Since 2001, rehabilitation of ill, injured, and disabled persons has been based on the bio-psycho-social model of the International Classification of Functioning, Disability and Health (ICF) developed by the World Health Organization.1 Rehabilitation is no longer limited to merely identifying an illness, injury, or disability but goes beyond this to comprehensively describe its impact on the daily life of affected patients. The ICF is used to systematically measure limitations on carrying out activities of daily living (ADLs) and difficulties in participating in family, business, and social life. With this as a basis, a patient-specific strategy for rehabilitation can then be developed that also takes factors related to the individual environment, for example, living on the third floor without an elevator, and personal context, for example, coronary heart disease with limited physical capacity, into consideration. The most important rehabilitation goal is the optimal restoration of the patient’s independence and reduction of difficulties that affect participation in family, business, and social life. Furthermore, the United Nations’ Convention on the Rights of the Persons With Disabilities2 aims not merely at participation but also at complete inclusion of the disabled person in social life. Inclusion means the complete equality and equal status of an individual, not conditional upon normality or setting unattainable standards for individuals. Every person’s individuality must be accepted by society and every person must be given the opportunity to participate fully in society.
For persons with amputated limbs, adequate fitting with a prosthesis is an important precondition for regaining independence and the greatest possible participation in social life. Amputees should therefore be fitted with prosthetic devices that enable them to be as functional as nondisabled persons to the greatest extent made possible by technology and their individual medical conditions. The microprocessor-controlled C-Leg® (Ottobock, Duderstadt, Germany; Minneapolis, MN, USA), introduced in 1997, was the first prosthetic knee joint to overcome the inverse relationship between safety and functionality that still exists for mechanical, non-microprocessor-controlled knee joints.
Well-established clinical practice asserts that the safer (i.e., the more stable) the mechanical knee is, the less functional the patient is. Conversely, the more functional the prosthesis is, the less safe the mechanical knee is. The unique combination of safety and functionality in the C-Leg has been proven in 27 English-language publications on biomechanical and clinical studies3–29 and a systematic review30 that made it the most widely researched prosthetic knee component ever. The C-Leg’s reduction in the frequency of stumbles and falls and simultaneous increase in functionality compared with mechanical prosthetic knee joints8–10,12,15,17,20 are especially significant.
The various microprocessor-controlled prosthetic knee joints available on the market today have widely differing technical designs and software controls.31 Because most manufacturers of other electronic knee joints have not yet produced evidence of the benefits of their products, it is not scientifically valid to simply transfer the results of the C-Leg studies to all microprocessor-controlled knees. This is also supported by a study that has shown considerable biomechanical differences between the various electronic and microprocessor-controlled knee joints that have a great impact on the safety of amputees when walking at different speeds, on stairs and ramps, and in simulated everyday situations with increased risk of stumbles and falls.8 The C-Leg has thus far proven to be the safest knee joint for patients in all critical situations. The other microprocessor-controlled knee joints achieve a similar safety level in, at best, only a few, but not all, situations where there is a risk of falling.
The Genium® Bionic Prosthetic Knee (Ottobock) offers the amputee functions and ambulation modes previously not available in prosthetic knee joints. Early biomechanical studies of immediate effects showed that the Genium enables additional activities compared with the C-Leg, such as climbing stairs and stepping over obstacles step over step.32,33 Furthermore, for many activities, there is an additional increase in safety and approximation of movement to that of a nonamputee. Among other advancements, this normalized movement leads to measurable reduction in excessive loading of the intact musculoskeletal system.
The extent to which these objective biomechanical improvements are subjectively perceived by patients and implemented in everyday use remains to be studied. The objective of this study was to examine whether the Genium Knee, as compared with the C-Leg, results in subjective, patient-perceived improvements in the difficulty and safety of functional ADLs. The amputee’s opinion, unfortunately often underestimated in research, is especially significant because prosthesis confidence and subjective perception of safety have a direct effect on participation in business, family, and social life. The lack of confidence in a prosthesis and its safety frequently leads to avoidance of activities34 and may contribute to a reduction in participation and an increase in comorbidities such as obesity and depression, as demonstrated in nonamputated subjects with fear of falling.35–38
The study was conducted on 10 unilateral transfemoral amputees (all men; mean age, 36.7 ± 10.2 years; average period since amputation, 12.5 ± 9.6 years; six patients Medicare Functional Classification level [MFCL] 4 and four patients MFCL 3, all traumatic amputees). All patients were experienced C-Leg users who had been fitted with this joint for an average of 5.4 ± 2.0 years and who gave written consent for participation. For this study, a test prosthesis consisting of a duplicate of the existing socket and the identical prosthetic foot was used. In this manner, the subjects were required to learn the functions of the Genium alone.
A questionnaire was developed for the study, with a total of 45 ADLs in five activity categories: Personal Hygiene and Dressing (4 activities), Family and Social Life (12 activities), Mobility and Transportation (19 activities), Sports (4 activities), and Other Activities (6 activities). The individual ADLs are listed in the Results section (Figures 2, 3, and 4). At the start of the study, the patients completed the questionnaire for their C-Leg prosthesis. The patients were asked to rate the importance of each individual activity to their everyday life and how difficult the activity was to perform with the C-Leg.
The importance of the ADLs could be rated as follows:
- very important (3 points)
- rather important (2 points)
- unimportant (1 point)
The subjectively perceived difficulty of performing ADLs could be rated as follows:
- very easy (6 points)
- easy (5 points)
- rather easy (4 points)
- rather difficult (3 points)
- difficult (2 points)
- very difficult (1 point)
The patients were then fitted with the Genium Knee, given 1 day of gait training, and then sent home to use the new prosthesis in their everyday lives. After a 3-month accommodation period, the patients completed the same questionnaire to evaluate the importance and difficulty of performing the 45 ADLs with the Genium. The patients did not have access to the answers from their evaluation of the C-Leg they had made 3 months earlier.
In addition to the individual knee ADLs questionnaire, the patients completed another questionnaire in which they were asked to subjectively compare perceived difficulty and safety of performing the same 45 ADLs between the C-Leg and the Genium. In this comparison questionnaire, the difficulty and safety could be evaluated as follows:
- much less difficult and/or much safer with the C-Leg (−2 points)
- less difficult and/or safer with the C-Leg (−1 point)
- no difference between the two joints (0 points)
- less difficult and/or safer with the Genium (+1 point)
- much less difficult and/or much safer with the Genium (+2 points).
The statistical analysis of the separate evaluations of the subjective difficulty of performing the 45 ADLs with the two joints was made using the Wilcoxon signed rank test with p < 0.05 and a power of 80% in Win STAT for MS Excel® (Microsoft Corp, Redmond, WA, USA).
The results of the comparative questionnaire could be subjected to only a descriptive statistical analysis because only one value per patient was given for the comparative difficulty and safety, respectively. For this, the clinical relevance of the difference was assumed when the group mean value for the respective activity reached at least 25% of the maximum possible difference of +2 points (much less difficult and/or much safer with the Genium) or −2 points (much less difficult and/or much safer with the C-Leg). A clinically relevant gain in function was assumed for the Genium when the group mean value was +0.5 or higher and for the C-Leg when the group mean value was −0.5 or lower. For group mean values between −0.49 and +0.49, it was assumed that there was no clinically relevant difference between the two joints.
IMPORTANCE OF THE ACTIVITIES FOR THE DAILY LIFE OF THE PATIENTS
Patients rated the importance of the 45 activities for their daily life at an average of 2.58 ± 0.64 for the C-Leg and 2.59 ± 0.63 for the Genium. Because the maximum possible rating was 3 points (“very important”), it can be concluded from these results that the questionnaire covers a range of very important ADLs.
SUBJECTIVELY PERCEIVED DIFFICULTY OF PERFORMING ACTIVITIES OF DAILY LIVING WITH THE C-LEG AND THE GENIUM
The average difficulty of performing all 45 ADLs was indicated to be 5.1 ± 0.07 for the C-Leg and 5.0 ± 0.06 for the Genium. The ADLs were thus assessed to be equally easy to perform, on average, with either joint.
The separate evaluation of the C-Leg or Genium for each individual activity showed a statistically significant reduction (p < 0.05) in the subjectively perceived difficulty in performing five ADLs using the Genium Bionic Prosthetic Knee (Table 1).
In addition to the significant differences in Table 1, there was a trend toward improvement in perceived difficulty with the Genium for three other ADLs: walking on uneven and unfamiliar ground, walking at varying speeds, and carrying heavy objects.
COMPARATIVE SAFETY AND DIFFICULTY IN PERFORMING THE ACTIVITIES USING THE TWO JOINTS
In the direct comparative evaluation of the two joints, the patients indicated that, on average, 20 ± 10 activities were less difficult to perform and 19 ± 11 activities were safer with the Genium (Figure 1).
Only one patient evaluated one activity (walking with different shoes) as less difficult and safer with the C-Leg. Another patient evaluated ascending stairs as less difficult with the C-Leg.
For the analysis of the comparative difficulty and safety of the individual ADLs, the threshold described in the Methodology section for a clinically relevant gain in function of the Genium (group mean value +0.5 or higher) or the C-Leg (group mean value −0.5 or lower) was used. In the group mean, not one of the 45 ADLs was rated by patients to be less difficult or safer with the C-Leg. However, 27 ADLs (60%) were rated to be safer and 24 ADLs (53%) were rated less difficult to perform with the Genium. A group mean of +1.0 or higher (≥50% of the maximum possible evaluation) was reached for 8 activities regarding safety and for 11 activities regarding difficulty. A trend toward an improvement in subjectively perceived safety and difficulty was found for the remaining 18 or 21 ADLs, respectively, without, however, reaching the previously set threshold of an average of at least +0.5 points considered clinically relevant.
The greatest functional gain using the Genium was achieved in the categories Family and Social Life and Mobility and Transportation. In the category Family and Social Life, 10 of the 12 ADLs (83%) were rated safer and 9 of the 12 ADLs (75%) were rated less difficult with the Genium (Figure 2).
In the category Mobility and Transportation, 12 of the 19 ADLs (63%) were rated safer and 11 of the 19 ADLs (58%) were rated less difficult with the Genium (Figure 3).
The functional gain was less clear in the categories Personal Hygiene and Dressing, Sports and Leisure Activities, and Other Activities (Figure 4).
When evaluating the performance of ADLs, the question that always arises is how many or which activities are representative for the requirements of daily life. To ensure that such questionnaires are practical to complete as well as to analyze, it is absolutely necessary to select a manageable number of the theoretically hundreds of possible ADLs. For this study, the questionnaire was limited to 45 ADLs. The average importance of the ADLs that were included was viewed by the patients to be very high. In addition, there was the option of naming other very important activities not included in the questionnaire in a free section. However, the patients hardly used this opportunity, which indicates that the ADLs included represented a good cross-section. Nevertheless, when analyzing the results, it should be kept in mind that the questionnaire used is not a validated instrument.
The extent to which patient surveys can replace objective biomechanical and/or clinical assessment procedures is subject of frequent debate. Objective measurement results are generally considered to be more significant than subjective patient statements. The Clinical Assessment Center for Orthopaedic Aids at the University of Muenster, Germany, has found that patient surveys are better than their reputation and should be considered valuable measuring instruments. As early as 2005, Wetz et al. stated in their study on the indications of the C-Leg, “The results of this (patient) survey closely match the objective biomechanical differences measured.”39 This statement was confirmed once more in another publication in 2010. “It has been shown that in many cases, the survey leads to the same results as the objective clinical biomechanical examination.”40 Of course, an evaluation should ideally be based on a combination of the results of objective measurements and subjective surveys. This approach was also taken in this study; its objective biomechanical results were already published previously.32,33
The separate evaluation of the two knee joints shows a significant improvement with the Genium in the subjectively perceived difficulty of five ADLs that are relevant to safety: ascending and descending stairs and slopes, respectively, and walking backward. This is the result of the new functions available in the Genium, for which clear biomechanical advantages for the amputee can also be proven objectively.32,33 In view of the fact that in a direct comparison more than half of the ADLs were rated safer and less difficult to handle with the Genium, it at first seems surprising that there is a significant difference for only five activities. However, this is due to the effect of the reference point for subjective evaluations. As long as the patients do not know about the benefits of a new technology, the evaluation of the existing prosthesis is clearly more favorable than if they were better informed of technological opportunities. This was apparent in a C-Leg study, for example, in which patients’ satisfaction with their mechanical knee joint was significantly reduced after they had experienced the C-Leg.20 It is thus conceivable that the benefits of the Genium would have been considerably clearer if the patients had been asked to rate the difficulty of performing ADLs with the C-Leg once again after 3 months of using the Genium. A further limitation is due to the scaling of the questionnaires. The possible answers such as “difficult” or “easy” are not objective point measurements but instead cover a more or less wide range of objective values that must be assigned subjectively to the same evaluation category. Changes within an answer category, for example, a reduction in the difficulty of an activity that is still rated “difficult,” cannot be measured using such a scale. An additional difficulty is that the initial level is very significant for a subjective evaluation of a change. If the initial situation is poor, even small objective improvements are subjectively perceived to be much greater than if the initial situation is good. As the optimal situation is approached, greater objective changes are needed to improve the subjective evaluation. Such ceiling effect is also reflected in this study. Because most of the ADLs included in the questionnaire were rated “easy” or “very easy” with the C-Leg, the initial situation was already good to very good. For the five ADLs for which the Genium significantly improved the level of difficulty, the initial situation was clearly poorer for the C-Leg, with ratings of “rather difficult” or “rather easy.”
Changes in the safety and difficulty of activities within the individual response categories were measured by eliciting a direct comparison of the two joints. Specifying the threshold for a clinically relevant difference as a group mean value of at least 25% of the maximum possible difference in evaluation in favor of one of the two knee joints is certainly arbitrary and may give rise to discussion. Mathematically, this threshold could mean that at least half of the patients rate one of the two joints safer or less difficult (or very much safer/less difficult), whereas the rest of the group finds no difference (or rates the other joint only safer/less difficult). Here, it must be considered that any other specification of a threshold for clinical relevance would have been just as arbitrary. The direct comparison of the two joints showed that, on average, patients rated 60% of the ADLs as safer and 53% as less difficult with the Genium Knee. The improvements were especially pronounced in the categories of Family and Social Life and Mobility and Transportation. Family and Social Life is an inseparable part of participation in society. Increasing the safety and reducing the difficulty of these activities are thus a very good basis for further reducing potential limitations of participation. Improvements in the safety and difficulty of activities in the category Mobility and Transportation contribute to enhancing the self-sufficiency and independence of amputees. They create the basis for improving patients’ participation in business and social life outside their own family. Even though the patients’ subjective perception cannot always be explained by objective measurements, it plays a decisive role for the patients’ behavior. It has been scientifically proven that for nonamputees and amputees alike, a reduced subjective sense of balance and safety is correlated with avoidance of ADLs and social participation.34–38 Over time, avoiding activities can lead to a (further) reduction in physical capacity and, in turn, the subjective sense of imbalance and loss of safety. At the end of this vicious circle, the worst-case scenario is the social isolation of the amputee.37,38 That is why the amputee’s perception of safety when walking with the prosthesis should contribute significantly to clinical decision making.
The results found in this and in previously published biomechanical studies32,33 are further proof that a microprocessor design alone is not a sufficient criterion for the assumption of comparable performance of all microprocessor-controlled prosthetic knee joints. This study showed that the new technological functions of the Genium Bionic Prosthetic Knee for transfemoral amputees of MFCL 3 and 4 lead not only to clear biomechanical benefits compared with the C-Leg but also to a further improvement in the subjective perception of safety and perceived difficulty of many ADLs. The greatest improvements were verified for the categories Family and Social Life and Mobility and Transportation. This creates the conditions for further improving patients’ independence and participation in family, business, and social life.
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Keywords:© 2013 by the American Academy of Orthotists and Prosthetists.
microprocessor-controlled knee; activities of daily living; Genium; C-Leg; transfemoral amputees