FUNCTIONAL, SIMULATIVE AND IMAGING APPROACHES TO … · Severe hip dysplasia is a common...
Transcript of FUNCTIONAL, SIMULATIVE AND IMAGING APPROACHES TO … · Severe hip dysplasia is a common...
Klinik für Kleintiere
Stiftung Tierärztliche Hochschule Hannover
FUNCTIONAL, SIMULATIVE AND IMAGING APPROACHES TO
EVALUATE THE OUTCOME AFTER TOTAL HIP REPLACEMENT IN
DOGS AND HUMANS
Habilitationsschrift
zur Erlangung
der Venia Legendi
an der Tierärztlichen Hochschule Hannover
Patrick Hans Wefstaedt
Hannover, im Dezember 2012
Tag der „nichtöffentlichen wissenschaftlichen Aussprache“: 17. Dezember 2012
Hiermit erkläre ich, Patrick Hans Wefstaedt, geboren am 17.04.1975, dass für
das Verfassen der vorliegenden Habilitationsschrift
“FUNCTIONAL, SIMULATIVE AND IMAGING APPROACHES TO EVALUATE THE
OUTCOME AFTER TOTAL HIP REPLACEMENT IN DOGS AND HUMANS“
folgende drei Aussagen zutreffen:
1. Ich habe die Arbeit ohne unerlaubte fremde Hilfe angefertigt.
2. Ich habe keine anderen als die von mir angegebenen Quellen und Hilfsmittel
benutzt.
3. Ich habe die den benutzten Werken wörtlich oder inhaltlich entnommenen Stellen
als solche kenntlich gemacht.
Hannover, im Dezember 2011
Patrick Hans Wefstaedt
„Falls Gott die Welt geschaffen hat, war seine Hauptsorge sicher nicht, sie so zu
machen, dass wir sie verstehen können.“
Albert Einstein
Contents
1 Preface .............................................................................................................. 7
2 Abbreviations ................................................................................................... 8
3 Introduction ...................................................................................................... 9
3.1 Functional analysis of the hind limb in dogs by means of the computerized gait
analysis .............................................................................................................. 9
3.1.1 Principles of computerized gait analysis .................................................... 9
3.1.2 Computerized gait analysis of the hind limb after total hip replacement and
surgical treatment of cranial cruciate ligament rupture ............................. 12
3.2 Total hip replacement and related bone remodeling processes ....................... 14
3.2.1 Bone remodeling processes in the human and canine periprosthetic femur:
Computerized simulation approaches ...................................................... 16
3.2.2 Bone remodeling processes in the periprosthetic femur: Imaging
approaches .............................................................................................. 17
4 List of Publications (contributing to the current work) ............................... 20
5 Results and Discussion ................................................................................. 23
5.1 Establishment and validation of a gait analysis laboratory ............................... 23
5.2 The computerized gait analysis as tool for quantitative assessment of lameness
in orthopaedic diseases of the canine hind limb ............................................... 27
5.3 Imaging analysis of bone remodeling processes in the canine and human
periprosthetic femur ......................................................................................... 32
5.4 Computerized simulations of bone remodeling processes in the canine and
human periprosthetic femur .............................................................................. 36
5.5 Establishment of a multibody simulation system for the determination of the
loading situation in the canine hip joint ............................................................. 40
6 Summary ......................................................................................................... 42
7 References ...................................................................................................... 45
Preface
7
1 Preface
Severe hip dysplasia is a common orthopaedic disease in humans as well as in dogs. In
this context total hip replacement (THR) represents a routine surgical treatment which is
performed in both species. However, long term success of THR still depends on many
factors. As one factor mainly influencing the outcome of THRs, an aseptic loosening of
the femoral component can occur. Current efforts to optimize THRs aim at a reduction of
stress shielding around the femoral stem in order to prevent periprosthetic bone loss and
implant loosening. The here presented work is an interdisciplinary collaboratory research
as most of the studies reported in here have been carried out together with human and
veterinary physicians, engineers and material scientists. Thus, the current work is to be
seen as a first step towards an integrated functional, imaging and simulative approach to
monitor limb function and morphologic changes in context with THRs.
Preface
8
2 Abbreviations
BFX biological fixation
BW body weight
CFX cemented fixation
CCLR cranial cruciate ligament rupture
DEXA dual-energy X-ray absorptiometry (DEXA)
FEA finite element analysis
FEM finite element method
GRF ground reaction force
GV greyscale value
HU Hounsfield unit
IFz vertical impulse force
MBS multibody simulation
MFz mean vertical force
N Newton
PVF peak vertical force
SI symmetry index
THR total hip replacement
TPLO tibial plateau levelling osteotomy
QCT quantitative computed tomography
Introduction
9
3 Introduction
3.1 Functional analysis of the hind limb in dogs by means of the computerized gait analysis
3.1.1 Principles of computerized gait analysis
The evaluation of the success of surgical or pharmacotherapeutic interventions in
orthopaedics is mainly based on the clinical lameness diagnosis and radiographic
examinations. In this context even with long term experience of the operating examiner
no sure localisation and quantification of movement disorders is possible (WAXMAN et
al. 2008). Although the classification of lameness on the basis of its severity is
standardized in many parts (BRUNNBERG 1999), it still represents a subjective process
(OFF and MATIS 1997a, 1997b). In particular, low-grade lameness is difficult to be
diagnosed and lameness assessment can be different between investigators. Therefore,
clinical lameness diagnosis does not allow for an evaluation of treatment success of
surgical interventions by a quantitative assessment of the gait pattern (OFF and MATIS
1997a, 1997b; WAXMAN et al. 2008). In order to obtain objective statements about the
gait of patients, computerized kinetic and kinematic measurements are carried out with
increasing amount (BATES et al. 1983; CHAO et al. 1983; NILSON and
THORSTENSON 1989; DE CAMP 1997; UNKEL-MOHRMANN 1999; BERTRAM et al.
2000; KAPATKIN et al. 2007). In kinematic studies, a description of motion without
consideration of the occurring forces and masses is possible. Among other parameters
kinematic analyses provide joint angle-time curves which describe for example the
Introduction
10
extension and flexion of a specific joint (ALLEN et al. 1994). Kinematic analyses are
carried out by means of special markers positioned on defined anatomic landmarks of
the patient´s body. Markers are either tracked by high-speed infrared or video cameras
and the motion data is processed by special computer programs (OFF and MATIS
1997b; KIM et al. 2008). In veterinary medicine, kinematic studies are mainly used for
the objective evaluation of orthopaedic disorders and the follow up control of surgical
interventions (BENNETT et al. 1996; DE CAMP et al. 1996, LEE et al. 2007). In contrast
to conventional lameness diagnosis, computerized gait analysis allows an objective
assessment of kinematic gait parameters and is capable of detecting even small
changes in joint angles.
In kinetic studies the occurring ground reaction forces during gait (DALIN and
JEFFCOTT 1985) are measured using instrumented treadmills or force plates (BELLI et
al. 2001; BREBNER et al. 2006). In addition to a vertical ground reaction force,
craniocaudal and mediolateral forces can be recorded. For a better comparison of data
between dogs of different body mass, a translation of the occurring forces in Newton (N)
to percentage of body weight (% BW) is carried out (CHAO et al. 1983; OFF 1997;
BOCKSTAHLER et al. 2005). One disadvantage of the measurement of ground reaction
forces is the limited size of the force plate making it difficult for the dog to hit the plate
with the correct limb (BELLI et al. 2001). Furthermore a high number of passes over the
force plate is necessary to ensure that a nearly constant gait speed of the dog is
maintained. Extensive examination time and a high variability of the measured values
due to the different gait speeds are the result (BREBNER et al. 2006). The
measurement of ground reaction forces in veterinary medicine using instrumented
Introduction
11
treadmills has been described by various authors (BAETZNER 1996; KOSFELD 1996;
OFF and MATIS 1997a, b; BOCKSTAHLER et al. 2005). One major advantage of
treadmill investigations is the selectable constant treadmill speed. In addition, treadmills
with four integrated force plates have been described to allow the measurement of
vertical ground reaction forces of all four limbs during gait (OFF and MATIS 1997a, b;
BOCKSTAHLER et al. 2005).
In summary, instrumented treadmills reveal three key benefits for the computer-based
kinematic and kinetic study of orthopedic patients: less bias of the examiner in the
evaluation of limb function, enhanced perception of limb dysfunction and a very large
capacity for data collection (DE CAMP 1997).
In early 2008 a gait analysis laboratory was installed at the Small Animal Hospital of the
University of Veterinary Medicine Hannover, Foundation. The central component of the
gait analysis laboratory is a four belt treadmill with four integrated, independently
working force plates. With the treadmill it is possible to detect vertical as well as
craniocaudal and mediolateral ground reaction forces of each limb separately while the
dog is walking. WHITE et al. (1998) reported that the gait of humans on treadmill and
runway differs slightly but significantly from each other. Comparative gait analyses of
dogs on treadmills and force plates have not yet been conducted. However, KASPER
and ZOHMANN (2005) described that weight bearing of the hind limbs of the dog is
reduced due to movement of the treadmill and the resulting decreased necessity of the
hind limb to participate in the acceleration process of the body. With the studies of
BÖDDEKER et al. (2010) and DRÜEN et al. (2010), the question was answered whether
the gait pattern and the ground reaction forces of the hind limb of dogs while walking on
Introduction
12
a novel instrumented treadmill differs fundamentally from the measurements performed
during passage over a force plate.
3.1.2 Computerized gait analysis of the hind limb after total hip replacement and surgical treatment of cranial cruciate ligament rupture
Surgical treatment of severe hip dysplasia in larger dogs can be carried out by total hip
replacement (THR) as the method of choice. In veterinary medicine currently a broad
range of different total hip prostheses is available. In addition to screwed systems mainly
cemented or uncemented prostheses are currently implanted. So far (2011) it is
unknown whether one of the last mentioned implant types reveals an advantage with
regard to the short and long term functional outcome of implanted dogs. Although many
investigations of the gait of dogs with hip dysplasia as well as before and/or after THR,
have been carried out (HOZACK et al. 1993; BENETT et al. 1996; SCHAEFER et al.
1998; POY et al. 2000; KENNEDY et al. 2003; BRADEN et al. 2004; MADORE et al.
2007; LASCELLES et al. 2010), so far no assessment of the lameness improvement
after cemented and cementless THR by means of the kinetic and kinematic gait analysis
has been carried out. However, MANLEY et al. (1990) performed force plate analyses
and described an earlier return to normal weight bearing in experimental dogs implanted
with a cemented THR system in comparison to a group treated with uncemented
implants. Furthermore, IWATA et al. (2008) analysed the outcome of dogs after
cemented and cementless THR by means of radiographic analyses and owner
interviews but found no significant differences between the groups. Therefore, aim of the
Introduction
13
study of DRÜEN et al. (2012) was to analyse the lameness progression in dogs within a
period of 4 months after surgical treatment by either a cemented Biomedtrix CFX™
(cemented fixation) or uncemented Biomedtrix BFX™ (biological fixation) prosthesis
system. In addition to hip dysplasia, in dogs cranial cruciate ligament rupture (CCLR) is
another very common orthopaedic disease of the hind limb (JOHNSON et al. 1989;
INNES et al. 2000). Similar to the treatment of severe hip dysplasia, also for the surgical
repair of the cranial cruciate ligament rupture various methods are described. These can
roughly be classified as intra-capsular ligament replacements, extra-capsular suture
techniques, neutralizing dynamic techniques and modified methods. The principle of all
of these techniques is to eliminate the cranial tibial thrust in the stance phase. However,
a gold standard for the surgical treatment of the ruptured ligament has not been defined
yet. Among the wide variety of the different surgical methods the tibial plateau levelling
osteotomy (TPLO) (COOK et al. 2010; FITZPATRICK and SOLANO 2010) and the
lateral suture stabilization of the stifle joint (ERTELT and FEHR 2009) are two very
commonly used techniques. Both techniques comprise advantages and disadvantages.
The TPLO seems to be superior for cranial cruciate surgery in active larger dogs
(STAUFFER et al. 2006) and is suggested to result in a quicker recovery after surgery
and less osteophyte formation (PRIDDY et al. 2003; RAYWARD et al. 2004;
BOUDRIEAU 2009). In contrast, the imbrication method might be of advantage with
regard to a shorter time for surgery, less technical demands and a lower complication
rate. However, so far there is no objective study comparing the lameness improvement
in cranial cruciate deficient dogs treated with TPLO and an extra-capsular stabilization
technique (CONZEMIUS et al. 2005).
Introduction
14
As described above, computer assisted kinetic and kinematic gait analyses are suitable
to objectively assess post-operative lameness improvement after treatment with different
surgical techniques (DE CAMP et al. 1997; UNKEL-MOHRMANN et al. 1999;
BERTRAM et al. 2000). Thus, the purpose of the studies of DRÜEN et al. (2012) and
BÖDDEKER et al. (2011) was to objectively analyse changes in lameness reduction in
dogs over a period of 4 months after cemented and cementless THR as well as in dogs
with CCLR treated by tibial plateau levelling osteotomy and capsular-fascial imbrication
method (ALLGOEWER et al. 2000). Therefore, kinematic and kinetic gait analyses on an
instrumented treadmill were carried out.
3.2 Total hip replacement and related bone remodeling processes
Hip dysplasia is a severe disabling disease in dogs and humans. In this context total hip
replacement with cemented or uncemented implants provides an excellent return to
function (BERGH et al. 2004a, b; NI et al. 2010) by restoring an adequate range of
motion of the affected hip joint and transferring load from the acetabulum (TONI et al.
1996). Among other factors, the long-term result of total hip replacements depends on
the alignment of the prosthetic stem within the femoral canal. As one reason for implant
failure aseptic loosening of the prosthetic stem or cup can occur. Aseptic loosening is
typically the result of an unphysiological load transmission from the prosthetic stem to
the femur which leads to bone remodeling processes and can finally end up in implant
loosening and the necessity for revision surgery (STAUFFER et al. 1982; EDWARDS et
al. 1997). In case of uncemented total hip replacement it has been described for humans
Introduction
15
that even poorly aligned prosthetic stems can achieve an adequate initial stability of the
implant within the femoral canal (PANISELLO et al. 2006). However, secondary long
term implant stability by progressive osseo-integration into the implant surface
(SUMNER and GALANTE 1992; TONI et al. 1996) may be altered in these cases as
malalignment of the prosthesis goes along with a process called stress shielding. This
process is characterized by loss of bone density due to resorptive bone remodeling
(TURNER et al. 1997) as a result of reduced mechanical stress in some areas of the
periprosthetic bone (WEINANS et al. 1993; TURNER et al. 1997). Especially the region
of the proximal femur is mostly affected by stress shielding processes as most of the
load is transferred from the implant to the femur in this region (OH and HARRIS 1978;
LEWIS et al. 1984; HUISKES 1987; BERGH et al. 2004a, b). In contrast, physiological
loading conditions result in a steady state equilibrium between bone formation and bone
loss (HUISKES et al. 1987; ENGH et al. 1988; HUISKES et al. 1989; TONI et al. 1996).
Stress shielding and related aseptic loosening can occur both in cemented and
uncemented prosthesis, whereas the extent is milder in cemented systems due to a
higher stem rigidity of this implant system (HUISKES 1990). Strategies to improve the
long-term result of THR aim at preventing an aseptic loosening of the prosthesis by
means of improved prosthesis design and an optimized alignment of the prosthesis
within the femoral canal (RHINELANDER et al. 1979).
Introduction
16
3.2.1 Bone remodeling processes in the human and canine periprosthetic femur: Computerized simulation approaches
As mentioned above, aseptic loosening of prostheses can occur as a result of bone
remodeling due to stress shielding (SUMNER and GALANTE 1992). Finite element
analyses (FEA) have been established as a valuable method to analyse stress shielding
processes by examining the load situation in the periprosthetic bone after THR. FEA has
been used in several studies to simulate femoral bone remodeling processes in humans
as well as in dogs (WEINANS et al. 1993; SHAHAR et al. 2003; BEHRENS et al. 2006).
Compared to clinical or radiographical observations FEA is less time and cost intensive
characterising it as a patient-friendly procedure which can be used in pre-clinical studies.
Bone remodeling processes can be realistically simulated by FEA if the load situation as
well as the physiological boundary conditions, the muscle forces and an appropriate
bone adaption model are taken into account. Furthermore, the mechanical properties of
the bone and the implant materials have to be considered. Morlock et al. (2001)
described, that a walking gait is the usual dynamic activity of human patients after THR.
However, this whole dynamic load simulation was yet too complex to be considered in
an FEA. Thus, to analyse the strain distribution or bone remodeling after THR usually
only one (NACKENHORST 1997; TAYLOR et al. 2004; EBBECKE et al. 2005;
BEHRENS et al. 2008) or a maximum of three (HUSIKES and VAN RIETBERGEN
1995; FERNANDES et al. 2002; TAI et al. 2003) static load situation(s) of the gait cycle
were used for the FEA so far. In this context the question arises whether the loading
situation of a complete gait cycle can be represented in an FEA based simulation of
Introduction
17
periprosthetic bone remodeling processes. Therefore the studies of BEHRENS et al.
(2009a, b) aim at FEA based investigations of bone remodeling processes in the canine
and human periprosthetic femur under static and dynamic loading conditions.
For the optimization of artificial components of the hip joint, a detailed knowledge of the
physiological loading situation in the canine hip joint is crucial. Multi-body simulations
(MBS) can be of great value to compute forces and moments in the hip joint during
different movements. In this context, MBS are able to provide information about the load
situation in a joint without the necessity of in vivo experiments by means of instrumented
implants (BERGMANN et al. 1984; BERGMANN 1997). Furthermore, MBS can be
combined with finite element analysis (BEHRENS et al. 2006; BEHRENS et al. 2008) in
order to identify areas of high loadings in the hip joint. The gained information about the
loading situation in the hip joint can help to optimize the tribological pairing of prostheses
(LIU et al. 2003; UDOFIA et al. 2004). Additionally, MBS can help to analyse the
influence of the stem position within the femoral canal with regard to an optimal load
transfer from the implant to periprosthetic bone. To provide a realistic MBS model for the
calculation of the acting forces and moments in the canine hip joint during gait, the
model has to be validated first by measured ground reaction force data.
3.2.2 Bone remodeling processes in the periprosthetic femur: Imaging approaches
Modern imaging modalities such as computed tomography (CT) or dual x-ray
absorptiometry (DEXA) are powerful tools to display the morphological correlation of
Introduction
18
bone remodeling processes. DEXA is known as a reliable imaging modality for the
evaluation of bone remodeling processes after THR using different stem designs
(ALBANESE et al. 2006; PANISELLO et al. 2006). This imaging method is based on the
principle that two X-ray sources of slightly different energy are used for the scan at the
same time. Accordingly, for tissues with different densities, two different attenuation
values for the two used X-ray energies are obtained which allows for the calculation of
areal density values (kg/ m²). In contrast, by means of CT for each volume element an
accurate gray scale value in Hounsfield units (HU) is assigned. To obtain e.g. bone
mineral density values (mg Hydroxylapatit/ mm3) from conventional CT scans, prior
calibration with test samples of known density is necessary. In addition to conventional
CT, quantitative computed tomography (QCT) allows for the determination of the
physical density of a voxel directly during the scan.
In human medicine, DEXA analyses of bone remodeling processes have been widely
used in the past 15 years (ENGH et al. 1992; KILGUS et al. 1993; NISHII et al. 1997;
MULLER et al. 2005) to determine the bone mineral density in 7 different zones (Gruen
zones) of the periprosthetic femur (GRUEN et al. 1979; PANISELLO et al. 2006;
SPEIRS et al. 2007; FALEZ et al. 2008). In this context the study of STUKENBORG-
COLSMAN et al. (2012) will be introduced as an example how DEXA investigations can
be used in human patients for the acquisition of bone remodeling data before as well as
1 week, 6 months and 12 months after implantation of a commonly used total hip
replacement system (Bicontact® AESCULAP AG, Tuttlingen, Germany). As DEXA
investigation facilities are not widely available in veterinary medicine, the quantitative
evaluation of the mean radiographic bone grayscale value (bone contrast) around the
Introduction
19
prosthetic stem would be of benefit using conventional ventrodorsal radiographs of the
canine pelvic limb. Hypothetically the grayscale value (GV) represents the regional
adaptive bone remodeling of each zone around the stem after total hip replacement in
dogs.
Publications
20
4 List of Publications (contributing to the current work)
I. BEHRENS, B.A., I. NOLTE, P. WEFSTAEDT, C. STUKENBORG-COLSMAN and A.
BOUGUECHA (2009a):
Numerical investigations on the strain-adaptive bone remodeling in the periprosthetic
femur: influence of the boundary conditions.
Biomed Eng Online. 8, 7
II. BEHRENS, B.A., A. BOUGUECHA, C. STUKENBORG-COLSMAN, P. WEFSTAEDT
and I. NOLTE (2009b):
Numerische Untersuchungen zum beanspruchungsadaptiven Knochenumbau im
periprosthetischen caninen Femur
Berl Munch Tierarztl Wochenschr. 122, 391-397
III. HELMS, G., B.A. BEHRENS, M. STOLORZ, P. WEFSTAEDT and I. NOLTE (2009):
Multi-body simulation of a canine hind limb: model development, experimental validation
and calculation of ground reaction forces.
Biomed Eng Online. 8, 36
IV. DRÜEN, S., J. BÖDDEKER, I. NOLTE and P. WEFSTAEDT (2010):
Bodenreaktionskräfte der caninen Hintergliedmaße: Gibt es Unterschiede beim Gang
auf Laufband und Kraftmessplatte?
Publications
21
Berl Munch Tierarztl Wochenschr. 123, 339-345
V. BÖDDEKER, J., S. DRÜEN, I. NOLTE and P. WEFSTAEDT (2010):
Vergleichende Bewegungsanalyse der caninen Hintergliedmaße beim Gang auf
Kraftmessplatte und Laufband.
Berl Munch Tierarztl Wochenschr. 123, 431-439
VI. MOSTAFA, A.A., I. NOLTE, S. DRÜEN and P. WEFSTAEDT (2011):
Radiographic evaluation of early periprosthetic femoral bone contrast and prosthetic
stem alignment after uncemented and cemented total hip prosthesis in dogs.
Vet Surg. Epub 2011 Dec 20; Vet Surg. 2012 41, 69-77
VII. BÖDDEKER, J., S. DRÜEN, A. MEYER-LINDENBERG, M. FEHR, I. NOLTE
and P. WEFSTAEDT (2011):
Computer-assisted gait analysis of the dog - Comparison of two surgical techniques for
the ruptured cranial cruciate ligament.
Vet Comp Orthop Traumatol. Epub 2011 Nov 22; Vet Comp Orthop Traumatol. 2012 25,
11-21
VIII. DRÜEN, S., J. BÖDDEKER, A. MEYER-LINDENBERG, M. FEHR, I. NOLTE and P.
WEFSTAEDT (2012):
Computer-based gait analysis of dogs - Evaluation of kinetic and kinematic parameters
after cemented and uncemented total hip replacement
Publications
22
Vet Comp Orthop Traumatol. 25, 375-384
IX. STUKENBORG-COLSMAN C.M., A. VON DER HAAR-TRAN, H. WINDHAGEN, A.
BOUGUECHA, P. WEFSTAEDT and M. LERCH (2012):
Bone remodeling around a cementless THA stem: a prospective dual-energy X-ray
absorptiometry study.
Hip Int. 22,166-171
Results and Discussion
23
5 Results and Discussion
5.1 Establishment and validation of a gait analysis laboratory
IV. DRÜEN, S., J. BÖDDEKER, I. NOLTE and P. WEFSTAEDT (2010):
Bodenreaktionskräfte der caninen Hintergliedmaße: Gibt es Unterschiede beim Gang
auf Laufband und Kraftmessplatte?
Berl Munch Tierarztl Wochenschr. 123, 339-345
V. BÖDDEKER, J., S. DRÜEN, I. NOLTE and P. WEFSTAEDT (2010):
Vergleichende Bewegungsanalyse der caninen Hintergliedmaße beim Gang auf
Kraftmessplatte und Laufband.
Berl Munch Tierarztl Wochenschr. 123, 431-439
In early 2008 a gait analysis laboratory was installed at the Small Animal Hospital of the
University of Veterinary Medicine Hannover, Foundation. The central component of the
gait analysis laboratory is a four belt treadmill (Bertec Corporation, Columbus, Ohio,
USA) with four integrated, independently working force plates. The treadmill allows for
the detection of vertical as well as of craniocaudal and mediolateral ground reaction
forces of each limb separately while the dog is walking. WHITE et al. (1998) reported
that the gait in humans on treadmill and runway differs slightly but significantly from each
other. Comparative gait analyses of dogs on treadmills and force plates have not yet
been conducted. KASPER and ZOHMANN (2005) however described, that weight
Results and Discussion
24
bearing of the hind limbs of the dog is reduced due to movement of the treadmill and the
resulting decreased necessity of the hind limb to participate in the acceleration process
of the body. With the studies of BÖDDEKER et al. (2010) and DRÜEN et al. (2010), the
question was targeted whether the gait pattern and the ground reaction forces of the
hind limb of dogs while walking on a novel instrumented treadmill differ fundamentally
from the measurements performed during passage over a force plate.
Main results of the study of DRÜEN et al. (2010) were that vertical ground reaction
forces of 60-90% BW of the hind limb measured on the treadmill and force plate are
comparable to values from other studies (JEVENS et al. 1993; RENBERG et al. 1999;
RUMPH et al. 1999). However, selected running speed of the dogs was higher in these
studies. UNKEL-MOHRMANN (1999) and BOCKSTAHLER et al. (2005) found
significantly lower peak vertical forces around the 40% BW for the hind limb during gait
on the treadmill. BOCKSTAHLER et al. (2005) explained the differences in the
appearance of forces between the different studies with different selected gait speeds. In
the study of DRÜEN et al. (2010) slightly but not significantly higher vertical ground
reaction forces were measured on the force plate in comparison to treadmill
measurements. These findings are in agreement with WHITE et al. (1998) who
described an energy transfer from the treadmill to the subjects walking on the treadmill
which results, in turn, in a reduction in the vertical ground reaction force values. As one
main result of the study of DRÜEN et al. (2010) no clear difference between the vertical
ground reaction forces on force plate and treadmill could be demonstrated. In contrast to
the vertical ground reaction forces mediolateral and craniocaudal ground reaction forces
showed no good agreement between force plate and treadmill. In addition to the
Results and Discussion
25
mentioned different weight bearing characteristics of the dogs also changes in kinematic
parameters have to be considered under the two measurement conditions. Therefore,
the study of BÖDDEKER et al. (2010) compared the gait of the dogs, in terms of joint
angles and certain parameters of the gait cycle of the hind limb, when walking on the
treadmill and force plate. Regarding the calculated maximum values for the extension
and flexion of the stifle and hock joint as well as abduction and adduction of the hip joint,
no significant differences were found between force plate and treadmill. However, flexion
and extension angles of the hip joint were found to differ significantly between both
conditions. The values measured in the study of BÖDDEKER et al. (2010) are
comparable with those of other studies (FEENEY et al. 2007). DE CAMP et al. (1993),
HOTTINGER et al. (1996) and SCHAEFER et al. (1998) didn’t analyse an explicit
minimum and maximum displacement of the joints, however, the joint angle curves
obtained in these studies are in accordance with the study of BÖDDEKER et al. (2010).
Differences of the kinematic data to previous studies carried out by BAETZNER (1996)
and KOSFELD (1996) can be due to the different skeletal architecture of the analysed
breeds (MANN et al. 1988). Another important factor that might have influenced the
kinematic results is the different gait speed in the mentioned studies in comparison to
the study of BÖDDEKER et al. (2010). Thus, even a slightly higher gait speed results in
a greater range of motion and larger flexion and extension angles of the joints
(HOTTINGER et al. 1996). Further factors influencing the kinematic data can be e.g.
slightly differently positioned markers or marker displacements caused by skin, muscle
or tendon motion (ALLEN et al. 1994). Treadmills offer a well established method to
perform gait analyses in dogs although it is clearly evident that the motion on the
Results and Discussion
26
treadmill is different from that on a normal surface (BOCKSTAHLER et al. 2007). The
study of BÖDDEKER et al. (2010) showed that the kinematic gait analyses of the canine
hind limb on force plate and treadmill show similar characteristics. However, significant
differences of individual parameters exist between the two measurement conditions.
One other limitation of the study is an only moderate correlation of the data between
treadmill and force plate. One reason for the demonstrated differences can be explained
by the reduced need for the involvement of the hind limb in the dogs´ forward movement
on the treadmill. Due to the belt movement on the treadmill the hind limb is relieved
(KASPER and ZOHMANN 2005), which in turn can result in variations of the measured
joint angles between treadmill and force plate. Another explanation for the different gait
behaviour might be due to the belt movement which might lead to an increased caution
of the dogs and thus less space-consuming steps. A direct similarity of kinematic data of
the hind limb of dogs between treadmill and force plate measurements could not be
demonstrated with the obtained data. Nevertheless, the study of BÖDDEKER et al.
(2010) provides important insights for the comparative analysis and evaluation of motion
studies that were conducted under these different conditions.
Gait analysis on the treadmill present, as shown by the studies of DRÜEN et al. (2010)
and BÖDDEKER et al. (2010), an advantageous alternative over force platform
analyses. Treadmill speed is individually and constantly adjustable to the subjects
comfort speed which allows a time-saving data acquisition with low variability and thus a
better overall comparability of the evaluated data. In contrast to force plate
measurements, all four limbs can be recorded simultaneously. In clinical studies, gait
analysis by means of instrumented treadmills can therefore be increasingly applied to
Results and Discussion
27
analyse gait characteristics in relation with orthopaedic diseases.
5.2 The computerized gait analysis as tool for quantitative assessment of lameness in orthopaedic diseases of the canine hind limb
VII. BÖDDEKER, J., S. DRÜEN, A. MEYER-LINDENBERG, M. FEHR, I. NOLTE
and P. WEFSTAEDT (2011):
Computer-assisted gait analysis of the dog - Comparison of two surgical techniques for
the ruptured cranial cruciate ligament.
Vet Comp Orthop Traumatol. Epub 2011 Nov 22; Vet Comp Orthop Traumatol. 2012 25,
11-21
VIII. DRÜEN, S., J. BÖDDEKER, A. MEYER-LINDENBERG, M. FEHR, I. NOLTE and P.
WEFSTAEDT (2012):
Computer-based gait analysis of dogs - Evaluation of kinetic and kinematic parameters
after cemented and uncemented total hip replacement
Vet Comp Orthop Traumatol. 25, 375-384
Aim of the studies of DRÜEN et al. (2012) and BÖDDEKER et al. (2011) was to evaluate
differences in the lameness progression of dogs within a four month period after
cemented and cementless total hip replacement as well as of dogs with CCLR treated by
TPLO and a capsular-fascial imbrication method.
To analyse the ground reaction forces in vertical direction, a symmetry index was used
in both studies for the comparison of the loading conditions of the affected and
Results and Discussion
28
contralateral extremity (BUDSBERG et al. 1993). This index is suitable only for dogs
with unilateral disease. To make sure that the symmetry index represents the correct
lameness condition of the dog, it is important that the contralateral limb is not worsening
over the examination time as subclinical contralateral orthopaedic disease may affect
the results of the symmetry index.
In case of the study of DRÜEN et al. (2012) all dogs, except two, suffered from bilateral
hip dysplasia. Also, in the study of BÖDDEKER et al. (2011) a worsening of the joint
status of the contralateral limb can not be excluded completely although no changes in
joint morphology could be found over the examination period. To ensure that the
lameness status was not influenced by disease onset or progression in the contralateral
limb, in addition to the symmetry index, weight bearing characteristics of only the affected
limbs were analyzed in both studies.
In the study of DRÜEN et al. (2012), prior to surgery symmetry indices for peak vertical
forces (PVF), mean vertical forces (MFz) and the vertical impulses (IFz) of over six
percent indicated lameness in all dogs of both groups. Four months after surgery,
symmetry indices were under six percent in both groups which indicates an almost
normal limb use. However, only in the BFX group the difference between prior to surgery
and four months after surgery was found to be statistically significant. These findings
might be due to a higher lameness level in the BFX group than in the CFX group prior to
surgery and a high variance in the kinetic data of both groups. Other factors explaining
the differences in lameness reduction in both groups could have been changes in the
bone implant interface, periosteal reactions or bone lysis which might have occurred in
Results and Discussion
29
both groups to a different extent. However, changes in these parameters could not be
observed by means of the radiographic analyses.
As the results of BÖDDEKER et al. (2011) show, a faster lameness reduction can be
observed in dogs of the TPLO group in comparison to the dogs of the imbrication group
within a period of four months after surgery. In the study of BÖDDEKER et al. (2011) the
medial meniscus was partially resected, as the study of ALT (2000) described that even
a partial resection of an intact medial meniscus has no negative effect on the therapeutic
outcome observed 6 months after CCLR surgery. However, advantages and
disadvantages of partial medial meniscectomy are discussed controversially and still
have to be investigated further as e.g. one other study reported that the load transfer
from the femur to the tibia is significantly altered in case of partial meniscectomy and
may finally result in degenerative joint disease (THIEMAN et al. 2010). Lameness
improvement analysed by means of the symmetry indices of the vertical ground reaction
forces was more obvious in the TPLO-group although dogs of the imbrication group
started with a more severe lameness prior to surgery. One explanation for the different
lameness levels in both groups could be that more dogs of the imbrication group had a
complete CCLR prior to surgery which is most likely to result in a higher degree of joint
pain and lameness, respectively. Another interesting finding of the study of BÖDDEKER
et al. (2011) was an increased symmetry index 4 days after surgery in the imbrication
group which might be the result of a more severe traumatization of the the joint capsule
due to the suturing technique in this group.
Kinematic gait analyses have been demonstrated to be of value for the quantitative
Results and Discussion
30
evaluation of limb movements (DE CAMP et al. 1993). The results of the studies of
DRÜEN et al. (2012) and BÖDDEKER et al. (2011) suggest that using kinematic
analyses of the lameness improvement in the hind limb of a heterogenous pool of dogs
is so far of limited informative value and therefore needs further improvement. In this
context it has to be stated that using dogs of different anatomy as subjects is no ideal
condition for kinematic analyses. However a heterogeneous pool of subjects is more
representative for the clinical situation than a pool of subjects represented by one single
breed.
Kinematic data in the study of DRÜEN et al. (2012) showed only a slight improvement in
the dogs of both groups although kinetic parameters clearly improved during the
observation period of 4 months after surgery. An explanation for the nearly unchanged
kinematic parameters in the time course after THR might be that dogs with different
grades of hip dysplasia usually have more difficulties while getting up or sitting down
whereas kinematic parameters during normal gait might be affected only in case of a
severe lameness. Therefore in future kinematic analyses in context with THR,
investigations of other movements like a getting up and sitting down movement should
be considered. In contrast to the findings of DRÜEN et al. (2012), in the study of
BÖDDEKER et al. (2011) changes in some of the analysed kinematic parameters could
be observed between prior to surgery and four months after surgery. Whereas the TPLO
group showed a significant increase in the flexion and extension angles of the affected
stifle joint between first and final gait analysis, no significant increase of these joint
angles could be observed in case of the imbrication group. It can be assumed that the
lesser improvement of these parameters in the imbrication group might be related to the
Results and Discussion
31
surgical technique which tightens the joint capsule and the surrounding tissue.
In summary, the studies of DRÜEN et al. (2012) and BÖDDEKER et al. (2011) were able
to show that kinematic and kinetic analyses are capable to analyse the lameness
improvement after THR with different types of implants and treatment of CCLR by two
different surgical techniques. With regard to the kinetic analyses, a similar improvement
of vertical GRF in between 4 months after cemented as well as uncemented THR but no
significant differences between the groups could be demonstrated by DRÜEN et al.
(2012). Also in case of the comparison between TPLO and imbrication treatment of
CCLRs most of the examined parameters were not significantly different between the
groups. However, slight differences could be observed as the TPLO group showed a
more symmetrical weight bearing of the hind limbs four months after surgery than the
imbrication group. For both of the mentioned studies it has to be kept in mind that only
the short-term improvement of kinetic and kinematic parameters was analysed.
Therefore, future studies are necessary to fully elucidate the long term outcome after the
different surgical procedures. As a conclusion it could be stated that decision making
whether one or the other surgical treatment is chosen for the treatment of either hip
dysplasia or CCLR should be carried out with regard to the individual case and not only
on the basis of the described findings. In the follow up of surgical treatments especially
kinetic analyses can be of great help to quantify worsening or improvement of hind limb
lameness.
Results and Discussion
32
5.3 Imaging analysis of bone remodeling processes in the canine and human periprosthetic femur
VI. MOSTAFA, A.A., I. NOLTE, S. DRÜEN and P. WEFSTAEDT (2011):
Radiographic evaluation of early periprosthetic femoral bone contrast and prosthetic
stem alignment after uncemented and cemented total hip prosthesis in dogs.
Vet Surg. Epub 2011 Dec 20; Vet Surg. 2012 41, 69-77
IX. STUKENBORG-COLSMAN C.M., A. VON DER HAAR-TRAN, H. WINDHAGEN, A.
BOUGUECHA, P. WEFSTAEDT and M. LERCH (2012):
Bone remodeling around a cementless THA stem: a prospective dual-energy X-ray
absorptiometry study.
Hip Int. 22,166-171
Stress transfer between stem and periprosthetic bone occurs as a combination of axial,
bending, and torsional loads (HUISKES et al. 1989; HUISKES 1990). Factors influencing
the location and the extent of stress transfer from the femoral stem to the periprosthetic
bone are the geometry and the material properties of the implant as well as of the
periprosthetic bone (GIBBONS et al. 2001). Furthermore implant positioning, the quality
of the initial fixation of the stem within the femoral canal as well as the immediate post
operative loading amount and direction in the tribological pairing of the artificial hip joint
can have an effect on the short- and long term success of THR (ENGH et al. 1987;
Results and Discussion
33
ENGH and BOBYN 1988; HUISKES et al. 1989; HUISKES 1990).
At present dual energy x-ray absorptiometry (DEXA) represents the gold standard for
the evaluation of periprosthetic bone remodeling processes after THR (ENGH et al.
1992; MULLER et al. 2005; PANISELLO et al. 2006). In the study of STUKENBORG-
COLSMAN et al. (2012) DEXA analyses were used to describe remodeling processes in
the periprosthetic femur before and 1 week, 6 months and 12 months after implantation
of a common uncemented THR system (Bicontact® AESCULAP AG, Tuttlingen,
Germany). As the results show, a significant decrease in the bone mineral density
occurs mainly in the proximal region of the calcar and the trochanter major of the femur
within the first 6 months after surgery. In the second half of the investigation period
STUKENBORG-COLSMAN et al. (2012) could show an adaptive increase of the bone
mineral density in the mentioned regions. The results of STUKENBORG-COLSMAN et
al. (2012) suggest that the load transfer from prosthesis to the periprosthetic bone is
located mainly in the proximal regions of the femur.
In veterinary medicine DEXA facilities are not widely available. Therefore, one aim of the
study of MOSTAFA et al. (2011) was to evaluate a radiological image processing
software for the determination of the mean periprosthetic radiographic grayscale value
after THR. These grayscale values measured from digitized standard canine pelvic
radiographs might be easy obtainable parameters to investigate bone remodeling
processes after THR in dogs.
As a conclusion from the results of MOSTAFA et al. (2011) cemented total hip
replacement results in a more dense periprosthetic bone contrast and better stem
Results and Discussion
34
alignment within the femoral canal 4 months after surgery than uncemented implants. To
evaluate bone remodeling processes in the canine periprosthetic femur MOSTAFA et al.
(2011) analysed five Gruen zones instead of the 7 widely accepted Gruen zones used in
DEXA analyses in humans (GRUEN et al. 1979; PANISELLO et al. 2006), as the dog
femur is of shorter length than in humans. Furthermore, the results of MOSTAFA et al.
(2011) suggest that the geometry and material properties of the prosthesis as well as the
alignment of the implant within the femoral canal have a strong impact on the stress
transfer from the prosthetic stem to the periprosthetic bone. In this context cemented
prostheses were found to show a better alignment of the femoral stem 4 months after
surgery than uncemented prostheses. In comparison to the immediate post surgery
alignment a 14% increase of varus-aligned femoral stems was measured 4 months after
cemented THR in comparison to the uncemented design with a 50% increase of varus-
aligned femoral components. The increased incidence of varus-aligned femoral stems
especially in the uncemented THR group might be due to a relatively poor initial stability
of the stem within the femoral canal which favours micromotion or even secondary
subsidence of the implant. A certain degree of initial instability of the uncemented
implant is also suggested by the results of MOSTAFA et al. (2011). In this context ENGH
and BOBYN (1988) and GLASSMANN et al. (2006) described that varus or valgus
alignment of the femoral prosthesis may result in stress shielding processes. These
processes may further lead to resorptive bone remodeling and implant loosening (ENGH
and BOBYN 1988; GILL et al. 1999). From these findings as well as from the results of
MOSTAFA et al. (2011) it can be concluded that the long term success of THR in dogs
and humans is dependent on a good alignment and initial stability of the prosthesis as
Results and Discussion
35
these factors are crucial to stimulate secondary adaptive remodeling in the periprosthetic
bone. From the results of other studies in humans (ROSENTHALL et al. 2000) and from
the results of the study of MOSTAFA et al (2011) it can be concluded that different
implant geometries can have varying effects on bone adaption as well as the long term
implant alignment in the dog.
For uncemented THRs in dogs MOSTAFA et al. (2011) were able to demonstrate a
reduction in bone density in the zone of the greater trochanter but in no other of the
examined zones 4 months after surgery. Stress shielding mechanisms due to initial
malalignment or a poor primary stability of the prosthesis are most likely the cause of
this adaptive bone remodeling process. In contrast to the findings of MOSTAFA et al.
(2011) studies in human found stress shielding related significant periprosthetic bone
losses in the region of the trochanter major as well as in the calcar region of the femur
(THEIS and BEADEL 2003; PANISELLO et al. 2006; TAPANINEN et al. 2010). The
demonstrated differences in periprosthetic bone remodeling processes in the human and
dog femur may be related to different load patterns on prosthetic hip joints (BERGMANN
et al. 1984) in these species.
In contrast to their findings concerning uncemented prosthesis MOSTAFA et al. (2011)
could show that bone contrast in the periprosthetic bone after cemented THR remained
statistically unchanged in all examined zones 4 months after surgery. These results are
in accordance with the studies of WAN et al. (1999) and NI et al. (2010) who
demonstrated a stable bone implant interface with improved adaptive bone remodeling
after cemented THR. This was explained by the high rigidity of the cemented stems
within the femoral canal and the resulting reduced stress shielding processes of the
Results and Discussion
36
periprosthetic femur (WAN et al. 1999; NI et al. 2010). However, periprosthetic bone
remodeling and aseptic loosening are mainly long term complications in cemented THR
in dogs (BERGH et al. 2004a; TAPANINEN et al. 2010). In this context future
investigations will have to elucidate the long term effect on periprosthetic bone
remodeling after cemented and cementless THR in dogs.
As a limitation of the study of MOSTAFA et al. (2011) so far no validation of the
measurements of periprosthetic bone contrast by means of the described 5 modified
GRUEN zones was realized, although the software was found reliable in one recent
study evaluating the bone density in mice with calvarial bone defects (COWAN et al.
2004). Therefore, future studies have to determine the reliability of the described method
in comparison to DEXA investigations as gold standard method for the measurement of
the periprosthetic bone density.
5.4 Computerized simulations of bone remodeling processes in the canine and human periprosthetic femur
I. BEHRENS, B.A., I. NOLTE, P. WEFSTAEDT, C. STUKENBORG-COLSMAN and A.
BOUGUECHA (2009a):
Numerical investigations on the strain-adaptive bone remodeling in the periprosthetic
femur: influence of the boundary conditions.
Biomed Eng Online. 8, 7
II. BEHRENS, B.A., A. BOUGUECHA, C. STUKENBORG-COLSMAN, P. WEFSTAEDT
Results and Discussion
37
and I. NOLTE (2009b):
Numerische Untersuchungen zum beanspruchungsadaptiven Knochenumbau im
periprosthetischen caninen Femur
Berl Munch Tierarztl Wochenschr. 122, 391-397
BEHRENS et al. (2009a, b) carried out FEA of bone remodeling processes around a
cemented prosthetic stem in dogs (Bioméchanique intégrée bioimplant, Bretigny sur
Orge, France) as well as in an uncemented femoral prosthesis in humans
(BiCONTACT® N (AESCULAP AG, Tuttlingen, Germany). BEHRENS et al. (2009a)
found out that for a realistic FE simulation of bone remodeling processes in the human
periprosthetic femur it is necessary to consider the whole loading situation within the gait
cycle. In contrast, other authors (WEINANS et al. 1992; HUISKES and VAN
RIETBERGEN 1995; KUIPER and HUISKES 1997; ENGH and AMIS 1999;
FERNANDES et al. 2002; TAI et al. 2003; GOETZEN et al. 2005) considered only two
loading cases of the gait cycle or from stair-climbing for the simulation. The studies of
BEHRENS et al. (2009a, b) confirmed the results of other numerical studies, that the
changed load distribution in the femur after hip arthroplasty results in biomechanically
induced bone remodeling processes in the periprosthetic canine femur (WEINANS et al,
1993; VAN RIETBERGEN et al 1993; WEINANS and SUMNER, 1997). In contrast to
these studies BEHRENS et al. (2009a, b) used a loading situation representing the in
vivo situation in more detail. Furthermore, the entire femur and not only the proximal part
of the femur, was considered in many other studies (WEINANS et al. 1992; WEINANS et
al. 1993; VAN RIETBERGEN et al. 1993; HUISKES and VAN RIETBERGEN 1995;
Results and Discussion
38
KUIPER and HUISKES 1997; WEINANS and SUMNER 1997; ENGH and AMIS 1999;
FERNANDES et al. 2002; BITSAKOS et al. 2005) was taken into account for the model
setup in the studies of BEHRENS et al. (2009a, b). According to Duda et al. (1998) and
Polgar et al. (2003) considering the whole femur for the simulation of the load transfer
from the prosthetic stem to the femur represents more realistically the occurring load
situation.
In case of the FEA bone remodeling processes of the canine periprosthetic femur, the
bone was divided in three regions of analysis (BEHRENS et al. 2009b). BEHRENS et al.
(2009b) could show that there are evident changes in the bone density in each of the
analysed areas. In particular the proximal and diaphyseal region of the periprosthetic
femur showed a significant loss of bone mass. Thus, statements about a possible
reduced secondary stability of the examined canine femoral component
Biomechanique® in these regions are possible by means of the finite element analysis.
For the verification of the obtained results comparative analyses between FE
calculations and X-rays from implanted dogs of the Small animal hospital were carried
out. A good qualitative agreement of bone remodeling processes in the analyzed areas
could be shown between the methods. Furthermore, the results from the finite element
analysis are in agreement with the results of GERVERS (1998) and GERVERS et al.
(2002). A direct comparison to the results of MOSTAFA et al. (2011) was not possible,
as a different type of implant was used in this study.
In case of the FEA of bone remodeling processes in the human prosthetic stem
Bicontact® BEHRENS et al. (2009a) used a reduced muscle system according to Heller
et al. (2005) and GOETZEN et al. (2005) due to the fact that a correct consideration of
Results and Discussion
39
muscle forces is highly relevant for the calculation of the load distribution as well as
resulting bone remodeling processes in the periprosthetic femur. For the bone
adaptation model, the model of HUISKES and VAN RIETBERGEN (1995) was modified
by consideration of an upper bound for the bone formation rate and an area of bone
lysis as this modified model reflects the physiological situation in more detail. In case of
the bone remodeling processes around the human prosthetic stem BEHRENS et al.
(2009a) found out that within the investigated loading regime bone mass loss is highest
in the proximal region of the femur and much less in the diaphyseal region. One
explanation for these findings is due to force transmission from the proximal coated part
of the prosthesis to the femur. These findings correspond to the clinical findings
described in other studies using the same type of prosthesis (FRITZ et al. 2001,
STUKENBORG-COLSMAN et al. 2012). However, BEHRENS et al. (2009a) used only
three analysed regions limiting the comparability with results of DEXA investigations as
carried out e.g. by STUKENBORG-COLSMAN et al. (2012) for the same type of
prosthesis. Future FE studies will have to use identical analyses regions for the FEA to
make a validation by the clinical DEXA investigations possible.
With the studies of BEHRENS et al. (2009a, b) it could be shown that the FEM is
suitable for the calculation of stress shielding related bone remodeling processes in the
periprosthetic femur of both humans and dogs. Furthermore BEHRENS et al. (2009a)
found out that considering the loading situation during a whole gait cycle results in a
high variation between bone formation and bone loss in contrast to simulations in which
only a static loading case was used. In this context it has to be kept in mind that the
conclusions made from the computations and models have to be validated by clinical
Results and Discussion
40
examinations of the long term outcome using the same types of prosthesis
(LENGSFELD et al. 2002). However, the FEM can be a valuable in silico method for the
evaluation of the secondary stability of prostheses both in humans and dogs.
5.5 Establishment of a multibody simulation system for the determination of the loading situation in the canine hip joint
III. HELMS, G., B.A. BEHRENS, M. STOLORZ, P. WEFSTAEDT and I. NOLTE (2009):
Multi-body simulation of a canine hind limb: model development, experimental validation
and calculation of ground reaction forces.
Biomed Eng Online. 8, 36
To investigate different loading conditions of the hip joint, computerized simulations are
highly desirable due to the fact that these simulations can be carried out without the
necessity of animal experiments. In contrast to investigations using dogs with
instrumented hip joint implants (BERGMANN 1997), computerized models such as
MBS-models allow for the investigation of different loading scenarios and implant
positions. At present several studies exist investigating ground reaction forces during
gait of dogs (BUDSBERG et al. 1987; ALLEN et al. 1994; BUDSBERG et al. 1996; LEE
et al. 2004). However, a direct measurement of hip joint forces is only possible by
means of the mentioned instrumented hip joint implants (BERGMANN 1997). Therefore
HELMS et al. (2009) established an MBS model of the hind limb capable for the
simulation of forces and moments in the hip joint. The model was comprised of an
Results and Discussion
41
anatomic muscle model obtained from CT and MRI data of a 28 kg dog. To calculate the
occurring forces during a walking gait, kinematic analyses of a dog with similar height
and size were used to animate the MBS model. The model was validated by comparison
of the simulated force data with measured ground reaction forces of the same dog
walking on an instrumented treadmill. The established multi-body simulation model of
the canine hind limb allows the simulation of vertical ground reaction forces during a
walking gait showing a similar curve characteristic to the treadmill measurements.
Furthermore measured as well as simulated values are in good accordance to measured
values of other working groups.
In contrast, MBS of forces in x- and y-direction showed only a poor similarity to
measured ground reaction force data. This finding is most likely to be associated with
the modelling of the pad ground contact, which was considered as a simple ellipsoid. To
improve simulations also of GRF in x- and y-direction, the model of the pad ground
contact has to be enhanced further. The established MBS-model described by HELMS
et al. (2009) can serve as a valuable method for future investigations of the detailed
dynamic loading situation in the canine hip joint after THR. Furthermore, the obtained
values from the dynamic loading situation can be combined with FEA of bone
remodeling processes parameters or for the determination of areas of high loadings
within the artificial tribological pairing (SHAHAR et al. 2003). Thus, the developed
simulation models of BEHRENS et al. (2009a, b) and HELMS et al. (2009) can help to
develop optimization strategies for the different components of artificial hip joint
prostheses in order to reduce the stress shielding phenomenon and an aseptic
loosening of THR.
Summary
42
6 Summary
Total hip replacement (THR) is a routine surgical treatment for severe hip dysplasia in
dogs as well as in humans. Aseptic loosening of prostheses components is one key
factor influencing the long term outcome of total hip replacements. Current collaborative
research between engineers and veterinary as well as medical physicians aim at the
improvement of prosthetic materials, prostheses geometries and prosthetic stem
alignment within the femoral canal to reduce stress shielding processes in the
periprosthetic bone and implant loosening thereof. In this context, computerized
modelling methods like the finite element method and multibody simulations can help to
provide knowledge about bone remodeling processes in the periprosthetic bone as well
as of the loading situation in the artificial joint. To set up these models accurate motion
analyses in combination with measured ground reaction forces of the patients are
needed. Gait analysis measurements can furthermore be used to quantify the lameness
improvement in dogs after orthopaedic surgical interventions such as THRs. To validate
the established computerized models and to gain a deep insight into the morphologic
processes in the periprosthetic bone modern imaging analyses are necessary.
Within the current work at first the establishment of a gait analysis laboratory at the
Small Animal Hospital of the University of Veterinary Medicine Hannover is described.
The laboratory was validated by comparative kinematic and kinetic gait analysis of the
hind limb function in dogs walking on a treadmill and force plate. As one result a lower
weight bearing behaviour could be demonstrated during walk on the treadmill in
comparison to the force plate measurements. In the following, gait analyses were carried
Summary
43
out for the comparison of the functional outcome of dogs undergoing different surgical
treatments of common orthopaedic hind limb diseases. Severe hip dysplasia was treated
with either cemented or uncemented THR. As one main result, both groups showed
similar weight bearing characteristics during a time course of four months after surgery.
Gait analysis data was further used to setup and validate an MBS model for the
calculation of joint forces and moments in the canine hind limb. The results of this study
show that measured and simulated vertical ground reaction forces are in good
accordance to each other. For that reason it can be concluded that the established MBS
can be used for the computing of the loading situation of the hip joint during different
movements. In this context also combined simulations between MBS and FEM are
wanted to simulate the influence of different loading conditions on bone remodeling
processes in the periprosthetic femur. Within the here introduced work two studies are
presented dealing with the numerical simulation of periprosthetic bone remodeling
processes in the canine and human femur after THR. Simulation results suggest that
bone remodeling processes mainly occur in the proximal analysis regions of the femur.
In addition to the results from the FEA in case of the dog quantitative measurements of
the periprosthetic bone density (grayscale value) by means of postoperative radiographs
were carried out to prove whether this technique is capable to allow insights into
periprosthetic bone remodeling processes or not. As the results show changes in
periprosthetic bone density can be sufficiently analysed for cemented as well as for
uncemented prostheses by means of the established technique. Significant bone loss
occurred mainly in the region of the greater trochanter of femurs implanted with the
uncemented prosthetic stem. For morphologic analysis of periprosthetic bone
Summary
44
remodeling processes in the human periprosthetic femur, DEXA analyses were carried
out at different time points before and after implantation of a widely used uncemented
THR system. By means of the carried out analyses the hypothesis of a proximal load
transfer from the prosthesis to the periprosthetic bone with initial bone loss in the calcar
region and the region of the trochanter major could be confirmed. To improve the
knowledge and understanding of morphological changes in the joints and the
periprosthetic bone after THR, future work will have to combine simulative and
morphological analyses of the bone implant interface with functional analyses of the
surgical outcome. In this context, the investigations reported here can serve as a basis
for the future establishment of optimized THR systems with long term stability.
References
45
7 References
ALBANESE, C.V., M. RENDINE, F. DE PALMA, A. IMPAGLIAZZO, F. FALEZ, F.
POSTACCHINI, C. VILLANI, R. PASSARIELLO and F.S. SANTORI (2006):
Bone remodeling in THA: A comparative DXA scan study between conventional implants
and a new stemless femoral component. A preliminary report.
Hip Int. 16, 9–15
ALLEN, K., C. E. DECAMP, T. D. BRADEN and M. BAHNS (1994):
Kinematic gait analysis of the trot in healthy mixed breed dogs.
Vet. Comp. Orthop. Traumatol. 7, 148-153
ALLGOEWER, I., A. RICHTER, G. GRÜNING, F.J. MEUTSTEGE and L. BRUNNBERG
(2000):
Zwei intra-extraartikuläre Stabilisationsmethoden zur Therapie der Ruptur des
Ligamentum cruciatum craniale im Vergleich: Methode (mod.) nach FLO und Methode
nach MEUTSTEGE.
Kleintierprax. 45, 95-103
ALT, F. (2000):
Vergleichende Untersuchung zur Therapie der Rutur des Ligamentum cruciatum
craniale beim Hund mit drei verschiedenen extraartikulären Operationsverfahren.
References
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Hannover, Tierärztliche Hochschule, Diss.
BAETZNER, E. (1996):
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