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Validation of a three-dimensional knee motion assessment system
488
Abstracts
DIRECT MEASURBMENTS OF TIBIO-FEMORAL CONTACT OF THE KNEE Ii Schmotzer*, CL Vaughan, ID Learmonth
PRESSURES
FOR VARIOUS DEFORMITIES
*Hospital of the Good Samaritan, Los Angeles, USA The objective of the study was to measure the contact pressure distribution in the knee joint for various deformities. Six knees without previous injury or malalignment were used. All soft tissues were removed preserving the ligaments, the capsule and the tendons of all muscles crossing the joints. Custom-built pressure transducers were inserted into the joint. Replacing all muscles by flexible cable provided adequate stability and allowed unconstrained self-alignment of the femur over the fixed tibia. The
knee was loaded in an INSTRON machine (BW=8OON). In neutral alignment, an even pressure distribution was observed. The average contact pressure was 0.74 MPa medially and 0.90 MPa laterally. In a deformity, the peak pressure shifted into the respective compartment (3.4 MPa med.110 dgr. vr; 2.66 MPa med./5 dgr. vr and 1.8 MPa lat.15 dgr. vl). Unloading of the opposite compartment could be observed for a deformity as small as 5 degree varus/valgus. The the peak pressure shifted postero-laterally. In a f lexion contracture, average pressure was 1.2 MPa laterally and 0.77 MPa in the medial compartment. high pressures could be seen over the meniscal In the case of any deformity, femoral contact areas.
PARAMETRIC VALIDATION OF A 3-D KNEE JOINT MODEL L. Blankevoort and R Huiskes Biomechanics Section, Institute of Orthopaedics, University of Nllmegen, The Netherlands 3-D kinematic knee joint models, presently operational, were previously validated through rough comparisons with average experimental data from literature. The object of this study was the parametric validation of a three-dimensional mathematical model of the human knee joint based on geometric data and kinematic data of a particular joint specimen. The 3-D mathematical knee model in this study calculates the position of the femur relative to the tibia for given external loads and kinematic constraints by solving the force and moment equilibrium equations. The model includes deformable articular surfaces, non-linear ligament behavior and ligament-bone interaction. Of a knee specimen, kinematic data and geometric data of the articular surfaces and the ligaments were obtained and used to model that particular joint. The ligament stiffnesses were based on literature data. An optimization procedure was used to minimize the differences between kinematic parameters from the model and those from the experiments, by variation of the the ligament reference strains, i.e. the strains in the ligaments for extension of the joint. Two motion pathways as simulated with the non-optimized model deviated from the experimental motions. Optimization of the reference strains yielded a good fit with respect to all motion components. While the geometry of the joint was precisely modelled and the ligament stiffnesses had realistic values, the a priori unknown ligament reference strains could be estimated through model optimization. With this, the knee model has matured to a powerful and realistic simulation tool.
VALIDATIONOF A THREE-DIMENSIONAL KNEE MOTIONASSESSMENT SYSTEM K. Deluzio, U. Wyss, J. Li, P.A. Coatigan Clinical Mechanics Group, Queen's University, Kingston Gen. Hosp., Kingston, CANADA The study objective was to determine the accuracy of 3D knee motion analysis baaed on an optoelectric system used to assess knee loading during walking and stair climbing. The accuracy of the 3D coordinates for a give infrared light emitting diode marker (LED) was tested and the optimum length between 2 markers to identify angular measurement accuracy determined. Rotations in 3 dtrections (as in the knee) ware calculated. In Model 1, a plexiglass plate was mounted vertically on the base so hhat it could be rotated. Rotation was simultaneously measured with a potentiometer. LEDs were placed on the plate 2 cm apart from each other. The position of the LEDs and the angle of the plate with respect to the recording system was then calculated and analyzed statistically. Model 2 was a mechanical representation of a human knee allowing 3 rotations at the "knee" joint. The axis of the 3 rotations was instrumented with potentiometers to accurately record the angles. Results show that the hardware and software used to study mechanical aspects of the genesis of OA perform well and the accuracy of the system could be determined. With proper spacing of markers of at least 180 mm, angular data can be corrected with an error of less than 2O, except for part of the ab-/adduction angles (error as high as 4O). Consequently, kinematic and kinetic data can be interpreted properly with systems errors known.
Abstracts
DIRECT MEASURBMENTS OF TIBIO-FEMORAL CONTACT OF THE KNEE Ii Schmotzer*, CL Vaughan, ID Learmonth
PRESSURES
FOR VARIOUS DEFORMITIES
*Hospital of the Good Samaritan, Los Angeles, USA The objective of the study was to measure the contact pressure distribution in the knee joint for various deformities. Six knees without previous injury or malalignment were used. All soft tissues were removed preserving the ligaments, the capsule and the tendons of all muscles crossing the joints. Custom-built pressure transducers were inserted into the joint. Replacing all muscles by flexible cable provided adequate stability and allowed unconstrained self-alignment of the femur over the fixed tibia. The
knee was loaded in an INSTRON machine (BW=8OON). In neutral alignment, an even pressure distribution was observed. The average contact pressure was 0.74 MPa medially and 0.90 MPa laterally. In a deformity, the peak pressure shifted into the respective compartment (3.4 MPa med.110 dgr. vr; 2.66 MPa med./5 dgr. vr and 1.8 MPa lat.15 dgr. vl). Unloading of the opposite compartment could be observed for a deformity as small as 5 degree varus/valgus. The the peak pressure shifted postero-laterally. In a f lexion contracture, average pressure was 1.2 MPa laterally and 0.77 MPa in the medial compartment. high pressures could be seen over the meniscal In the case of any deformity, femoral contact areas.
PARAMETRIC VALIDATION OF A 3-D KNEE JOINT MODEL L. Blankevoort and R Huiskes Biomechanics Section, Institute of Orthopaedics, University of Nllmegen, The Netherlands 3-D kinematic knee joint models, presently operational, were previously validated through rough comparisons with average experimental data from literature. The object of this study was the parametric validation of a three-dimensional mathematical model of the human knee joint based on geometric data and kinematic data of a particular joint specimen. The 3-D mathematical knee model in this study calculates the position of the femur relative to the tibia for given external loads and kinematic constraints by solving the force and moment equilibrium equations. The model includes deformable articular surfaces, non-linear ligament behavior and ligament-bone interaction. Of a knee specimen, kinematic data and geometric data of the articular surfaces and the ligaments were obtained and used to model that particular joint. The ligament stiffnesses were based on literature data. An optimization procedure was used to minimize the differences between kinematic parameters from the model and those from the experiments, by variation of the the ligament reference strains, i.e. the strains in the ligaments for extension of the joint. Two motion pathways as simulated with the non-optimized model deviated from the experimental motions. Optimization of the reference strains yielded a good fit with respect to all motion components. While the geometry of the joint was precisely modelled and the ligament stiffnesses had realistic values, the a priori unknown ligament reference strains could be estimated through model optimization. With this, the knee model has matured to a powerful and realistic simulation tool.
VALIDATIONOF A THREE-DIMENSIONAL KNEE MOTIONASSESSMENT SYSTEM K. Deluzio, U. Wyss, J. Li, P.A. Coatigan Clinical Mechanics Group, Queen's University, Kingston Gen. Hosp., Kingston, CANADA The study objective was to determine the accuracy of 3D knee motion analysis baaed on an optoelectric system used to assess knee loading during walking and stair climbing. The accuracy of the 3D coordinates for a give infrared light emitting diode marker (LED) was tested and the optimum length between 2 markers to identify angular measurement accuracy determined. Rotations in 3 dtrections (as in the knee) ware calculated. In Model 1, a plexiglass plate was mounted vertically on the base so hhat it could be rotated. Rotation was simultaneously measured with a potentiometer. LEDs were placed on the plate 2 cm apart from each other. The position of the LEDs and the angle of the plate with respect to the recording system was then calculated and analyzed statistically. Model 2 was a mechanical representation of a human knee allowing 3 rotations at the "knee" joint. The axis of the 3 rotations was instrumented with potentiometers to accurately record the angles. Results show that the hardware and software used to study mechanical aspects of the genesis of OA perform well and the accuracy of the system could be determined. With proper spacing of markers of at least 180 mm, angular data can be corrected with an error of less than 2O, except for part of the ab-/adduction angles (error as high as 4O). Consequently, kinematic and kinetic data can be interpreted properly with systems errors known.