MECH 4013 Lab 3 Spinal fixation

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Carleton University *

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4013

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Mechanical Engineering

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Jan 9, 2024

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MECH 4013 – BIOMEDICAL DEVICE DESIGN Experiment 4 1 MECH 4013 – BIOMEDICAL DEVICE DESIGN EXPERIMENT 3: Posterior Spinal Fixation ( Location: 7103 Canal building ) 1. Introduction Four out of five adults experience at least one episode of low back pain during their life. Although not all of these patients will require surgery, there is an increasing number of people that need fusion of one or more levels of their vertebrae. The major challenge in spinal fusion surgery is to achieve a rigid clinical stabilization (i.e. reduce the movement of two adjacent vertebrae) to allow the vertebrae to fuse through bone growth. There are a number of techniques used to fuse vertebrae, but the most common is known as posterior stabilization. The major challenge for the orthopaedic surgeon is to achieve sufficient “stabilization” so that bony fusion can occur. In this lab we will measure the 3D motion of a porcine cadaveric cervical spine before and after the implantation of a posterior instrumentation 2. Safety • Every student is required to bring a lab coat and safety goggles. • While handling the biological tissue, students are required to wear surgical gloves. • Please advise the instructor beforehand if you are allergic to latex. • You may use a scalpel to remove soft tissues from the cadaveric porcine bone. Use caution when using the scalpel. A special container is provided for disposal of scalpel blades after use. 3. Materials • Cadaveric porcine cervical spine • Scalpel • A custom designed posterior fixation device with pedicle screws. • Drill bit • Drill press/ hand drill • Custom spine tester • Optotrak system with computer • Orthopaedic Research pins with Rigid Bodies • 6-axis load cell • Computer to record force and moment data.

MECH 4013 – BIOMEDICAL DEVICE DESIGN Experiment 4 2 4. Experimental Procedure 1. Dissect any extraneous soft tissue such as muscles and tendon. Do not damage the facet joint capsules or the ligaments. 2. Clamp lowest vertebra in the lower fixture, with the thin plate and four clamping screws anterior, and the other side within the spinal canal. This should leave an intervertebral disc exposed just above the plate. If the lowest vertebra does not fit in the clamp, it can be removed and the next vertebra secured in the clamp. Record the number of vertebral bodies in the spine segment that is used. 3. Mount the upper fixture on the axis (C2) vertebra and screw into place. 4. Place the lower fixture in the clamps of the six axis load cell so that the left side is facing the torque device. This will orient the specimen for flexion-extension loading. Align the plate so that it is flush with the back of the load cell. Tighten the four bolts. 5. Attach the torsion arm to the upper fixture using two bolts. 6. Use two orthopaedic research pins with rigid bodies and insert in the transverse process above the lowest exposed disc. These should be inserted with one above the vertebral disc that will be ‘injured’ (the lowest exposed disc) and the other in the top vertebra. These can be inserted without pre-drilling (Figure 1). A third rigid body is mounted on the load cell and is used as a reference for the bottom vertebra within the fixture. 7. Use a third orthopaedic research pin with rigid body that has been calibrated as a digitiser with the NDI First Principles software. With the help of the TA, place the tip of the device Figure 1:

MECH 4013 – BIOMEDICAL DEVICE DESIGN Experiment 4 3 on each landmark listed below and record the coordinates with the NDI First Principles program. Record landmarks for the lowest two vertebra, above and below the injury level, and the top vertabra; coordinates will be associated with the orthopaedic research pin secured to the same vertebra so that the 3D coordinates of the landmarks (virtual markers) are tracked and recorded during spine motions. Landmarks to be recorded: anterior vertebral body; left lateral vertebral body; right lateral vertebral body. Repeat for each required vertebra and ensure that each set of three points are not collinear. 8. Set the angle control to 15 degrees for both directions in the Labview program and run three preconditioning cycles. 9. Set the Collection Settings in NDI First Principles to record for 10 seconds. 10. Set the angle control to 15 degrees for both directions in the Labview program. 11. Ensure that all orthopaedic research pins are visible to the Optotrak camera throughout the range of motion. 12. Press start on Labview and Record in the First Principles software and the test will run for three cycles. Do not stand between the Optotrack camera and the specimen during this time. Once the collection is complete, save both the Labview and Optotrack data files with appropriate file names (e.g. Intact_flex-ext). 13. Rotate the specimen so that anterior is facing the torque device. This will align the specimen for lateral bending. BE EXTREMELY CAREFUL NOT TO BUMP THE TRACKING DEVICES. Ensure that the Optotrak rigid bodies are visible. Note that the camera and/or entire test apparatus may be moved between tests. The spine must not be moved within the clamp. 14. Re-attach the torsion arm and repeat the test. Save the data files with appropriate names (e.g. Intact_lateralbending) 14. Various injury models may be applied to the specimen shown below, after which the specimen will be retested in flexion-extension and lateral bending. The configurations are: a. Cut the capsules and cartilage of the facet joints on both sides, between the lowest and next lowest vertebrae. b. Cut the lowest exposed disc (as described in #2). c. Apply pedicle screw fixation to the posterior spine, across the injured level. Locate the pedicles by resecting soft tissues in the posterior and lateral region above and below the cuts in part a. Drill a small hole down the pedicle and insert a pedicle screw. Repeat above and below the injury on both sides. Fix a connecting rod between upper and lower pedicle screws (Figure 2). Choose one injury model to apply to your specimen (a or b above, or both simultaneously) and report your choice. Include photo(s) of the injury. After testing the injured spine, apply pedicle screw fixation described in c. Note you will have three configurations: in-tact, injured and with fixation, with two test directions for each (flexion-extension and lateral bending). Note: For each test you will have two files, one from each computer. The Labview file will contain measurements from all six axes of the load cell. The Optotrak file will have the rigid

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MECH 4013 – BIOMEDICAL DEVICE DESIGN Experiment 4 4 body data of each tracking device. This will be explained in more detail by the TA. You may have to manually synchronize the two data collections when analyzing the data. 5. Analysis Document the preparation of the specimen and how the simulated injuries were performed. From the Optotrak data calculate the relative rotation of the adjacent vertebrae and the entire spine. Using the 6-axis load cell data, plot rotation vs moment for the complete last testing cycle of the intact specimen, the injury model and for the posterior fixation for each of the six test cases, and include all plots in your report. From this data set determine the range of motion (ROM) and the neutral zone (NZ). Summarise your ROM and NZ results in a bar graph. Comment on how the injury model and the posterior fixation affect the ROM and NZ. Remember to do this analysis for both the two adjacent vertebrae and the entire spine. Figure 2: