In addition to the body function ICF component of sitting posture and/or postural control, 5 studies also examined the effects of adaptive seating on activity/participation components for children with CP (Table 7). Main outcomes included UE function,14,24,32,34 mobility,34 and social skills and performance of ADL.32,34 No significant difference in UE function was noted in the studies using saddle position or seat insert14,32,34 and mixed results were reported in another study using different back/seat surface inclinations.24 Mobility increased with the use of a saddle position.34 In 2 studies,32,34 social skills and ADL performance improved in children when in the saddle position or seat insert. Overall, the outcomes of interest in the 14 studies were focused primarily at the body structure and function component of the ICF model. Fewer studies included outcomes that fall under the activity and participation components.14,24,30,32,34
Effect of Adaptive Seating on Sitting Posture and Postural Control
The saddle position consists of a saddle-shaped seat that maintains hip abduction and outward rotation and incorporates a forward slope to facilitate anterior rotation of the pelvis.34 It is thought to encourage a midline posture as well as increase dynamic and equal weight bearing through the lower extremities, thereby increasing postural control.34
Three studies in our review examined a saddle seat position. Stewart and McQuilton33 reported improved sitting postural control based on qualitative observation in children with hypertonic or hypotonic CP. A major limitation in this level V study is that only subjective measures were used with no reports of reliability. As well, details of the actual seating intervention were sparse.
Pope et al34 reported no to little improvement in sitting posture and postural control (no p values given). However, these results must be interpreted with caution. A small sample (n = 9) with a large variance was used, limiting statistical power and posing a risk for type II error.35 In addition, no reports of reliability were given. Investigators also failed to control for confounding variables, such as the treatment environment and amount of parental support. Such limitations to internal validity, in addition to poor adherence by the children to the intervention, limit the accuracy of the results and clinical applicability of the intervention.
Reid14 reported improvements in sitting postural control as shown by significant decreases in Total Rest and Total Abnormal Postural Response scores on the Sitting Assessment for Children with Neuromotor Dysfunction clinical rating scale. There was also a significant increase in spinal extension, reflecting a more erect sitting posture. However, the researcher did not control for the potential confounding variable of postural cueing; thus it is unknown if observed changes were due to cueing or the seat design. Generalizability of the findings is also limited because the researchers did not define mild and moderate CP. There is mixed evidence to support the use of saddle seats, with one study34 (level IV evidence) reporting no to slight improvement in sitting posture/postural control and another study (level II evidence) finding a significant increase in those domains.14
Seat Position Angles.
Controversy exists in the literature and in clinical practice as to whether seat bases should be inclined anteriorly or posteriorly. Anteriorly tipped seat bases are thought to allow for more upright and stable sitting postures and reduce kyphosis in children with CP.27 These seats are generally designed to shift the center of gravity forward, maintain lumbar lordosis, decrease posterior pelvic rotation, reduce effects of tight hamstrings on the pelvis,27 and decrease tonic reflex influences on the trunk and hip extensors. Posteriorly tipped seats have been recommended also for children with CP.36 The design goal is usually to decrease the seat-to-back angle as a means of achieving greater hip flexion and decreasing posterior pelvic rotation and activity in overactive hip and trunk extensors.
Four studies that examined different positional angles were included in our review. Sochaniwskyj et al27 reported that for children with diplegia a 10° anterior tilt of the seat base significantly increased back extension whereas a 15° anterior tilt significantly decreased postural stability in sitting and produced greatest EMG activity of the erector spinae muscles (no p value given).
Nwaobi et al26 found lowest EMG activity in the back extensors when the back rest was at 90° and seat at 0°. This result may have differed from that of the previous study27 because of differences in study participants (ranges of types and severities of CP) and differences in the seating intervention. Both studies had similar limitations including relatively small samples and potential sampling bias with the use of convenience samples. Because the researchers only examined low back extensors, they may have missed simultaneous activity of other muscle groups, eg, the hamstrings, that could have influenced sitting posture.
In a third study, McClenaghan et al24 found that lower limb stability improved with a 5° posterior tilt of the seat base, whereas head stability decreased in a 5° anterior tilt during quiet sitting. In active sitting, no segmental displacement differences were observed between tilt conditions; however, the center of pressure moved forward in the 5° anterior tilt position. There was high intersubject variability in the children’s performance and thus the effects of seat-surface inclination on postural stability were thought to be individual and task-specific.
In preschool-aged children, Miedaner28 found that an anterior sitting posture on a forward-tilted bench increased trunk extension, thus encouraging upright posture. Specifically, a 20° forward tilted bench compared with floor or level bench sitting provided increased trunk extension as measured by an increase in sitting height. Use of a randomized complete block design in this study allowed for measurement of a true mean difference among the different seating positions.
Overall, 2 studies supported the use of an anterior tilt seat—1 to improve trunk extensor muscle activity27 and 1 to improve trunk extension.28 One study reported an increase in lower limb stability with a posterior tilt24 and 1 supported the use of 0° seat tile for optimal trunk extensor activity.26
Seat inserts can be added to an adaptive seating device to improve postural control. Two studies23,32 examined unique seat inserts: contoured foam seating (CFS) and biofeedback. CFS is a custom-made insert intended to improve pelvic alignment, increase postural stability, and improve somatosensory feedback.32 Advantages of CFS include its cost-effectiveness, transportability, and ease of fabrication and modification. Washington et al32 analyzed the effects of CFS on postural alignment and reported a significant increase in time spent in midline compared with a control condition, suggesting improved postural control. Parents of the children also reported that they perceived improvement in postural alignment of the children when in the CFS. The investigators theorized that the position of the pelvis dictates the posture in the rest of the body and the CFS keeps the pelvis in a neutral position, thus improving postural control. Use of a single-subject research design allowed these investigators to explore individual changes in the participants. This level II single-subject study supports the use of CFS in a highchair to improve sitting posture and/or postural control in young children with CP. Limitations of the study are the potential difficulties which may be encountered in applying the seating intervention in typical practice, ie, a therapist with 12 years’ experience prescribed and fabricated the contoured foam inserts used in the study.
Biofeedback devices used as seat inserts are believed to improve postural stability by increasing the amount of time a child practices correct postural control. Bertoti and Gross23 used a biofeedback seat insert to improve erect sitting posture in children with CP. Subjective assessment by the therapist reported increased ability to achieve erect posture without undesirable postural deviations. However, internal and external validity of the study were threatened. A small sample (n = 5) was used which increases the standard error and sample variability. Also, only children with CP of “normal intelligence” were included, limiting applicability of the results to the general CP population. Uncertainty exists regarding the amount of daily use needed to optimize gains, feasibility of adherence, and long-term effects.
These two studies of different types of seat inserts (a level II single-subject design and a level IV group design) involved only 7 children with CP, making it difficult to provide firm recommendations about the benefits of this type of seating intervention.
Three-Point Trunk Supports.
External lateral supports can be added to an adaptive seating device to improve sitting posture in children with CP and scoliosis.22 Such supports can be applied based on a 3-point force system, an engineering concept whereby 2 parallel forces are opposed by a force acting in the opposite direction. Holmes et al22 examined the effects of lateral supports arranged according to the 3-point force system, compared with 2 other arrangements of lateral supports, in improving scoliosis in children with spastic CP. Sitting posture was examined by measuring spinous process angles. Significantly smaller mean spinous process angles were reported in the 3-point force system. Because a convenience sample was used in which all subjects had scoliosis, generalizability is limited. No reports of long-term effects on posture or ability to tolerate this management were included. As well, the study only looked at the spinous process angles in 2 dimensions, even though scoliosis deformation is 3-dimensional. As a result, the changes reported may not accurately reflect the true outcome. One level IV study supports the use of lateral supports arranged in a 3-point force system to improve trunk alignment in children with spastic CP who have scoliosis.22
Modular Seating System.
In an attempt to optimize seating for children with CP, researchers have created modular seating systems consisting of a combination of positional adjustments and positioning components. It has been suggested that these seating systems allow for a functional sitting position, in which the users obtain adequate postural control to maximize their ability to use their upper limbs.31 Three studies25,29,31 examined the effects of a modular seating system designed by Myhr and von Wendt. In the customized seating device, children symmetrically bore weight on their ischial tuberosities with the line of gravity of the upper body anterior to the axis of rotation at the ischial tuberosities. The children’s hips were also fixed with a belt under the seat, and their thighs were separated by an abduction orthosis. The seat base itself was either horizontal or anteriorly tipped.
A 1990 pilot study by Myhr and von Wendt31 found that subjects in the modular seating system had the longest duration of head control and the least number of pathological movements, which the researchers identified as indicators of improved postural control. Although the study results were promising, there were limitations. The sample was small (n = 2) which increases the standard error, as well as decreasing generalizability of the findings. Internal validity of the study was further affected because the intervention was not standardized across subjects. The seat base was inclined 5° forward for one subject and 0° for the other. Reliability of outcome measures was not reported. Postural control was examined solely through duration of head control, thus suggesting limited construct validity. Similarly, only the most typical pathological movements were recorded as a measure of overall spasticity. Neglecting to examine tone in other areas of the body undermined the findings that overall spasticity was reduced. Standardization of the intervention, specifically the type and amount of help the children received to regain postural head control, was not explicit. This level V study31 revealed that a modular seating system increases head control and decreases pathological movements, relating to improved sitting postural control in children with CP.
Myhr and von Wendt25 followed up their pilot study a year later and named their modular seating system the “Maxit” or “Real” chair. This system was found to improve overall sitting control as shown by increases in postural control of the head, foot, arm, and hand, increased duration of head control, and reduction in the number of pathological movements. Nevertheless, there were several limitations. Standardization of the intervention was not present as the seat base angles varied from 0° to 15°. This diminishes the capacity to establish a specific cause-effect relationship between the intervention and outcomes, as well as limiting generalizability of the findings. Researchers also used a Sitting Assessment Scale that was uniquely created for this study. While the researchers reported high intrarater and interrater reliability of those using this scale, the reliability results are difficult to interpret because of the type of reliability coefficient used (Spearman rho). Scale validity was not reported.
In 1995, Myhr et al29 published a follow-up to the 1991 study25 to reassess the children who were introduced to and tested in the functional sitting position 5 years earlier. The purpose was to address the long-term effects of various sitting positions in children with CP. Eight of the 10 children had continued to use the functional sitting position and showed significant improvement in head, trunk, and foot control as well as arm and hand function. The 2 children who did not maintain the functional sitting position had deteriorated on all items assessed and their trunk control had worsened. The methods of the follow-up study were similar to those of the original, with the same limitations noted. There was no control group in this study as the researchers felt it would be unethical. This level IV study29 reported that the “Maxit” or “Real” chair encouraged a functional sitting position; improved control of the head, foot, arm, and hand; increased duration of head control; and decreased the number of pathological movements in children with CP. Furthermore, significant development in sitting postural control continued to occur in children who maintained the functional sitting position for 5 years.29
In a level II study, Miedaner28 examined use of the commercial Ther Adapt Posture Chair (Ther Adapt Product Inc.), designed with an adjustable seat height, kneepads and lumbar support to obtain a stabilized sitting posture for the individual child. Overall, the Ther Adapt Posture Chair (compared with floor sitting) provided the best position for increasing trunk extension (p < 0.05). A limitation in this study was the failure to report the specific adjustments made to the chair to obtain the improved sitting posture, thus limiting external validity of the findings.
These 4 studies of modular seating systems (1 at level II, 2 at level IV, and 1 at level V) suggest that modular seating may improve postural control and duration of head control,25,29,31 decrease the number of pathological movements,25,29,31 and increase trunk extension28 in children with CP.
Effect of Adaptive Seating on Functional Ability
Upper Limb Function.
In clinical practice, postural control of the trunk is purported to be an important contributor to voluntary UE function, including motor control and dexterity.37 Researchers have suggested that improved postural control of children with CP will affect UE ability.38 Upper limb function is a critical determinant of the ability to perform daily activities and to participate in the surrounding environment.
Two studies14,34 found that saddle seating had no significant impact on improving fine motor, dexterity, and UE functions in children with CP. McClenaghan et al24 found a significant increase in thumb-press performance when the seat was 5° anteriorly tilted; conversely, a 5° posteriorly tilted seat was significantly related to a decrease in linear tapping test performance. No clear effects of CFS on UE ability were determined in the study of Washington et al.32 The differing findings in these studies may have resulted from the differences in seating interventions or outcome measures. None of the studies used the same measure of upper limb function.
Pope et al34 found an overall increase in mobility with the use of a saddle seat (no p value given). Given that there is only 1 study that examined the effect of adaptive seating on mobility, more research is needed to examine this activity component of the ICF model.
Social Interaction and Performance of Daily Activities.
Two studies included parents’ and/or teachers’ subjective reports of children’s social skills and ADL performance. Washington et al32 (level II single-subject design) noted that parents perceived improvement in their children’s social interactions and in the parents’ ease of performing caregiving tasks, such as feeding, when using the CFS. In the level IV study by Pope et al,34 teachers and parents also commented that children improved in feeding ability and functional performance. More objective measures are needed to capture the magnitude of change in these outcomes.
Limitations of the Current Review
Limitations of this SR must be considered. Studies were not adequately homogeneous to conduct a meta-analysis, making it impossible to infer the overall magnitude of the effect of adaptive seating. It was also difficult to compare study participants in terms of severity because of lack of consistent descriptors across studies. Similarly, it was difficult to compare the effects of age, type of CP, and type of motor impairment because of the heterogeneous samples used. Furthermore, the search strategy was restricted solely to English-language studies. As it is more likely that studies with positive results were included in the review, the findings may not thoroughly represent the research involving adaptive seating and its effect on sitting posture and postural control in children with CP.
Implications of the Systematic Review
Although our SR reports a wide variety of adaptive seating interventions for children with CP, no intervention has been shown to be more effective than others in improving sitting posture and postural control. Because children with CP present with varied issues that limit their postural ability, adaptive seating should be individualized to meet each child’s needs. Research in this area is limited and of lower-level evidence. Therefore, results need to be interpreted with caution.
Therapists should be patient when developing an appropriate seating device for a child, as multiple adjustments over a series of visits may be required. They can experiment with various modifications including saddle-seats, angles of backrests or seat bases, and positions of lateral supports to determine what type(s) of intervention are most effective for each child. Biofeedback can also be incorporated into the seat as a training tool. Research has demonstrated the potential of adaptive seating in improving sitting posture/postural control in children with CP by facilitating upright sitting and improving the ability to interact with peers and the surrounding environment; in turn, this may increase participation in the home or classroom.
This search resulted in 14 studies of level II to V evidence. To make definitive recommendations, studies with higher levels of evidence need to be conducted. Replications of studies using larger samples are recommended. A closer look at factors such as age, motor impairment, and motor disorder may be warranted. New studies can assess the value of currently used adaptive seating devices. Future research should use validated classification systems to describe the motor function of the children in their studies (eg, Gross Motor Function Classification Scale and/or the Level of Sitting Scale) to enable comparisons across studies in terms of motor severity. In addition, agreement on a standardized outcome measure for postural control would allow for better comparisons across studies and overall evaluation of findings. Finally, it is imperative that future studies be extended to include outcomes beyond posture and postural control to enable exploration of whether improvements in sitting posture and postural control will carry over to improved functional skills and increased participation in the social roles of daily life.
Children with CP have significant impairments that affect their sitting posture and postural control. Adaptive seating has been prescribed to manage a child’s impairments and optimize function but there is limited high-quality research available to determine the effectiveness of adaptive seating in improving sitting posture and postural control in these children. The present SR reports on a variety of interventions, including saddle seats, seat inserts, external supports, modular seating systems, and adjustments to seat and back angles. Mixed results were found for use of saddle seats and there is no optimal seat or back angle. Although results are positive for other interventions, evidence is limited and of low-level. Furthermore, few studies examined the effects of improved postural control on functional ability in children with CP. Saddle seating has no effect on overall UE function but has been shown to increase mobility and social skills. An anteriorly tilted seat results in a significant increase in fine motor skills. Finally, a CFS demonstrated no effect on UE ability but was shown to improve performance of ADL in children with CP.
Our review demonstrates that no single intervention has been shown to be more effective than others in improving sitting posture and/or postural control. Furthermore, there is limited evidence to suggest whether improved sitting posture and/or postural control will lead to improved functional abilities.
The authors thank Dr Elizabeth Dean and Dr Angela Busch for their assistance in preparing the manuscript for submission. In addition, the authors acknowledge Steven Ryan, Tanja Mason, and Janice Evans for offering their clinical expertise in the field of adaptive seating and children with cerebral palsy and Ms. Charlotte Beck for her assistance with the data base literature searches.
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Keywords:© 2008 Lippincott Williams & Wilkins, Inc.
adaptive seating; assistive device; child; cerebral palsy/physiopathology; cerebral palsy/therapy; human movement system; infant equipment; movement disorders/physiopathology; movement disorders/therapy; musculoskeletal equilibrium/physiology; orthoses; physical therapy/methods; state of the art review; treatment outcome