-
po
dRickard Branemark c, John H. Evans a,b, Mark J. Pearcy a,b
a
reect the dierent strategies used in controlling the prosthetic
knee joint.
used for over a century, problems of pain in the residual too
short to support the use of a conventional socket.In part to
overcome these problems, a surgical technique
(osseointegration) has been developed to allow a prosthesisto be
directly anchored to the bone through a xationbased on a titanium
implant. A coupling device (the abut-ment) is attached to the
implant, while its distal end
* Corresponding author. Address: Institute of Health and
BiomedicalInnovation, Queensland University of Technology, Victoria
Park Road,Kelvin Grove Qld 4059, Australia.
E-mail address: [email protected] (W.C.C. Lee).
Clinical Biomechanics 22 (2Interpretations. This study increases
the understanding of biomechanics of bone-anchored osseointegrated
prostheses. The loadingdata provided will be useful in designing
the osseointegrated xation to increase the fatigue life and to rene
the rehabilitation protocol. 2007 Elsevier Ltd. All rights
reserved.
Keywords: Transfemoral amputation; Prosthetics;
Osseointegration; Transducer; Activities of daily living
1. Introduction
The most common method of attaching a prosthesis to aresidual
limb is by means of a prosthetic socket, often withsome suspensory
devices to retain the socket when notload-bearing. Although this
attachment method has been
limb and skin breakdown sometimes arise (Gallagheret al., 2001;
Hagberg and Branemark, 2001; Mak et al.,2001). High pressure
applied from the prosthetic socketto the soft tissue of a residual
limb that is not adapted totolerate load has been suggested as the
cause of the painand skin breakdown. In addition, some residual
limbs areSchool of Engineering Systems, Queensland University of
Technology, Brisbane, Australiab Institute of Health and Biomedical
Innovation, Queensland University of Technology, Brisbane,
Australia
c Centre of Orthopaedic Osseointegration, Sahlgrenska University
Hospital, Goteborg, Swedend Department of Prosthetics and
Orthotics, Sahlgrenska University Hospital, Goteborg, Sweden
Received 12 December 2006; accepted 12 February 2007
Abstract
Background. Direct anchorage of a lower-limb prosthesis to the
bone through an implanted xation (osseointegration) has been
sug-gested as an excellent alternative for amputees experiencing
complications from use of a conventional socket-type prosthesis.
However,an attempt needs to be made to optimize the mechanical
design of the xation and rene the rehabilitation program.
Understanding theload applied on the xation is a crucial step
towards this goal.
Methods. The load applied on the osseointegrated xation of nine
transfemoral amputees was measured using a load transducer,when the
amputees performed activities which included straight-line level
walking, ascending and descending stairs and a ramp as wellas
walking around a circle. Force and moment patterns along each gait
cycle, magnitudes and time of occurrence of the local extrema ofthe
load, as well as impulses were analysed.
Findings. Managing a ramp and stairs, and walking around a
circle did not produce a signicant increase (P > 0.05) in load
comparedto straight-line level walking. The patterns of the moment
about the medio-lateral axis were dierent among the six activities
which mayKinetics of transfemoral amxation performing comm
Winson C.C. Lee a,b,*, Laurent A. Frossar0268-0033/$ - see front
matter 2007 Elsevier Ltd. All rights
reserved.doi:10.1016/j.clinbiomech.2007.02.005utees with
osseointegratedn activities of daily living
a,b, Kerstin Hagberg c, Eva Haggstrom d,
www.elsevier.com/locate/clinbiomech
007) 665673
-
iomprotrudes through the soft tissue to provide the
attachmentfor the external prosthesis. In addition to alleviating
theskin problems and residual limb pain (Sullivan et al.,2003),
studies have also shown that amputees using trans-femoral
osseointegrated prostheses enjoy a greater rangeof hip motion and
better sitting comfort compared to thesocket-type (Hagberg et al.,
2005). They can walk furtherand be more active than using a
conventional prosthesis(Robinson et al., 2004; Sullivan et al.,
2003), and can haveimproved sensory feedback (through
osseoperception)(Branemark et al., 2001). External components of
the pros-thesis can be attached to and detached from the
abutmenteasily and the alignment is faithfully preserved. To
date,there are over 80 transfemoral amputees world-wide whohave
been tted with the transfemoral osseointegrated x-ation developed
by Dr. R. Branemark (Branemark et al.,2001). However, factors such
as steroid medication oranti-tumour chemotherapy which may
interfere with bonehealing, heavy smoking or diabetes which may
increase riskof bone sepsis, and body weight in excess of 100 kg
are pos-sibly contraindications to the tting of lower-limb
osseoin-tegrated prostheses (Robinson et al., 2004).
As with amputees using socket-type prostheses, thosewho use
osseointegrated prostheses undergo a rehabilita-tion process, which
involves incremental static loadingson the abutment to prepare the
bone to tolerate forcestransmitted from the implant when performing
essentialactivities. Understanding the load experienced during
var-ious activities might help rene the rehabilitation
process.Previous studies have also indicated certain gait
deviationsamong transfemoral amputees in walking on level anduneven
terrains (Jaegers et al., 1995; James and Oberg,1973; Murray et
al., 1983; Schmalz et al., 2007), in spiteof the improved
prosthetic knee joint designs in lockingand bending mechanics. In
addition, mechanical failuresof the abutment sometimes occur after
long use or as theresult of excessively high magnitude load
application usu-ally induced by a fall (Sullivan et al., 2003). The
abutmentis designed to fail in order to protect the bone from
over-load, but attempts can be made to optimize the strengthof the
xation and to develop safety devices to protectthe xation and the
bone with the understanding of theloads developed during common
daily activities. To renethe rehabilitation program as well as to
develop the xationsystem, safety devices and dierent prosthetic
componentsto address the mechanical problems and improving
walkingability, it is important to have a comprehensive
under-standing of the load applied on the xation.
Over the past two decades, loadings applied at the distalend of
prosthetic sockets have been studied (DiAngeloet al., 1989;
Stephenson and Seedhom, 2002; Nietertet al., 1998; Berme et al.,
1975; Frossard et al., 2003).The load has been calculated using
inverse dynamicsrelying on the motion of the prosthesis captured by
amotion analysis system and the ground reaction forces
666 W.C.C. Lee et al. / Clinical Bmeasured by a force plate
(DiAngelo et al., 1989; Stephen-son and Seedhom, 2002). The load
can also be measureddirectly using appropriate load transducers
(Berme et al.,1975; Nietert et al., 1998). Frossard and colleagues
(Fros-sard et al., 2003) measured the direct load applied at
thetransfemoral socket end using a commercial load trans-ducer
mounted between the prosthetic knee joint and thesocket, and
suggested that direct load measurement couldimprove accuracy and
allow measurement to be taken forunlimited walking steps. In
addition, direct measurementallows loadings to be measured for any
type of activityand on any terrain.
Although the application of such direct measurementtechniques to
transfemoral amputees using osseointegratedprostheses has been
reported (Frossard et al., 2001), thedata were limited to one
subject only. Comprehensiveunderstanding of the load applied on
osseointegrated xa-tion during level walking is important. It is
also crucial tounderstand the load in various activities of daily
living suchas climbing stairs and walking inclines. Because of the
lossof some musculature and joint mobility, functionaldemands may
increase dramatically when performing dailyactivities. In addition,
amputees may employ dierent load-ing strategies to help them manage
dierent activities, all ofwhich may pose a potential danger to the
structural integ-rity of the xation system and the bone.
The aim of this study is to use a direct measurementmethod to
compare the load applied on the osseointegratedxation of nine
transfemoral amputees performing severalactivities of daily living
including managing ramps, stairsand walking around a circle which
are believed to be themost commonly performed activities during
daily living.
2. Methods
2.1. Participants and prostheses
A total of two female and seven male unilateral transfe-moral
amputees tted with osseointegrated xation partic-ipated in this
study. The demographic details of eachsubject are summarized in
Table 1. All participants havebeen walking with the xation for at
least one year, andcan walk 200 m independently without additional
walkingaids. Load measurement took place in a clinical environ-ment
at Sahlgrenska University Hospital, Gothenburg,Sweden where the
participants were recruited. Humanresearch ethical approval was
received from the Queens-land University of Technology. Written
consent wasobtained from all participants.
Amputees were tted with their regular prosthetic com-ponents, as
presented in Table 1, with the load transducersubstituted for the
adaptor which connected the Rotasafeto the knee joint. Rotasafe is
a safety device, based on aclutch, which prevents excessive torque
on the abutment.A compromise was made for three participants who
couldnot retain a Rotosafe due to the lack of space to t the
loadtransducer. The transducer was tted by a prosthetist who
echanics 22 (2007) 665673replicated the usual alignment of the
prosthesis for eachamputee.
-
Table 1Subject characteristics
Subjectnumber
Gender(M/F)
Age(years)
Height(m)
Total massa
(kg)Side of amputation(R/L)
Footwear Prostheticfoot
Prostheticknee
Rotasafe
1 F 57 1.63 61.1 R Sandals Totalconcept
Total knee Yes
2 M 50 1.81 74.3 L Sandals TruStep Total knee No3 M 59 1.89 87.1
R Leather
shoesTruStep Total knee No
4 F 49 1.58 53.3 R Sandals Totalconcept
Total knee Yes
5 M 41 1.77 96.6 R
6 M 26 1.78 90 R
7 M 46 1.99 99.5 L8 M 50 1.82 99.8 R
9 M 45 1.72 80.4 R
Mean 47 1.78 82.5
prosthesis.
W.C.C. Lee et al. / Clinical Biomechanics 22 (2007) 665673
6672.2. Apparatus
The technique used to measure the load is similar to theone
described in previous studies (Frossard et al., 2003;Frossard et
al., 2001). A six-channel load transducer(Model 45E15A; JR3 Inc.,
Woodland, USA) was used tomeasure directly the 3-dimensional forces
and momentsapplied to the abutment. The transducer was mounted
tocustomized plates that were positioned between the abut-ment and
the prosthetic knee. The transducer was aligned
Standard deviation 9.7 0.12 16.8
a The total mass includes body mass plus the mass of the
instrumentedso that its vertical axis was co-axial with the long
(L) axisof the abutment and femur. The other axes correspondedto
the anatomical antero-posterior (AP) and medio-lateral(ML)
direction of the abutment as depicted in Fig. 1.
Fig. 1. Example of a typical prosthetic leg setup used to
directly measurethe forces and moments applied on the xation of
transfemoral amputee(left: front view, right: side view). A
commercial transducer (A) wasmounted to specially designed plates
(B) that were positioned between theadaptor (C) connected to the
xation (D) and the knee mechanism (F).Forces acting along the AP,
ML and L axes were denotedas FAP (anterior was positive), FML
(lateral was positive),and FL (compression was positive),
respectively. Momentsabout the three axes were denoted as MAP
(lateral rotationwas positive), MML (anterior rotation was
positive) andML (external rotation was positive), respectively. The
max-imum capacity was 2273 N for FL, 1,136 N for FAP andFML, and
130 Nm for moments about the three axes. Accu-racy was 0.1% of the
maximum capacity. Each channel wassampled at 200 Hz. A wireless
modem (Ricochet ModelRunningshoes
C-walk Total knee No
Leathershoes
Carbon copy C-leg Yes
Sandals C-walk Total knee YesLeathershoes
Flex foot GaitMaster Yes
Runningshoes
TruStep Total knee Yes21062; Metricom Inc., Los Gatos, USA) was
used to trans-mit data from the transducer to a nearby laptop
computer.
2.3. Protocol
Approximately 15 min of practice with the instrumentedprosthetic
leg was allowed before load measurement toensure subject condence
and comfort. Then, the partici-pants were asked to perform each of
the activities includ-ing: straight-line level walking; walking
upstairs,downstairs, upslope, and downslope; and walking along
a
Table 2Descriptions of the six various activities performed
during directmeasurement of load
Activities Descriptions
Levelwalking
Level walking along a level, straight-line walkway
Downslope Descending a 6.5 degrees of slopeUpslope Ascending a
6.5 degrees of slopeDownstairs Descending stairs of 30 cm height 34
cm deepUpstairs Ascending stairs of 30 cm height 34 cm deepCircle
Level walking around a circle of 2 m diameter with the
prosthetic leg outside
-
circle. Detailed descriptions of each activity are shown inTable
2. Load data were measured for at least ve stepsof the prosthetic
limb for each activity. The amputees wererequired to walk and
manage the stairs and slope at a self-selected, comfortable speed.
The order of each activity wasrandomized. Finally, the prosthesis
was detached from theresiduum to enable a one-minute recording
without loadapplied on the transducer for calibration purposes.
2.4. Data processing
The raw force and moment data were imported and pro-cessed by a
customized Matlab software program (TheMathWorks Inc., MA, USA).
The load data were osetaccording to the magnitude of the load
recorded duringunloaded conditions. The rst and last strides
recordedfor each trial were also removed in order to avoid the
ini-tiation and termination of walking. The patterns of
thethree-dimensional forces and moments for each gait cyclewere
analysed. The heel contact and toe-o time weredetermined according
to the curve of the long-axis force.
300
400
500
600
700
800
Forc
e (N
)
FAP
FML
FL
Resultant
FL1
FL1
FAP+
Toe off
10
t (N
m ML+
a
668 W.C.C. Lee et al. / Clinical Biom0 10 20 30 40
-30
-20
-10
0
% gait cycle
Mom
en
MML-
50 60 70 80 90 100
Fig. 2. The local extrema and typical patterns of (a) forces and
(b)-100
0
100
200
0 10 20 30 40 50 60 70 80 90 100
% gait cycleFAP-
FML+
20
30
40
)
MAP
MML
ML
MAP+MML+
Toe off bmoments along the antero-posterior (AP), medio-lateral
(ML), and long-axis (L) axes of subject 1 performing straight-line
level walking.A gait cycle was dened as the period between two
consec-utive heel contacts.
The magnitude of local extrema of the three componentsof forces
and moments presented in Fig. 2 were determinedfor each step of the
prosthetic limb. Resultant forces (Fr)were calculated by the vector
sum of FAP, FML and FL.The time of occurrence (expressed in
percentage of stancephase time) as well as the magnitude (expressed
in percent-age of body weight) of the local extrema of Fr were
identi-ed. Impulse (IAP, IML, IL and IR) for each step of
theprosthetic limb were calculated by using the
conventionaltrapezoid method to integrate the area under the
forcetime curves (FAP, FML, FL and Fr). Each parameter (thelocal
extrema, time of occurrence and impulse) was aver-aged across steps
for each subject. To discuss the dier-ences in loading strategies
among various activities ofdaily living, the means and standard
deviations of eachparameter across subjects were computed for each
activity.Statistical analyses were performed in SPSS statistical
soft-ware (LEAD technologies, Inc.). Dierences among theactivities
were determined by repeated measures analysisof variance (ANOVA). A
post-hoc Tukeys test was usedto identify the signicant dierence. A
signicance levelof P < 0.05 was used.
3. Results
3.1. Patterns of forces and moments
Fig. 2 shows the typical patterns of forces and momentsin
straight-line level walking. It can be seen that althoughthe three
loading axes (AP, ML, L) were xed relative tothe limb during
ambulation, the three components offorces followed a pattern that
was similar to the groundreaction forces obtained with a xed
force-plate (Perry,1992; Zahedi et al., 1987). As expected, FL was
the largestin magnitude among the three components of forces
andpresented two peaks and a valley. Small plateaus werefound
immediately before the rst peak of the curve in afew subjects,
which may be explained by a sense of insecu-rity or discomfort.
During level walking, the abutmentexperienced some posterior
braking forces at the earlystance phase, and anterior propulsive
forces at the latestance phase, and consistently experienced some
lateralforces throughout the entire stance phase of the
gait.Lateral rotational moment was consistently experiencedduring
the stance phase of the gait. Anterior rotationalmoment was
experienced during the mid-stance phase,and posterior rotational
moment at the late-stance phaserelated to unlocking of the
prosthetic knee joint was expe-rienced when performing level
walking. Due to the tractioncreated by gravity acting on the mass
of the prosthesiswhich was located below the transducer, the forces
andmoments had small magnitudes during the swing phase.All subjects
demonstrated similar patterns of forces and
echanics 22 (2007) 665673moments for level walking, except for
ML which showedinconsistent patterns among participants (Fig.
3).
-
When performing the other activities of daily living,
thepatterns of forces and moments were close to those of
levelwalking as described above. However, there were excep-tions
for FAP, ML, and MML. Fig. 4a and b show FAPalong a gait cycle when
the majority of the subjects walkedupstairs and downstairs. Unlike
level walking with someposterior forces exerted at the abutment at
the early stancephase and anterior forces at the late stance phase,
the
for walking inclines and around a circle follow those
forstraight-line level walking. All subjects
demonstratedinconsistent ML patterns among the six activities
depictedin Fig. 5. Fig. 6ad display the dierent patterns of MMLfor
all subjects among the four activities: ascending anddescending
stairs and a ramp. Walking upslope andupstairs produced an average
anterior rotational momentof 17 Nm and 10 Nm, respectively, while
walking down-slope and downstairs did not produce a prominent
peakanterior rotation moment (Fig. 6). Walking around a
circleproduced similar MML patterns to level walking along
astraight-line.
3.2. Local extrema
A total of 10 local extrema for the three components offorces
and moments were studied, which represented thekey features of the
curve plotting force/moment dataagainst time as presented in Fig.
2. The local extrema werethe turning points of the curves which
presented the highestabsolute magnitude of loads. Two local extrema
were iden-tied for the maximum anterior (FAP+) and posterior
-8
-6
-4
-2
0
2
4
6
8
0 10 20 30 40 50 60 70 80 90 100
% gait cycle
ML
(Nm
)
External rotation
Internal rotation
Fig. 3. External/internal rotational moment (ML) for all
subjectsperforming straight-line level walking.
c
W.C.C. Lee et al. / Clinical Biomechanics 22 (2007) 665673
669abutments of seven subjects experienced posterior forcesmost of
the time at the stance phase when they walkeddownstairs. When
walking upstairs, the abutment of sixsubjects experienced anterior
forces during the entirestance phase. The FAP patterns of the
remaining subjectsare displayed in Fig. 4c and d, which show
entirely dier-ent curve patterns. In calculating the local extrema
of FAP,those remaining subjects were excluded. Patterns of FAP
-150
-100
-50
0
50
100
0 10 20 30 40 50 60 70 80 90 100
F AP (
N)
AnterioraDownstairs, n=7
Upstairs, n=6
-300
-250
-200
% gait cyclePosterior
-250Posterior
-50
-30
-10
10
30
50
70
90
% gaitcycle
F AP
(N)
Anterior
Posterior
1000 10 20 30 40 50 60 70 80 90
b d
Fig. 4. Antero-posterior force for (a) seven subjects walking
downstairs, and(c) walking downstairs, and (d) walking upstairs,
which showed dierent curv Downstairs, n=2
Upstairs, n=3
F AP (
N)
-300 % gait cycle
-50
-30
-10
10
30
50
70
90
% gait cycle
Anterior
Posterior
1000 10 20 30 40 50 60 70 80 90(FAP) forces, one for the maximum
lateral force (FML+),and two peaks for the axial force (FL1 and
FL2). One localextrema was identied for the maximum lateral
rotationalmoment (MAP+), two for the maximum anterior (MML+)and
posterior (MML) rotational moments and two localextrema were
identied for the peak external (ML+) andinternal (ML) rotational
moments. In addition, the mag-nitudes of the two peaks (Fr1 and
Fr2) and the time of
F AP (
N)
-200
-150
-100
-50
0
50
100
100
Anterior
0 10 20 30 40 50 60 70 80 90(b) six subjects walking upstairs.
The remaining subjects are shown ine patterns from the majority of
the amputees.
-
occurrence of the two peaks (TFR1 and TFR2) wereidentied.
Table 3 shows the mean and standard deviation acrosssubjects of
each local extrema in six dierent activities.There was no
statistical dierence among activities in eachlocal extrema of the
three components of forces andmoments. As far as the body weight
normalized resultantforces are concerned as presented in Table 4,
it was foundthat the Fr1 in walking upstairs [101% (SD 14%)
bodyweight] was statistically higher than in walking downstairs[78%
(SD 12%) body weight]. Meanwhile, the TFR2 inwalking downstairs
[56% (SD 11%) stance phase] was sta-tistically earlier than other
activities except walking down-slope. The TFR1 in walking
downstairs [26% (SD 33%)stance phase], in addition, appeared
statistically earlierthan walking upstairs [39% (SD 8%) stance
phase]. Timeof occurrence of local extrema in each particular
compo-nent of force and moment was not computed because ofthe
highly inconsistent patterns in some activities.
-8
-6
-4
-2
0
2
4
0 10 20 30 40 50 60 70 80 90 100
% gait cycle
ML
(Nm
)
DownslopeUpslopeDownstairsUpstairsWalkingCircle
External rotation
Internal rotation
Fig. 5. Typical external/internal rotational moment (ML) for the
sixdierent activities
-30-20-10
010203040
0 10 20 30 40 50 60 70 80 90 100
MM
L(N
m)
Anterior rotation
-70-60-50-40-30-20-10
010203040
0 10 20 30 40 50 60 70 80 90 100
% gait cycle
MM
L(N
m)
Anterior rotation
Posterior rotation
-70-60-50-40-30-20-10
010203040
0 10 20 30 40 50 60 70 80 90 100
% gait cycle
MM
L(N
m)
Anterior rotation
Posterior rotation My-
My+
My+
My-
-70-60-50-40-30-20-10
010203040
0 10 20 30 40 50 60 70 80 90 100
% gait cycle
MM
L(N
m)
Anterior rotation
Posterior rotation
a
b
c
d
Fig. 6. Moment about the medio-lateral axis (My) for all
subjects man
Table 3Mean and standard deviation (in bracket) across subjects
of the nine local ext
Walking Downslope Upslo
FAP (N) 74 (36) 93 (44) 53 (3FAP+ (N) 101 (19) 87 (29) 90
(25FML+ (N) 89 (35) 79 (22) 93 (39FL1 (N) 671 (139) 699 (149) 697
(1FL2 (N) 675 (138) 660 (146) 704 (1MAP+ (Nm) 21 (10) 25 (9) 22
(8)
(120 (9(1.
670 W.C.C. Lee et al. / Clinical Biomechanics 22 (2007)
665673MML+ (Nm) 9 (10) 17MML (Nm) 20 (9) 30 (20) 2ML+ (Nm) 3.7
(1.2) 5.3 (2.7) 3.2
ML (Nm) 5.0 (2.0) 3.8 (1.3) 6.3 (No statistical dierences were
found in those local extrema. (A indicates-70-60-50-40 % gait
cycle
Posterior rotation
aging (a) downslope, (b) downstairs, (c) upslope, and (d)
upstairs.
rema
pe Downstairs Upstairs Circle
4) 137 (98) 69 (29)) 74 (20) 84 (27)) 53 (14) 76 (30) 93 (34)53)
587 (157) 769 (171) 706 (165)44) 649 (112) 715 (170) 703 (148)
18 (8) 19 (8) 27 (9)) 10 (14) 11 (11)) 18 (6)7) 5.3 (3.6) 3.0
(1.1) 3.8 (1.7)
2.5) 3.5 (1.0) 3.7 (1.2) 5.4 (1.2)that there were no consistent
peaks/valleys in that activity)
-
ltan
slop
91 (94 (39 (72 (
e
(39)(47)(79)(85)
iom3.3. Impulses
The overall loading of the prosthesis over the supportphase
represented by the impulse is provided in Table 5.As expected, the
impulse produced in long-axis (IL) wasthe largest in magnitude
among the three axes. IAP in walk-ing upslope was statistically
higher than that of walkingdownslope and downstairs, while IL and
IR in walkingdownstairs was statistically lower than other
activitiesexcept walking down the slope.
4. Discussion
Conventionally, the load experienced by prosthetic com-ponents,
including implants in the lower-limbs, can be esti-
Table 4Mean and standard deviation (in bracket) across subjects
of the peak resu
Walking Downslope Up
Fr1 (%BW) 89 (6) 89 (8)Fr2 (%BW) 93 (9) 86 (7)TFR1 (%SP) 32 (8)
30 (6) *
TFR2 (%SP) *70 (3)&,$63 (8) #,&
A pair of *,#,+,&,$ in each parameter represents a
statistical dierence.
Table 5Mean and standard deviation (in bracket) across subjects
of impulses
Walking Downslope Upslop
IAP (Ns) 108 (37) *75 (38) *,#130
IML (Ns) 58 (41) 51 (36) 65IL (Ns) *363 (76) 332 (56)
#385IR (Ns) *386 (81) 348 (59)
#415
A pair of *,#,+, in each parameter represents a statistical
dierence.
W.C.C. Lee et al. / Clinical Bmated using inverse dynamics
methods which are based onthe motion of the limb and the ground
reaction forces(DiAngelo et al., 1989; Stephenson and Seedhom,
2002).The drawbacks of this method are that only one or twosteps of
walking can usually be measured, force-plate tar-geting can produce
un-natural gait (Wearing et al.,2001), and accurate determination
of inertia of naturaland prosthetic limb segments is needed. In
addition, loadscannot be measured easily using force plates when
walkingon uneven terrain. This study used a portable
recordingsystem based on a load transducer and a wireless
modem.This allowed direct measurement of load applied to
theabutment. In addition, the wireless system allowed the
trueloading to be measured in dierent environments, and sub-jects
could walk unimpeded when they performed the var-ious
activities.
The main objective of this study was to examine the dif-ferences
in load applied on osseointegrated xation duringvarious activities
of daily living. If level straight-line walk-ing is considered to
be the baseline, it was found thatthe other ve activities which
were believed to be morephysically demanding did not produce any
statisticallysignicant increase in loading when compared to the
base-line. This may imply that these ve activities would notinduce
higher risk to the structural integrity of the xationsystem.
Impulses represented the utilisation of the prosthe-sis. IL in
walking downstairs was statistically lower than instraight-line
walking, but it was also statistically lower thanwalking upslope,
upstairs and around a circle.
There was no statistical dierence in local extrema iden-tied in
the three components of forces and momentsbetween every pair of
activities. Although there were largedierences in some cases, for
instance, FAP in walkingdownstairs was 47% higher than the average
of all the otheractivities, a statistical dierence was not reached
because ofthe large standard deviations across subjects. Some
statisti-cal dierences were found in the magnitude and the time
of
t forces and the time of occurrence of the peaks
e Downstairs Upstairs Circle
5) *78 (20) *101 (14) 91 (6)8) 85 (16) 94 (7) 93 (6)8) *26 (11)
30 (6) 34 (7)4) *,#,+,56 (11) +,$79 (3) 70 (4)
Downstairs Upstairs Circle
#67 (33) 104 (35) 113 (33)42 (27) 54 (38) 62 (42)
*,#,+,256 (31) +367 (69) 388 (79)*,#,+,271 (35) +388 (72) 411
(82)
echanics 22 (2007) 665673 671occurrence of peak resultant
forces. Fr1 in walking down-stairs was on average the lowest among
all activities andwas statistically lower than in walking upstairs.
In addi-tion, TFR2 in walking downstairs and downslope
werestatistically earlier than some other activities, while TFR1in
walking downstairs was statistically earlier than in walk-ing
upslope. The earlier peaks as well as lower magnitudeof Fr1 are
likely to be due to the rapid forward progressionof the prosthetic
limb, resulting from the lack of plantarexion and active knee exion
of the prosthetic joints,which are important in maintaining
stability when descend-ing from a step or a ramp. This also
explains the signicantreduction of impulses in walking downstairs.
In addition,because of the lack of active motion of the joints,
amputeestend to roll the prosthetic foot over the step edges
whenmanaging stair descent as reported for conventional
trans-femoral amputees (Schmalz et al., 2007).
Similar patterns of forces and moments were seen inthe six
dierent activities, except for FAP, ML and MML.Rotational moment
(ML) was inconsistent among subjectsand activities. The maximum
absolute value of externaland internal rotational moment fell
within a narrow range
-
I impulse of F (integrated the area under the
Berme, N., Lawes, P., Solomonidis, S., Paul, J.P., 1975. A
shorter pylon
iombetween 3.0 Nm and 6.3 Nm among the six activities. Thiscould
have implications in the minimal torque required totighten the
abutment to the implant, as well as thresholdvalue for the Rotasafe
rational protective devices. The vari-ations in the patterns of FAP
and MML could suggest thatamputees use dierent strategies in
prosthetic knee jointcontrol when they manage dierent activities.
Walking ups-lope and upstairs produced some anterior
rotationalmoment during stance phase. Walking downslope
anddownstairs, on the other hand, did not produce a promi-nent peak
anterior rotation moment (Fig. 5), which indi-cates the line of
action of the ground reaction force wasalways kept behind the knee
joint. There was a peak pos-terior rotational moment at the late
stance phase of the gaitwhen the subjects performed level walking,
managingslope, and walking around a circle. This could be
explainedby the eort of initiating knee exion in order to
providefoot clearance during the swing phase.
Various strategies of prosthetic knee control mightexplain the
dierent loading recorded in dierent activities.A good control of
the prosthetic knee is critical for asmooth ambulation and there
are dierent prosthetic kneesin the market that employ various
control mechanisms ingiving motion and stability to the knee. The
dierences inloading may also be explained by the dierent walking
pat-terns. For example, rolling the prosthetic foot over the edgeof
the step may explain the reduction of loads. Prostheticalignment,
which refers to the special position of the pros-thetic foot
relative to the residual limb, is also important.Variation in
alignment can change the load transfer biome-chanics as well as
walking ability. In order to aid in preciseexplanation of the load,
control of the prosthetic knee andalignment, future studies can
collect simultaneous kineticand kinematic data to determine body
motion, knee jointangle and loading. Studies can also be performed
to inves-tigate the eect of dierent knee mechanisms and align-ment
on gait.
This study focuses on the loading applied on the xationsystem
which will be helpful in the future mechanicaldesign of the system
and rening of the rehabilitation pro-cess. Future studies will
perform experimental structuraltests and computational stress
analyses to investigate thestress/strain distribution at the
bone-implant interfaceand the entire xation system and estimate the
fatigue lifeusing the existing load data.
5. Conclusions
This study measured and compared the load acting onthe xation of
nine transfemoral amputees tted withosseointegrated xation
performing six dierent activitiesof daily living. The magnitudes of
local extrema as wellas the curve patterns of each component of
forces andmoments were revealed. Results suggested that
managingramp and stairs, and walking around a circle did not
pro-
672 W.C.C. Lee et al. / Clinical Bduce a signicant increase in
load compared to straight-line level walking. Results also
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forcetime curve)IML impulse of FML (integrated the area under
the
forcetime curve)IL impulse of FL (integrated the area under the
force
time curve)IR impulse of FR (integrated the area under the
force
time curve)
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Acknowledgements
The authors would like to express their gratitude tomembers of
the School of Engineering Systems and Insti-tute of Health and
Biomedical Innovation, particularlyDr James Smeathers, for their
valuable contribution andfeedback during the writing of this
manuscript. This studywas partially funded by ARC Discovery
Project(DP0345667), ARC Linkage (LP0455481), QUT StrategicLink with
Industry and IHBI Medical Device DomainGrants.
Appendix.
FAP antero-posterior forceFML medio-lateral forceFL long-axis
(of residual femur) forceFr resultant forceMAP moment about the
antero-posterior axisMML moment about the medio-lateral axisML
moment about the long-axisFAP, FAP+ the most positive and negative
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W.C.C. Lee et al. / Clinical Biomechanics 22 (2007) 665673
673
Kinetics of transfemoral amputees with osseointegrated fixation
performing common activities of daily
livingIntroductionMethodsParticipants and
prosthesesApparatusProtocolData processing
ResultsPatterns of forces and momentsLocal extremaImpulses
DiscussionConclusionsAcknowledgementsAppendixReferences