Abstract
Background It is recognized that multifactorial assessments are needed to evaluate balance and locomotor function in people with lower limb amputation. There is no consensus on whether a single screening tool could be used to identify future issues with locomotion or prosthetic use.
Objective The purpose of this study was to determine whether different tests of locomotor performance during rehabilitation were associated with significantly greater risk of prosthetic abandonment at 12 months postdischarge.
Design This was a retrospective cohort study.
Method Data for descriptive variables and locomotor tests (ie, 10-Meter Walk Test [10MWT], Timed “Up & Go” Test [TUGT], Six-Minute Walk Test [6MWT], and Four Square Step Test [FSST]) were abstracted from the medical records of 201 consecutive participants with lower limb amputation. Participants were interviewed and classified as prosthetic users or nonusers at 12 months postdischarge. The Mann-Whitney U test was used to analyze whether there were differences in locomotor performance. Receiver operating characteristic curves were generated to determine performance thresholds, and relative risk (RR) was calculated for nonuse.
Results At 12 months postdischarge, 18% (n=36) of the participants had become prosthetic nonusers. Performance thresholds, area under the curve (AUC), and RR of nonuse (95% confidence intervals [CI]) were: for the 10MWT, if walking speed was ≤0.44 ms−1 (AUC=0.743), RR of nonuse=2.76 (95% CI=1.83, 3.79; P<.0001); for the TUGT, if time was ≥21.4 seconds (AUC=0.796), RR of nonuse=3.17 (95% CI=2.17, 4.14; P<.0001); for the 6MWT, if distance was ≤191 m (AUC=0.788), RR of nonuse=2.84, (95% CI=2.05, 3.48; P<.0001); and for the FSST, if time was ≥36.6 seconds (AUC=0.762), RR of nonuse=2.76 (95% CI=1.99, 3.39; P<.0001).
Limitations Missing data, potential recall bias, and assessment times that varied were limitations of the study.
Conclusions Locomotor performance during rehabilitation may predict future risk of prosthetic nonuse. It may be implied that the 10MWT has the greatest clinical utility as a single screening tool for prosthetic nonuse, given the highest proportion of participants were able to perform this test early in rehabilitation. However, as locomotor skills improve, other tests (in particular, the 6MWT) have specific clinical utility. To fully enable implementation of these locomotor criteria for prosthetic nonuse into clinical practice, validation is warranted.
Prosthetic nonuse, or abandonment of prosthetic use, after discharge from rehabilitation has been associated with several factors, including higher amputation level, multiple-limb amputation, older age, energy cost, atraumatic amputation cause, multiple comorbidities, poor premorbid mobility, impaired single-limb balance, delay to prosthetic gait retraining, locomotor skills at discharge, mobility aid use, cognition, pain, and psychosocial factors.1–6 At 12 months, many individuals with lower limb amputation have discontinued using their prosthesis for locomotor activities,1,7,8 and mortality rates up to 48% for individuals with atraumatic amputation9,10 have been reported. In contrast to young or elderly able-bodied people,11–14 those with lower limb amputation may have impaired speed, distance, and balance when walking.15–19 However, there is limited knowledge3,6,16,19,20 on how performance in these functional domains during rehabilitation relates to their future ability to perform daily living, work, or recreational activities using a prosthesis.
Clinical utility is the usefulness of a test at determining a diagnosis or outcome for an intervention and how effectively it can be implemented into clinical practice.21 Some important elements of clinical utility include cost, equipment, training, time, safety, interpretation, and relevance of the test.21 Although it is recognized that multifactorial assessments are needed to evaluate balance and locomotor function in people with lower limb amputation, there is no consensus on whether a single screening tool could be used to identify future issues with locomotion or prosthetic use.22,23 The 10-Meter Walk Test (10MWT), Timed “Up & Go” Test (TUGT), Six-Minute Walk Test (6MWT), and Four Square Step Test (FSST) are examples of locomotor tests that may be used during rehabilitation after lower limb amputation.16–20,22,24–27 Knowledge of walking speed, distance, and balance gained from these tests may inform health professionals about impairments that are potentially modifiable with physical therapy and prosthetic intervention. Normative population data and the implications of respiratory, cardiovascular, aging, and neurological disorders are established for the 10MWT, TUGT, 6MWT, and FSST.12,14,28–33 However, there are limited studies that assist with interpretation of variation in locomotor performance of amputation cohorts or that identify people who are more likely to abandon prosthetic use within 12 months of discharge.16,25
In contemporary rehabilitation models of care for people with amputation, Medicare Functional Classification Level (MFCL) K-levels are the main criteria used to subjectively allocate prosthetic components.16,34 Health professionals have been slow to adopt performance-based evidence into clinical practice.16,34–36 Construct validity has been demonstrated through known group differences for MFCL K-levels and 6MWT distance16 and for multiple faller classification in people with transtibial amputation and FSST time.17 In cohorts with lower limb amputation, reliability has been reported for the 6MWT25,37,38 and TUGT18,25; however, reliability has not been determined for the 10MWT19,27,39,40 and FSST.17 Concurrent validity has been demonstrated for the 10MWT,19,27 6MWT,16 and TUGT18 with other amputation outcome measures.
The majority of lower limb amputation cohort studies have used samples of convenience whose rehabilitation was completed many years prior to study recruitment16,20,25,41 or controlled for characteristics such as amputation level.17,37,38 Analysis of stable prosthetic user subgroups has minimized confounding factors that potentially affect locomotor performance in people with recent amputations (eg, stump and medical complications). However, these results cannot be readily generalized to early, heterogeneous cohorts undergoing rehabilitation after amputation. As prosthetic rehabilitation represents a potential lifelong cost to health care services, early detection of individuals at high risk of prosthetic nonuse by using performance criteria during rehabilitation may inform clinical decision making, lead to prosthetic innovations, and facilitate implementation of targeted models of care.1
The hypothesis generated for this study was: People who discontinue prosthetic use at 12 months postdischarge will have poorer performance results on locomotor tests during rehabilitation than those who sustain prosthetic use. Therefore, the study objective was to determine whether different tests of locomotor performance during rehabilitation were associated with significantly greater risk of prosthetic abandonment at 12 months postdischarge.
Method
Participants
A research assistant who was unknown to potential participants recruited and obtained informed verbal consent from participants.
Participants were included if they had at least one recent major lower limb amputation (ie, transtibial level or above) as their primary admission diagnosis; had multiple limb amputation; lived in the community; were ambulant before amputation surgery; were classified at MFCL K-levels 1 to 4; and had received prosthetic rehabilitation and been discharged from Royal Perth Hospital (RPH), the state center for rehabilitation after amputation. Recent major lower limb amputation was defined as surgery in the weeks or months preceding rehabilitation admission. This classification enabled identification of new cases of people undergoing rehabilitation for amputation from multidiagnostic cases with a past medical history of amputation (eg, fractured neck of femur, past amputation).
K-levels were assigned collaboratively in the postoperative period by the rehabilitation physician and senior physical therapist as part of the RPH assessment procedure for rehabilitation admission based on criteria outlined in the study by Roffman et al.1 Abbreviated MFCL K-level definitions for this study were: K-level 0—nonambulatory; K-level 1—prosthesis used for transfers, limited or unlimited household ambulation; K-level 2—limited community ambulation; K-level 3—community ambulation; and K-level 4—high-level prosthetic use typical of a child, active adult, or athlete.16
Exclusion criteria for this study were: K-level 0 classification, unable to communicate, and did not consent to participate. K-level 0 participants were monitored through the multidisciplinary outpatient clinic for amputation rehabilitation for the duration of the study and remained at K-level 0.
Figure 1 details participant eligibility and recruitment into the study. A total of 307 consecutive potential participants were identified from the Amputee Physiotherapy Service database from June 2006 to July 2011, and 264 of these participants were classified at K-levels 1 to 4; however, 37 participants had died. Of the 211 eligible participants, a total of 201 were interviewed, and the final response rate was 95%. No interviewed participants died during the 12-month follow-up period.
Flowchart showing participant recruitment and eligibility for the study.
Rehabilitation Intervention
Royal Perth Hospital provides comprehensive multidisciplinary rehabilitation for approximately 85% of all individuals with lower limb amputation in Western Australia.1,34 The 5 stages of rehabilitation for amputation,42 service demographics, and rehabilitation interventions are shown in eFigure 1 (see Roffman et al1 for full intervention details). Physical therapy commenced in the postoperative stage once participants were medically stable. K-level 0 to 4 participants received multidisciplinary inpatient rehabilitation. K-level 1 to 4 participants also attended 2 or 3 outpatient physical therapy sessions per week and were discharged when individualized rehabilitation goals were achieved.
Data Collection During Rehabilitation
The RPH senior physical therapist routinely assessed locomotor milestones to monitor rehabilitation progress and to facilitate client goal setting. Once participants were able to walk outside the parallel bars, they were assessed using the 10MWT, TUGT, 6MWT, and FSST. Procedures, scoring, and psychometric properties for these locomotor tests are reported in the eAppendix. The senior physical therapist provided standardized training for all physical therapy staff in the center in performing the 10MWT, TUGT, 6MWT, and FSST, using standardized equipment. Physical therapy records were kept for participants who were unable to attempt, independently perform, or complete any of the locomotor tests, and for types of mobility aids if used. Locomotor tests were repeated as participants progressed from using mobility aids (eg, walking frames, elbow crutches and sticks) to walking without aids.
Procedure
Locomotor test data (ie, date, results, mobility aid use) and cohort descriptive variables were retrospectively abstracted from the medical records by the senior physical therapist, who was blinded to the participant interviews. Figure 2 details the abstracted descriptive variables, locomotor test data, and assessment time frames relative to physical therapy discharge.
Descriptive variables, available locomotor test data assessed during rehabilitation, and time frames relative to physical therapy discharge abstracted from the medical records. IQR=interquartile range, 10MWT=10-Meter Walk Test, 6MWT=Six-Minute Walk Test, TUGT=Timed “Up & Go” Test, FSST=Four Square Step Test.
In this study, above transtibial amputation level was defined as knee disarticulation level or above.1 Major bilateral lower limb amputation was defined as transtibial amputation level or above of both lower limbs.1 The type and number of medical comorbidities (including musculoskeletal pathology and mental health issues) were counted and recorded for each participant.1 Charlson Comorbidity Index (CCI) and age-adjusted CCI were calculated43–45 for each participant. The last participant assessment results obtained prior to discharge for 10MWT, 6MWT, TUGT, and FSST performance were analyzed in this study.
Participants were interviewed by the senior physical therapist regarding their prosthetic use, amputation, social, accommodation, demographic, and general health details from 4 months onward after discharge from physical therapy. To improve recall accuracy, participants were interviewed at approximately 2-month intervals after discharge from physical therapy and verbally prompted using important calendar events (eg, birthday, Christmas) on their prosthetic use over 12 months.1 If participants were prosthetic nonusers, their reasons for nonuse and time at which they ceased prosthetic use after discharge from physical therapy were recorded.
The operational definition of prosthetic nonuse was permanent abandonment of prosthetic use for locomotor activities on any weekdays, or wearing a prosthesis only for cosmesis.1 Participants who used their prosthesis for locomotor activities on one or more weekdays were classified as users.1 Interview data on time elapsed from physical therapy discharge until prosthetic nonuse enabled classifying participants as users or nonusers at 12 months after discharge. Participants were monitored at the multidisciplinary outpatient clinic for amputation rehabilitation to ensure that those who became prosthetic nonusers had remained prosthetic nonusers.
Data Analysis
Walking speed (ms−1), distance (meters), and time (seconds) were derived from the 10MWT, 6MWT, TUGT, and FSST data.
Shapiro-Wilk tests demonstrated that the locomotor test data were not normally distributed (P<.01). Nonparametric analyses using the Mann-Whitney U test (95% confidence intervals [95% CI]) were performed to determine whether differences were significant between rankings of locomotor test results for prosthetic users and nonusers.
The descriptive amputation, demographic, and comorbidity variables abstracted from the medical record were analyzed for prosthetic users and nonusers at 12 months postdischarge. Depending on data distribution, 2 population proportion z tests (95% CI) were used to determine whether there were any differences in descriptive variables for prosthetic users and nonusers.
Receiver operating characteristic (ROC) curves were used to generate the performance criteria that balanced sensitivity and specificity,46,47 predicting prosthetic nonusers for the continuous variables of walking speed, distance, and time derived from the 10MWT, 6MWT, TUGT, and FSST. The nonparametric method of DeLong et al46 was used to calculate ROC, performance thresholds, area under the curve (AUC), Youden index J, specificity, and sensitivity (95% CI). Optimal performance thresholds (criteria) for prosthetic nonuse were calculated for an equal balance of sensitivity and specificity at the maximum correct classification.47 The Youden index J was the farthest vertical point on the ROC curve from the diagonal line of chance.47 Area under the curve was calculated using the trapezoidal method.46,47
The risk stratification literature reports that when there is no difference between distributions of 2 groups for the investigated variable, AUC equals 0.5 and is not predictive; however, if there is perfect separation of these distributions, AUC equals 1, and the variable is highly predictive.47–49 Threshold criteria were derived from 10MWT, 6MWT, TUGT, and FSST performance for prosthetic users and nonusers at 12 months postdischarge, using 2 × 2 contingency tables (95% CI). Relative risk (RR) was calculated as part of the chi-square analyses to determine the ratio of probability for the outcome of prosthetic nonuse.
Data Scoring and Reduction
Figure 2 details the percentage of participants with missing locomotor test data who were excluded from the statistical analyses. Participants with missing data did not systematically differ from the tested cohort in terms of demographic, comorbidity, or amputation details. The main reasons that locomotor test data were missing included participants being medically unfit to attempt the test (eg, stump wound), declining to perform the test, or not attending their outpatient appointment.
Participants who were unable to complete or perform the assessment during rehabilitation were included in the statistical analyses (Fig. 2). These participants could not independently perform or attempt the locomotor tests (ie, required physical assistance from another person or used their prosthesis for transfers only). To enable statistical analyses, these participants were scored as 0 for the 10MWT and 6MWT (tests where low scores reflect poor performance)32,33,50 and 999 for the TUGT and FSST (tests where high scores reflect poor performance). As nonparametric (distribution-free) statistics were used in this study, assigning the lowest score (0) and highest score (999) for participants who were unable to perform the test allowed this important subgroup to be analyzed.51,52 This approach contributed to the external validity of the clinical study. Both parametric and nonparametric ROC and AUC methods have been demonstrated as robust and accurate for a wide range of distributions in continuous data.52 Similar statistical management of participants unable to perform locomotor tests has been documented in the spinal and stroke literature.32,33,50
Role of the Funding Source
This study was supported by an International Society for Prosthetics and Orthotics (ISPO) Australia Research Grant.
Results
A total of 201 consecutive participants were interviewed from November 2009 to December 2012 at a median of 1.5 years (interquartile range=1.2–2.2) after discharge. At 12 months after discharge, 18% (n=36) of the participants were prosthetic nonusers. Table 1 outlines cohort characteristics from the medical record abstraction for prosthetic users and nonusers at 12 months. Prosthetic users and nonusers were similar in terms of age, demographics, amputation cause, and comorbidities (P≥.055). However, prosthetic nonusers had significantly higher rates of cardiac conditions, transfemoral amputation, and residing in a metropolitan area and lower rates of transtibial amputation level than prosthetic users (P≤.015).
Demographic, Comorbidity, and Amputation Details Abstracted From the Medical Records of People Who Remained Prosthetic Users and Became Prosthetic Nonusers at 12 Months After Discharge From Rehabilitationa
Figure 2 details the percentage of participants who were unable to perform the 10MWT, 6MWT, TUGT, and FSST at discharge, and the time locomotor tests were assessed before physical therapy discharge. The 10MWT, 6MWT, TUGT, and FSST ROCs for prosthetic users and nonusers are demonstrated in eFigures 2–5, respectively.
Table 2 details locomotor test results for participants who were prosthetic users and nonusers at 12 months after discharge. Thresholds, AUC, and associated accuracy statistics (95% CI) for prosthetic nonuse at 12 months postdischarge were as follows (full details are shown in Tab. 3).
Median (IQR) and Mann-Whitney U Test Performance Results for People Who Remained Prosthetic Users and Became Nonusers at 12 Months After Dischargea
Locomotor Test Thresholds From Receiver Operating Characteristic Curve Analysis and Associated Accuracy Statistics (95% Confidence Interval) for People Who Became Prosthetic Nonusers at 12 Months After Dischargea
10MWT
If walking speed was ≤0.44 ms−1 (AUC=0.743; 95% CI=0.675, 0.804), RR of prosthetic nonuse increased to 2.76 (95% CI=1.83, 3.79; P<.0001).
TUGT
If time was greater than 21.4 seconds (AUC=0.796; 95% CI=0.731, 0.851), RR of prosthetic nonuse increased to 3.17 (95% CI=2.17, 4.14; P<.0001).
6MWT
If distance was 191 m or lower (AUC=0.788; 95% CI=0.724, 0.843), RR of prosthetic nonuse increased to 2.84 (95% CI=2.05, 3.48; P<.0001).
FSST
A very high number of the total cohort (32%, n=65) were recorded as unable to perform the FSST by discharge, consisting of 72% (n=26) nonusers and 25% (n=39) users. If time was 36.6 seconds or greater (AUC=0.762; 95% CI=0.694, 0.820), RR of prosthetic nonuse increased to 2.76 (95% CI=1.99, 3.39; P<.0001).
Self-reported reasons for prosthetic nonuse were multifactorial, with both modifiable and nonmodifiable issues reported (full details are shown in Tab. 4).
Multifactorial Reasons for Prosthetic Nonuse Self-Reported by Participants Who Were Prosthetic Nonusers at 12 Months After Discharge From Rehabilitationa
Discussion
Clinical Utility of Locomotor Tests Predicting Prosthetic Nonuse
The primary finding of this study was that locomotor test performances while in rehabilitation were significantly associated with the likelihood of an individual sustaining prosthetic use 12 months after discharge. The 4 tests used in this study (10MWT, TUGT, 6MWT, and FSST) represent an ascending continuum of locomotor skill acquisition during rehabilitation for people with lower limb amputation. The 10MWT has the lowest locomotor and cognitive demand, as it involves fast walking in a straight line early in rehabilitation. The TUGT incorporates the indoor locomotor skills of sit-to-stand, walking, and turning.27 The 6MWT assesses cardiovascular capacity, which is required for community ambulation.16 In our study, locomotor skill progression was demonstrated by the 6MWT prosthetic nonuse criterion of 191 m having a slightly faster walking speed of 0.53 ms−1 than the 10MWT criterion of 0.44 ms−1. The FSST has the greatest locomotor and cognitive demand, as participants need to perform dual tasks by simultaneously stepping over obstacles while changing directions, skills required for walking in challenging environmental contexts.17,53
Although these locomotor tests vary in physical and cognitive demand, they all require the ability to modulate walking speed and control center of mass.54 This common functional domain may be reflected in the fact that all of the locomotor tests had similar AUC and RR scores that suggest all the tests were moderately predictive (ie, AUC >0.7 and <0.9).48,49 Therefore, to select one test in preference over another, the clinician would need to consider other factors affecting overall clinical utility.21 All tests on the locomotor continuum (10MWT, TUGT, 6MWT, and FSST) are low cost and require minimal training, equipment, and time for implementation in health care settings.21 In the context of a test that can be used safely by clinicians on the highest proportion of clients at an early stage of gait retraining within the hospital setting, the 10MWT may be suggested as having greatest clinical utility as a single screening tool for prosthetic nonuse. The 10MWT is widely used and benchmarked in health care for performance of activities of daily living across a variety of clinical conditions.11,12,29,32,39,40,55 Having repeated assessments of walking speed also may be a valuable gauge to progressing rehabilitation. Walking speed has been shown to be more important than balance for achieving longer walking distances following stroke,56 whereas reduced walking speed is a marker of capacity to ambulate in the community and mortality in other clinical cohorts.32,33,57
Although the 10MWT is able to be used earlier and on more clients with lower limb amputation in the hospital setting, our study supports previous findings16 that the 6MWT is an important tool for identifying risk of prosthetic nonuse in the mid to later stages of rehabilitation. The 6MWT had the highest sensitivity, correctly classifying 80.6% of individuals who became prosthetic nonusers. This finding is in contrast to the 10MWT, which had a lower overall accuracy. Therefore, clinicians need to understand the value of different locomotor tests in rehabilitation and progress the locomotor test protocol as clients improve. Future research should examine the association between the changes in the 10MWT and 6MWT to elucidate if there is a recognizable subgroup in the amputation cohort that both tests could identify as high risk. It is likely that if factors that have been shown to affect 6MWT performance (eg, bilateral lower limb amputation, body mass, height,41 and symptoms such as dyspnea, claudication, and musculoskeletal pain58) also affect prosthetic use after discharge, then potentially a combined test protocol could be more predictive.
In contrast to the 10MWT, TUGT, and 6MWT was the difficult dual-task paradigm of the FSST.53 Regardless of being a significant predictor of nonuse, the FSST has limited clinical utility due to the high number of individuals who were unable to perform the test in the late stages of rehabilitation. Participants who could perform the FSST were at low risk of prosthetic nonuse.
Comparison of Locomotor Performance in Lower Limb Amputation and Other Cohorts 10MWT
Comfortable gait speed in able-bodied participants ranges from 1.39 ms−1 for men and 1.41 ms−1 for women aged in their second decade and slows to 1.33 ms−1 for men and 1.27 ms−1 for women aged in their seventh decade.11 An interesting finding was that our walking speed criterion for prosthetic nonuse of ≤0.44 ms−1 was identical to the criterion for not being a community ambulator in people with incomplete spinal cord injury.32,33 This speed may represent a minimum criterion for efficient walking in amputation cohorts, given inability to walk outdoors has been identified as an early predictor of discontinuing prosthetic use.1 Walking speeds up to 1.3 ms−1 have been reported for individuals following traumatic amputations,15,39,40 and walking speeds up to 0.75 ms−1 have been reported for individuals with vascular causes of unilateral lower limb amputation.15 Waters et al15 reported that walking speed in participants with lower limb amputation was reduced by 13% to 66% compared with able-bodied participants. Previous studies have shown slower walking speeds for people with older ages and transfemoral, bilateral, and vascular amputations.15,19,39,40
TUGT.
Times ranging from 7.2 to 102 seconds and slower performance for older people with transfemoral and vascular amputation have been reported in the literature for the TUGT.3,6,17,18,25,59 However, ceiling effects also have been noted for the TUGT in individuals with lower limb amputation and a high level of functioning.27 A criterion of ≥19 seconds was reported for people with transtibial amputation performing the TUGT who became multiple fallers,17 which is similar to the prosthetic nonuse criterion of ≥21.4 seconds in our study.
6MWT.
The 6MWT distance has been reported as ranging from 4 to 858 m in cohorts with lower limb amputation.16,20,25,37,40,41 Inability to walk 200 m nonstop using a prosthesis was identified as a potential barrier to efficient community ambulation.60 Gailey et al16 reported that participants in K-level 0 to 1 (ie, prosthetic nonusers or prosthesis used for transfers or household ambulation) had a mean 6MWT distance of 49.86 m (SD=29.82). The 6MWT prosthetic nonuse criterion (≤191 m) in our study was similar to the limited community ambulator (K-level 2), with a mean of 189.9 m (SD=111.3).16 Previous studies40,41 have shown that 6MWT distance was significantly greater in people with transtibial, unilateral, and traumatic amputations.
FSST.
A criterion of ≥24 seconds for the FSST has been reported for individuals with unilateral transtibial amputation who have multiple falls,17 which is lower than the prosthetic nonuse criterion of 36.6 seconds in this current study. In this study of a heterogeneous cohort with bilateral, unilateral, and differing amputation levels, 32% of participants were unable to perform the FSST by discharge. Consistent with our findings, a longitudinal study of patients with stroke revealed that up to 15% were unable to perform the FSST.61
High variance of locomotor test performance results for this and other studies16,18,41 may be explained by the temporal relationship with prosthetic fitting and the commencement of gait retraining in cohorts with different causes of amputation. The starting point of prosthetic gait retraining following surgery is rarely uniform in heterogeneous amputation cohorts (ie, may range from 21 days to 6 months or greater depending on stump wound or fracture healing) and may be affected by variabilities in service delivery models.4,5 If walking is delayed, greater functional impairments in locomotor and balance skills are expected, as preprosthetic rehabilitation programs may not be of sufficient intensity to counteract the physiological effects of being nonambulant.1 Diversity in amputation cohorts with factors such as amputation level, cause, age, skill level (eg, military service personnel), and comorbidities also contributes to variance in locomotor test performance.23
Prosthetic Nonuse
In this study, issues with the residual limb (ie, stump wounds), prosthetic issues, high burden of comorbid disease, remaining lower limb pathology, and pain were reported most frequently by participants as their multifactorial reasons for discontinuing prosthetic use, which was consistent with the literature.1–5,60,62,63 These self-reported issues were supported by the fact that a significantly higher proportion of prosthetic nonusers in our study had transfemoral amputation–level and cardiac conditions, which have both been demonstrated as factors contributing to abandonment of prosthetic use.1–5,16,60 Prosthetic technologies such as gel liners, componentry, and suspension techniques may have the potential to improve prosthetic use and satisfaction by addressing wound or prosthetic issues that are often associated with higher amputation levels.62–64 Impaired balance, falls, and fear of falling were reported less frequently by participants as reasons for prosthetic nonuse, which was surprising because other studies17,60,65,66 have reported prosthetic gait limitations due to multiple falls and fear of falling. Furthermore, validated predictors of prosthetic nonuse, such as mobility aid use and inability to walk outdoors on concrete,1 are often related to balance impairment. Reasons for prosthetic nonuse reported by clients were multifactorial and complex, so further research to examine the relationship of these factors to locomotor and balance function is indicated.
Clinical and Research Implications
From a clinical perspective, knowledge of prosthetic nonuse indicators from locomotor performance across a continuum of clinical tests increasing in difficulty is very useful for appropriate goal setting, guiding treatment plans, prosthetic intervention required, and discharge planning. If clients do not achieve the 10MWT, TUGT, 6MWT, or FSST thresholds identified in this study, specific strategies should be adopted to optimize managing the client's daily needs given the high risk of prosthetic nonuse. These strategies include targeted rehabilitation to address modifiable impairments. Interventions may include gait retraining to improve walking efficiency in different environmental contexts; strength, speed, endurance, and balance exercises; prosthetic intervention; mobility aids; and adaptive equipment for carrying objects while walking. Furthermore, poor performance on locomotor tests may reflect greater issues with the model of care for people with amputation, such as delay to rehabilitation or inadequate intervention intensity to overcome impairments in muscular strength, joint range of motion, cardiovascular fitness, and balance.
From a research perspective, performance criteria for future prosthetic nonuse raise the question of whether there should be minimum locomotor test performance standards to be achieved by clients during an interim prosthetic trial before progressing to a definitive prosthesis or accessing more expensive prosthetic componentry. Furthermore, the minimum clinically important difference has yet to be established for the 10MWT, TUGT, 6MWT, and FSST in cohorts with amputation, so the value of improved locomotor and balance function from rehabilitation intervention remains undefined.16,17,25 These performance criteria for prosthetic nonuse may support clinical decisions and resource allocation; however, caution should be exercised as further research to validate the tests in a new cohort with lower limb amputation is necessary.
Limitations
There were some limitations in this study that have implications in interpretation of the results. There were some missing retrospective performance measure data, and the interview relied on participant recall, which are potential sources of bias. Individuals who were unable to attempt, independently perform, or complete the tests were included, but although their inclusion did not affect the distribution-free statistical analysis,52 this subgroup highlights the limitations of the more difficult performance measures in heterogeneous cohorts with amputation. Assessment time frames for locomotor tests varied, as they were dependent on the participants' individualized rehabilitation progress. Future studies may control assessment timeframes. As this was a retrospective study, these locomotor criteria for prosthetic nonuse warrant prospective validation.
This study demonstrated that progressive tests of increasing locomotor and cognitive demand (ie, 10MWT, TUGT, 6MWT, and FSST) may be predictive of future prosthetic nonuse when used during hospital rehabilitation. It is the first study, to our knowledge, to generate criteria for the functional domains of walking speed, distance, and balance. It may be implied that the 10MWT has the greatest clinical utility as a single screening tool for prosthetic nonuse, given the highest proportion of participants were able to perform this test early in rehabilitation. However, as locomotor skills improve, other tests on the continuum (in particular, the 6MWT) have specific clinical utility. To fully enable implementation of these locomotor criteria for prosthetic nonuse into clinical practice, validation is warranted.
Footnotes
All authors provided concept/idea/research design, writing, fund procurement, institutional liaisons, and consultation (including review of manuscript before submission). Ms Roffman and Professor Buchanan provided data collection, project management, participants, and facilities/equipment. Ms Roffman and Professor Allison provided data analysis. Ms Roffman provided administrative support.
The Royal Perth Hospital and Curtin University human research ethics committees approved this study.
This study was supported by an International Society for Prosthetics and Orthotics (ISPO) Australia Research Grant and by staff and administrators at the Physiotherapy Department, Royal Perth Hospital.
- Received May 7, 2014.
- Accepted November 22, 2015.
- © 2016 American Physical Therapy Association
References
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