FUNCTIONAL, SIMULATIVE AND IMAGING APPROACHES TO … · Severe hip dysplasia is a common orthopaedic disease in humans as well as in dogs. In this context total hip replacement (THR)

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.


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


V. BÖDDEKER, J., S. DRÜEN, I. NOLTE and P. WEFSTAEDT (2010):

Vergleichende Bewegungsanalyse der caninen Hintergliedmaße beim Gang auf

Kraftmessplatte und Laufband.


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

http://www.ncbi.nlm.nih.gov/pubmed/21935621


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):




V. BÖDDEKER, J., S. DRÜEN, I. NOLTE and P. WEFSTAEDT (2010):


Kraftmessplatte und Laufband.


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


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


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


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


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





11-21

VIII. DRÜEN, S., J. BÖDDEKER, A. MEYER-LINDENBERG, M. FEHR, I. NOLTE and P.

WEFSTAEDT (2012):




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


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


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


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


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.


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):




IX. STUKENBORG-COLSMAN C.M., A. VON DER HAAR-TRAN, H. WINDHAGEN, A.




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;




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


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


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


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):




II. BEHRENS, B.A., A. BOUGUECHA, C. STUKENBORG-COLSMAN, P. WEFSTAEDT


37





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;


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


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


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):




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


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

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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.

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ALLGOEWER, I., A. RICHTER, G. GRÜNING, F.J. MEUTSTEGE and L. BRUNNBERG

(2000):

Zwei intra-extraartikuläre Stabilisationsmethoden zur Therapie der Ruptur des

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Numerical Investigations of Stress Shielding in Total Hip Prostheses.

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BEHRENS, B.A., I. NOLTE, P. WEFSTAEDT, C. STUKENBORG-COLSMAN and A.

BOUGUECHA (2009a):




BEHRENS, B.A., A. BOUGUECHA, C. STUKENBORG-COLSMAN, P. WEFSTAEDT





BELLI, A., P. BUI, A. BERGER, A. GEYSSANT and J.R. LACOUR (2001):

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measurement during walking.

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BENNETT, R.L., C.E. DECAMP, G.L. FLO, J.G. HAUPTMAN and M. STAJICH (1996):

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FUNCTIONAL, SIMULATIVE AND IMAGING APPROACHES TO … · Severe hip dysplasia is a common orthopaedic disease in humans as well as in dogs. In this context total hip replacement (THR)