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Predisposing Factors Related to Prosthetic Use by People with a Transtibial and Transfemoral Amputation

Christiane Gauthier-Gagnon, MSc
Marie-Claude Grise, MSc
Diane Potvin, MSc

ABSTRACT

A survey was conducted to evaluate prosthetic use and factors predisposing to prosthetic use among 396 adults with unilateral amputations. A response rate of 76% was obtained. Eighty-five percent of the respondents were prosthetic wearers; 53% actively used their prosthesis for the majority of their indoor activities; and 64% did so for the majority of their outdoor activities. Adaptation to the amputation and prosthesis and level of amputation were significantly correlated with prosthetic wear and active use indoors and outdoors. Presence of arthritic problems in the nonamputated limb were negatively related to prosthetic wear, but for activities outdoors, muscle cramps and sores were the limiting factors. Long delays in limb fitting, prolonged training, cardiac and respiratory problems, and constant stump pain were significantly related to disuse. Linear and logistic regression analyses further identified the combined factors that could be predictive of prosthetic use.

Key Words: Amputation; artificial limbs; leg; rehabilitation; treatment outcome.

Introduction

Over the last decade, the average incidence of lower-extremity amputations in the province of Québec (Canada) was estimated to be 31.4 per 100,000 inhabitants per year in the general population; the incidence was higher (to 42.5 per 100,000) in the adult population and still higher in the older age group.1 The incidence of lower-limb amputations has been reported to remain relatively stable since 1986.1 Approximately 80% of the lower-extremity amputations originate from peripheral vascular disease and diabetes; these diseases affect primarily the older adult aged 60 years and over.1,2

Despite improvement of medical and surgical technologies, nearly 1,000 persons-46% of the persons with lower-extremity amputation-still require prosthetic fitting every year for amputations above the foot and ankle level. The majority of these amputations are either transtibial or transfemoral. Persons with a lower-extremity amputation need considerable hospital and community resources, especially when rehabilitation with a prosthesis is attempted. For humanistic and functional considerations, every effort is made to return the person with an amputation of the lower limb to a satisfying locomotor status in his personal living environment. Members of the rehabilitation team have serious concerns, however, as to the actual use of the prosthesis and the problems encountered in the months and years following discharge from the rehabilitation center. In the province of Québec, this issue assumes consequential proportions since prosthetic and rehabilitation services are entirely funded by the government. Cost-effective use of resources demands that realistic goals be set for people with lower-limb amputations. This requires an awareness of factors that are likely to influence outcome.

According to Green's theoretical model,3 three categories of factors are assumed to potentially affect prosthetic use by persons with a lower-limb amputation: the predisposing, enabling, and reinforcing factors. The predisposing factors relate to physical condition, demographic profile, rehabilitation program, and motivation. The enabling factors concern locomotor skills and resources, and the reinforcing factors pertain to social as well as physical and environmental benefits. This article analyzes the predisposing factors.

Since the mid-1980s, various predisposing factors affecting the use of prostheses following discharge have been reported: the effect of age, sex, level of amputation, cause of amputation, and health condition.4-8 Studies on the impact of prosthetic training programs,4-6,9 condition of the nonamputated lower limb and stump,7,10,11 social status,7,9,12,13 and motivation on prosthetic use and disuse are scarce. Few recent studies have reported statistical relationships between these predisposing factors and the use of the artificial limb.6-8,13-16 Comparisons between studies are difficult because definitions of prosthetic use vary considerably. Prosthesis use has been defined variously as wearing the prosthesis "regularly," using it "daily," using it with or without assistive ambulatory devices; with reference to independence, supervision required, and home and community ambulation; and finally, in terms of the number of hours per day the prosthesis is worn and proportions of ambulatory activities done with the prosthesis.

The purposes of this study were to evaluate the frequency and extent of prosthetic use of those transtibial and transfemoral amputation in their home setting and identify factors that significantly predispose to prosthetic wear and active use for locomotor activities indoors and outdoors.

This study was meant to statistically verify already reported observations, and more importantly, to provide a comprehensive report of all factors predisposing to prosthetic wear and active use. Subsequent papers will report factors enabling and reinforcing prosthetic use.

The predisposing factors investigated (Table 1) were identified by a group of professionals and persons with lower-limb amputations using the nominal group technique.17 The dependent variables were defined as prosthetic wear and active use of the prosthesis. Prosthetic wear was the number of hours the prosthesis was worn per week, whereas the active prosthetic use was the percentage of ambulatory activities done with the prosthesis (almost 0%, 25%, 50%, 75%, and almost 100%) indoors and outdoors. Almost 0% means that the prosthesis was seldom used when ambulatory activities were necessary either in the house or outdoors.

Methods

Initial Cohort

The medical charts from April 1986 to December 1991 of 1,776 lower-extremity amputees from 10 rehabilitation centers well distributed throughout Québec were reviewed retrospectively. Adult subjects who had undergone a unilateral transfemoral (TF) or transtibial (TT) amputation and had completed a prosthetic training program for at least one year during that period were eligible for the present follow-up study. During the preselection process, the number of potential participants dropped to 817, due mainly to death and determinations of noneligibility based on bilateral amputation, level of amputation, and absence of prosthetic training.

During the review of medical records, information was collected specifically on age, sex, cause and level of amputation, health problems, time delay between amputation and prosthetic program, duration of preprosthetic training, length of stay in the rehabilitation center, duration of prosthetic training, and functional status at discharge.

Study Instrument

The Prosthetic Profile of the Amputee (PPA) questionnaire was used to evaluate prosthetic use and the factors related to use or disuse. The PPA was developed by Grisé and colleagues17 based on Green's theoretical framework.3 The PPA questionnaire consists of 44 close-ended questions in which measurement scales are primarily qualitative nominal and ordinal scales with a few quantitative ratio scales. The questions are arranged in six sections: (1) the physical condition of the subjects, (2) their satisfaction and adaptation to the prosthesis, (3) the prosthetic use, (4) the physical and social environment, (5) leisure activities, and finally, (6) the demographic characteristics of the respondents. The PPA questionnaire has been tested for construct validity and reliability.18 The PPA was shown to be reliable in terms of repeatability and valid for clinical and research use.

Procedure

The questionnaire was sent, following Dillman's strategy,19 to the preselected 817 persons with a lower-limb amputation. The original mailing was followed by a duplicate questionnaire sent three weeks later. After another three weeks, a second postal reminder was sent to nonrespondents or a telephone interview was set up if required. A total of 396 questionnaires were filled out and returned. The attrition was due mainly to death, amputation of the other limb,. or inability to locate the subject. Dillman's formula19 was used to determine the response rate. This formula excludes noneligible subjects, lost contacts, and deceased persons. A response rate of 76% was obtained. A response rate of 75% is considered sufficient to eliminate the possibility of response bias from the research sample.20

Data Analysis

The three dependent variables were frequency of prosthetic wear in hours per day and days per week, and active use of the prosthesis indoors and outdoors. Active use of the prosthesis was defined as the percentage (0%, 25%, 50%, 75%, and 100%) of ambulatory activities done with the prosthesis.

Statistical analyses were performed with SPSS/PC+a (Statistical Package for the Social Sciences) Version 3.0 software on an IBM-compatible computer. Chi-square tests were computed for nominal variables to determine which predisposing factors were associated with each dependent variable: prosthetic wear (prosthetic wear was split into categories) and active use indoors and outdoors. Pearson's product-moment correlation coefficients were used for ordinal and continuous variables, treating prosthetic wear as a continuous variable. To analyze the relationship between each outcome variable and the sets of independent variables, multivariate analyses were performed using stepwise linear and logistic regression models, for the continuous and categorical dependent variables respectively.

For logistic regressions, the categorical dependent variables were reorganized into two categories (1= 0%, 25%, and 50%; 2= 75% and 100% of ambulatory activities).

Levels of amputation (TT and TF) as well as users and nonusers were compared using Chi-square tests for nominal data (e.g., cause of amputation, health problems) and Students' t-tests for continuous and categorical quantitative data (e.g., time interval between amputation and fitting, duration of training). A p-value less than 0.05 was taken as significant.

Results

In this section, descriptive statistics on the population (person with TT and TF amputations, users, and nonusers) will first be presented followed by the results of inferential analyses that tested relationships between each predisposing factor and prosthetic wear, active use indoors, and active use outdoors.

Description of the Study Population by Level of Amputation and Prosthetic Use

The physical health status (Table 2) pertains to cause and level of amputation, concurrent medical conditions, and condition of the nonamputated leg and stump. Peripheral vascular disease was the predominant cause of amputation. The frequency distribution of peripheral vascular disease was higher for people with TF amputations (X2 = 22.5, df = 2, p < .005). Of the 396 respondents, 57.6% had undergone an amputation below the knee. Among prosthetic users, 63% had a TT amputation, whereas 73% of nonusers were amputated above the knee.

Visual (X2 = 3.82, df = 1, p < 0.05) and diabetic (X2 = 10.76, df = 1, p < 0.001) problems were more frequent among persons with TT amputations. When comparing users and nonusers, Chi-square analyses showed that the incidence of cardiac (X2 = 7.71, df = 1, p < 0.01), respiratory (X2 = 4.11, df = 1, p < 0.05), neurological (X2 = 10.88, df = 1, p < 0.001), and visual (X2 = 4.78, df = 1, p < 0.05) problems was significantly higher among nonusers. Fifteen percent of the study sample reported other problems such as arthritis, back problems, poor standing balance, depression, and cancer.

The most frequently reported problems with the nonamputated limb (Table 2) were poor blood circulation, joint pain when walking, and limb swelling. Chi-square tests showed no significant differences in the condition of the nonamputated limb between persons with TT and TF amputations. Significantly higher rates of poor circulation (X2 = 7.00, df = 1, p < 0.01) and joint problems (X2 = 6.66, df = 1, p < 0.01) were recorded among nonusers.

Although only 19% of nonusers reported constant stump pain, compared to 8.7% for prosthetic users (Table 2) , the observed difference was significant (X2 = 6.10, df = 1, p < 0.01). It was further shown (Table 2) that people with TT amputations were less affected by phantom pain than persons with TF amputations (X2 = 10.10, df = 1, p < 0.001), but were more prone to develop sores on their stump (X2 = 13.20, df = 1, p < 0.001).

Demographic factors are presented in Table 3 . The demographic profiles of persons with TT and TF amputations and of users and nonusers were not significantly different.

Data collected on rehabilitation programs pertain to delays in limb fitting after amputation and duration of preprosthetic and prosthetic training (Table 4) . Other information on the training program could not be compiled and analyzed because the data from chart to chart were not uniform. Delays between amputation and fitting were not significantly different for persons with TT and TF amputations (t = 0.23, df = 260.42, p = 0.976), but were significantly longer for nonusers (r = -0.17, p < 0.005). Duration of preprosthetic training was significantly longer for nonusers (r = -0.173, p < 0.005). Differences in mean duration of the prosthetic training were not significant for persons with TT and TF amputations (t = 0.09, df = 373.00, p = 0.07) or for users and nonusers (r = -0.08, p = 0.07).

Adjustment to the amputation and the prosthesis was evaluated using a five-point ordinal scale. Respondents were asked how adapted they felt they were to the amputation and the prosthesis (on a scale of 1 to 5, from not at all adapted to completely adapted). Significant differences were observed between users and nonusers. Fifty-seven percent (see detailed proportions under (Figure 1) of nonusers answered that they were not at all adapted to the prosthesis (r = 0.57, p < 0.001), whereas 60.2% of users were quite well (4) to completely (5) adapted to the prosthesis (r = 0.30, p < 0.001) and 69.1% of users felt the same way about their amputation (Figure 1) . With regard to their adaptation to amputation, no statistical differences were noted between person with TT and TF amputations. Sixty-five percent of all the respondents who were not at all adapted to the prosthesis had amputations above the knee (X2 = 19.95, df = 4, p < 0.01).

Prosthetic Use

The results have shown that 85% (65.7% TT and 34.3% TF) of the respondents (n=396) were prosthetic users. Ninety percent reported wearing their prosthesis daily and 75% for more than 9 hours per day. Mean prosthetic use was 11.5 ? 4.1 hours per day and 6.7 ? 1.0 days a week for a total mean of 78.7 ? 30.9 hours a week (TT: 84.8 ? 30.4, TF: 75.0 ? 31.6). These descriptive statistics include both active users and cosmetic wearers. Significant differences exist between persons with TT and TF amputations (t = 4.98, df = 299.72, p < 0.001).

The respondents were also asked to report the proportion of ambulatory activities done with their prosthesis daily (Table 5) . It was found that indoors, 53% were using their prosthesis to perform the majority (75% and 100% combined) of their ambulatory activities (56.4% for TT and 46.5% for TF). Outdoors, the proportion of active users increased to 64% (66.3% for TT and 62.4% for TF). No significant differences were found between people with amputations above or below the knee.

Thirty-three percent of the nonusers (n = 63) reported discarding their prosthesis during the first year following discharge, 23.8% reported using it for at least two years, and 27%, 3 to 4 years. Sixteen percent never wore the prosthesis.

Four Sets of Predisposing Factors Related to the Dependent Variables

In this section, levels of amputation have been combined for data analysis, since no significant differences were found between groups with TT and TF amputations for the majority of the predisposing factors listed in Table 1 , except for education, peripheral vascular disease, visual and diabetic problems, stump sores, and phantom pain.

To determine the level of significance of the relationship between the potentially predisposing factors and prosthetic use, each independent variable was associated with each of the three dependent variables. Significance levels of variables related to prosthetic wear and active use are presented in Table 6 . Items not appearing in Table 6 failed to reach significance.

First Set of Factors: Physical Health Status. Cause of amputation was not significantly related to the dependent variables, but level of amputation (Table 6) was found to be a significant factor predisposing to prolonged prosthetic wear (X2 = 32.46, df = 4, p < 0.001) and active use of the prosthesis indoors (X2 = 11.21, df = 4, p < 0.05). In fact, a greater proportion of persons with TF amputations (37.7%) compared to TT amputations (8.1%) had discarded their prosthesis in the five years following discharge.

Cardiac (X2 = 15.39, df = 4, p < 0.005), respiratory (X2 = 11.33, df = 4, p < 0.005), and neurological (X2 = 12.13, df = 4, p < 0.01) problems were found to be significantly related to limited prosthetic limb wearing but not to active use. Chi-square analyses also demonstrated a significant level of association between diabetes mellitus and active use of the prosthesis for indoor (X2 = 15.38, df = 4, p < 0.005) ambulatory activities with the prosthesis.

Vascular (X2 = 9.36, df = 4, p < 0.05) and arthritic problems in the nonamputated leg (X2 = 16.41, df = 4, p < 0.005) significantly hampered prosthetic wear, whereas claudication cramps (X2 = 10.42, df = 4, p < 0.05) and sores (X2 = 9.88, df = 4, p < 0.05) were unfavorably related to active use of the prosthesis outdoors. Stump problems were not severe enough to be contributory factors in limiting the use of the prosthesis.

Second Set of Factors: Demographic Profile. Age was not found to be associated with prosthetic wear, but among those who wear the prosthesis on a regular basis, age was negatively correlated to active use of the prosthesis for ambulation indoors (r = -0.09, p < 0.05) and outdoors (r =-0.21, p < 0.001) (Table 5 and Table 6 ).

As expected, there was a preponderance of male subjects (74%) in the sample population, but sex did not influence prosthetic wear or active use. People with a low educational level (wear: r = 0.15, p < 0.005; indoor use: r = 0.12, p < 0.05; outdoor use: r = 0.19, p < 0.001) and low income (wear: r = 0.16, p < 0.005; outdoor use: r = 0.19, p < 0.001) were found to be wearing the prosthesis for shorter periods of time and to be less active users outdoors. On the other hand, employment (vocational status) was favorably related to prosthetic wear (X2 = 10.78, df = 2, p < 0.01) and active use of the prosthesis outdoors (X2 = 10.20, df = 4, p < 0.05).

Persons living at home tended to use their prosthesis more extensively for their ambulatory activities in the house (X2 = 22.17, df = 12, p < 0.05) and outside (X2 = 28.16, df = 12, p < 0.005) as compared with people residing in senior citizens homes or chronic care hospitals. Furthermore, persons living alone tended to wear their prosthesis for longer periods of time (X2 = 10.54, df = 4, p < 0.05).

Third Set of Factors: Time Frames of Rehabilitation Programs. The average time interval between amputation and fitting was 145 days. Delays were negatively correlated with prosthetic wear (r = -0.12, p < 0.01) and active use outdoors (r = -0.09, p < 0.05). Correlations are low but significant.

The duration of preprosthetic training was negatively correlated to prosthetic wear (r = -0.14, p < 0.05) and active use outdoors (r = -0.20, p < 0.001). Negative correlations were also obtained between duration of prosthetic training and active use of the prosthesis outdoors (r = -0.24, p < 0.001).

Fourth Set of Factors: Adaptation. Adaptation to amputation, and particularly to the prosthesis, was positively associated with prosthetic wear (adaptation to amputation r = 0.30, p < 0.001; adaptation to prosthesis r = 0.57, p < 0.001) and active use of the prosthesis indoors (adaptation to the amputation r = 0.16, p < 0.001; adaptation to the prosthesis r = 0.28, p < 0.001) and outdoors (same order r = 0.23, p < 0.001 and r = 0.27, p < 0.001).

Regression Analyses

A multiple, stepwise linear regression analysis was used to determine the importance of the predisposing factors discussed previously in predicting prosthetic wear. Respiratory problems, level of amputation, and adaptation to prosthesis, when combined, were shown to be good indicators of weekly prosthetic use (Table 7) . The adjusted R-square indicating the percent of explained variance was 35%.

Stepwise logistic regression analyses were used to predict active use of the prosthesis indoors and outdoors. With regard to indoor ambulatory activities (Table 8) , adaptation to the prosthesis and duration of the preprosthetic training were the only factors that remained significant (p < 0.05). Level of amputation and health problems failed to reach significance. For outdoor ambulatory activities, place of abode, claudication pain, time lag between amputation and prosthetic fitting, and duration of prosthetic training were the variables retained in the regression model.

Discussion

Prosthetic Wear and Active Use

The results of this survey indicated that a small proportion of our sample of persons with lower-extremity amputations had discarded their prosthesis one to five years following their discharge from the rehabilitation center. In fact, 85% of these subjects wore their prosthesis daily for periods ranging from one to 16 hours per day. Over the last 10 years, from one study to the next, results varied from 74% to 89%.4,8-9,10,13,16,21-23 Variations may be imputable to the definition of prosthetic wear, which may include people who wear their prosthesis regularly, part of the day, for transfers only, or for cosmetic purposes.

In the present study, when a more stringent definition of prosthetic wear was considered, the proportion of prosthetic wearers dropped considerably. Only 75% of the respondents reported wearing the prosthesis nine hours or more per day, and hence could be considered as primary users. Using similar outcome measures, previous studies reported that 65% to 75% of the lower-limb amputees wore their prosthesis nine hours or more per day and 59% to 73% wore the prosthesis all waking hours.4-5,9,14,23-25 The observed perseverance of the person with a TT amputation compared to the TF amputation, 77.7% vs 65.2%, to wear the prosthesis nine hours or more per day was also substantiated by a number of investigators.5,26

The amount of time the prosthesis is worn may be of interest but gives no indication as to locomotor activities done with the artificial limb. The active use of the prosthesis or prosthetic ambulation is a concept that has been operationalized in many different ways in the literature, and consequently, results vary considerably. In fact, it has been reported that 61% (67.8% TT and 52.9% TF) were using it "regularly,"21 that 59.1% were "using the prosthesis on a daily basis" with or without assistive ambulatory devices26 and that 36% were walking for "at least 20 feet" one year after discharge.11 When the population was classified according to its "level of independence" with the prosthesis, 71% of the respondents were considered independent with or without a cane, 68% of the persons with lower-extremity amputations made extensive and regular use of the prosthesis, 79% were able to walk indoors, and 60% were useful ambulators indoors and outdoors.5 Again, people with TT amputations were using the prosthesis more extensively than were people with TF amputations. Finally, as in the present series, Subbarao and McPhee4 investigated the percentage of ambulatory activities performed with the prosthesis. They found more than 80% of the subjects were using the prosthesis for the majority of their ambulatory activities (75% and more) but only 56% felt the prosthesis was used to best advantage. Their population had a mean age of 33 years. In the present study, the mean age of the respondents was 62.6 years, and age was shown to be negatively correlated to active use of the prosthesis indoors and outdoors. This may explain why only 53% of the people with lower-limb amputations of our sample were using the prosthesis for most of their ambulatory activities indoors.

It is interesting to note that, in our study, more subjects used their prosthesis to ambulate outdoors. However, it must be noted that 65% of these persons were under 65 years of age, the age group that makes up the work force. Furthermore, 86.5% of our population lived at home where one is more likely to perform basic chores in the community and use community services. Ambulation in the community requires that a person circulate through environments not adapted for wheelchairs and best managed on foot; for example, passing through turnstiles, venturing in narrow aisles in the drugstore or restaurant, climbing stairs or curbs, and going in and around houses not adapted for wheelchair use. It can further be assumed that cosmetics plays an important role in social gatherings, thus encouraging prosthetic use.

The primary reasons for curtailed or limited use of the prosthesis indoors and outdoors expressed by people with lower-extremity amputations were walking with the artificial limb was too exhausting (29.0% in the house vs 35.3% outside); problems with the nonamputated leg (37.4% vs 38.8%); discomfort or perspiration problems from the prosthesis (36.1% vs 30.2%); and stump irritations or sores (28.4% vs 27.6%). Distances to cover outdoors were too long for 52.6% of them and 25% mentioned the fear of falling outside their home. Some of these reasons were also reported by Beekman and Axtell.10

Predisposing Factors Related to Prosthetic Wear and Active Use of the Prosthesis

Physical Status

Among the factors predisposing to prosthetic use, the level of amputation is, by far, the most frequently discussed factor in the literature. Our survey has confirmed the view that people with TT amputations have better functional outcomes with the prosthesis than do people with TF amputations. Quantitative monitoring of the number of steps taken daily by a person with a lower-extremity amputation, as measured by electronic step counters, demonstrated that the TT subjects walked more than the TF subjects just prior to discharge and during their first and second year after discharge.27 People with transfemoral amputations have poorer walking prognosis than do people with TT amputations; one of the primary reasons is that physiologic energy expenditure of gait with a prosthesis, increases dramatically with the level of amputation.28

Energy requirements for prosthetic walking cannot easily be met by people with lower-extremity amputations suffering from other concomitant health problems. In the present study, people with cardiac and respiratory problems were shown to wear their prosthesis significantly less than people with a favorable cardiorespiratory status and these problems were significantly more frequent in the nonusers group (Table 2) . Similarly, Siriwardena and Bertrand6 demonstrated that persons with lower-extremity amputations who have ischemic heart disease and chronic obstructive pulmonary disease, such as bronchitis, did not perform as well as their healthy colleagues on the Walking Ability Index 12 months following discharge. Normal walking requires little energy, but following amputation of a lower limb, the muscular activity needs to be modified to enable walking with a prosthesis. Energy expenditure is correspondingly increased. Energy production depends on the oxygen delivery capacity of the cardiovascular and pulmonary systems, and these systems become less efficient with age.29 The elderly amputee with vascular insufficiency must accommodate for these impairments, and the requirements for walking may impose excessive demands on the cardiovascular and pulmonary systems. In cases where these systems are deficient, the physiological stress may be overwhelming and deter locomotor activities with the prosthesis.

Peripheral arterial disease, with or without diabetes mellitus, is the major pathology leading to amputation of the lower limb. Peripheral arterial disease is a systemic disorder, which over the years may seriously affect the condition of the remaining limb, the stump, and many other organs. In this study, 36% of the respondents indicated a poor circulation in the remaining limb (31% reported in the medical charts), 20% had claudication pain (muscle cramp when walking), and 8% to 11% suffered from constant pain or sores. These problems were found to hamper prosthetic wear and active outdoor use (Table 6) . Even though it is generally accepted that ambulation with the prosthesis reduces stress on the nonamputated limb and equalizes weight bearing, in more advanced stages of the disease, because of intermittent claudication pain and sores on that limb, a person may need to discard the prosthesis to protect the limb. In the current study, intermittent claudication (muscle cramps) and sores were factors limiting active use of the prosthesis, specifically outdoors, when long distances needed to be covered, as in community ambulation (Table 6) . Similarly, Sussak,30 who assessed blood flow with the Doppler Ultrasound Flowmeter and prosthetic use, offered evidence that the sound leg, but not the stump, becomes the factor restricting mobility. Sussak30 also observed that the vascular status of the TF group was generally worse than that of the TT group, and argued that when an amputation above the knee was necessary, the severity of the disease was such that the other leg was also badly affected.

Time Frames of Rehabilitation Programs

The information regarding rehabilitation programs pertains to delays between amputation and prosthetic fitting and duration of preprosthetic and prosthetic training. Those were the types of data routinely stored for analysis in the rehabilitation centers that participated in the present study.

In the current study, time-to-provision of the prosthesis following amputation was on the average 145.2 ? 124.0 days, that is 20.7 ? 17.8 weeks. Shorter time intervals have been reported and vary from 6 to 16 weeks.4-6,8,31 In some cases, the shorter intervals were attributed to a younger, cancer-related population; in others, to centers that developed an integrated approach to amputation surgery and stump healing.32 The most probable explanation of the undue delay reported in the current survey may be the presence of severe concurrent chronic illness; long periods of hospitalization while attempting to save the ischemic limb; and delays in wound healing, which occur frequently in advanced stages of peripheral arterial diseases and diabetes mellitus. A long delay between amputation and prosthetic limb fitting and walking may result in prolonged inactivity and consequently in cardiovascular deconditioning and loss of the metabolic reserves required for walking. This is of prime importance for the elderly people with amputations whose capacities and reserves are already reduced. In 1972, Hamilton and Nichols33 stated that "any period longer than four weeks postoperatively" was considered as "undue delay for limb fitting for the geriatric lower-limb amputee." In agreement with previously reported studies,15,33 our results show that a prolonged delay is negatively associated with prosthetic wear and active indoor and outdoor use. Delays are significantly longer for nonusers. Hence, these results demonstrate the benefit of early prosthetic fitting and training.

Duration of preprosthetic and prosthetic training has been shown to exceed 6 and 7 weeks, respectively, for a global hospital stay of approximately 13 weeks during the rehabilitation process. Jones and colleagues 9 reported an average length of hospital stay of 10 weeks for persons with unilateral TT amputations and 13.8 weeks for persons with TF amputations, whereas Francis and Renton 31 demonstrated that the rehabilitation program could be completed in 4.6 weeks (32 days) for people with TF amputations and 5.4 weeks (38 days) for persons with TT amputations. This last set of data was obtained from a longitudinal study on amputation surgery and stump healing conducted in a surgical center specializing in arterial surgery and where the different phases of the rehabilitation process were optimally coordinated and delays reduced to a minimum.

Duration of preprosthetic and prosthetic trainings were negatively related to prosthetic use outdoors (Table 6) . Hence, a long preprosthetic and prosthetic training period does not necessarily result in increased prosthetic use. Again, prolonged preprosthetic and prosthetic training may be related to the previously mentioned chronic health problems and delayed wound healing. This could apply specifically to nonusers who have a significantly higher incidence of cardiac, respiratory, and neurological problems, as well as constant stump pain and vascular and arthritic problems in the nonamputated limb. The length of prosthetic training was not significantly different for nonusers, but one may hypothesize that for people with a poor rehabilitation prognosis, the health professional may tend to concentrate on the achievement of minimal functional activities in order to fulfill basic individual needs, thereby limiting unnecessary and unrealistically prolonged hospitalization, especially in a population with a short life expectancy.

Adaptation to Amputation and Prosthesis

Acceptance and adaptation to the handicap plays a crucial role in rehabilitation and can strongly influence the outcome of the rehabilitation program. People who adjust to the loss of a limb may eventually make an effort to improve their function with the use of the prosthesis. Hence, adjustment to the prosthesis depends upon the personal adjustment to amputation.34 This adaptation is also dependent upon the person's personality and the degree of integration of the artificial limb into the person's personality profile, thereby restoring body image. Persons with a strong self-image are generally self-assured, confident, and have a more stable motivation.34 This is clearly supported in the present study by the consistently positive relationships observed between adaptation to both amputation and prosthesis and prosthetic wear, and active use indoors and outdoors (Table 6) . People with poor motivation may use the prosthesis for the period of training or as long as external support is provided by the health system, but as soon as a minor event interferes with prosthetic use, the artificial limb is discarded. This survey showed that 16% of nonusers never wore the prosthesis after discharge and 28.5% rejected the prosthesis because it no longer fitted. In these cases the prosthesis was not returned to the prosthetic laboratory for repairs, even though the workshop was said to be close enough to their home and appointments readily available.

In addition, the lack of motivation for acceptance of a prosthesis was reported as a problem in delays between amputation and provision of a limb.6 Our results support this allegation: Nonusers do have longer time-to-provision periods (Table 4) , longer preprosthetic training, and half of the nonusers consider themselves "not at all adapted" to the prosthesis (Figure 1) .

Predictors of Prosthetic Use

The influence of motivation is further emphasized by the results of regression analyses, which show that adaptation to a prosthesis, when combined with level of amputation and respiratory tract disorders, or with the duration of preprosthetic training, are predictive of prosthetic wear and active use for ambulatory activities indoors. In fact, from this model one can predict (formula in Table 7 ) that a person with a TT amputation who has respiratory problems and claims to be moderately adapted to the prosthesis would wear the prosthesis 53 hours per week. On the other hand, a person with a TT amputation who has no respiratory problems and also claims to be moderately adapted to the prosthesis could wear his prosthesis 85 hours per week, that is, 12 hours per day, 7 days per week.

As discussed earlier, people with TF amputations have greater energy requirements when using a prosthesis. Breathing being the main source of oxygen intake, cardiorespiratory dysfunction imposes higher limitations on the person with a TF amputation. Hence, motivation to walk must be strong in order to accomodate for the added restrictions.

Using stepwise logistic regressions, adaptation to the prosthesis and duration of preprosthetic training were found to be the factors that best explained active use of the prosthesis in the home. From this model (Table 8) , it can be predicted that an individual whose adaptation to the prosthesis is quite good and for whom the preprosthetic training lasted 90 days has a 61% chance of using his prosthesis for the majority of his ambulatory activities indoors. A person who is also quite well adapted to the prosthesis but requires a preprosthetic training of 30 days has a 74% chance of using his prosthesis for the majority of his ambulatory activities indoors.

A previous study11 identified higher level of amputation, older age, confinement to an institution, presence of stump pain, confusion, and poor self-rated health as variables that best explained dependence in activities of daily living. In the current study, level of amputation, age, health problems, problems with the stump and nonamputated leg, place of abode, and living arrangements (living alone or with someone else) were rejected from the logistic regression equations. But these variables may have been technically discarded from the model because they were highly correlated with the two predictors-adaptation to the prosthesis and duration of preprosthetic training.

For outdoor ambulatory activities, place of abode, claudication pain, time lag between amputation and prosthetic fitting, and duration of prosthetic training were found to be predictors of prosthetic use (Table 8) . According to the equation, an individual who lives at home, has no claudication pain in the nonamputated leg, has been fitted within 135 days after amputation, and took 55 days to complete the walking training would have a 65% chance of using his prosthesis for the majority of his ambulatory activities outdoors, but the probability would drop to 38% if that person had claudication pain and a longer prosthetic fitting after amputation, for example, 185 days.

The negative associations between claudication pain, time lag between amputation and prosthetic fitting, duration of prosthetic training, and prosthetic use outdoors may reflect the presence of serious health problems. Long intervals between amputation and prosthetic fitting and training are usually attributed to the presence of severe concurrent diseases. Outdoors, greater distances need to be covered and people with claudication pain or with severe health problems may not have the tolerance to walk long distances or to walk around in a shopping center. As a matter of fact, people who do not use their prosthesis for getting around outside their home reported that it was because distances were too long (52.6%), they tired easily (35.3%), or they were afraid of falling (25.0%), and 40% could walk from a few steps to less than a block, nonstop. The importance of early prosthetic fitting and training and pain have also been pointed out by Pohjolainen and colleagues11 who found an unfavorable association between time lag from surgery to prosthetic fitting, phantom pain, increasing age, occurrence of cerebrovascular disease, and reduced prosthetic use, outdoor walking, and walking distances.

The originality of this research relies on the analysis of data providing statistical evidence of factors related to prosthetic wear and active use indoors and outdoors and gives some insight on predictors of functional prosthetic outcome. The limits of this study, however, are the same as those found in transversal studies. The results reflect the condition and behavior of the amputee population at one point in time.

This research is also unique in that it is based on a theoretical model that organizes variables in three meaningful categories of factors potentially related to prosthetic use. These are factors that predispose to, enable, and reinforce a specific behavior, which was defined as prosthetic use. The predisposing factors that were presented in this paper are antecedent to the behavior and provide the rationale or motivation for the behavior. Some of these factors cannot be altered (e.g., level of amputation, health problems) but when factors can be interacted upon, the rehabilitation team should make every effort to provide early support and set rehabilitation goals that may contribute to the persistence of the behavior.

Conclusion

A survey was conducted throughout the province of Québec using the PPA questionnaire, which was developed by the authors to evaluate the actual use of the prosthesis by people with lower-limb amputations following reintegration into the home setting and to identify the predisposing factors related to prosthetic use. The results of the study revealed that 85% of people with amputation wore the prosthesis weekly, 53% used the prosthesis to perform the majority of their ambulatory activities in the house, and 64% used it for outdoor ambulatory activities. The categories of factors investigated included the physical health status, motivation, demographic profile, and time frames for rehabilitation programs. The factors predisposing to prosthetic wear and active use indoors and outdoors were substantiated, and among those, level of amputation, the absence of respiratory problems, and adaptation to the prosthesis were found to be predictors of prosthetic wear. Stepwise logistic regression models have also shown that adaptation to the prosthesis and short periods of preprosthetic training were good indicators of active use of the prosthesis for most of ambulatory activities indoors, whereas, place of abode, claudication pain, delays in prosthetic fitting, and duration of prosthetic training were predictors of active use of the artificial limb outdoors. The results of this study may be beneficial for health care professionals working with people with lower-limb amputations in that patients who seem to have a nonuser's profile may be targeted and support provided. Further research to clearly identify the prosthetic profile of a person with a lower-extremity amputation in the year following discharge from the rehabilitation program is ongoing.

Enabling and reinforcing factors were also investigated and the results will be published later.

Acknowledgements

This research was funded by grant No. 6605-3025-59 from the National Health Research and Development Program, Health and Welfare Canada.


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