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Valid and Reliable Instruments for the Clinical Assessment of the Effect of an Ankle-Foot Orthoses on Balance

Seale, Jill PT, PhD(c), NCS

JPO Journal of Prosthetics and Orthotics: October 2010 - Volume 22 - Issue 10 - p P38-P45
doi: 10.1097/JPO.0b013e3181f301ab
Proceedings
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Balance, a complex integration of the somatosensory, visual, and vestibular systems, has a substantial impact on functional ability in persons with locomotor disorders or sports-related injury. Ankle-foot orthoses (AFOs), by virtue of their observable impacts on the somatosensory system, are likely to influence balance. To investigate the effect of AFOs on balance, valid, reliable, and clinically justifiable balance measures need to be identified and used. The purpose of this article is to review the psychometric properties of those outcome measures with established clinical utility in the assessment of balance and to identify the potential balance measures for use in orthotic management, both clinically and in future research. This review includes the testing procedures and psychometric data for the following outcome measures: Berg Balance Scale, Pediatric Balance Scale, Activity-Specific Balance Confidence Scale, Timed Up and Go Test, Functional Reach Test, Single-Leg Stance Test, Star Excursion Balance Test, and Balance Error Scoring System. Assessments are discussed related to the target subjects: adult with locomotor disorder, pediatric with locomotor disorder, or athlete. All measures in this review were found to have at least acceptable psychometric properties. Of all the measures reviewed within the locomotor dysfunction category, the Timed Up and Go Test seems to have the most sound psychometric properties as a measure of dynamic balance and seems to be the most sensitive balance measure used thus far in research investigating the effects of AFOs on balance. Of the recommended measures of balance for the athletes, both the Star Excursion Balance Test and the Balance Error Scoring System have similar psychometric pros and cons and limited use in orthotics research. Utilization of more than one measure is suggested, so that assessment can be made of more than one health-related domain.

JILL SEALE, PT, PhD(c), NCS, is affiliated with the Department of Physical Therapy, University of Texas Medical Branch, Galveston, Texas.

Disclosure: The authors declare no conflict of interest.

Correspondence to: Jill Seale, PT, PhD(c), NCS, University of Texas Medical Branch, Department of Physical Therapy, 301 University Blvd, Galveston, TX 77555; e-mail: jiseale@utmb.edu.

Balance is a complex integration of the somatosensory, visual, and vestibular systems. Whether standing or walking, the goals of balance are to maintain postural alignment, facilitate voluntary movement, and recover equilibrium in the presence of external influence.1,2 A person's postural control provides them with the ability to sense and respond to those threats to their stability that might move their center of gravity outside of the base of support. This is done through the use muscle activation to counteract such threats and prevent falls.3 Many studies have found that changes in balance ability correlate strongly with changes in function. Therefore, interventions that impact balance may have direct influence on function.

Ankle-foot orthoses (AFOs) are used in a variety of pathologies to treat a host of different impairments and their consequential functional limitations. Balance compromise is common in many of these musculoskeletal and neuromuscular pathologies. Because of their inherent effects on the ankle joint, AFOs may have positive or negative impacts on balance. Therefore, balance should be assessed before and after the prescription, fabrication, and fitting of the orthoses. However, to objectively assess the effects of AFOs on balance, valid and reliable balance measures are needed.

The literature is replete with measures of balance and postural stability. Choosing the “right” measure can be a daunting task. Physical therapists, orthotists, and physical medicine and rehabilitation physicians alike should be consistently using valid and reliable balance measures to guide the decision-making process for AFO prescription, fitting, and training. When evaluating an outcome measure, it is important to consider the health or health-related domain addressed in the measure. According to the International Classification of Functioning, Disability, and Health (ICF),4 these domains are body functions and structure, activities, and participation. Each of these domains is impacted by both environmental and personal factors specific to the patient in question (Figure 1). When evaluating an intervention, it is important for clinicians to assess its impact on more than simply the impairment level. The resultant effects on specific activities and the overall participation of the patient are necessary to truly determine the impact of the intervention.

Figure 1.

Figure 1.

The goal of this review is to highlight those balance outcomes with the greatest utility, validity, and reliability for clinical use in the orthotist's office, rehabilitation hospital, outpatient clinic, or physician's examination room. Many measures have been proven reliable and valid within a variety of populations. This article will focus on clinical measures of balance in athletes (primarily musculoskeletal) and those with locomotor disorders (primarily neuromuscular in origin). The review will key in on measures that can be performed quickly and without specialized equipment in the clinical setting. The review will also seek to identify measures at all levels of the ICF. The purpose of this article is to review the psychometric properties of those outcome measures with established clinical utility in the assessment of balance and to identify the potential balance measures for use in orthotic management, both clinically and in future research.

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CLINICAL MEASURES OF BALANCE

Functional balance assessments in the clinic environment allow clinicians a means of assessing balance status over time and in the presence of various interventions by evaluating individual performances on a variety of functional tasks. These tests can range from subjective descriptions to quantitative scoring of performance variables. A recent review of clinical balance assessment tools by Mancini and Horak5 summarized the most commonly used approaches to assess balance. These authors identified the Activities-Specific Balance Confidence (ABC) Scale, the Berg Balance Scale (BBS), the Tinetti Balance and Gait Assessment, the Timed Up and Go (TUG) Test, Single-Leg Stance (SLS) Test, the Functional Reach Test (FRT), the Balance Evaluation Systems Test (BESTest), and the Physiological Profile Approach (PPA). Of these, the last two are considered to be system assessments aimed at determining not only the presence of a balance problem, but also to discern the underlying cause of the balance deficit. In addition to identifying the presence of balance problems, both the BESTest and the PPA are designed to further determine the underlying causes of the balance deficit. The Tinetti Balance and Gait Assessment, the BESTest, and the PPA will not be considered in this article because of the time and/or equipment necessary to complete each test. The article by Mancini and Horak5 did not address the balance measures for pediatrics or athletes; therefore, other resources were used to determine appropriate balance measures for the athlete.

For the purpose of this review, the following clinical measures of balance will be discussed: the BBS, Pediatric Balance Scale (PBS), ABC Scale, TUG Test, FRT, SLS Test, Star Excursion Balance Test (SEBT), and Balance Error Scoring System (BESS). These measures were selected based on their ease of administration, both in terms of time and equipment needed, and their psychometric properties. Assessments taking longer than 15 minutes to complete or requiring excessive or complicated equipment were excluded. Assessments will be discussed related to the target subject: adult with locomotor disorder (Table 1), pediatric with locomotor disorder (Table 2), or athlete (Table 3).

Table 1

Table 1

Table 2

Table 2

Table 3

Table 3

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CLINICAL MEASURES OF BALANCE FOR ADULTS WITH LOCOMOTOR DISORDERS

The ABC Scale is a self-report questionnaire that measures perceived balance confidence for the performance of 16 activities of daily living. The ABC Scale captures balance confidence in progressively more challenging contexts, from moving about the home to ambulating in the community in demanding environments. Respondents rate items from no confidence to complete confidence.6 The ABC Scale has good test-retest reliability (intraclass correlations [ICCs] 0.7–0.92), good internal consistency, and greater item responsiveness than the Falls Efficacy Scale.6 The ABC Scale has demonstrated good convergent and criterion validity and can be completed in less than 15 minutes. However, it is important to keep in mind that this is a measure of self-perception, rather than an identification of actual balance impairment. This measure typically identifies the activities that a person avoids, rather than predicting future falls.7 The ABC Scale has been used within the elderly population and with persons with lower limb amputation, stroke, multiple sclerosis (MS), postpolio syndrome, and incomplete spinal cord injury. To the best knowledge of the author, no published investigations of AFOs have incorporated the ABC Scale as an outcome measure.

The BBS was identified by Korner-Bitensky et al.8 as the most commonly used assessment tool throughout the continuum of health care in stroke rehabilitation. The BBS is a 14-item assessment of functional tasks in sitting, standing, and postural transitions.9 The BBS takes approximately 15 minutes to complete and requires only a ruler, stopwatch, chair, and stool or step. A recent review by Blum and Korner-Bitensky10 found that 21 studies of the BBS in patients with stroke demonstrated excellent internal consistency (Cronbach α = 0.92–0.98), interrater reliability (ICCs = 0.95–0.98), intrarater reliability (ICC = 0.97), and test-retest reliability (ICC = 0.98) for the BBS. Sixteen studies within this review found excellent correlations with many functional measures including (but not limited to) the Fugl-Meyer Assessment, the Functional Independence Measure, and the FRT.10 The BBS was found to have moderate to excellent sensitivity, and BBS scores have demonstrated predictive value for discharge destination, length of stay, motor ability, and disability.10 However, this is contradictory to two other studies that found sensitivity of the BBS as poor to moderate in the elderly and the patients with acute stroke.9,11 According to Blum and Korner-Bitensky,10 three studies demonstrated either floor or ceiling effects, and because of this, the authors suggested that the BBS should be used in conjunction with other balance measures such as the ABC Scale. Cut-off scores have been identified, which indicate an increased risk of falling, with a score of <45/56 indicative of increased fall risk in the elderly.12 However, the BBS has not been shown to be predictive of falls in all populations.

A shortened, seven-item version of the BBS was developed (the BBS-3P). This version was found to be psychometrically similar in validity, reliability, and responsiveness to the original BBS when used for persons with stroke.13,14 Chou et al.13 found the BBS-3P to be simpler and faster to complete than the BBS.

The BBS has been used in a small number of studies investigating the efficacy of AFOs. Wang et al.15 investigated the effects of AFOs on balance in persons with hemiplegia of short and long duration and used the BBS as a measure of functional balance. The BBS demonstrated no significant differences between the no AFO and AFO conditions in this study, even though static and dynamic Balance Master Systems measures did show significant differences.15 Anterior and posterior AFOs were compared in persons with hemiplegia, and the BBS scores did not differ significantly for any condition (barefoot, anterior AFO, or posterior AFO), although gait measures did differ significantly between the barefoot and AFO conditions.16 It is also important to note that the average BBS in this study was 37.3, meaning that the average subject was at the upper end of the medium fall risk category. Simons et al.17 found that AFOs did significantly improve BBS score, when compared with no AFO, in stroke survivors. These findings were despite no significant improvements in weightbearing symmetry and dynamic balance control as measured by forceplates on a movable platform. Finally, lower BBS scores were identified as being associated with the use of AFOs at discharge from an inpatient rehabilitation unit, with those patients scoring 25 or less being significantly more likely to receive an AFO on discharge.18 No orthotics research has used the BBS-3P as an outcome to date.

The Equiscale test is a derivative of the BBS and was created to evaluate balance in persons with MS.19 It has been used to assess the impact of two different AFO designs within the MS population.20 The results suggest that nonarticulated AFOs may improve static balance but have a negative effect on dynamic balance. In contrast, articulated ground reaction AFOs with a dorsiflexion stop at 90° and available plantar flexion motion seem to improve both static and dynamic balance.

The TUG Test is a timed test requiring the person to rise from a chair, walk 3 m, turn around, walk back, and sit down.21 This is a very quick test, taking 3 minutes or less and needs only a stop watch and a chair to complete. Yelnik and Bonan22 suggest that the TUG Test is the simplest and most reliable clinical tool for assessing balance, because it is a timed measure as opposed to a rating scale. The TUG Test is widely used and was found to be a sensitive and specific measure for pinpointing community-dwelling older adults at risk for falls.23 The TUG Test has demonstrated sound psychometric values in many populations, including, but not limited to frail elderly, persons with Alzheimer's disease, Parkinson's disease, and stroke.5,24–26 The TUG Test has a strong correlation with the BBS (r = 0.72), with conflicting reports of a possible ceiling effect.5,27 A recently modified dual task version of the TUG Test can include either a cognitive component (such as counting backward from 100) or a manual component (such as completing the TUG Test while carrying a glass of water).28

The TUG Test has been used as an outcome measure in several studies investigating the effects of AFOs. Simons et al.17 investigated the use of AFOs in persons poststroke and found significant differences in TUG scores with and without AFO, even though no significant differences were found in weightbearing asymmetry or dynamic balance as measured by instrumented devices. A study investigating the effect of an AFO in persons with MS found that mean times for the TUG Test were greater using the AFO than no device; however, these results were not statistically significant, and further analysis found that the TUG scores were not related to the type of AFO used.29 A randomized control trial for persons with chronic stroke found a 3.6-second improvement in TUG scores for patients with AFOs as opposed to no AFO.30 A similar study by Pavlik31 revealed a 3.42-second improvement in TUG score in those patients wearing an AFO.

The SLS or One-Leg Stance Test is a simple, quick measure of static balance, with application to both adults with locomotor dysfunction and athletes. The SLS Test is a timed measure of single-limb stance with eyes open and can be repeated with eyes closed. The time is captured from when one foot leaves the ground until: the arms come uncrossed, the raised foot touches down, the weightbearing foot is moved, the eyes are opened during the eyes closed trial, or a maximum of 45 seconds elapses. Springer et al.32 suggest that three trials be completed of each condition and that these occur in alternate order. The SLS Test has demonstrated good intersubject reliability (ICC = 0.73) and interrater reliability (ICC = 0.75–0.998).5,32 Although this is only one test of static balance, it takes only 1 minute to complete and has been able to identify those at increased risk of falls.5 Normative values have been established for eyes open and closed, and a significant age-dependent decrease has been demonstrated in both eyes open and eyes closed conditions.32 To the best knowledge of the author, SLS Test has not been used as an outcome in any prior orthoses research in persons with locomotor dysfunction. However, Jerosch et al.33 demonstrated a significant difference in SLS scores between injured and noninjured ankle joints and showed a significant difference in SLS scores in no brace condition compared with two athletic type braces (Mikros and Aircast), with better SLS scores in the brace conditions. Also important to note, it has been suggested that the ability to maintain SLS is linked to the proprioception of the ankle.34 Further in this article, SLS Test will be used as one of three positions in a measure to identify postural instability in persons after mild traumatic brain injury.

The FRT was developed by Duncan et al.35 to assess limits of stability by measuring maximal reach while maintaining a fixed standing position. However, it has been suggested that the FRT is not a true measure of displacement of center of mass because of compensations at the shoulder.36 Reaching can occur forward, backward, and laterally. As with SLS Test, the FRT takes 1 minute to complete and requires only a measuring stick. The FRT has good interrater and test-retest reliability (ICCs = 0.98 and 0.92, respectively).5 The FRT has demonstrated excellent predictive validity of fall risk, with FRT ≤6 in predicting a fall.37 The FRT has not been used in any orthoses research thus far.

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CLINICAL MEASURES OF BALANCE FOR PEDIATRICS WITH LOCOMOTOR DISORDERS

Children with cerebral palsy (CP) or other pathologies often have impairments in biomechanical alignment, motor control, and postural control, all of which can impact balance. Poor balance can be detrimental to many activities of daily living and play activities. Gan et al.38 examined the reliability and validity of three functional balance measures (FRT, BBS, and TUG Test) in children with CP. They found that the three measures had excellent test-retest reliability (ICC >0.95) and interrater reliability (ICCs = 0.98–1.00). All three measures correlated highly with the Gross Motor Function Measure total score, with the BBS having the most significant correlation (Spearman ρ = 0.97). However, in the domain of discriminant validity, the FRT was the only measure able to distinguish children across all five levels of the Gross Motor Function Classification System levels (the BBS and TUG Test were unable to distinguish between Gross Motor Function Classification System levels I and II). Gan et al.38 found that all three of these measures were suitable for use in clinical practice with children with CP, citing that each measure was simple, valid, and reliable in this population.

The PBS is a modified version of the BBS.39 This scale was developed for the purpose of evaluating balance in school-age children with mild to moderate motor impairments. The original 14 items of the BBS were modified to create the PBS. These modifications included reordering of the items, decreasing the time standards for static postures, and some clarification of directions. The PBS was pilot tested with 40 normally developing children aged 5 to 7 years and found to have high test-retest reliability (ICC (3,1) = 0.85). The PBS also demonstrated high test-retest (Spearman signed ranked correlation = 0.89–1.0 and ICC (3,1) = 0.998) and interrater reliability (ICC (3,1) = 0.997) for children aged 5 to 15 years with mild to moderate motor impairments.39 Validity of this measure has yet to be investigated.

Few studies currently exist in which the effect of AFOs on balance has been investigated using these recommended outcome measures in children. Kott and Held40 used the PBS in a study of the effects of orthoses on upright functional skills in children with CP. This study found no significant difference between performance on the PBS with or without orthoses. However, the study neither specified the types of orthoses used nor standardized the time of previous orthosis wearing.

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CLINICAL MEASURES OF BALANCE FOR ATHLETES

Measures of balance for the athlete must be easily conducted on the sidelines or in the locker room. Therefore, tests that can be completed quickly and without lots of special equipment are necessary.

The SEBT consists of a series of eight single-limb stance tests. Hertel et al.41 suggest that the SEBTs is a superb method for measuring dynamic balance, because it combines neuromuscular control of the stance leg with an integration of sensory input from the visual, vestibular, and somatosensory systems. Although in single-limb stance on one side, the athlete uses his opposite leg to reach for specified targets on the floor, challenging postural control. The subject stands at the center of a grid taped off on the floor with eight lines extending at 45° increments from center. The point touched by the subject's foot is marked, and the distance from the center is measured. Hertel et al.41 investigated the intratester and intertester reliability of the SEBT. The authors found ICCs for intratester reliability ranging from 0.78 to 0.96 on day 1 and 0.82–0.96 on day 2. Intertester reliability yielded ICCs of 0.35–0.84 on day 1 and 0.81–0.93 on day 2. The SEBT was found be to be predictive of lower limb injury in athletes.42 Validity has not been well established for the SEBT. One study investigated the relationship between the SEBT and the static and dynamic postural-control tests, with only weak correlation between the SEBT and COP in either the static or dynamic test.43 Significant learning effects have been noted with the SEBT, so at least six practice trials before baseline measures are suggested.41 The SEBT was used as a main outcome measure in a study investigating the affect of prophylactic ankle braces on dynamic balance.44 This study found that the bracing had no impact on the SEBTs measures, concluding that prophylactic use of ankle braces in healthy subjects did not disrupt lower limb dynamic balance. Nakagawa and Hoffman43 used the SEBT in an investigation of postural control in persons with recurrent ankle sprains. In this study, the SEBT was unable to distinguish between those subjects with recurrent ankle sprains and the uninjured controls, suggesting that it might not be sensitive enough to detect some deficits.

The SLS Test, as previously described, measures ability to maintain balance on a single lower limb. It has been readily used in many studies to determine proprioceptive deficits in persons with ankle instability. This test, with and without eyes closed, can also be used as a quick and easy measure of balance in athletes. The SLS Test is often combined into other balance measures. One such measure that uses SLS Test, along with other tests, is the BESS. The BESS was developed as a means to evaluate postural stability in persons with mild head injury or concussion.45 Sideline decisions regarding return to play are often made on the basis of subjective evaluation. The BESS has been used both with athletes with concussion and military personnel who do not seem to recover rapidly from mild traumatic brain injury. The BESS was developed based on the laboratory assessment techniques of the Sensory Organization Test and the Clinical Test of Sensory Interaction and Balance to evaluate postural stability quickly and without expensive equipment.45 The BESS is a series of tests in three different positions (SLS, feet together, and tandem stance). The subject is instructed to stand in each of these positions with eyes closed and hands on hips. The three tests occur on a firm surface and again on a foam surface. Each position is held for 20 seconds, and an error point is given for each error during the test, such as opening eyes, remaining out of test position greater than 5 seconds, and lifting hands off iliac crest.45 The BESS has shown significant correlations with forceplate sway measures in normal subjects, with interrater reliability ranging from 0.78 to 0.96.45 Intrarater reliability was demonstrated at 0.87 to 0.98,46 although recent studies have questioned the interrater and intrarater reliability of the total BESS, possibly due to a learning effect.47 To combat the potential learning effect, Broglio et al.48 suggested using the average of three trials and comparing outcome with normative data. Hunt et al.49 went one step further and suggested the removal of the double limb stance position, conducting three trials of the remaining four conditions. This increased intraclass reliability to 0.88.

One investigation to date has looked at the effect of ankle support (via taping or the McDavid Ultralight Ankle with Strap) versus barefoot using the BESS as an outcome measure. The results of this study suggested that ankle support had a negative impact on BESS performance, even though Sensory Organization Testing using the NeuroCom system showed no differences between any of the three conditions.50

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CONCLUSION

There are many balance measures a clinician can choose from when assessing the impact of an AFO on balance. Choosing the most appropriate measure can be a daunting task. The goal of this review was to present outcomes that were simple to perform, took little time to complete, and did not use special equipment that might not be available in the average clinical setting. In addition, the psychometric properties of a selected outcome should be considered to determine whether they are optimal for the patient and the patient's stated goals. In attempting to assess the effect of AFOs on balance, outcomes that assess both static and dynamic balance are suggested. Intuitively, one would surmise that a particular design of AFO might improve one type of balance while making no change or even deterring the other. Indeed, there is some evidence in the literature that supports this as noted in the evidence report of these proceedings. The BBS, PBS, and TUG Test would all be considered as measures of dynamic balance, whereas the FRT, SLS Test, SEBT, and BESS capture more of a static balance measure.

All measures in this review have at least acceptable psychometric properties. All the locomotor dysfunction measures have been validated in the stroke population, and most have been validated in all the most common neurological pathologies. Of all the measures reviewed within the locomotor dysfunction category, the TUG Test seems to have the most sound psychometric properties as a measure of dynamic balance. Of the recommended measures of balance for the athletes, both the SEBT and BESS have similar psychometric pros and cons. Both measures may be susceptible to a learning effect, so multiple tests need to be conducted, and practice of the test before formal testing may provide a more stable, accurate measure.

The clinician also needs to consider the various domains of the ICF guidelines when choosing an assessment tool (Figure 1). All measures in this review, with the exception of the ABC Scale, are measuring at the body functions or structures and activities level. The ABC Scale is the only included measure that captures the participation component of the ICF model and takes into account both environmental and personal factors. Tinetti et al.51 identified subject confidence as an important “independent determinant” of function and suggested that interventions should simultaneously improve physical performance and confidence.52

Accordingly, the clinician should consider using more than one balance measure, such as an activity measure like the TUG Test along with a self-report measure such as the ABC Scale to get a more complete picture of balance and its impact on the whole person. This will help to define what constitutes a meaningful improvement in balance.

Finally, when considering an outcome for the specific purpose of assessing the impact of an orthosis on balance, the previous literature should to be taken into account. Although historically there have been few investigations of AFOs that measured balance using a clinical outcome tool, the TUG Test seems to be the most sensitive to change. This may be due in part to the higher overall functional levels of the subjects included in these studies as the BBS seemed to have a significant ceiling effect in many of the studies reviewed.

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Keywords:

balance; AFO; outcome measure

© 2010 American Academy of Orthotists & Prosthetists