Although there are varying and invalidated criteria for grading and diagnosing hypotonia, the hypotonic syndrome has been characterized in a survey of physical therapists and occupational therapists by decreased strength, decreased activity tolerance, delayed motor skill development, rounded shoulder posture, leaning on supports, hypermobile joints, and increased flexibility.1,2 Hypotonia may be associated with many different conditions, including those of neuromuscular, genetic, central nervous system, connective tissue, and/or metabolic origins.1 Down syndrome (DS) is arguably the most common condition associated with hypotonia.
The estimated incidence of DS worldwide is 1 in 1000 live births.3 Hypotonia and ligamentous laxity are often associated with DS; however, these characteristics are also known components of several other disorders, including Prader Willi and other developmental syndromes. Both hypotonia and ligamentous laxity may lead to lower extremity malalignment and orthopedic issues up the kinetic chain. Lauteslager et al4 have suggested that joint instability, contributing to nonoptimal musculoskeletal alignment, is influenced not only by joint laxity but also by decreased postural tone and insufficient cocontraction around a joint.
Hypotonia and ligamentous laxity are seen in children with DS and other developmental syndromes. As a result, the foot and ankle complex of these children may be predisposed to a biomechanical disadvantage. This disadvantage may reflect inadequate stability and thus negatively affect postural control. Furthermore, bony alignment may be abnormal when compared with children who are developing typically. Abnormal pull of foot and ankle musculature on the maturing bony structure may lead to abnormal positioning and loading of the foot and ankle, possibly having a detrimental effect over time on the growth and remodeling of bone.5
The use of foot orthoses (FOs) and supramalleolar orthoses (SMOs) as an intervention to promote stability and functional mobility in children with hypotonia is the current standard of care. Mulvey et al6 have suggested that children with DS struggle to achieve sufficient joint stability in the lower extremities because of hypotonia and ligamentous laxity. They also theorized that the common delay in independent walking might be due to the child waiting until a higher level of stability and motor control develops. Children with hypotonia may also demonstrate difficulty exploring their environment secondary to poor postural control and balance. The use of orthoses may help to provide the additional stability necessary to allow a child to get on her feet and more effectively explore the environment and thus enhance overall development.
The use of FOs and SMOs has become the standard of care for many children with hypotonia, yet many questions remain about the efficacy of this intervention for this population. Thus, the purpose of this study was to systematically review the literature on the efficacy of orthotic use for children with hypotonia and to provide a concise summary of the state of the evidence in this area.
We independently completed a literature search using 5 databases and search engines between January 2012 and February 2012 (Table 1). Fifteen individual search terms were used alone and in combination to capture a broad range of articles. The search focused on articles addressing children with hypotonia or DS, orthotic use, and physical therapy (PT). The search was updated in May 2012 and again in September 2012 using the same search terms.
Articles were initially included by title relevance, then screened by abstract, and finally full-text analysis (Figure 1). Each author independently evaluated each full-text article to determine final inclusion.
Inclusion criteria for articles included participants who were children from birth to 21 years of age with hypotonia and/or DS. Impairments such as flexible flat feet and hyperpronation were excluded unless explicit acknowledgement of hypotonia or low muscle tone was also included. The intervention of interest was the use of orthoses. Simultaneous intervention with PT was neither an inclusion nor an exclusion criterion. Articles were excluded if the article was not peer-reviewed, was solely an abstract, did not include children with hypotonia as participants, did not examine the efficacy of orthoses as the intervention, or was not accessible in English.
Once the final collection of articles was chosen, the articles were then graded according to the level of evidence on the basis of the American Academy for Cerebral Palsy and Developmental Medicine (AACPDM)7 guidelines for randomized controlled trials and single and group design studies (Table 2). The AACPDM rating system has been shown to have acceptable interrater reliability.15 Case studies were graded using a scale we developed by adapting Atkins and Sampson16 single case study guidelines (Table 3). Each author initially performed an independent grading of articles. If we did not agree on a grade for an article, we discussed the grading to see whether a consensus could be reached. If a consensus was not reached, a third independent reader was used. Articles were included regardless of the AACPDM score or the level of evidence.
The search strategy resulted in a total of 10 articles that met the criteria for this review. No level I evidence was found that met inclusion criteria during this search. Three level II articles, 5 level IV articles, and 2 level V articles were identified and included in this analysis (Table 4).
Of the 10 articles reviewed, 5 articles concerned FOs only,12–14,17,18 4 addressed SMOs only,5,8,9,11 and 1 compared FOs and SMOs.10 In all studies, participants ranged in age from 18 months to 10 years. Data on PT or other structured physical activity were presented in 5 studies.8,9,12,17,18 Five studies5,10,11,13,14 did not include any additional activity beyond what the child was already doing before the study. The International Classification of Functioning, Disability and Health (ICF)19 body structure and function component12,14,17 was assessed in 3 studies, and outcomes for the ICF activity component were included in all 10 studies. The authors of 1 study attempted to correlate body structure measures (barefoot) to an activity component outcome when subjects used orthoses.10
We examined titles and abstracts for exclusion with an agreement kappa of 100% (κ = 1). When grading group studies, we had good overall agreement (Cronbach α = 0.96; Pearson r = 0.9264; 95% confidence interval = 0.639-0.986). The 2 case studies were not included in the Cronbach α and Pearson calculations because of limited data, nor were they included with the group studies calculations because the grading criteria for these reports were different. Within the group and case studies, the kappa values of each individual question of the grading rubric were calculated. These calculations show that overall the questions were consistent within each rater, but when a disagreement did occur, the kappa value was very low because of the small data pool. Furthermore, the statistics showed that the AACPDM grading rubric used had good internal consistency and was valid (Table 5).
The 10 included studies are summarized in Table 4. They are reported here according to the ICF framework.
Foot Orthoses and ICF Body Structure and Function Component
An FO intervention was used in the 3 studies with an ICF body structure and function outcome measure.12,14,17 The body structure outcome measures included the arch index12 and visual analysis of static standing alignment.14,17 The studies had a total of 52 participants (30 experimental and 22 control) with DS, developmental delay (DD), autism, or Prader Willi syndrome with ages ranging from 18 months to 6 years. Although Looper et al10 included an FO and body structure measures in the study, the anthropomorphic and biomechanical measures were used to examine correlations and not as outcome measures.
Supramalleolar Orthoses and ICF Body Structure and Function Component
The effect of an SMO intervention on body structure and function was not investigated in any of the studies reviewed.
Foot Orthoses and ICF Activity Component
Intervention with an FO was the focus of 6 studies that reported activity outcomes. One presented level II evidence,12 3 provided level IV evidence,10,13,14 and 2 studies included level V evidence.17,18 The studies had a total of 84 (62 experimental and 22 control) participants with DS, DD, and lower extremity hypotonia, or flexible flat feet ranging from 18 months to 7 years. Various editions and sections of the Peabody Developmental Motor Scales (PDMS) were used in 3 studies.13,17,18 However, instrumented gait analysis techniques were used in 3 studies.10,12,14 Bilateral custom-made FOs were examined in 3 studies14,17,18 and off-the-shelf FOs were studied in the other 3 reports.10,12,13 George and Elchert18 also included PT in the intervention, focusing on strength, upright balance, proprioceptive feedback, core stability, and functional mobility, whereas Ross and Shore12 included “gross motor therapy” as a part of their intervention. Looper et al10 used both SMOs and FOs and compared their effects on gait characteristics.
Supramalleolar Orthoses and ICF Activity Component
Supramalleolar orthoses were investigated in 5 studies5,8–11: 2 were level II8,9 and 3 were level IV5,10,11 evidence articles in the activity component category. These studies included a total of 31 participants ranging in age from 19 months to 7 years. Two of the studies included treadmill training as an additional intervention.8,9
In this systematic review, 10 studies were found that investigated the use and efficacy of FOs and SMOs for children with hypotonia and that met the specific inclusion/exclusion criteria. However, no level I evidence was found, and the overall quality of the evidence was poor because of small sample sizes, lack of randomization or a control group, lack of blinding of assessors, and lack of power analyses.
ICF Body Structure and Function Component
The effects of an FO intervention on outcomes representing the ICF component of body function and structure were reported in 3 studies.12,14,17 Generally, the conclusion of the authors of these studies indicated that the addition of FOs modified the structural alignment of the foot and arch, specifically providing more stable foot alignment, and, therefore, body alignment. The authors of all 3 of these studies recommended the use of FOs for their participants; however, Selby-Silverstein et al14 suggested that additional PT interventions aimed at (1) strengthening lower extremity musculature to improve push-off and augment support of the knee, (2) heel cord stretching, and (3) dynamic balance activities should be provided as an adjunct to the FOs.
Ross and Shore12 concluded that the addition of orthoses modified the dimension of the arch index, thus contributing to future joint protection and prevention of damage. However, this conclusion was based on an outcome measurement (arch index) that has not been validated or correlated to function representing the ICF activity component, and the researchers did not report inter- or intrarater reliability. Buccieri17 also concluded that FOs improved foot alignment in her case report, but this was based on a subjective analysis of static standing alignment using visual appearance and palpation. Thus, the reported outcomes do not have strong support. Furthermore, these outcome measures do not address the potential harmful effects on foot structure of using or not using an orthosis. Examination of possible harmful effects on foot structure would enhance future orthotic studies.
Both group studies12,14 had a control group, but this fact did not strengthen the conclusions about orthotic efficacy. Although Selby-Silverstein et al14 used a control group of children who were developing typically, they did not discuss any comparisons to the experimental group. Ross and Shore's12 control group received the same interventions as the experimental group, but both groups received gross motor therapy and an orthosis-only condition was not examined, thus limiting the credibility of the author's conclusion that the FOs enhanced the development of a medial longitudinal arch.
For the ICF body function and structure component, the evidence suggested that FOs were effective; however, the quality of the evidence is poor. Sample sizes were small, and the reliability and validity of key dependent measures (arch index, visual inspection) was not reported. Thus, all 3 of these studies have limited generalizability and applicability.
ICF Activity Component
All 10 studies included outcome measures of the ICF activity component. Overall, evidence for the ICF activity component is mixed with 7 studies concluding that orthoses may be beneficial for the gross motor development of children with hypotonia.5,11–14,17,18 The authors of 3 of the studies suggested that orthoses might be detrimental to the rate of gross motor development.8–10 However, these authors do not dismiss the value of orthoses, but rather question when to introduce them for the population of children with hypotonia, and they suggest waiting until after the acquisition of independent walking.
The authors of the studies with outcome measures reflecting the ICF activity component using an FO intervention concluded that these orthoses might be beneficial.10,12–14,17,18 However, all of these studies have some major limitations; thus, the results of these studies must be considered with caution. Three of the 6 studies included the confounding intervention of additional therapy focusing on motor development and functional mobility.12,17,18 Two of the studies were level V case reports,17,18 and most group studies12–14 lacked a meaningful control comparison.
Using parts of the original PDMS17 or its second edition,13,18 the results of 3 studies indicated an increase in raw scores and reported that the children progressed and sometimes met age-equivalent norms. Although Pitetti and Wondra13 found that FOs improved motor capabilities for all participants, they found that children with DD improved more than children with DS. Although not based on the data from the study, the authors theorized that children with DS might benefit from a more supportive orthosis such as an SMO rather than an FO.
Three studies used various forms of gait analysis as an outcome measure. Authors of 2 studies10,12 were unable to find significant changes in most gait parameters using the GAITRite™ system (CIR Systems, Inc, Sparta, NJ). Ross and Shore12 did note, however, that both the experimental and control groups moved closer to age-appropriate norms. The results of the study by Selby-Silverstein et al14 showed decreased variability in gait parameters using 3-dimensional video analysis and pressure mapping. As their participant populations were different, the comparison of the results of these studies is challenging. Ross and Shore12 studied children with DD and flexible flat feet, whereas the authors of the other 2 studies10,14 included children with DS.
Drawing a conclusion about the effect of FOs on the ICF activity component outcomes given the current state of the evidence is risky at best. Although some studies seem to support the benefit of FOs for this population, others have failed to confirm those results and serious methodological flaws exist in all of the studies. However, no adverse events were reported in any of the studies, thus the use of FOs with children with hypotonia might be considered as a reasonable part of the overall plan of care.
An SMO intervention with an ICF activity component outcome measure, and children with DS as the participants, was used in 5 studies.5,8–11 Studies by Tamminga et al5 Looper et al,10 and Martin11 included only an orthotic intervention, but the studies by Looper and Ulrich8,9 also used treadmill training. The same type of SMO8,9,11 (SureStep, Midwest Orthotic and Technology Center, Inc, South Bend, IN) was used in 3 studies, whereas Tamminga et al5 compared 2 types of SMOs and Looper et al10 compared an SMO to an FO, both off-the-shelf designs. As with the FO studies, all of these studies had limitations that affect the generalizability and validity of the conclusions.
We only found 2 studies5,10 in which the authors attempted to compare different orthoses to identify which orthosis produced better results. In both of these studies, the authors seemed to assume that orthoses were indeed beneficial, but that not all types of orthoses were equally effective. Tamminga et al5 were the only authors to use a single subject design and the only ones to compare 2 types of SMOs (SureStep SMO vs DAFO #4 [Cascade DAFO, Inc, Ferndale, WA]). On the basis of their results, these authors suggest that children with DS may indeed benefit from SMOs, but a more flexible and less restrictive design may be preferred. However, this study only included 2 participants and 1 child refused to wear the more restrictive design, and thus the results must be interpreted cautiously.
The authors of the SureStep SMO studies with children with DS had varying conclusions. Martin11 concluded that these SMOs contributed to improved postural stability, with some immediate improvement upon initial fitting of the orthoses and even greater improvement after 6 weeks of use. Looper and Ulrich's8,9 data initially showed earlier acquisition of walking for children with DS in the experimental SMO group, but further analysis of the data showed that the control group had more variety in skill acquisition. These results led Looper and Ulrich8,9 not only to conclude that SMOs were likely beneficial but also to question when to initiate the use of SMOs for children with hypotonia. Their concern was that the SureStep SMO constrained the child's ability to explore movement strategies and that this could be detrimental during the time the child was learning to walk.
A topic presented by both Martin11 and Looper et al10 is the consideration of joint laxity and the effectiveness of orthoses. These authors posed the question whether or not joint laxity should be a consideration in orthotic prescription. Martin11 found that even though the more lax group in her study overall had lower scores on measures of gross motor function, the degree of joint laxity was not a factor in the participants' response to the SMOs. Looper et al10 suggested that the degree of laxity might indeed matter. Looper et al10 stated about both Martin's11 and her own work, “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.”10(p.318) Both authors bring to light a topic of future research that may affect orthotic prescription.
Within the studies that reflect the ICF activity component outcomes for SMOs, again, evidence is at a low level. Looper and Ulrich's8,9 level II studies are the highest ranked. However, just as in Martin11 and Tamminga et al,5 the studies by Looper and colleagues8–10 had small sample sizes. Furthermore, Looper8,9 used the same cohort in both studies. The small sample sizes do not allow for the generalization of findings. Looper and Ulrich8 reported a moderate effect size, otherwise no power analyses were reported in these studies.
The authors of these studies not only suggest some benefits of SMOs for children with DS but also seem to contradict each other. The differences may be in how authors interpreted the respective data from varying theoretical perspectives. Martin11 and Tamminga et al5 suggest that providing improved stability and biomechanics via orthoses allows motor development to progress. Tamminga et al5 suggested that orthoses created the circumstances for the participants to develop the motor skills that allowed them to perform better even after orthotic intervention was discontinued. They theorized that from the dynamical systems and biomechanical perspectives, the orthoses might have provided the right environment to allow the children to practice and develop their gross motor skills. In contrast, Looper and Ulrich8,9 suggested that early use of orthoses might limit the exploration of movement patterns and thus slow down motor development, at least initially. Looper and Ulrich8,9 suggested waiting to implement orthoses until after the child achieved independent ambulation. After independent ambulation has been achieved, all authors seem to agree that orthoses have a beneficial effect on gross motor skills. The researchers' perspective is an important factor to consider when analyzing their conclusions.
Correction of biomechanical alignment has been the predominant theoretical framework used to make orthotic decisions for children with hypotonia, but Looper and colleagues8–10 have been the first researchers to question this and apply a motor-learning framework instead. The key question seems to be whether the stability provided by orthoses is beneficial and allows new motor skill to emerge, or do orthoses restrict variability and exploration, thereby limiting the acquisition of new skills? Vereijken20 has stated that intervention for children with developmental disorders should be focused on increasing the variability of their repertoire of movement so that they can explore more possible solutions. However, she also notes that variability can be “both a curse and a blessing, depending on one's ability to control it.”20(p.1857) In the context of orthotic intervention, the question becomes this: do orthoses help a child control excessive variability or unnecessarily limit it? The evidence to date on orthotic intervention for children with hypotonia is insufficient to answer this important question.
Comparing FOs With SMOs
When comparing FOs with SMOs, several authors have come to varying conclusions. Although not a conclusion of their study, Pitetti and Wondra13 theorized that children with DS might have benefited more from an orthosis that was more supportive than an FO, and several other studies provide preliminary evidence to support this hypothesis.5,11 However, this conflicts with the conclusions of Looper et al8–9 who suggested that the support provided by SMOs may have a deleterious effect on exploration of resources while developing the motor pattern for gait. All of the studies5,11 supporting SMO use were level IV evidence, whereas Looper and Ulrich's8,9 studies were level II and Looper et al10 was level IV. Of all the group studies, Looper et al's8–10 studies had the smallest sample sizes and their conclusions based on motor-learning theory may not be shared by researchers using a biomechanical framework. Looper et al10 were the first to attempt to correlate body structure measures to orthotic outcomes in an attempt to help clinicians decide between an FO and an SMO. Their pilot data seemed to suggest that anthropomorphic data and degree of joint laxity might be more relevant than biomechanical data; however, their sample size was too small to present any definitive recommendations. In summary, the main question of which type of orthosis is most effective for children with hypotonia and/or DS is still unanswered.
Strength/Weakness of the Evidence
Of the 10 articles reviewed, there were no level I evidence studies, and only 3 studies were level II evidence. Looper and Ulrich's8,9 reports both presented level II evidence; however, the AACPDM quality scores for these 2 articles are 5 and 4 out of 7, respectively. These scores indicate the moderate quality of the studies. The study by Ross and Shore12 was rated level II evidence, with a quality score of 4. The 7 additional studies in this systematic review were rated level IV or level V evidence. Traditionally, level IV and V studies are not rated by the AACPDM rubric. Because so few high-quality studies have been published, we chose to give these studies scores for the sake of comparison (Tables 1 and 2).
In an effort to promote higher-level evidence in this area, detailed methods that allow replication of studies are of utmost importance. The methods of 3 studies8,9,12 were described in enough detail to replicate the study. However, difficulty may arise from the outcome measures used in the studies. For example, coding video, although well described by Looper and Ulrich,9 might prove to be difficult to replicate with regard to error of measurement and analysis. Furthermore, Ross and Shore's12 measurement of the arch index has not been validated and the researchers' interrater reliability was not reported. Thus, additional attempts to use these same measures may lead to varying results.
A possible strength and simultaneous weakness of the current literature is that authors used varying theoretical frameworks and philosophies. For example, Looper and Ulrich's study9 on the use of upper extremity support in standing with and without orthoses may be considered from a different perspectives: the control group relied more on their trunks in standing play and used less upper extremity propping, whereas the experimental group (SMO + treadmill) did not lean as much as the control group but used more hand support. The goal of intervention—trunk control (not leaning on surface) or manual exploration (having hands free to explore)—may vary. These differences help stimulate discussion and research.
The current standard of practice related to prescribing orthoses for children with hypotonia is to provide either FOs or SMOs at the onset of standing activities, in addition to ongoing PT. Because this is the standard of care for children with DS and hypotonia, further research will likely continue to be rated as lower level evidence because institutional review boards might be reluctant to approve a study that withholds the standard of care to obtain an appropriate control group. However, research in this area can and should continue. Key questions remain unanswered: When is the optimal time to introduce orthoses? Which is better: FO or SMO? What is the optimal intervention: orthoses only or in combination with PT?
This study reviewed the state of the evidence regarding the use of orthoses for children with hypotonia. As the topic of enhancing the quality of life and participation of children has rightfully become a central focus of intervention, the treatment of painful feet in patients with DS and hypotonia is imperative because foot pain leads to relative immobilization. Therefore, early recognition and treatment of the orthopedic problems associated with hypotonia can make the difference in overall function and quality of life.21
We thank Dr Clyde Killian and Dr Margaret Finley at the Krannert School of Physical Therapy for their assistance with the reliability analysis. Their insight and expertise was greatly appreciated.