Practical Benefits of Flex-Foot(TM) in
Below-Knee Amputees
H. Alaranta, M.D.
A. Kinnunen, C.P.O.
M. Karkkainen, M.Sc.(Eng.)
T. Pohjolainen, M.D.
M. Heliovaara, Research Officer
Abstract
The Flex-Foot? (FF) prosthesis has been
used in the Prosthetic Foundation's workshop since 1987. Subjective feedback from
the first 32 below-knee (BK) amputees fitted
with the FF was analyzed. Ratings were generally favorable in comparison with those for
the conventional prosthesis with solid ankle
cushion heel (SACH) foot and patellar-tendon-bearing (PTB) socket. The most pronounced advantages of the new prosthesis as
shown by the ratings were in walking upstairs
or uphill. However, the FF does not seem to
provide any major advantage for the less active amputee whose movements are mainly
indoors.
Introduction
Most BK amputees can achieve an efficient gait within the limits of their disability.
For optimum gait efficiency it is imperative
that prostheses keep energy expenditure to a
minimum. During recent years many energy-storing feet have been developed (1). It
has been reported that for BK amputees,
ambulation with the FF conserves energy at
higher walking velocities, resulting in lower
relative levels of exercise intensity and enhanced gait efficiency (2). Wagner's biomechanical analysis showed improvements in
range of ankle motion and gait symmetry for
the FF as compared with the SACH foot (3).
Although the FF has many advantages, some
disadvantages have also been reported, including high cost and complexity in fabrication and alignment; moreover, the FF has
not been suitable for very long residual limbs
(1). During recent years, dynamic alignment
options-a Symes configuration and a "split
toe" option allowing pronation-supination-have been developed (4).
Beyond purely mechanical data, there has
been no analysis of the subjective benefits of
the FF in comparison with a conventional
prosthesis (CP). The purpose of this study
was to evaluate subjective advantages for
walking of the FF and the CP - the SACH
foot with PTB socket.
Method
Since 1987, the workshop of the Prosthetic
Foundation has fitted BK prostheses using
the modular FF system. Our selection criterion for the FF prosthesis was that the patient should have at least moderate physical
activity using the CP. The progress of the
first 32 BK amputees fitted with the FF prostheses was followed for at least three months
and was then analyzed by means of a structured questionnaire and a personal interview. One amputee did not accept the invitation to take part in the study. The final study
comprised 31 amputees: one woman and 30
men. A total of 28 patients had undergone
traumatic amputation, while three patients
had some other cause of amputation (diabetes, congenital amputation or malignoma).
Three patients had undergone bilateral BK
amputation. The age range was 16 to 75
years, the mean age being 39.0 (+/-16.2
years). All the patients had previously used
conventional PTB prostheses for a period of
eight months to 42 years. The follow-up period for the FF prostheses varied from three to
16 months.
In the questionnaire, the subjects were
asked to classify their walking disability as
0 - like normal walking, no problems
1 - only mild disability
2 - moderate disability
3 - severe disability
The assessment also included 10 different
items concerning the amputees' current FF
and their previous prosthesis.
The chi-square statistics for heterogeneity
were calculated to test whether the distributions of subjective ratings for walking disability differed between FF and CP, and the
chi-square test for trend was used to test the
gradient of disability according to the type of
prosthesis (5). The results of these tests were
expressed as exact p-values. Since there
were few or no extreme ratings of items for
walking disability, the categories 0 and 1 of
the item "running" and the categories 2 and
3 of the other items were combined to calculate the test statistics.
Results
A comparison was made between the use
of the FF and that of the CP on the basis of
subjective ratings for all 10 items of movement (Table 1)
. The BK amputees gave the
FF higher ratings (represented by a systematic shift to lower points) in all 10 items. This
finding was independent of age. The differences were greatest in respect to walking upstairs and walking uphill in the street. Two of
the three bilateral amputees reported that
(with FF) walking upstairs and walking uphill in the street presented no problems
(highest ratings). In the whole study group
the difference between the prostheses for indoor walking was less pronounced and did
not reach statistical significance.
Up to now all the patients but one have
been generally pleased with the new prosthesis and have expressed their satisfaction at
the flexibility and elasticity of the FF. A total
of 11 amputees have reported as a disadvantage that the physical appearance of the
prosthesis is rather clumsy and that there are
difficulties in walking indoors without shoes.
Discussion
The FF prosthesis may provide beneficial
effects in walking for most BK amputees.
However, since there was no control group
in our series and a "placebo effect" remains
possible, our results should be interpreted
with caution. According to our subjective
experience, moderately active persons benefit from an energy storage prosthetic foot
system. If an amputee walks uphill out of
doors or upstairs indoors, the FF seems to be
particularly beneficial. However, for the amputee who is less active and who walks mainly indoors, the FF is less likely to provide as
much advantage.
The increased flexibility of the FF may
help to avoid skin abrasions of the stump.
However, its increased energy storage and
release mechanism may in some cases aggravate skin problems as a result of more vigorous lower limb motions. For this reason,
non-vigorous walking is recommended at the
beginning of training.
The cost of the FF is double that of the CP
(6). This limits its general use and makes it
desirable to develop criteria for selecting patients who will be fitted with the FF. El
Hannu Alaranta, M.D.is a physiatrist at the Prosthetic Foundation, Tenholantie 12, SF 00280 Helsinki, Finland,
and the Rehabilitation Unit of the Invalid Foundation.
A. Kinnunen, C.P.O., is with the Prosthetic Foundation,
Tenholantie 12, SF 00280 Helsinki, Finland. M.
Heliovaara, research officer, is with the Social
Insurance Institution.
M. Kairkkainen,
M.Sc.(Eng.), is with the Prosthetic Foundation,
Tenholantie 12, SF 00280 Helsinki, Finland. M.
Heliovaara, research officer, is with the Social
Insurance Institution.
T. Pobjolainen,
M.D., is a physiatrist at the Prosthetic Foundation, Tenholantie 12, SF 00280 Helsinki, Finland,
and the Rehabilitation Unit of the Invalid Foundation.
References:
- Michael J. Energy-storing feet: a clinical
comparison. Clinical Prosthetics and Orthotics
1987;11:154-68.
- Nielsen DH, Shurr DG, Golden JC, Meier
K. Comparison of energy cost and gait efficiency
during ambulation in below-knee amputees using
different prosthetic feet: a preliminary report.
JPO Journal of Prosthetics and Orthotics
1988;1 :24-31.
- Wagner J, Sienko 5, Supan T, Barth D. Motion analysis of SACH vs. Flex-Foot in moderately active below-knee amputees. Clinical Prosthetics and Orthotics 1987; 11:55-62.
- Schuch CM. Dynamic alignment options for
the Flex-Foot. JPO Journal of Prosthetics and
Orthotics 1988;1:37-40.
- Armitage P. Statistical methods in medical
research. Oxford: Blackwell Scientific Publications 1971;1-504.
- Wing DC, Hittenberger DA. Energy-storing
prosthetic feet. Archives of Physical Medicine
and Rehabilitation 1989;70:330-5.
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