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Computer Methods in Biomechanics and Biomedical
Engineering
Publicat ion det ails, including inst ruct ions f or aut hors and subscript ion inf ormat ion:
ht t p: / / www. t andf online. com/ loi/ gcmb20
A Comparative Analysis of Different Treatments for
Distal Femur Fractures using the Finite Element
Method
J. Cegoñino
a
, J. M. García Aznar
a
, M. Doblaré
a
, D. Palanca
b
, B. Seral
b
& F. Seral
b
a
Aragón Inst it ut e of Engineering Research , Universit y of Zaragoza , María de Luna, 3. 50018,
Zaragoza, Spain
b
Depart ment of Surgery and Traumat ology, Facult y of Medicine , Universit y of Zaragoza,
Ciudad Universit aria. , 50010, Zaragoza, Spain
Published online: 21 Aug 2006.
To cite this article: J. Cegoñino , J. M. García Aznar , M. Doblaré , D. Palanca , B. Seral & F. Seral (2004) A Comparat ive
Analysis of Dif f erent Treat ment s f or Dist al Femur Fract ures using t he Finit e Element Met hod, Comput er Met hods in
Biomechanics and Biomedical Engineering, 7: 5, 245-256, DOI: 10. 1080/ 10255840412331307182
To link to this article: ht t p: / / dx. doi. org/ 10. 1080/ 10255840412331307182
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Computer Methods in Biomechanics and Biomedical Engineering
Vol. 7, No. 5, October 2004, pp. 245–256
A Comparative Analysis of Different Treatments for Distal
Femur Fractures using the Finite Element Method
J. CEGOÑINOa, J.M. GARCÍA AZNARa, M. DOBLARÉa,*, D. PALANCAb, B. SERALb and F. SERALb
a
Aragón Institute of Engineering Research, University of Zaragoza, Marı́a de Luna, 3. 50018 Zaragoza, Spain;
Department of Surgery and Traumatology, Faculty of Medicine, University of Zaragoza, Ciudad Universitaria. 50010 Zaragoza, Spain
b
Downloaded by [University of Zaragoza] at 01:16 09 July 2015
(Received 23 July 2003; In final form 26 July 2004)
The main objective of this work is the evaluation, by means of the finite element method (FEM) of the
mechanical stability and long-term microstructural modifications in bone induced to three different
kinds of fractures of the distal femur by three types of implants: the Condyle Plate, the less invasive
stabilization system plate (LISS) and the distal femur nail (DFN). The displacement and the stress
distributions both in bone and implants and the internal bone remodelling process after fracture and
fixation are obtained and analysed by computational simulation. The main conclusions of this work are
that distal femoral fractures can be treated correctly with the Condyle Plate, the LISS plate and the
DFN. The stresses both in LISS and DFN implant are high especially around the screws. When respect
to remodelling, the LISS produces an important resorption in the fractured region, while the other two
implants do not strongly modify bone tissue microstructure.
Keywords: Internal bone remodelling; Finite element simulation; Distal femur fractures; Distal femur
nail; Condyle plate; LISS plate
INTRODUCTION
The femur is a long bone that constitutes the skeletal of the
thigh. It is articulated at its upper part with the coxal bone
and at its lower with the knee complex (tibia, patella and
knee tendon system). Two important parts can be
distinguished in the femur: the diaphysis or central body
and two epiphysis or extremities. The thick cortical walls
of the diaphysis, mainly formed by dense cortical bone,
become thinner as they form the metaphysis, being the
epiphysis mainly conformed by a complex heterogeneous
mixture of cortical and cancellous bone [1]. The thick,
dense, tubular cortical structure of the diaphysis provides
maximum resistance to bending and torsion, while the
thinner cortices and cancellous bone in the metaphysis and
epiphysis form an articular surface, designed to absorb
impact and directionally dependent loads.
The main role of the musculoskeletal system of
supplying a rigid structure to the rest of the body is
affected when one of its elements is fractured, becoming
essential to know the main factors that affect the correct
treatment of these fractures. In fact, the worrying
increment of fractures of the musculoskeletal system is
*Corresponding author. E-mail: mdoblare@unizar.es
ISSN 1025-5842 print/ISSN 1476-8259 online q 2004 Taylor & Francis Ltd
DOI: 10.1080/10255840412331307182
generating prevention campaigns and promoting research
that have lead to new therapeutic methods [2,3].
One of the most important factors to achieve an
adequate fracture healing is the appropriate stabilisation of
the fractured zone after the implantation of a specific
fixation [4].
Five independent variables can be considered, in
general, to evaluate the efficacy of an implant [5]:
.
.
.
.
.
Bone quality and its evolution (remodelling);
Geometry and position of the fractured fragments;
The reduction of the fracture;
The design of the implant employed;
The location of the implant;
The only variable that can be chosen by the surgeon is
the implant and its position. Moreover, these strongly
affect the other three after surgery.
Despite the low number of distal femoral fractures, a
3.59% of the total, they are very important due to their
difficult in the treatment.
Distal femoral fractures affecting the lower epiphysis
may be classified according to the specific location of the
fracture zone as shown in Table I based on the AO/ASIF
246
J. CEGOÑINO et al.
TABLE I AO classification [5]
Type A
Extra-articular fracture
A1—simple
A2—metaphyseal wedge
A3—metaphyseal complex
Type B
Articular parcial fracture
B1—lateral condyle, sagittal
B2—medial condyle, sagittal
B3 –frontal condyle, sagittal
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Type C
Articular fracture, articular simple
C1—metaphyseal simple
C2—metaphyseal multifragmentary
C3—articular multifragmentary
classification [5]. The fractures here considered are
of the following types: extra-articular metaphyseal
wedge (A2.3), articular complete metaphyseal multifragmentary (C2.1) and articular complete multifragmentary (C3.1).
Some of these fractures can be treated by plate-type
fixations achieving an appropriate reduction of the fracture.
In other cases however, it is necessary to use a nail fixation.
Techniques of operative treatment of supra and
intercondylar fractures have changed in recent years.
These changes refer to reduction techniques and implant
selection. Operative approach concepts, which have
remained unchanged for several decades, were critically
evaluated and modified leading to the so-called minimal
invasive osteosynthesis concept [6]. This included for
intraarticular fractures a transarticular joint reconstruction
and a retrograde plate osteosynthesis. For extraarticular
fractures a minimally invasive percutaneous plate
osteosynthesis via stab incisions only or retrograde
intramedullary nailing is available.
Many authors have performed biomechanical studies of
the distal femur fractures. Most of them are based on
clinical studies [7 – 12], experimental essays [13 –15] and
finite element simulations [16]. The advantage of
computer simulations is the possibility of performing
parametric analyses and personalised virtual tests,
reducing the economic and social cost in comparison to
experimental techniques and allowing in addition to test
different situations impossible to simulate in real practice.
This paper is focussed in the application of the finite
element method (FEM) to the study of the femur
functional performance, after fracture and fixation by
three types of implants: the Condyle Plate [17 – 18], the
less invasive stabilization system plate (LISS) [6,19,20]
and the distal femur nail (DFN) [21 –23].
Its main conclusions are that distal femoral fractures
can be treated correctly with all types of fixations. With
respect to the stresses on the implant, the highest values
appear in the LISS plate in the zone surrounding the
screws and in the DFN on the central nail, particularly in
the zone around the transversal screws. Regarding the
bone remodelling performance, the LISS plate produces a
high resorption in the fractured region due to the bridge
effect induced by the position of the fixation screws, while
the other two implants do not strongly modify bone tissue
microstructure.
MATERIAL AND METHODS
A femur, tibia and fibula of a 76 years old woman donor
were scanned to obtain a set of slices by computed
tomography (CT). The distance chosen between each two
slices was in the epiphysis about 2 and 4 mm, and in
the diaphysis about 5 and 9 mm. From these slices, the
geometry and associated mesh was reconstructed with the
help of the CAD package I-DEAS (SDRC, Milford, Ohio).
The resulting mesh was composed by 17,631 brick
elements and 18,291 nodes (Fig. 1)
A simplified constitutive behaviour was established for
bone tissue, considering it as a homogeneous isotropic
linear elastic material, although distinguishing between
cortical and trabecular bone. This is in fact a very
simplified model, since bone is actually heterogeneous,
non-linear and anisotropic [24 – 26]. However,
for comparative purposes and taking into account
that our main goal is the analysis of the stabilisation
performance, that is clearly a non-local problem,
the use of average properties is accurate enough.
The mean mechanical properties considered for each
type of bone tissue [1,26] and soft tissue [27] are shown
in Table II.
The loading conditions on the femur are multiple and
variable along time, depending on its position [27 –29].
Moreover, due to the amount of ligaments and muscles
inserted in the femur, it is necessary to perform some
simplifications. Following different other authors [30],
only one loading condition was considered in this work,
corresponding to the stance phase of the gait cycle. This is
one of the most important and unfavourable loading stages
appearing in the femur. In the model we considered a load
of 2460 N acting on the femoral head with angles of 238
with the frontal plane and 68 with the sagittal plane. A
second load acting on the greater trochanter that
corresponds to the reaction of three muscles (gluteus
minimus, medius and maximus) was also included. This
load had a modulus of 1700 N, with angles of 248 with the
frontal plane and 158 with the sagittal plane. Finally, a
third load was applied in the lesser trochanter, due to the
effect of the psoas-iliac muscle, with a value of 771 N and
forming angles of 418 with the frontal plane and 268 with
the sagittal plane.
With respect to the boundary conditions, as a first
approach, we considered the tibia constrained at its
proximal part. In particular, several nodes were constrained at its proximal epiphysis. Again, this situation is
not real, since there is a complex interaction between the
femur, the knee system and the ankle system. However,
this model has shown to be useful to perform a
comparative analysis between different distal femur
fixations, studying the stabilisation and the stress state of
the fractured distal femur.
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DIFFERENT TREATMENTS FOR DISTAL FEMUR FRACTURES
247
FIGURE 1 FE mesh of the femur and knee. (a) Slices obtained by computed tomography. (b) Evolving surface (c) Final FE mesh.
The most important knee ligaments were also
considered as non-compression uniaxial truss elements
with average elastic modulus [31].
Finally, fractures were modelled with gap contact
elements avoiding the interpenetration between
the surfaces, that is, establishing a node-to-node unilateral
contact. This is possible in this case, since fractures were
created by separating face elements of the original mesh of
the intact femur, and the displacements are small, leading
to consistent meshes for both contacting surfaces.
All of these analyses were performed by using the
commercial FE package ABAQUS [32].
TABLE II Averaged mechanical properties (Evans, 1973; Jacobs, 1994;
Fithian, 1990)
Bone Tissue
Cortical
Trabecular
Medular
Meniscus
Young modulus (N/mm2)
Poisson coeff.
14,217
100
1
50
0.32
0.3
0.3
0.3
In this work we used three of the most common
fixations employed: the Condyle Plate, the LISS plate and
the DFN
Treatment with Condyle Plate
The Condyle Plate [17 –18] is composed by a long and
narrow plate that adjusts its shape to the distal part of the
femur (transition zone between diaphysis and epiphysis
and condyles). The distal part of the plate has shape of
petals of clover, being these petals curved for a better
adjustment to the faces of the condyles. The plate is
attached to the diaphysis and to the condyles through
several screws inserted along a set of holes that exist all
along the plate, allowing a perfect joint between fixation
and bone. These holes are oval and without thread. The
screws, placed along the plate, cross over the two cortical
layers having different lengths depending of the zone of
the bone. The Condyle Plate is available in a wide range of
different measures in order to adapt to each different
femur. We chose the geometrical parameters appropriate
for the proposed femur, following the surgeons advice.
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J. CEGOÑINO et al.
FIGURE 2
(a) FE mesh of the Condyle Plate. (b) Position of the implant in the fractured femur.
The finite element model was composed by 27,096
brick elements (31,691 nodes). The screws were modelled
by brick elements with a circular section of 6.5 mm
of diameter. The FE mesh of the plate and screws and the
positioning of the Condyle Plate after fixation along
the femur as shown in Fig. 2.
The material used is stainless steel with the
following mechanical properties: Young’s modulus of
2,00,000 N/mm2 and a Poisson’s ratio of 0.28.
The fixation was considered in perfect contact with
bone (same displacements) by connecting the respective
nodes of the screws. The plate is not in contact with
the periosteum (different displacements) mimicking the
clinical situation.
Treatment using the Less Invasive Stabilization System
The LISS is a new type of fixation [6,19,20] designed
following the principles of “minimally invasive
percutaneous osteosynthesis” (MIPO) [31], giving precedence to biological aspects to stabilization.
It consists of a plate and screws joined to the plate by
means of threaded holes. The implant is positioned close
to the bone but without contact and the screws only
cross one cortical layer, promoting a better vascularisation. The screws are placed along the implant avoiding the
fractured zone.
The LISS plate is also available in a wide range
of sizes. In this case, we used a plate with 16 cm of
length and with five holes. The FE mesh was composed
by 28,896 brick elements (33,821 nodes) as shown
in Fig. 3, which also includes its location along the
fractured femur.
The LISS is composed by an alloy of titanium, aluminium
and niobium, with the following average mechanical
properties: Young’s modulus of 1,05,000 N/mm2 and
Poisson’s ratio of 0.28.
With respect to the interaction conditions between
the implant and bone, we considered a perfect union
between the screws and the bone, while the contact
between the plate and the cortical external surface of the
femur was avoided.
Treatment using the Distal Femur Nail
The DFN [21 –23] consists of a long nail and four
transversal screws. The nail can be smooth or grooved.
The nail is placed along the marrow cavity of the femur
perforating an orifice between the condyles. It is attached
to the femur by means of transversal screws at the begin
and at the end of the nail (see Fig. 4).
The FE mesh of the DF nail in our case (included in
Fig. 4a) was composed by 18,437 brick elements (20,745
nodes). The placement of the nail along the fractured
femur is also shown in the Fig. 4.
FIGURE 3 (a) FE mesh of the LISS plate. (b) Position of the implant in
the fractured femur.
DIFFERENT TREATMENTS FOR DISTAL FEMUR FRACTURES
249
TABLE III Values and orientations of the three load cases used in the
3D case acting on the femoral head. Orientations are referred to the
frontal (FP) and sagittal planes (SP)
Force acting on the head
Load case
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1
2
3
FIGURE 4 (a) FE mesh of the DFN nail. (b) Position of the implant in
the fractured femur.
The mechanical properties are the ones of the LISS
plate and the screws were considered in perfect contact
with bone, avoiding contact between the nail and bone.
Remodelling Behaviour
As it is well-known, bone is a living material that optimally
modifies its structure according to its specific mechanical
environment [25,26,35 –38]. It is therefore very important
to establish the main trends of the bone density distribution
(both directional and in average) after modification of the
natural stress distribution due, for instance, to the inclusion
of a specific implant. This will allow therefore, not only
to analyse the short-term behaviour after fracture
(stabilisation) but also the evolution of bone tissue (longterm behaviour) with important clinical consequences like
implant-induced osteoporosis and the associated weakening of the bone structure.
Bone remodelling theories allow us to simulate the
evolution of bone microstructure and its mechanical
behaviour due to the acting loads [26,35 – 38]. Some of
these models have been used to perform biomechanical
studies after implantation, trying to predict the alteration
suffered by bone when a fixation is implanted, in order to
optimise its design [16,30,35].
In this work we have employed a new bone remodelling
theory, based on the principles of damage mechanics, and
able to predict the evolution of the heterogeneity
and anisotropy of bone. This theory is described in
detail in [38]. This model, uses two independent variables
that can be quantified experimentally: the apparent
density (a measure of the porosity) and the Cowin’s
fabric tensor [39] (a measure of the directionality of bone
trabeculae).
Since remodelling is induced by cyclic loads, we
considered now the loads corresponding to the gait cycle
(instant when the foot touches the floor and the other
Cycles per block
Value
(N)
Orientation
(8FP)
(8SP)
6000
2000
2000
2317
1158
1548
24
215
56
6
35
220
two alternative moments of abduction and adduction
respectively) [27,28], that are representative of the
daily forces producing remodelling. The three loads
in Table III were applied to the femoral head sequentially
in blocks of 10,000 cycles with different frequencies as
shown in Table III.
In the stress analysis, a simplified constitutive behaviour
was considered: a homogeneous isotropic linear elastic
material. In the remodelling analysis, it was initially started
from an ideal homogeneous and isotropic material with an
average apparent density of 0.5 g/cm3. The above forces
were applied 300 blocks until convergence in the
constitutive behaviour and microstructure, that is, in the
apparent density and anisotropy, obtaining a density
distribution very close to the actual (Fig. 5). After fracture
and implantation and starting from this density and
anisotropy distributions, the same load blocks were applied
again until new convergence. The corresponding results are
presented in the next section.
RESULTS
In this section we present the comparison between the
results obtained both for the vertical displacements and
stresses that are considered in this case the most important
for comparison. These were analysed for each type of
implant and three types of fractures: an extra-articular
metaphyseal wedge fracture (A2.3), an articular complete
metaphyseal multifragmentary fracture (C2.1) and an
articular complete multifragmentary fracture (C3.1). These
distributions were also compared to the ones of the intact
femur under the same loads and boundary conditions.
The stresses on the implant were also computed and
discussed.
Finally, a study of the modification of the bone tissue
average density due to remodelling in the case of the extraarticular metaphyseal wedge fracture was conducted for the
three implants using the bone remodelling approach
presented in [38]. Although this model had several
limitations (i.e the femoral head constraints with the pelvic
acetabulum and the tibia constraints were not exhaustively
analysed, the healing process was not considered, etc.),
we obtained important qualitative comparative conclusions
as will be discussed later on.
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J. CEGOÑINO et al.
FIGURE 7
Vertical distribution of stress in the intact femur.
Results using the Condyle Plate
FIGURE 5 Density distribution in a frontal section of the intact femur.
Figures 6 and 7 show respectively the vertical
displacements and the distribution of vertical stresses
in the intact femur under the loads described in the
previous section. The maximum level of stresses was
about 90 MPa in compression and 45 in tension, while the
maximum compression and tension strengths are about
150 MPa [40] and 60 MPa [41], respectively. Tension
stresses appeared mainly in the concave part of the femur,
while compressive stresses were in the convex part of
the diaphysis.
The results of displacements for the three types of
fractures after the implantation of the Condyle Plate are
shown in Fig. 8. It is clear that this type of implant
achieves a good stability of the fractured zone (the relative
displacement between the fractured surfaces is less than
0.06 mm), which benefits fracture healing. The inclusion
of the plate, although modifies the stress distribution
reducing the stress level, did not lead to important
alterations of the maximum values in comparison with the
intact femur (Fig. 9).
The stress level was higher for the fracture A2.3 than for
the other two. In all cases, the fractured zone had very low
stresses (an average value of about 10 MPa was obtained).
Finally, in Fig. 10 the von Mises stress distribution
along the implant is presented, being clear the bending
effect in the fixation. The maximum stress was about
1000 MPa close to the yield stress of the material of
1200 MPa. This stress in the plate was however very much
concentrated along the fractured zone, specifically near
the holes and the screws, being these regions the ones
with the highest probability of failure. The fracture that
induced the greatest stress level is the A2.3.
Results using the LISS Plate
FIGURE 6 Vertical displacements in the intact femur.
Figure 11 shows the results of vertical displacements for
the three types of fractures using the LISS plate. From
them it is clear that this implant also achieves a good
stability of the fractured zone in the three cases, being the
relative displacements of the two fractured fragments
close to zero.
The vertical stress distribution was slightly modified in
comparison with the one of the intact femur (the maximum
stress is about 10 MPa lower than in the intact femur),
being very similar to the one of the previous implant
DIFFERENT TREATMENTS FOR DISTAL FEMUR FRACTURES
251
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FIGURE 8 Distributions of vertical displacements in mm in the fractured femur, after treatment with a Condyle Plate of fractures A2.3, C2.1 and C3.1.
(Fig. 12). The stress in the fractured region was very low
due to the “bridge effect” that produces this implant, since
there is no connection with bone in this zone. This is
probably the cause of a stronger resorption in this part that
will be detected in the remodelling analysis.
The von Mises stress distribution along the implant is
presented in Fig. 13. The maximum stress was about
1000 MPa slightly higher than the yield stress of the
material of 900 MPa. The zone closest to the holes had
the highest stress level. In fact, the rigid connections of the
screws with the plate induced stress concentrations in
those joints as is clearly seen in that figure.
Results using the DFN Implant
As shown in Fig. 14, the relative displacements in the
region around the fracture were very low (an average value
of 0.2 mm for the vertical displacements) demonstrating
the correct stabilisation achieved by this implant in all
the three different fractures very much like the other types
of implants.
Again, the distribution of vertical stresses was modified,
like in the previous cases, reducing the stresses in the
fractured zone with respect to the intact case (an average
value of about 15 MPa appeared also in this region). This
value increased when going up along the diaphysis as
shown Fig. 15.
Figure 16 shows the von Mises stress distribution along
the implant, being clear the bending effect on the nail.
The maximum stress in the nail was about 850 MPa
clearly lower than the yield stress of the material
1200 MPa. In the transversal screws the average stress
value was of 500 MPa.
Bone Remodelling
As explained in the Material and Methods section, the aim
of this study is the prediction of the evolution of the bone
FIGURE 9 Distributions of vertical stresses in N/mm2 in the fractured femur, after treatment with a Condyle Plate of fractures A2.3, C2.1 and C3.1.
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J. CEGOÑINO et al.
FIGURE 10 von Mises stress distribution in the Condyle Plate in
N/mm2 for the three types of fractures A2.3, C2.1 and C3.1.
microstructure after fracture and treatment with the three
different implants. In order to get this evolution, an
adequate initial density distribution has to be obtained.
This may be done using results of a densitometry or after a
correlation between the grey levels in a set of
tomographies with bone density. However, we have used
the same simulation approach later used after fracture as
explained in the previous section.
Although the obtained results were only qualitative (i.e.
fracture healing and other biological processes were not
considered although they strongly modify the loading
transmission) they gave us information about the global
mechanical environment and therefore the most probable
regions in which problems could appear.
Taking into account that the characteristic time for the
remodelling process is much longer than the one of
healing, we also analysed the remodelling evolution
without fracture, that is, in the intact femur with the
implants, that leaded to more realistic results.
FIGURE 11 Distributions of vertical displacements in mm in the fractured femur, after treatment with a LISS Plate of fractures A2.3, C2.1 and C3.1.
FIGURE 12 Distributions of vertical stresses in N/mm2 in the fractured femur, after treatment with a LISS Plate of fractures A2.3, C2.1 and C3.1.
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DIFFERENT TREATMENTS FOR DISTAL FEMUR FRACTURES
FIGURE 13 von Mises stress distribution in the LISS Plate in N/mm2
for the three types of fractures A2.3, C2.1 and C3.1.
253
Only the A2.3 fracture was considered and all the next
figures show the different density distributions obtained
after convergence.
The density distributions after 150 and 300 load blocks
with the fractured femur and with implantation of the
Condyle plate are shown in Fig. 17. In the same figure
the density distribution after 150 load blocks is shown for
the intact femur after implantation of the Condyle plate.
A slight resorption in the fractured region can be
observed, caused by the higher stiffness of the implant that
causes the load to be mainly transferred through the
implant, decreasing consequently the stress in bone. On the
contrary, far away of the fractured zone, bone mass is
formed increasing the cortical layer.
In the case of the LISS plate the density distribution
after convergence was different (Fig. 18). An important
resorption is observed in the cortical layer just around the
fractured zone. The bridge effect produced by the way the
plate is inserted, strongly modifies the way in which load
is transferred, reducing the stress in this part and
increasing the reaction and the associated stresses down
FIGURE 14 Distributions of vertical displacements in mm in the fractured femur, after treatment with a DFN implant of fractures A2.3, C2.1 and C3.1.
FIGURE 15 Distributions of vertical stresses in N/mm2 in the fractured femur, after treatment with a DFN implant of fractures A2.3, C2.1 and C3.1.
254
J. CEGOÑINO et al.
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FIGURE 16 von Mises stress distribution in the DFN implant in N/mm2 for the three types of fractures A2.3, C2.1 and C3.1.
FIGURE 17 Density distribution in a frontal section after inclusion of a Condyle Plate in a type A2.3 fracture (150 and 300 time steps in the fractured
femur and 150 steps in the intact femur).
FIGURE 18 Density distribution in a frontal section after inclusion of a LISS Plate in a type A2.3 fracture (150 and 300 time steps in the fractured
femur and 150 steps in the intact femur).
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DIFFERENT TREATMENTS FOR DISTAL FEMUR FRACTURES
255
FIGURE 19 Density distribution in a frontal section after inclusion of a DFN implant in a type A2.3 fracture (150 and 300 time steps in the fractured
femur and 150 steps in the intact femur).
the fracture, which produces bone formation that is easily
noticed in the same figure. Of course, this effect is much
more important if no healing is considered, but is also
detected in the intact case, predicting bone weakening
near fractures treated with the LISS system.
Finally, Fig. 19 shows the density distribution in the
same three situations for the DFN, being very similar to
the case of the Condyle plate. A small resorption in the
fractured region is observed, caused again by the higher
stiffness of the implant in comparison to bone, although
this is not very important, specially in the intact case, in
contrast to the LISS implant.
DISCUSSION
Distal femoral fractures are an important problem, risk
and difficult treatment that imply important economical
and social costs.
The choice of the appropriate implant is one of the
key factors to achieve an appropriate stabilisation and
an adequate stress distribution on the femoral bone in
order to produce a correct heal and small changes in its
density distribution during the subsequent remodelling
process and, therefore, a low probability of appearance
of undesired effects like induced osteoporosis.
The use of simulation tools like the FEM to analyse the
global functional performance of different implants in the
treatment of distal fractures allows us to carry out a cheap
and extensive qualitative comparison between them,
becoming more and more an essential help in preoperative planning and clinical decisions assessment.
Although these models still present important limitations, it is possible to get important qualitative
conclusions useful from the clinical point of view. In this
case, for instance, the use of an isotropic behaviour of
bone, the establishment of simplified contacts between
prosthesis and bone, the consideration of a perfect union
between the screws and bone or the use of a simplified
single load case and boundary conditions are some of
these limitations.
In distal fractures (A2.3, C2.1 and C3.1), the Condyle
plate, the LISS plate and the DFN give rise to similar
results regarding stability (the three treatments get the
appropriate stabilisation of these types of fractures) and
the overall stress distribution on the femur. Only in the
LISS plate stress values higher than the yield stress of the
material appeared around the threaded joints of the screws
and therefore a more likely failure of the implant, although
very much concentrated. This could lead maybe not to an
unstable fracture but to a fatigue one.
Bone remodelling leads to different results depending
of the type of fixation. With the Condyle plate and the
DFN a small resorption in the fractured region appears,
whereas an increase of the cortical layer is clearly detected
far from this zone. On the contrary, with the LISS plate, an
important resorption is observed in the cortical layer just
on the fractured zone, due to a strong alteration of the way
in which load is transferred.
Although these last conclusions are only tentative since
some important effects have not been considered in the
model like a correct fracture healing process and other
biological and metabolic effects like implant-induced
necrosis, they are in agreement with well-known clinical
tests, validating in a qualitative sense this simulation
approach [42 –43].
Acknowledgements
This work has been partially funded by the Diputación
General de Aragón as a part of the project D.G.A. P-79/96.
References
[1] Evans, F.G. (1973) In: Evans, F.G., ed., Mechanical Properties of
Bone (Charles C. Thomas, Springfield, Illinois).
Downloaded by [University of Zaragoza] at 01:16 09 July 2015
256
J. CEGOÑINO et al.
[2] Lips, P. and Cooper, C. (1998) “Osteoporosis 2000-2010”, Acta
Orthop Scand 69(281), 21–27.
[3] Connolly, J.F. (1999) “The next 10 years. The bone and joint
decade”, Clin. Orthop. 358, 255–256.
[4] McKibbin, B. (1978) “The biology of fracture healing in long
bones”, J. Bone Joint Surg. 60B, 150–162.
[5] Müller, M.E. (1991) “Femur”, In: Müller, M.E., Allgöwer, M.,
Schneider, R. and Willenegger, H., eds, Manual of Internal Fixation.
Teniques Recommended by the AO-ASIF Group (Springer, Berlin),
pp 485– 500.
[6] Krettek, C., Schandelmaier, P. and Tscherne, H. (1999) “Liss: less
invasive stabilization system”, Dialogue I, 7.
[7] Rizzo, E., et al. (1998) “Biomechanical behaviour at the distal third
of the femur: possible use of a medial metaphyseal plate”, Injury
29(6), 451–456.
[8] Sanders Roy, et al. (1991) “Double-plating of comminuted, unstable
fractures of the distal part of the femur”, J. Bone Joint Surg.
73-A(3), 341– 346.
[9] Siliski John, M., et al. (1989) “Supracondylar-intercondylar fractures of the femur”, J. Bone Joint Surg. 71-A(1), 95–104.
[10] Johnson Kenneth and Hicken Greg (1987) “Distal femoral
fractures”, Orthop. Clin. North Am. 18(1), 115 –131.
[11] Schatzker Joseph (1998) “Fractures of the distal femur revisited”,
Clin. Orthop. 347, 43–56.
[12] Krettek, C., Schandelmaier, P., Richter, M. and Tscherne, H. (1998)
“Distal femoral fractures”, Swiss surg.(6), 263 –278.
[13] Firoozbakhsh, K., et al. (1995) “Mechanics of retrograde nail versus
plate fixation for supracondylar femur fractures”, J. Orthop. Trauma
9(2), 152–157.
[14] Harder, Y., et al. (1999) “The mechanics of internal fixation
of fractures of the distal femur: a comparison of the condlar
screw (DCS) with the condlar plate (CP)”, Injury(30 suppl.),
A31–A39.
[15] Krettek, C., Schandelmaier, P. and Tscherne, H. (1996) “Distal
femoral fractures. Transarticular reconstruction, percutaneous plate
osteosnthesis and retrograde nailing”, Unfallchirurg 99(1), 2–10.
[16] Reiter, J.T., Böhm, H.J., Kratch, W. and Rammerstorfer, F.G. (1994)
“Some applications of the finite-element method in biomechanical
stress analyses”, Int. J. Comput. Appl. Technol. 7, 233–241.
[17] Böstman, O.M. (1990) “Refracture after removal of a condylar plate
from the distal third of the femur”, J. Bone Joint Surg. 72-A(7),
1013–1018.
[18] Simon, J.A., Hale, J., Kummer, F. and Koval, K.J. (1997) “Improved
fixation in osteoporotic bone: a novel locked supracondylar buttress
plate”. OTA Posters, Scientific Basis for Fracture Care.
[19] Krettek, C., Schandelmaier, P. and Tscherne, H. (1997)
“New developments in stabilization of dia- and metaphyseal
fractures of long tublar bones” 26(5), 408–421.
[20] Helfet, D.L., Shonnard, P.Y., Levine, D. and Borrelli, J., Jr. (1997)
“Minimally invasive plate osteosynthesis of distal fractures of the
tibia”, Injury 28(supp 1), 42–48.
[21] Iannacone William M., et al. (1994) “Initial experience with the
treatment supracondylar femoral fractures using the supracondylar
intramedullary nail: a preliminary report”, J. Orthop. Trauma 8(4),
322–327.
[22] Helfet David, L. and Lorich Dean, G. (1998) “Retrograde
intramedullary nailing of supracondylar femoral fractures”,
Clin. Orthop.(350), 80–84.
[23] Hora, N. (1999) “Biomechanical analysis of supracondylar femoral
fractures ficed with modern retrograde intramedullary nails”,
J. Orthop. Trauma 13(8), 539 –544.
[24] Buckwalter, J.A., Glimcher, M.J., Cooper, R.R. and Recker, R.
(1995) “Bone biology. Part I: structure, blood supply, cells, matrix
and mineralization”, J. Bone Joint Surg. 45, 1256–1275.
[25] Fung, Y.C. (1993) Biomechanics. Mechanical Properties of Living
Tissues (Springer-Verlag, Berlin).
[26] Jacobs, C.R. (1994) “Numerical simulation of bone adaptation to
mechanical loading”, Dissertation for the Degree of Doctor of
Philosophy, Stanford University).
[27] Pedersen, D.R., Brand, R.A. and Davy, D.T. (1997) “Pelvic muscle
and acetabular contact forces during gait”, J. Biomech. 30(9),
959–965.
[28] Bergmann, G., Graichen, F. and Rohlmann, A. (1993) “Hip joint
loading during walking and running, measured in two patients”,
J. Biomech. 26(8), 969–999.
[29] Duda, G.N., Schneider, E. and Chao, E.Y.S. (1997) “Internal forces
and moments in the femur during walking”, J. Biomech. 30(9),
933–941.
[30] Verdonschot, N. and Huiskes, R. (1995) “Can polished stems reduce
mechanical failures of the cement/bone interface in THA?”, Trans.
Eur. Orthop. Res. Soc. 5, 42.
[31] Li, G., et al. (1999) “A validated three-dimensional computational
model of a human knee joint”, J. Biomech. Eng. 121, 657–662.
[32] Hibbit, Karlsson, Sorensen, Inc., 2001. ABAQUS. User’s Manual.
Version, 6.2.
[33] Perren and Stephan, M. (2001) “Evolution and rationale of
locked internal fixator technology. Introductory remarks”, Injury
32, S-B-3-9.
[34] Terrier, A., Rakotomanana, R.L., Ramaniraka and Leyvraz, P.F.
(1997) “Adaptation models of anisotropic bone”, Comput. Methods
Biomech. Biomed. Eng. 1, 47–49.
[35] Huiskes, R., et al. (1987) “Adaptive bone-remodeling theory
applied to prosthetic-design analysis”, J. Biomech. 20, 1135– 1150.
[36] Beaupré, G.S., Orr, T.E. and Carter, D.R. (1990) “An approach for
time-dependent bone modeling and remodeling-theoretical
development”, J. Orthop. Res. 8, 551–651.
[37] Carter, D.R., Orr, T.E. and Pyhrie, D.P. (1989) “Relationships
between loading history and femoral cancellous bone architecture”,
J. Biomech. 22, 231 –244.
[38] Doblaré, M. and Garcı́a, J.M. (2002) “Anisotropic bone remodelling
model based on a continuum damage-repair theory”, J. Biomech.
35(1), 1–17.
[39] Cowin, S.C. (1986) “Wolff’s law of trabecular architecture at
remodeling equilibrium”, J. Biomech. Eng. 108, 83–88.
[40] Keller, T.S. (1994) “Predicting the compressive mechanical
behaviour of bone”, J. Biomech. 27, 1159–1168.
[41] Keyak, J.H. and Rossi, S.A. (2000) “Prediction of femoral fracture
load using finite element models: an examination of stress- and
strain-based failure theories”, J. Biomech. 33, 209–214.
[42] McKibbin, B. (1978) “The biology of fracture healing in long
bones”, J. Bone Joint Surg 60B, 150 –162.
[43] Kerner, J., Huiskes, R., van Lenthe, G.H., Weinans, H., van
Rietbergen, B., Engh, C.A. and Amis, A.A. (1999) “Correlation
between pre-operative periprosthetic bone density and postoperative bone loss in THA can be explained by strain-adaptive
remodelling”, J. Biomech. 32, 695–703.