- Email: [email protected]
Statistical analysis of patellar resurfacing in Caucasian and Japanese subjects
Track 4. Implants for Trauma and Orthopedics-Joint ESB Track The highflex Sigma RP-F showed lower yield volumes within the high flexion range as compared to the conventional Sigma RE Furthermore, it showed similar yield volumes within the normal flexion range. However all calculated yield volumes reached the maximum value within the high flexion range. In conclusion, the highflex TKA is more suited for the high flexion range as compared to conventional TKA. Furthermore, the improved performance within the high flexion range does not lead to an adverse performance within the normal flexion range. However, the maximum stresses and yield volumes are reached at the high flexion range: the range in which the Sigma RP-F is intended to function. Hence, the implant safety factor reduces in high flexion. 7146 We-Th, no. 33 (P58) Failure of the united rotating hinge total knee prosthesis - A case report T.-Y. Huang 1, H.-M. Ma 1, E-'~ Ho 2, C.-'~ Lung 3, C.-H. Huang 1,4.
1Department of Orthopaedic Surgery, Mackay Memorial Hospital, Taipei, Taiwan, 2Biomechanics Research Laboratory, Mackay Memorial Hospital, Taipei, Taiwan, 3production Development Department, United Orthopedic Department, Taipei, Taiwan, 4Institute of Biomedical Engineering, National Yang Ming University, Taipei, Taiwan. A 61 years old female patient, 160cm high and 68kg weight, with chondrosarcoma at proximal tibial of left knee. She had obviously valgus deformity before surgery. She received a chondrosacroma reconstruction in 1998. During surgery, the PCL, ACL and MCL were sacrificed, and a 21 cm resection of proximal tibia was done. The fibular head and LCL were reserved. United oncology reconstruction knee system (United Orthopedic Co., Taiwan) was used. After five years, she heard crackle sound while walking and felt pain at left knee suddenly. A megaprosthesis revision was performed with a United custom-made knee system (United Orthopedic Co., Taiwan) in 2003. Tibial PE stopper wear and breakage was found at the revision surgery. On the basis of macrography, the fracture occurred at the thinnest site of PE stoper. Scratching and slight delamination were observed overall articulating surface of PE stopper. There was no fracture source or particular material defect was detected by SEM analysis, but the fusion of PE was poor. Furthermore, the PE bushing was thinned. The design of axis in rotating hinge knee prosthesis should be reconsidered, especially for the LCL preserved cases. The bushing thickness should be thickened for guaranty of prosthesis. Also, the design of tibial and femur components should be more constraint in newer generation rotating hinge knee system for complex knee arthroplasty. We suggested patient with intact LCL and preserved fibular head was not suit for 70 valgus of femoral stem. Also, we suggested increase of femoral cutting surface, increase the space between the stem and flange, and increase length of stem could increase the stability of femur. 4576 We-Th, no. 34 (P58) Improving accuracy of fluoroscopic estimation of 3D-pose of total knee arthroplasty using radiographic stereometry K. Kobayashi 1, M. Sakamoto 1, T. Sato 2, '~ Koga 2, G. Omori 3, '~ Tanabe 4.
1Dept. Japan, Japan, Japan,
of Health Sciences, Niigata University School of Medicine, Niigata, 2Department of Orthopaedic Surgery, Niigata Kobari Hospital, Niigata, 3Center for Transdisciplinary Research, Niigata University, Niigata, 4Dept of Mechanical Engineering, Niigata University, Niigata Japan
X-ray fluoroscopy has been a useful method for analyzing joint kinematics of total knee arthroplasty in vivo. However, this method is less accurate for measuring translation in the out-of-plane direction. In this study, a method was developed for improving the accuracy of fluoroscopic three-dimensional (3D) pose estimation of knee prostheses using radiographic stereometry. Femoral and tibial components of a knee prosthesis were fixed using polyurethane rods. Steel balls were attached to the component surfaces. To obtain a truth relative pose (rotation and translation vectors) of the two components, coordinates of the center of the balls were measured by a coordinate measuring machine with an accuracy of 1 ~tm. A single-plane fluoroscopic image of the entire prosthesis was taken in the medial-lateral direction. A semi-automated 3D-pose matching algorithm was performed for obtaining a relative pose from the single-plane image with an initial relative translation vector determined arbitrary or with that was determined by radiographic stereometry using bi-plane X-ray images of the two components. A relative error of translation vector in the out-ofplane direction exceeded 3.5 mm with the arbitrary initial vector. This error was improved to 0.9 mm with the initial relative translation vector determined by radiographic stereometry. In the two in-plane directions, relative errors in the translation vector were within 0.6 mm. The maximum relative error in the rotation vector was also improved from 1.10 to 0.80 by introducing the initial relative translation vector determined by radiographic stereometry.
4.3 Knee Endoprosthetics
$519
4504 We-Th, no. 35 (P58) The influence of tibial baseplate position on stress distribution of tibial bone after total knee arthroplasty J.-J. Liau 1, W.-P. Ho 2, C.-K. Cheng 3. 1School and Graduate Institute
of Physical Therapy, College of Medicine, National Taiwan University, 2Department of Orthopaedic Surgery, Wan-Fang Hospital, Taipei Medical University, Taiwan, 3Institute of Biomedical Engineering, National Yang Ming University; Taiwan Anthropometric or morphometric data on resected proximal tibia have been widely investigated for the shape design of tibial baseplate of total knee prostheses. Maximum bony coverage of the tibial baseplate on the resected surface can minimize the stress in the bone-implant interface. However, the relationship between the tibial coverage and the stress distribution in the resected tibial bone was not investigated extensively. A three dimension finite element model of the tibial baseplate and tibial bone was constructed. The lateral translation (1, 2, 3 mm) relative to the optimal position of tibial baseplate on the resected tibial surface was simulated. The fixed boundary condition was specified on the most distal surface of tibial bone. A symmetrical loading with a compressive load of 3000N, 1500N on each medial and lateral side was applied on the upper surface of tibial baseplate. The bony coverage and the maximum von Mises stress were calculated to investigate the effects of tibial baseplate position on stress distribution of tibial bone. The result showed that the tibial baseplate at the optimal position provides the maximum bony coverage and the minimum von Mises stress in the tibial bone. When tibial baseplate was placed laterally relative to the optimal position, bony coverage decreased and the von Mises stress in the tibial bone increased. This study revealed that the maximum bony coverage of tibial resected surface provide the minimum stress in the tibial bone. A tibial baseplate with a slight posteriorlateral overhang produces stress concentration on the upper lateral proximal tibia and a 3 mm lateral translation of tibial baseplate relative to the optimal position will increase maximum von Mises stress by 18%. 7090 We-Th, no. 36 (P58) Effects of stem end design on stem pain in TKR '~-H. Kim 1, K.M. Koo 1, O.-S. Kwon 2, D.-K. Bae 1. 1Kyung Hee University,
Korea, 2 The Catholic University of Korea, Korea Stems are frequently revised in total knee arthroplasty (TKA) both to provide additional fixation and to assist in ensuring more consistent component alignment. Many clinical studies have investigated that cemented implant with longer stem length provides better stability and less micro-motion. However, previous studies have reported the incidence of end-of-stem pain on the tibial side when press-fit component with 140 mm stem extension was applied. The problem of pain related to the long stem in total knee arthroplasty is defined poorly and the biomechanical rational to explain this problem is not provided. In this study, we investigated the effects of stem end design on stem pain in revision TKR. The finite element model of tibia, including the cortical bone, the cancellous bone and canal, was developed based on CT images. The stem models with various stem lengths, diameters and frictional coefficients, and press-fit effects were considered as a parametric study. The pressure distribution on the interface of stem and Von-Mises stress around the stem end were investigated to predict the effects of stem end design on stem end pain. The results showed that the longer stem length, the stronger press-fit, the bigger stem diameter, and the higher frictional coefficient increased both peak contact pressure and the highest Von-Mises stress values. In this study, we hypothesized that the different stem design creates different contact pressure and Von-Mises stress distribution around the stem, and the locally higher pressures and stresses may be related to the stem end pain. Our clinical data supported the biomechanical findings hypothesized in this study. This study will be useful to modify the stem end design and reduce the end-of-stem pain in revision TKR. 7478 We-Th, no. 37 (P59) Statistical analysis of patellar resurfacing in Caucasian and Japanese subjects C. Fitzpatrick 1, D. FitzPatrick 1, J. Lee 2, D. Auger 2. 1Mechanical Engineering,
University College Dublin, Dublin, Ireland, 2DePuy Orthopaedics Inc., Warsaw, Indiana, USA Introduction: Many knee implant designs rely upon good coverage of the bone for proper healing, reduced soft tissue impingement and load transfer across the joint. This patellar study compared the performance of a circular footprint with an anatomically designed implant in both Caucasian and Japanese subjects. Methods: Data consisted of 32 Caucasian and 42 Japanese CT scans of the knee. Resection depth was taken at 35% patellar thickness (near the soft tissue attachment boundary), the profile being defined by 12 points at
$520
Poster Presentations
Journal o f Biomechanics 2006, Vol. 39 (Suppl 1)
equiangle intervals about the midpoint of the median ridge. The geometric centre of each resection profile relative to the median ridge was calculated. Caucasian and Japanese profiles were compared. An anatomic design was created using mean dimensions of the profile data. The circular design was centred on the geometric centre of the resection profile. Cluster analysis was utilized to determine five groupings of size, and each style of footprint was scaled to best fit each grouping. For each resection profile the best size was selected and the goodness-of-fit (GOF) of that size was measured using differences in dimensions between the profile and the design. Results: There was no difference in geometric centre location between ethnic groups (p=0.5). Overall, mean location was 1 . 3 ± 1 . 0 m m lateral to the median ridge. Laterally, there was no difference between groups (p =0.5). Medially, mean Caucasian measurements were an average 6% larger than Japanese (p<0.05). There was significant improvement in fit of the anatomic (GOF = 40.5 mm 2) design over the circular designs (GOF = 64.3 mm 2) (p <(~:0.001 ). Discussion: Caucasian and Japanese resection profile dimensions were similar. Both populations used the full range of implant sizes, although the average Japanese size was 2/3's of a size smaller than the average Caucasian size (p < 0.05). The asymmetric shape of the anatomic implant requires double the number of implants to accommodate left and right knees, however it aligns more optimally and covers significantly better than the circular design.
System (I)) was created by the Pro-E software (Pro/Engineer Wildfire 2.0). The boundary condition was that the distal end of the tibia was fixed and a 1950N compression load was applied from the proximal of the femur at knee extension. To simulate the surgical malalignment, the proximal tibia was recected and the tibial component was placed on the medial tibial condyle with ten different orientations, from valgus 6 to varus 10 degrees with increment of 2 degrees in coronal plane, while incorporating a 5 degrees posterior inclination, with the same height of knee surface. The contact stress on the cancellous bone increased from 3.781 to 5.308 MPa when the tibial component was placed from valgus 6 to varus 10 degrees. The maximum von Mises stress was observed on the proximal end of the medial diaphyseal cortex, and the values were from 13.835 to 21.038 MPa. Our results demonstrated that the stress was obviously increased especially when valgus of knee alignment was simulated. Therefore, slight valgus placement of tibial component in UKA was suggested to reduce excessive stress on the proximal tibia.
7145 We-Th, no. 38 (P59) The Effect of femoral component design on conformity of the patellofemoral joint F.-Y. Ho 1, H.-M. Ma 2, T.-G. Kwok 2, C.-Y. Huang 3, C.-H. Huang 2,4.
An instrumented tibial tray was developed to enable six-component load measurements in a primary total knee replacement [1]. Such data is useful for improving knee arthroplasty and advising patients. The goal of this investigation was to prove the functionality of the instrumented prosthesis and measuring technique in a cadaver experiment. Six semiconductor strain gages were placed inside the hollow stem of a custom-made telemeterized tibial tray. For calibration 21 points on top of the tibial tray were loaded causing combinations of 6 known load components [2]. For each loading point the six strain gages produce six signals which are dependent on these six load components. Calibration was performed at room temperature to accommodate to the conditions for cadaver testing. The prosthesis was implanted using conventional surgical technique in a fresh frozen cadaver. After closing all soft tissue, the power coil and antenna were fixed to the leg. Manipulations to the lower extremity were performed including varus-valgus stress, anterior and posterior drawer forces and flexion-extension movements. The external loads were applied manually using a spring scale. All activities were captured on a digital video tape simultaneously with the strain gage signals [3]. The calibration resulted in an accuracy of the prosthesis better than 5% for all load components including crosstalk. Only the medio-lateral force component had a slightly lower accuracy. Stable signals were obtained immediately. The simultaneous recordings of video and strain gage signals on one tape enables the detailed analysis of the measured forces with respect to different coordinate systems plus control of the performed activities. Ranges of measured loads were - 4 to +10 Nm for varus-valgus stress and up to 800 N compressive force during flexion-extension movement. Acknowledgement: This study was supported by Zimmer GmbH, Winterthur, Switzerland
1Biomechanics Research Laboratory, Department of Biomedical Research, Mackay Memorial Hospital, Taipei, Taiwan, 2Department of Orthopaedic Surgery, Mackay Memorial Hospital, Taipei, Taiwan, 3Institute of Mechanical Engineering, Chang Gung University, Taipei, Taiwan, 4Institute of Biomedical Engineering, National Yang Ming University, Taipei, Taiwan. To determine the effects of different femoral component designs on conformity of the patellofemoral joint, 5 total knee prostheses (Low Contact Stress, MillerGalante II, NexGen, Porous-Coated Anatomic, and Total Condylar prosthesis) were investigated. Three-dimensional models of the prostheses and a native patella were developed. The conformity (curvature) of 5 different prosthetic femoral components to their corresponding patellar component and to the native patella at different flexion angles were assessed by measuring the intersect angles of tangential lines. The Total Condylar prosthesis had poor conformity with the native patella (maximum of 29.55 degrees) and even with its patellar component (up to 38.19 degrees). In the other 4 prostheses, the conformities were reasonable (average, less than 6.06 degrees) when articulated with their corresponding patellar component. The Porous-Coated Anatomic femoral component showed relatively satisfactory conformity with the native patella (range, 4.95 to 8.15 degrees). The result was better than Miller-Galante II prostheses (range, 10.9 to11.52 degrees). Although the Nexgen prosthesis had inferior conformity to native patella at low flexion angle, the conformity was good at mid or high flexion angles (average, 3.57 and 4.54 degrees respectively). The Low Contact Stress femoral component had optimal conformity with native patella (range, 2.29 to 2.54 degrees). There were no significant differences (p >0.208) in the conformity with native patella and its patellar component at any flexion angle. The geometry of the anterior flange of the femoral component in total knee prosthesis is critical to allow normal patellofemoral joint kinematics. A more anatomical femoral component design should be chosen when surgeons decide not to resurface the patella at the time of operation. 4758 We-Th, no. 39 (P59) The influence o f surgical malalignment on contact stress o f unicompartmental knee prosthesis - A finite element analysis T.-W. Chang 1, J.-J. Liau 2, C.-H. Wu 1, C.-H. Huang 1, C.-K. Cheng 1. 1Institute
of Biomedical Engineering, National Yang Ming University; Taipei, Taiwan, 2School and Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University, Taipei, Taiwan The treatment of unicompartmental knee arthritis with unicompartmental knee arthroplasty (UKA) has had renewed popularity in recent years. Aseptic loosening and subsidence of a tibial component are recognized as the main complications in UKA. Excessive stress on the supporting cancellous bone is thought to contribute to the loosening and subsidence. The purpose of this study was to analyze the influence of surgical malalignment on contact stress of uni-compartmental knee prosthesis by finite element model. A threedimensional finite element model of human knee joint including proximal femur, distal tibia, articular cartilage and meniscus was constructed from the computed tomography (CT) data of one normal subject. In addition, a unicompartmental knee prosthesis (Zimmer M/GTM Unicompartmental Knee
4503 We-Th, no. 40 (P59) In vitro measurements of loads and moments using an instrumented tibial tray B. Heinlein 1, A. Halder 2, A. Rohlmann 1, E Graichen 1, G. Bergmann 1. 1Charit&
Universit~tsmedizin Berlin, CBF, Berlin, Germany, 2Hellmuth_Ulrici_Kliniken, Klinik fEtrEndoprothetik, Sommerfeld, Germany
References [1] Heinlein et al. Proc. ORS 2005. [2] Bergmann et al. J. Biomech. 1985. [3] Graichen et al. Med Eng Phys. 1996. 7156 We-Th, no. 41 (P59) Mechanical aspects of the development o f a ceramic bicondylar femoral knee component T. Pandorf, M. Kuntz, M. Muhr-Schenk, P. Merkert. CeramTecAG, Plochingen,
Germany While alumina and zirconia ceramic bearings have been widely used in hip endoprosthetics the experience with ceramics in knee arthroplasty is limited. As a consequence, mechanical concepts to assess the design of femoral knee components with respect to their ability to carry maximum in-vivo stresses are not established nor can be found in standards. Thus, a new mechanical test concept has been developed to provide a high reliability of the ceramic knee components. This concept consists of three main steps: First, a finite element analysis of the in-vivo implant situation is performed. With this, the highest values of the maximum principle stresses and their locations are determined. Second, a invitro test design is developed which is able to reproduce the locations of the previously detected locations of the maximum stresses. Third, the forces for the test configurations are quantified. The steps are explained in more detail below. Using finite element analysis (FEA) for different loading scenarios a design adaptation using a metal design to meet special ceramic requirements (e. g.
1Department of Orthopaedic Surgery, Mackay Memorial Hospital, Taipei, Taiwan, 2Biomechanics Research Laboratory, Mackay Memorial Hospital, Taipei, Taiwan, 3production Development Department, United Orthopedic Department, Taipei, Taiwan, 4Institute of Biomedical Engineering, National Yang Ming University, Taipei, Taiwan. A 61 years old female patient, 160cm high and 68kg weight, with chondrosarcoma at proximal tibial of left knee. She had obviously valgus deformity before surgery. She received a chondrosacroma reconstruction in 1998. During surgery, the PCL, ACL and MCL were sacrificed, and a 21 cm resection of proximal tibia was done. The fibular head and LCL were reserved. United oncology reconstruction knee system (United Orthopedic Co., Taiwan) was used. After five years, she heard crackle sound while walking and felt pain at left knee suddenly. A megaprosthesis revision was performed with a United custom-made knee system (United Orthopedic Co., Taiwan) in 2003. Tibial PE stopper wear and breakage was found at the revision surgery. On the basis of macrography, the fracture occurred at the thinnest site of PE stoper. Scratching and slight delamination were observed overall articulating surface of PE stopper. There was no fracture source or particular material defect was detected by SEM analysis, but the fusion of PE was poor. Furthermore, the PE bushing was thinned. The design of axis in rotating hinge knee prosthesis should be reconsidered, especially for the LCL preserved cases. The bushing thickness should be thickened for guaranty of prosthesis. Also, the design of tibial and femur components should be more constraint in newer generation rotating hinge knee system for complex knee arthroplasty. We suggested patient with intact LCL and preserved fibular head was not suit for 70 valgus of femoral stem. Also, we suggested increase of femoral cutting surface, increase the space between the stem and flange, and increase length of stem could increase the stability of femur. 4576 We-Th, no. 34 (P58) Improving accuracy of fluoroscopic estimation of 3D-pose of total knee arthroplasty using radiographic stereometry K. Kobayashi 1, M. Sakamoto 1, T. Sato 2, '~ Koga 2, G. Omori 3, '~ Tanabe 4.
1Dept. Japan, Japan, Japan,
of Health Sciences, Niigata University School of Medicine, Niigata, 2Department of Orthopaedic Surgery, Niigata Kobari Hospital, Niigata, 3Center for Transdisciplinary Research, Niigata University, Niigata, 4Dept of Mechanical Engineering, Niigata University, Niigata Japan
X-ray fluoroscopy has been a useful method for analyzing joint kinematics of total knee arthroplasty in vivo. However, this method is less accurate for measuring translation in the out-of-plane direction. In this study, a method was developed for improving the accuracy of fluoroscopic three-dimensional (3D) pose estimation of knee prostheses using radiographic stereometry. Femoral and tibial components of a knee prosthesis were fixed using polyurethane rods. Steel balls were attached to the component surfaces. To obtain a truth relative pose (rotation and translation vectors) of the two components, coordinates of the center of the balls were measured by a coordinate measuring machine with an accuracy of 1 ~tm. A single-plane fluoroscopic image of the entire prosthesis was taken in the medial-lateral direction. A semi-automated 3D-pose matching algorithm was performed for obtaining a relative pose from the single-plane image with an initial relative translation vector determined arbitrary or with that was determined by radiographic stereometry using bi-plane X-ray images of the two components. A relative error of translation vector in the out-ofplane direction exceeded 3.5 mm with the arbitrary initial vector. This error was improved to 0.9 mm with the initial relative translation vector determined by radiographic stereometry. In the two in-plane directions, relative errors in the translation vector were within 0.6 mm. The maximum relative error in the rotation vector was also improved from 1.10 to 0.80 by introducing the initial relative translation vector determined by radiographic stereometry.
4.3 Knee Endoprosthetics
$519
4504 We-Th, no. 35 (P58) The influence of tibial baseplate position on stress distribution of tibial bone after total knee arthroplasty J.-J. Liau 1, W.-P. Ho 2, C.-K. Cheng 3. 1School and Graduate Institute
of Physical Therapy, College of Medicine, National Taiwan University, 2Department of Orthopaedic Surgery, Wan-Fang Hospital, Taipei Medical University, Taiwan, 3Institute of Biomedical Engineering, National Yang Ming University; Taiwan Anthropometric or morphometric data on resected proximal tibia have been widely investigated for the shape design of tibial baseplate of total knee prostheses. Maximum bony coverage of the tibial baseplate on the resected surface can minimize the stress in the bone-implant interface. However, the relationship between the tibial coverage and the stress distribution in the resected tibial bone was not investigated extensively. A three dimension finite element model of the tibial baseplate and tibial bone was constructed. The lateral translation (1, 2, 3 mm) relative to the optimal position of tibial baseplate on the resected tibial surface was simulated. The fixed boundary condition was specified on the most distal surface of tibial bone. A symmetrical loading with a compressive load of 3000N, 1500N on each medial and lateral side was applied on the upper surface of tibial baseplate. The bony coverage and the maximum von Mises stress were calculated to investigate the effects of tibial baseplate position on stress distribution of tibial bone. The result showed that the tibial baseplate at the optimal position provides the maximum bony coverage and the minimum von Mises stress in the tibial bone. When tibial baseplate was placed laterally relative to the optimal position, bony coverage decreased and the von Mises stress in the tibial bone increased. This study revealed that the maximum bony coverage of tibial resected surface provide the minimum stress in the tibial bone. A tibial baseplate with a slight posteriorlateral overhang produces stress concentration on the upper lateral proximal tibia and a 3 mm lateral translation of tibial baseplate relative to the optimal position will increase maximum von Mises stress by 18%. 7090 We-Th, no. 36 (P58) Effects of stem end design on stem pain in TKR '~-H. Kim 1, K.M. Koo 1, O.-S. Kwon 2, D.-K. Bae 1. 1Kyung Hee University,
Korea, 2 The Catholic University of Korea, Korea Stems are frequently revised in total knee arthroplasty (TKA) both to provide additional fixation and to assist in ensuring more consistent component alignment. Many clinical studies have investigated that cemented implant with longer stem length provides better stability and less micro-motion. However, previous studies have reported the incidence of end-of-stem pain on the tibial side when press-fit component with 140 mm stem extension was applied. The problem of pain related to the long stem in total knee arthroplasty is defined poorly and the biomechanical rational to explain this problem is not provided. In this study, we investigated the effects of stem end design on stem pain in revision TKR. The finite element model of tibia, including the cortical bone, the cancellous bone and canal, was developed based on CT images. The stem models with various stem lengths, diameters and frictional coefficients, and press-fit effects were considered as a parametric study. The pressure distribution on the interface of stem and Von-Mises stress around the stem end were investigated to predict the effects of stem end design on stem end pain. The results showed that the longer stem length, the stronger press-fit, the bigger stem diameter, and the higher frictional coefficient increased both peak contact pressure and the highest Von-Mises stress values. In this study, we hypothesized that the different stem design creates different contact pressure and Von-Mises stress distribution around the stem, and the locally higher pressures and stresses may be related to the stem end pain. Our clinical data supported the biomechanical findings hypothesized in this study. This study will be useful to modify the stem end design and reduce the end-of-stem pain in revision TKR. 7478 We-Th, no. 37 (P59) Statistical analysis of patellar resurfacing in Caucasian and Japanese subjects C. Fitzpatrick 1, D. FitzPatrick 1, J. Lee 2, D. Auger 2. 1Mechanical Engineering,
University College Dublin, Dublin, Ireland, 2DePuy Orthopaedics Inc., Warsaw, Indiana, USA Introduction: Many knee implant designs rely upon good coverage of the bone for proper healing, reduced soft tissue impingement and load transfer across the joint. This patellar study compared the performance of a circular footprint with an anatomically designed implant in both Caucasian and Japanese subjects. Methods: Data consisted of 32 Caucasian and 42 Japanese CT scans of the knee. Resection depth was taken at 35% patellar thickness (near the soft tissue attachment boundary), the profile being defined by 12 points at
$520
Poster Presentations
Journal o f Biomechanics 2006, Vol. 39 (Suppl 1)
equiangle intervals about the midpoint of the median ridge. The geometric centre of each resection profile relative to the median ridge was calculated. Caucasian and Japanese profiles were compared. An anatomic design was created using mean dimensions of the profile data. The circular design was centred on the geometric centre of the resection profile. Cluster analysis was utilized to determine five groupings of size, and each style of footprint was scaled to best fit each grouping. For each resection profile the best size was selected and the goodness-of-fit (GOF) of that size was measured using differences in dimensions between the profile and the design. Results: There was no difference in geometric centre location between ethnic groups (p=0.5). Overall, mean location was 1 . 3 ± 1 . 0 m m lateral to the median ridge. Laterally, there was no difference between groups (p =0.5). Medially, mean Caucasian measurements were an average 6% larger than Japanese (p<0.05). There was significant improvement in fit of the anatomic (GOF = 40.5 mm 2) design over the circular designs (GOF = 64.3 mm 2) (p <(~:0.001 ). Discussion: Caucasian and Japanese resection profile dimensions were similar. Both populations used the full range of implant sizes, although the average Japanese size was 2/3's of a size smaller than the average Caucasian size (p < 0.05). The asymmetric shape of the anatomic implant requires double the number of implants to accommodate left and right knees, however it aligns more optimally and covers significantly better than the circular design.
System (I)) was created by the Pro-E software (Pro/Engineer Wildfire 2.0). The boundary condition was that the distal end of the tibia was fixed and a 1950N compression load was applied from the proximal of the femur at knee extension. To simulate the surgical malalignment, the proximal tibia was recected and the tibial component was placed on the medial tibial condyle with ten different orientations, from valgus 6 to varus 10 degrees with increment of 2 degrees in coronal plane, while incorporating a 5 degrees posterior inclination, with the same height of knee surface. The contact stress on the cancellous bone increased from 3.781 to 5.308 MPa when the tibial component was placed from valgus 6 to varus 10 degrees. The maximum von Mises stress was observed on the proximal end of the medial diaphyseal cortex, and the values were from 13.835 to 21.038 MPa. Our results demonstrated that the stress was obviously increased especially when valgus of knee alignment was simulated. Therefore, slight valgus placement of tibial component in UKA was suggested to reduce excessive stress on the proximal tibia.
7145 We-Th, no. 38 (P59) The Effect of femoral component design on conformity of the patellofemoral joint F.-Y. Ho 1, H.-M. Ma 2, T.-G. Kwok 2, C.-Y. Huang 3, C.-H. Huang 2,4.
An instrumented tibial tray was developed to enable six-component load measurements in a primary total knee replacement [1]. Such data is useful for improving knee arthroplasty and advising patients. The goal of this investigation was to prove the functionality of the instrumented prosthesis and measuring technique in a cadaver experiment. Six semiconductor strain gages were placed inside the hollow stem of a custom-made telemeterized tibial tray. For calibration 21 points on top of the tibial tray were loaded causing combinations of 6 known load components [2]. For each loading point the six strain gages produce six signals which are dependent on these six load components. Calibration was performed at room temperature to accommodate to the conditions for cadaver testing. The prosthesis was implanted using conventional surgical technique in a fresh frozen cadaver. After closing all soft tissue, the power coil and antenna were fixed to the leg. Manipulations to the lower extremity were performed including varus-valgus stress, anterior and posterior drawer forces and flexion-extension movements. The external loads were applied manually using a spring scale. All activities were captured on a digital video tape simultaneously with the strain gage signals [3]. The calibration resulted in an accuracy of the prosthesis better than 5% for all load components including crosstalk. Only the medio-lateral force component had a slightly lower accuracy. Stable signals were obtained immediately. The simultaneous recordings of video and strain gage signals on one tape enables the detailed analysis of the measured forces with respect to different coordinate systems plus control of the performed activities. Ranges of measured loads were - 4 to +10 Nm for varus-valgus stress and up to 800 N compressive force during flexion-extension movement. Acknowledgement: This study was supported by Zimmer GmbH, Winterthur, Switzerland
1Biomechanics Research Laboratory, Department of Biomedical Research, Mackay Memorial Hospital, Taipei, Taiwan, 2Department of Orthopaedic Surgery, Mackay Memorial Hospital, Taipei, Taiwan, 3Institute of Mechanical Engineering, Chang Gung University, Taipei, Taiwan, 4Institute of Biomedical Engineering, National Yang Ming University, Taipei, Taiwan. To determine the effects of different femoral component designs on conformity of the patellofemoral joint, 5 total knee prostheses (Low Contact Stress, MillerGalante II, NexGen, Porous-Coated Anatomic, and Total Condylar prosthesis) were investigated. Three-dimensional models of the prostheses and a native patella were developed. The conformity (curvature) of 5 different prosthetic femoral components to their corresponding patellar component and to the native patella at different flexion angles were assessed by measuring the intersect angles of tangential lines. The Total Condylar prosthesis had poor conformity with the native patella (maximum of 29.55 degrees) and even with its patellar component (up to 38.19 degrees). In the other 4 prostheses, the conformities were reasonable (average, less than 6.06 degrees) when articulated with their corresponding patellar component. The Porous-Coated Anatomic femoral component showed relatively satisfactory conformity with the native patella (range, 4.95 to 8.15 degrees). The result was better than Miller-Galante II prostheses (range, 10.9 to11.52 degrees). Although the Nexgen prosthesis had inferior conformity to native patella at low flexion angle, the conformity was good at mid or high flexion angles (average, 3.57 and 4.54 degrees respectively). The Low Contact Stress femoral component had optimal conformity with native patella (range, 2.29 to 2.54 degrees). There were no significant differences (p >0.208) in the conformity with native patella and its patellar component at any flexion angle. The geometry of the anterior flange of the femoral component in total knee prosthesis is critical to allow normal patellofemoral joint kinematics. A more anatomical femoral component design should be chosen when surgeons decide not to resurface the patella at the time of operation. 4758 We-Th, no. 39 (P59) The influence o f surgical malalignment on contact stress o f unicompartmental knee prosthesis - A finite element analysis T.-W. Chang 1, J.-J. Liau 2, C.-H. Wu 1, C.-H. Huang 1, C.-K. Cheng 1. 1Institute
of Biomedical Engineering, National Yang Ming University; Taipei, Taiwan, 2School and Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University, Taipei, Taiwan The treatment of unicompartmental knee arthritis with unicompartmental knee arthroplasty (UKA) has had renewed popularity in recent years. Aseptic loosening and subsidence of a tibial component are recognized as the main complications in UKA. Excessive stress on the supporting cancellous bone is thought to contribute to the loosening and subsidence. The purpose of this study was to analyze the influence of surgical malalignment on contact stress of uni-compartmental knee prosthesis by finite element model. A threedimensional finite element model of human knee joint including proximal femur, distal tibia, articular cartilage and meniscus was constructed from the computed tomography (CT) data of one normal subject. In addition, a unicompartmental knee prosthesis (Zimmer M/GTM Unicompartmental Knee
4503 We-Th, no. 40 (P59) In vitro measurements of loads and moments using an instrumented tibial tray B. Heinlein 1, A. Halder 2, A. Rohlmann 1, E Graichen 1, G. Bergmann 1. 1Charit&
Universit~tsmedizin Berlin, CBF, Berlin, Germany, 2Hellmuth_Ulrici_Kliniken, Klinik fEtrEndoprothetik, Sommerfeld, Germany
References [1] Heinlein et al. Proc. ORS 2005. [2] Bergmann et al. J. Biomech. 1985. [3] Graichen et al. Med Eng Phys. 1996. 7156 We-Th, no. 41 (P59) Mechanical aspects of the development o f a ceramic bicondylar femoral knee component T. Pandorf, M. Kuntz, M. Muhr-Schenk, P. Merkert. CeramTecAG, Plochingen,
Germany While alumina and zirconia ceramic bearings have been widely used in hip endoprosthetics the experience with ceramics in knee arthroplasty is limited. As a consequence, mechanical concepts to assess the design of femoral knee components with respect to their ability to carry maximum in-vivo stresses are not established nor can be found in standards. Thus, a new mechanical test concept has been developed to provide a high reliability of the ceramic knee components. This concept consists of three main steps: First, a finite element analysis of the in-vivo implant situation is performed. With this, the highest values of the maximum principle stresses and their locations are determined. Second, a invitro test design is developed which is able to reproduce the locations of the previously detected locations of the maximum stresses. Third, the forces for the test configurations are quantified. The steps are explained in more detail below. Using finite element analysis (FEA) for different loading scenarios a design adaptation using a metal design to meet special ceramic requirements (e. g.