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Exercise in Persons with Unilateral Lower-Limb Amputation and Contralateral Limb Knee Injury: A Pilot Study

Caldwell, Mary E. DO; Marshall, Benjamin DO; Semik, Patrick BA; Huang, Mark E. MD

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Journal of Prosthetics and Orthotics: January 2019 - Volume 31 - Issue 1 - p 51-57
doi: 10.1097/JPO.0000000000000220
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Exercise habits and return to exercise in individuals with lower-limb amputation (LLA) have been reported in up to 11% to 61% of individuals with amputation.1,2 In the United States, approximately 82% of all LLAs are due to vascular conditions, whereas 16% of amputations are due to trauma, with the remainder being congenital or due to malignancy.3 Often younger individuals with unilateral transtibial amputations due to nonvascular causes are more active than older individuals with vascular cause for amputation.4,5 A 2011 systematic review determined that between 11% and 61% of persons with LLA participated in sports or physical activities (Figure 1). Physical exercise varied with sex, energy requirement, and load on the prosthetic limb.1 Types of activity were typically fishing, swimming, golfing, walking, and cycling.6 In persons with traumatic amputations 20 years after amputation, 54% were involved in sports on average for 6.7 hours per week.2 Participation in sports is known to benefit the cardiopulmonary system as well as contribute to psychological well-being and physical functioning, and is often encouraged for patients with amputation.1 In fact, recent programs have used sport and recreational activity as a means to reintegrate individuals with amputation due to combat injuries back into a civilian lifestyle.7 The positive effects of exercise have long been thought to outweigh the risk of injury associated with exercise; however, overuse injuries or acute injuries in a person with amputation can be devastating to his or her everyday life, especially when it involves the contralateral (intact) limb.

Figure 1
Figure 1:
Adaptive athlete with transtibial amputation exercising.

Intact-limb knee pain and knee osteoarthritis has been described as a common secondary complication from prosthesis use in patients with LLA.8 Intact-limb knee pain seems to occur with a higher prevalence in individuals with traumatic LLAs when compared with the general population (40.3% vs 20.2%). Even in the absence of knee pain, individuals with traumatic amputations have higher rates of radiographic knee osteoarthritis.9,10 There is some evidence that this may be related to the intensity of activity performed in the post-amputation period. For instance, volleyball players with amputation have significantly higher rates of intact-limb knee pain when compared with time postamputation matched “nonathletic” persons with amputation.11 Despite this finding being widely referenced in the literature,12–14 there have been no investigations to address if exercise intensity with sports participation correlates to the development of intact-limb knee injury in patients with LLAs. Given this gap in knowledge and the need for clinicians to best educate the population of individuals with amputation, this study focused on knee injuries in the intact limb rather than all injuries in individuals with amputation.

With the recent trend of increased participation in exercise programs and sports by persons with amputation,2 developing exercise guidelines for patients with amputations can provide guidance for these individuals with respect to their participation in sports and exercise. The purpose of this pilot study is to describe the exercise habits of persons with unilateral LLAs in relation to the American College of Sports Medicine (ACSM) exercise guidelines. Furthermore, we wish to determine if exercise intensity is correlated to rates of intact-limb knee injuries. Developing specific exercise guidelines may allow for patients with amputation to maintain their health while minimizing the risk of injury from exercise.


This questionnaire-based cross-sectional cohort was carried out using a telephone survey, after receiving approval from the Northwestern University Institutional Review Board; subjects also gave oral consent. Subjects were identified via a chart review. Subjects seen between January 1, 2000, and January 1, 2014, at a university hospital in an outpatient clinic and subjects that participated in the institution's adaptive sports and fitness program (or an affiliated adaptive sports event) were eligible. Subjects were included if they were as follows: 18 years or older in age, had a history of single LLA of any level, and any etiology of LLA except vascular cause (diabetes or peripheral artery disease). Subjects were excluded if they had a history of cognitive impairment, if they had expired at time of chart screenings or survey, if they were non–English-speaking, if they had pain in intact-limb knee before amputation of the amputated limb, or a history of rheumatoid arthritis or gout.

An institutional review board–approved recruitment letter was sent to those individuals who met inclusion criteria, notifying them that they could call to participate in the survey or that they would be called within the next few weeks by a study investigator to be given the option to participate in the survey at that time. Before any participant underwent the survey, he or she gave oral consent. No identifying data were collected and responses were anonymous. This consent process was approved by the institutional review board and was outlined in the recruitment letter to all participants and again at the time of telephone contact.

The 8 sections of survey inquired about demographics, limb loss etiology, anatomic level, medical/surgical history (including intact-limb knee injuries before amputation), exercise habits before and after amputation (including perceived intensity, frequency, and duration), and intact-limb knee injuries.

ACSM guidelines on exercise can be referenced via the position statement released in 2011.15 Based on those guidelines, persons with amputation were determined to meet cardiorespiratory (CR) guidelines, by exercising at a moderate intensity of 30 minutes or more per day on 5 days or more per week for a total of 150 minutes or more per week or by exercising at a vigorous-intensity CR exercise training for 20 minutes or more per day on 3 days or more per week (or 75 minutes or more per week).15

Exercise intensity was determined using a subjective outcome measure called the talk test.16–18 The idea of the talk test is that it is practical and inexpensive and differentiates between exercise intensities.17,18 Subjects were asked to recall, for a majority of exercise, which description best matched their workout:

  1. Talk comfortably for hours (at a conversation pace) during exercise (light intensity);
  2. May break a sweat and “just being able to converse comfortably” with exercise (moderate intensity);
  3. Break a sweat and comfortable conversation was not likely possible (vigorous intensity);
  4. If they would break a sweat and only speak a word/no words possible (near maximal or maximal effort).

Resistance exercise guidelines were defined as met or not met if the person met training each major muscle group 2 or 3 days a week with between 8 and 20 repetitions.15

Statistical Analysis

Data were checked for normal distributions using descriptive statistics with Shapiro-Wilks test for normality. Pearson χ2 test was used to compare outcome groups on categorical variables and one-way analysis of variance (ANOVA) to compare groups on numerical variables with normal distribution and Kruskal-Wallis one-way ANOVA for variables with non-normal distribution. The level of significance was set at 0.05 for all statistical tests. Two-sided testing was used for all hypothesis testing. Cases with missing data were excluded. Data were analyzed using IBM SPSS version 20.


A total of 25 individuals participated in the survey. Demographic, clinical, and amputation classifications are demonstrated in Table 1. Of the 25 subjects, etiology of amputation was as follows: transmetatarsal/Symes (n = 2), transtibial (n = 13), transfemoral (n = 7), and hip disarticulation (n = 3). The mean (SD) age was 46 (20.6) years, and the mean (SD) years since amputation was 14 (16.6) years. The mean body mass index was 25.9 with an SD of 6.1. The predominant etiology of amputation was traumatic (n = 20). There was no significant difference between groups.

Table 1
Table 1:
Demographics and amputation etiology

Exercise habits before and after amputation in subjects is demonstrated in Table 2. Before amputation, 84% (n = 21) reported they exercise, and 68% (n = 17) met CR exercise guidelines. After amputation, only 48% (n = 12) met CR guidelines. Those individuals who exercised before amputation were significantly more likely to exercise after amputation (90%) when compared with respondents with no history of regular exercise before amputation (P = 0.04). Only 16% (n = 4) met resistance guidelines after amputation.

Table 2
Table 2:
Preamputation and postamputation exercise

Of the amputation groups, 100% (n = 2) of transmetatarsal group, 91% (n = 10) of the transtibial group, and 83% (n = 5) of the transfemoral group exercised with a prosthesis. The remaining person with transfemoral amputation exercised without a prosthesis (n = 1), whereas the remaining person with transtibial amputation reported exercising with the prosthesis intermittently (n = 1). The hip disarticulation group reported 50% (n = 1) exercising without their prosthesis and 50% (n = 1) exercising with a prosthesis intermittently. There was no statistical significance between groups (P = 0.09).

Intact-limb knee injury and exercise is demonstrated in Table 3. In those who met CR exercise guidelines postamputation (n = 12), five subjects reported intact-limb knee injuries during exercise. In those who reported exercise less than moderate intensity (n = 13), none had intact-limb knee injuries (P = 0.009). Respondents who met CR guidelines were at significantly higher risk of knee injury (P = 0.05). With respect to meeting resistance guidelines, two patients reported knee pain who met the resistance guidelines, whereas three patients had knee pain who did not meet guidelines (P = 0.10).

Table 3
Table 3:
Intact-limb knee injuries and exercise guidelines

Exercise intensity and intact-limb knee injury is demonstrated in Table 4. In subjects that reported exercise at light intensity (n = 7; not meeting CR exercise guidelines) or a moderate intensity (n = 4; while meeting CR guidelines), there were zero injuries. In subjects who reported exercise at both moderate and vigorous intensity while meeting exercise guidelines (n = 6), there were 4 intact-limb knee injuries. In subjects who reported always exercising at a vigorous or maximal exercise level (n = 3), there was one intact-limb knee injury. This was significant between groups (P = 0.01). Type of exercise reported by participants with amputation is demonstrated in Figure 2. The most common modes of exercise included walking, running, and weight resistance training.

Table 4
Table 4:
Exercise intensity and intact-limb knee injury
Figure 2
Figure 2:
Sport participation for persons with amputation.


Maintaining a balance between physical fitness through exercise and minimizing risk of injury is critical in patients with amputation. Patients with amputation are at risk for weight gain as a result of their injury and increased physical inactivity.19 Likewise, patients are at risk for increased knee pain and osteoarthritis as previously described.8 Patients with amputations have been shown to have gait abnormalities that included increased load on the sound limb. Furthermore long-term prosthesis use has been associated with a greater prevalence of knee arthritis. Ironically, these patients may have been more active users and, as a result, are chronically placing increased stress on their sound limbs that may accelerate any increased predisposition to knee osteoarthritis.

The ACSM has recommended that otherwise healthy individuals with nonvascular amputations should adhere to the ACSM general exercise guidelines and “emphasize improving efficiency of locomotion with the prosthesis.”20 Our study population excluded those with amputations from vascular etiology. This explains the low recruitment numbers given that the majority of amputations in the United States are due to peripheral vascular disease.3 Although more than 80% of individuals with unilateral LLAs in the current study report regular exercise, less than 50% were doing so at a level that would be considered adherent to current ACSM CR guidelines. These numbers reported are higher than reported physical activities in larger surveys in the United States, but may reflect the method of recruitment, which involved soliciting subjects involved with a local rehabilitation fitness center.21,22 We did see a small decline in adherence to the CR guidelines following amputation in the current study, although resultant levels of adherence were similar to matched national survey rates and therefore may be more representative of an age-related decline in physical activity and are not necessarily the result of a nonvascular amputation event. There was, however, a lower rate of adherence to resistance exercise guidelines than has been described in large national populations.23 This reduced adherence in our population could be a result of greater barriers to access of adaptive weight training equipment or facilities. Interestingly, weight training was still one of the most common modes used by subjects in this study. Further investigation into the etiology of such a gap could elicit targets for intervention to increase adherence to resistance exercise recommendations by persons with amputation.

Among survey participants who met ACSM CR (intensity, frequency, and duration) guidelines, we noted a significantly higher prevalence of intact-limb knee injury (Table 3). This statistically correlated to the level of reported exercise intensity as participants who engaged in exercise at a vigorous or maximal level of intensity were the most likely to report an intact-knee injury (Table 4). Although high-intensity exercise has been linked to such knee injury in persons without amputation, it seems to mainly predispose a subset of individuals with preexisting chondral or meniscal injury and does not appear to be independently associated with injury, pain,24,25 or osteoarthritis development.26 Although we did exclude individuals reporting preexisting intact-knee pain, such an injury may be latent in these individuals until they obtain the level of exercise intensity necessary to provoke symptoms. Latent pathology could explain the findings with respect to knee pain in the current study. Of course, there are other factors that may predispose patients with amputation to knee injury with exercise. Alteration in gait mechanics inherent in the individual with LLA has been suggested to contribute to such injuries.1,27 Such abnormalities in gait may increase the risk of knee injury, which may be more pronounced with moderate to vigorous exercise.

There is evidence in the literature that lower-limb resistance exercise can be protective and/or therapeutic for many pathologic knee conditions.28–30 The lower incidence of meeting resistance exercise recommendations in our population relative to a national cohort could have also predisposed them to such injuries, particularly if engaged in the more demanding dynamic physical tasks that come with more vigorous CR sport-based exercise.

Because this is the first study to examine the relationship between exercise intensity and intact-limb injury in individuals with unilateral LLAs, additional prospective investigation of any of these proposed potential contributors may help guide future clinicians and exercise recommendations in this population. These preliminary findings suggest that individuals with unilateral nonvascular LLAs should likely exhibit caution when exercising at more than a moderate (breathing hard, but conversing more than a sentence) level of CR intensity. The moderate exercise level appears to represent the best balance between garnering the health benefits from participation in CR exercise while minimizing the likelihood of knee injury in the intact limb. It would also be reasonable to address any perceived barriers to resistance exercise training that may be discouraging persons with LLAs from adherence to recommended resistance guidelines.

There are several weaknesses to the current study besides those inherent in any cohort design. First is the small number of subjects that participated in the pilot study. As a result, the number of patients at each level of amputation was small. However, we attained a sample size comparable to other investigations of orthopedic conditions specific to individuals with amputation.1,11,31 Furthermore, the level of LLA in our study had disproportionally elevated percentage of transfemoral and hip disarticulation patients compared with prior study populations,8 which is likely secondary to the patient population seeking care at our hospital and fitness center, but may not be as representative of a national population. As with any retrospective analysis of behavior, the accuracy of patient-reported exercise intensity and injury definition were both subject to recall bias. Although the talk test has proved reliable to determine exercise intensity, it is typically performed prospectively. This may have influenced the accuracy of determining reported preamputation and postamputation exercise intensity.

Of note, in multiple subjects, many replied that “they could carry on conversation with exercise” and other times that they were very limited. This led to the unanticipated combination group of “mod/vigorous,” and patients not wanting to define their exercise as just one subgroup. If they had picked “moderate” over “vigorous” and had a knee injury with picking just moderate, this could have changed the study outcome with regard to moderate being safe over vigorous. However, the results suggest that if the patient is reporting vigorous exercise intermittently, this person may be the demographic that needs to be educated on injury prevention. Interestingly, in those patients reporting “light” or “maximal effort,” these subjects appeared absolute in their answers with not crossing over subgroups.

Lastly, our questionnaire did not specifically address the subjects' prosthetic components or proficiency with prosthesis use. Although we did assess if subjects engaged in exercise with or without prosthesis, the difference was not significant between groups. Participants with amputation also reported intermittent use of prosthesis with exercise but many were unable to quantify specific time of use. Therefore, no further statistical analysis was performed to relate if exercising with or without a prosthesis related to intact-limb knee injury. Another confounding factor limiting the ability to analyze use of prosthesis with injury risk was that the actual prosthetic fit could have contributed to injury, but this could not be formally assessed due to the interview assessment method.

This pilot study serves as a foundation for a future larger study that more closely examines knee injury in patients with amputation. A prospective study with a larger cohort and more subjects for each level of amputation would be ideal. Prospective data collection focusing on exercise intensity can address any recall bias issues and the impact of injury on activity. Additional data such as prosthesis use, socket fit, and type of prosthetic components may provide further insight.


This preliminary study is a first important step in determining the benefits and risks of exercise for patients with nonvascular-etiology LLAs. Although exercise is often viewed as beneficial, patients with LLAs may need to use caution when attempting a moderate to vigorous exercise regimen as defined by ACSM CR guidelines. A larger prospective study would be beneficial to clarify the relationship between knee injury and exercise intensity to provide further recommendations for activity in patients with unilateral LLAs.


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amputation; exercise; exercise intensity; knee injuries; injury; ACSM; intact limb

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