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The Effect of Long-Term Ankle-Foot Orthosis Use on Gait in the Poststroke Population

Andrea J. Pavlik, CO

ABSTRACT

The goal of this study was to determine the clinical relevance of ankle-foot orthosis (AFO) use on walking ability and other gait parameters in the poststroke population. The study design was a crossover one with randomization. Four stroke patients wearing a thermoplastic AFO for at least the past 6 months and who had completed individualized rehabilitation programs were included. Walking ability of each subject was measured on a 10-m paper walkway and via the timed "Up and Go" (TUG) test. Patients were measured for their walking ability both wearing and not wearing their AFO. Step and stride lengths were calculated from the paper walkway. The mean difference in favor of the AFO for walking speed was 21.58 cm/s, and for the TUG 3.42 seconds. The mean difference for step and stride lengths in favor of the AFO was 3.63 and 5.93, respectively. Seventy-five percent of subjects reported feeling less exertion while wearing the AFO. The effect of AFO use on walking ability is statistically significant, but when compared with the predefined values for clinical relevance, only walking speed and step and stride lengths are clinically relevant. The effect on subjectively reported rates of perceived exertion suggests that other factors play a role in the motivation to use an AFO. The ability to walk is perhaps one of the most functionally significant goals of any rehabilitation process after stroke. The ability to independently ambulate ultimately determines the degree to which an individual will be able to return to the community. Often individuals with stroke are prescribed an ankle-foot orthosis (AFO) to assist in functional ambulation because of the loss of muscle strength, spasticity, impaired sensorimotor control, or the loss of cognitive function. 1 The AFO functions primarily in stance to correct deformity and control motion and in swing phase to compensate for muscle weakness-in the case of the individual with stroke to promote dorsiflexion to provide toe clearance in swing. The AFO can also be sued to indirectly affect knee position in stance. However, the long-term effects on gait and daily use leave conflicting evidence in the literature.

Hemiplegic gait is described as slow and asymmetric. The greatest deficit in gait patterning is perhaps the plantarflexed position the foot assumes through the swing phase of the gait cycle.1 Hemiparetic patients usually have less dorsiflexion during midswing and terminal swing because of a loss of motor control, spasticity of the gastrocnemius-soleus group, and ankle contracture,2 altering the position of the foot for initial contact and blocks toe clearance during swing. The positioning of the foot also blocks tibial advancement because of the presence of an extensor synergy pattern that produces hyperextension at the knee. The combination of these gait deficits ultimately leads to a decrease in walking ability. Use of an AFO allows control of plantarflexion at the ankle and allows for a more normal heel strike to occur at initial contact, thus beginning the stance period of gait in a more normal manner. Lehmann3 found that hemiplegic gait speed ranged from 13 to 92 cm/s as compared with 82 to 132 cm/s for comparably aged "normal" individuals, or that hemiplegic gait is on average half the speed of "normal" gait. Hemiplegic patients also showed an increase in asymmetry-walking with a shortened stance phase and a longer swing phase on the affected side.4 Roth et al.5 also found that gait velocity correlated with balance, limb strength, cadence, and ambulatory independence. Literature reveals few randomized control trials concerning AFO use and walking ability in stroke patients.6 Beckerman et al. reported no clinically relevant benefits of an AFO on walking ability; however, there are several studies7,8 that suggest improvements in walking speed and stride length.

It is well published that AFOs are the most versatile and most frequently used lower extremity orthosis to overcome stroke-related gait deficits. Leung and Moseley 7 reported that overall, research shows positive evidence on the improvement of walking ability using an AFO. However, the effect of daily independent practice or use remains unclear. Consequently, the aim of this study was to determine the clinical relevance of long-term AFO use on the walking ability of stroke patients who have been discharged from rehabilitative services. ( J Prosthet Orthot . 2008;20:49–52.)

METHODS

Subjects were recruited from a list of individuals receiving an AFO fitting the L-code billing descriptors of any plastic fabricated AFO at Actra Rehabilitation facilities in Wisconsin. All AFOs were constructed of polypropylene and were either jointed or solid ankle. To be eligible for this study, patients were required to have had an initial infarct within the past 10 years and were at least 6 months post incident, did not have more than one infarct and had only one hemiparetic side involved. Patients were required to have worn an AFO fabricated from polypropylene for at least the past 6 months and to have completed a poststroke rehabilitation program. Patients were also required to be able to independently ambulate both with and without their AFO (the use of other assistive devices was allowed for safety).

From a sample size of 25, four patients met the inclusion criterion and agreed to participate in the research. All patients meeting the criterion were diagnosed as having ischemic strokes and having blockages in an artery leading to the brain with resultant hemiparesis. The mean age of subjects was 60 ±13.4 years with an average of 75 months (minimum of 10 months, maximum of 120 months) since initial infarct. There were three male and one female patient volunteers, two having left-sided hemiparesis and two with right-sided hemiparesis. All patients had a primary poststroke diagnosis of foot drop as a result of cerebral vascular accident. All four patients reported wearing their AFOs full time since the time of fitting of the device. As a side, three of the four subjects used a cane for safety and balance purposes.

Subjects were excluded if they had more than one stroke or had other comorbidities that negatively affected walking ability.

ANKLE-FOOT ORTHOSIS

Patients who met all inclusion criteria used a polypropylene AFO that had been custom-fabricated from a cast of the patient's limb to optimally address each individual's specific needs. All left hemiplegic patients used an articulated AFO (Tamarack dorsiflexion assist joints and an adjustable plantarflexion stop). All right hemiplegic patients used a solid AFO. Each AFO was designed based on each individual's specific deficits and was fabricated and fit at least 6 months before the start of this study.

OUTCOME MEASURES

Walking ability was operationalized by using the following:

  1. Comfortable walking speed

  2. Timed "Up and Go" (TUG) test

  3. Footprint recording

All subjects were measured ambulating both wearing their prescribed AFO and without the AFO. Each subject wore his or her individual shoes for each trial condition. The sequence of AFO use or nonuse was randomized.

COMFORTABLE WALKING SPEED

Comfortable walking speed, defined as the self-selected speed the patient felt most stable with, was determined for each participant on a 10-m paper walkway. The middle 7 m was timed to ensure that optimal velocity was reached and to help negate the effects of gait initiation and termination. Each subject walked the 10-m walkway three times for each condition (with and without the AFO) while the number of steps taken and the time to complete the task was recorded. On the third trial under each condition, powdered chalk was applied to the subject's shoes to record the footprints along the walkway. These footprints were later analyzed for gait symmetry.

TIMED "UP AND GO" TEST

In this test, the subjects were asked to rise from a seated position, walk 3 m, turn around, walk back to the chair, and return to sitting. Each subject performed three trials for each condition with the average time to complete the task recorded.

The TUG has been documented to be a reliable test for quantifying functional walking ability in the elderly population with varied and mixed medical histories, including stroke. In poststroke subjects, TUG tests can be highly responsive providing that gait speed does not approach normal values.9

RATE OF PERCEIVED EXERTION

The Borg Rating of Perceived Exertion (RPE) 6- to 20- point scale was used to determine the activity intensity of each trial for each test. Perceived exertion is a subjective description of how hard an individual is working. It is based on the physical sensations a person experiences during physical activity, including increased heart rate, increased respiration rate, increased sweating, and muscle fatigue. Although RPE is a completely subjective measure, an individual's exertion rating may provide a fairly good estimate of the actual heart rate during physical activity, which correlates with the intensity of the activity. 10 In this study, the scale was used to determine each individual's subjective attitude toward the difficulty of each trial.

DATA ANALYSIS

TUG, walking speed, and step and stride lengths were statistically analyzed using a paired t-test. The rate of perceived exertion results were analyzed using the Fisher's test.

1. Walking speed: A difference of 20 cm/s in walking speed with and without the AFO was defined as clinically relevant based on the study by Perry et al. 11 Perry assigned walking speed into one of six categories, termed the Hoffer Functional Ambulation Scale. The last three categories of this scale, most-limited, leastlimited community, and community walkers, were deemed to be the most relevant based on the inclusion criterion of independently ambulatory. Between these categories, a mean difference of 20 cm/s was observed.

2. TUG test: A difference of 10 seconds was defined as clinically relevant based on the study by Podsiadlo and Richardson. 9 Podsiadlo found significant differences in Barthel scores (a rank of functional independency after stroke) with a TUG score of less than 20, 20 to 30, and more than 30 seconds.

3. Gait parameters: It has been observed that in normal adult individuals, step length is, on average, 75 cm and stride length is 150 cm, with these values gradually decreasing in the elderly. 1 Healthy men over the age of 60, on average, walk at a speed of 118 cm/s; comparably, women aged 64 or over have an average speed of 96 cm/s. 2 Therefore, it was determined by the author that improvements of 20% or more were significant in both parameters.

4. Rate of perceived exertion: According to Borg, 10 a high correlation exists between perceived exertion rate X10 and actual heart rate; for example, an RPE score of 10 correlates to heart rate of 100 beats/minute. Thusly, a decrease of 2 points indicated a decrease in heart rate of approximately 20 beats/minute. For the purpose of this study, a decrease of 2 points or more was considered significant because of this correlation with heart rate, and consequently, a decrease in energy expenditure.

RESULTS

Table 1 shows the descriptive statistics and the results of the paired t-test (p values) for the 10-m walk and the TUG tests. Table 2 shows the descriptive statistics and the results of the paired t-test (p values) for step length and stride length.

EFFECT ON WALKING ABILITY

The mean difference in favor of the AFO for walking speed was 21.58 cm/s, and for the TUG test 3.42 seconds. The mean difference for step and stride lengths in favor of the AFO was 3.63 and 5.93, respectively. Results show a statistically significant effect in favor of AFO use in walking speed, TUG, and step and stride lengths. However, when the predefined significance values are taken into account, only the walking speed and step and stride lengths showed clinical relevance.

EFFECT ON RATE OF PERCEIVED EXERTION

Of the four subjects studied, three reported less exertion while wearing the AFO ( > 2 points change on the RPE scale) in all trials. These differences were also judged as clinically relevant.

DISCUSSION

The aim of this study was to determine the clinical relevance of the effect of long-term AFO use in stroke patients who have been independently ambulating and who have successfully completed all prescribed rehabilitation programs. Results show that the effect of an AFO on walking ability and RPE is statistically significant. Statistical significance was defined at the a = 0.05 level. Compared with the predefined relevance values, only the TUG showed differences too small to be considered clinically relevant, which is in opposition to the study by Beckerman et al. 6

The rate of perceived exertion values obtained are clearly in favor of the AFO and judged as clinically relevant. The use of the Borg RPE scale has been shown to be a valid and reliable way of subjectively correlating activity performed to heart rate, and thus, energy expenditure. 10 All patients in this study reported feeling that it was not as difficult to perform the same activity when wearing their AFO, as compared with not wearing the AFO. It was also noted that the dependence on the use of a cane was decreased with the AFO (less lean on the cane). In the present study, all four subjects mentioned the beneficial effects of the AFO and reported that they could perform longer ambulation tasks with the AFO and were less fatigued when using the AFO. Two of the four subjects also reported feeling more stable while wearing the AFO.

The mean difference in walking speed in favor of the AFO is 21.58 cm/s. This finding is comparable with the findings in literature; Leung and Moseley 7 reported in a series of four studies similar to this investigation that walking speed varied between 0 and 12 cm/s with a moderate degree of variability in the 95% confidence interval.

The clinically relevant variances in walking speed and TUG test were based on the studies of Perry et al. 11 and Podsiadlo and Richardson, 9 respectively. When comparing differences in walking speed for each patient both with and without the AFO, only two of the four subjects changed to a higher category in Perry's classification.11 The value for determining clinical relevance defined value for the TUG may be too high. In a study by Geiger et al., 12 smaller differences in TUG were found following physical therapy immediately after and in recovery of 3 months after stroke. Conversely, the values chosen for clinical relevance were based on functional scores of the modified Hoffer Functional Ambulation Scale and the Barthel Index.

In conclusion, for stroke patients using an AFO for activities of daily living, the AFO is beneficial for their walking ability and for their subjective exertion and self-confidence. When relating performance scores to clinically relevant changes, only small differences in increasing functional scores are seen. Differences in walking speed, step and stride lengths, and RPE are statistically significant, but only walking speed was determined to be clinically relevant. Lehmann 13 has stated that "one must recognize that these orthoses are worn by many patients who can walk without them but who cannot walk safely," so perhaps one needs to accept that the effect of an AFO may often be too small to be clinically relevant.

ACKNOWLEDGMENTS

The author thanks Tom Current, CPO, and Jack Schultz, CO, from Actra Rehabilitation Associates for their technical and professional assistance.

Disclosure: The authors declare no conflict of interest.

Correspondence to: Andrea J. Jeske, CO, Actra Rehabilitation, 10700 W Burleigh St, Milwaukee, WI 53222; e-mail:


ANDREA J. PAVLIK, CO, is affiliated with the Actra Rehabilitation, Milwaukee, Wisconsin.

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