Slide 1

Report
Measurement of tibial translation in dogs with anterior cruciate ligament rupture
Team Members: Alex Bloomquist, Graham Bousley, James Madsen, Mike Nonte
Department of Biomedical Engineering
Advisor: Wan-Ju Li, PhD
Client: Peter Muir, PhD
Load Cell Assembly
Hypodermic needles were placed at the anatomical markers, located at the fabella and
the tendon between the patella and femur. The device was secured by snapping the
needles onto the bottom of the device. The long stabilizing rod was lowered so that it
was resting on the dissecting table, and the other stabilizing rod was placed on the
canine’s leg. Force was applied to the tarsal, displacing the tibia and a voltage
difference from the Hall Effect sensor was recorded. Testing was conducted on both a
ruptured and intact ACL. The south and north pole magnet configurations were tested,
and it was determined that the north pole towards the Hall Effect sensor allowed for
better data. Five trails were performed for each set up. The load cell was tested to
ensure an accurate reading. Finally, both devices were used at the same time period to
gauge how they worked together. The device, and load cell recorded reliable and
repeatable data. The results of the north pole ruptured and north pole intact testing
are displayed below.
•Milled, Lexan holder and base
•Made with cemented Lexan sheet
•Load cell in between two bases to
measure torsion
•Attached to an op-amp circuitry for
voltage data acquisition
Background
The development of a canine arthrometer is desirable due to the non-quantitative
nature of current methods of ACL deterioration diagnosis. The tibial thrust and drawer
sign tests involve a veterinarian applying force to the canine tarsal or tibia, respectively,
then subjectively assessing the displacement of the tibia. While these methods are
accurate in diagnosing full ACL rupture, they are less effective in diagnosing partial
ACL rupture [1]. Arthroscopy, an endoscopic procedure, gives direct visual assessment
of the ACL and is effective in diagnosing rupture, however this procedure costs $1700
on average [2]. Deterioration and rupture of the ACL is far more common in canines
than in humans because it occurs as a result of natural joint wear rather than a severe
strain. Due to the prevalence and high cost of diagnosing ACL deterioration, a method
of diagnosis that is both cost-effective and quantitative is needed.
Testing and Results
3
Comparison of Displacement In
Intact and Ruptured ACL
0.1
Force vs Output
0
0
2.8
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
-0.1
2.6
Figure 3: Load cell
on canine knee in
resting position.
-0.2
2.4
-0.3
2.2
2
-0.4
1.8
Figure 4: Load cell.
1.6
Average Intact
Displacement
1.4
1.2
Hall Effect Sensor
Average
Ruptured
Displacement
1
0.8
Output (V)
Arthritis is the major cause of ACL rupture in canines and a quantitative, minimally
invasive diagnostic device is needed to increase the quality of healthcare for canines as
well as reduce costs. The device will measure tibial translation and force exerted on the
canine’s paw during the tibial thrust test. This data will be used to determine the
severity of ACL rupture. The design consists of two needles inserted at anatomical
markers in line with the ACL. The distance that separates these two markers is
measured by the Hall Effect sensor. The goal of this project was to develop a device
that could be used in conjunction with the tibial thrust test that would provide
quantitative measurement of the tibial displacement and force applied by the
veterinarian.
Final Design
Average Maximum Displacement (mm)
Abstract
-0.5
-0.6
-0.7
-0.8
0.6
Figure 1: The canine’s knee is shown in
the resting position of the tibial thrust
test. The needles are in the anatomical
markers located at the fabella and the
patellar tendon.
Figure 2: The canine’s knee is
shown in the flexed position of the
tibial thrust test. The needles are
in the anatomical markers located
at the fabella and the patellar
tendon.
•Easily attachable to needle tips placed at specific anatomical markers in the leg
•Hall Effect sensor and magnet system must stay in the same plane during the
measurement
•Measure tibial displacement of 1-10 mm accurately
•Minimally invasive to the canine leg
•Internalized system to increase accuracy and cleanliness
•Slider must be able to move with minimal force applied to needle
•Force measured must be accurate between 0-15 N
0.4
•Utilized a flat bar for stability
•Poles on ends for stabilizing the device
during testing
•Longer pole reaches to the table while
shorter is on the dogs upper leg
•Detachable needles with taper fitting for
ease of use and cleaning
•Case helps improve repeatability of data
by removing chance of internal changes
•Data acquired by a DAQ card for input
into LabView for analysis
•Circuits powered by 9V battery for ease
of portability
Force (N)
y = -0.035x + 0.0584
R² = 0.9999
0.2
0
Cost Analysis
Figure 5: Device with Hall
Effect sensor and case.
Design Requirements
-0.9
Figure 6: Device attached
at anatomical markers.
Item
Cost
18x24 Acrylic Sheet
$6.97
Hall Effect Sensors
$2.00 x8
6”x 12” Clear Polycarbonate Lexan sheet
$10.99
Glides
$2.69
Threaded Rod 1
$2.47
Hex nuts
$0.06 x2
Aluminum Rod
$0.97
Aluminum sheet metal
$7.98
Threaded Rod 2
$0.97
Total
$49.16
Acknowledgements
Future Work
•Design a more ergonomic force assembly
•Develop a more easily set up data
acquisition method
•Add measurement markers to case
•Improve the robustness of the design
Special Thanks to: Dr. Peter Muir, Amit Nimunkar, Lacey Halfen, Prof. Li, Peter
Klomberg
References
[1] DeRooster et. Al. "Morphologic and Functional Features of the Canine Cruciate Ligaments ". Veterinary Surgery. 2006.
[2] Veterinary Sports Medicine
http://www.vetsportsmedicine.com/newsAndEvents/documents/Proof_CCLInjurya.pdf. Accessed 9/15/09

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