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An Advanced Ground Reaction Design Ankle-Foot Orthosis to Improve Gait and Balance in Individuals With Post-Stroke Hemiparesis: A Case Series

Hale, Jennifer PT, DPT, NCS; Seale, Jill PT, PhD, NCS; Jennings, Jason CO, LO, FAAOP; DiBello, Thomas CO, LO, FAAOP

JPO Journal of Prosthetics and Orthotics: January 2013 - Volume 25 - Issue 1 - p 42–47
doi: 10.1097/JPO.0b013e31827ba11e
Case Report

ABSTRACT The purpose of this case series was to explore the impact of a novel design for an ankle-foot orthosis (AFO) on gait and balance in persons with post-stroke hemiparesis. Five subjects with hemiparesis after cerebrovascular accident were referred for evaluation for an AFO because of gait and balance impairments. All subjects were found to have difficulty in both the swing and stance phases of gait, exhibiting difficulty with swing limb clearance and stance limb stability. The advanced ground reaction design of AFO (A-GRAFO) was chosen as the most appropriate device for orthotic management. The specific orthotic design used in this study was a Dynamic Bracing Solutions Balancer™. Advanced triplanar control of the limb was achieved through the use of a unique segmented weight-bearing impression technique, specific cast modifications, specific alignment parameters, intimate fit, and rigid materials. Gait speed, gait endurance, and balance were assessed for each subject using the 10-m walk test, 6-minute walk test, and Timed Up and Go Test (TUG) before and after receiving the A-GRAFO. All subjects improved in gait speed and gait endurance, whereas four of the five improved in balance. Gait speed increased an average of 0.30 m/second (55%), 6-minute walk distance increased an average of 96 m (52%), and time to complete the TUG decreased by 5 seconds (24%) for subjects using the A-GRAFO compared with the no-orthosis condition. The results of this case series suggest that this orthosis design should be considered for patients with residual hemiparesis after stroke. Further research is warranted to compare the A-GRAFO against more traditional designs.

JENNIFER HALE, PT, DPT, NCS is affiliated with TIRR Memorial Hermann Adult and Pediatric Outpatient Rehabilitation, The Challenge Program, Houston, Texas, and Texas State University, San Marcos.

JILL SEALE, PT, PhD, NCS is affiliated with the University of Texas Medical Branch, Galveston, Texas.

JASON JENNINGS, CO, LO, FAAOP, AND THOMAS DIBELLO, CO, LO, FAAOP are affiliated with Hanger Clinic/Dynamic Orthotics and Prosthetics, Houston, Texas.

Disclosure: The authors declare no conflict of interest.

Correspondence to: Jennifer Hale, PT, DPT, NCS, 601 University Drive, San Marcos TX, 78666; e-mail: jhale@txstate.edu

In patients with stroke, hemiparesis is common. Impairment from stroke can cause compromised gait patterns, which can result in accidents, lack of independence, and inability to work.1,2 Walking is limited in some manner for 60% of survivors.3,4 Therefore, restoration of gait is a common priority for persons after a stroke. An ankle-foot orthosis (AFO) is often prescribed for patients with hemiparesis to facilitate restoration of walking ability and can aid in functional recovery by improving the quality of gait and decreasing likelihood of falls.5

There are several types of AFOs that may be prescribed for the person with hemiparesis, and the choice of design should be made based on the individual needs and goals of the person with hemiparesis. Clinical indications for prescription of an AFO for persons with hemiparesis can be described in two broad categories, representing two essential functions: 1) impaired limb clearance in swing and 2) single-limb stance instability.6 Both impaired swing limb clearance and stance instability may be present in persons with hemiparesis after stroke. Clinicians frequently recognize the need for an orthosis to manage impaired swing limb clearance but less consistently prescribe an orthosis to compensate for single-limb stance instability. Orthoses that limit the degree of plantarflexion can facilitate effective swing limb clearance. Stance limb instability is often caused by weakness in the plantarflexors, quadriceps, and hip extensor muscles. An orthosis that limits the degree of dorsiflexion can control the tibia and increase stance limb stability. Lehmann et al.7 suggests that persons with weakness in the plantarflexors should wear an orthosis that rigidly resists dorsiflexion, so that the orthosis can simulate the function of the plantarflexors during terminal stance and preswing. A study by Gok and colleagues8 found that a more rigid design of AFO improved gait to a greater degree than a more flexible design did. Moderate declines in strength of the plantarflexors in persons after stroke have been demonstrated in multiple studies.9–11 Ankle plantarflexor work and power output is greatly reduced on the paretic side in persons with hemiparesis.12,13

The ground reaction AFO (GRAFO) is a specific type of AFO that is designed to harness the ground reaction moment around the ankle to increase the stability of the knee in stance.14,15 The GRAFO has been used most frequently in children with spina bifida and cerebral palsy. The GRAFO has a solid pretibial shell, as opposed to the pretibial strap of a traditional AFO. The GRAFO transfers the ground reaction force though a solid ankle to the anterior tibia, creating a mechanical plantarflexion moment at the ankle, which results in a knee extension moment of the knee though the mid and terminal phases of stance, thereby restoring the plantarflexion-knee extension couple.16–18 The nonarticulated GRAFO provides maximum resistance to dorsiflexion, as recommended by Lehmann et al.7 for stance stability.

Although commonly used in children as described above, the GRAFO has not been used in adults with post-stroke hemiparesis. To date, there is no published research on the GRAFO in adults with hemiparesis, despite the fact that many adults with hemiparesis have inability to control plantarflexion, dorsiflexion, knee flexion, and knee extension during the stance phase of gait. Given the biomechanical effects of the GRAFO design, it seems likely that this orthosis would benefit adults with post-stroke hemiparesis.

The ability to safely and efficiently ambulate after a stroke is vital. Orthotic devices are often prescribed to facilitate improved ambulation, but little research has investigated specific designs of these orthoses. The purpose of this case series was to describe the impact of a novel advanced GRAFO (A-GRAFO) on gait and balance in persons with post-stroke hemiparesis.

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METHODS

SUBJECTS

The subjects in this study included five individuals with the diagnosis of acquired brain injury (ABI). All subjects had hemiparesis as a result of a cerebrovascular accident and were seen for orthotic management between October 2010 and September 2011. The case series included three women and two men, and the age of the subjects ranged from 48 to 64 years (mean, 56 years). One of the subjects had right hemiparesis, four had left hemiparesis. Time since onset ranged from 6 to 55 months (mean, 25.4 months) (Table 1).

Table 1

Table 1

Each subject was able to ambulate at least 10 m with supervision or modified independence. Four subjects used an assistive device (1 = rolling walker, 1 = single point cane, 2 = walking stick). Subjects 2 and 4 were more chronic and had used an AFO previously. Subject 2 had a solid AFO, in which the trim lines were modified in an attempt to improve fit. These modifications made the orthosis function as a posterior leaf spring AFO, leading to knee hyperextension, knee pain, and overall stance instability. Subject 4 also experienced knee pain, and his current AFO was deemed ineffective because it did not control his stance phase instability. All subjects had a manual muscle test grade of two or less in the plantarflexors, contributing to significant stance phase instability of the affected lower limb.

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ORTHOTIC INTERVENTION

Each subject in this case series was evaluated by the same physical therapist and orthotist to determine the most appropriate orthotic management. The A-GRAFO design was chosen as the most appropriate device for orthotic management, as each of the subjects had significant weakness of dorsiflexors and plantarflexors, poor structural alignment, and stance phase instability.

The specific orthotic design used in this study was a Dynamic Bracing Solutions Balancer™*.This device uses the concepts described in the background to reestablish sagittal, coronal, and transverse plane alignment of the limb. The very rigid carbon graphite laminate materials maintain this structural alignment during weight bearing through the limb.19 This design also extends a rigid toe ramp that is designed specifically to each patient’s physical geometry to the end of the toes, allowing the device to affect the knee through terminal stance.

The design and casting method used incorporated a rigorous assessment and evaluation process. This entailed a careful and thorough gait evaluation, using observational gait analysis, and video gait analysis as needed, to assess step length symmetry, stance phase time, and deviations noted at the trunk, pelvis, hip, knee, and ankle of the affected lower limb. Careful range of motion and manual muscle testing, most notably plantarflexion strength and dorsiflexion range of motion of the impaired lower limb, was performed. Assessment of the patient’s flexibility in the affected limb indicated the degree of correction possible and enabled the orthotist to make decisions about the structural alignment and optimal casting position. The sagittal plane ankle angle was determined by the angle at which the subtalar joint begins to rotate into pronation or supination from its neutral position as the ankle is dorsiflexed with the knee extended. Casting at this angle reduces the stretch on the gastrocnemius tendon when the knee is in full extension and can accommodate for the presence of neuromuscular spasticity of the plantarflexors and prevent abnormal alterations of lower limb alignment that may occur in the weight-bearing position. The subtalar joint was rotated into a neutral posture as the patient’s flexibility allows. This alignment permits the foot to most effectively resist pronatory and supinatory forces.20 Finally, a decision was made regarding the best shank to vertical angle (SVA). This looks at the angle of the shank (which consists of the leg below the knee, AFO, and shoe) relative to vertical and can be described in terms of the angle of incline or recline.21 Alignment was designed to minimize or control the external moments generated at the knee during loading response, midstance, and terminal stance, which ultimately affects the hip as well. For all subjects, the SVA was set at 5°–10° of inclination.

A three-stage, partial weight-bearing casting procedure was used to accomplish a starting point for the optimal alignment for that particular patient. Fabrication involved evaluation of the negative impression, alignment corrections as needed to achieve optimal alignment, positive model rectification, diagnostic check orthosis (DCO), wet carbon graphite lamination, trimming, and strapping (Figure 1).

Figure 1

Figure 1

The fit of the device involved assessment of the DCO on the limb. Force application in multiple three-point pressure systems with adequate force distribution to achieve the necessary structural alignment and comfort was accessed. Adequate clearance over bony prominences and neurovascular structures close to the surface was verified, and an intimate total contact fit in all others areas was achieved. Next, a static weight-bearing assessment of the device was performed and the device was evaluated for control of the weight-bearing structural alignment of the limb and the functional alignment of the device. The final fabrication of the device took place, and the patient was seen for final fitting and tuning of the device, wedge, and shoe combination. Subjects selected their own shoe wear; however, adjustments to the wedging of the orthosis were made to optimize the vertical component of the ground reaction vector anterior to the ankle and knee and posterior to the hip using a Laser Assisted Static Alignment Reference Posture (Ottobock) instrument. This static alignment was indicative of a midstance limb alignment. The contralateral shoe was adjusted to level the pelvis, and finally, the permanent shoe modifications were completed. Dynamic alignment was assessed with the patient walking and involved careful observational analysis. Key points involve a confident pelvic shift of the patient’s center of mass over the involved limb, reduced pelvic retraction, reduced lateral trunk lean, good swing phase clearance, and smooth movement through stance period, reestablishing all three rockers.

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OUTCOMES

Each subject completed pre-AFO and post-AFO assessments, which included measures of gait speed, gait endurance, and balance. The 10-m walk test (10MWT) was used to capture self-selected gait velocity and was performed in a level clinic hallway, free of obstructions, and included a 5-m acceleration and deceleration phase before and after the timed portion of the walk test. Subjects were provided with the same standardized instructions to walk at their comfortable walking pace during the test. Not only is this measure reliable and valid in persons with hemiparesis, it is also a good predictor of overall functional outcome.22–24 Walking endurance was assessed using the 6-minute walk test (6MWT). The 6MWT has been found reliable and valid in patients after stroke.25,26 The Timed Up and Go Test (TUG) is a test that combines balance, transitional movements, and gait and has demonstrated sound psychomotor properties in persons with stroke.27,28 The TUG was recommended by the American Academy of Orthotists and Prosthetists’ State-of-the-Science Conference on “The Effects of Ankle-Foot Orthoses on Balance” as the balance measure of choice for research investigating the effects of AFOs on balance.29

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RESULTS

Five subjects with hemiparesis from stroke who were receiving physical therapy at a neurological outpatient clinic participated in this study. Outcome measures were collected retrospectively for all five subjects just before their initial casting for the A-GRAFO and within 1 to 3 days after receiving the orthosis, to minimize practice time in the brace. Pre- and post-AFO values for self-selected gait speed, walking endurance, and TUG are reported in Tables 2–4.

Table 2

Table 2

Table 3

Table 3

Table 4

Table 4

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WALKING FUNCTION (SPEED AND ENDURANCE)

All subjects showed improvements in both self-selected walking speed (10MWT) and walking endurance (6MWT) when using the A-GRAFO compared with no orthosis. Three of the five subjects showed a change in self-selected walking speed that was large enough to meet or exceed the minimal detectable change (MDC) of 0.30 m/seconds at the 90% confidence interval for persons with stroke.30 Four of the five subjects showed a change in walking endurance that was large enough to exceed the MDC of 54.1 m.31 Although subject 3 did not meet or exceed the MDC, she demonstrated a 30% improvement in walking endurance.

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TIMED UP AND GO

Four of the five subjects showed a decrease (improvement) in time required to complete the TUG, with three of these exceeding the MDC of 3.2 seconds.26 Subject 3 completed the TUG 4.7 seconds slower after orthotic management compared with pretesting. This finding may be attributed to the subject having increased difficulty with the sit-to-stand portion of the TUG because of the rigidity of the A-GRAFO ankle section.

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DISCUSSION

The purpose of this case series was to describe the effects of an A-GRAFO on walking function and balance for individuals with hemiparesis from ABI. Of these five subjects, 100% experienced an increase in walking speed and endurance, and 80% had improvements in balance. The subjects in this case series had immediate improvements, despite relative chronicity, and most of the improvements seen were meaningful as defined by the MDC.

Gait speed increased an average of 0.30 m/seconds (55%) for subjects using the A-GRAFO, compared with the no-orthosis condition. These findings far exceed improvements seen in other literature that compared gait speed in no-AFO conditions with more traditional AFOs. Improvements in gait speed in patients with chronic hemiparesis in these previous studies ranged from 0.02 to 0.12 m/seconds.32–35

Gait endurance increased an average of 96 m (52%) in the A-GRAFO condition. Only one previous study has investigated the effect of an AFO on gait endurance in patients with hemiparesis using the 6MWT measure. Hung et al.36 demonstrated an increase of 19.75 m in the 6MWT in a group of subjects who had used a traditional AFO for at least 5 months.

The time to complete the TUG decreased (improved) by an average of 5 seconds (24%) during A-GRAFO use. Several previous works analyzed the impact of traditional AFOs on balance using the TUG. In four studies of patients with chronic hemiparesis, improvements in the TUG ranged from 3.42 to 5.7 seconds.32–37 However, in one study of the functional effect of an AFO in patients with multiple sclerosis, a small average decrease (0.2 seconds) was found.38 Because the TUG combines sit to stand, walking, and stand to sit, it was hypothesized that an AFO might restrict a patient’s ability to position the foot and shift weight forward over the foot to rise from the chair. This may also explain the one subject in this case series who had a 4.7-second increase in TUG time.

As previously stated, clinical indications for prescribing an AFO include impaired swing limb clearance and stance limb instability.6 The residual plantarflexor weakness experienced by each of the subjects resulted in stance limb instability. Studies by Lehmann et al.7 and Gok et al.8 suggest that rigid AFOs designed to resist dorsiflexion during stance are vital to establish stance limb stability in patients with plantarflexor weakness. Yamamoto and colleagues39 made contrasting conclusions that substitution for plantarflexors was not necessary and might even be detrimental to gait. This conclusion was based on a study in which a small group of patients with hemiplegia were studied while using an experimental AFO that allowed the magnitude of the dorsiflexion and plantarflexion assist moments to be changed easily and independently. These authors concluded that the plantarflexion assist moment was not necessary for hemiplegic gait; however, they did not describe the plantarflexor strength of their subjects. Each of the subjects in this case series had clear plantarflexor weakness, with manual muscle test grades of less than two out of five in all subjects.

Limitations of this study included a small sample size and the retrospective design, which limited standardization. Time between pretesting and posttesting varied from 24 to 72 hrs among the five subjects. The authors recognize this as a limitation because it may have impacted motor learning and contributed to differences in walking and balance outcomes in those subjects that had more practice time within the orthosis.

The A-GRAFO design used in this case series provides the rigid resistance to dorsiflexion that Lehmann et al.7 suggest is necessary to substitute for weak plantarflexors. To date, there have been no published studies using the GRAFO for adults with hemiparesis, yet our findings suggest that this design of A-GRAFO should be considered for this population. Future prospective research is needed to compare the A-GRAFO with more traditional solid and articulated designs in people with hemiparesis. A randomized controlled trial with a larger sample size is essential and should be designed to control for confounders such as neuromuscular spasticity, type of shoe wear, and the amount of training received in each of the orthoses.

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Keywords:

ankle-foot orthosis (AFO); ground reaction; ground reaction AFO (GRAFO); gait; balance; hemiparesis; stance limb instability; stroke; acquired brain injury

© 2013 American Academy of Orthotists & Prosthetists