1. Department of Biomedical Engineering
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
Abstract
Final Design
Testing and Results
Load Cell Assembly
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.
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.
Figure 3: Load cell on canine knee in resting position.
Figure 4: Load cell.
Hall Effect Sensor
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.
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
Cost Analysis
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
Total
$49.16
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.
Figure 5: Device with Hall Effect sensor and case.
Design Requirements
Figure 6: Device attached at anatomical markers.
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
Acknowledgements
Special Thanks to: Dr. Peter Muir, Amit Nimunkar, Lacey Halfen, Prof. Li, Peter Klomberg
Future Work
References
Design a more ergonomic force assembly
Add measurement markers to case
Develop a more easily set up data acquisition method
Improve the robustness of the design
[1] DeRooster et. Al. "Morphologic and Functional Features of the Canine Cruciate Ligaments ". Veterinary Surgery
[2] Veterinary Sports Medicine
Accessed 9/15/09