Down syndrome (DS), one of the most common genetic conditions, occurs in 13.65 of 10 000 live births annually in the United States.1 Individuals with DS present with orthopedic and neuromuscular impairments such as hypotonicity, ligamentous laxity, and bony abnormalities, which lead to several secondary complications and functional impairments. As a result of structural and functional impairments, children with DS have delayed motor development and are often slow to attain developmental milestones seen in children who are typically developing (TD).2 Impairments such as joint hypermobility also lead to characteristic deviations in gait3,4 and further impair the development of more complex motor tasks such as running, jumping, and navigating stairs.2
Children with DS learn to stand and walk independently between the ages of 18 months and 3 years,2 whereas children who are TD attain these motor milestones between 11 and 15 months of age.5 Whereas independent walking represents an important achievement in the gross motor development of infants, it is also critical for their social development and precipitates systemwide changes across several developmental domains.6 Delays in the motor development of children with DS therefore have social and cognitive implications that result from an impaired ability to effectively explore and interact with others or the environment.
Within the last decade, the use of interventions such as partial body-weight–supported treadmill training (PBWSTT) and foot and ankle orthoses have become increasingly common for children with DS. Research suggests that PBWSTT for as little as 8 minutes 5 days per week facilitates earlier onset of independent walking in children with DS.7 Despite the effectiveness of PBWSTT to accelerate the development of independent walking in this population,7,8 children with DS continue to demonstrate stereotypical gait deviations, illustrating the need for interventions to address their musculoskeletal impairments.
The use of orthoses to correct abnormal alignment and provide external support to joints is a widely accepted practice in physical therapy and is commonly used to address musculoskeletal abnormalities and prevent the development of secondary complications. Among the most common conditions affecting individuals with DS are pes planus (flat foot deformity) and hypotonicity.9 Characteristic gait deviations that develop as a result of these conditions include increased gait variability, out-toeing, flat foot at initial contact, a wider base of support, and poor foot control.10 Because orthoses provide a biomechanical correction to the foot and therefore to the forces passing through the foot, many people believe that orthoses will help improve gait parameters in children with DS. Studies show that children with DS between the ages of 3 and 8 years do show changes in their gait parameters when wearing a custom made foot orthoses (FOs) as well as improvements to their functional balance when wearing Surestep SMOs (South Bend, IN).3,11 However, others believe that orthoses limit the child's ability to develop upright locomotor skills. Newer evidence on orthotic use in children with DS who are not yet walking suggests that limiting movement around the ankle during the development of standing and walking may reduce the child's ability to control the ankle joint independently.12 Despite the prevalence of orthotic prescription to correct and support hypermobile joints in children with DS, current research concerning the use of orthotic devices in this population is limited. The questions of “when? why? and for how long?” are not fully answered and may be more complex than we thought.
Two of the most commonly prescribed orthoses for children with DS include FOs, which provide support to the plantar surface of the foot, and supramalleolar orthoses (SMOs), which support the foot and ankle above the malleoli.3,11,12 Both types of orthoses not only provide support but also help direct and redistribute forces caused by the interaction of the ground with the foot. Current literature provides evidence that both FOs and SMOs improve standing posture, gait, and functional mobility11–15; however, the available research fails to distinguish which is more effective or to provide a clear understanding of when FO or SMO prescription is indicated.
Foot orthoses have been shown to produce immediate effects on posture and gait in children with DS by facilitating foot control without inhibiting the ankle's normal range of motion.11 Selby-Silverstein and colleagues11 demonstrated an immediate reduction in abnormal eversion and foot pronation in standing with custom made FOs in children with DS. They also measured decreased variability in foot angle, pronation-supination index, foot length contact, and walking speed during ambulation with FOs.11 Several other case studies further suggest FOs improve the performance of functional activities,14 balance, and locomotion15 in children with hypermobility.
Alternatively, SMOs provide support at the ankle and are proposed to have greater effects in controlling abnormal gait mechanics than FOs.13 As with FOs, there is evidence to suggest SMOs improve functional mobility in children with DS.3 In a study by Martin,3 children with DS demonstrated significant improvement in walking, running, and jumping immediately after donning SureStep SMOs and maintained functional improvements after 7 weeks of use. Conversely, some critics believe SMOs limit ankle mobility and reduce variability in experience, which may impair a child's motor learning.16
Despite the efficacy of both PBWSTT and SMOs in improving the gait of children with DS, recent research suggests the combination of these interventions may not improve overall gross motor development if initiated too early.16 Looper and Ulrich16 demonstrated a moderate effect on the rate of walking development in infants with DS by combining SureStep SMOs with treadmill training. Results showed that infants with SMOs developed independent ambulation slightly faster than those without orthoses; however, infants who received PBWSTT and no orthoses demonstrated greater proficiency in performing functional tasks such as walking, running, and jumping than infants who received both PBWSTT and SMOs. Looper and Ulrich16 suggest that early intervention with orthoses during the period of walking development may limit the child's ability for exploratory learning and thus slow the development of several gross motor tasks.
The development of walking and subsequently more challenging motor tasks is a complex process involving both the child's specific characteristics and the process of experiential motor learning. In children with DS, musculoskeletal impairments alter the normal trajectory of motor development and lead to deviations in gait as well as developmental delays.2,4,9,17 Application of orthoses too early in the developmental process may result in deleterious effects;15,16 however, the use of FOs and SMOs in children with DS who are ambulatory may improve their motor function. As demonstrated by previous research, altering the physical characteristics of children with DS through orthoses can have a tremendous effect on motor skill development. To facilitate motor development and prevent the stifling of variability needed for motor learning, it is important to choose interventions specific to the child's individual needs. Although orthoses are frequently prescribed for children with DS, no available evidence exists to determine what type of orthoses will be most beneficial for a particular child with DS. Several studies suggest the importance of performing individual gait assessment in children with DS for treatment planning; however, no algorithms exist to aid clinicians in decisions concerning orthotic use.
This study was conducted with 2 primary objectives: (1) to compare the effects of FOs and SMOs on the gait parameters of children with DS, and (2) to develop specific criteria using anthropometric and biomechanical measures for the use of FOs and SMOs in children with DS.
This study was approved by the Institutional Review Board at the University of Puget Sound, and all subjects' guardians signed informed consent forms prior to data collection. The sample included 6 children with DS aged 4 to 7 years. Participants were recruited through convenience sampling from the Tacoma-Seattle region with flyers and by word of mouth. Inclusion criteria were male or female children with DS between the ages of 3 and 10 years with an ability to walk at least 50 feet at one time independently or with an assistive device. Participants were required to have at least 6 months of walking experience and the ability to follow simple verbal instructions. Exclusion criteria included a history of uncorrected visual and inner-ear impairments or lower extremity orthopedic surgical corrections.
This study used a 1-way repeated measures design, in which participants served as their own control. Each child participated in a single testing session that lasted approximately 1 hour and included obtaining anthropometric and biomechanical measurements in addition to gait parameter analysis on a GAITRite system (Sparta, NJ).
The gait parameters of each participant were assessed under the conditions of barefoot, shoes with FOs, and shoes with SMOs. The order of testing for each condition was determined randomly by drawing from a hat. Participants completed multiple walking trials under each condition until 3 successful trials were obtained. Successful trials were defined as the participant taking at least 3 consecutive steps while walking. Trials in which participants ran or jumped were excluded. Participants were given verbal encouragement by the researchers and the participants' parents throughout data collection as a means of motivation. The gait parameters assessed included step width, step length, cadence, velocity, single-leg support time, double-leg support time, cycle time, stride length, heel-to-heel base of support, and toe-in/toe-out.
Anthropometric and biomechanical data were collected by the same 3 researchers for each participant. Anthropometric measurements included height (while standing against a wall), weight, leg length (in standing from the greater trochanter to the floor), and hypermobility using the 9-point Beighton scale (Table 1). Each task on the Beighton scale was scored bilaterally, with either a 0 (unable to complete) or a 1 (able to complete), with a higher total score representing greater hypermobility. Biomechanical measurements consisted of calcaneal eversion, tibial torsion, and navicular drop. Calcaneal eversion was measured in relaxed standing as the angle between the lines that bisected the shank and calcaneus. This is a reliable measurement in children and adults.18 Tibial torsion was measured in prone with the knee flexed to 90° and the ankle at 90°. To determine tibial torsion, the angle between the line of the longitudinal axis of the thigh and the line perpendicular to the axis that connected the most prominent portions of the medial and lateral malleolus was measured.19 This measure has moderate validity and good reliability in children with cerebral palsy.20 Navicular drop was measured by taking the difference between the height of the navicular tuberosity and the floor in a subtalar neutral position and in a relaxed foot position. The literature shows that this measure has moderate to good reliability.21–23 Navicular drop was not collected on subject 6 due to subject refusal. Intrarater reliability for each measurement except weight was established using an intraclass correlation coefficient (ICC [3,1]) prior to data collection in a small sample of children who were TD. Reliability was found to be 0.83 for calcaneal eversion, 0.88 for hypermobility, 0.89 for tibial torsion, 0.91 for navicular drop, 0.99 for leg length, and 1.00 for height
The orthoses used in this study were unmodified Cricket FO and Leap Frog SMO, which were provided by Cascade DAFO, Inc (Ferndale, WA). These orthoses were chosen because they are designed for children with low tone, pronation, arch collapse, heel eversion, and forefoot abduction. Prior to data collection, participants were fitted for the appropriate size orthoses by their school physical therapists using the Cascade sizing jig. On the day of data collection, the lead investigator rechecked the fit of the device, making sure that the calcaneus sat in the heel cup and that the medial arch of the device ended at the base of the first metatarsal head. In cases where the fit was incorrect, the correct size was given to the patient to use during data collection. Each participant received either the Cricket or Leap Frog orthoses following data analysis, based on their individual performance in each condition. They received the orthoses that led to the greatest improvements in the most gait parameters measured.
GAITRite Gait Analysis System
The GAITRite system consists of a 16-foot mat containing 12 sensor pads with a total of 18 432 pressure-activated sensors placed on 0.5-inch centers. Data are collected at 120 hz. The mat is connected to a personal computer, which collects the spatial and temporal gait parameters of the participant while walking over the sensors. The reliability of the GAITRite system for measuring these parameters has been established by Paterson and colleagues.24
Statistical analysis was done using SPSS version 17.0 (Chicago, IL). Statistical significance was set at α = .05 for all tests. One-way repeated measures analyses of variance were conducted on the gait parameter data to compare the effects of walking barefoot, with FOs or with SMOs, where appropriate post hoc comparisons were performed using Bonferroni corrections.
To determine the relationship between gait parameters and subject characteristics, correlations were run for each condition on all 6 subjects. Pearson Product Moment Correlations were conducted to determine the relationship between gait parameters and height, weight, leg length, tibial torsion, navicular drop, and calcaneal eversion. A Spearman rank correlation coefficient was calculated to determine the relationship between gait parameters and the hypermobility score because the hypermobility score yields ordinal data. Correlations of 0 to 0.25, 0.25 to 0.5, 0.5 to 0.75, and greater than 0.75 were considered small, fair, moderate, and strong, respectively.25
Anthropometric and biomechanical data for each subject can be found in Table 2. The average number of steps per trial was 8 steps (±2.4). The descriptive statistics for the gait parameters in each condition can be found in Table 3. One-way repeated measures analyses of variance showed significant differences between conditions for cadence (P = .002) and cycle time (P = .001). Post hoc analysis showed that children displayed a significantly decreased cadence while wearing SMOs when compared with barefoot (P = .04) (Figure 1). There was also a significantly greater cycle time while wearing SMOs than while wearing FOs (P = .05) and barefoot (P = .03) (Figure 2). No significant differences were found among barefoot, FOs, and SMOs in mean step length, stride length, heel-to-heel base of support, single support time, or velocity.
In the SMO condition, correlations coefficients revealed several statistically significant relationships. Strong correlations were found between height and cycle time (r = 0.81, P = .05) as well as height and single support time (r = 0.93, P = .006). Single support time showed strong correlations with leg length (r = 0.82, P = .047) and weight (r = 0.92, P = .009). In addition, hypermobility showed a strong correlation with cadence (r = −0.94, P = .005), cycle time (r = 0.94, P = .005), and single support time (r = 0.96, P = .003).
Significant correlations were also found in the FO condition. Height was strongly correlated to single support time (r = 0.85, P = .033) and hypermobility was strongly correlated to cadence (r = −0.82, P = .046), cycle time (r = 0.82 P = .046), single support time (r = 0.82, P = .046).
In the barefoot condition, the only significant correlation found was a strong correlation between hypermobility and single support time (r = 0.82, P = .046). All other correlations for the barefoot, FO, and SMO conditions were not significant. All of these correlations were positive (as one variable increased, the other also increased) except for the hypermobility correlation with cadence. In these cases, as hypermobility increased, cadence decreased.
On the basis of gait analysis, FOs were recommended for 3 children. SMOs were recommended for 2 children. One child showed the best gait pattern without orthoses.
The purpose of this study was to compare the effects of FOs and SMOs on gait parameters in children with DS and to develop specific criteria using anthropometric and biomechanical measures for the use of FOs and SMOs in this population. It was originally hypothesized that both FOs and SMOs would produce differences in an individual's gait parameters when compared with barefoot gait. It was further hypothesized that some participants would demonstrate improved gait while wearing FOs and others while wearing SMOs, which would allow closer assessment of anthropometric and biomechanical data to create criteria for orthotic prescription. The results of this study, however, were somewhat surprising.
Data analysis revealed no significant difference among barefoot, FO, and SMO conditions for a majority of the gait parameters examined. However, there was a statistically significant difference between barefoot and SMOs for both cadence and cycle time and between FOs and SMOs for cycle time: cadence decreased with SMO use (P = .04) and cycle time increased with SMO use (P = .03 when compared with barefoot and P = .05 when compared with FOs). Cadence, or steps per minute, is inversely related to cycle time; as cadence increases cycle time decreases. As this relationship is demonstrated in our data, discussion of the effect of FOs and SMOs on these gait parameters can be considered together. When comparing SMOs with the barefoot and FO conditions, participants in this study demonstrated decreased cadence and increased cycle time, indicating that, on average, participants took fewer steps when wearing SMOs. Whereas SMOs are used to increase stability at the foot and ankle, in the short term they appear to destabilize the gait cycle, as each stride takes longer to complete. This is not to say that a SMO is never the right option for a child with DS, but rather that providing more support than a child needs may be detrimental to the gait cycle.
Many clinicians presume that SMOs provide greater support to the ankle than FOs and are necessary to control the overpronation in children with DS.13 However, it has been suggested that SMOs limit ankle mobility, leading to deviations in gait and limitations in functional mobility.16 Looper and Ulrich16 demonstrated in a group of 22 infants with DS that the use of SMOs in combination with PBWSTT resulted in an overall reduction in gross motor function development compared with controls who received SMOs after acquiring independent walking ability. The researchers proposed that by limiting the children's ankle mobility, SMOs may have reduced the variability in their experience, limiting their ability to problem solve and acquire motor skills and making tasks such as crawling and kneeling more difficult.16 In line with this reasoning, our data suggest that the support provided by SMOs may be too great for some individuals with DS and may have deleterious effects on their gait patterns.
There was no statistical difference between the FO and barefoot conditions relative to cadence and cycle time in our participants. It may be that the FOs provided the necessary foot control but did not disrupt the gait cycle as the SMOs did. Research shows that children with DS have increased variability in gait patterns and that FOs reduce this variability,11 suggesting increased control of the gait pattern. Selby-Silverstein and colleagues11 demonstrated an immediate reduction in variability in foot angle, pronation-supination index, foot length contact, and walking speed during ambulation with FOs. Future research should examine the relationship between foot control and cadence in children with DS to better understand the relationship between these variables.
The findings of this study did not demonstrate a clear division between participants who benefited from FOs and those who benefited from SMOs as was previously hypothesized. However, data analysis revealed significant relationships between the tested gait parameters and height, weight, leg length, and hypermobility under multiple conditions. In fact, hypermobility strongly correlated to multiple gait parameters across all 3 conditions. Traditionally, physical therapists have focused on the use of biomechanical measures such as calcaneal eversion to determine the need for orthotic prescription. The effects of orthoses on eversion, overpronation, and tibial rotation have also been the focal point for much of the research on orthotic use in children with DS and hyperpronation.11,15,26 However, a study by Whitford and colleagues26 demonstrated that clinical measures of overpronation (navicular drop) and calcaneal eversion were not related to motor proficiency, pain, or exercise efficiency. Although the study by Whitford and colleagues26 was performed on children who were TD and without significant ligamentous laxity or hypotonicity, their findings call into question the relevance of prescribing orthoses, based on measures such as arch height and calcaneal eversion. Likewise, the data from this study demonstrate greater correlation between anthropometric measures of height, hypermobility, and leg length with gait parameters than measures of navicular drop, calcaneal eversion, and tibial torsion. Intuitively, one can assume that certain anthropometric characteristics will be associated with specific gait characteristics. For example, it can be reasonably assumed leg length will be strongly correlated with step length. However, the strength of the correlations between these anthropometric factors and gait parameters, as well as the lack of significant correlations with biomechanical measures and gait parameters warrant further investigation into relevant clinical measurements for orthotic prescription. As in the study by Whitford and colleagues,26 the lack of significant correlations with biomechanical data in this study may suggest that these data are not the most appropriate to consider in orthotic prescription.
Several moderate to strong correlations were found between hypermobility and gait parameters including cadence, cycle time, heel-to-heel base of support, and double support time. Hypermobility was negatively correlated with cadence, while positively correlated with the remaining gait parameters. The negative relationship between hypermobility scores and cadence suggests that greater degrees of joint laxity result in fewer steps per minute. To explore the influence of joint laxity on SMO treatment effect, Martin3 used range of motion measurements at multiple joints to assess hypermobility in a group of 17 children with DS. Martin3 classified subjects in her study into either a more lax or less lax group and found that participants in the more lax group scored lower on all balance and functional outcomes, but demonstrated benefit from SMO use equal to participants in the less lax group. Similar to Martin,3 our data suggest hypermobility has an influence on functional tasks such as walking; however, it remains unclear whether or not the degree of hypermobility should play a role in orthotic prescription.
This pilot study had several limitations and the results should be interpreted cautiously. This study had a very small sample size and thus low statistical power in addition to limited generalizability. This means that differences that may be apparent in a larger sample may not have reached statistical significance in this study. Participants were also recruited through convenience sampling and thus are not representative of a random sample of children with DS. Behavioral issues from participants also made biomechanical measurements difficult to obtain, whereas anthropometric data were quicker and easier to gather due to increased compliance from participants. Because of time and behavioral constraints of the participants, we were unable to allow an accommodation period for each type of orthosis, which may have resulted in abnormal gait patterns as the participants were still getting used to them. Finally, these results represent immediate effects of Cricket DAFO FOs and Leap Frog DAFO SMOs on walking and do not take into account long-term changes in temporal spatial gait parameters.
The difference in the effects of FOs and SMOs on the gait of children with DS, as well as the method for choosing one orthosis over the other remains unclear. Future research should look closely at the ability to use hypermobililty, weight, and height to predict orthotic prescription in children with DS. Future studies should also be appropriately powered and provide a period for the children to accommodate to the orthoses. In addition, it would be beneficial to compare the long-term effects of FOs and SMOs on the gait of children with DS.
Leap Frog SMOs appear to lead to a decrease in cadence and an increase in cycle time when compared with barefoot walking but do not lead to a change in velocity. The Cricket FOs also seem to improve cycle time over the Leap Frog SMOs. In addition, weight, height, leg length and hypermobility appear to be the most promising measures when considering orthotic intervention. Clinicians should use caution when relying on measures of features such as navicular drop, calcaneal eversion, and tibial torsion when recommending orthoses to improve gait in children with DS because these measures do not seem to correlate to gait parameters. Until criteria are developed to assist clinicians in choosing either FOs or SMOs for a patient with DS, therapists should perform individual gait assessment and try both types of orthoses before prescribing them.
The authors thank the children and families who took time out of their busy schedules to participate in this study. The authors also like to thank the physical therapists in the Edmonds Washington School District who generously gave us their time and allowed us to use their space.
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biomechanics; body measures; child; Down syndrome; gait; lower extremity; orthoses© 2012 Lippincott Williams & Wilkins, Inc.