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Alterations of the ratio of ligament patellae and quadriceps tendon forces by total knee replacements
809
Abstracts of the Fifth Meeting of the European Society of Biomechanics
hypothesised that beyond a specific (relative) prosthetic rigidity, bone cannot obtain a stable configuration. provided that the assumed (but widely accepted) relation between ‘stress shielding’ and osteolysis is true. ALTERATIONS
OF THE RATIO K. WEINSNNN
PATELLAE AND QUADRICEPS KNEE REPLACEMENTS
OF LIGAMENT
FORCES
BY TOTAL
(Orthopadische
Klinik, Universitat
TENDON
Zlunchen, F.R.G.)
The ratio of ligamentum patellae and quadriceps tendon forces changes dependent on the knee flexion angle. Total knee replacements may change patellae positions at the patellofemoral joint and alter those force ratios. Measuring of forces in the quadriceps tendon and the ligamentum patellae in cadaver knee joints with and without joint replacement was carried out to investigate the influence of the positioning of the knee joint replacements for biomechanical interactions at the patello-femoral joint. The physiological characterization of the course of the ratio of ligamentum patellae and quadriceps tendon forces for the knee flexion range may be maintained after total knee joint replacement. Results show that patellae alta or baja effect a shift of the characteristical course of force ratios and anteriorly positioned tibia components increase ligamentum patellae tensions.
C. ORTHOPAEDIC STRESS
TRANSFER
ACROSS
BIOMECHANICS:
THE HIP JOINT
IiMPLANTS
IN RECONSTRUCTED
ACETABCLI
F. HUISKES and T. J. SLOOFF (Biomechanics Section, Laboratory of Experimental Orthopaedics, Department of Orthopaedics, University of Nijmegen, P.O. Box 9101, 6500 HB Nijmegen. The Netherlands) Using finite element methods, the stress patterns in the acetabulum after prosthetic reconstruction were evaluated. The objectives of the present study were twofold. Firstly to study the effects of model characteristics, i.e. plane vs axisymmetric geometry, external force orientation and femoral-acetabular contact coupling. Secondly, to investigate the effects ofseveral cup designs relative to the intact situation (HDPE sockets. cemented and non-cemented, metal backing. surface replacement cups, and cementless threaded cups). It was found, amongst others, that the elastic interaction between femoral head and acetabulum has a very significant effect on the stress patterns, which will affect the precision of analyses in which the boundary stress is a priori assumed. A MATHEMATICAL
MODEL
OF HUMAN KNEE-MOTION ENDOPROSTHESES
AND EVALUATION
OF KNEE
J. HOSCHEKand J. HALT (Technische Hochschule, D-6100 Darmstadt), G. SELVIK (University of Lund, S223 62 Lund) and U. WEBER (Orthopldische Universitltsklinik D-6300 GieOen, F.R.G.) A mathematical oriented method for a three dimensional modelling of the knee motion is introduced. The mathematical model leads to a new method for evaluating of mating surfaces of knee endoprostheses. To determine movements between femur and tibia markers (tantalum balls) were attached to each bone. The position of these markers during a motion of a knee can be determined by measurements on radiographics (methods introduced by Selvik). From the three dimensional coordinates of the markers we receive by spline approximation of a matrix equation of the knee motion for each volunteer. This mathematical description of the knee motion is the base for evaluation of the mating surfaces of knee endoprostheses by the help of methods from Computer Aided Design. INFLUENCE
OF COMPONENT
ORIENTATION ON PEG FAILURE REPLACEMENTS
OF PATELLAR
SURFACE
E. J. CHEAL, W. C. HAYES, J. D. HARRY,T. N. GERHARTand D. PAGE* (Orthopaedic Biomechanics Laboratory, Charles A. Dana Research Institute, Beth Israel Hospital and Harvard Medical School, Boston, MA 02215; *Orthopaedic Division, Johnson & Johnson Products Inc., Braintree, MA, U.S.A.) The objectives of this investigation were to examine the influence of peg orientation and bone ingrowth characteristics for a porous coated patellar surface component. Two three-dimensional finite element models were generated, with the pegs in the proximaldistal (PD) and medial-lateral orientation (ML). For the assumption of complete ingrowth, the stresses were highest for the PD orientation. The ML orientation reduced
Abstracts of the Fifth Meeting of the European Society of Biomechanics
hypothesised that beyond a specific (relative) prosthetic rigidity, bone cannot obtain a stable configuration. provided that the assumed (but widely accepted) relation between ‘stress shielding’ and osteolysis is true. ALTERATIONS
OF THE RATIO K. WEINSNNN
PATELLAE AND QUADRICEPS KNEE REPLACEMENTS
OF LIGAMENT
FORCES
BY TOTAL
(Orthopadische
Klinik, Universitat
TENDON
Zlunchen, F.R.G.)
The ratio of ligamentum patellae and quadriceps tendon forces changes dependent on the knee flexion angle. Total knee replacements may change patellae positions at the patellofemoral joint and alter those force ratios. Measuring of forces in the quadriceps tendon and the ligamentum patellae in cadaver knee joints with and without joint replacement was carried out to investigate the influence of the positioning of the knee joint replacements for biomechanical interactions at the patello-femoral joint. The physiological characterization of the course of the ratio of ligamentum patellae and quadriceps tendon forces for the knee flexion range may be maintained after total knee joint replacement. Results show that patellae alta or baja effect a shift of the characteristical course of force ratios and anteriorly positioned tibia components increase ligamentum patellae tensions.
C. ORTHOPAEDIC STRESS
TRANSFER
ACROSS
BIOMECHANICS:
THE HIP JOINT
IiMPLANTS
IN RECONSTRUCTED
ACETABCLI
F. HUISKES and T. J. SLOOFF (Biomechanics Section, Laboratory of Experimental Orthopaedics, Department of Orthopaedics, University of Nijmegen, P.O. Box 9101, 6500 HB Nijmegen. The Netherlands) Using finite element methods, the stress patterns in the acetabulum after prosthetic reconstruction were evaluated. The objectives of the present study were twofold. Firstly to study the effects of model characteristics, i.e. plane vs axisymmetric geometry, external force orientation and femoral-acetabular contact coupling. Secondly, to investigate the effects ofseveral cup designs relative to the intact situation (HDPE sockets. cemented and non-cemented, metal backing. surface replacement cups, and cementless threaded cups). It was found, amongst others, that the elastic interaction between femoral head and acetabulum has a very significant effect on the stress patterns, which will affect the precision of analyses in which the boundary stress is a priori assumed. A MATHEMATICAL
MODEL
OF HUMAN KNEE-MOTION ENDOPROSTHESES
AND EVALUATION
OF KNEE
J. HOSCHEKand J. HALT (Technische Hochschule, D-6100 Darmstadt), G. SELVIK (University of Lund, S223 62 Lund) and U. WEBER (Orthopldische Universitltsklinik D-6300 GieOen, F.R.G.) A mathematical oriented method for a three dimensional modelling of the knee motion is introduced. The mathematical model leads to a new method for evaluating of mating surfaces of knee endoprostheses. To determine movements between femur and tibia markers (tantalum balls) were attached to each bone. The position of these markers during a motion of a knee can be determined by measurements on radiographics (methods introduced by Selvik). From the three dimensional coordinates of the markers we receive by spline approximation of a matrix equation of the knee motion for each volunteer. This mathematical description of the knee motion is the base for evaluation of the mating surfaces of knee endoprostheses by the help of methods from Computer Aided Design. INFLUENCE
OF COMPONENT
ORIENTATION ON PEG FAILURE REPLACEMENTS
OF PATELLAR
SURFACE
E. J. CHEAL, W. C. HAYES, J. D. HARRY,T. N. GERHARTand D. PAGE* (Orthopaedic Biomechanics Laboratory, Charles A. Dana Research Institute, Beth Israel Hospital and Harvard Medical School, Boston, MA 02215; *Orthopaedic Division, Johnson & Johnson Products Inc., Braintree, MA, U.S.A.) The objectives of this investigation were to examine the influence of peg orientation and bone ingrowth characteristics for a porous coated patellar surface component. Two three-dimensional finite element models were generated, with the pegs in the proximaldistal (PD) and medial-lateral orientation (ML). For the assumption of complete ingrowth, the stresses were highest for the PD orientation. The ML orientation reduced