Volume 49 Number 9, 2012
Pages 1321 — 1330
Transtibial prosthetic suspension: Less pistoning versus easy donning and doffing
Hossein Gholizadeh, MEngSc;1* Noor Azuan Abu Osman, PhD;1 Arezoo Eshraghi, MSc;1 Sadeeq Ali, BSc;1 Stefan Karl Sævarsson, MSc;2 Wan Abu Bakar Wan Abas, PhD;1 Gholam Hossein Pirouzi, BSc1
1Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia; 2Department of Biomedical Engineering, University of Calgary, Calgary, Canada
Abstract—Poor suspension increases
slippage of the residual limb inside the socket during ambulation. The
main purpose of this article is to evaluate the pistoning at the
prosthetic liner-socket interface during gait and assess patients’
satisfaction with two different liners. Two prostheses with seal-in and
locking liners were fabricated for each of the 10 subjects with
transtibial amputation. The Vicon motion system was used to measure the
pistoning during gait. The subjects were also asked to complete a
Prosthesis Evaluation Questionnaire. The results revealed higher
pistoning inside the socket during gait with the locking liner than with
the seal-in liner (p < 0.05). The overall satisfaction with the locking liner was higher (p
< 0.05) because of the relative ease with which the patients could
don and doff the device. As such, pistoning may not be the main factor
that determines patients’ overall satisfaction with the prosthesis and
other factors may also contribute to comfort and satisfaction with
prostheses. The article also verifies the feasibility of the Vicon
motion system for measuring pistoning during gait.
Key words: amputation, gait, Iceross,
lower-limb amputation, motion analysis, pistoning, satisfaction,
suction, suspension, transtibial prosthesis.
*Address
all correspondence to Hossein Gholizadeh, MEngSc; Department of
Biomedical Engineering, Faculty of Engineering, University of Malaya,
50603, Kuala Lumpur, Malaysia; 603-7967-4581; fax: 603-7967-4579.
Email:
gholizadeh@um.edu.my The main roles of the suspension systems incorporated into
lower-limb prostheses are to hold the prosthesis on the residual limb
and to decrease the motion that takes place at the
bone-skin-liner-socket interface during ambulation (pistoning, vertical
movements within the socket) [1]. Effective suspension systems and
prosthetic components can improve a person with amputation’s gait and
decrease his or her energy expenditure [2–3]. Prosthetic limbs should
have an intimate fit with the residual limb in order to replace the lost
body part with a device that offers high levels of comfort and
satisfaction [3–6].
Individuals with amputation believe that both the suspension
method and the fitting of a prosthetic device have significant effects
on their overall satisfaction with the prosthesis [6–8]. Several
questionnaires have been developed and a number of prosthetics surveys
have been conducted to analyze patient satisfaction with prosthetic
devices. The majority of researchers prefer the Prosthesis Evaluation
Questionnaire (PEQ) as a means of evaluating differences in function,
performance, and satisfaction between the different components or
techniques of prosthetics fabrication and adjustment (
Appendix, available online only) Good reliability and validity have been reported for the PEQ [9–11].
Evidence shows that silicone liners are preferred by many
people with lower-limb amputation because they offer enhanced suspension
and fit within the socket as well as improved function [3,7–8,12].
Previous research on the silicone liners has found that patient comfort
and satisfaction are particularly higher in contrast with other
suspension systems, such as the belt for patellar tendon bearing socket
[3,8,12]. Silicone liners are believed to be more effective in
controlling the pistoning within the prosthetic socket than polyethylene
foam (pelite) liners. Pistoning at the socket-liner interface is said
to be lower with silicone liners (1–5 mm) than with pelite liners
(6.0–41.7 mm) [13–21].
Based on the literature, the pistoning is correlated with the
prosthetic suspension system and fit [15]. Thus, both clinicians and
researchers should be able to determine the quality of suspension and
prevent the negative effects of pistoning (such as gait deviation, skin
breakdown, and discomfort) by pistoning measurement [13–22].
A number of methods exist to measure the pistoning of various
interfaces within the socket (liner-socket) or the residual limb
(bone-soft tissue). These include X-ray [12,20,23–25], spiral
computerized tomography [26], and photoelectric sensors [22]. These
measurement methods are mostly useful for measuring the bone movement
inside the socket. Recently, two new methods were introduced for the
liner-socket interface in transtibial prostheses: a photographic method
and a motion analysis system [16–19]. The literature review revealed
that the majority of researchers measured the pistoning during quiet
standing (static) and only a few had evaluated the pistoning that
occurred inside the socket during gait (dynamic) [15].
A previous study by Gholizadeh et al. revealed low levels of
pistoning for the seal-in suspension (Seal-In X5 liner, Össur;
Reykjavik, Iceland) than the locking system (Dermo liner, Össur) during
standing [16]. The findings of that study motivated this current
research and prompted investigation on the effects of these suspension
systems during gait along with patient satisfaction. To our knowledge,
no study has previously compared the quality of suspension systems
during gait and the associated levels of patient satisfaction.
Ten subjects with unilateral transtibial amputation
participated in this study. We determined the participants’ mobility
grade based on the guidelines of the American Academy of Orthotists
& Prosthetists [27].
Table 1 lists subject characteristics.
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*Inferior edge of patella to distal end of residual limb. †Based
on American Academy of Orthotists & Prosthetists scale. K2 =
Patient has ability or potential for ambulation with ability to traverse
low-level environmental barriers such as curbs, stairs, or uneven
surfaces—a typical community ambulator. K3 = Patient has ability or
potential for ambulation with variable cadence—a typical community
ambulator with ability to traverse most environmental barriers and may
have vacation, therapeutic, or exercise activity that demands prosthetic
use beyond simple locomotion. |
In order to be eligible for the study, subjects with
transtibial amputation were required to be unilateral, without pain or
ulcer on the residual limb, and with a residual-limb length not less
than 13 cm. Furthermore, they could not have volume fluctuation in the
residual limb, could not depend on assistive devices such as a cane or
crutches for ambulation, and had to have good upper-limb strength.
Two transtibial prostheses (
Figure 1)
were manufactured for each subject. Two different suspension systems
were used: Seal-In X5 liner with valve (Icelock Expulsion Valve 551,
Össur) and Dermo liner with shuttle lock (Icelock Clutch 4H 214, Össur).
All prosthetic feet were Flex-Foot Talux (Össur) [16,18].
Figure 1. Transtibial suspension systems: (a) Seal-In X5 liner (Össur; Reykjavik, Iceland) with transparent socket and valve and (b) Dermo liner (Össur) with transparent socket and shuttle lock. |
One of the researchers (registered prosthetist) designed, fit,
and aligned all the prosthetic limbs. Two separate total surface bearing
sockets were fabricated individually for each of the two liners that
were used in the study. Transparent thermoplastic material (NorthPlex 12
mm, North Sea Plastics Ltd; Glasgow, United Kingdom) enabled us to
check the socket fit. The subjects attended a gait training session in
the Brace and Limb Laboratory (Department of Biomedical Engineering,
University of Malaya, Malaysia).
The prosthetist ensured that there was no gait abnormality and
that the fit of the prosthetic sockets was satisfactory. We determined
prosthetic alignment through bench, static (standing in an upright
position), and dynamic (during walking) alignment. All subjects had an
acclimation period of 4 weeks for each prosthetic device. To ensure
subject safety, one definite socket was also made for each liner type
for the 4-week acclimation period. Check sockets were used only during
the kinematic experiments.
Following the trial period, we performed pistoning evaluation
in the motion analysis laboratory with the Vicon 612 system using seven
MXF20 motion capture cameras (Vicon; Los Angeles, California), which is
believed to have an accuracy level of less than ±0.1 mm [28]. We adopted
a sampling rate of 200 Hz for the data collection. The signals from the
motion analysis system were filtered by a Butterworth filter (cutoff
frequency of 10 Hz).
We fixed 16 reflective markers to the subjects’ lower limbs in
accordance with the Helen Hayes marker set. The knee and tibia markers
for the prosthetic leg were located on the lateral proximal socket wall
and the lateral distal end of the socket, respectively (
Figure 2). We placed two additional markers on the liner under the knee joint level (LLin1) and 5 cm below that (LLin2) [16].
![Figure 2. Marker positions on socket (lateral proximal socket wall [LPS] and lateral distal end of socket [LDS]) and liner (LLin1 and LLin2).](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sGbDkfvnd_h50VJ4wP5PUB7zjam_Td_LY4ky-gMHBvSexSKDWXXBdyKRvIcfuTiTK6eT_CuDEMyRUutGITY-gYjbYq6n3IfaFZEJK6h__fdeKilwk7p92TteTaddEv1LFQEk4i4bDxEdyUpwBi4A=s0-d)
Figure 2. Marker
positions on socket (lateral proximal socket wall [LPS] and lateral
distal end of socket [LDS]) and liner (LLin1 and LLin2). |
Because knee joint movement could affect the actual pistoning
values, we positioned the additional markers (LLin1 and LLin2), aligned
by laser liner, on the liner below the knee joint. With the transparent
socket, the markers were visible through the hard socket and detectable
by the cameras [16]. By fixing the markers to one segment (the shank),
we avoided knee movements leading to unreal displacement.
The transparent socket could create some reflections that could
be mistakenly considered as markers, therefore we used paper tape
(except for the areas where additional markers were located) to mask the
socket wall [16]. Prior to the test, we asked subjects to walk in the
motion analysis laboratory in order to accustom themselves to the
environment. Afterward, the subjects walked at a self-selected speed on
an 8 m walkway. We recorded five successful trials per subject with each
type of liner. We considered a trial to be successful if the cameras
could capture all the markers. We could measure the pistoning by
analyzing the markers’ positions; however, in order to detect one gait
cycle in each trial, we also used two Kistler force plates. There was a 1
min rest interval between the trials. We used the distance between the
markers on the liner and on the socket to identify the piston motion.
The reproducibility of measurements was evaluated by
intraobserver intrasession, intraobserver intersession, and
interobserver intersession variabilities. Two observers performed the
experiments over two sessions with a 1 week interval.
Following the experiments, we asked the subjects to complete
one PEQ for each studied liner. We used some parts of the PEQ to
quantitatively assess patient satisfaction [10]. The PEQ consisted of
the following three sections:
• |
Demographic data (sex, age, weight, height, time since amputation, and cause of amputation). |
• |
Satisfaction (fit,
donning and doffing, sitting, walking on level surface, walking on
unlevel ground, ascending and descending stairs, cosmesis, and overall
satisfaction). |
• |
Problems (sweat, wound, skin irritation, pistoning, pain, swelling [edema], smell, and unwanted sounds). |
We rated the responses on a scale from 0 to 100, where 0
indicated "dissatisfaction or extreme problems" with the system and 100
indicated "complete satisfaction or no problems."
We used SPSS 18.0 (IBM Corporation; Armonk, New York) for the data analyses, with
p-values set at 0.05. A paired-samples
t-test
compared the effects of the two different liners on pistoning during
each gait cycle. We divided the gait cycle (stance and swing) into eight
phases. We divided the stance phase by initial contact, loading
response, midstance, terminal stance, and preswing. Initial swing,
midswing, and terminal swing formed the swing phase of gait. In order to
analyze the data, we first calculated the peak pistoning that occurred
during each phase of one gait cycle for one gait trial of each subject.
Following that, we computed the average peak pistoning that occurred
across five successful gait trials. Finally, we found the overall
average of peak pistoning across the different phases of gait for all 10
subjects for the comparison between the liners.
The mean time since amputation was 7 years and all subjects had
undergone amputation at least 3 years prior to study participation. The
reproducibility of the measurements across the different trials of one
session and between two sessions by two observers was shown to be high.
The intraclass correlation coefficients of intraobserver intrasession,
intraobserver intersession, and interobserver intersession were 0.92,
0.87, and 0.79, respectively.
The results of the motion analysis revealed that the amount of
pistoning that occurred when the Seal-In X5 liner was used was
significantly less than the pistoning with the Dermo liner throughout
the gait cycle (
p < 0.05),
with the exception of loading response (0.5 mm), midstance (0.0 mm) and
terminal stance (0.0 mm). Both liners exhibited no pistoning during
preswing (
Table 2,
Figures 3–4).
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*Össur; Reykjavik, Iceland. †Statistically significant. |
Figure 3. Sample pistoning patterns with Seal-In X5 liner (Össur; Reykjavik,
Iceland) and Dermo liner (Össur) during one gait cycle for subjects (a) 2 and (b) 5. |
Figure 4. Comparison of mean displacement in different phases of gait cycle (n = 10). |
During initial contact, the Dermo liner was displaced 5.1 ± 0.7
mm (mean ± standard deviation) within the socket. However, this value
decreased rapidly to 0.0 mm at the end of loading response and remained
the same until the initial swing. Only 1.9 ± 0.4 mm of pistoning was
found with the Seal-In X5 liner during initial contact. Maximum
displacements in 10 subjects were 5.4 ± 0.6 mm for the Dermo and 2.5 ±
0.4 mm for the Seal-In X5 liners during the initial swing.
The PEQ revealed that the subjects were overall more satisfied (
p
< 0.05) with the Dermo liner than the Seal-In X5 liner.
Nevertheless, many of them mentioned increased levels of pain and
pistoning when using the Dermo liner. Donning and doffing the Seal-In X5
liner was more difficult, but the satisfaction with the socket fit was
higher (
Table 3). The
participants also stated that the prosthesis with the Seal-In X5 liner
acted like a natural part of their body and that they did not experience
any traction at the end of the liner.
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*Greater mean indicates higher satisfaction. †Greater mean indicates less complaints/problems. ‡Statistically significant. |
Selecting a suitable suspension system for individuals who have
undergone transtibial amputation is a critical issue in rehabilitation
[7,16,18]. In this study, we evaluated two different prosthetic
suspension systems in 10 subjects with transtibial amputation to compare
pistoning movement and patient satisfaction with the device during
ambulation. The Vicon motion system was introduced for the purpose of
evaluating pistoning during gait.
The literature review revealed that the majority of existing
research was based on pistoning measurement in the static position of
quiet standing as opposed to walking [15]. The complications of taking
such measurements during gait and concerns over subject safety by
exposure to X-ray hampered such practice [22]. A few studies attempted
to use videofluoroscopy [29], photoelectric sensors [22], or axial
movement detectors [30] to measure the pistoning that occurred during
ambulation. However, they were only able to measure vertical movement
between the pelite liner and socket [22,30]. Among them, only Sanders et
al. provided the value of the pistoning that occurred across different
phases of gait [22].
In this study, the Vicon motion system was shown to be an
efficient method of measuring the pistoning at the liner-socket
interface during the gait. It also offered a harmless method of
pistoning measurement [22]. However, it is unable to detect bone
displacement within the soft tissue.
This study showed that the Seal-In X5 liner helps to decrease
pistoning by developing suction against the socket wall. The resultant
suction ensures firm attachment between the liner and the socket wall.
The purpose of silicone liners is to provide enhanced suspension by
causing less pistoning within the prosthetic socket [3,8,12,15]. The
findings of this study support this statement because the pistoning
values with both Seal-In X5 and Dermo liners were lower than those found
with the polyethylene foam liners [22,29–30].
With the exception of the preswing phase, we found significant differences between the two liners during the gait cycle (
p < 0.05) (
Figures 3–4,
Table 2).
These significant differences can be attributed to the different
elongation properties of the liners used [16,18]. The pistoning that
occurred during the initial swing might have been high as a result of
peak flexion in the knee joint.
Finally, as a result of centrifugal forces, the pistoning
increased between the liners and socket during the terminal swing. We
noted significant difference in pistoning between the studied liners
during this phase of the gait (
p < 0.05), which can be associated with the firm attachment between the Seal-In X5 liner and the socket.
Prosthetic satisfaction is an issue influenced by several
factors. Prosthetic users require more time and energy to don and doff
the Seal-In X5 liner [16,18]. They also need lubricant sprays to
facilitate donning. Moreover, hand dexterity is more critical for
donning and doffing a Seal-In
X5
liner than for the Dermo liner. All locking liners usually have an
umbrella-shaped feature at the distal part that is connected distally to
a pin. Weight bearing during ambulation over this rigid and small pin
may result in pain at the distal end of the residual limb [31].
The Seal-In X5 liner seems to resolve the so-called problem of
"milking" (distal tissue stretch caused by the pin and lock) [32]. This
milking phenomenon can also result in pain, particularly at the end of
the tibia and along the tibial crest. The subjects in the current study
had more pain with the pin and lock suspension (Dermo liner) than the
Seal-In
X5 liner.
Little is known about the effects of different prosthetic
components and systems on patient satisfaction with prostheses.
Effortless donning and doffing does appear to have a positive effect on
satisfaction with a prosthesis [6]. The participants of this study were
mainly dissatisfied with the Seal-In X5 in terms of donning and doffing
and many of them specified that donning and doffing was significantly
easier with the Dermo liner than with the Seal-In X5 liner. As such, the
subjects stated a preference for this suspension system over the
Seal-In X5 liner for long-term use.
One limitation of this study was the small sample size,
particularly for the satisfaction survey. In addition to this, further
research is needed to compare more suspension alternatives in order to
provide a better guideline for suspension system selection. Future
research should also investigate and compare the effects of these
suspension systems on proprioception.
In conclusion, amputation rehabilitation is influenced by
appropriate choice of prosthetic components in accordance with the real
needs of the individual. We can infer from the results of this study
that the Seal-In X5 liner decreased the pistoning within the prosthetic
socket significantly, possibly as a result of the strong suction seal
between the liner and the socket. Nevertheless, the subjects had
difficulty with donning and doffing. We can therefore conclude that
pistoning may not be the main factor that determines subjects’ overall
satisfaction with the prosthesis.
The study introduced a new method for evaluating the pistoning
at the liner-socket interface in transtibial prostheses during gait. The
Vicon system has the potential to detect the pistoning during gait
while also offering a safer alternative to X-ray. Further studies are
needed to come to a "gold standard" for pistoning.
Funding/Support:
This material was based on work supported by the Malaysia UM/MOHE/HIR
(grant D000014–16001) and the prosthetic components were donated by
Össur.
Additional Contributions: The authors would like to thank Mrs. Elham Sadat Yahyavi, Ms. Ása Guðlaug Lúðvíksdóttir,
Dr. Nader Ale Ebrahim, and Mr. Scott Elliott for providing technical advice.
Institutional Review: The
ethical approval was granted from the University of Malaya Medical
Centre Ethics Committee. All subjects were asked to provide written
informed consent.
Participant Follow-Up: The authors do not plan to inform participants of the publication of this study due to a lack of contact information.
1. |
Michael JW. Prosthetic suspensions and components. In: Smith DG, Michael JW, Bowker JH, editors. Atlas of amputations and limb deficiencies: Surgical, prosthetic, and rehabilitation principles. 3rd ed. Rosemont (IL): American Academy of Orthopaedic Surgeons; 2004. p. 409–25. |
19. |
Gholizadeh H, Abu Osman NA, Lúðvíksdóttir ÁG, Kamyab
M, Eshraghi A, Ali S, Wan Abas WA. A new method for measuring pistoning
in lower limb prosthetic. Proceedings of 5th Kuala Lumpur International
Conference on Biomedical Engineering; 2011 Jun 20–23; Kuala Lumpur,
Malaysia. Berlin Heidelberg (Germany): Springer; 2011. p. 728–31. |
This article and any supplementary material should be cited as follows:
Gholizadeh
H, Abu Osman NA, Eshraghi A, Ali S, Sævarsson SK, Wan Abas WA, Pirouzi
GH. Transtibial prosthetic suspension: Less pistoning versus easy
donning and doffing. J Rehabil Res Dev. 2012;49(9):1321–30.
http://dx.doi.org/10.1682/JRRD.2011.11.0221
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Last Reviewed or Updated
Tuesday, January 8, 2013 11:11 AM
The article may be used freely, for a noncommercial purpose, as long as the original source is properly acknowledged.
![Figure 2. Marker positions on socket (lateral proximal socket wall [LPS] and lateral distal end of socket [LDS]) and liner (LLin1 and LLin2).](http://www.rehab.research.va.gov/jour/2012/499/images/gholizadeh499f02lb.jpg)
