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Pediatric Physical Therapy:
doi: 10.1097/PEP.0b013e3181b126fb
Research Report

Effects of Ankle-Foot Orthoses for Children with Hemiplegia on Weight-Bearing and Functional Ability

O’Reilly, Tara BAppSc (Phty)(Hons); Hunt, Adrienne GradDipPhys, GradDipPaedPhys, MBiomedE, PhD; Thomas, Bronwyn BAppSc (Phty), MHS; Harris, Lynne BSc(Psych)Hons1, MPsych(Clinical)Hons1, PhD(Psych); Burns, Joshua PhD, BAppSc(Pod)Hons

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Author Information

The Children’s Hospital at Westmead (T.O., B.T.), Sydney, Australia; Faculty of Health Sciences (A.H., L.H.) and Institute for Neuromuscular Research, The Children’s Hospital at Westmead and Discipline of Paediatrics and Child Health, Faculty of Medicine (J.B.), The University of Sydney, Australia

Address correspondence to: Adrienne E. Hunt, GradDipPhys, GradDipPaedPhys, MBiomedE, PhD, Discipline of Physiotherapy, The University of Sydney, PO Box 170, Lidcombe, NSW 1825, Australia. E-mail: a.hunt@usyd.edu.au

Grant Support: Supported by The Children’s Hospital at Westmead Small Grants Scheme.

This research was conducted as part of the requirements for the degree of Bachelor of Applied Science (Physiotherapy) (Hons) of Tara O’Reilly.

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Abstract

Purpose: To compare the effects of a leaf spring ankle-foot orthosis (LAFO) and a hinged AFO with plantar flexion stop with that of shoe only on weight-bearing and function in children with hemiplegia.

Methods: The study used an experimental single-subject alternating treatment design with replication. Outcomes measured were weight-bearing symmetry, weight-bearing on the hemiplegic rear foot compared with that of the forefoot, functional ability, and child and parent preference.

Results: Both AFOs increased relative contact area of the hemiplegic foot. The LAFO increased relative force through the hemiplegic foot. There was increased pressure through the rear foot, time spent on the rear foot, and force through the forefoot. Rear foot contact area increased in the LAFO. Neither AFO affected function. Patient preference for AFO condition was inconsistent.

Conclusion: Both AFOs increased weight-bearing through the hemiplegic foot and rear foot, indicative of potential benefit to growth. Neither the LAFO nor the hinged AFO with plantar flexion stop improved function of the children.

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INTRODUCTION AND PURPOSE

Children with hemiplegia have a characteristically asymmetrical gait. Step length is decreased on the hemiplegic side1 and heel strike is typically absent, with the ankle in equinus.2 Ankle-foot orthoses (AFOs) are frequently prescribed for children with hemiplegia to support the foot in correct alignment and hence address the impairment of ankle equinus.3 An additional benefit could be derived from wearing an AFO if weight-bearing increased through the hemiplegic leg and/or heel, because programs aiming to increase weight-bearing have been shown to increase bone mineral accrual4 and therefore reduce the risk of decreased bone density on the hemiplegic side.5 However, such a possibility has not been investigated. Indeed, knowledge of AFO effectiveness on impairments and activity limitations in children with hemiplegia is limited. Shortcomings of the published research include insufficiently detailed patient profiles and AFO descriptions and comparing the AFO-in-shoe condition with the bare foot rather than the shoe-only condition, with the possible consequence of concluding a greater gait improvement with an AFO than would be the case for a shoe-only comparison.6

Effectiveness of AFOs has been assessed for outcomes related to walking and functional ability. For walking, improvements have been reported for the spatiotemporal measures of velocity,6–8 step and stride length,6,7,9,10 and single-limb stance time.8,9 Improvements have also been found for kinematics11 (ie, angular displacements of joints and angular velocities of limb segments) and for kinetics11 (ie, factors that cause or control movement, such as joint moments and powers). Kinematic improvements include increased dorsiflexion alignment at initial foot contact.6,7,9,10,12 Kinetic improvements include increased plantar flexor power during the push-off phase6 (the period late in stance and before the foot leaving the surface), despite the belief that AFOs reduce ability to generate ankle joint power because of movement restriction.7,10,12 For functional ability, AFO effect on ascending and descending stairs was investigated using the observational Pediatric Evaluation of Disability Inventory,13 with no AFO effect found.7,14 Interestingly, when Buckon et al7 evaluated AFO effect on walk/run/jump skills, they found improvement on the Gross Motor Performance Measure (GMPM),15 but no AFO effect on the Gross Motor Function Measure (GMFM).16 It is possible that the GMPM, which incorporates assessment of the quality of performance, had higher sensitivity than the GMFM.

Common AFO models include the posterior leaf spring AFO (LAFO) and the hinged AFO with plantarflexion stop (HAFO),6 which are more effective than other models in achieving heel strike for children with spastic hemiplegia.17 Either type may be prescribed for a child attending the Physical Disabilities Clinic or the Brain Injury Service of The Children’s Hospital at Westmead. Currently, the decision about which AFO to prescribe is based on the knowledge about its likely effectiveness for a particular child. For example, although a HAFO will be effective in controlling knee hyperextension in stance and allows greater dorsiflexion than a LAFO, thus enabling an increased push-off force and a more normal gait,7,9 a LAFO is useful in promoting knee extension.7 Additional considerations in choice of AFO include practical aspects, such as easier shoe fitting and cost of fabrication of a LAFO. Although both types of AFO have been linked to improvements on the GMPM dimension of weight-shifting,7 the specific outcomes of weight-bearing symmetry and weight-bearing through the heel have not been measured biomechanically, and, therefore, the potential for either type of AFO to increase loading is not known.

The aims of the current study were to determine whether the HAFO or the LAFO was superior to the shoe-only condition for improving weight-bearing symmetry between the hemiplegic and nonhemiplegic leg, weight-bearing on the rear foot (heel) of the hemiplegic foot, performance in functional activities reflecting balance and speed, and gross motor functions requiring dorsiflexion such as jumping and descending stairs. An experimental single-subject alternating treatment design with replication was chosen for the current study because the expected heterogeneity of impairments among those with hemiplegia can make interpretation of group comparisons difficult.18,19 Compared with case studies, and pre-experimental single-subject designs, the alternating treatment design controls threats to internal validity, so that the effects of interventions can be clearly determined,20 and has the advantage that it requires fewer assessments and is relatively quick to implement.21 The external validity of the single-subject design was increased by replication across 3 participants.20

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METHODS

Participants

A purposive sample of participants was identified initially from the client database of the Rehabilitation Department of The Children’s Hospital at Westmead (Sydney, Australia). Letters of invitation to participate were sent to parents of children who met the criteria of having a diagnosis of hemiplegia due to cerebral palsy or acquired brain injury, currently using AFOs or history of AFO use, having no history of botulinum toxin A administration or of orthopedic surgery, between 10 and 15 years of age, and residing within sufficiently close proximity to the hospital to attend the testing sessions. The final sample of children was obtained from those who attended an assessment and were found to have at least 5° of ankle dorsiflexion with the knee extended to allow for fitting and function of a HAFO and who were considered to follow instructions during testing. Three children aged between 11 and 15 years of age took part in the study; their characteristics are presented in Table 1. All children had a diagnosis of hemiplegia due to cerebral palsy or acquired brain injury and performed at level 1 on the Gross Motor Function Classification System, ie, they were able to walk without restrictions but had limitations in more advanced gross motor activities.22 All had an equinus gait pattern and had worn various types of AFOs since early childhood. One of the intentions of the current study was to obtain data with which to demonstrate the advantages of AFO use to reluctant AFO wearers, thereby encouraging AFO use. For this reason, the study intentionally recruited children and parents who were experienced with both types of AFO, were interested in participating in a study to compare the 2 AFO types, and were willing to be measured on numerous occasions. Ethics approval for the study was obtained from The Children’s Hospital at Westmead Ethics Committee and The University of Sydney Human Research Ethics Committee. Informed consent was given by the participants and their parents.

Table 1
Table 1
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Procedures

A HAFO (Fig. 1) and a posterior LAFO (Fig. 2) were fabricated for the hemiplegic side of each participant by an experienced orthotist and fitted 2 weeks before data collection by the orthotist. This time frame allowed the participants to acclimate to both new AFOs. All participants had previously worn both types of AFO for everyday activities, including sports, and all participants had normal cognitive function. Participants were, therefore, allowed to decide the time that they spent in each new AFO during the 2 weeks of acclimating and were instructed to alternate between the AFOs over the 2-week period, spending as much time as possible in both types for them to feel confident in both.

Fig. 1
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Fig. 2
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Each participant attended 3 testing sessions over a 2-week period. The 18 main outcome measures are described below: 4 assessed weight-bearing between legs, 4 assessed weight-bearing of the rear foot compared with that of the forefoot of the hemiplegic foot, and 10 assessed performance of functional activities. Child and parent preferences were also considered as outcome measures. Three conditions, no AFO (NAFO), LAFO, and HAFO, were tested in a random order at each session. For each condition, functional data were obtained before weight-bearing data. However, because the innovation of the study was to investigate whether an AFO increased loading, measures of weight-bearing symmetry and of weight-bearing on the rear foot compared with that of the forefoot are described before measures of functional ability throughout this report. At the end of each session, participants were asked their preferred AFO condition. At the conclusion of the study, participants and their parents each completed questionnaires about activities that they thought were easier or harder when wearing an AFO, their AFO condition preference and reasons, and what they liked or disliked about wearing an AFO.

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Measures of Weight-Bearing Symmetry and Weight-Bearing on the Rear Foot Compared with Those of the Forefoot

Outcome measures for weight-bearing were derived from pressure data (Fig. 3), using the Pedar Mobile in-shoe system (Novel GmbH, Munich, Germany) and proprietary software (Pedar-m expert 8.3 software; Novel GmbH) with proven reliability and validity.23 The 99-sensor pressure insole was placed in the shoe for the NAFO condition and on the AFO for the AFO conditions and connected to the Pedar Mobile box, carried in a small backpack. Each participant wore the same socks and shoes at every testing session to ensure standardization of pressure data. After a familiarization period of walking with the equipment, data were collected at 50 Hz while the participant walked at a self-selected pace in a straight line back and forth along a 5-m walking track. Cadence and speed were monitored but not controlled to ensure a natural gait.24 Three variables (maximum mean pressure, mean contact area, and maximum force) were derived from the average value of data for the sampled frames per step from sensors activated within the defined area (ie, rear foot, forefoot, or whole foot). Maximum mean pressure (in Newtons per square centimeter) was the maximum value of the mean pressure recorded in each sampled frame. Contact area (in square centimeters) was the average for the step of the area in contact. Maximum force (in Newtons) was the maximum force of all frames for that step. Contact time (in milliseconds) was the time that a sensor within the defined area was in contact. Variables were averaged over 10 steps and are henceforth referred to as pressure, contact area, force, and contact time.

Fig. 3
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Outcome measures for weight-bearing symmetry were calculated from the relative magnitude of hemiplegic to unaffected side for each of pressure, contact area, force, and contact time. A normal, symmetrical gait would have a ratio of 1:1 on each variable, and this was considered to be the desired outcome. The resulting outcome measures for weight-bearing symmetry were pressure symmetry, contact area symmetry, force symmetry, and contact time symmetry.

Outcome measures for weight-bearing on the rear foot compared with that of the forefoot of the hemiplegic foot were calculated from the relative magnitude of rear foot (posterior half of the foot) to forefoot (anterior half of the foot) of pressure, contact area, contact time, and force. An increase in the rear foot-to-forefoot ratio was the desired outcome. The resulting outcome measures for foot loading characteristics were rear foot-to-pressure, rear foot-to-forefoot contact area, rear foot-to-force, and rear foot-to-forefoot contact time.

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Measures of Functional Ability

Ten outcome measures for functional ability were obtained in a set order. These were the Berg Balance Scale25 score, the GMFM26,27 score, 1-legged balance time, number of hops, standing long jump distance, walking speed, running speed, ascending stairs speed, descending stairs speed, and shuttle run speed. Seven of the measures (1-legged balance time, number of hops, standing long jump distance, walking speed, running speed, ascending stairs speed, and descending stairs speed) were derived from the walking/running/jumping dimension (dimension 5) of the GMFM. For 1-legged balance time, the participant had 3 attempts to balance on each leg for a maximum of 30 seconds. Similarly, for number of hops, the participant had 3 attempts on each leg to a maximum of 30 hops, and for standing long jump distance, the participant had 3 attempts to jump with both feet together from a standing start. For walking speed and running speed (each recorded as time over 10 m) and ascending and descending stairs speeds (time over 2 flights of 13 steps with a small landing between), the participant had 2 attempts. Shuttle run speed was recorded as the time taken to run 4 laps of a 5-m track as fast as possible, thus challenging dynamic balance as the participant changed direction.

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Preference of the Child and Parents

At the end of each of testing session, the child was asked to indicate preferred AFO condition for each of the 7 types of activities assessed: balancing, hopping, jumping, walking, running, ascending stairs, and descending stairs. To ensure accurate recording of the child’s preference, the chief investigator (T.O.) entered on a recording sheet the number 1, 2, or 3 beside each condition. The score was recorded as 1-1-3 for tied first preference or 1-3-3 for tied last preference. At the final session, each child and his or her parents completed a separate questionnaire of open-ended questions. The child was asked to state the activities that he or she found easier and harder to do when wearing an AFO, his or her preference for one over the other and the reasons for that, and what he or she liked and disliked about wearing an AFO. The parents were asked to state the activities that they believed their child found easier and harder in an AFO, their AFO preference and the reasons, what they believed were advantages and disadvantages of the 2 AFO types and their reasons for those views.

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Analysis

For each child, graphs were generated for each of the outcomes measured in the categories of weight-bearing symmetry, weight-bearing on the rear foot compared with that of the forefoot and functional ability. Visual analysis of the graphs for trends within each participant and between participants was conducted. Statistical significance (at the p < 0.05 level) was determined from 2-SD band analysis to confirm the observations from visual analysis.28,29 A statistically significant difference between conditions was indicated if the mean of the intervention (LAFO or HAFO) was >2 SDs from the mean of the baseline (NAFO) or if at least 2 consecutive data points fell beyond 2 SDs from the baseline mean. Following the method of Backman et al,20 evidence of AFO effectiveness was indicated by replication of statistically significant differences between conditions for at least 2 of the 3 study participants.

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RESULTS

Measures of Weight-Bearing Symmetry and Weight-Bearing on the Rear Foot Compared with Those of the Forefoot

Results for the 4 outcome measures of weight-bearing symmetry (hemiplegic side:unaffected side) are presented in Figures 4–7. There was no AFO effect on pressure symmetry (Fig. 4). Contact area symmetry (Fig. 5) increased in all children in the LAFO and in child 2 and child 3 in the HAFO. Force symmetry (Fig. 6) increased in child 1 and child 3 in the LAFO. Contact time symmetry (Fig. 7) increased in child 3 for both types of AFO. Therefore, a statistically significant effect on weight-bearing for both types of AFO was found for the outcome measure of contact area symmetry but only for the LAFO for the outcome measure of force.

Fig. 4
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Fig. 5
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Fig. 6
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Fig. 7
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Results for the 4 outcome measures of weight-bearing on the hemiplegic rear foot compared with those of the forefoot are presented in Figures 8–11. Results for the unaffected side are also displayed. Rear foot-to-forefoot pressure (Fig. 8) increased in child 1 and child 3 when wearing the LAFO and in child 1 and child 2 when wearing the HAFO. Rear foot-to-forefoot contact area (Fig. 9) increased in child 1 and child 3 in the LAFO but increased only in child 3 in the HAFO. Rear foot-to-forefoot force (Fig. 10) decreased in child 1 and child 2 in both types of AFO. Rear foot-to- forefoot contact time (Fig. 11) increased in all participants with both AFOs. There was, therefore, a statistically significant effect of both AFOs on rear foot-to-forefoot pressure, rear foot-to-forefoot force, and rear foot-to-forefoot contact time. Only the LAFO affected rear foot-to-forefoot contact area.

Fig. 8
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Fig. 9
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Fig. 10
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Fig. 11
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Measures of Functional Ability

Results for 10 measures of functional ability are presented in Figures 12–21. For 6 of the measures, there was no effect of the LAFO or HAFO for any of the children. These were the Berg Balance Scale score (Fig. 12), 1-legged balance time (Fig. 14), walking time (Fig. 17), running time (Fig. 18), descending stairs time (Fig. 20), and shuttle run time (Fig. 21). For each of the other 4 measures, there was an intervention effect for only 1 child. GMFM score (Fig. 13) improved only for child 3 when wearing the HAFO. Number of hops (Fig. 15) increased only for child 3 with the HAFO. Standing long jump distance (Fig. 16) increased only for child 2 in the LAFO. Ascending stairs time (Fig. 19) changed only for child 3, being slower in the LAFO than when in the HAFO or in a shoe only. In summary, there were no statistically significant effects on functional performance of either type of AFO.

Fig. 12
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Fig. 13
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Fig. 14
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Fig. 15
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Fig. 16
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Fig. 18
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Fig. 19
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Fig. 20
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Fig. 21
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Preference of the Child and Parents

Each child’s AFO preference scores were averaged across the 3 sessions for each type of functional activity and are presented in Table 2. These data show that there was no discernible pattern of preferences for AFO condition among the children associated with these activities. Each child’s AFO preferences among the 3 testing sessions (not shown) were also inconsistent. The comments from children about the specific activities that were easier and harder when wearing an AFO were not consistent with the preferences recorded at the end of each test session. Child 1 found it easier to run; child 2 found that AFOs restricted running and jumping; child 3 found it easier to go upstairs and come downstairs in an AFO but more difficult to hop and jump. Two children (child 1 and child 3) preferred the LAFO over the HAFO, and child 2 preferred the HAFO over the LAFO. Child 1 believed that the LAFO was less bulky, fitted more easily into shoes, did not make a clicking sound, and looked better, even though she also perceived that the LAFO limited ankle movement to a greater extent than the HAFO. Child 3 preferred the LAFO over the HAFO because it could be put on more quickly and fitted more easily into shoes. However, child 2 preferred the HAFO over the LAFO because he perceived that it was easier to perform physical activities, especially jumping, when wearing the HAFO.

Table 2
Table 2
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Despite the lack of consistency in AFO preference, the questionnaire responses of the children and their parents at the final test session revealed a consensus about the benefits of wearing both types of AFO. These included the relative ease in walking long distances when wearing an AFO. The children’s responses indicated that this was because of additional support provided by the AFO: “it gave me much more control over my left side” and “because it gives my foot extra support.” However, children perceived problems with AFOs, in that they sometimes rubbed or pinched at the back of the ankle or leg and were unattractive. Parents stated that their children seemed to walk better in an AFO, with “more fluidity” and with more even steps. One parent noted that her child’s calf muscle rapidly tightened when not wearing an AFO, and this led to toe dragging and tripping. Parents perceived the advantages of wearing an AFO to be maintaining muscle length, correcting foot drop, better stability and balance, and better distribution of weight leading to a decreased risk of falls. Perceived disadvantages to wearing an AFO included teasing, embarrassment, and social difficulties at school; difficulty in fitting the AFO (especially the HAFO) into shoes and purchasing suitable shoes; the AFO was hot in summer; and the child having difficulty putting the AFOs on independently. Two parents noted that jumping and hopping activities seemed to be more difficult when wearing an AFO, although 1 parent noted that this situation was improved with the HAFO. In contrast to the children (child 1 and child 3) who preferred the LAFO, the HAFO was preferred by 1 parent because the free dorsiflexion that it allowed resulted in a better walking pattern and by the other parent because it resulted in a more parallel foot placement. The third parent stated that although her child’s doctor and physiotherapist preferred the LAFO for correction of foot drop, her child (child 2) preferred the HAFO.

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DISCUSSION

This study sought to determine the usefulness of the LAFO and/or the HAFO compared with a shoe-only control condition in improving weight-bearing symmetry, weight-bearing through the rear foot, and performance of functional activities. Both AFOs were successful in increasing the contact area symmetry of the hemiplegic foot (Fig. 5), suggestive of additional foot support with an AFO compared with a shoe alone. The increase in force symmetry (Fig. 6) for the LAFO suggests that only this AFO was effective in increasing weight-bearing through the hemiplegic foot, and, hence, the LAFO might be the type of AFO more likely to provide a favorable stimulus to bone mineral accrual,4 with potential for improved bone density and growth. Previous findings of kinematic studies, in which an AFO increased the time spent on the hemiplegic foot during walking,8,9 were not supported by the current study because although there was a finding of increased time in both AFO types, this only pertained to child 3 (Fig. 7).

Both types of AFO affected 3 (pressure, time, and force) of the 4 measures of weight-bearing through the rear foot compared with the forefoot during walking. The findings that both the LAFO and HAFO increased the pressure through the rear foot (Fig. 8) and the time spent on the rear foot during walking (Fig. 11) complement previously reported improvements in ankle dorsiflexion at heel contact7,10 and terminal swing.12 Therefore, they provide further evidence that AFOs are effective in correcting equinus deformity and are useful for maintaining muscle length. The increased pressure (distributed force) and time through the rear foot are indicative of increased weight-bearing through the rear foot and also suggest a potentially favorable effect of wearing an AFO on musculoskeletal growth and development. For the fourth measure (contact area; Fig. 11), there was an intervention effect only with the LAFO. The increase in contact area with the LAFO compared with that of both the NAFO condition and the HAFO suggests that the LAFO provides better support to the rear foot than the HAFO or a shoe alone. Both types of AFO resulted in less force through the rear foot compared with the shoe only (Fig. 10). Although the clinical significance of this is unclear, it could indicate that there were reduced peak impact forces though the rear foot, which would be a beneficial finding. The increased forefoot force most likely reflects the plantar flexion restriction of an AFO, which requires the wearer to push off more forcefully through the forefoot to progress forward, thereby increasing the peak forces through the forefoot. As such, it is consistent with previous findings that AFOs increase plantar flexor power during the push-off phase.6

There was no significant AFO effect on any of the measures of functional activities with their varying demands of stability and mobility. Thus, the stability afforded by the AFO did not improve the children’s abilities in balance tasks, such as 1-legged balance, and neither did the restriction to plantar flexion caused by the AFO adversely affect ability. However, this lack of AFO influence is consistent with reports from group design studies of AFO effect on walking speed,30 GMFM scores,7 Pediatric Balance Scale scores,31 and ascending and descending stairs.14 The inability to detect change using the standardized scales of the GMFM and Berg Balance Scale seems to be at odds with conclusions that such scales are responsive to change.25,26,32 In the current study, a ceiling effect was probably encountered,25,33 because the children achieved near maximum possible scores for all conditions. For some functional measures, the wide variation in the data may have increased the SD and hence the chance of a type II error. However, this possibility was minimized by the 2-SD band analysis with which there was less than a 5% chance of type II error. Furthermore, even if the study lacked power, differences were so small that they were unlikely to be clinically significant.

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CONCLUSIONS

Overall, the findings of the current study lend some support to the effectiveness of the LAFO and the HAFO in improving weight-bearing through the hemiplegic leg and through the rear foot during walking and possibly in assisting with push off. Although both AFO types provide foot support, the LAFO supported the rear foot more than the HAFO. Whether an increase in forefoot force is a desirable AFO outcome for children with hemiplegia is uncertain. Neither type of AFO assisted with functional ability, perhaps because of ceiling effects on the measures used. Important information about AFO effect on function might be obtained by replicating this study with younger children with emerging or less developed skill levels or with children who have more severe hemiplegia (such as at Gross Motor Function Classification System, level 2). For older children with established motor skills, it may be necessary to use more challenging measures or a patient-specific functional scale than those used. Despite the lack of consistency in AFO preference, the children and their parents had an important opinion regarding AFO type, and all perceived a benefit from greater foot support. When choosing the type of AFO, the desired effects on functional ability and weight-bearing, along with patient and parent preference and the cost of fabrication, should be considered. The findings of the current study of AFO effects indicate topics worthy of further research such as the biomechanical/physiological and functional advantages of increased foot support, the potential long-term benefit of bone growth, and the effect of increased forefoot force.

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Keywords:

ankle joint/physiology; child; foot; forefoot; growth and development; heel; hemiplegia; orthosis; pressure; weight-bearing

© 2009 Lippincott Williams & Wilkins, Inc.

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