Regaining the ability to walk after transfemoral amputation is challenging for lower-functioning individuals who often experience various comorbidities and physical deconditioning. The commonly practiced prosthetic fitting in many countries for these individuals with transfemoral amputation involves locked, brake, and polycentric prosthetic knees. Although offering a high degree of stability, locked knees are characterized by very unphysiological gait. Brake and polycentric knees are default swing knees that require several conditions to be fulfilled to provide a safe and stable stance phase.1 Brake knees, for example, require full knee extension and weight loading. In polycentric knees, a user needs to ensure that instantaneous center of rotation is behind the vector of the vertical ground reaction force at full knee extension. Both of these knees may fail to provide stability when those prerequisites are not fulfilled. This might be particularly critical during daily activities that involve walking in confined spaces, shifting of weight and center of mass, stepping in different directions, walking on ramps or uneven terrain, and so on.
Some 20 years ago, microprocessor-controlled knees (MPKs) were introduced on the market. They have been extensively tested and in many countries are accepted as a standard fitting for active persons with amputation (community ambulators, Medicare Functional Classification Level [MFCL]-3). The clinical evidence is accumulating that suggests that such knees also offer advantages to lower-activity individuals with amputation for whom safety is extremely important and oftentimes is a limiting factor in their reintegration into normal life. Several studies investigated the effect of MPKs in limited community ambulators (MFCL-2) and suggest that they significantly improve subjects' safety in comparison to non-MPKs (NMPKs). For example, when transitioning from mechanical knees to C-Leg, limited community ambulators reported an 81% decrease in falling.2,3 Similarly, the number of uncontrolled falls decreased by 80%.4 The performance-based tests that correlate to risk of falling also report improvement in safety. For example, the time required to complete the timed up and go (TUG) test decreased with the transition from NMPKs to C-Leg by 38% from 17.7 to 24.5 seconds.5 Furthermore, significant improvements in balance confidence are reported as measured by the Activities-specific Balance Confidence Scale (ABC).5 Microprocessor-controlled knees were also investigated in terms of their effect on the functional mobility of persons with amputation. Significant improvements in self-selected comfortable and fast speeds during level walking are reported,2 partially resulting from an increase in stride length and cadence.6 Significant improvements during stair descent were observed as measured by the Stair Assessment Index (173% score improvement) and the Montreal Rehabilitation Performance Profile (67% score improvement). Speed, as well as quality of ramp ascent and descent, was significantly improved.3,5 Around 50% of subjects belonging to mobility grade MFCL-2 with mechanical knee transitioned to MFCL-3 with MPKs.2,3,7 Functional benefits as perceived safety, reduction of effort, gait pattern harmonization, and walking with varying gait speed could be used in similar proportion between MFCL-2 and MFCL-3.7 Health-related quality of life that assesses life with the prosthesis was also significantly improved as measured by the Prosthetic Evaluation Questionnaire (PEQ).2,3,5,8 In particular, improvements in PEQ subscores dealing with mobility, satisfaction with walking, residual limb health, utility, and ambulation are among the most affected. In a systematic review, it could be shown that many outcomes favored the use of MPKs in MFCL-2, whereas no outcome favored the NMPK in this population.1 Finally, the studies investigating prosthetic preference suggest that MFCL-2 subjects overwhelmingly prefer the C-Leg over mechanical knees.2,9
Kenevo is a new MPK designed specifically for the activities and challenges of lower-activity persons with amputation. It offers specifically designed new functions to support the unique needs of this population: supported sitting down and standing up functions, standing function, safety functions (including stumble recovery), and wheelchair function. The knee adapts to individual mobility capabilities by offering programmable stance and swing release control. Three activity modes allow adaptation to the individual needs of persons with amputation that may change during the rehabilitation process over time. In the locked mode (mode A), the knee joint is locked and it stays locked during the swing phase. In such a configuration, the knee offers maximum safety; however, the gait is far from physiological. Such mode is recommended for persons with amputation having little control over their residual limb and that are more inactive, ambulating mostly short distances indoors. Mode B refers to semilocked knee with stance phase flexion. It allows up to 10° of flexion in stance phase at heel strike and is therefore beneficial when traversing slopes. Mode C is also called yielding mode because the stance phase is not locked but has a high attenuation. It supports walking on level ground, slopes, and stairs. More dynamic movement is furthermore supported by earlier initiation of the swing phase.
The objective of this research was to collect and analyze first clinical experiences with Kenevo. Patient-reported measures were conducted to assess patient safety, mobility on level walking, stairs and ramps and preference. In addition, feedback from certified prosthetists/orthotists (CPOs) was collected regarding fitting process, acclimation, and patient benefits.
A prospective observational study was conducted to collect first clinical experiences with Kenevo. It was planned to fit 30 subjects with Kenevo knees in five countries. The following inclusion criteria were used when selecting the patients: subjects with knee disarticulation or transfemoral amputation; subjects using a mechanical knee joint; mobility grades MFCL-1, MFCL-2, and low MFCL-3; maximum bodyweight of 125 kg; and no significant comorbidities that would prevent participation and pose increased risk (e.g., unstable cardiovascular conditions that preclude physical activity such as walking). All the subjects consented in writing before their inclusion. Data collection, extraction, and analysis were in full compliance with Declaration of Helsinki and all applicable national legislations.
Subjects' data were collected first with their old prosthesis. User demographic data were collected as well as data on current prosthetic fitting. A questionnaire was designed and given to each subject to obtain information on user's daily prosthetic utilization (“baseline subject questionnaire”). In particular, the questions addressed topics such as pain, satisfaction with current prosthetic fitting, stumbles, and falls. Once the subjects completed the baseline measurements, they were fitted with the Kenevo. All the prosthetic components were kept the same; only the knee was changed. After initial device fitting, prosthetists were instructed to record needed visits to obtain satisfactory prosthetic alignment and parameter setting. A questionnaire designed for prosthetists was administered to collect information on fitting process and to obtain prosthetists' impression of the new knee (baseline CPO questionnaire). Two months after fitting the Kenevo, subjects returned for follow-up testing. Questionnaires were provided to support data collection and to retrieve feedback from certified prosthetists as well as the subjects (follow-up subject questionnaire and follow-up CPO questionnaire). In addition to asking about pain, satisfaction with the new prosthetic fitting, stumbles, and falls, there were also questions comparing the subjects' perception of Kenevo to their previously worn prosthesis in terms of activities of daily living, walking on level ground and with different speeds, walking on ramps and stairs, and others. Finally, subject preference was assessed by asking the question, “If you could choose one prosthesis, which one would it be?”
In addition to the questionnaires, validated clinical tests were performed during baseline and follow-up testing. The selected patient-reported outcome measures are recommended for use in clinical and research settings and included Locomotor Capabilities Index 5 (LCI-5), Prosthetic Limb Users Survey of Mobility (Plus-M), and Houghton scale.10,11 The LCI-5 computes the global, basic, and advanced locomotor skills of the individual with lower-limb amputation with the prosthesis and assesses level of independence.12 Two subscales emerge from this general construct: basic (seven items) and advanced (seven items) locomotor capabilities with the prosthesis. The LCI-5 was used to evaluate the ambulatory skills with the prosthesis of persons with lower-limb amputations. The LCI tests the ability to perform a number of motor tasks. It provides an aggregated score for 14 items. The maximum total score of the index was 56. Plus-M assesses prosthetic users' ability and difficulty in carrying out activities that relate to locomotion and/or postural transition.13 Finally, the Houghton scale measures the function of persons with lower-limb amputations fitted with a prosthesis by measuring time spent wearing the prosthesis and its functional use.14 It consists of four items: amount of time the prosthesis is used, manner in which it is used, individual's perception of stability, and whether walking aids are used while walking outside on a variety of terrains. Each item is scored on a 4-point ordinal scale, and the perception of stability questions is binary yes/no answers. The maximum score is 12.
After completion of the study, the collected data were returned for analysis. Descriptive statistics were calculated whenever possible. Since comparison between two knees was dependent, paired t tests were used when data were normally distributed and at the interval or ratio scale level. Otherwise, the nonparametric Wilcoxon signed rank test was used for differences in medians. In the case of the questions that directly compared the two knees, that is, “(much) better with Kenevo” and “(much) better with previous knee,” only descriptive statistics were possible, and therefore, only percentages are reported. Finally, correlation analysis was performed in SPSS (Spearman ρ). Various parameters (i.e., age, time since amputation, and previous knee) that could influence selected Kenevo mode as well as the benefit as measures in terms of outcome measures (Houghton, LCI-5, and PLUS-M) were analyzed.
Data taken during first routine fittings with Kenevo between February and May 2015 were analyzed. The fittings took place at selected prosthetic centers in Germany (5), Canada (3), Sweden (1), Benelux (4), and Austria (1). Twenty-nine persons with amputation were fitted with Kenevo. Owing to the observational nature of the study, no monitoring of data collection and strict way to ensure data completeness was in place. Therefore, completeness of data collected at different centers varied. For example, “baseline subject questionnaire” and “baseline CPO questionnaire” were collected for 66% and 59% subjects, respectively. Respective follow-up questionnaires for subjects and CPOs were collected for 69% and 55% subjects, respectively. Outcome measures were also not collected for all subjects. Although there were cases where the test was conducted for a subject only at baseline or only at follow-up, analysis was performed only for subjects where data for both visits was available.
Subjects were mostly individuals with unilateral transfemoral amputations belonging to the MFCL-2 ambulatory category (Table 1). Before receiving Kenevo, they were using different prosthetic knees, including polycentric knees, brake knees, locked knees, and, although not according to inclusion criteria, mechatronic knees. They were, on average, 63.2 years old and 62% were male. They lost their limb 6.3 years ago, on average, and the cause was in most cases vascular disease (46%) and infection (38%).
FITTING AND ACCLIMATIZATION
Satisfying alignment and Kenevo parameter settings were achieved for 40% of subjects during the first visit, for 13% during the second visit, for 33% during the third visit, and for 13% during the fourth visit with the prosthetist. Participating prosthetists were instructed on different modes that the knee can offer. Together with the person with amputation, they made the decision regarding the most appropriate mode. Mode A was recommended for individuals with reduced residual limb control (i.e., unable to control knee flexion during swing phase) who ambulate very short distances and practice a mainly sitting lifestyle. Mode B was recommended for those subjects having medium residual limb control who walk short indoor and outdoor distances and are able to control knee flexion during swing. Mode B was often preferred by polycentric knee users who feel unsafe on those knees. Finally, mode C was for persons with amputation who perform more challenging activities of daily living, are relatively active, and are able to control a yielding knee joint during walking. Activity mode B (locked stance phase and free swing phase) was chosen for 10 subjects (67%). For four subjects (27%), the CPO set the Kenevo to mode C (yielding mode), and in one case (7%), to mode A (locked knee). Correlation analysis was performed to determine whether patient characteristics (age and time since amputation), previous knee, or score on baseline outcome measures correlate with the Kenevo mode that subjects received. The Kenevo mode that the subjects received strongly correlated to the baseline scores on Houghton scale (r2 = 0.700, p = 0.008) and moderately to the LCI-5 Basic (r2 = 0.544, p = 0.055). In other words, the higher the score at the baseline, the higher was the probability that the subject received more advanced Kenevo mode.
The acclimatization time was reported for 19 subjects and lasted, on average, 7.8 days (range, 1–60 years). A total of 42% needed 1 day, 37% needed between 2 and 7 days, and the remaining 21% more than 7 days.
Stumbling and falling was evaluated by asking subjects, “How often do you stumble or fall with your current prosthesis?” The possible answers included the following: “never,” “less than once per month,” “1–3 times per month,” “1–3 times per week,” and “daily.” Although overall difference was not significant (p = 0.161), the number of subjects who reported never falling increased from 45% with their old prosthesis to 72% with Kenevo (Figure 1). In the case of stumbling, subject-reported frequency of stumbles was significantly reduced when transitioning to Kenevo (p = 0.044), with 50% of subjects reporting of never stumbling with Kenevo compared with 8% with their previous prosthesis. In particular, the subjects reported improvements in the following situations: toe clearance in swing phase, perceived safety during walking, stability during walking, perceived safety during standing, standing stability, and rising from a chair (Figure 2).
Fear of falling was assessed on a 10-point scale (1, not afraid, to 10, extremely afraid). The mean (SD) score obtained from 12 subjects was reduced from 3.5 (2.78) with the previous prosthetic knee to 2.2 (1.99) with Kenevo (p = 0.075). A total of 50% of the subjects reported an improvement in fear of falling, whereas 8% (1/12) reported a worsening.
MOBILITY AND ACTIVITIES OF DAILY LIVING
Mobility was assessed by asking the individuals with amputation to compare the two knees during walking on even and uneven ground, ramps, and stairs. From 19 subjects who evaluated walking on level ground, 15 subjects (79%) found Kenevo as being better or much better, 2 (11%) equal, and 1 (5%) worse than their previous prosthetic knee. This was especially true for slow and medium walking speeds, where Kenevo was ranked as better or much better by 74%, and, to a smaller extent, during fast walking speed, where this number was 59% (Figure 3).
Walking on uneven ground improved for 64% of the subjects with Kenevo (Figure 4). Sixteen subjects provided feedback on stair ambulation. Stair ascent was perceived by 63% as being not affected by Kenevo and by 37% as improved. Stair descent was ranked by more than half of the subjects as being improved with Kenevo. Similar feedback was also obtained from the 19 subjects when asked about ramp ambulation. Thirteen reported improved ramp descent and 10 reported improved ramp ascent with Kenevo. The Kenevo knee's new standing function, which provides increased flexion damping during standing, was found to be beneficial by 69% of the subjects.
The subjects were additionally asked to complete two validated questionnaires: LCI-5 and PLUS-M (Table 2). Both of them showed a positive trend when transitioning to Kenevo; however, this was not statistically significant. Amount of benefit in those two scales was not correlated to the subjects' age, time since amputation, previous knee, frequency of falling/stumbling, nor fear of falling.
PERCEIVED CONCENTRATION AND EXERTION
Kenevo was also compared with the previous prosthesis in terms of concentration and exertion during walking (n = 19). The necessary concentration during walking was ranked as “much less or less with Kenevo” by 79%, as “not different” by 11%, and as “more or much more with Kenevo” by 10%. Exertion during walking was ranked as “much less or less with Kenevo” by 84% of the subjects, as “not different” by 11%, and as “more or much more with Kenevo” by 5%.
PAIN AND COMFORT
Pain, comfort, and perceived loading were assessed by asking subjects to directly compare the Kenevo with their previous knees. No differences in pain were found between Kenevo and their previous prosthesis (sound limb, residual limb, and back). However, when asked about their perceived loading of the sound side, 47% (7/15) felt a distinct reduction in load and another 27% (4/15) felt a little load reduction on the sound side. Comfort was also assessed. Walking comfort, standing comfort, and sitting comfort were ranked as improved by 66%, 69%, and 42% of subjects, respectively.
PROSTHETIC USE, SATISFACTION, AND PREFERENCE
The use of Kenevo did not result in change of walking aids that subjects use for ambulation. Wheelchair use, however, was significantly reduced when transitioning to Kenevo. Whereas 87% of subjects reported using a wheelchair with their previous prosthesis, this number decreased to 37% with Kenevo (p = 0.0046). Complete data set for the Houghton scale was available for 11 subjects. Six subjects improved their score after receiving Kenevo, one subject had no change, and for two subjects, there was decrease in Houghton score. On average, the score increased from 7.0 to 8.0 after receiving Kenevo (p = 0.068). A correlation analysis revealed that the improvement in Houghton scale did not correlate to the subjects' age, time since amputation, previous knee, frequency of falling and stumbling, nor fear of falling. Satisfaction with the prosthesis was assessed by asking subjects to select the term that best describes their situation: “very satisfied,” “satisfied,” “neutral,” “unsatisfied,” and “very unsatisfied.” There was a trend of higher satisfaction with Kenevo, but it was not significant (p = 0.187). Of 19 subjects, 17 reported being “very satisfied” or “satisfied” with Kenevo. Finally, 89% of the persons with amputation fitted with Kenevo prefer Kenevo over their previous fitting. One subject who was previously fitted with a mechatronic knee and one with a locked knee preferred their previous fitting (Figure 5).
Lower-activity individuals with transfemoral amputation represent a difficult population to fit with a prosthesis. This population often experience various comorbidities, which further become worse with age, such as diabetes (type I and II), peripheral arterial disease, cardiac conditions, renal failure, stroke, arthritis, and others. A recent study suggests that a high number of comorbidities are significantly predictive of prosthetic nonuse.15 Selection of a prosthetic knee after transfemoral amputation is one of the key steps in achieving satisfactory prosthetic use. While restoring knee biomechanics, the knee needs to provide maximum stability and safety for the users.16–19 Standard prosthetic knees used in this population are various types of locked, brake, and polycentric knees. Although several studies demonstrated that MPKs are beneficial for lower-activity persons with transfemoral amputation, their use is still not widely practiced.
The first clinical experiences collected during this observational study suggest that a new MPK could offer several advantages to lower-activity individuals with amputation, particularly in the area of safety, functional mobility, preference, and satisfaction. Stumbling and wheelchair use reached statistical significance. Positive trends were also observed in fear of falling (p = 0.075), Houghton scale (p = 0.068), and LCI-5 (p = 0.097). Safety is the most important prerequisite of successful prosthetic ambulation. Falling and its detrimental consequences pose serious clinical challenges for persons with amputation, especially elderly, lower-functioning individuals. Recurrent falls and fear of falling are associated with activity avoidance and decreased independence and mobility.20–24 The current results as well as published literature show that falling is very common in this patient population.2,3 Although not reaching statistical significance (p = 0.161), the number of subjects reporting “never falling” increased by 79% when they transitioned from mechanical knees to Kenevo. Similar results were also reported in the studies conducted on people MPKs (C-Leg and C-Leg Compact) in lower-activity persons with amputation. In addition to reduction of self-reported number of falls by approximately 80%,2,3 improved safety was also measured by means of validated clinical instruments. For example, a significant reduction in the TUG test was reported when transitioning from mechanical knees to MPK with stance control (C-Leg Compact) and was highly clinically relevant.25 Furthermore, the same study reported significant improvements in balance confidence when performing various activities (ABC).
The self-reported impact of Kenevo on functional mobility and activities of daily living was also assessed by asking subjects to directly compare the knees, in which case descriptive statistics were appropriate. Approximately three-fourths of users reported improvements during level walking. Whereas more than half reported no change when ascending stairs with Kenevo, more than half reported improvement during stair descent. This result is not surprising because stair ascend with Kenevo enables a step-to manner similarly to NMPKs, whereas during stair descent, Kenevo allows step-over-step, which is not possible with locked knees and safer than with polycentric and brake knees. Similar observations have been also reported in published literature investigating the effect of MPKs on stair ambulation.2,3 In particular, in a study comparing mechanical knees with C-Leg, the authors reported a 173% increase in the Stair Assessment Index during stair descent.3 In a different study, transitioning to MPKs resulted in an increase in Montreal Rehabilitation Performance Profile Composite Score for stair descent.2
Ramp ambulation was also perceived by subjects as improved, especially descent and standing on ramps. Similar function supporting standing on ramps is implemented in Genium MPK, which has been the subject of several studies in more active individuals with amputation.26 The particular functionality resulted in significantly more loading and significantly less postural sway on prosthetic side in comparison with measurements done with a knee not offering similar functionality. The literature reports of improvement in ramp descent with MPKs of 39% as measured by the Hill Assessment Index.3 Increase in walking velocity on ramps and improved gait symmetry when lower-activity individuals with transfemoral amputation transitioned from mechanical knees to MPKs have also been reported.5 Similar to the patient-reported improvement when walking on uneven ground are the results of published studies. Kahle et al.2 reported 20% in fastest walking speed during 38 m of uneven terrain with MPKs, whereas Hafner et al.3 measured an 11% increase in walking speed when performing an obstacle course consisting of grass, wooden chips, sand, a cement ramp and a cement stairs.
Increased comfort with Kenevo was reported, as well as perceived reduction in loading of the sound side. Studies investigating the effect of the C-Leg on lower-activity persons with amputation reported improvement of around 20% in the PEQ score and especially in the subscales of residual limb health and utility, which, among others, also includes questions about comfort, fit, and feel.3,5,8 Although Kenevo resulted in a reduction in perceived concentration and exertion during walking, Hafner et al.3 suggest that MPKs reduce cognitive demand as measured by tests involving multitasking or tasks requiring attention demand in lower-activity individuals with amputation.
The use of Kenevo did not affect walking aids use but did result in significant reduction of wheelchair use. The Houghton scale, which measures function of people with lower-limb amputation fitted with a prosthesis in terms of prosthesis wear and use, improved with Kenevo; however, this was not significant. Burnfield et al.5 reported improvements with C-Leg in a similar population group. Satisfaction and preference were high with Kenevo. A total of 89% of the subjects preferred Kenevo over their previous prosthesis, similar to the values reported in several studies with a similar population, in which 90% or more preferred C-Leg/C-Leg Compact over mechanical knees.2,9
One of the limitations of this study is its observational nature and the inherent fact that many biases cannot be minimized as in the case of studies involving for example control group, randomization, blinding, and others. Therefore, higher-quality research is needed to confirm the conclusions reached in this study. The collected data in the study were, in many cases, not complete, and therefore, it could be possible that there is a bias in the response. While in most of the cases, the low response rate might be due to insufficient time that prosthetists and subjects had to complete the questionnaires, it cannot be eliminated that reasons for it might be related to the knee. However, no adverse experiences with the knee were reported during the study. Furthermore, four subjects entering this study were users of mechatronic knees, and this comparison to Kenevo is not a focus of this research. Because of small sample size, subgroup analysis excluding these users was performed, but it did not significantly affect the results and therefore is not reported here. Finally, whether patient-reported surveys can replace more objective clinical tests or biomechanical analysis is still debated in the community. Performance-based measurements are generally considered to be more reliable 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. In the ideal case, research should be conducted containing both performance-based and patient-reported outcome measures, which then would provide a more complete picture. In the current study, no performance-based measures were conducted; however, the results are in agreement with higher-quality research including performance-based measures investigating the effect of MPKs on lower-activity individuals with transfemoral amputation.1–8,27
High patient satisfaction with Kenevo was observed in lower-activity individuals with transfemoral amputation. New knee functionalities designed specifically to target the safety challenges of this population seem to be effective and beneficial. The first clinical experiences collected during this observational study suggest that Kenevo offers several advantages to lower-activity people with amputation, particularly in the areas of safety, functional mobility, preference, and satisfaction. These observations are in agreement with published evidence on effects of MPKs in limited community ambulators.1–8,27 Higher-quality research is needed to confirm the conclusions reached in this observational study.
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