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EXPERIMENTAL EVALUATION OF FEMORAL COMPONENT MICROMOTION AFTER TOTAL KNEE ARTHROPLASTY
Presentation 1589 − Topic 27. Joint arthroplasty
S359
EXPERIMENTAL EVALUATION OF FEMORAL COMPONENT MICROMOTION AFTER TOTAL KNEE ARTHROPLASTY Noel Conlisk (1, 2), Pankaj Pankaj (1, 2), Colin R Howie (2)
1. School of Engineering, The University of Edinburgh, UK; 2. Edinburgh Orthopaedic Engineering Centre, The University of Edinburgh, UK
Total knee arthroplasty (TKA) is generally considered to be a successful operation [Weir, 1996], however studies have also shown the potential for failures or complications arising post implantation. Currently one leading cause of failure is aseptic loosening of the femoral component. The aim of this study was to determine the effect implant design has on the levels of bone-implant micromotion post total knee arthroplasty.
Methods A custom DVRT sensor rig was developed. The test rig allowed the relative motions and rotations between the point of fixation on the bone and the femoral components to be captured. Three different femoral components from the Stryker triathlon series (Stryker, UK) were investigated (PS, TS short stem and TS long offset stem), with each femoral component being implanted into a 4th generation composite femur (Sawbones, Vashon, WA, USA) by a qualified orthopaedic surgeon. Loading was based on three peaks corresponding to 0°, 10° and 20° flexion (Fig. 1) during the stance phase of gait from a normal walking cycle [Bergmann, 2008]. The bone was secured in a custom holder which permitted variation in bone orientation. Once fixed at the desired angle a cyclical compressive load was applied using a Zwick/Roell materials testing machine. Each test consisted of 40 cycles at each of the three flexion angles investigated. Previous studies have shown that micromotion of uncemented implants can be detected with relatively few cycles [Schneider, 1989]. Data acquisition was carried out using virtual instrumentation software (LabView 7.0) and a 728.5N
1186N
1643N
Results Micromotion at the bone implant interface was found to increase with flexion angle. The addition of a stem was shown to reduce motions in comparison to stemless implants. Once cemented bone-implant micromotions were found to reduce to a 1/3 of their original levels as shown in Fig. 2. Similar trends were also observed for implant rotations. Magnitude of Relative Bone-Implant Motions 250
PS uncemented
200
Micromotion (μm)
Introduction
National Instruments DAQpad-6070E (National Instruments, Austin, TX). For each test the signal was logged at a rate of 10 samples a second. This signal was then converted from voltage to microns using each individual sensors calibration curves and then filtered using a 3rd order Butterworth filter to reduce noise.
TS short stem uncemented TS long offset stem uncemented
150
PS cemented TS short stem cemented
100
TS long offset stem cemented 50
0 0
10
20
Flexion angle (°)
Figure 2: Typical results for levels of relative motion over the course of the walking cycle.
Discussion Traditionally most implants tend to be tested in extension only. This study highlights the importance of testing implants at a number of functional flexion angles to more adequately capture the levels of motion. This study also suggests that stemmed implants perform better than stemless implants in uncemented cases, however once cemented all implants have comparable levels of motion. These findings indicate that the use of long stems is not necessary for cemented implants.
References Figure 1: Experimental loading protocol for 0°, 10°and 20°flexion for a normal walking cycle.
Bergmann, G, 2008; from: www.orthoload.com Schneider, E, Clin Orthop 248:200-209, 1989. Weir, D.J, J Bone Joint Surg [Br] 78:907-11, 1996.
ESB2012: 18th Congress of the European Society of Biomechanics
Journal of Biomechanics 45(S1)
S359
EXPERIMENTAL EVALUATION OF FEMORAL COMPONENT MICROMOTION AFTER TOTAL KNEE ARTHROPLASTY Noel Conlisk (1, 2), Pankaj Pankaj (1, 2), Colin R Howie (2)
1. School of Engineering, The University of Edinburgh, UK; 2. Edinburgh Orthopaedic Engineering Centre, The University of Edinburgh, UK
Total knee arthroplasty (TKA) is generally considered to be a successful operation [Weir, 1996], however studies have also shown the potential for failures or complications arising post implantation. Currently one leading cause of failure is aseptic loosening of the femoral component. The aim of this study was to determine the effect implant design has on the levels of bone-implant micromotion post total knee arthroplasty.
Methods A custom DVRT sensor rig was developed. The test rig allowed the relative motions and rotations between the point of fixation on the bone and the femoral components to be captured. Three different femoral components from the Stryker triathlon series (Stryker, UK) were investigated (PS, TS short stem and TS long offset stem), with each femoral component being implanted into a 4th generation composite femur (Sawbones, Vashon, WA, USA) by a qualified orthopaedic surgeon. Loading was based on three peaks corresponding to 0°, 10° and 20° flexion (Fig. 1) during the stance phase of gait from a normal walking cycle [Bergmann, 2008]. The bone was secured in a custom holder which permitted variation in bone orientation. Once fixed at the desired angle a cyclical compressive load was applied using a Zwick/Roell materials testing machine. Each test consisted of 40 cycles at each of the three flexion angles investigated. Previous studies have shown that micromotion of uncemented implants can be detected with relatively few cycles [Schneider, 1989]. Data acquisition was carried out using virtual instrumentation software (LabView 7.0) and a 728.5N
1186N
1643N
Results Micromotion at the bone implant interface was found to increase with flexion angle. The addition of a stem was shown to reduce motions in comparison to stemless implants. Once cemented bone-implant micromotions were found to reduce to a 1/3 of their original levels as shown in Fig. 2. Similar trends were also observed for implant rotations. Magnitude of Relative Bone-Implant Motions 250
PS uncemented
200
Micromotion (μm)
Introduction
National Instruments DAQpad-6070E (National Instruments, Austin, TX). For each test the signal was logged at a rate of 10 samples a second. This signal was then converted from voltage to microns using each individual sensors calibration curves and then filtered using a 3rd order Butterworth filter to reduce noise.
TS short stem uncemented TS long offset stem uncemented
150
PS cemented TS short stem cemented
100
TS long offset stem cemented 50
0 0
10
20
Flexion angle (°)
Figure 2: Typical results for levels of relative motion over the course of the walking cycle.
Discussion Traditionally most implants tend to be tested in extension only. This study highlights the importance of testing implants at a number of functional flexion angles to more adequately capture the levels of motion. This study also suggests that stemmed implants perform better than stemless implants in uncemented cases, however once cemented all implants have comparable levels of motion. These findings indicate that the use of long stems is not necessary for cemented implants.
References Figure 1: Experimental loading protocol for 0°, 10°and 20°flexion for a normal walking cycle.
Bergmann, G, 2008; from: www.orthoload.com Schneider, E, Clin Orthop 248:200-209, 1989. Weir, D.J, J Bone Joint Surg [Br] 78:907-11, 1996.
ESB2012: 18th Congress of the European Society of Biomechanics
Journal of Biomechanics 45(S1)