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Comparative study of probabilistic methods applied to a 3D finite element model of a THR
Track 3. Musculoskeletal systems and Performance - Joint ISB/ESB Track 4301 Mo, 08:30-08:45 (P5) Hip abductor function after total hip replacement: a comparison of the anterior and lateral approaches V.M. Klausmeier 1, L.-S. Chou 1, W. Gum 1, B. Jewett 2, D. Collis 2. 1Department
of Human Physiology, University of Oregon, Eugene, OR, USA, 2Orthopedic Healthcare Northwest, Eugene, OR, U.S.A
3.1. Joints - Hip
$67
5601 Mo, 09:00-09:15 (P5) The effect of muscle loads on the interface micromotion of hip stems M.R.A. Kadir 1,2, U.N. Hansen 1, A.A. Amis 1, R. Klabunde 3. 1Department
of Mechanical Engineering, Imperial College London, UK, 2Biomechanics Laboratory, Universiti Teknologi Malaysia, Malaysia, 3Zimmer European Headquarters, Winterthur, Switzerland
More than 220,000 artificial hip joints are being implanted annually in the USA making this surgery very common [1]. There have been new approaches that utilize the anterior portion of the hip joint in hopes of decreasing recovery time. This type of procedure has been shown obviate the risk of dislocation for a patient [2], however, there is a lack of longitudinal study exploring if this approach actually decreases the damage caused to the abductor muscle group. The purpose of this study is to quantify differences in the functional recovery between the anterior and lateral approaches to total hip replacement by measuring the hip abductor performance in both static and walking situations. It was hypothesized that a faster recovery in the hip abductor function will be observed in patients with the anterior approach. Three-dimensional joint kinematics and kinetics during walking and the isometric hip abductor muscle strength were evaluated for the involved lower extremity preoperatively, 6 and 16-week postoperatively. Three subject groups, including Group 1:10 patients using the anterior approach (age: 57.6±4.06), Group 2 : 6 patients using the lateral approach (age: 57.6±7.96), and Group 3 : 1 0 healthy adults (age: 59.5±5.13). Isometric muscle strength measurements indicated that, by the 16-week postoperative, the hip abductor of Group 2 is still significantly weaker than the control group while Group 1 continued to return to the normal strength. During walking, the peak hip abductor moments of Group 2 were significantly decreased at 6-week postoperative as compared to the control group when Group 1 have the same hip abductor performance as the control group. Both patient groups proceeded to return to a similar magnitude of hip abductor moment in walking 16-week postoperatively. Our results indicated that the anterior approach does not appear to compromise the hip abductor muscles in both static and walking situations as much as the lateral approach to total hip replacement.
Loosening and thigh pain are two of the most common complications after hip arthroplasty, both of which are attributed to insufficient primary fixation. Accurate predictions of hip stem's stability are therefore crucial to the preclinical assessment of hip arthroplasty. One of the most important parameters affecting the stability is the muscle loads acting on the hip joint. The importance of including muscle forces to correctly simulate femoral stresses and strains distribution has been reported, but their effects on stability have not received much attention. These muscles acting on the hip joint are usually ignored in experimental or finite element (FE) micromotion work due to their complex nature and the large variations found between patients during physiological activities. Most in-vitro experimental work on micromotion used only the joint contact force and ignored any muscle forces while others included certain muscle groups such as the abductors and extensors. This study used finite element analysis to study the effects of muscle forces on micromotion and predicted the stability of femoral stems. Two sets of muscle forces data simulating physiological activities of walking and stair-climbing were used in this study. An in-house experimentally validated algorithm was used to calculate and display micromotion at the bone-implant interface. Using a threshold limit for bone ingrowth of 50 ~tm, the iterations continued until either a stable-state condition was achieved or loosening occurred. The results showed that the overall distribution of micromotion was similar whether or not all muscle forces were included. However, the magnitude of micromotion was larger by up to six times in cases where all muscle forces were included. This was due largely to the direction of the muscle forces which oppose the direction of the joint contact force. It is therefore important to include the muscle forces when analyzing micromotion in order not to over-predict the stability of femoral stems.
References [1] Survey, N.C.f.H.S.N.H.D. 2003. [2] Siguier T., Siguier M., Brumpt B. Mini-incision anterior approach does not increase dislocation rate: a study of 1037 total hip replacements. 2004.
5461 Mo, 09:15-09:30 (P5) Hip joint centre position estimation for clinical gait analysis Z. Yuan 1, M.E. Harrington 2, A.B. Zavatsky 1. 1Department efEngineering
5830 Mo, 08:45-09:00 (P5) Comparative study of probabilistic methods applied to a 3D finite element model of a THR L. Mehrez, A. New, M.T. Bah, M. Browne. Bioengineering Sciences Research
Group, School of Engineering Sciences, University of Southampton, UK When performing a computational analysis of a construct subject to parameter uncertainties, such as a joint replacement, the analysis becomes increasingly complex and impractical as the simultaneous effect of more and more parameters is considered. An attempt to address problems such as this has been made in recent years with the development of probabilistic analyses (which compute the probability of failure and provide measures of sensitivity to each parameter). A number of these methods are available but to date, there has been little or no investigation into their relative efficiencies. A 3D FE contact model of the femoral part of a THR was constructed using ANSYS. Probabilistic analyses were conducted considering uncertainties inherent in the geometry, material properties and joint load. The model was loaded and the axial inducible displacement of the implanted stem was used as a performance function [1]. All probabilistic analyses were conducted using the probabilistic design analysis tool NESSUS [2], in conjunction with ANSYS. The Monte Carlo Simulation Technique (MCST) is usually applied to benchmark probabilistic results; however, this is impractical for FE models due to the scale of the complexity involved. In the present work, Advanced Mean Value Methods (AMV, AMV+) and Response Surface Models (RSM) were used as alternatives. Latin Hypercube Sampling (LHS), Central Composite Design sampling (CCD), and Box-Behmken Matrix Sampling (BBM) were used in conjunction with RSM. In these methods, the performance function could be expressed explicitly in terms of the uncertain parameters by approximating it either by a first-order surface or a quadratic surface. In this study, the goodness-of-fit of these surfaces was examined by benchmarking the corresponding parametric variation studies with that of the FE model. Thereafter, MCST was applied using the explicit forms of the performance function. The comparison study showed that the optimum method could be selected based on the required level of accuracy and the available computational resources. References [1] Maher, Prendergast. J. Biomech. 2002; 35(2). [2] Riha, Tacker. AIAA 2004.
Science, University of Oxford, Oxford, UK, 2Oxford Gait Laboratory, Nuffield Orthopaedic Centre NHS Trust, Oxford, UK Inaccuracy in locating the hip joint centre (HJC) can lead to errors in joint angles and moments, which may propagate through the kinematic and kinetic calculations for the entire lower limb. Functional methods of finding the HJC assume that the hip is a ball-and-socket joint, so that motions of points on the femur relative to the pelvis all rotate about the HJC. This aim of this study is to compare several mathematical formulations of HJC functional methods using motion data from a mechanical linkage and from healthy adults whose HJCs were also located using magnetic resonance imaging (MRI). A 12-camera Vicon 612 was used to track the motion of five retro-reflective markers on a mechanical ball-and-socket linkage with known centre of rotation (CoR). The data was processed using five methods: sphere-fitting (S-method), Reuleaux method, finite helical axis, Gamage and Lasenby sphere-fitting (G1 method), along with Halvorsen's refinement of it (G2 method). The average CoR location errors for all five functional methods were below 2 mm. When applied to pelvis and thigh motion data collected from a healthy adult subject, S and both G methods gave the most consistent results, even with limited data. S and G2 methods were then applied to leg-swing and level-walking motion data from three healthy adult subjects whose HJCs had also been located using MRI. For the leg swing data, the average HJC location error was 20 mm for both methods. For level walking, the errors were twice as large, with the majority of error in the superior-inferior and medial-lateral directions. For G2method, the error in the anterior-posterior direction was under 3 mm. Hence, for level walking, it may be best to use a functional method for the a-p direction only and to use a standard prediction method (regression equation) for the other two HJC coordinates. 7394 Mo, 09:30-09:45 (P5) Optimisation of the stress distribution in ceramic hip joint balls by implementation of biological growth Ch. Affolter 1, B. Weisse 1, A. Stutz 1, S. K6bel 2 . 1Swiss Federal Laboratories
for Materials Testing and Research (EMPA), Laboratory for Materials and Engineering, Duebendoff, Switzerland, 2METOXITAg, Thayngen, Switzerland The bottom of the bore hole in a ceramic hip joint ball experiences high stress concentration and is thus a potential location for crack initiation, which can lower the static strength of such balls. Classic designs cause a high notch factor, or they are difficult to manufacture (undercut with consequently lower surface quality). The aim of this study was the development of an
of Human Physiology, University of Oregon, Eugene, OR, USA, 2Orthopedic Healthcare Northwest, Eugene, OR, U.S.A
3.1. Joints - Hip
$67
5601 Mo, 09:00-09:15 (P5) The effect of muscle loads on the interface micromotion of hip stems M.R.A. Kadir 1,2, U.N. Hansen 1, A.A. Amis 1, R. Klabunde 3. 1Department
of Mechanical Engineering, Imperial College London, UK, 2Biomechanics Laboratory, Universiti Teknologi Malaysia, Malaysia, 3Zimmer European Headquarters, Winterthur, Switzerland
More than 220,000 artificial hip joints are being implanted annually in the USA making this surgery very common [1]. There have been new approaches that utilize the anterior portion of the hip joint in hopes of decreasing recovery time. This type of procedure has been shown obviate the risk of dislocation for a patient [2], however, there is a lack of longitudinal study exploring if this approach actually decreases the damage caused to the abductor muscle group. The purpose of this study is to quantify differences in the functional recovery between the anterior and lateral approaches to total hip replacement by measuring the hip abductor performance in both static and walking situations. It was hypothesized that a faster recovery in the hip abductor function will be observed in patients with the anterior approach. Three-dimensional joint kinematics and kinetics during walking and the isometric hip abductor muscle strength were evaluated for the involved lower extremity preoperatively, 6 and 16-week postoperatively. Three subject groups, including Group 1:10 patients using the anterior approach (age: 57.6±4.06), Group 2 : 6 patients using the lateral approach (age: 57.6±7.96), and Group 3 : 1 0 healthy adults (age: 59.5±5.13). Isometric muscle strength measurements indicated that, by the 16-week postoperative, the hip abductor of Group 2 is still significantly weaker than the control group while Group 1 continued to return to the normal strength. During walking, the peak hip abductor moments of Group 2 were significantly decreased at 6-week postoperative as compared to the control group when Group 1 have the same hip abductor performance as the control group. Both patient groups proceeded to return to a similar magnitude of hip abductor moment in walking 16-week postoperatively. Our results indicated that the anterior approach does not appear to compromise the hip abductor muscles in both static and walking situations as much as the lateral approach to total hip replacement.
Loosening and thigh pain are two of the most common complications after hip arthroplasty, both of which are attributed to insufficient primary fixation. Accurate predictions of hip stem's stability are therefore crucial to the preclinical assessment of hip arthroplasty. One of the most important parameters affecting the stability is the muscle loads acting on the hip joint. The importance of including muscle forces to correctly simulate femoral stresses and strains distribution has been reported, but their effects on stability have not received much attention. These muscles acting on the hip joint are usually ignored in experimental or finite element (FE) micromotion work due to their complex nature and the large variations found between patients during physiological activities. Most in-vitro experimental work on micromotion used only the joint contact force and ignored any muscle forces while others included certain muscle groups such as the abductors and extensors. This study used finite element analysis to study the effects of muscle forces on micromotion and predicted the stability of femoral stems. Two sets of muscle forces data simulating physiological activities of walking and stair-climbing were used in this study. An in-house experimentally validated algorithm was used to calculate and display micromotion at the bone-implant interface. Using a threshold limit for bone ingrowth of 50 ~tm, the iterations continued until either a stable-state condition was achieved or loosening occurred. The results showed that the overall distribution of micromotion was similar whether or not all muscle forces were included. However, the magnitude of micromotion was larger by up to six times in cases where all muscle forces were included. This was due largely to the direction of the muscle forces which oppose the direction of the joint contact force. It is therefore important to include the muscle forces when analyzing micromotion in order not to over-predict the stability of femoral stems.
References [1] Survey, N.C.f.H.S.N.H.D. 2003. [2] Siguier T., Siguier M., Brumpt B. Mini-incision anterior approach does not increase dislocation rate: a study of 1037 total hip replacements. 2004.
5461 Mo, 09:15-09:30 (P5) Hip joint centre position estimation for clinical gait analysis Z. Yuan 1, M.E. Harrington 2, A.B. Zavatsky 1. 1Department efEngineering
5830 Mo, 08:45-09:00 (P5) Comparative study of probabilistic methods applied to a 3D finite element model of a THR L. Mehrez, A. New, M.T. Bah, M. Browne. Bioengineering Sciences Research
Group, School of Engineering Sciences, University of Southampton, UK When performing a computational analysis of a construct subject to parameter uncertainties, such as a joint replacement, the analysis becomes increasingly complex and impractical as the simultaneous effect of more and more parameters is considered. An attempt to address problems such as this has been made in recent years with the development of probabilistic analyses (which compute the probability of failure and provide measures of sensitivity to each parameter). A number of these methods are available but to date, there has been little or no investigation into their relative efficiencies. A 3D FE contact model of the femoral part of a THR was constructed using ANSYS. Probabilistic analyses were conducted considering uncertainties inherent in the geometry, material properties and joint load. The model was loaded and the axial inducible displacement of the implanted stem was used as a performance function [1]. All probabilistic analyses were conducted using the probabilistic design analysis tool NESSUS [2], in conjunction with ANSYS. The Monte Carlo Simulation Technique (MCST) is usually applied to benchmark probabilistic results; however, this is impractical for FE models due to the scale of the complexity involved. In the present work, Advanced Mean Value Methods (AMV, AMV+) and Response Surface Models (RSM) were used as alternatives. Latin Hypercube Sampling (LHS), Central Composite Design sampling (CCD), and Box-Behmken Matrix Sampling (BBM) were used in conjunction with RSM. In these methods, the performance function could be expressed explicitly in terms of the uncertain parameters by approximating it either by a first-order surface or a quadratic surface. In this study, the goodness-of-fit of these surfaces was examined by benchmarking the corresponding parametric variation studies with that of the FE model. Thereafter, MCST was applied using the explicit forms of the performance function. The comparison study showed that the optimum method could be selected based on the required level of accuracy and the available computational resources. References [1] Maher, Prendergast. J. Biomech. 2002; 35(2). [2] Riha, Tacker. AIAA 2004.
Science, University of Oxford, Oxford, UK, 2Oxford Gait Laboratory, Nuffield Orthopaedic Centre NHS Trust, Oxford, UK Inaccuracy in locating the hip joint centre (HJC) can lead to errors in joint angles and moments, which may propagate through the kinematic and kinetic calculations for the entire lower limb. Functional methods of finding the HJC assume that the hip is a ball-and-socket joint, so that motions of points on the femur relative to the pelvis all rotate about the HJC. This aim of this study is to compare several mathematical formulations of HJC functional methods using motion data from a mechanical linkage and from healthy adults whose HJCs were also located using magnetic resonance imaging (MRI). A 12-camera Vicon 612 was used to track the motion of five retro-reflective markers on a mechanical ball-and-socket linkage with known centre of rotation (CoR). The data was processed using five methods: sphere-fitting (S-method), Reuleaux method, finite helical axis, Gamage and Lasenby sphere-fitting (G1 method), along with Halvorsen's refinement of it (G2 method). The average CoR location errors for all five functional methods were below 2 mm. When applied to pelvis and thigh motion data collected from a healthy adult subject, S and both G methods gave the most consistent results, even with limited data. S and G2 methods were then applied to leg-swing and level-walking motion data from three healthy adult subjects whose HJCs had also been located using MRI. For the leg swing data, the average HJC location error was 20 mm for both methods. For level walking, the errors were twice as large, with the majority of error in the superior-inferior and medial-lateral directions. For G2method, the error in the anterior-posterior direction was under 3 mm. Hence, for level walking, it may be best to use a functional method for the a-p direction only and to use a standard prediction method (regression equation) for the other two HJC coordinates. 7394 Mo, 09:30-09:45 (P5) Optimisation of the stress distribution in ceramic hip joint balls by implementation of biological growth Ch. Affolter 1, B. Weisse 1, A. Stutz 1, S. K6bel 2 . 1Swiss Federal Laboratories
for Materials Testing and Research (EMPA), Laboratory for Materials and Engineering, Duebendoff, Switzerland, 2METOXITAg, Thayngen, Switzerland The bottom of the bore hole in a ceramic hip joint ball experiences high stress concentration and is thus a potential location for crack initiation, which can lower the static strength of such balls. Classic designs cause a high notch factor, or they are difficult to manufacture (undercut with consequently lower surface quality). The aim of this study was the development of an