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Patient Evaluation of a Novel Prosthetic Foot with Hydraulic Ankle Aimed at Persons with Amputation with Lower Activity Levels

Moore, Raymond BScPros/Orth

Journal of Prosthetics and Orthotics: January 2017 - Volume 29 - Issue 1 - p 44–47
doi: 10.1097/JPO.0000000000000120
Case Reports

Introduction Since their release, prosthetic feet with integrated hydraulic ankle units have proved a popular prescription choice among individuals with amputation, as quantified in previous studies. Since the release of the Avalon foot, a new design specifically aimed at less active individuals with amputation, all the patients prescribed this foot within our clinic have been asked to trial and then evaluate it using the Seattle Prosthesis Evaluation Questionnaire.

Materials and Methods Fourteen established K2 activity level patients with amputation were asked to evaluate their existing prosthetic foot using the Seattle Prosthesis Evaluation Questionnaire before beginning a trial of the new Avalon foot for a period of 4 weeks. The Avalon foot was then evaluated using the same tool after this trial.

Results The results showed the patients recorded an improvement in all the domains evaluated. There were significant improvements noted in both the overall prosthetic satisfaction and in the patients' overall gait satisfaction.

Conclusions The results showed a marked improvement in the patients' perception of their prosthesis when using the Avalon foot, and further studies including gait analysis are warranted to help in our understanding of this.

RAYMOND MOORE, BSc, Pros/Orth, is affiliated with the Prosthetics Department, Luton and Dunstable, Bedfordshire, United Kingdom.

Disclosure: The author declares no conflict of interest.

Correspondence to: Raymond Moore, BSc, Pros/Orth, Prosthetics Department, Luton and Dunstable, Lewsey Rd, Luton, Bedfordshire, United Kingdom LU40EP; email:

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Since the launch of the Echelon foot from Blatchford, many patients have trialed prosthetic feet with integrated mechanical hydraulic ankle units. The inclusion of a hydraulic ankle has been proved to allow users more control when walking up and down inclined surfaces1,2 as the hydraulic ankle unit adapts to match these. It has also been shown to help descend and ascend stairs3 and reduce the likelihood of falling by aiding toe clearance in swing phase,4 with users reporting significant improvements in many facets of prosthetic use.5 This new category of prosthetic components also provided biomechanical advantages such as smoother center of pressure transition and reduced interface pressures.2,6,7 Other manufacturers have adopted this idea and brought to market variations including designs with built-in shock modules or a greater planterflexion range, but one similarity in all the units is that they are specifically designed and marketed for persons with amputation in the K3 activity class.

Amputation K levels8–10 are a commonly used activity scale ranging from 0 to 4, where the levels are defined based on an individual's potential functional ability. These are derived from the grading scale used by the United States national social insurance program Medicare and are as follows:

  • K0. Does not have the ability or potential to ambulate or transfer safely with or without assistance and a prosthesis does not enhance their quality of life or mobility
  • K1. Ability or potential to use a prosthesis for transfers or ambulation on level surfaces at fixed cadence
  • K2. Ability or potential for ambulation with the ability to traverse low-level environmental barriers such as curbs, stairs, or uneven surfaces
  • K3. Community ambulator who has the ability to traverse most environmental barriers and may have vocational, therapeutic, or exercise activity that demands prosthetic utilization beyond simple locomotion and has ability or potential for ambulation with variable cadence
  • K4. Ability or potential for prosthetic ambulation that exceeds basic ambulation skills, exhibiting high impact, stress, or energy levels typical of the prosthetic demands of the child, active adult, or athlete

With the advent of the Avalon foot,11 the hydraulic ankle concept now has a foot specifically tailored to persons with amputation at the K2 activity level; however, there were concerns that patients with lower activity levels may not feel the same benefits that have already been shown by K3 patient's trialing feet with hydraulic ankle units as demonstrated by Sedki and Moore.4 This is because of the functional difference and the comorbidities such as decreased muscle strength or impaired balance and compromised vascularity or increased likelihood of degenerative bone and joint disease in individuals with K2 amputation. To test this hypothesis, we have used the Seattle Prosthesis Evaluation Questionnaire on a sample group of K2 patients prescribed with this foot module.

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Fourteen patients, 12 men and 2 women, aged between 38 and 84 years, were prescribed Avalon feet by the prosthetics department's multidisciplinary team composed of rehabilitation consultant, prosthetist, physiotherapist, psychologist, and occupational therapist. The breakdown by amputation level of these patients was 11 unilateral transtibial patients, 1 bilateral transtibial patient, and 2 transfemoral patients. The breakdown by amputation cause was 10 dysvascular amputations (6 of which were diabetic), 2 traumatic, and 2 caused by chronic infection. The decision to provide the Avalon feet was based on clinical need and level of mobility. The criteria for suitability for prescription were discussed at a meeting of the multidisciplinary team and were decided as follows:

  • An activity level of K2 (10)
  • SIGAM (Special Interest Group in Amputee Medicine) mobility grade of D/b (able to walk 50 m or more on level ground in good weather with one stick/crutch) or higher12,13
  • Individuals with unilateral amputations who have musculoskeletal problems in the contralateral limb (e.g., arthrodesis)
  • Bilateral patients with difficulty traversing inclines and gradients
  • No current prosthetic socket fitting problems
  • No other component changes required
  • Body weight under 150 kg (10)

Before any changes, patients were asked to evaluate their current prosthesis using the validated Seattle Prosthesis Evaluation Questionnaire.14–17 All 14 patients' previous foot/ankle prescription was the Multiflex foot by Endolite. This meant that the patients were already used to walking on a foot with rubber foot shell with foam cosmetic cover and a three-quarter-length keel unit, the only difference/change being the hydraulic ankle mechanism and a subsequent increase in weight. The patients' prescription would then be changed and replaced with the Avalon foot (or feet). With the exception of reestablishing prosthetic height, no other alterations were carried out on the limb build to isolate the effect. The patients would then be supplied with the prosthesis and asked to trial it with the new foot for a period of 4 weeks. An appointment was made at the center at the end of this trial at which the patient would reevaluate his/her prosthesis, again using the Prosthesis Evaluation Questionnaire. Both questionnaires would then be analyzed for their results. Informed consent was received from all patients involved.

The Prosthesis Evaluation Questionnaire is a validated self-report questionnaire containing 54 questions organized into nine functional domain scales where the patient indicates a score ranging from 0% to 100%. Each of the scales may be used individually to measure only a specific domain of interest. We analyzed data in relation to the following six domains. Ambulation: A total of eight questions regarding general walking, close spaces, up stairs, down stairs, up steep hills, down steep hills, sidewalks and streets, and slippery surfaces. Transferring: A further five questions regarding the ease of transferring while using the prosthesis in different situations. Prosthetic utility: Eight questions related to socket fit, weight, comfort while standing, and comfort while sitting, balance, energy, feel of the surface, donning. General well-being: Two questions about quality of life. Prosthetic satisfaction: One general question about how satisfied they have been with their prosthesis. Then lastly, gait satisfaction: One general question about how satisfied they have been with walking. The other three domains were not included as these had less of a direct bearing on the foot evaluation.

It was felt unnecessary to add any form of activity monitor to the prosthesis as previous studies had shown no significant increase or decrease in activity when changing a patient to a foot with a hydraulic ankle unit.18 Local ethics approval was sought, but as study classified as a service evaluation, the approval was not required.

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The results from the Prosthesis Evaluation Questionnaire showed that patient satisfaction was higher with the Avalon foot in all six domain categories when compared to patients' previous feet without the hydraulic ankle. Across all amputation levels and all six of the category domains, this averaged out at a considerable 14.7% (p = 0.0003) improvement (see Figure 1). When broken down and compared by amputation level, the transtibial patients experienced a more significant improvement across all the domains, with the six domains averaging out at a 15.6% (p = 0.0004) improvement (see Figure 2). There was still an overall improvement reported for the transfemoral patients, but this was reduced to almost a third at 6.2% (p = 0.009) (see Figure 3). When the evaluation questionnaire is broken down further and each of the domains is looked at within all the amputation levels, then the amount of improvement shows a marked variance. For instance there was a marginal drop of 0.7% in “well-being” with the transfemoral amputation participants compared with a 23.4% improvement in “prosthetic satisfaction” for transtibial amputation participants.

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

When the results are assessed together for the all participants as a collective whole, then all the categories showed an improvement. The domain showing the smallest level of improvement was “well-being,” with an increase of 7.2% (p = 0.08). This was followed by “transferring” and “utility,” which registered increases of 12.5% (p = 0.02) and 12.3% (p = 0.005), respectively. The domains where patients indicated the largest average improvement were “ambulation satisfaction,” showing a 17.3% (p = 0.005) improvement; “prosthetic satisfaction,” showing a 17.2% (p = 0.0003) improvement; and “gait satisfaction,” with a 21.9% (p = 0.0007) increase.

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The results shown are taken from a limited sample group and indicate the patient's subjective view of the foot after only a 4-week trial period; however, they do demonstrate a marked preference toward the hydraulic ankle unit (Avalon foot). In the specific domains of “utility” and “well-being,” there was only a marginal improvement expressed by patients; however, all patients reported a significant improvement in relation to “transferring,” “ambulation,” and “gait” domains, as well as the patients' overall impression of the prosthesis. This echoed the previous studies by Sedki/Moore5 and McDougall/Wood18 looking into satisfaction rate for higher activity (K3) patients using the Echelon foot.

The only marked deviation from these results in these previous studies is that the satisfaction levels for the patients with transfemoral amputations declined slightly with the Avalon, dropping by a third from the satisfaction studies with K3 patients using hydraulic ankle units. One possible explanation for this is that with the higher amputation levels, the added distal weight did begin to have an increased effect on function of the prosthesis and the patient's energy consumption and that this was expressed in an only marginally increased score. Although it has to be noted there were only two participants with transfemoral amputation in the study, it will be interesting to compare these results and see if they continue when the study is repeated with a larger cohort. Similarly, as only one of the patients in the trial had bilateral amputations, more work will have to be done before the effects can be evaluated for this particular patient group.

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All the patients taking part in this study reported a statistically significant improvement in their ambulation/gait and an increase in overall satisfaction with their prosthesis/prostheses when their prosthetic prescription was changed to include the Avalon foot with its hydraulic ankle unit. However, the author does acknowledge the limitations of this study in that the sample group was small and the results were based purely on feedback gathered after a month's trial. It is hoped that through further examination with the aid of detailed gait analysis, we will be able to fully explain the mechanism and biomechanics that lead to the improvement in satisfaction levels from the patients using hydraulic ankles units. This will be important to justify the extra funding and cost involved in the use of these devices.

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hydraulic ankle; prosthetics; Avalon foot

© 2017 by the American Academy of Orthotists and Prosthetists.