EFFECTS OF SEAT-SURFACE INCLINATION ON POSTURAL STABILITY AND FUNCTION OF THE UPPER EXTREMITIES OF CHILDREN WITH CEREBRAL PALSY Bruce A . McClenaghan Lori Thombs Morris Milner
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Children with cerebral palsy often exhibit abnormal synergies, reflexes and tone, which inhibit the acquisition of voluntary motor control of the extremities. In addition, these children often develop skeletal deformities due to poor postural control. Specialized seating plays an important role in the rehabilitative management of children with mild to severe cerebral palsy (Seeger et al. 1984). Improvements in a variety of functional abilities have been attributed to the use of specialized seating, including pulmonary function (Nwaobi and Smith 1986), vocalization (Hulme et al. 1988a), use of the upper extremity (Nwaobi et al. 1986, Hulme et al. 1988a), and eating and drinking (Hulme el al. 1987). Custom seating for the child with cerebral palsy aims to improve voluntary motor control and reduce neuromuscular and skeletal impairments through improved postural control. It has been recognized that proper seating, especially stabilization of the pelvis and postural control of the trunk, is an important factor contributing to voluntary control of the upper extremity; similarly, an unstable seating posture can negatively influence the development and refinement of upper-extremity motor control (Hardy 1984). Inadequate control of the trunk and
proximal musculature may contribute to inefficient control of the upper extremity of the child with cerebral palsy. A proper sitting posture, expecially one that promotes good postural alignment and stability, is a critical prerequisite to efficient motor control. Use of the upper extremities is vital to successful performance of tasks of daily living and participation in a wide variety of recreational activities. Since poor postural reactions, balance control and inefficient manual dexterity are characteristic of children with cerebral palsy, improper seating may contribute to impaired upper-extremity motor control. Selected components of seat design traditionally are manipulated in the clinical setting to try to improve motor function. Several studies (Nwaobi 1984, Seeger et al. 1984, Bablich et al. 1985, Reid et al. 1991) have implicated seat inclination as an important factor in seat design for the child with cerebral palsy. These investigations have found improvements in postural stability, alignment and increased efficiency of the upper extremity with a forward-inclined seat surface. Questions are constantly raised regarding the efficacy of specially designed seating systems to improve postural stability and whether this improved control results in increased functional ability. One aspect
of seating that has received considerable attention is the seat surface. Mandal (1982) alluded to the importance of this when he noted that it carried approximately 80 to 95 per cent of an individual's bodyweight. Several studies have suggested that manipulation of the seat surface aids postural alignment (Nwaobi 1984; Bablich et al. 1985, 1986), and others have suggested that improved postural control of children with cerebral palsy will affect the use of the upper extremities (Finnie 1974, Cristarella 1975, Noronha et a/. 1989). There has been a disagreement in the literature regarding the direction of the inclination of the seat for improved comfort and increased function. Bendix (1984), in his review of seating for nonimpaired children, noted that some investigators recommended a 5" posterior inclination of the seat surface, and Zacharkow (1984) found that posterior inclination prevented the individual's buttocks from sliding forward on the seat. However, others have suggested that there are benefits to a forward inclination of the seat surface, including reduced lumbar flexion (Mandal 1982, Stewart and McQuilton 1987). Although specialized seating is a primary rehabilitative technique used for children with cerebral palsy, improvements in the design and application of these devices are unlikely to occur until a more thorough understanding of the effects of seating are quantified. This study was designed to focus on one aspect of seating for the child with cerebral palsy-the interrelationship of seat-surface inclination on postural stability and functional use of the upper extremities.
Instrumentation A chair frame was designed to allow modifications in seating position and to allow the collection of postural data. A Kistler Measuring Platform (9281 B) was mounted on this frame and served as the seating surface. The design allowed adjustments to the backrest, lower-leg angle, foot supports and seat angle. Kistler amplifiers (9861A) provided analog voltages proportional to the magnitude of the dynamic forces exerted at the seat surface. Analog signals were fed into a laboratory computer through a 12-bit A / D converter (DT2801). Force data were sampled at looHz and stored for analysis at the end of each trial. A detailed description of this instrumentation is published elsewhere (McClenaghan and Peters 1988). Positional data were obtained using a 2D video digitizing system designed for real-time acquisition of segmental information. Selected skeletal segments (head, shoulder, hip, knee and ankle) were monitored during the testing session. Each frame of video data was digitized using a video acquisition and display board (Datacube IVG-128), and the coordinates of segmental points were stored for future analysis. Upper-extremity performance was evaluated using functional measures of motor control developed for this study. These tasks (Table I) were designed to replicate a variety of upper-extremity motor patterns. For the drawing tasks an accuracy (percentage of drawing beyond lmm from tracing) and a time measurement were used to calculate a weighted score.
Method
Experimental conditions Seat-surface inclinations of 0" (0), 5" anterior tilt (SA), and 5" posterior tilt (SP) were used as the experimental conditions. Although other investigations have used more severe seat-surface tilts, previous work conducted in our laboratory has suggested that a tilt of > 5 " degrees is difficult to tolerate for an extended period. Leg-rest positions remained at 90" from the seat surface for all experimental conditions. The angle of the backrest was 90" from the seat surface for both the flat (0) and posteriorly inclined seat surface
Patients Twenty children, aged between four and 15 years, participated in the study: 10 were non-impaired and 10 had mild to moderate spastic cerebral palsy. The children with cerebral palsy could sit independently and were able to ambulate with or without mobility aids. Additional criteria for selection included willingness to participate in the study and ability to follow simple directions. The children were screened for visual problems that would impair eye-hand co-ordination.
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TABLE 1 Upper-extremity motor control tasks Task
Description
Performance measure
Finger-tapping (linear)
Alternate finger-tapping on two targets (5cm') placed on a table directly in front of child. Targets were 30cm apart and orientated horizontally to child As above, with an obstacle placed between targets-forcing child's hand to move in curved path Picking up and placing 10 round pellets (1.5cm diam.) into a container (7cm opening) directly in front of child Turning of eight pegs (Icm diam.). Pegs were oriented horizontally to child and held vertical in holes (1.5crn diam.) 4cm apart Repeated pressing of a toggle switch using thumb. Switch was positioned on a dowel and held in child's palm Pencil-tracing of three figures, including 20cm horizontal line, triangle (10crn sides) and circle (5cm radius)
N target strikes/ 10s
Finger-tapping (curved) Pellet pick-up Peg-turn Thumb-press
L
Pencil-tracing
N target strikes/ 10s Total time (s) to complete task Total time (s) to complete task N switch closures/l5s Time; taken to complete task; Accuracy: %age of drawing f lmrn outside template
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was positioned at 95" when the seat surface was inclined anteriorly (5A) to allow the child to sit with the trunk in a vertical position. The depth of the seat was adjusted individually so that the anterior edge of the seat surface was 2cm from the popliteal crease. Knee and ankle angles initially were positioned as close to 90" as possible, and the child's feet remained in contact with the footrests throughout the testing session. Table height was standardized by placing an adjustable table in front of the child when seated in the 0" position and adjusting the bottom of the table surface to 4cm above the thighs. The resulting shoulder-totable-top distance was recorded and used for the remaining experimental conditions. ( 5 ~ ) ; it
Experimental protocol Before participation in the study, informed consent was obtained from the children and their parentdguardians. The children were familiarized with the laboratory environment, -equipment and experimental protocol before data collection. Data were collected during three sessions and one of the experimental conditions was randomly presented at each. Each session was divided into three randomly presented monitoring phases: quiet sitting, performance on upperextremity motor tasks and active sitting
(sitting while performing an upperextremity motor task). Force and positional data were collected during each condition (0, 5A and 5~ tilt) during a period of quiet sitting (hands placed flat on the table) and while performing an upper-extremity motor task (peg-turning). Data for quiet and active sitting were collected over a two-minute period. Upper-extremity motor performance was evaluated using the motor tasks designed for this study between the collection of quiet and active sitting. Motor tasks were presented in a random order to prevent a patterned response to their presentation.
Data analysis Dependent measures for this investigation were postural alignment, force and upperextremity motor control; postural data included the mean segmental displacements of selected segmental points (head, shoulder, hip, knee and ankle). Force measures included the location and variability of the centre of pressure. The location of this point in the anterior/ posterior direction and the seat depth were used to calculate the location of the centre of pressure as a percentage of total seat depth. Variability of the centre of pressure was quantified using a composite standard deviation calculated from the movement of the centre of pressure
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F&. 1. Mean segmental displacemeni during quiet and aciive silting. Three experimental conditions (0,5A and 5P) plotted f o r each segment.
during each trial. Dependent measures were analysed using inferential and descriptive techniques. Data were statistically analysed using a 2 (subject involvement) x 2 (quiet-active) x 3 (experimental condition) factorial ANOVA. Pairwise comparisons were used t o identify significant effects.
Results
surface inclination significantly influenced displacement of several skeletal segments of the children with cerebral palsy during quiet sitting @ < 0.05): they had increased displacement of the head while in the anterior position, but decreased displacement of the hip, knee and ankle when sitting in the posterior, compared with anterior, position.
,
Posture Posture was evaluated using measures of mean segmental displacement over the duration of each trial. Segmental displacements across each experimental condition (0, 5A, 5 ~ for ) both quiet and active sitting are presented in Figure 1. Significant differences @< 0.05) were obtained between the non-impaired and CP children and between quiet and active sitting on measures of segmental displacement, with the exception of the knee and ankle which were positioned before data collection. During quiet sitting, children with cerebral palsy exhibited significantly greater head, hip and shoulder displacement than non-impaired children @< 0.05). During active sitting children with cerebral palsy exhibited significantly greater shoulder displacement than the non-impaired children @ < 0.05). Experimental conditions did not affect segmental displacements of either group during active sitting. Changes in seat-
Force Two dependent measures of seat reaction force were used as indicators of postural stability, including the trial variability of the path of the centre of pressure and the mean location of the centre of pressure in the anterior/posterior direction, standardized across children as a percentage of seat depth (100 per cent = anterior edge of seat surface; 0 per cent = posterior edge of seat surface). Children with cerebral palsy exhibited greater variability of the centre of pressure than non-impaired children during active sitting @ < 0 05). During quiet sitting, both groups exhibited decreased variability of the centre of pressure in the posterior position (Table 11). The mean location of the centre of pressure did not differ across experimental conditions during quiet sitting. However, experimental conditions did influence its location for children with cerebral palsy during active sitting: they tended to sit with their centre of pressure forward
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TABLE I 1 Variability (cm) of centre of pressure during each experimental condition
Group
Quiet sitting
Non-impaired Cerebral palsy
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0.342 0.631
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EXPERIMENTAL CONDITION
Fig. 2. Mean location of centre of pressure, reported as percentage of seat depth (100 =anterior edge of seat surface), during quiet and active sitring.
when seated in the anterior position, compared with the posterior (p = 0.004) or flat @=0*08) positions. Similarly, a difference in location of the centre of pressure was found between the flat and posterior conditions (Fig. 2).
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Discussion
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Upper-extremity motor tasks Non-impaired children performed better than those with cerebral palsy on all upper-extremity motor tasks, with the exception of two tracing tasks (horizontal line and circle) and thumb-press. Only two upper-extremity motor tasks were significantly affected by changes in the seat-surface inclination ( p < O - O 5 ) . For both groups linear tapping performance was similar in both flat and anterior positions. Performance on the linear tapping task decreased significantly for both groups when tilted posteriorly, while thumb-press performance was better when in the anteriorly tilted position.
Specific research questions addressed by this investigation were: (a) do changes in seat inclination affect the ability of children with cerebral palsy to maintain postural stability while performing upperextremity motor tasks; ( 6 ) how is functional use of the upper extremity influenced by seat-surface inclination; and (c) which seat inclination provides greatest postural stability and/or increased efficiency of the upper extremity? As expected, significant differences were observed between non-impaired and disabled children on most dependent measures of postural alignment, seat reaction forces and upper-extremity motor control. Similarly, differences were observed in most postural and force measures when sitting quietly and while performing an upper-extremity motor task. Seat inclination did not affect most dependent measures of postural stability or upper-extremity motor performance. During quiet sitting, non-impaired children tended to exhibit increased stability of the head and shoulder as the seat surface was tilted, with the lowest displacements observed during posterior sitting. In contrast, children with cerebral palsy demonstrated increased instability of the head and shoulder while sitting quietly in the anterior position. Results of this investigation contradict Myhr and von Wendt (1991), who found improved head control with an anteriorly tilted seat surface. They concluded that this was a result of the increased stability obtained from the arms against the table in front of the children. Although children with cerebral palsy exhibited significantly increased head displacement during quiet sitting, this was not observed during active sitting. The
children were not directed to use their non-dominant hand, but it was observed that during active sitting many children used this hand to stabilize the trunk. It is suggested that the need to concentrate on the upper-extremity task and a possible increased use of the non-dominant hand to stabilize the trunk during active sitting may have contributed to this head/ shoulder stabilization of the child with cerebral palsy during active sitting. Children with cerebral palsy exhibited increased variability of the location of centre of pressure compared with the nonimpaired children, although during active sitting both groups had increased variability. Variability of the centre of pressure was not influenced by seat-surface angle. Variability has been used previously to quantify postural stability (Zernicke et a/. 1978) and provides an indirect measure of sitting comfort (Branton 1966). Similarly, a significant difference in location of the centre of pressure was observed between groups: children with cerebral palsy sat with their centre of pressure significantly more anteriorly. These results were supported by McClenaghan (1989), who found that impaired children applied force to the seat surface significantly more anteriorly than the non-impaired children. Myhr and von Wendt (1990) suggested that this placement of the line of gravity of the upper body anterior to the ischial tuberosities was an important factor resulting in the reduction of spasticity. Seat inclination did not significantly influence the mean location of the centre of pressure during quiet sitting. Both groups exhibited a similar trend for this measure during quiet and active sitting, with the centre of pressure closest to the backrest during posterior sitting (except for the non-impaired children during active sitting). Sitting on the anteriorly inclined seat surface tended to move the centre of pressure forward; this was significant for the children with cerebral palsy when performing the upper-extremity motor task. Bablich eta/. (1986) found that anterior tilting of the seat resulted in a more upright (decreased hip angle) posture for children with cerebral palsy. Results of the present study suggest that factors other than hip angle influence location of the centre of
pressure of children with cerebral palsy during active sitting on an anteriorly inclined seat surface. The importance of the location of the centre of pressure in relation to the hip joint lies in the need for rotational equilibrium (Nwaobi 1984). As it is moved forward, the perpendicular distance between the line of gravity and the hip joint increases, creating greater rotational forces (torque). These gravitational forces must be countered by increased muscular action to maintain equilibrium. Myhr and von Wendt (1991) have suggested that the location of the line of gravity should pass anterior to the ischial tuberosities for a functional sitting position for children with cerebral palsy. The position of the centre of pressure is the result of the torque generated by the trunk, the muscular action of the back and the counter-forces applied through the extremities. As the seat surface is inclined forward an increased counterforce must be generated by the arms and feet to maintain the centre of pressure toward the posterior of the base of support. The forward shift in the line of gravity during active sitting for the child with cerebral palsy, not observed during quiet sitting, may be explained by these children’s inability to transfer the increased forward torque experienced in an anterior position through the feet. This suggests that sitting is a dynamic event and its assessment must consider the multiple factors that contribute to stability. Tilting of the seat surface did not significantly influence the ability of either group to perform upper-extremity motor tasks. Both groups performed more slowly on the linear tapping task when in a posterior position, while the thumbpress task was improved during anterior sitting. Decreased linear tapping performance with posterior sitting may be attributed to restricted vision of the targets, resulting from the position of the head in relation to the horizontal table top in this position. The results of the present investigation support the findings of Seeger et al. (1984), who found that increased hip flexion did not improve hand function of children with cerebral palsy. McPherson
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et al. (1991), in a study comparing the upper-extremity movements of children with and without cerebral palsy at different seat angles, also found no significant differences attributable to seat position. Nwaobi et al. (1986) suggested that hipflexion angle influenced upper-extremity function of individuals with cerebral palsy. They observed that a decreased hip angle ( S O " ) resulted in significantly slower movement of the upper extremity than increased angles (70", 90" and 110"). However, no significant differences were observed in most measures of upperextremity motor control across experimental conditions in the present study. Limitations of this investigation which may have contributed to the results and which merit further investigation include: the angle of seat-surface inclination, lack of padding and contour of the seat surface, position of the backrest and slope of the working surface. A 5" seat inclination was chosen on the basis of observed acceptability during pilot investigations. Although increasing this angle tended t o increase the effects of the seating, tolerance of this posture for long periods was poor. Although Mandal (1976) used a 15" forward tilt and suggested that for every degree forward lumbar lordosis is increased, Bendix (1984) noted increased patient intolerance to inclinations of > 5 " . Others who have reported benefits of the anteriorly tilted seat surface have used a variety of angles. The seat surface used for this study was the Kistler Measuring Platform, which provided a flat surface, although most seat surfaces contain some degree of foam and concavity t o allow for anatomical contours. Lack of contour in a seat causes greater weight-bearing over the ischial tuberosities and discomfort over extended periods. However, the relatively short trial duration (less than one hour) of this investigation should not have resulted in discomfort for the children (Hertzberg 1958). The desk was positioned parallel t o the seat surface for each experimental condition. It has been suggested that a forward-sloping desk may facilitate trunk stability (Bendix and Hagberg 1984) and reduce fatigue and discomfort (Eastman and Kamon 1976).
The upper-extremity motor tasks, although selected to represent movements encountered during daily living, were quantitatively scored: changes in upperextremity function resulting in modifications to the seat inclination for patients with cerebral palsy may be detected better using qualitative techniques (Kluzik et a/. 1990). In summary, a 5" inclination (anterior or posterior) of the seating surface had little effect on functional ability of the upper extremities of children with cerebral palsy. Sitting anteriorly decreased postural stability of these children by increasing head movement during quiet sitting. In addition, the anteriorly tilted seat resulted in a significant shift forward of the centre of pressure during active sitting, whereas posterior sitting during movement of the upper extremities appeared to increase postural stability (decreased variability and a backward shift in the centre of pressure). These results suggest that children with cerebral palsy can sit on a flat surface during quiet sitting if proper head support is provided, and that the seat should be tilted posteriorly slightly during periods of active upper-extremity function. It is important to point out that during the data collection sessions a high intersubject variability was noted in the performances of children with cerebral palsy. These observations and the work of others (Brunswic 1984, Eklund 1987, Reid et al. in press) demonstrate that the effects of seat-surface inclination on the postural stability of individuals may be individual and task-specific. Although anterior tilting of the seat suface generally had negative results on selected postural and force measures for children with cerebral palsy, several children's posture actually improved. Similar conclusions were noted in a study conducted with children with cerebral palsy evaluating the myo-electric activity of the extensor muscles of the lumbar spine with varying seat positions (Nwaobi et al. 1983). Results of this investigation and others suggest that, due to the variability among such children, identification of a universal seating position is not practical. Anterior tilting of the seat is not justified because of the resulting increased instability and the lack
of evidence of improved functional ability of the upper extremity. Accepied f o r publicu,ion 19th September 1991. Ackno wledgemeni This study was funded by Health Services and Promotions Branch, Health and Welfare, Canada.
Authors' Appointments *Bruce A . McClenaghan, Motor Rehabilitation Laboratory, Department of Exercise Science; Lori Thombs, Department of Statistics; University of South Carolina, Columbia, SC 29208. Morris Milner, Director, Rehabilitation Engineering Department, Hugh MacMillan Rehabilitation Centre.
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*Correspondence io first auihor.
SUMMARY This study investigated the effects of seat-surface inclination on parameters of postural stability and functional use of the upper extremity. 10 non-impaired children and 10 children with cerebral palsy, aged between four and 15 years, were studied. Seat-suface inclinations of 0", 5" anteriorly and 5" posteriorly were used as the experimental conditions. Significant differences were observed on most dependent measures between the t w o groups. The results suggest that anteriorly tilting the seats of children with cerebral palsy may disturb postural stability, without improving performance of the upper extremity. RESUME Effets de I'inclinaison de surface de siege sur la stabilite posturale et la fonction des mains chez les enfants I . M . C . Cette etude analyse les effets de I'inclinaison de surface des sieges sur les parametres de la stabilite posturale et I'usage des mains. 10 enfants indemnes et 10 enfants I.M.C., 5ges de quatre a 15 ans, ont ete etudies. Des inclinaisons de la surface de siege de O + , 5 + vers I'avant et 5 - t vers I'arriere, ont defini les conditions experimentales. Des differences significatives ont ete observees sur la plupart des variables dependantes entre les deux groupes. Les resultats suggerent que I'inclinaison anterieure du siege des enfants I.M.C. peut alterer leur stabilite posturale, sans arneliorer pour autant les performances rnanuelles.
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ZUSAMMENFASSUNG EinfluJ3 der Sitzneigung auf die Haltungsstabilitat und die Funktion der oberen Extremitai bei Kindern mit Cerebralparese In dieser Studie wird der Einflufi der Sitzneigung auf Parameter der Haltungsstabilitat und die Funktion der oberen Extremitat untersucht. 10 nicht behinderte Kinder und 10 Kinder mit cerebralparese, irn Alter zwischen vier und 15 Jahren, wurden untersucht. Sitzneigungen von 0", von 5" nach vorne und 5" nach hinten wurden getestet. Fur die rneisten Parameter wurden signifikante Unterschiede zwischen den beiden Gruppen gefunden. Die Ergebnisse zeigen, dal3 nach vorn geneigte Sitze die Haltungsstabilitat von Kindern rnit Cerebralparese storen konnen, ohne die Funktion der oberen Extremitat zu verbessern. RESUMEN Efectos de la inclinacion de la superficie del asiento sobre la estabilidad postural y la funcion de las extremidades superiores en niiios con paralisis cerebral Este estudio investigo 10s efectos de la inclinacion de la superficie del asiento sobre 10s parametros de la estabilidad postural y el us0 funcional de la extrernidad superior. Se estudiaron 10 niiios no patologicos y 10 con paralisis cerebral, de edad entre cuatro y 15 arlos. Corno condiciones experimentales se utilizaron la inclinacion de la superficie del asiento de 0" a 5 " hacia adelante y 5 " hacia atras. Se observaron diferencias significativas en las rnediciones mas dependientes entre ambos grupos. Los resultados sugieren que la inclinacion hacia adelante de 10s asientos en nitlos con paralisis cerebral puede alterar la estabilidad postural, sin rnejoral la realizacion de la extrernidad superior.
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Eklund, J . A. E. (1987) ‘Evaluation of spinal loads and chair design in seated work tasks.’ Clinical Biomechanics, 2, 27-33. Finnie, N. R. (1974) Handling the Young Cerebral Palsied Child at Home, 2nd Edn. London: Heinemann Medical. Hardy, S. (1984) ‘Neuro-motor development and its implications for therapeutic seating.’ I n Trefler, E. (Ed.) Seatingfor Children with Cerebral Palsy. Memphis: University of Tennessee Center for the Health Services. Hertzberg, H. T. E. (1958) ‘Seat comfort.’ I n Hertzberg, H. T. E. (Ed.) Annotated Bibliography of Physical Anthropology in Human Engineering. WADC Technical Report 56-30. Dayton, OH: Wright Air Development Center, Wright-Patterson Air Force Base. Appendix I , pp. 297-300. Hulme, J . B., Shaver, J., Archer, S., Mullette, L., Eggert, C. (1987) ‘Effects of adaptive seating devices on the eating and drinking of children with multiple handicaps.’ The American Journal of Occupational Therapy, 41, 8 1-89, - Archer, S., Shaver, J . (1988) ‘Behavioral changes observed with adaptive seating for multihandicapped clients.’ Developmental Medicine and Child Neurology, 30, Suppl. 57, 34. ( Abstract.) - Bain, B., Hardin, M. A . (1988) ‘The influence of adaptive seating devices on vocalization.’ Developmen fa1 Medicine and Child Neurology, 30, Suppl. 57, 35. (Abstract.) Kluzik, J . , Fetters, L., Coryell, J. (1990) ‘Quantification of control: a preliminary study of the effects of neurodevelopmental treatment on reaching in children with spastic cerebral palsy.’ Physical Therapy, 70, 65-76. Mandal, A. C. (1976) ‘Work-chair with tilting seat.’ Ergonomics, 19, 157-164. - (1982) ‘The seated man: theories and realities.’ In Proceedings of the Human Factors Socierv, 26lh Annual Meeting. McClenaghan, B. A. (1989) ‘Sitting st:bility of selected subjects with cerebral palsy. Clinical Biomechanics, 4, 213-216. - Peters, W. (1988) ‘Design and development of instrumentation to quantify postural stability while sitting.’ In Proceedings of the I C A A R T Conference, Montreal, Canada. McPherson, J . J., Schild, R., Barsamian, P., Transon, C., White, S. C. (1991) ‘Quantitative analysis of the quality of upper extremity movement: a comparison of individuals with
cerebral palsy and without ccrebral palsy In four. sitting posit ions. ’ American Journul (!/ Occupational Therapy, 45, 123-129. Noronha, J . , Bundy, A , , Groll, H . (1989) ‘The effect of positioning on the hand function of boy\ with cerebral palsy.’ Ainericun Jou,-nul o/. Occupational Therapy, 43, 507-5 12. Nwaobi, 0. M. (1984) ‘Biomechanics of seating.’ In Trefler, E. (Ed.) Seating of Children with Cerebral Palsv. Memphis, TN: University of Tennessee Rehabilitation Engineering Program. - Smith, P. (1986) ‘Effect of adaptive seating on pulmonary function of children with cerebral palsy .’ Developmental Medicine and Child Neurolog.v, 28, Suppl. 53, 24. (Abstract.) - Brubaker, C. E . , Cusick, B., Sussman, M. D. (1983) ’Electromyographic investigation of extensor activity in cerebral-palsied children in different seating positions.’ Developmental Medicine and Child Neurology, 25, 175-1 83. - Hobson, D. A., Trefler, E. (1986) ‘Hip angle and upper extremity movement rime of children with cerebral palsy.’ Developmental Medicine and Child Neurology, 28, Suppl. 53, 24. (Abstract.) Myhr, U., von Wendt, L. (1990) ‘Reducing $pasticity and enhancing postural control for the creation of a functional sitting position in children with cerebral palsy: a pilot study.’ Physiotherap,v Theory and Practice, 6 , 65-76. - - (1991) ‘Improvement of functional sitting position for children with cerebral palsy.’ Developtnentul Medicine and Child Neurology, 33, 246-256. Reid, D. T., Sochaniwskyj, A , , Milner, M. (1991) ‘An investigation of postural sway in sitting of normal children and children with neurological disorders.’ Physical and Occupational Therap-v in Pedialrics (in press). Seeger, B. A , , Caudrey, D. J . , O’Mara, N. A. (1984) ‘Hand function in cerebral palsy: the effect of hipflexion angle.’ Developmental Medicine and Child Neurology, 26, 60 1-606. Stewart, P. C., McQuilton, G . (1987) ‘Straddle seating for the cerebral palsied child.’ British Journal of Occupational Therapy, 50, 136-1 38. Zacharkow, D. (1984) Wheelchair Posture and Pressure Sores. Springfield: C . C . Thomas. Zernicke, R . F., Gregor, R . J., Cratty, B. J . (1978) ‘Quantification of postural sway in normal children.’ In Assmussen, E., Jorgenson, K. (Eds.) Biomechanics VI-A. Baltimore: University Park Press.
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Children with cerebral palsy often exhibit abnormal synergies, reflexes and tone, which inhibit the acquisition of voluntary motor control of the extremities. In addition, these children often develop skeletal deformities due to poor postural control. Specialized seating plays an important role in the rehabilitative management of children with mild to severe cerebral palsy (Seeger et al. 1984). Improvements in a variety of functional abilities have been attributed to the use of specialized seating, including pulmonary function (Nwaobi and Smith 1986), vocalization (Hulme et al. 1988a), use of the upper extremity (Nwaobi et al. 1986, Hulme et al. 1988a), and eating and drinking (Hulme el al. 1987). Custom seating for the child with cerebral palsy aims to improve voluntary motor control and reduce neuromuscular and skeletal impairments through improved postural control. It has been recognized that proper seating, especially stabilization of the pelvis and postural control of the trunk, is an important factor contributing to voluntary control of the upper extremity; similarly, an unstable seating posture can negatively influence the development and refinement of upper-extremity motor control (Hardy 1984). Inadequate control of the trunk and
proximal musculature may contribute to inefficient control of the upper extremity of the child with cerebral palsy. A proper sitting posture, expecially one that promotes good postural alignment and stability, is a critical prerequisite to efficient motor control. Use of the upper extremities is vital to successful performance of tasks of daily living and participation in a wide variety of recreational activities. Since poor postural reactions, balance control and inefficient manual dexterity are characteristic of children with cerebral palsy, improper seating may contribute to impaired upper-extremity motor control. Selected components of seat design traditionally are manipulated in the clinical setting to try to improve motor function. Several studies (Nwaobi 1984, Seeger et al. 1984, Bablich et al. 1985, Reid et al. 1991) have implicated seat inclination as an important factor in seat design for the child with cerebral palsy. These investigations have found improvements in postural stability, alignment and increased efficiency of the upper extremity with a forward-inclined seat surface. Questions are constantly raised regarding the efficacy of specially designed seating systems to improve postural stability and whether this improved control results in increased functional ability. One aspect
of seating that has received considerable attention is the seat surface. Mandal (1982) alluded to the importance of this when he noted that it carried approximately 80 to 95 per cent of an individual's bodyweight. Several studies have suggested that manipulation of the seat surface aids postural alignment (Nwaobi 1984; Bablich et al. 1985, 1986), and others have suggested that improved postural control of children with cerebral palsy will affect the use of the upper extremities (Finnie 1974, Cristarella 1975, Noronha et a/. 1989). There has been a disagreement in the literature regarding the direction of the inclination of the seat for improved comfort and increased function. Bendix (1984), in his review of seating for nonimpaired children, noted that some investigators recommended a 5" posterior inclination of the seat surface, and Zacharkow (1984) found that posterior inclination prevented the individual's buttocks from sliding forward on the seat. However, others have suggested that there are benefits to a forward inclination of the seat surface, including reduced lumbar flexion (Mandal 1982, Stewart and McQuilton 1987). Although specialized seating is a primary rehabilitative technique used for children with cerebral palsy, improvements in the design and application of these devices are unlikely to occur until a more thorough understanding of the effects of seating are quantified. This study was designed to focus on one aspect of seating for the child with cerebral palsy-the interrelationship of seat-surface inclination on postural stability and functional use of the upper extremities.
Instrumentation A chair frame was designed to allow modifications in seating position and to allow the collection of postural data. A Kistler Measuring Platform (9281 B) was mounted on this frame and served as the seating surface. The design allowed adjustments to the backrest, lower-leg angle, foot supports and seat angle. Kistler amplifiers (9861A) provided analog voltages proportional to the magnitude of the dynamic forces exerted at the seat surface. Analog signals were fed into a laboratory computer through a 12-bit A / D converter (DT2801). Force data were sampled at looHz and stored for analysis at the end of each trial. A detailed description of this instrumentation is published elsewhere (McClenaghan and Peters 1988). Positional data were obtained using a 2D video digitizing system designed for real-time acquisition of segmental information. Selected skeletal segments (head, shoulder, hip, knee and ankle) were monitored during the testing session. Each frame of video data was digitized using a video acquisition and display board (Datacube IVG-128), and the coordinates of segmental points were stored for future analysis. Upper-extremity performance was evaluated using functional measures of motor control developed for this study. These tasks (Table I) were designed to replicate a variety of upper-extremity motor patterns. For the drawing tasks an accuracy (percentage of drawing beyond lmm from tracing) and a time measurement were used to calculate a weighted score.
Method
Experimental conditions Seat-surface inclinations of 0" (0), 5" anterior tilt (SA), and 5" posterior tilt (SP) were used as the experimental conditions. Although other investigations have used more severe seat-surface tilts, previous work conducted in our laboratory has suggested that a tilt of > 5 " degrees is difficult to tolerate for an extended period. Leg-rest positions remained at 90" from the seat surface for all experimental conditions. The angle of the backrest was 90" from the seat surface for both the flat (0) and posteriorly inclined seat surface
Patients Twenty children, aged between four and 15 years, participated in the study: 10 were non-impaired and 10 had mild to moderate spastic cerebral palsy. The children with cerebral palsy could sit independently and were able to ambulate with or without mobility aids. Additional criteria for selection included willingness to participate in the study and ability to follow simple directions. The children were screened for visual problems that would impair eye-hand co-ordination.
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TABLE 1 Upper-extremity motor control tasks Task
Description
Performance measure
Finger-tapping (linear)
Alternate finger-tapping on two targets (5cm') placed on a table directly in front of child. Targets were 30cm apart and orientated horizontally to child As above, with an obstacle placed between targets-forcing child's hand to move in curved path Picking up and placing 10 round pellets (1.5cm diam.) into a container (7cm opening) directly in front of child Turning of eight pegs (Icm diam.). Pegs were oriented horizontally to child and held vertical in holes (1.5crn diam.) 4cm apart Repeated pressing of a toggle switch using thumb. Switch was positioned on a dowel and held in child's palm Pencil-tracing of three figures, including 20cm horizontal line, triangle (10crn sides) and circle (5cm radius)
N target strikes/ 10s
Finger-tapping (curved) Pellet pick-up Peg-turn Thumb-press
L
Pencil-tracing
N target strikes/ 10s Total time (s) to complete task Total time (s) to complete task N switch closures/l5s Time; taken to complete task; Accuracy: %age of drawing f lmrn outside template
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was positioned at 95" when the seat surface was inclined anteriorly (5A) to allow the child to sit with the trunk in a vertical position. The depth of the seat was adjusted individually so that the anterior edge of the seat surface was 2cm from the popliteal crease. Knee and ankle angles initially were positioned as close to 90" as possible, and the child's feet remained in contact with the footrests throughout the testing session. Table height was standardized by placing an adjustable table in front of the child when seated in the 0" position and adjusting the bottom of the table surface to 4cm above the thighs. The resulting shoulder-totable-top distance was recorded and used for the remaining experimental conditions. ( 5 ~ ) ; it
Experimental protocol Before participation in the study, informed consent was obtained from the children and their parentdguardians. The children were familiarized with the laboratory environment, -equipment and experimental protocol before data collection. Data were collected during three sessions and one of the experimental conditions was randomly presented at each. Each session was divided into three randomly presented monitoring phases: quiet sitting, performance on upperextremity motor tasks and active sitting
(sitting while performing an upperextremity motor task). Force and positional data were collected during each condition (0, 5A and 5~ tilt) during a period of quiet sitting (hands placed flat on the table) and while performing an upper-extremity motor task (peg-turning). Data for quiet and active sitting were collected over a two-minute period. Upper-extremity motor performance was evaluated using the motor tasks designed for this study between the collection of quiet and active sitting. Motor tasks were presented in a random order to prevent a patterned response to their presentation.
Data analysis Dependent measures for this investigation were postural alignment, force and upperextremity motor control; postural data included the mean segmental displacements of selected segmental points (head, shoulder, hip, knee and ankle). Force measures included the location and variability of the centre of pressure. The location of this point in the anterior/ posterior direction and the seat depth were used to calculate the location of the centre of pressure as a percentage of total seat depth. Variability of the centre of pressure was quantified using a composite standard deviation calculated from the movement of the centre of pressure
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Shoulder
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F&. 1. Mean segmental displacemeni during quiet and aciive silting. Three experimental conditions (0,5A and 5P) plotted f o r each segment.
during each trial. Dependent measures were analysed using inferential and descriptive techniques. Data were statistically analysed using a 2 (subject involvement) x 2 (quiet-active) x 3 (experimental condition) factorial ANOVA. Pairwise comparisons were used t o identify significant effects.
Results
surface inclination significantly influenced displacement of several skeletal segments of the children with cerebral palsy during quiet sitting @ < 0.05): they had increased displacement of the head while in the anterior position, but decreased displacement of the hip, knee and ankle when sitting in the posterior, compared with anterior, position.
,
Posture Posture was evaluated using measures of mean segmental displacement over the duration of each trial. Segmental displacements across each experimental condition (0, 5A, 5 ~ for ) both quiet and active sitting are presented in Figure 1. Significant differences @< 0.05) were obtained between the non-impaired and CP children and between quiet and active sitting on measures of segmental displacement, with the exception of the knee and ankle which were positioned before data collection. During quiet sitting, children with cerebral palsy exhibited significantly greater head, hip and shoulder displacement than non-impaired children @< 0.05). During active sitting children with cerebral palsy exhibited significantly greater shoulder displacement than the non-impaired children @ < 0.05). Experimental conditions did not affect segmental displacements of either group during active sitting. Changes in seat-
Force Two dependent measures of seat reaction force were used as indicators of postural stability, including the trial variability of the path of the centre of pressure and the mean location of the centre of pressure in the anterior/posterior direction, standardized across children as a percentage of seat depth (100 per cent = anterior edge of seat surface; 0 per cent = posterior edge of seat surface). Children with cerebral palsy exhibited greater variability of the centre of pressure than non-impaired children during active sitting @ < 0 05). During quiet sitting, both groups exhibited decreased variability of the centre of pressure in the posterior position (Table 11). The mean location of the centre of pressure did not differ across experimental conditions during quiet sitting. However, experimental conditions did influence its location for children with cerebral palsy during active sitting: they tended to sit with their centre of pressure forward
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TABLE I 1 Variability (cm) of centre of pressure during each experimental condition
Group
Quiet sitting
Non-impaired Cerebral palsy
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0.342 0.631
0.347 0.449
0.731
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0.737
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EXPERIMENTAL CONDITION
Fig. 2. Mean location of centre of pressure, reported as percentage of seat depth (100 =anterior edge of seat surface), during quiet and active sitring.
when seated in the anterior position, compared with the posterior (p = 0.004) or flat @=0*08) positions. Similarly, a difference in location of the centre of pressure was found between the flat and posterior conditions (Fig. 2).
44
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Discussion
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Upper-extremity motor tasks Non-impaired children performed better than those with cerebral palsy on all upper-extremity motor tasks, with the exception of two tracing tasks (horizontal line and circle) and thumb-press. Only two upper-extremity motor tasks were significantly affected by changes in the seat-surface inclination ( p < O - O 5 ) . For both groups linear tapping performance was similar in both flat and anterior positions. Performance on the linear tapping task decreased significantly for both groups when tilted posteriorly, while thumb-press performance was better when in the anteriorly tilted position.
Specific research questions addressed by this investigation were: (a) do changes in seat inclination affect the ability of children with cerebral palsy to maintain postural stability while performing upperextremity motor tasks; ( 6 ) how is functional use of the upper extremity influenced by seat-surface inclination; and (c) which seat inclination provides greatest postural stability and/or increased efficiency of the upper extremity? As expected, significant differences were observed between non-impaired and disabled children on most dependent measures of postural alignment, seat reaction forces and upper-extremity motor control. Similarly, differences were observed in most postural and force measures when sitting quietly and while performing an upper-extremity motor task. Seat inclination did not affect most dependent measures of postural stability or upper-extremity motor performance. During quiet sitting, non-impaired children tended to exhibit increased stability of the head and shoulder as the seat surface was tilted, with the lowest displacements observed during posterior sitting. In contrast, children with cerebral palsy demonstrated increased instability of the head and shoulder while sitting quietly in the anterior position. Results of this investigation contradict Myhr and von Wendt (1991), who found improved head control with an anteriorly tilted seat surface. They concluded that this was a result of the increased stability obtained from the arms against the table in front of the children. Although children with cerebral palsy exhibited significantly increased head displacement during quiet sitting, this was not observed during active sitting. The
children were not directed to use their non-dominant hand, but it was observed that during active sitting many children used this hand to stabilize the trunk. It is suggested that the need to concentrate on the upper-extremity task and a possible increased use of the non-dominant hand to stabilize the trunk during active sitting may have contributed to this head/ shoulder stabilization of the child with cerebral palsy during active sitting. Children with cerebral palsy exhibited increased variability of the location of centre of pressure compared with the nonimpaired children, although during active sitting both groups had increased variability. Variability of the centre of pressure was not influenced by seat-surface angle. Variability has been used previously to quantify postural stability (Zernicke et a/. 1978) and provides an indirect measure of sitting comfort (Branton 1966). Similarly, a significant difference in location of the centre of pressure was observed between groups: children with cerebral palsy sat with their centre of pressure significantly more anteriorly. These results were supported by McClenaghan (1989), who found that impaired children applied force to the seat surface significantly more anteriorly than the non-impaired children. Myhr and von Wendt (1990) suggested that this placement of the line of gravity of the upper body anterior to the ischial tuberosities was an important factor resulting in the reduction of spasticity. Seat inclination did not significantly influence the mean location of the centre of pressure during quiet sitting. Both groups exhibited a similar trend for this measure during quiet and active sitting, with the centre of pressure closest to the backrest during posterior sitting (except for the non-impaired children during active sitting). Sitting on the anteriorly inclined seat surface tended to move the centre of pressure forward; this was significant for the children with cerebral palsy when performing the upper-extremity motor task. Bablich eta/. (1986) found that anterior tilting of the seat resulted in a more upright (decreased hip angle) posture for children with cerebral palsy. Results of the present study suggest that factors other than hip angle influence location of the centre of
pressure of children with cerebral palsy during active sitting on an anteriorly inclined seat surface. The importance of the location of the centre of pressure in relation to the hip joint lies in the need for rotational equilibrium (Nwaobi 1984). As it is moved forward, the perpendicular distance between the line of gravity and the hip joint increases, creating greater rotational forces (torque). These gravitational forces must be countered by increased muscular action to maintain equilibrium. Myhr and von Wendt (1991) have suggested that the location of the line of gravity should pass anterior to the ischial tuberosities for a functional sitting position for children with cerebral palsy. The position of the centre of pressure is the result of the torque generated by the trunk, the muscular action of the back and the counter-forces applied through the extremities. As the seat surface is inclined forward an increased counterforce must be generated by the arms and feet to maintain the centre of pressure toward the posterior of the base of support. The forward shift in the line of gravity during active sitting for the child with cerebral palsy, not observed during quiet sitting, may be explained by these children’s inability to transfer the increased forward torque experienced in an anterior position through the feet. This suggests that sitting is a dynamic event and its assessment must consider the multiple factors that contribute to stability. Tilting of the seat surface did not significantly influence the ability of either group to perform upper-extremity motor tasks. Both groups performed more slowly on the linear tapping task when in a posterior position, while the thumbpress task was improved during anterior sitting. Decreased linear tapping performance with posterior sitting may be attributed to restricted vision of the targets, resulting from the position of the head in relation to the horizontal table top in this position. The results of the present investigation support the findings of Seeger et al. (1984), who found that increased hip flexion did not improve hand function of children with cerebral palsy. McPherson
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et al. (1991), in a study comparing the upper-extremity movements of children with and without cerebral palsy at different seat angles, also found no significant differences attributable to seat position. Nwaobi et al. (1986) suggested that hipflexion angle influenced upper-extremity function of individuals with cerebral palsy. They observed that a decreased hip angle ( S O " ) resulted in significantly slower movement of the upper extremity than increased angles (70", 90" and 110"). However, no significant differences were observed in most measures of upperextremity motor control across experimental conditions in the present study. Limitations of this investigation which may have contributed to the results and which merit further investigation include: the angle of seat-surface inclination, lack of padding and contour of the seat surface, position of the backrest and slope of the working surface. A 5" seat inclination was chosen on the basis of observed acceptability during pilot investigations. Although increasing this angle tended t o increase the effects of the seating, tolerance of this posture for long periods was poor. Although Mandal (1976) used a 15" forward tilt and suggested that for every degree forward lumbar lordosis is increased, Bendix (1984) noted increased patient intolerance to inclinations of > 5 " . Others who have reported benefits of the anteriorly tilted seat surface have used a variety of angles. The seat surface used for this study was the Kistler Measuring Platform, which provided a flat surface, although most seat surfaces contain some degree of foam and concavity t o allow for anatomical contours. Lack of contour in a seat causes greater weight-bearing over the ischial tuberosities and discomfort over extended periods. However, the relatively short trial duration (less than one hour) of this investigation should not have resulted in discomfort for the children (Hertzberg 1958). The desk was positioned parallel t o the seat surface for each experimental condition. It has been suggested that a forward-sloping desk may facilitate trunk stability (Bendix and Hagberg 1984) and reduce fatigue and discomfort (Eastman and Kamon 1976).
The upper-extremity motor tasks, although selected to represent movements encountered during daily living, were quantitatively scored: changes in upperextremity function resulting in modifications to the seat inclination for patients with cerebral palsy may be detected better using qualitative techniques (Kluzik et a/. 1990). In summary, a 5" inclination (anterior or posterior) of the seating surface had little effect on functional ability of the upper extremities of children with cerebral palsy. Sitting anteriorly decreased postural stability of these children by increasing head movement during quiet sitting. In addition, the anteriorly tilted seat resulted in a significant shift forward of the centre of pressure during active sitting, whereas posterior sitting during movement of the upper extremities appeared to increase postural stability (decreased variability and a backward shift in the centre of pressure). These results suggest that children with cerebral palsy can sit on a flat surface during quiet sitting if proper head support is provided, and that the seat should be tilted posteriorly slightly during periods of active upper-extremity function. It is important to point out that during the data collection sessions a high intersubject variability was noted in the performances of children with cerebral palsy. These observations and the work of others (Brunswic 1984, Eklund 1987, Reid et al. in press) demonstrate that the effects of seat-surface inclination on the postural stability of individuals may be individual and task-specific. Although anterior tilting of the seat suface generally had negative results on selected postural and force measures for children with cerebral palsy, several children's posture actually improved. Similar conclusions were noted in a study conducted with children with cerebral palsy evaluating the myo-electric activity of the extensor muscles of the lumbar spine with varying seat positions (Nwaobi et al. 1983). Results of this investigation and others suggest that, due to the variability among such children, identification of a universal seating position is not practical. Anterior tilting of the seat is not justified because of the resulting increased instability and the lack
of evidence of improved functional ability of the upper extremity. Accepied f o r publicu,ion 19th September 1991. Ackno wledgemeni This study was funded by Health Services and Promotions Branch, Health and Welfare, Canada.
Authors' Appointments *Bruce A . McClenaghan, Motor Rehabilitation Laboratory, Department of Exercise Science; Lori Thombs, Department of Statistics; University of South Carolina, Columbia, SC 29208. Morris Milner, Director, Rehabilitation Engineering Department, Hugh MacMillan Rehabilitation Centre.
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*Correspondence io first auihor.
SUMMARY This study investigated the effects of seat-surface inclination on parameters of postural stability and functional use of the upper extremity. 10 non-impaired children and 10 children with cerebral palsy, aged between four and 15 years, were studied. Seat-suface inclinations of 0", 5" anteriorly and 5" posteriorly were used as the experimental conditions. Significant differences were observed on most dependent measures between the t w o groups. The results suggest that anteriorly tilting the seats of children with cerebral palsy may disturb postural stability, without improving performance of the upper extremity. RESUME Effets de I'inclinaison de surface de siege sur la stabilite posturale et la fonction des mains chez les enfants I . M . C . Cette etude analyse les effets de I'inclinaison de surface des sieges sur les parametres de la stabilite posturale et I'usage des mains. 10 enfants indemnes et 10 enfants I.M.C., 5ges de quatre a 15 ans, ont ete etudies. Des inclinaisons de la surface de siege de O + , 5 + vers I'avant et 5 - t vers I'arriere, ont defini les conditions experimentales. Des differences significatives ont ete observees sur la plupart des variables dependantes entre les deux groupes. Les resultats suggerent que I'inclinaison anterieure du siege des enfants I.M.C. peut alterer leur stabilite posturale, sans arneliorer pour autant les performances rnanuelles.
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ZUSAMMENFASSUNG EinfluJ3 der Sitzneigung auf die Haltungsstabilitat und die Funktion der oberen Extremitai bei Kindern mit Cerebralparese In dieser Studie wird der Einflufi der Sitzneigung auf Parameter der Haltungsstabilitat und die Funktion der oberen Extremitat untersucht. 10 nicht behinderte Kinder und 10 Kinder mit cerebralparese, irn Alter zwischen vier und 15 Jahren, wurden untersucht. Sitzneigungen von 0", von 5" nach vorne und 5" nach hinten wurden getestet. Fur die rneisten Parameter wurden signifikante Unterschiede zwischen den beiden Gruppen gefunden. Die Ergebnisse zeigen, dal3 nach vorn geneigte Sitze die Haltungsstabilitat von Kindern rnit Cerebralparese storen konnen, ohne die Funktion der oberen Extremitat zu verbessern. RESUMEN Efectos de la inclinacion de la superficie del asiento sobre la estabilidad postural y la funcion de las extremidades superiores en niiios con paralisis cerebral Este estudio investigo 10s efectos de la inclinacion de la superficie del asiento sobre 10s parametros de la estabilidad postural y el us0 funcional de la extrernidad superior. Se estudiaron 10 niiios no patologicos y 10 con paralisis cerebral, de edad entre cuatro y 15 arlos. Corno condiciones experimentales se utilizaron la inclinacion de la superficie del asiento de 0" a 5 " hacia adelante y 5 " hacia atras. Se observaron diferencias significativas en las rnediciones mas dependientes entre ambos grupos. Los resultados sugieren que la inclinacion hacia adelante de 10s asientos en nitlos con paralisis cerebral puede alterar la estabilidad postural, sin rnejoral la realizacion de la extrernidad superior.
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the trapezius muscle whilst sitting at sloping desks.' Ergonomics, 27, 873-882. Branton, P. (1966) The Comfort of Easy Chairs. Stevenage, Herts: The Furniture Industry Research Association. Brunswic, M. (1984) 'Seat design in supported sitting.' In Proceedings of the International Conference o/ Occupaiional Ergonomics. pp. 294-298. Cristarella, M. C. (1975) 'Comparison of straddling and sitting apparatus for the spastic cerebral palsied child.' American Journal of Occupational Therapy, 29, 273-276. Eastman, M. C., Karnon, E. (1976) 'Posture and subjective evaluation of flat and slanted desks.' Human Factors, 18, 15-26.
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a .Y)
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Eklund, J . A. E. (1987) ‘Evaluation of spinal loads and chair design in seated work tasks.’ Clinical Biomechanics, 2, 27-33. Finnie, N. R. (1974) Handling the Young Cerebral Palsied Child at Home, 2nd Edn. London: Heinemann Medical. Hardy, S. (1984) ‘Neuro-motor development and its implications for therapeutic seating.’ I n Trefler, E. (Ed.) Seatingfor Children with Cerebral Palsy. Memphis: University of Tennessee Center for the Health Services. Hertzberg, H. T. E. (1958) ‘Seat comfort.’ I n Hertzberg, H. T. E. (Ed.) Annotated Bibliography of Physical Anthropology in Human Engineering. WADC Technical Report 56-30. Dayton, OH: Wright Air Development Center, Wright-Patterson Air Force Base. Appendix I , pp. 297-300. Hulme, J . B., Shaver, J., Archer, S., Mullette, L., Eggert, C. (1987) ‘Effects of adaptive seating devices on the eating and drinking of children with multiple handicaps.’ The American Journal of Occupational Therapy, 41, 8 1-89, - Archer, S., Shaver, J . (1988) ‘Behavioral changes observed with adaptive seating for multihandicapped clients.’ Developmental Medicine and Child Neurology, 30, Suppl. 57, 34. ( Abstract.) - Bain, B., Hardin, M. A . (1988) ‘The influence of adaptive seating devices on vocalization.’ Developmen fa1 Medicine and Child Neurology, 30, Suppl. 57, 35. (Abstract.) Kluzik, J . , Fetters, L., Coryell, J. (1990) ‘Quantification of control: a preliminary study of the effects of neurodevelopmental treatment on reaching in children with spastic cerebral palsy.’ Physical Therapy, 70, 65-76. Mandal, A. C. (1976) ‘Work-chair with tilting seat.’ Ergonomics, 19, 157-164. - (1982) ‘The seated man: theories and realities.’ In Proceedings of the Human Factors Socierv, 26lh Annual Meeting. McClenaghan, B. A. (1989) ‘Sitting st:bility of selected subjects with cerebral palsy. Clinical Biomechanics, 4, 213-216. - Peters, W. (1988) ‘Design and development of instrumentation to quantify postural stability while sitting.’ In Proceedings of the I C A A R T Conference, Montreal, Canada. McPherson, J . J., Schild, R., Barsamian, P., Transon, C., White, S. C. (1991) ‘Quantitative analysis of the quality of upper extremity movement: a comparison of individuals with
cerebral palsy and without ccrebral palsy In four. sitting posit ions. ’ American Journul (!/ Occupational Therapy, 45, 123-129. Noronha, J . , Bundy, A , , Groll, H . (1989) ‘The effect of positioning on the hand function of boy\ with cerebral palsy.’ Ainericun Jou,-nul o/. Occupational Therapy, 43, 507-5 12. Nwaobi, 0. M. (1984) ‘Biomechanics of seating.’ In Trefler, E. (Ed.) Seating of Children with Cerebral Palsv. Memphis, TN: University of Tennessee Rehabilitation Engineering Program. - Smith, P. (1986) ‘Effect of adaptive seating on pulmonary function of children with cerebral palsy .’ Developmental Medicine and Child Neurolog.v, 28, Suppl. 53, 24. (Abstract.) - Brubaker, C. E . , Cusick, B., Sussman, M. D. (1983) ’Electromyographic investigation of extensor activity in cerebral-palsied children in different seating positions.’ Developmental Medicine and Child Neurology, 25, 175-1 83. - Hobson, D. A., Trefler, E. (1986) ‘Hip angle and upper extremity movement rime of children with cerebral palsy.’ Developmental Medicine and Child Neurology, 28, Suppl. 53, 24. (Abstract.) Myhr, U., von Wendt, L. (1990) ‘Reducing $pasticity and enhancing postural control for the creation of a functional sitting position in children with cerebral palsy: a pilot study.’ Physiotherap,v Theory and Practice, 6 , 65-76. - - (1991) ‘Improvement of functional sitting position for children with cerebral palsy.’ Developtnentul Medicine and Child Neurology, 33, 246-256. Reid, D. T., Sochaniwskyj, A , , Milner, M. (1991) ‘An investigation of postural sway in sitting of normal children and children with neurological disorders.’ Physical and Occupational Therap-v in Pedialrics (in press). Seeger, B. A , , Caudrey, D. J . , O’Mara, N. A. (1984) ‘Hand function in cerebral palsy: the effect of hipflexion angle.’ Developmental Medicine and Child Neurology, 26, 60 1-606. Stewart, P. C., McQuilton, G . (1987) ‘Straddle seating for the cerebral palsied child.’ British Journal of Occupational Therapy, 50, 136-1 38. Zacharkow, D. (1984) Wheelchair Posture and Pressure Sores. Springfield: C . C . Thomas. Zernicke, R . F., Gregor, R . J., Cratty, B. J . (1978) ‘Quantification of postural sway in normal children.’ In Assmussen, E., Jorgenson, K. (Eds.) Biomechanics VI-A. Baltimore: University Park Press.
