Evaluation of vertical forces in the pads of Pitbulls with cranial cruciate ligament rupture

Abstract

Cranial cruciate ligament rupture (CCLR) is one of the most important stifle injuries and a common cause of lameness in dogs. Our objective was to measure the vertical forces in the pads of Pitbulls with cranial cruciate ligament rupture (CCLR) using a pressure sensitive walkway. A pressure sensitive walkway was used to collect vertical force data from the pads of 10 Pitbulls affected with unilateral CCLR. Ten healthy Pitbulls were included in the study as controls. Velocity varied between 1.3 and 1.6 m/s and acceleration was kept below +/- 0.1 m/s2. Differences between groups and between pads in the same limb within groups were investigated using ANOVA and the Tukey test. The paired Student t-test was employed to assess gait symmetry (p < 0.05).
Peak vertical forces (PVF) were lower in the affected limb, particularly in the metatarsal pad. Increased PVF values in the forelimb and the contralateral hind limb pads of affected dogs suggest a compensatory effect.
A consistent pattern of vertical force distribution was observed in the pads of dogs with CCLR. These data are important for increased understanding of vertical force distribution in the limb of dogs with CCLR disease. Kinetic analysis using pressure sensitive walkways can be useful in follow-up assessment of surgically treated dogs regardless of the surgical technique employed.

Full text

R E S E A R C H A R T I C L E Open Access
Evaluation of vertical forces in the pads of Pitbulls
with cranial cruciate ligament rupture
Alexandre Navarro Alves Souza
1*
, Angelica Cecilia Tatarunas
2
and Julia Maria Matera
1
Abstract
Background: Cranial cruciate ligament rupture (CCLR) is one of the most important stifle injuries and a common
cause of lameness in dogs. Our objective was to measure the vertical forces in the pads of Pitbulls with cranial cruciate
ligament rupture (CCLR) using a pressure sensitive walkway. A pressure sensitive walkway was used to collect vertical
force data from the pads of 10 Pitbulls affected with unilateral CCLR. Ten healthy Pitbulls were included in the study as
controls. Velocity varied between 1.3 and 1.6 m/s and acceleration was kept below ± 0.1 m/s
2
. Differences between
groups and between pads in the same limb within groups were investigated using ANOVA and the Tukey test. The
paired Student t-test was employed to assess gait symmetry (p < 0.05).
Results: Peak vertical forces (PVF) were lower in the affected limb, particularly in the metatarsal pad. Increased PVF
values in the forelimb and the contralateral hind limb pads of affected dogs suggest a compensatory effect.
Conclusions: A consistent pattern of vertical force distribution was observed in the pads of dogs with CCLR. These
data are important for increased understanding of vertical force distribution in the limb of dogs with CCLR disease.
Kinetic analysis using pressure sensitive walkways can be useful in follow-up assessment of surgically treated dogs
regardless of the surgical technique employed.
Keywords: Vertical forces, Cranial cruciate ligament rupture, Dogs, Kinetic analysis, Pads
Background
Cranial cruciate ligament rupture is one of the most
important stifle injuries and a common cause of lameness
in dogs [1]. CCLR results in joint instability and leads to
the development of degenerative joint disease over time
[2-5]. Kinetic analysis is commonly employed for objective
lameness evaluation in horses and dogs, among other
species [6]. Peak vertical force (PVF) and vertical impulse
(VI) are the most accurate parameters for lameness diag-
nosis [7] and can be measured using pressure sensitive
walkways [8-10]. PVF and VI are significantly decreased in
dogs with CCLR [6,11-14].
Vertical force redistribution studies in dogs with CCLR
report a significant overload of the contralateral limb
[9,10,15,16]. Similar to pedobarographic analysis in humans,
the isolated analysis of specific areas of the limb during the
stance phase of the stride can be performed in dogs using
modern kinetic analysis equipment. Data obtained via these
methods can be relevant when clinical decisions and patient
follow-uparebasedonimproved weight bearing (transfer
of load through the paw to the rest of the limb) [17,18].
Studies on vertical forces in the pads of dogs [17,18] are
scarce and unrelated to orthopedic disease. The aim of
this study was to analyze vertical forces in the pads of
dogs affected with CCLR. The description of PVF and
VIindogswithCCLRmaycontributeforabroader
understanding of the changes that result in decreased
weight bearing in these patients. It may also represent
a more comprehensive method for patient follow-up
and the critical evaluation of the surgical techniques
currently employed to treat the condition.
Methods
This research was approved by the Bioethics Committee
of the Faculty of Veterinary Medicine and Animal Science
of the University of São Paulo –FMVZ/USP. Ten healthy
Pitbulls (control group) and 10 Pitbulls presenting with
unilateral CCLR (CCLR group) were used in this study.
Previous informed consent was given for the owners.
All dogs were submitted to physical and radiographic
* Correspondence: telha68@yahoo.com.br
1
Department of Surgery, School of Veterinary Medicine and Animal Science,
University of São Paulo (FMVZ/USP), São Paulo, SP, Brazil
Full list of author information is available at the end of the article
© 2014 Souza et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly credited.
Souza et al. BMC Veterinary Research 2014, 10:51
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examination, and the tibial thrust test prior to kinetic ana-
lysis. Dogs were aged between 2 and 6 years and weighed
between 20 and 36 kg. Exclusion criteria were obesity,
cachexia, pregnancy, estrous, history of previous ortho-
pedic surgery, concurrent systemic or orthopedic disease,
and medication of any kind over the preceding 4 weeks
(minimum washout period of 4 weeks).
Kinetic analysis
Kinetic analysis was performed on a 1.5 × 0.5-m pressure
sensitive walkway
a
equipped with a series of 3 plates
instrumented with a total of 6864 sensors and connected
to a dedicated computer.
Five valid trials were evaluated for each dog. Valid trials
consisted of controlled velocity and acceleration in a
straight line without sidestepping or deviation of the
head. Out of a maximum of 20 consecutive passages re-
corded, 5 valid trials were selected for each dog. The first
4 passages were always excluded to avoid data collection
before dogs were familiar with the setup. Only full stride
cycles recorded in the middle of the platform were consid-
ered. The same operator (A.N.A.S.) was responsible for
valid trail selection and analysis. To avoid potential interfer-
ences with kinetic analysis trials were always performed in
the morning, before physical examination and before daily
physical activities were resumed.
Before each session all sensors were calibrated according
to a known standard weight. All trials were started 2 meters
before the walkway, so that dogs had enough room to
complete two full stride cycles before stepping on the plat-
form. Walking velocity varied between 1.3 and 1.6 m/s and
acceleration was kept below ± 0.1 m/s
2
. Velocity was given
bythesoftwareasstridelengthdividedbythedurationof
the stride cycle. Acceleration was controlled based on the
difference between initial and final velocity divided by time.
For increased strictness and to assure constant velocity,
only stance phases with a variation of ± 0.01 seconds be-
tween consecutive foot strikes were considered for each
leg. Dogs were walking fast during data collection in this
study. Given gait analysis at the trot was not intended,
only duty factors above 50% were considered. Duty factor
ranged from 54.1 to 63.4% (mean, 58%).
Peak vertical force (PVF, Newtons) and vertical im-
pulse (VI, N*s) were calculated from the vertical force
curve generated automatically by the software
b
. For each
foot strike evaluated, measurements of PVF and VI
(expressed as percentage of body weight) were obtained
from metacarpal/metatarsal pads and digital pads 2, 3, 4
and 5. These areas were manually outlined according to
previously reported methods [18].
Statistical analysis
Normal distribution of the data was investigated using the
Kolmogorov-Smirnov test. Analysis of variance (ANOVA)
and the Tukey test (post hoc) were used to compare the
means and to assess the differences between groups and
among pads in the same limb within each group. Gait
symmetry between the right and left limbs in control dogs
and between the healthy and the diseased limb in CCLR
dogs was assessed using the paired Student’s t test. The
level of significance was set at 5% (p <0.05). Sample power
(difference between means based on standard deviation)
greater than 80% confirmed the quality of the data.
Results
The CCLR group consisted of 5 intact males and 5 intact
females weighing 31.1 ± 3.9 kg and aged 4.2 ± 1.6 years.
All dogs in this group had a history of lameness of at
least 1 month duration (2.8 ± 1.5 months) but were not
showing signs of acute lameness at the time of data
collection. All dogs had been treated with non-steroidal
anti-inflammatory drugs, but had completed the minimum
washout period. The control group consisted of 4 intact
males and 6 intact females weighing 28.8 ± 5 kg and aged
4.5 ± 1.2 years. Age and body weight did not differ between
groups. Mean PVF and VI values expressed as percentage
of body weight and respective standard deviations are
summarized in Tables 1, 2 and 3.
No gait asymmetries were observed in the control group
(Table 1). However, important differences were observed
in CCLR dogs. PVF and VI were lower in affected limb
than in the contralateral limb and in the fore limbs when
compared to control (Table 1), indicating that the affected
limb, particularly the contralateral limb, is spared at the
expense of the remaining limbs in cases of CCLR. Given
no gait asymmetries were observed in the control group,
theleftandrightfrontandhindlimbsweregrouped
together (i.e. healthy forelimb and hindlimb) and used
as a reference for pad evaluation. In the CCLR group,
the most prominent decrease in PVF was documented
in the metatarsal pad of the affected limb. Mean PVF
values in digital pads 3 and 4 were similar to mean values
recorded in control dogs (Tables 2 and 3). Vertical force
curves of healthy hindlimbs and hindlimbs with CCLR are
shown in Figure 1.
Table 1 Peak vertical force (PVF) and vertical impulse (VI)
for total of the limbs (mean ± SD)
Control group Forelimb Hind limb
Right Left Right Left
PVF 54.6 ± 6.7
a
55.2 ± 6.0
a
34.2 ± 5.7
b
33.4 ± 5.3
b
VI 23.4 ± 2.9
a
24.5 ± 3.3
a
13.0 ± 1.6
b
13.0 ± 1.4
b
CCLR group Ipsilateral Contralateral Affected Contralateral
PVF 60.5 ± 6.1
c
58.8 ± 6.7
c
23.6 ± 7.4
d
39.3 ± 6.0
e
VI 25.7 ± 1.9
a
27.0 ± 2.5
c
7.7 ± 1.2
d
16.8 ± 1.6
e
PVF = peak verti cal force; VI = vertical impulse. Groups with different letters in
the same row are significantly diff erent (p < 0.05). Mean values expressed as %
of body weight.
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Discussion
Kinetic analysis is more sensitive than subjective evaluation
for lameness diagnosis in dogs [19,20]. Although cranio-
caudal forces can also be measured using force plates,
such forces are less reliable than PVF and VI for lameness
diagnosis in dogs due to greater variability [7,20]. Vertical
forces have 90% sensitivity and specificity for lameness de-
tection and can be accurately documented using pressure
sensitive walkways [8,9,21], as performed in this study.
Despite the wide popularity of kinetic analysis, studies
on kinetic analysis in canine pads are scarce [17,18,22].
Changes in vertical forces lead to a decrease in PVF and
VI in dogs with CCLR [10-16,23,24].
The few kinetic studies on load distribution in canine
pads published to date report important contribution of
the metatarsal pad for total weight bearing in German
Shepherds [18], Labradors and Greyhounds [17]. In this
study, the lower mean vertical forces documented in
CCLR dogs reflected decreased weight bearing on the
metatarsal pad in particular. While vertical forces in the
affected limb corresponded to approximately 70% of the
mean values documented in control dogs, vertical forces
on the metatarsal pad were as low as 30% of controls.
The effect of breed on limb [25,26] and pad [17,18]
kinetic analysis has been reported in dogs. Therefore
dogs of the same breed were used in this study. All dogs
had a history of lameness of at least 1 month duration.
Lameness may be more severe in acute cases or shortly
after surgery [27].
As previously reported, the classical M-shape of the
vertical force curve reflects the specific dynamics involved
in the stance phase of the stride, that begins with braking
(footstrike) and ends with propulsion as the dogs lifts the
limb off ground (toe off). The first vertical force peak cor-
responds to the maximum force generated during braking
and is followed by a second peak representing the max-
imum force generated by propulsion. The valley between
both peaks represents the movement of the limb from
footstrike to toe off (mid-stance) [6,18]. The characteristic
M-shaped pattern may be absent in faster gaits, particularly
in the front limbs. A single force peak may then be visu-
alized due to superimposition of the force peaks corre-
sponding to footstrike and toe off respectively [18,22].
In this study, the M-shaped waveform typically seen dur-
ing walking was observed in healthy hindlimbs, but not in
hindlimbs affected with CCLR (Figure 1). Whenever the
Table 2 Peak vertical force (PVF) for the pads (mean ± SD)
Forelimbs Metacarpalpad Digital pads
2345
Healthy 15.0 ± 3.5
aA
5.6 ± 1.6
aB
11.3 ± 1.7
aC
12.6 ± 1.4
aD
11.2 ± 1.9
aC
Ipsilateral 22.3 ± 4.7
bA
6.0 ± 1.4
aB
12.6 ± 2.5
bC
14.3 ± 2.2
bC
15.1 ± 2.7
bC
Contralateral 20.3 ± 5.3
cA
5.9 ± 1.5
aB
12.9 ± 2.5
bC
14.3 ± 1.9
bC
14.4 ± 2.6
cC
Hind limbs Metatarsalpad Digital pads
23 4 5
Healthy 7.7 ± 2.2
aA
3.1 ± 0.7
aB
8.1 ± 1.3
aA
9.1 ± 1.4
aC
6.9 ± 1.3
aD
Affected 2.5 ± 2.2
bA
2.5 ± 1.2
bA
7.7 ± 1.9
aB
8.4 ± 2.9
aB
4.1 ± 1.4
bC
Contralateral 14.0 ± 3.2
cA
5.0 ± 1.6
cB
11.1 ± 2.0
bC
10.9 ± 1.5
bC
8.1 ± 2.0
cD
Groups with different letters are significantly different (p < 0.05).
Capital letter- row/low case letter –column. Mean values expressed as % of body weight.
Table 3 Vertical impulse (VI)for the pads (mean ± SD)
Forelimbs Metacarpalpad Digital pads
2345
Healthy 4.8 ± 0.7
aA
1.8 ± 0.4
aB
4.6 ± 0.7
aA
5.5 ± 0.8
aA
5.1 ± 0.8
aA
Ipsilateral 7.1 ± 0.9
bA
2.1 ± 0.3
aB
4.6 ± 0.6
aC
6.0 ± 0.6
aD
6.0 ± 0.7
bD
Contralateral 6.7 ± 1.2
bA
2.3 ± 0.5
aB
5.1 ± 0.6
aC
6.2 ± 0.6
aD
6.2 ± 0.8
bD
Hind limbs Metatarsalpad Digital pads
2345
Healthy 1.6 ± 0.3
aA
0.7 ± 0.2
aB
3.5 ± 0.5
aC
4.4 ± 0.9
aD
2.3 ± 0.4
aE
Affected 0.5 ± 0.3
bA
0.7 ± 0.2
aA
2.5 ± 0.5
bB
3.0 ± 0.5
bB
1.2 ± 0.3
bC
Contralateral 3.0 ± 0.4
cA
1.6 ± 0.3
bB
4.6 ± 0.5
cC
4.8 ± 0.5
aC
2.8 ± 0.5
cA
Groups with different letters are significantly different (p < 0.05).
Capital letter- row/low case letter –column. Mean values expressed as % of body weight.
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M-shaped waveform was observed the first vertical force
peak was associated with the metacarpal or the metatarsal
pad and the second with the digital pads, particularly the
3rd and 4th hindlimb pads.
Vertical forces are usually distributed among all pads
during the stance phase of the stride in dogs. However,
our results suggest that the aforementioned areas were
possibly responsible for a higher percentage of weight
bearing and for the braking and propulsion vertical
force peaks. This may be related to CCLR given the
braking phase of the stride is one of the most affected by
the instability of the joint due to the cranial movement of
the tibia [28], as simulated during physical examination
using the tibial thrust test [29]. Vertical force magnitude
in metatarsal pad may thus constitute an important
parameter for post-surgical follow-up of CCLR cases.
Vertical force measurements may also indirectly aid in
the identification of residual joint instability with po-
tential impact on weight bearing, as shown in ex vivo
studies [30].
Weight bearing can also be measured based on cra-
niocaudal force measurements although this method is
less accurate due to lower force magnitudes and greater
variability. Also, craniocaudal force measurements require
the use of a force plate for evaluation of forces generated
in three orthogonal planes during movement. Conversely,
vertical forces may be measured in any pressure sensitive
walkway at a lower cost.
A setup containing a series of instrumented plates
capable of sampling a complete stride cycle during the
same passage would reduce examination time and the
degree of physical exertion required from subjects [9],
while permitting consistent data collection [7,31]. Good
quality portable craniocaudal force measurement systems
and pressure sensitive walkways are currently available and
yield reliable data despite differences in calibration and
PVF readings [9].
Conclusions
The results of this study suggest that evaluation of vertical
forces in the pads using pressure sensitive walkways may
be a promising method for evaluation of dogs with CCLR.
The application of this diagnostic tool in other orthopedic
diseases that are currently evaluated based on conven-
tional kinetic analysis [32-35] may also contribute for
increased understanding of the weight bearing changes
observed in affected dogs.
The relevance of kinematic analysis of the tibiotarsal
joint in dogs predisposed to CCLR has been reported
[36] and important changes in weight bearing have
been observed in the distal limb of affected dogs in this
study. A comprehensive assessment of locomotion in
these patients may be invaluable for critical evaluation
of the surgical techniques currently employed to treat
the condition.
Figure 1 Vertical force curve in the pads of a dog affected with CCLR. Force curves reflect vertical force analysis of each footpad of a dog
affected with CCLR during a valid passage. The same passage was sagitally separated to facilitate visualization and comparison between the
affected and the contralateral hindlimb. The typical M-shaped waveform can be seen in the healthy, but not in the affected hindlimb. Peak
vertical force is lower in the metatarsal pad of the affected hindlimb.
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Endnotes
a
7100 QL Virtual Sensor 3 Mat System, Tekscan Inc.
South Boston, MA, USA.
b
I-scan 5.231, Tekscan Inc., South Boston, MA,USA.
Abbreviations
CCLR: Cranial cruciate ligament rupture; PVF: Peak vertical forces; VI: Vertical
impulse.
Competing interests
This study did not involve competing interests.
Authors’contribution
ANAS, ACT and JMM designed this study. ANAS and ACT examined all dogs
involved. ANAS was responsible for kinetic data collection and analysis. ANAS
and JMM prepared this manuscript. This manuscript was read and approved
by all authors involved.
Acknowledgements
The authors thank FAPESP (Fundação de Amparo à Pesquisa do Estado de
São Paulo) for financial support (Process number 2004/08706-0).
Author details
1
Department of Surgery, School of Veterinary Medicine and Animal Science,
University of São Paulo (FMVZ/USP), São Paulo, SP, Brazil.
2
Department of
Veterinary Medicine, School of Animal Science and Food Engineering,
University of São Paulo (FZEA/USP), Pirassununga, SP, Brazil.
Received: 22 July 2013 Accepted: 25 February 2014
Published: 1 March 2014
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doi:10.1186/1746-6148-10-51
Cite this article as: Souza et al.:Evaluation of vertical forces in the pads
of Pitbulls with cranial cruciate ligament rupture. BMC Veterinary Research
2014 10:51.
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