MECH 4013 Lab 2 Primary Stability

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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 3 1 MECH 4013 – BIOMEDICAL DEVICE DESIGN EXPERIMENT 2: Primary Stability of Total hip Replacements (THR) ( Location: 7103 Canal building ) 1. Introduction Total hip replacement (THR) is the gold standard to treat hip osteoarthritis. The objectives of this laboratory exercise are to give students practical experience of how to implant a total hip replacement (THR) into a cadaveric porcine femur and asses the primary stability of the implant. The primary stability tests of THR are used as an indication for their clinical success. While subjected to regular physical load the initial distal migration of the implant should not exceed a few millimetres; to achieve biological integration of the implant the micro-motion should not exceed 150 μm. 2. Safety • Every student is required to bring a lab coat and safety goggles. • While handling the biological tissue, the 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. • While operating the drill press and the oscillating saw the students are required to wear the face shields provided. • The servo-hydraulic testing machine will be operated by the teaching assistant (TA). • Ref [1] contains information pertinent to the safe operation of this machine. 3. Materials • Servo-hydraulic testing machine MTS (Canal Building Room 7103) • Cadaveric porcine femur • A custom designed femoral stem. • Custom designed reamer • Large drill bit, 0.086” drill bit, 5/16” bit • Drill press • Marker • LVDT and support • Computer to record LVDT, force and torque data.

MECH 4013 – BIOMEDICAL DEVICE DESIGN Experiment 3 2 4. Experimental Procedure Note: Document the procedure of implanting the THR. Note any difficulties during the implantation procedure. Take coronal and transverse (top view) photographs of the intact and implanted femur so that you can determine how accurate you were able to restore joint anatomy. Place a ruler next to the specimen and ensure it is visible in the photographs in order to calibrate your pictures. 1. Align implant with proximal femur and mark line to cut neck (Figure 1). Also remove the condyles from the distal femur so that the bone will fit into the lower fixture. With neck resected, use a large drill bit to start a hole in the medullary canal. This should be as lateral as possible (Figure 2). 2. Use the reamer to prepare the cavity for the implant (Figure 3). The reamer should be impacted into the femur until all teeth are within the femur. Figure 1 Figure 2

MECH 4013 – BIOMEDICAL DEVICE DESIGN Experiment 3 3 3. Test the fit of the implant by inserting firmly by hand. 4. Remove the implant and secure the shoulder to the drill fixture using the screw provided (Figure 4). Secure the 0.086” drill bit in the chuck of the drill press. Adjust the table height so that the tip of the drill just reaches the implant surface as the drill press reaches the end of its stroke. Secure the fixture with the clamps provided. Figure 3

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MECH 4013 – BIOMEDICAL DEVICE DESIGN Experiment 3 4 5. Mount the prepared femur on the implant and tap the distal femur with the mallet to press-fit the stem. Make sure the implant is firmly in the bone otherwise application of hip loads during the experiment will cause the machine screw (see step 6) to contact the side of the drill hole and deflect, invalidating test results. Take care not to move the fixture during this step. Drill a pilot hole in the bone. Replace the drill bit with a 5/16” bit and drill a clearance hole. DO NOT DRILL TOO DEEP to avoid damaging the implant. 6. Remove the implant from the drill fixture and insert the #4-40 machine screw in the distal implant (Figure 5). Figure 4

MECH 4013 – BIOMEDICAL DEVICE DESIGN Experiment 3 5 7. Insert the femur in the MTS bottom fixture with the screw pointing to the front. The distal femur may need to be trimmed circumferentially to achieve this. Insert the metal plates and tighten the screws to align the implant bearing surface with the cavity of the upper MTS fixture (Figure 6). Figure 5

MECH 4013 – BIOMEDICAL DEVICE DESIGN Experiment 3 6 8. Using c-shaped fixtures provided, mount the LVDT support to the bone. Rest the fixture on the temporary support and tighten the set screws until the support is firmly mounted to the bone (Figure 7). The set screws should not penetrate the bone. Figure 6

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MECH 4013 – BIOMEDICAL DEVICE DESIGN Experiment 3 7 9. Mount the LVDT on the support with the magnetic clips. Adjust the LVDT such that it reads approximately +2.5 to +3.0 mm before the implant is loaded. Ensure the LVDT cable does not contact the actuator. 10. NOTE: The TA will operate the MTS. Begin by manually loading the implant to approximately 100N. Start the data acquisition on the secondary computer. The MTS program will then increase the load and cycle between 50 and 500N for 500 cycles. 11. Repeat step 10. In this step a torque of +/- 1.0 Nm will be applied in addition to the axial load. Ensure that the data collection is started on the secondary computer before the MTS program starts. 5. Analysis Estimate, using your photographs, how accurate you were able to restore joint anatomy, using the lateral offset (in-tact vs implant) and change in inferior-superior location of the hip centre. Comment on your findings. From the LVDT data recorded, calculate the average position within each cycle; plot migration (i.e. average position) vs. cycle number from the two experiments. Determine the total migration by subtracting the average LVDT data of the first 5 from last 5 cycles of each test. Determine the micro-motions at the beginning and end of each test i.e. motion amplitude from the LVDT data; report the average micro-motion in the first 5 and last Figure 7

MECH 4013 – BIOMEDICAL DEVICE DESIGN Experiment 3 8 5 cycles for both load cases. Would this implant likely be successful clinically? How could you improve the design of the implant you used in the experiment? 7 References [1] Authors unknown, (2008) Series 370 Load Unit Product Information Manual Part Number 100-184-093 A, 100-184-093 B, MTS systems corporation, Minnesota