Biomechanical investigation of uniplanar and biplanar cuts in ...

Biomechanical investigation of
uniplanar and biplanar cuts in openingwedge
high tibial osteotomy
Biomechanische Untersuchung zur
uni- und biplanaren Schnittführung
bei der hohen opening-wedge
Osteotomie der Tibia
Die Studie wurde mit dem Ziel durchgeführt, die biomechanischen
Eigenschaften der uniplanaren (UPO) und der biplanaren dreidimensionalen
(BPO) Osteotomie bei der medial öffnenden hohen
Tibiakopfosteotomie (HTO) in einem Sawbone-Modell zu vergleichen.
Sawbones der dritten Generation wurden standardisiert osteotomiert
und die Osteotomie mit einer speziellen winkelstabilen
Spacer-Platte fixiert. Danach wurde die Steifigkeit nach einem und
nach 20 Belastungszyklen (5 bis 1000 N) bestimmt. Weiterhin wurden
die Verschiebung im Osteotomiespalt und die Versagenslast
ermittelt. Nach einem Belastungszyklus zeigte sich kein Unterschied
bezüglich der Steifigkeiten in beiden Gruppen (n=5 in beiden
Gruppen). Dagegen wurde in beiden Gruppen nach 20 Belastungszyklen
eine deutliche Abnahme der Steifigkeit ermittelt. Nach
BPO hatten die Osteotomien eine Steifigkeit von 1755,9 ± 129,2
N/mm. In der UPO Gruppe war diese mit 1018,5 ± 15,5 N/mm signifikant
niedriger. Die durchschnittliche Versagenslast betrug in
der UPO Gruppe 2633,1 ± 229,4 N. In der BPO Gruppe war die Versagenslast
mit 4554,8 ± 342,8 signifikant höher. Das Versagen in
der BPO Gruppe war ausschließlich durch einen Bruch der lateralen
Kortikalis bedingt. Dagegen wurde in der UPO Gruppe zusätzlich
zweimal eine zusätzliche komplette Dislokation des Tibiakopfes
nach dorsal beobachtet. Die Untersuchung, die mit dem Ziel durchgeführt
wurde, Unterschiede im biomechanischen Verhalten von
UPO und BPO für die HTO zu ermitteln, lässt schlussfolgern, dass die
BPO günstiger bezüglich der axialen Steifigkeit und auch in Bezug
auf die Versagenslast ist.
Introduction
High tibial osteotomy (HTO) is an established treatment of
younger patients who are suffering from unicompartimental
medial osteoarthritis [3] [8].
1. Center of Trauma and Orthopaedic Surgery Eisenach (Sophienstr. 16, D-99817 Eisenach,
Germany)
2. Department of Trauma, University of Jena (Erlanger Allee 101, D-07743 Jena, Germany)
3. Department of Orthopedics, University of Göttingen (Robert-Koch-Straße 40, Göttingen
D-37075, Germany)
4. University of Applied Sciences Munich (Lothstr. 34, D-80336 München, Germany)
ARBEITEN
Autoren:
Dr. med. Gunter
Spahn 1, Dr. med.
Thomas Mückley 2,
Dr. med. Enrico Kahl 3,
Dr. med. Hans-Michael
Klinger 3,Prof. Dr.-Ing.
Erwin Steinhauser 4,
Prof. Dr. med. Dr. rer.
nat. Gunther O. Hofmann
2
Schlagworte: Knie,
Osteotomie, openingwedge,
Biomechanik,
biplanar, uniplanar
Keywords: Knee; osteotomy;
opening-wedge;
biomechanics; biplanar;
uniplanar
Zitierweise dieses Beitrages:
BIOmaterialien
2007; 8 (2): S. 71-75
Classically, the HTO is performed in the lateral closed wedge
technique as firstly described by Coventry [2].
The lateral HTO includes a number of potential pitfalls as loss
of osseous substance, requirement of a large soft-tissue exposition,
fibular osteotomy, and neurological complications such
as peroneal nerve palsies [10]. Furthermore the lateral operation
can overcome the difficulties associated with a total knee
replacement [1].
These may be reasons for the development of alternative treatments
like hemicallotasis [4] or opening-wedge HTO. In the
BIOmaterialien 8 (2), 2007
71
ORIGINAL

ORIGINAL ARBEITEN Gunter Spahn: Biomechanical investigation of uniplanar cuts in opening-wedge high tibial osteotomy
Figure 1 Technique of transversal uniplanar (UPO) and biplanar (BPO) osteotomy.
The osteotomy by using an oscillating saw started on the medial
cortex 2.5 cm below the medial joint space.
For transversal, uniplanar osteotomy (UPO) the cut started 4 cm below the
medial joint line and was aimed at a point 3 cm below the lateral joint line
(figure 1a).
The dorsal cut of the biplanar osteotomy (BPO) also started 4 cm below the
medial joint line and was directed to a point 3 cm below the lateral joint line.
Only the posterior two thirds of the tibia were cut. The frontal third of
the tibia was leaved intact. The anterior cut was aimed to a point 2 cm below
the ventral joint line (figure 1b).
last years the medial opening-wedge HTO became very popular.
This operation is able to avoid typical complications of lateral
procedure and is relatively easy to perform. But also, the
medial technique includes some potential pitfalls and specific
complications [11].
On the one hand, the success of the medial HTO depends on the
quality of the internal fixation. The fixation is generally possible
by conventional plates [16] with or without autologous bone
grafts or bone substitutes [5]. Puddu created a spacer plate
which is able to support the osteotomy gap during osseous consolidation
[15]. In the last year’s angle stable plates for internal
fixation after HTO became popular [6]. In recent studies the biomechanical
properties of different implants were evaluated [6].
Stoffel et al. [14] compared the biomechnical properties of a
very massive implant (Tomofix, Synthes) with a small implant
(Puddu plate, Arthrex). The differences in dimension produced
different mechanical behaviour [13]. Against Spahn et al. found
a superior biomechanical behavoir in internal fixation by plates
which combine angle stability and spacers [12].
On the other hand, the stability after HTO depends on the oste-
Figure 2 Angle stable and a mobile spacer containing plate for opening wedge
HTO (Varibale-winkelstabile HTO Platte, Königsee-Implantate, Germany)
otomy technique during the operation. Classically, the osteotomy
is performed as a transverse, single cut [2]. The cut was
aimed at the caudal third of the tibiofibular joint [9]. Alternatively
Lobenhoffer et al. published the results of 112 patients
who were treated by a biplanar osteotomy technique [6] Biplanar
osteotomy: in addition to the transverse osteotomy of
the posterior tibia a second ascending osteotomy in the coronary
plane underneath the tibial tuberosity is performed. This
shall improve rotational stability of the osteotomy and create
an anterior buttress against sagittal tilting of the osteotomy
planes.
This study was aimed to compare the biomechanical properties
of uniplanar transversal with the biplanar cutting technique
in HTO in a sawbone model.
Materials and Methods
Specimen preparation, HTO, and fixation
The bone model consisted of Sawbones third-generation composite
tibiae (No. 3302) (Sawbones Europe, Malmö, Sweden).
The specimen were shortened to a length of 20 cm.
The transversal, uniplanar osteotomy (UPO) the cut started 4
cm below the medial joint line and was aimed to a point 3 cm
below the lateral joint line (figure 1a).
The dorsal cut of the biplanar osteotomy (BPO) also started 4
cm below the medial joint line and was aimed to a point 3 cm
below the lateral joint line. Only the posterior two thirds of
the tibia were cut. The frontal third of the tibia was leaved intact.
The anterior cut was aimed to a point 2 cm below the
ventral joint line (figure 1b). A total of five specimens was
prepared in each group.
A HTO angle of 10° was used in all experiments.
The osteotomies were fixed by an osteotomy plate which contained
a mobile spacer (Variabel-winkelstabile HTO-Platte®,
Königsee-Implantate, Germany). The implant is designed as
angle stable and a mobile spacer containing plate (figure 2
and 3).
Biomechanical test
The distal parts of the specimens were embedded with dental
plaster (Sockeldent, Albaum, Lehrte, Germany) in a steel cylinder
(5 x 10 cm). The tests were performed in a mechanical
testing machine (Z010, Zwick Germany). The proximal stamp
was a femoral part of an endoprosthesis as shown in figure 4.
An even axial load of the specimens was possible by using
this experimental design.
Preliminary measurements with five native saw-bones had demonstrated
a high reproducibility of this testing design.
In the first step, the specimens had undergone a preload of 50
N for 3 minutes. The distance of the dorsal part of the osteotomy
gap was measured by a precision measurement instrument
(Kraftfix, Schalkaldia GmbH, Schmalkalden, Germany).The
device has a precision of 0.1 mm. The point for me-
BIOmaterialien 8 (2), 2007
72
Figure 3
Osteotomy specimen
after internal fixation

Gunter Spahn: Biomechanical investigation of uniplanar cuts in opening-wedge high tibial osteotomy
Figure 4
Biomechanical test setup
asurement was marked with a water proof fine liner on the
dorsal tibial edge.
The load was increased from 50 to 1000 N at a velocity of 5
mm/s. After a preconditioning load cycle the test was stopped
by a 1000 N load for 1 minute.
Than a total of 20 cycles were performed. The load-displacement
curves were registered for the 1st and in the 20th cycle.
The machine was stopped again at a load of 1000 N for 1 minute
to determine the distance of the osteotomy gap.
Finally the specimens were stressed by an increasing load to
failure (5 mm/min). After failure the load decreased rapidly.
The tests were stopped by achieving 30% of the maximum load.
The failure tests were recorded by a video tape. This had made
it possible to register the cause of failure for every specimen.
Statistics
The software program testXpert 10.0 (Zwick, Ulm, Germany)
was used to evaluate the results of the mechanical tests.
Statistical analyses were performed on a personal computer
using SPSS version 13.0, SPSS Inc Chicago IL, USA. The Kolmogorov-Smirnov
test and analysis of variance were used in
addition to the Mann-Whitney U-test and chi-square test for
statistical analysis, with the level of significance set at p <
0.05.
Results
Displacement and Stiffness
The mean load-dependent displacement is shown in figure 5.
All specimens showed a load-dependent displacement. After
20 loading cycles the displacement increased in both groups.
Stiffness was calculated for 1000 N axial load. The stiffness
in BPO specimens after 1 cycle was 2102.8 ± 167.8 N/mm. After
1 cycle UPO specimen had a significant minor stiffness
(1500.6 ± 121.0 N/mm) than BPO specimens.
The undergoing of 20 loading cycles caused a significant loss
of stiffness. After these 20 cycles BPO specimen had a stiffness
of 1755.9 ± 129.2 N/mm. The stiffness in UPO specimen
was 1018.5 ± 15.5 N/mm. The difference between the groups
was significant.
Displacement within the Osteotomy Gap
The osteotomy gap underwent a deformation during axial loading.
This deformation depended on the number of loading
cycles, on the one hand. On the other hand, the osteotomy
techniques also influence the displacement within the osteotomy
gap. After one loading cycle no differences between
BPO and UPO specimens were evaluated. After 20 cycles BPO
specimen had a significant minor deformation under an axial
load of 1000 N (table 1).
Failure Tests
The mean maximum load at failure in UPO specimen was
2633.1 ± 229.4 N. Always the failure was caused by an infraction
of the lateral cortex. Two times a dorsal dislocation of
the tibial head was registered.
Specimens after BPO had a significant higher maximum load
at failure of 4554.8 ± 342.8 N. Every time, the failure also was
caused by an infraction of the lateral cortex but no dislocation
regarding to the longitudinal axis of the tibia was observed.
Discussion
The success after medial opening HTO in treatment of unicompartimental
osteoarthritis mainly depends on a sufficient
operation technique. This requires sufficient internal fixation
in the first line. In the last years the results of numerous investigations
for evaluating the biomechanical properties of
different internal fixations after opening wedge HTO were published
(Spahn et al., 2006c, Spahn and Wittig, 2002, Stoffel et
al., 2004c, Stuart et al., 1999). In these studies a relative high
primary stability of various internal fixations was suggested.
Another important biomechanical aspect in HTO is the direction
and the design of the osteotomy. The osteotomy classically
is performed as a transversal uniplanar cut which spares
the lateral 1/4 of the tibia.
Lobenhoffer et al. [6] [7] had hypothesized that a three-dimensional
biplanar osteotomy produces a higher primary stable
osteotomy than a uniplanar transversal (“classical”) osteotomy.
This biomechanical study was undertaken to compare
the UPO with the tri-dimensional BPO in a Sawbone osteotomy
model.
In the last years synthetic bone models e.g saw bones became
important in biomechanical investigations. The synthetic specimens
have identical dimensions and material properties. They
are available in high numbers and there are no individual limitations
given by age, sex, or osteoporosis.
The main effect of the medial opening wedge is the carefully
widening of the elastic bone within the osteotomy gap by chisels,
aimed to spare an intact lateral 1/4 of the tibial bone.
Because the osteotomy specimens had identical dimensions
and disposition of the sawing cuts, the biomechanical tests
BIOmaterialien 8 (2), 2007
73
ORIGINAL
ARBEITEN
Figure 5
Mean load-displacement curves for the specimens had undergone a total of
20 load-relief-cycles. The power-dependent displacement was evaluated
from the protocol of the testing machine. The stiffness was calculated after
one and after twenty cycles.

ORIGINAL ARBEITEN Gunter Spahn: Biomechanical investigation of uniplanar cuts in opening-wedge high tibial osteotomy
Width the dorsal osteotomy gap [mm]
under a load of 1000 N
After 1 cycle After 20 cycles
BPO 9.6±0.3 8.6±0.5
UPO 9.6±0.1 7.8±0.4*
Table 1: Load dependent displacement within the osteotomy gap
with an identically fixed osteotomy are sufficient for evaluation.
The tibia undergoes a significant loss of stiffness after medial
opening HTO. This loss of stiffness correlates with the number
of loading cycles. In our tests the specimens were loaded within
a range of 50 to 1000 N. This is according to the load of 20
gait cycles. Our results are conforming to the results of other
investigators. Stoffel et al. [14] also found a significant reduction
of axial stiffness. In Sawbone models fixed by a spacer
containing a Puddu plate this reduction was 76% [15]. By
usage of an angle-stable plate (Tomofix) the loss of reduction
only amounted 41% [6]. These experiments always were performed
by an UPO. In our experiments, the loss of axial stiffness
in UPO was 32.1%. This minor loss of stiffness may be
caused by a better biomechanical property of an angle-stable
and spacer containing internal fixation. The BPO produced a
significant minor loss of axial stiffness (16.5 %). This correlated
with a significant lesser displacement within the osteotomy
gap.
Finally, the main load of failure was significantly higher in
BPO specimen compared with UPO specimen. In BPO specimens
the failure always was caused by an infraction of the lateral
cortex. This is the weak point of the system anyway. These
dislocations have clinical relevance in vivo (Spahn, 2004b).
A displacement of the tibial head after HTO can namely produce
a catastrophically clinical outcome. Our results suggest
that BPO widely prevents this dislocation during axial loading.
Conclusions
This study was undertaken to evaluate the biomechanical properties
of a UPO and BPO in medial wedge osteotomy. The results
offer a significant superior axial stiffness under cyclic
loading as well as resistance against load to failure in BPO
specimens.
Abstract
This study was aimed to determine the biomechanical properties
of uniplanar tranversial (UPO) and biplanar, three-dimensional
(BPO) osteotomy in medial opening wedge high tibial
osteotomy (HTO) in a comparable Sawbone model.
Third generation tibial Sawbones were osteotomized in a standardized
manner and fixed with an angle-stable, spacer containing
plate. Axial stiffness after one and twenty loading cycles
(range 50 to 1000 N) was registered as well as displacement
within the osteotomy gap and load at failure.
After one loading cycle no differences between BPO (n=5) and
UPO (n=5) specimens were evaluated. The undergoing of 20
loading cycles caused a significant loss of stiffness. After the
cycles BPO specimen had a stiffness of 1755.9 ± 129.2 N/mm.
The stiffness in UPO specimen was 1018.5 ± 15.5 N/mm. The
difference between the groups was significant.
The mean maximum load at failure in UPO specimens was
2633.1 ± 229.4 N. Specimens after BPO had a significant higher
maximum load at failure of 4554.8 ± 342.8 N. In BPO specimens
the failure always was caused by an infraction in the lateral
cortex, whereas in UPO the failure was caused in two-times
by an additional dorsal dislocation of the tibial head.
This study was undertaken to evaluate the biomechanical properties
of a UPO and BPO in medial wedge osteotomy. The results
offer a significant advantage for the BPO regarding to
axial stiffness under cyclic loading as well as resistance against
load to failure.
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BIOmaterialien 8 (2), 2007
74
Dr. med.
Gunter Spahn
Korrespondenzadresse:
Center of Trauma and
Orthopaedic Surgery Eisenach
Sophienstr. 16
D-99817 Eisenach
Phone +49-3691-73500
Fax +49-3691-735011
Mail spahn@pk-eisenach.de and spahn.esa@t-online.de
Akademischer Lebenslauf
1980 – 1985 Medizinstudium an der
Friedrich-Schiller-Universität Jena
1985 Promotion
1985 – 1986 Pflichtassistenz am Klinikum Gera
1986 – 1988 Militärarzt in Spremberg
1988 – 1994 Klinikum Gera: Klinik für Allgemein-
Visceral- und Kinderchirurgie, Klinik
für Unfallchirurgie
1993 Facharzt für Chirurgie
1994-1997 Chefarzt der Medical Center Praxisklinik
Eisnach und ärztlicher Leiter des
Reha Zentrums für Orthopädie und
Traumatologie Eisenach
seit 1997 Praxisklinik für Unfallchirurgie und
Orthopädie in Eisenach
Schwerpunkte: Knorpelschaden und Arthrose,
Biomechanik, Implantatentwicklung

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ARBEITEN