmental angle from marker coordinates (upper thoraciclower thoracic).
4
Journal of Motor Behavior
Measuring Postural Sway in Sitting
the older group and increased in a consistent bottom-up manner for both groups with marker amplitude increasing from 1.21 mm (SACR) to 7.38mm (midhead) in the younger group and from 0.27 (SACR) to 2.72 mm (midhead) in the older group. These differences were significant for the SACR, T7, T3, and C7 markers (p D .016, .011, .018, and .023, respectively) and highly significant for the L3, T11, and midhead markers (p D .009, .005, and .009, respectively). Mean ML direction marker velocities were approximately four times larger for the younger group in comparison with the older group and increased in a consistent bottom-up manner for both groups with marker velocity increasing from 0.55 (SACR) to 5.18 mm/s (midhead) in the younger group and from 0.11 (SACR) to 1.69 mm/s (midhead) in the older group. These differences were significant for the L3, T11, and T7 markers (p D .015, .012, and .010, respectively) and highly significant for the T3, C7, and midhead markers (p D .007, .005, and .003, respectively). We performed post hoc two-way analyses of variance using marker and age group as independent variables to investigate whether the increase cranially in AP and ML marker sway amplitude and velocity for both age groups were significant. The analyses showed a significant main effect of marker level on AP marker sway, F(6, 126) D 8.335, p < .001; on ML marker sway, F(6, 126) D 6.854, p < .001; on AP marker velocity, F(6, 126) D 6.590, p < .001; and ML marker velocity, F(6, 126) D 8.626, p < .001. Sitting position and intersegmental angular sway are shown in Table 2.
tests. Statistical analysis was performed using IBM SPSS Statistics Version 19. A p value of
