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. Author manuscript; available in PMC: 2021 May 1.
Published in final edited form as: Physiother Theory Pract. 2018 Jun 28;36(5):607–614. doi: 10.1080/09593985.2018.1490939

Balance-Confidence is Associated with Community Participation, Perceived Physical Mobility, and Performance-Based Function among Individuals with a Unilateral Amputation

Jaclyn Megan Sions a, Tara Jo Manal b, John Robert Horne c, Frank Bernard Sarlo d, Ryan Todd Pohlig e
PMCID: PMC6310658  NIHMSID: NIHMS976010  PMID: 29952694

Abstract

Objective

To explore relationships between balance-confidence and 1) community participation; 2) self-perceived mobility; and 3) performance-based physical function among individuals with a lower-limb amputation using a prosthetic.

Design

Retrospective, cross-sectional study.

Setting

Outpatient, multidisciplinary amputee clinic.

Participants

Patients (n=45) using a prosthesis, aged ≥18 years, with a unilateral transfemoral or transtibial amputation of ≥1 year, were included.

Methods

Participants completed the following self-report measures: the Activities-Specific Balance Confidence Scale (ABC); the Community Integration Questionnaire (CIQ); the Locomotor Capabilities Index (LCI); and two performance-based measures (i.e. the Timed Up and Go and the 6 Minute Walk Test). Linear regression modeling was used to explore relationships between balance-confidence (i.e. ABC) and self-report (i.e. CIQ and LCI) and performance-based measures (p ≤ 0.0125).

Results

After controlling for potential covariates (i.e. age, sex, and body mass index), balance-confidence explained 47.4% of the variance in CIQ (p = 0.000), 53.0% of the variance in LCI (p = 0.000), 20.3% of the variance in Timed Up and Go (p = 0.001), and 18.2% of the variance in 6 Minute Walk Test (p = 0.001).

Conclusion

Lower balance-confidence is associated with less community participation, lower self-perceived mobility, and poorer performance among patients with a unilateral lower-limb amputation.

Keywords: amputees, lower extremity, social participation

INTRODUCTION

In 2005 in the United States, it was estimated that 1.6 million people were living with limb loss, a number that is projected to increase to 3.6 million by 2050 (Ziegler-Graham et al, 2008). Lower-limb amputation is associated with impaired balance, decreased physical function, and reduced societal participation (van den Berg-Emons, Bussmann, Stam, 2010; Beltran, Dingwell, Wilken, 2014; Amtmann, Morgan, Kim, Hafner, 2015). Post-amputation, balance has been assessed through the use of performance-based measures (e.g. the Four-Square Step Test and the Berg Balance Scale) (Samitier et al, 2016). Distinct from performance, but critical to balance, is balance-confidence. Balance-confidence assesses the individual’s belief that they have the capability to perform a task or activity without losing their balance (Miller and Deathe, 2011). According to a systematic review, balance-confidence post-amputation has received little exploration (Ku, Abu Osman, Wan Abas, 2014).

Balance-confidence may be a target for improved functional mobility. Among individuals with lower-limb amputations, reduced balance-confidence has been associated with reduced self-reported mobility (Miller, Deathe, Speechley, 2001), poorer physical performance (Deathe and Miller, 2005), falls in the past year (Wong et al, 2015), and reduced physical activity (Mandel et al, 2016). Further, balance-confidence, as part of a clinical prediction rule that also includes items related to self-reported mobility and balance performance, helps to predict adults with lower-limb amputations that will not achieve a community-walking level at 1 year (Wong, Young, Ow-Wing, Karimi, 2016).

From a community reintegration perspective, Miller and Deathe (2011) reported that balance-confidence independently predicts social engagement at 3 months post-discharge from a prosthetic rehabilitation program. Importantly, patients may not return to vocational and volunteer activities for 9 months to > 2 years post-amputation (Schoppen et al, 2001; Bruins, Geertzen, Groothoff, Schoppen, 2003). Therefore, administration of participation questionnaires beyond the acute post-amputation period is necessary to fully capture community reintegration. Further, questionnaires must capture participation categories that are popular for both those who return to the paid workforce, as well as categories (i.e. caretaking and volunteerism) pertinent to individuals who are retired and/or disabled. Some participation questionnaires, such at the Frenchay Activities Index, while reliable in adults with lower-limb amputation (Miller, Deathe, Harris, 2004), do not contain such categories.

Relationships between balance-confidence and clinically important outcome measures in adults with lower-limb loss may be impacted by patient demographics. For example, shorter 6 Minute Walk Test distances are associated with older age (Reid, Thomson, Besemann, Dudek, 2015). Longer Timed Up and Go times are associated with advanced age and being female (Sansam, O’Connor, Neumann, Bhakta, 2012). Higher body mass indices (BMIs) are associated with poorer balance performance on the Berg Balance Scale (Wong et al, 2015). Consequently, when evaluating relationships between balance-confidence and clinical measures (particularly performance-based measures) in adults post-amputation, controlling for age, sex, and body mass index, can be informative.

Greater understanding of relationships between balance-confidence and clinical outcomes (e.g. community participation, self-perceived mobility, and performance-based function) may allow clinicians to optimize post-amputation interventions and outcomes. The primary purpose of this retrospective, cross-sectional data analysis was to explore associations between balance-confidence and community participation as assessed with the Community Integration Questionnaire (CIQ) among adults with lower-limb amputations. Secondary objectives included evaluating associations between balance-confidence and self-perceived physical mobility, assessed via the Locomotor Capabilities Index (LCI), as well as performance-based function, assessed with the Timed Up and Go and 6 Minute Walk Test. We hypothesized that lower balance-confidence would independently help to explain reduced community participation, lower self-perceived functional mobility, and poorer performance-based function in the post-acute amputation period, after controlling for age, sex, and BMI.

METHODS

Overview and Participants

Clinical data, including past medical history related to the amputation and concurrent comorbidities, were collected by physical therapists, prosthetists, and a physiatrist during multidisciplinary amputee clinics held September of 2013 through December of 2015. The research project was approved by the University of Delaware Human Subjects Institutional Review Board (IRB) and all participants consented to participate either in person or via mailers.

Individuals were included in this retrospective, cross-sectional data analysis if they were: 1) aged ≥ 18 years; 2) had a unilateral transfemoral or transtibial amputation that occurred ≥ 1 year prior; 3) were currently wearing a prosthetic device; and 4) completed the relevant self-report and performance-based measures. Individuals with bilateral transfemoral or transtibial amputations were excluded from this analysis, but those with more distal amputations of the contralateral limb were included.

Examiners were trained in administration of the standardized evaluation by the principal investigator, although reliability was not formally assessed. Height and weight was assessed to allow determination of BMI. Participants completed a demographics questionnaire, the General Practice Physical Activity Questionnaire (Ahmad et al, 2015), and rated their average residual limb pain from 0-10, where 0 indicated “no pain” and 10 indicated “worst possible pain”. Participants completed 2 additional self-report questionnaires (i.e. ABC, CIQ) and 2 performance-based measures of physical function (i.e. Timed Up and Go, 6 Minute Walk Test).

Primary Self-Report Measures

For the ABC, individuals rate their confidence during 16 tasks that vary from reaching overhead to walking on an icy sidewalk (Powell and Myers, 1995). Higher percentages denote greater balance-confidence (Powell and Myers, 1995). Test-retest reliability in adults with limb-loss has been previously demonstrated (ICC=.91) (Miller, Deathe, Speechley, 2003). The CIQ, which assesses social role and community limitations and participation, has been shown to have test-retest reliability in various patient populations (ICCs=.83-.96) (Zhang et al, 2002; Dalemans et al, 2010). The total CIQ score is a sum of three subscales, i.e. Home Integration (including caretaking), Social Integration, and Integration into Productive Activities (including volunteerism) (Zhang et al, 2002). Perceived functional mobility while using a prosthetic is a predictor of quality-of-life post-amputation (Asano, Rushton, Miller, Deathe, 2008). The LCI, which assesses perceived ability on 14 transitioning and ambulation-related tasks, has been shown to have test-retest reliability (ICC=.98) and construct validity in adults with lower-limb amputations; higher scores indicate greater self-reported functional ability (Franchignoni, Orlandini, Ferriero, Moscato, 2004).

Performance-Based Measures

For the Timed Up and Go, participants were asked to stand from a standard chair with armrests independently, using their hands if necessary, walk 3 meters at a normal pace to a line on the floor, turn, walk back to the chair and sit down (Schoppen et al, 1999; Resnik and Borgia, 2011). Task completion time was recorded. Assistive device use was allowed. Test-retest reliability (ICC=.88) and concurrent validity of the Timed Up and Go has been previously reported in patients with lower-limb loss (Resnik and Borgia, 2011). Longer Timed Up and Go times have been found to be predictive of multiple falls (Dite, Connor, Curtis, 2007) and prosthetic nonuse (Roffman, Buchanan, Allison, 2016) post-amputation.

The 6 Minute Walk Test is a submaximal test of aerobic capacity that assesses both walking function and endurance (Harada, Chiu, Stewart, 1999; King, Judge, Whipple, Wolfson, 2000; Bellet, Adams, Morris, 2012). Instructions for the 6 Minute Walk Test were to “cover as much ground as possible in 6 minutes, walking as fast as possible.” If necessary, participants were allowed to use their assistive device (Resnik and Borgia, 2011). Examiners walked slightly behind the participant to avoid pacing and refrained from conversing with the individual to encourage maximal effort. Vital signs were assessed pre- and post-testing. Test-retest reliability has been reported in adults post-amputation (ICC=.97) (Resnik and Borgia, 2011). Distance walked during the 6 Minute Walk Test has been correlated (r=0.67, p<.010) to 7-day step counts among individuals with lower-limb amputations (Lin et al, 2014). Emerging evidence suggests 6 Minute Walk Test distances ≤191 meters may be predictive of prosthetic nonuse (Roffman, Buchanan, Allison, 2016).

Statistical Analysis

Data was analyzed using IBM SPSS Statistics 24 (Armonk, NY). Assumptions for regression modeling were met after outliers and overly influential cases, i.e. values beyond 1.5 times the interquartile range, were identified and removed. These instances were identified using boxplots of unstandardized residuals. Normality of residuals was tested using the Kolmogorov-Smirnov test (p>.050), linearity and homoscedasticity were evaluated through residual plots, and multicollinearity through examining variation inflation factors, condition indices, and tolerances. Linear regression modeling was used to test the association of balance-confidence (ABC), the primary independent variable, with the following dependent variables: community participation (CIQ), self-perceived functional mobility (LCI), and performance-based function (Timed Up and Go, 6 Minute Walk Test), using four separate regression models. We opted to control for three potential covariates: age, sex, and body mass index, in the first block of each model. Covariates were limited to these three to reduce the potential overspecification of the regression model by including too many covariates. Having four predictors in each model allowed us to maintain the 10:1 sample size to predictor ratio that is commonly used (Austin and Steyerberg, 2015). Balance-confidence was entered into the second block of each model to assess the independent relationship of balance-confidence with each dependent variable (p≤0.0125; conservatively adjusted for the four independent models). The percent of variance for block 2 (i.e. the amount of additional variance explained above and beyond block 1) is reported as the change in R2.

RESULTS

Of the 101 patients clinically evaluated, 80 consented to research study participation. Eight individuals were excluded from this analysis due to hip disarticulation (n=3), knee disarticulation (n=1), and bilateral amputations at the knee or more proximally (n=4). An additional 10 were excluded due to no prosthetic device at the time of evaluation and 17 due to incomplete data sets, resulting in a sample of 45 participants. Participant demographics are provided in Table 1. The main causes of the transfemoral (n = 20) or transtibial (n = 25) amputation were trauma (n = 14) and peripheral vascular disease (n = 13). Fifteen participants used an assistive device (walker = 5, bilateral crutches = 1, cane = 9). The median time since amputation was 6.0 years and 6 individuals had amputations of the contralateral limb (n = 1 at transverse tarsal joint, n = 3 at tarsometarsal joint, n = 2 at unspecified joint of foot).

Table 1.

Patient Demographics (n=45)

Variable
n (% of sample)
Sex, males 33 (73.3)
Amputation level, transtibial 25 (55.5)
Amputation of contralateral limb 6 (13.3)
Diabetes 19 (42.2)
Cardiovascular disease* 25 (55.6)
Assistive Device Use, yes 15 (33.3)
Activity Level, inactive 28 (62.2)
Mean (SD)
Age, years 56.8 (14.1)
Time since amputation, yearsa 6.0 (14.5)
Body mass index, kg/m2 28.3 (5.2)
Residual limb pain rating, 0-10a 0 (6)
Activities-Specific Balance Confidence Scale, 0-100%a 71.0 (53)
Community Integration Questionnaire, 0-29 18.1 (6.2)
Locomotor Capabilities Index, 0-56a 48 (22)
Timed Up and Go, secondsa 12.20 (7)
6 Minute Walk Test, m 286.3 (121.6)
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Abbreviations: SD, standard deviation; kg, kilograms; m, meters.

*

Cardiovascular disease was defined as self-reported presence of any of the following: heart disease, prior heart attack, angina, arrhythmia, valve problems, congestive heart failure, high or low blood pressure, high cholesterol, blood disorder (e.g. anemia, leukemia).

a

Data is presented as median (interquartile range).

Two separate linear regression models for self-reported measures are provided in Table 2. Models sought to determine the independent contribution of balance-confidence to self-reported measure scores, i.e. what percentage of the variance in community participation and self-perceived functional mobility scores the balance-confidence score explained after accounting for age, sex and body mass index. After adjusting for the covariates, balance-confidence, as measured with the ABC, explained 47.4% of the variance in the CIQ (p<0.001) and 53.0% of the variance in LCI (p<.001). Unstandardized beta coefficients indicate that for each 1% increase in ABC score there is a .155 increase in CIQ and a .353 point increase in LCI. The covariates of age (p=0.001) and BMI (p=0.003) were significant covariates in the LCI model, with every 1 year increase in age leading to a .233 point decrease in LCI and every 1 kg/m2 increase in BMI associated with a .561 point increase in LCI. Two outliers were removed for the CIQ model and 4 were removed for the LCI model.

Table 2.

Models for Primary Self-Reported Measures

Block Statistics Individual Predictor Statistics
R2 AdjR2 ΔR2 F-change df1 df2 p-value* b SE p-value
Community Integration Questionnaire (n=43)
Block 1 .093 .023 – 1.333 3 39 .278
Block 2 .567 .521 .474 41.564 1 38 .000a
 Age −.030 .047 .525
 Sex −1.039 1.418 .468
 BMI .122 .123 .328
 ABC .155 .024 .000*
Locomotor Capabilities Index (n=41)
Block 1 .290 .232 – 5.037 3 37 .005a
Block 2 .820 .801 .530 106.366 1 36 .000a
 Age −.233 .065 .001a
 Sex 2.051 .074 .307
 BMI .561 .178 .003a
 ABC .353 .762 .000a
Block 1: covariates
Block 2: Block 1 + ABC
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Abbreviations: df, degrees of freedom; SE, standard error; BMI, Body Mass Index; ABC, Activities-Specific Balance Confidence Scale.

*

This p-value is for the test in the change in R2, where the change in R2 represents the additional variance explained above and beyond block 1.

a

Statistically significant (p≤.0125).

Results for performance-based measures for two separate models, one for Timed Up and Go and one for the 6 Minute Walk Test, are provided in Table 3. After adjusting for the covariates, the ABC explained 20.3% of the variance in the Timed Up and Go (p=.001) and 18.2% of the variance in 6 Minute Walk Test (p=.001). The covariates collectively explained 26.7% of the variance in Timed Up and Go time (p=.010) and 24.1% of the variance in the 6 Minute Walk Test distance (p=0.012). Unstandardized beta coefficients indicate that for each 1% increase in ABC score, there is a .09 second decrease in TUG time and a 1.8 meter increase in distance ambulated during the 6 Minute Walk Test. With respect to the Timed Up and Go, age appears to be the most important covariate of those investigated, as this was the only covariate that was individually statistically significant (p=0.008); for every 1 year increase in age there was a .15 second increase in Timed Up and Go time. Age approached statistical significance (p=0.027) in block 2 for the 6 Minute Walk Test. Five outliers were removed for the Timed Up and Go model, while 2 were removed for the 6 Minute Walk Test.

Table 3.

Models for Performance-Based Measures

Block Statistics Individual Predictor Statistics
R2 AdjR2 ΔR2 F-change df1 df2 p-value* b SE p-value
Timed Up and Go (n=40)
Block 1 .267 .206 – 4.378 3 36 .010a
Block 2 .471 .410 .203 13.453 1 35 .001a
 Age .151 .053 .008a
 Sex 1.105 1.652 .508
 BMI −.133 .137 .337
 ABC −.096 −.469 .001a
6 Minute Walk Test (n=43)
Block 1 .241 .183 – 4.126 3 39 .012a
Block 2 .423 .362 .182 11.962 1 38 .001a
 Age −2.395 1.044 .027
 Sex −37.462 32.147 .251
 BMI 4.195 2.684 .126
 ABC 1.839 .532 .001a
Block 1: covariates
Block 2: Block 1 + ABC
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Abbreviations: df, degrees of freedom; SE, standard error; BMI, Body Mass Index; ABC, Activities-Specific Balance Confidence Scale.

*

This p-value is for the test in the change in R2, where the change in R2 represents the additional variance explained above and beyond block 1.

a

Statistically significant (p≤.0125).

DISCUSSION

In adults with a major lower-limb amputation who were using a prosthetic device, lower balance-confidence was significantly associated with less community participation as assessed with the CIQ. Lower balance-confidence was also significantly associated with lower self-perceived functional mobility per the LCI and poorer performance-based function. Specifically, lower balance-confidence was significantly associated with longer Timed Up and Go times and walking shorter distances during the 6 Minute Walk Test in this sample of adults who had undergone a unilateral transtibial amputation at least 1 year prior. Clinically, for each 1 unit increase in balance-confidence (ABC by 1%), an examiner might expect greater community integration (per CIQ of .15 points) and improved (a) self-report functional mobility (per LCI of .3 points) and (b) physical performance (per approximately a .1 second decrease in Timed Up and Go time and 2 meters greater 6 Minute Walk Test distance).

Clinicians should consider balance-confidence when devising interventions post-amputation. Results of this study support administration of the ABC in conjunction with population-specific, self-reported functional mobility and performance-based functional outcome measures. Lower scoring items identified by a patient on the ABC may provide insight to a clinician on activities that require additional exposure and training, so that these activities can be incorporated into the patient’s intervention. Such interventions may provide patients renewed confidence in their ability to maintain stability in community environments.

Unlike other factors (i.e. age, mental status, amputation level) that have been previously related to post-amputation participation, balance-confidence may be a modifiable factor that if addressed, may improve functional mobility and community reintegration. Younger adults who experience an amputation are more likely to return to work post-amputation (Darter et al, 2018). At 1 year post-amputation, better baseline mental status and premorbid mobility, as well as lower levels of amputation, have been associated with higher levels of societal participation (Roepke et al, 2017). We report higher balance-confidence is associated with better self-perceived functional mobility and more community participation. Our findings in Delawareans are similar to those reported by Miller, Deathe, and Speechley (2001) in Canadians, although Miller et al used the Frenchay Activities Index to assess participation and the Prosthetic Evaluation Questionnaire-mobility section to assess functional mobility.

Our ABC findings are similar to Miller and Deathe (2011) and Wong and colleagues (2014), who studied similarly aged adults with unilateral amputations and found average scores of 71% and 65%, respectively. In active adults, Myers and colleagues have suggested that ABC scores < 80%, which are associated with lower physical functioning, warrant intervention (Myers, Fletcher, Myers, Sherk, 1998). While the ABC threshold for targeted interventions among individuals with limb loss remains unknown, collectively data suggest balance-confidence remains sub-optimal post-amputation. Given persistent sub-optimal balance-confidence post-amputation and associations between balance-confidence and (a) community participation, (b) self-reported mobility, and (c) performance-based function, reported in this study, clinicians should evaluate and target balance-confidence in this patient population.

In our study, balance-confidence was associated with physical performance, independently explaining 20.3% and 18.2% of the variance in the Timed Up and Go and 6 Minute Walk Test, respectively. In the Miller and Deathe (2011) study, acutely post-amputation, balance-confidence remained status quo despite an improvement in performance-based function as assessed with the L Test, a modified version of the Timed Up and Go (Deathe and Miller, 2005; Miller and Deathe, 2011). Given that balance-confidence explained only a portion of physical performance variance in our study and the recognition by Miller and Deathe (2011) that even when performance improves, balance-confidence does not automatically increase, clinicians must also consider other factors (e.g. patient demographics) that may be impacting physical function.

In our study, greater age was significantly associated with reduced self-reported functional mobility per the LCI and slower Timed Up and Go times among adults who were > 1 year post-amputation. Our results align with prior mobility research conducted among individuals acutely post-amputation, which had similar age-related findings (Franchignoni, Orlandini, Ferriero, Moscato, 2004; Sansam, O’Connor, Neumann, Bhakta, 2012). Collectively, results suggest that when interpreting mobility data in adults post-amputation, regardless of the time elapsed since amputation, clinicians must consider the impact that age may have on performance.

Study Limitations

While we utilized both self-report and performance-based measure of physical function, we did not employ an objective measure of participation. Future studies may use advancing technology, such as GPS and accelerometers to objectively evaluate community participation, given that individuals tend to under- and over-estimate their involvement in activities (Prince et al, 2008). While data was obtained during standardized evaluations of patients with lower-limb amputations being seen in clinical practice, several participants had missing or incomplete data sets, resulting in study exclusion. Inter-examiner reliability for performance testing was not evaluated. Sample size limited our ability to control for additional potential covariates, such as time since amputation, residual limb pain, comorbidities, and physical activity level.

Future Research

Based on our findings, longitudinal studies among individuals in the post-acute amputation period are warranted to determine the extent that balance-confidence predicts long-term community-integration, self-reported mobility, and physical performance, while controlling for age. If causal relationships can be established, future interventional trials may seek to address balance-confidence as a means of improving clinically important outcomes, i.e. physical function and participation, among individuals with lower-limb amputations. Ultimately, balance-confidence may be a modifiable factor among individuals with lower-limb amputations, that when addressed as part of a multifaceted rehabilitation program, improves clinical outcomes. A program to address balance-confidence may include exposure to mobility tasks viewed with trepidation, gaming (Miller et al, 2012), body-weight supported gait training (Miller et al, 2012), strengthening (Pauley, Devlin, Madan-Sharma, 2014; Miller et al, 2017), balance training (Miller et al, 2017), and/or agility training (Miller et al, 2017).

CONCLUSION

Among American adults with a major lower-limb amputation, lower balance-confidence, as assessed with the ABC, was associated with less community participation, lower self-perceived functional mobility, and poorer performance-based physical function. The ABC may be used clinically to evaluate if balance-confidence may be a factor in mobility limitations and participation restrictions for patients with a unilateral limb loss who are using a prosthesis in the post-acute amputation period. Age is an important consideration when interpreting clinical outcomes, specifically the LCI and the Timed Up and Go, in adults with a unilateral lower-limb amputation. Advancing age has a negative impact on a patient’s self-perceived mobility, as well as their physical performance.

Acknowledgments

The authors wish to thank the clinicians, residents, and students from Independence Prosthetics-Orthotics, Inc. and the University of Delaware Physical Therapy Clinic who assisted with the standardized data collections.

Funding: This work was supported, in part, by the National Institutes of Health under grant number R03HD088668.

Footnotes

DECLARATION OF INTEREST

The Authors report no conflict of interest.

Contributor Information

Jaclyn Megan Sions, Email: megsions@udel.edu.

Tara Jo Manal, Email: tarajo@udel.edu.

John Robert Horne, Email: jhorne@independencepo.com.

Frank Bernard Sarlo, Email: fsarlo@christianacare.org.

Ryan Todd Pohlig, Email: rpohlig@udel.edu.

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