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Pediatric Physical Therapy:
doi: 10.1097/PEP.0b013e318181fb34
Research Report

Efficacy of Ankle-Foot Orthoses on Gait of Children with Cerebral Palsy: Systematic Review of Literature

Figueiredo, Elyonara Mello PT, ScD; Ferreira, Gisela Bastos PT; Maia Moreira, Rodrigo César PT; Kirkwood, Renata Noce PT, PhD; Fetters, Linda PT, PhD

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Author Information

Department of Physical Therapy (E.M.F., R.N.K.), Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Universidade Federal de Minas Gerais, Brazil; Physical Therapy Graduate Program (G.B.F., R.C.M.M.), Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Universidade Federal de Minas Gerais, Brazil; and Department of Pediatrics (L.F.), Keck School of Medicine, University of Southern California, Los Angeles, California

Address Correspondence to: Elyonara Mello Figueiredo, PT, ScD, Rua Perdigão Malheiros, 195-901, Belo Horizonte, MG, Brazil 30380-050. E-mail: elyonara@ufmg.br

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Abstract

Purpose: To perform a literature review evaluating the quality of current research on the influence of ankle-foot orthoses (AFOs) on gait in children with cerebral palsy (CP).

Methods: A qualitative systematic review of intervention studies including the following words/phrases in the title/abstract: children with CP, AFO, gait and inferential statistical analysis, and outcomes related to gait. Databases searched included PubMed, Cochrane Library, PEDro, OTSeeker, Lilacs, and Scielo. Level of evidence was graded using the PEDro Scale.

Results: Two between-group and 18 within-group studies met the inclusion criteria indicating a low level of evidence. Between-group studies each scored 4 on the PEDro Scale, and 17 within-group studies scored 3 and 1 scored 2, indicating low quality. Standard terminology for AFOs was not used and only 6 studies described functional status using appropriate instruments.

Conclusions: Studies using high quality methods are still needed to support evidence-based decisions regarding the use of AFOs for this population.

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INTRODUCTION AND PURPOSE

The gait patterns of children with cerebral palsy (CP) are different from those of children with typical development.1 The variations depend on the type and severity of CP.2 These patterns are influenced by the intrinsic characteristics of the child such as muscle stiffness3 and strength4 as well as by environmental characteristics, such as the surface conditions or the presence of mechanical obstacles.5 The emergent gait pattern may be the best solution available to the child, but this functional solution might increase the risk for structural alterations such as limited joint mobility and misalignment.3

Efficient and effective walking is an important treatment goal for children with CP since mobility is associated with functional independence and participation of the child in society.6 Ankle-foot orthoses (AFOs) have been suggested to improve the dynamic efficiency of the gait of children with CP, that is, the degree to which the gait is well controlled and energy efficient.7 Many authors report positive effects of different types of AFOs on gait kinetics and kinematics,8,9 as well as on functional activities of the children with CP.10,11 These effects include increased ground reaction force and plantar flexion moment,8 increased stride length,8,9 and improvement on the walking, running, and jump dimensions of the Gross Motor Function Measure10 with the use of AFOs. However, a previous review of the literature, up to the year 2000, reported that the research to date was of poor quality with inadequate methods and that the literature did not support the efficacy of AFOs for the gait of children with CP.12 Differences in designs of the AFOs associated with the intrinsic variability observed in children with CP were suggested as major contributing factors for poor evidence.12

The purpose of this report is to update the review of literature on the influence of AFOs on gait in children with CP to determine if higher quality research that might clarify the scientific basis for the use of AFOs has been recently conducted. The following questions guided our review: (1) does evidence from high quality research support the efficacy of AFOs on the gait of children with CP? (2) is standard terminology used to describe AFOs and are appropriate measures used to describe the participants' functional status?

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METHOD

The methods for conducting this systematic review and for assessing the quality of evidence were based on the processes outlined by the Center of Reviews and Dissemination at the University of York.13 This method aims to produce good quality reviews by following internationally accepted systematic review guidelines. Studies published at and before the year 2000 were included in the present review since the previous review, which included studies published up to the year 2000, did not follow these same rigorous guidelines.

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Types of Studies

To comprehensively document the quality of evidence, quasi-experimental research designs were also considered in this review in addition to randomized controlled trials (RCTs). Study designs included prospective and retrospective studies that included within-and/or between-group comparisons (cross-sectional study designs).

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Types of Participants

The study population in this review included children (both boys and girls) with CP. We included studies in which participants were in late adolescence so as to include all studies with children as participants.

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Types of Interventions

Inclusion criteria incorporated all studies that evaluated the effect of any type of AFO on the gait of children with CP associated or not with other types of therapies, for example, botulinum toxin or surgery. Exclusion criteria eliminated studies that did not include AFOs as a therapeutic intervention and gait as the outcome measure.

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Types of Outcome Measures

Only outcome measures related to gait were considered in this review, including gait kinetic, kinematics, and electromyography, as well as standardized tests that evaluate outcomes related to locomotion at the level of impairment, motor function, and participation in society.

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Data Sources

To identify all relevant studies for this review, the search strategy included bibliographic databases: PubMed, Cochrane Library, PEDro, OTSeeker, Lilacs, and Scielo. The last 2 are databases from Latin America and Caribbean countries. Bibliographies of retrieved articles from the bibliographic databases were also searched. This strategy involved checking the title of the articles against the inclusion criteria. Inclusion was validated by checking the abstracts against the inclusion criteria.

Abstract-only study reports were not considered in this review because they provide limited information about intervention and participants' characteristics, thus making it difficult to determine the specific quality of these studies. Hand searching for published and unpublished data was not performed because a systematic and thus reproducible strategy could not be guaranteed. The date of the last search was January 20, 2006.

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Search Strategy

All relevant studies without language and date restriction, published between 1960 and January of 2006 were located for assessment against the inclusion criteria. The key words, defined from the MeSH database in Medline were CP, orthoses, ankle-foot, gait, and walking. For the key words orthoses and walking, truncation was also used as search strategy to retrieve articles with words composed of the root orth and walk (eg, orthosis, orthoses, orthotic devices, walk, walking). Initially, a search was performed for each key word. As a second step, keywords were combined in pairs, then in trios, and finally a conclusive search was performed with all key words combined. To improve the likelihood of retrieving the articles of interest and to avoid bias during the selection, 2 independent researchers (G.F. and R.M.) conducted the search separately and a third researcher (E.F.) did the final selection by checking the abstracts against the inclusion criteria. Because this search strategy did not identify any RCTs, the Robinson and Dickersin14 search strategy was then applied to access the Medline database. This is a highly specific and sensitive search strategy for the retrieval of reports of controlled trials for use with PubMed. The use of this search strategy increases the likelihood of retrieving the studies of interest and decreases the chances of false positives, ie, retrieving studies that do not conform to the inclusion criteria.

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Study Selection

Studies were eligible for inclusion in this review if the following information was in the title or abstract: (1) participants were individuals with CP; (2) intervention included AFOs; (3) any outcome measure of gait; and (4) inferential statistical analysis of results. Relevant studies were identified from the hits produced from each bibliographic database or reference list by applying the eligibility criteria. The full text version of all studies was obtained, checked once more against the inclusion criteria, and then assessed for method quality.

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Level of Evidence

To describe potential for bias, the level of evidence of each retrieved study was assessed according to the criteria suggested by Law and Webb15 (Table 1). These criteria were chosen because it was suggested as adequate for the rehabilitation scientific literature.15

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Method Quality

The method quality of the included studies was critically appraised by 2 independent reviewers by applying the PEDro Scale.16 This is an ordinal scale comprised of 11 items with each item scored present (1 point) or absent. The scale includes aspects of external, internal, and statistical validity. The PEDro Scale total is a 10, with the item “specified eligibility criteria” not scored. Higher scores represent higher method quality.17 Score differences were discussed between the 2 reviewers (G.F. and R.M.) and in consultation with a third party (E.F.) until consensus was reached.

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Data Extraction

In addition to a PEDro rating, we extracted data describing each study so that we could compare these features across studies. We included general information about the study such as authors, journal and data of publication, subject demographics, service delivery setting, study design, intervention characteristics, outcome measures characteristics, and key results. Information was extracted independently by 2 reviewers (G.F. and R.M.) and disagreements were resolved by discussion with a third party (E.F.).

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Data Synthesis

We did not identify studies that provided adequate information to use quantitative description of the data, for example, effect sizes, means and standard deviations. Therefore, findings are presented qualitatively as narrative summaries. Levels of evidence were cited and key outcomes described in agreement with the International Classification of Functioning, Disability and Health (ICF).18 The details of each study are described chronologically by date of publication.

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RESULTS

Description of the Included Studies

The search strategy identified 42 potentially relevant studies, published between 1960 and January 2006. Twenty-six were retrieved from databases and 16 from the bibliography of the retrieved studies. Twenty studies fulfilled the inclusion criteria and are considered in this review. Nine studies were published in the 1990s and 11 were published in the 2000s (9 of them were published after the year 2000 when the last review was published). The processes of selecting the studies for this review are detailed in Figure 1.

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Method Quality of Included Studies

Two studies were nonrandomized clinical trials with healthy subjects as the comparison group9,32and the other 18 studies had a cross-sectional design with within-group comparison, indicating level III of evidence15 for all of them. Two studies scored 4,9,32 17 scored 3, and 1 study27 scored 2 on the PEDro Scale. The 2 studies that scored 4 were published on the years 200232 and 2005.9 Scoring details are displayed in Table 2.

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Characteristics of Participants

Across all studies, a total of 446 participants were investigated, 304 participants with a diagnosis of spastic diplegia, 113 participants with a diagnosis of spastic hemiplegia, 1 with brain injury in early childhood, and 28 participants who were healthy served as controls. The sample sizes ranged from 6 to 115 (average = 22.3) participants, ages 2.5 to 19 (average = 8.6) years. Although 8 studies reviewed included older participants,11,21,25,26,28,32–34 these studies also included children. We included studies in which participants were in late adolescence so as to include all studies with children as participants. The severity of CP was classified in 3 studies10,30,33 by the Gross Motor Function Classification System35 at levels I to III, and in another 3 studies spasticity was classified using the Modified Ashworth Scale8,22,28 at grades 1 to 3. The other 14 studies used clinical descriptors of the participants such as independence during ambulation and gait pattern9,11,19–21,23–27,29,31,32,34 but these descriptors were not consistent across studies. Detailed information about participants' characteristics is provided in Table 3.

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Types of Interventions

Among the 20 studies reviewed, there were different types of AFOs and different terms were used to describe the same type of AFOs. The terminology used in the studies is as follows: AFO,9,19,31 rigid AFO,26 fixed AFO,20,23–25,27 solid AFO (SAFO),8,10,11,22,33,34 supramalleolar orthosis (SMO),24,29,34 flexible AFO,28 hinged AFO,8,10,11,23,29,30,32,33 articulated AFO,27,34 dynamic AFO (DAFO),9,22,32 posterior leaf spring (PLS),10,11,21 spring type AFO,26 and tone-reducing AFO (TRAFO).29 The variety of types and descriptors made it difficult to summarize results. Therefore, we used the following terminology to define AFOs37 although the original terms are preserved in the tables. Solid AFO (SAFO) refers to AFO, rigid AFO, fixed AFO, solid AFO, conventional AFO; hinged AFO (HAFO) refers to flexible AFO, hinged AFO, articulated AFO; posterior leaf spring (PLS) refers to posterior leaf spring and spring type AFO; dynamic AFO (DAFO); and tone-reducing AFO (TRAFO); and supramalleolar orthosis (SMO) was not included in the terminology of Alexander and Xing.37 Therefore, we kept the SMO terminology in the text.

Four studies investigated only the effects of SAFO,19,20,25,31 2 only the effects of HAFO,28,30 1 only on PLS,21 5 investigated the effects of SAFO and HAFO,8,22,23,27,33 2 investigated the effects of SAFO and DAFO,9,26 1 investigated the effects of HAFO and DAFO,32 1 the effects of SAFO and SMO,24 3 the effects of SAFO, HAFO, and PLS,10,11,34 and 1 reported the effects of HAFO, SMO, and TRAFO.29 Shoes or barefoot were used as the control conditions for the 18 cross-sectional studies, and healthy subjects were used as comparison groups for the 2 nonrandomized clinical trials.9,32 The studies' procedures are detailed in Table 3.

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Types of Outcomes

A summary of the studies' results based on the outcomes described in terms of the ICF recommendations, as well as authors' conclusions when available are presented in Table 3. Two studies reported outcomes only at the body function and structure level,19,28 2 studies reported only at the activity level,31,33 and 16 studies reported outcomes at both body function and structure and activity levels.8–11,20–27,29,30,32,34 Outcomes at the participation level of the ICF were not investigated in any of these studies.

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Body Function and Structure Outcomes
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Lower Extremity Range of Motion.

The effects of AFOs on passive and active ankle range of motion were measured with either goniometry11,23 or kinematic analysis,9,11,24,27,34 respectively. The use of SAFO,23 HAFO,11,23 and PLS11 significantly increased passive ankle dorsiflexion with knees flexed and extended.11,23 There were also positive effects of the use of SAFO and HAFO when compared with the barefoot condition on ankle dorsiflexion at initial contact,9,11,24,27 midstance9 and swing phase,9,34 and of HAFO during terminal stance of the gait cycle.27 Also, the peak of dorsiflexion was higher compared with the barefoot condition when SAFO, HAFO, and PLS11 were used, and peak dorsiflexion was greatest with HAFO.11 Knee flexion increased at both initial contact and swing phase of the gait cycle when SAFO,34 HAFO,34 and DAFO9 were worn.

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Lower Extremity Muscle Timing.

The effects of AFOs on muscle timing were measured by surface electromyography during the gait cycle. SAFO and DAFO significantly increased total duration of contraction and led to higher median frequency activation for the lower limb muscle groups.9 No differences were observed in timing of lower limb muscle activation during stance phase with SAFO and HAFO.8,22

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Energy Expenditure.

The effects of AFOs on energy expenditure during gait were measured by the physiologic cost index,19,34 the energy expenditure index,28 the dilution mode method,10,11 and the rate of expired gas and heart rate30 at both preferred and fastest walking speeds. Four studies reported decreased energy expenditure with the use of SAFO,10,19 PLS,10 and HAFO.10,11,30 In one study, differences were not reported between the use of SAFO, HAFO, and PLS and barefoot condition,34 and in one study increased energy expenditure was reported with the use of HAFO compared with barefoot condition.28

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Kinetic Analysis.

In most studies, a decreased peak ankle power generation during the stance phase of the gait cycle was observed when participants wore SAFO,24 HAFO,29 TRAFO,29 and PLS,21 and in one study an increase in the ankle power generation at the preswing phase was observed when participants wore HAFO.8 Peak ankle power absorption during the first half of stance phase decreased with SAFO,24 HAFO,32 and DAFO,32 but in one study PLS increased the amount of mechanical energy absorbed during midstance.21 A reduction of abnormal ankle moment in early stance and an increase in ankle moment in late stance with SAFO25 was also observed, as well as a decrease in the ankle mediolateral shear force when SAFO and HAFO were not worn.23 Plantar-flexor moment increased with SAFO,8,24,26 HAFO,8,27 DAFO,9 and PLS.26 The SMO neither significantly alters the power nor moment values at the ankle joint.24 A decrease in the magnitude of the knee-extending moment arm toward normal was observed after 4 to 6 months use of SAFO.20 In 1 study, no change was documented in joint kinetics of the pelvis, hip or knee when HAFO, SAFO, and PLS were used.10

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Activity Outcomes.

Gait kinematics and temporal-spatial gait characteristics, standardized tests of gross motor function (Gross Motor Function Measure-GMFM, Bruininks-Oseretsky Test of Motor Proficiency-BOTMP), upper limb coordination skills (BOTMP), and independence in daily life activities (Pediatric Evaluation of Disability Inventory-PEDI) were outcome measures at the activity level.

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Kinematics and Temporal-Spatial Gait Characteristics.

Seventeen studies used kinematic data obtained by either video analysis or motion analysis systems to investigate the positioning of the ankle, knee, hip, and pelvis during specific phases of the gait cycle as well as the temporal-spatial characteristics of gait.8–11,20–27,29,31–34

During heel strike, the use of SAFO,9,20,22–24,27,31 HAFO,23,27,29,32 DAFO,9,22 and TRAFO29 improved the ankle position by either decreasing ankle plantar-flexion or increasing dorsiflexion, therefore, leading to a closer to normal gait pattern, ie, from toe walking or flat foot strike to heel-strike. SAFO,10,22 HAFO,10 DAFO,22 and PLS10,21 reduced excessive equinus during midstance, and SAFO27 and HAFO8,27 led to an increased dorsiflexion at terminal stance. Both, SAFO and DAFO9 improved ankle positioning at the swing phase of the gait cycle. On the other hand, 2 studies have reported negative effects of the use of AFOs.8,34 One documented increased abnormal ankle dorsiflexion with the use of SAFO, HAFO, and PLS34 compared with the barefoot condition. In another study, the authors reported that HAFO produced more excessive plantar- flexion than the barefoot condition.8 The kinematics of other joints was reported in 3 studies.9,10,11 HAFO was effective in controlling knee hyperextension in stance, whereas PLS was effective in promoting knee extension in children with greater than 10° knee flexion in stance.11 Knee flexion at initial contact increased with DAFO.9 Joint kinematics at the pelvis, hip, or knee were not changed with the use of SAFO, HAFO, and PLS.10

Stride and step length, gait velocity, and single support time increased with the use of SAFO,8–10,22,25,26,31,33 HAFO,8,10,32,33 DAFO,9,22 and PLS.10 The authors of 1 study did not find significant differences in gait velocity and stride length with the use of SAFO, HAFO, and PLS34 and in another study, the researchers reported increased double support time with the use of SAFO.26 Cadence decreased with SAFO,10,22,26 HAFO,10 DAFO,22 and PLS10,26 when compared with no AFO. In 2 studies, the authors reported no change in cadence with SAFO,33,34 HAFO,33,34 and PLS.34

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Standardized Tests.

Functional skills were measured in 3 studies.10,11,30 Three studies used the GMFM,10,11,30 2 applied the GMPM10,11 and the PEDI10,11 test, and 1 used the BOTMP.10 Buckon et al10 identified significant positive effects of SAFO, HAFO, and PLS on the walking/running/jumping dimensions of the GMFM whereas Maltais et al30 and Buckon et al11 did not find statistical differences in the GMFM scores of children with spastic diplegia30 and hemiplegia.11 The use of SAFO, HAFO, and PLS did improve the upper limb coordination of children with spastic diplegia, as measured by the BOTMP.10 Buckon et al11 also demonstrated positive effects of the use of SAFO, HAFO, and PLS on the mobility dimension of the PEDI for children with spastic hemiplegia but the same positive effects were not observed for children with spastic diplegia.10

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GENERAL DISCUSSION

All 20 studies in this review had a cross-sectional design. In 18 of the studies, a one-group pretest–posttest design (within-group comparison)8,10,11,19–31,33,34 was used and 2 studies (both published after the last review on the topic) had a pretest–posttest with control group design, but without randomization procedures (within-and between-group comparison).9,32 Of the 9 studies published after 2000 (last published review on the topic), only 2 included between-group comparisons. However, these 2 studies did not provide data with adequate internal validity, as demonstrated by low scores on the PEDro scale. The studies flaws included lack of randomization procedures, lack of parity among groups, no masking of examiners' and attrition not reported or controlled. These more recent studies have not substantially improved the quality of the research. There is a continuing need for high quality experimental studies in this area. A high-quality RCT provides the best design to control for potential bias, thus offering the strongest evidence of cause-effect inferences between interventions and outcomes.38 However, the large number of participants necessary for randomization into groups and the homogeneity among participants required by this design might make it difficult to conduct a RCT study on the use of AFOs by children with CP. In addition, results from a RCT are typically expressed as group averages and generalizations from groups to individuals may be challenging due to the uniqueness of each patient.36 Alternative designs to RCTs, when implemented rigorously, could provide more realistic and perhaps equally valid results regarding the present topic. A cross-over design represents a special experimental design where there is not a separate comparison group. It provides a within-group comparison, therefore, demanding smaller numbers of homogeneous participants while controlling for confounding factors.36 The one-group, interrupted time-series design (single-subject design) is also a powerful alternative design to RCT. It has been suggested that this is superior to the one-group pretest–posttest design because the multiple pretests and posttests typical of single-subject designs act as a pseudocontrol condition, by demonstrating temporal trends that naturally occur in the data or the confounding effects of extraneous variables.36 Furthermore, this design allows the detailed investigation of individual characteristics that are important in a population with a large variety of structural and functional characteristics as in children with CP. Both cross-over and single-subject designs have been used successfully to investigate the effects of electrical stimulation39 and botulinum toxin40 on the gait of children with CP, indicating their feasibility.

Twelve different terms were used to describe different types of AFOs, indicating the lack of standard terminology, although terminology based on the material used to construct the AFO as well as on the movements to be restricted, maintained or facilitated is provided by Alexander and Xing.37 By using this terminology, we successfully collapsed the original 12 terms into 5 types of AFOs. This procedure led to a clearer description of which types of AFOs were associated with which effects. The use of standard terminology should be considered in future studies. In addition, of the 20 studies reviewed, only 6 used specific measures to describe participants' functional status.8–10,28,30,33 The remaining 14 studies used subjective clinical descriptors.11,19–27,29,32–34 The lack of consistency in the terms used for AFOs associated with the variety of descriptors in the classification of functional status of the participants made it difficult to identify which subgroups of children would benefit from which type of AFO as well as to make comparisons between studies. Future studies should consider the application of a severity classification system such as the Gross Motor Function Classification System 35 that could allow parity among treatment groups.

A lack of information about the parameters used for the prescription of AFOs for specific subgroups of participants was apparent. Although some researchers did include AFOs already prescribed, others prescribed the orthosis as part of the intervention protocol. In either case, precise descriptions of movements to be controlled with a specific AFO were typically not included. A lack of information about the specific intervention protocols used associated with the AFOs was also apparent. These flaws compromise the replication of these studies as well as the implementation of the intervention protocol in the clinical setting. Information that allows generalizability of the data to the clinical setting should be considered in the development of future studies.

Outcomes were restricted to the body structure and function and activity domains of the ICF with not one study including outcomes at the level of participation. Perhaps those studies exist but were not retrieved in our search strategy because they did not include outcomes specifically related to gait. The use of the ICF in future studies would provide a framework for the investigation of all the components of functioning and of the relationships among components. Furthermore, it would provide a common language to improve communication among healthcare providers, researchers, policy makers, and people with disabilities.18

The use of the PEDro Scale in the present review provided quantitative information about studies' methodological quality. Use of the PEDro Scale in future systematic reviews would provide comparable data to identify progress in the gathering of scientific evidence on this topic.

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SUMMARY AND IMPLICATIONS FOR RESEARCH AND CLINICAL PRACTICE

The results of the reviewed studies suggest positive effects of the use of AFOs on the passive and active ankle ROM, gait kinetics and kinematics, as well as on functional activities related to mobility of children with CP. However, the quality of the methods of the 20 studies reviewed is low (level III of evidence). From the 8 studies published after the year 2000 (last review on the topic), only 2 included between-group comparisons. Moreover, these 2 studies were also of poor quality, as demonstrated by the low scores on the PEDro Scale. Consequently, there has been little progress in the quality of the evidence since the last published review on the topic. Future studies should consider stronger designs that can control for confounding factors, such as a cross-over and single-subject designs. These designs have been successfully used to investigate gait related outcomes in children with CP.39,40 A lack of standard terminology used to define AFOs was noted. Furthermore, only 6 of the 20 studies reviewed described participants' functional status using appropriate measures. These results made it difficult to identify which group of children would benefit from each type of AFO. Clinicians should rely on their clinical experience and patient values to guide the clinical decision-making process on the use of AFOs to improve gait of children with CP. They should also be in search of new studies that provide valid and applicable evidence to support their clinical practice.

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Keywords:

ankle; children; cerebral palsy; cross-sectional studies; equinus deformity/prevention and control; foot; gait; orthoses/classification; prospective studies; randomized control trials as topic; treatment outcome

© 2008 Lippincott Williams & Wilkins, Inc.

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