Many different types of ankle-foot orthoses are available for controlling dynamic equinus in children with spastic diplegic cerebral palsy. The ankle-foot orthosis improves gait by providing mediolateral stability in stance phase (limiting ankle and subtalar movement) and by facilitating toe clearance during swing phase and heel strike at initial contact1-4. In studies involving patients with cerebral palsy, braces have been found to increase temporal gait parameters, including walking speed, stride length, step length, and single-limb stance time, while significantly decreasing cadence and oxygen consumption4-9. Ankle kinematics and kinetics also have been shown to improve with bracing, but their effects on proximal joint kinematics and kinetics are unclear2,5,7,9-16.
Normal gait has five major attributes: stability in stance phase, sufficient foot clearance during swing phase, appropriate swing phase pre-positioning of the foot, conservation of energy, and adequate step length. These may be lost in pathologic gait but can be improved with braces4. Ankle-foot orthoses also have been shown to improve postural stability; fine motor speed and dexterity; upper extremity coordination; and walking, running, and jumping skills7,17,18. Although those studies have demonstrated the benefits of ankle-foot orthosis usage, it is unclear whether one type of brace is superior.
A common choice in brace prescription for children with diplegic cerebral palsy is between a hinged ankle-foot orthosis and a dynamic ankle-foot orthosis. A hinged ankle-foot orthosis incorporates a hinge at the ankle joint and is constructed to limit plantar flexion to neutral while allowing free dorsiflexion. It is made from sturdy polyethylene and extends from 2 cm below the fibular head out to the tips of the toes. A dynamic ankle-foot orthosis has a contoured foot plate constructed with flexible polypropylene, which wraps around the forefoot and malleoli closely. For children with substantial amounts of equinus, the brace extends to the proximal third of the tibia. It has a solid ankle component but allows dorsiflexion through the flexibility of the brace and the absence of a restraining shin strap (Fig. 1).
Variability in studies of cerebral palsy can be attributed to not clearly defining the study population's characteristic features. Different authors have used different terms and definitions to describe children with cerebral palsy. The Gross Motor Function Classification System (GMFCS) was recently introduced to provide orthopaedic surgeons, therapists, and pediatricians with a common language to describe children with cerebral palsy19. The GMFCS is a five-level system that is used to describe gross motor function with an emphasis on self-initiated movements, the ability to sit and walk, and the need for assistive devices. Children with cerebral palsy who walk independently and climb stairs without a handrail but have some limitation in speed, balance, and coordination are classified as level I. Children who walk independently but need to use a handrail to negotiate stairs are classified as level II.
To further improve the clinical management of children who have cerebral palsy, a classification of gait patterns has been developed on the basis of a biomechanical model to link spasticity and musculoskeletal pathology in the lower limbs20. Deviations from normal gait in the sagittal plane kinematics of the ankle, knee, hip, and pelvis were characterized into five groups as true equinus (Group I), jump gait (Group II), apparent equinus (Group III), crouch gait (Group IV), and asymmetric gait (Group V). Children who have cerebral palsy and have a dynamic jump gait demonstrate increased hip and knee flexion with ankle equinus during stance4,20.
The goal of the present study was to characterize the gait and function offered by two commonly prescribed orthotics (a hinged ankle-foot orthosis and a dynamic ankle-foot orthosis) in a highly functional (GMFCS level-I) subset of patients with cerebral palsy who walked with a jump gait pattern. We designed the study to detect if one brace is superior to the other. It was also hypothesized that both ankle-foot orthoses offer significant improvements over barefoot walking in children with mild diplegic cerebral palsy. We specifically investigated the primary outcome of gait (kinematics, kinetics, and temporal/stride parameters) and secondary patient-based outcomes.
Materials and Methods
We conducted a prospective study of fifteen children with a diagnosis of spastic diplegic cerebral palsy who were able to walk independently without an assistive device (cerebral palsy group); the patients had a mean age (and standard deviation) of 7.5 ± 2.9 years. All fifteen subjects exhibited a jump gait pattern4,20 during walking, with a GMFCS score of level I19. The patients had had no surgical intervention in the previous twelve months and no botulism toxin A injections in the previous six months. All children had a range of ankle dorsiflexion to at least neutral on static physical examination with the knee extended, which allowed them to be able to wear the orthotic devices being tested. Twenty normally developing children (control group) with a mean age of 10.6 ± 2.8 years underwent gait analysis for comparison. Informed consent was obtained from the parents of all subjects, and the hospital's institutional review board approved the study.
The cerebral palsy group was evaluated under four separate conditions: (1) while barefoot (baseline 1), (2) after wearing the first ankle-foot orthosis for four weeks, (3) while barefoot after wearing no orthosis for two weeks (baseline 2), and (4) after wearing the alternative ankle-foot orthosis for four weeks. The sequence of bracing was randomized, and the second baseline evaluation was performed to prevent any carryover effects between the two braces. The data for the cerebral palsy group were compared with those for the control group.
The primary analysis was performed with use of a twelve-camera Vicon Motion Analysis System (Vicon, Oxford, United Kingdom), which was used to acquire gait data. Two AMTI force plates (Advanced Mechanical Technology, Watertown, Massachusetts) were used to measure ground-reaction forces, from which joint moments and powers were calculated. Sample sizes were based on a therapeutic study to compare two types of orthoses with use of kinematic, kinetic, and temporal/stride parameters. On the basis of confidence intervals, the aim was to detect a 10% change in ankle dorsiflexion during terminal swing to pre-swing with a power level of 80% at p ≤ 0.05. This required a sample size of fifteen subjects.
A secondary analysis included sections D and E of the Gross Motor Function Measure-88 (GMFM-88), which were administered to assess function involving standing, walking, running, and jumping21. The subjects were tested while wearing the ankle-foot orthoses at the end of the wear periods. Parents completed the Pediatric Outcomes Data Collection Instrument (PODCI)22, which addressed each child's walking ability, standing balance, brace fit, and endurance. Sample size considerations for the patient-based outcomes, using a confidence interval analysis post hoc, indicated that the observed differences in PODCI and GMFM-88 measures were below detectable levels. This finding agreed with the recent findings of the study by Oeffinger et al., in which treatment effects were not seen in highly functional individuals with cerebral palsy (GMFCS level I)23.
Two types of ankle-foot orthoses were custom-fitted for each subject with use of the same positive mold by the same orthotic shop. The hinged ankle-foot orthosis was fabricated from 1/8-inch (0.32-cm) polypropylene extending up the calf to 2 cm distal to the fibular head. Ankle plantar flexion was set at neutral by means of a stop, and free dorsiflexion was allowed through the Gillette hinge (Becker Orthopedic Appliance, Troy, Michigan). The dynamic ankle-foot orthosis was fabricated from 3/32-in (0.24-cm) polypropylene with use of a contoured footplate, wraparound forefoot control, and a plantar flexion block, with dorsiflexion being allowed through the flexibility of the plastic and the absence of a calf strap. There was no hinge, and the brace extended two-thirds of the way up the calf. Subjects had one month to wear and to accommodate to each ankle-foot orthosis, with a two-week period without brace wear between ankle-foot orthosis usage periods.
Polygon software (Vicon) was used to calculate and plot temporal gait parameters, sagittal plane motion, and kinetic data. This system incorporated infrared-sensitive solid-state cameras for locating and tracking reflective markers. The markers were 25-mm spheres covered with reflective tape affixed to osseous landmarks. A videotape recording was made simultaneously from the front and sides during walking. Patients were asked to walk at a self-selected speed along a 10-m walkway. A minimum of three trials were collected for each testing condition.
Data were analyzed with use of multiple one-way repeated-measures analysis of variance to determine if there were significant differences within the cerebral palsy group under the four conditions tested (while barefoot, after wearing the first ankle-foot orthosis for four weeks, while barefoot after wearing no orthosis for two weeks, and after wearing the alternative ankle-foot orthosis for four weeks) and the control group. The kinematic and kinetic data obtained in the present study were chosen for their relevance to the proposed benefits of bracing: improved foot position during stance phase, improved swing-phase foot positioning and clearance, energy conservation, and improved stride length4. The level of significance for differences in kinematic, kinetic, and functional measures was set at p ≤ 0.05. A kinematic difference of 1°, a kinetic difference of 0.02 Nm/kg, and a power difference of 0.05 W were considered to be clinically important in the current study. These values are consistent with those reported by others in similar studies of clinical importance in motion analysis24,25. If significant differences were found, linear contrasts were used to determine where the significant differences occurred. Because of the number of variables analyzed with use of analysis of variance, Bonferroni corrections were used to set the level of significance for each variable category. For each subject and treatment period, a multiple regression was used to fit a Fourier series to the measurements for each anatomical site and measurement plane. The resulting regression model was then used to estimate the average response and associated variance for each subject. Peak values for each subject and treatment period were determined with use of the maximum or minimum value estimated at a predetermined range in the gait cycle. Wilcoxon signed rank sum tests were used to test the hypothesis of no difference of the two barefoot measurements (baseline 1 and baseline 2). As none of the comparisons were significant, they were treated as a single baseline measure. A mixed-effect linear model with a random effect for subject was used to test for treatment period differences in the GMFM mean scores and the PODCI subscores. An adjusted significance level of 0.05 was used to control for multiple testing26-30.
Source of Funding
Shriners Hospitals for Children Foundation, Grant #8540 did not play any role in the conduct of the study.
Temporal Gait Parameters
Temporal gait parameters were compared among the conditions (Table I). Significant increases in stride length and walking speed and a significant decrease toward normal cadence were seen when the hinged ankle-foot orthosis and dynamic ankle-foot orthosis conditions were compared with the barefoot condition. Significant differences in stride length and cadence were seen between the control group and the cerebral palsy group during the barefoot trials. With the numbers studied, the cerebral palsy group under the two different ankle-foot orthosis conditions did not differ significantly from the control group in terms of stride length, walking speed, or cadence.
Kinematic changes during brace usage were most notably found at the ankle, with minimal changes at the knee and hip (Table II). At the ankle, significant differences between the ankle-foot orthosis and barefoot conditions were found during the stance and swing phases (p ≤ 0.05) (Fig. 2). The most notable differences were ankle dorsiflexion at initial contact (0% gait cycle), peak dorsiflexion at terminal stance to pre-swing (34% to 56% gait cycle), peak plantar flexion in pre-swing to initial swing (56% to 70% gait cycle), and peak dorsiflexion in swing (70% to 100% gait cycle). At initial contact, the ankle was significantly more plantar flexed in the barefoot condition (−4.9°) than it was in the dynamic ankle-foot orthosis (+4.6°) and hinged ankle-foot orthosis (+2.6°) conditions. During terminal stance to pre-swing, the ankle was significantly less dorsiflexed in the barefoot condition (+3.5°) than it was in the control group (+15.6°), in the dynamic ankle-foot orthosis condition (+14.2°), and in the hinged ankle-foot orthosis condition (+13.9°). During pre-swing to initial swing, the ankle was significantly less plantar flexed in the dynamic ankle-foot orthosis (−1.0°) and hinged ankle-foot orthosis (−1.3°) conditions than it was in the control group (−15.2°) and in the barefoot condition (−17.7°). During swing phase, the ankle was significantly more plantar flexed in the barefoot condition (−3.1°) than in the control group (+3.6°), the dynamic ankle-foot orthosis condition (+6.0°), and the hinged ankle-foot orthosis condition (+4.6°). No significant differences were found between the two types of ankle-foot orthoses.
The hip and knee joints were minimally affected. At the knee, only peak flexion during swing (60% to 90% gait cycle) was found to be significantly different between the dynamic ankle-foot orthosis condition and the barefoot condition. Bracing had no effect on hip kinematics in the cerebral palsy group. For the hip, significant increases in peak hip flexion during mid-swing to terminal swing (80% to 98% gait cycle) were found when the cerebral palsy group was compared with the control group.
During initial contact to midstance (0% to 16% gait cycle), the cerebral palsy group under the barefoot and braced conditions exhibited a significant increase in plantar flexor demand moment in comparison with the control group (Fig. 3). During terminal stance to pre-swing (40% to 60% gait cycle) in the cerebral palsy group, the ankle moment significantly increased for both the dynamic ankle-foot orthosis condition (0.98 Nm/kg) and the hinged ankle-foot orthosis condition (1.05 Nm/kg) when compared with the barefoot condition (0.80 Nm/kg). During terminal stance to pre-swing (40% to 60% gait cycle), ankle power generation in the control group was significantly higher than that in the cerebral palsy group under the barefoot and braced conditions (Fig. 4). No significant differences in ankle moments and powers were found between the two braces.
Functional Outcome Measures
In the cerebral palsy group, PODCI subscales were analyzed to examine differences among the barefoot and braced conditions (p ≤ 0.05). No significant differences were found among the barefoot, dynamic ankle-foot orthosis, and hinged ankle-foot orthosis conditions (Table III). For the GMFM, the mean score and sections D and E were evaluated. Regardless of treatment, the children exhibited high GMFM scores, with no significant differences noted among the conditions (Table III).
The present study supports the benefits of ankle-foot orthosis use for children with diplegic cerebral palsy and a jump gait pattern2,6,7,13. Both the hinged ankle-foot orthosis and the dynamic ankle-foot orthosis were equally effective for improving temporal, kinematic, and kinetic parameters. The analysis comparing the two baselines indicated no significant differences in kinematic, kinetic, or temporal/spatial parameters, confirming that there was no carryover effect from the first treatment. Effective brace prescription should result in improved gait and perhaps prevent deformity. Previous studies have shown that braces improve walking parameters, but those studies have included children with cerebral palsy with various GMFCS levels7,12,14. The purpose of the present study was to compare the effectiveness of hinged and dynamic ankle-foot orthoses for improving gait and motor function in a homogeneous group of children with diplegic cerebral palsy exhibiting a jump gait pattern.
Gait analysis is beneficial in the evaluation of treatment methods for children with cerebral palsy. Kinematic and kinetic data allow the clinician to evaluate multiple joints simultaneously to determine the primary, secondary, and tertiary deficits4,31. The recognition of common pathologic gait patterns (such as jump gait, crouch gait, and stiff gait) in children with cerebral palsy provides a basis for description and treatment among clinicians4,32. Our patient population had a jump gait pattern that was characterized by increased hip flexion, knee flexion, and ankle equinus during stance phase in the gait cycle. The type of gait pattern along with the GMFCS level of the child with cerebral palsy may be very important for brace prescription. The ultimate goal of the clinician is to improve the quality of life of the patient. Gait analysis is an important tool in helping the clinician to achieve this goal4,14,31. Outcome measures such as the GMFM and the PODCI are tools to measure motor function and quality of life. The GMFM and gait parameters have been reported to directly correlate, suggesting the GMFM may serve as an indicator for gait analysis. Typically, as the GMFCS level becomes greater, the GMFM scores and gait parameters move away from the norm2,33. In our study, the gait parameters of the children who had cerebral palsy improved with bracing, with no significant changes in the GMFM scores. Because the children in the present study were highly functional (GMFCS level I), the GMFM scores were high for all conditions tested and failed to discriminate between conditions.
In one previous study of patients with cerebral palsy that demonstrated significant differences in GMFM scores between the barefoot and hinged ankle-foot orthosis conditions, twelve of the sixteen children were more severely affected by cerebral palsy (GMFCS level II) than the patients in our population were7. Another study demonstrated that the GMFM-88 was sensitive to functional changes when walking aids or orthoses were worn; however, the study evaluated children at all GMFCS levels34. In that study, the subset of children at level I showed a small but significant change on section E of the GMFM. An additional study demonstrated that supramalleolar braces were associated with significant improvements in the GMFM-88, but the investigators studied children who were less than 7.5 years of age with GMFCS levels that ranged from I to IV, and the braces were only worn one day35.
The perception of the benefits of ankle-foot orthoses is important for both the clinician and the patient. Improvements in kinematics may have limited impact on satisfaction and function in these children. The children may not receive sufficient benefit from the orthoses to offset the cosmetic dissatisfaction associated with using the brace. We are not aware of any studies that have used the PODCI to assess the effects of braces. Although gait analysis showed marked improvements during brace wear, with the outcome tools used in the present study, parents did not detect any improvements in their child's daily functional activities. Bagley et al. reported that functional assessments (including the PODCI, GMFM, Pediatric Quality of Life Inventory, Functional Independence Measure for Children, and Gillette Functional Assessment Questionnaire) varied in their ability to distinguish between children with different GMFCS levels (e.g., level I, II, III), indicating that the quality of life is not related to the level of involvement36.
As all groups scored high on the PODCI subscales in the present study, a ceiling effect also may have occurred in this highly functional group. It is possible that the benefits of improved gait were not perceived by the patient or their parents or were offset by other factors such as the inconvenience of brace wear. Other studies of orthopaedic treatments for cerebral palsy have also demonstrated possible ceiling effects with the administration of the PODCI, threatening the utility of this questionnaire in this patient population36,37. Meaningful differences in PODCI and GMFM scores are reported when accompanied by a change in GMFCS level. Some authors also have noted that treatment effects are more frequently seen at higher GMFCS levels23. In the current study, there was no change in GMFCS level; therefore, no significant differences in PODCI and GMFM scores were detected among the conditions.
The debate whether dynamic ankle-foot orthoses are effective for improving walking in children with cerebral palsy continues. The dynamic ankle-foot orthosis in the present study extended to the proximal third of the tibia to provide greater ankle stability and a plantar flexion stop. It was comparable with the hinged ankle-foot orthosis in terms of ankle support, allowing us to objectively evaluate the biomechanical effects produced by the contoured footplate of the dynamic ankle-foot orthosis. Because the two braces were equally effective for improving gait parameters, the height of the ankle-foot orthosis on the calf seems more important for controlling ankle equinus than the footplate and wraparound design. The contour of the footplate of the dynamic ankle-foot orthosis did not yield further kinematic improvements in the children tested in the present study. For an older child, the dynamic ankle-foot orthosis may not be the best option as the high posterior portion of the brace is left behind when the tibia translates over the foot between the second and third rockers, and it may get caught in the pants leg. It may be a viable option for younger children when a brace without a hinge is easier to fit in a small shoe. The absence of a hinge also allows the brace to be more contoured to the hindfoot and ankle. Cosmesis is important to encourage compliance and acceptance by the parent and child, but we were unable to measure that effect on brace preference in the present study. Recently, Gage theorized that hinged ankle-foot orthoses enable crouching during long-term use in children with diplegic cerebral palsy4. We are not aware of any studies that have substantiated this theory. However, long-term follow-up of brace wear is needed to determine the overall effect on the proximal joints and muscles as the child matures.
The present study is a preliminary evaluation of ankle bracing in children with diplegic cerebral palsy. The limitations of the present study include the use of a one-segment foot model with markers placed on the brace and shoe instead of directly on the foot. A midfoot break, if present, would falsely increase stance-phase dorsiflexion. The foot position inside the orthosis cannot be detected by external markers. For instance, the ankle in equinus could be undetected with shoe deformation during second rocker in stance phase. A better approach would be to use a foot and ankle model in which the motion of the hallux, forefoot, midfoot, and hindfoot could be measured. The only way to assess the true position of the foot in the brace and shoe is through a static or dynamic radiograph measurement38. Second, the manufacturing of orthotics has not been standardized, resulting in dynamic ankle-foot orthoses with different thicknesses and brace heights, which may make comparisons difficult. Different ankle-foot orthosis fabrications may alter the child's gait pattern and will impact brace durability and longevity. Third, the controls for the present study were a sample of convenience and were an average of three years older than the test subjects. Mature gait (as determined on the basis of kinematics and kinetics) is established by the age of seven years39. Pierce et al., in gait studies of 213 norms, reported no significant differences in the walking speed of children who were six to fourteen years of age40. In that study, however, significant differences were identified in terms of stride length and cadence. The three-year age difference in our two populations falls within this age span. Our results also demonstrated no significant differences in walking speed between the control and cerebral palsy groups. There were, however, significant differences in terms of cadence and stride length, which could be attributed to the age difference between the two populations. Finally, long-term follow-up studies with a larger population of subjects must be performed to determine the effects of ankle-foot orthoses on the proximal joints as well as to evaluate higher functioning skills such as stair-climbing, running, and jumping.
Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from Shriners Hospitals for Children, Grant #8540. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at Motion Analysis Laboratory, Shriners Hospitals for Children, Chicago, Illinois
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