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R Huiskes

Publications and source records attributed to R Huiskes.

At least 145 records · Page 8Linked to original sources
PubMed1992

Intramedullary fixation with screwed, conical stems--unsolicited results from animal experiments.

For the purpose of studying bone remodeling around prostheses, a segmental replacement for the goat tibia was designed, using a conical, screw-threaded, hydroxyapatite-coated stem for fixation. Eight goats were provided with the implant, seven of which loosened within 10 days post-operatively, displaying progressive radiolucency and gross rotational motion. The eighth one also loosened radiographically, but developed a stabilizing callus bridge to prevent motion. A second design of similar shape and coating, but lacking the screw threads, was designed and also applied in eight animals. In this case, no loosening occurred in the first 6 weeks post-operatively. It is concluded that the application of screwed intramedullary stems for prosthetic fixation is not a viable concept, because the threads prevent the stem from subsiding and restabilizing when minor initial interface stress-relaxation and remodeling has occurred.

Animals↗
PubMed1992

The relationship between stress shielding and bone resorption around total hip stems and the effects of flexible materials.

Bone resorption around hip stems is a disturbing phenomenon, although its clinical significance and its eventual effects on replacement longevity are as yet uncertain. The relationship between implant flexibility and the extent of bone loss, frequently established in clinical patient series and animal experiments, does suggest that the changes in bone morphology are an effect of stress shielding and a subsequent adaptive remodeling process. This relationship was investigated using strain-adaptive bone-remodeling theory in combination with finite element models to simulate the bone remodeling process. The effects of stem material flexibility, bone flexibility, and bone reactivity on the process and its eventual outcome were studied. Stem flexibility was also related to proximal implant/bone interface stresses. The results sustain the hypothesis that the resorptive processes are an effect of bone adaptation to stress shielding. The effects of stem flexibility are confirmed by the simulation analysis. It was also established that individual differences in bone reactivity and mechanical bone quality (density and stiffness) may account for the individual variations found in patients and animal experiments. Flexible stems reduce stress shielding and bone resorption. However, they increase proximal interface stresses. Hence, the cure against bone resorption they represent may develop into increased loosening rates because of interface debonding and micromotion. The methods presented in this paper can be used to establish optimal stem-design characteristics or check the adequacy of designs in preclinical testing procedures.

Biomechanical Phenomena↗
PubMed1991

The effect of the extracorporeal shock wave lithotriptor on bone cement.

For the purpose of studying its applicability for acrylic cement removal during total hip revision surgery, experiments with an extracorporeal shock wave lithotriptor were carried out. High-energy shock waves (HESW) were focussed on discs of polymethylmethacrylate bone cement. The average discharge was 18.1 kV; the number of shock waves 0, 100, 250, 500, 1000, and 2000; the application rate was 85 shocks/min. Macroscopic or radiographic effects were not in evidence. Microscopically, typical lesions in a small concentric focal area with a diameter of 8.5 (+/- 2.5) mm were found. The individual lesions were smaller than 0.1 mm, and displayed characteristic shapes. The area porosity increased with the number of shocks. The maximal area porosity caused by the HESW, measured by quantitative microscopy, was 4% after 2000 shock waves. The lesions were also studied by scanning electron microscopy. It can be concluded that HESW causes only microscopic lesions on the frontal surface of discs of bone cement, and that these lesions are small compared to the pores normally present in bone cement, when applied clinically.

Bone Cements↗
PubMed1991

Human carpal ligament recruitment and three-dimensional carpal motion.

In five fresh human cadaver wrist joints six carpal ligaments and seven carpal bones were marked with small, radio-opaque pellets. Using a roentgenstereophotogrammetric measuring system, the ligamentous length changes and the kinematics of carpal bones were determined in different flexion and deviation positions of the hand. The data generated by this method differ significantly from lengthening data predicted by current concepts on carpal ligament functioning. The motions of carpal bones and the lengthening of the carpal ligaments were related to each other. It appeared that most carpal ligaments lengthen only during one half of a full movement cycle. Hence, ligaments seem to constrain either a dorsal- or a palmar-directed motion of the hand, or an ulnar- or a radial-directed motion of the hand. When the hand is in maximal radial deviation or maximal palmar flexion, none of the ligaments has a greater length than in the neutral situation. The tested parts of the lunatotriquetrum palmar ligament do not lengthen during any movement of the hand. Significant lengthening relative to the neutral situation was found for the radiocapitate palmar ligament (6.5% in maximal ulnar deviation and 11.7% in maximal dorsal flexion of the hand), and for the distal string of the radiolunate palmar ligament (6.4% in maximal ulnar deviation). It was confirmed that the carpals, apart from moving in the plane in which the hand motion takes place, also execute considerable out-of-plane motions during hand motions. The combination of these experimentally and simultaneously determined data on length change and on the movements of carpal bones are found to be necessary in order to give suitable explanations for the observed separate kinematical phenomena.

Carpal Bones↗
PubMed1991

Articular contact in a three-dimensional model of the knee.

This study is aimed at the analysis of articular contact in a three-dimensional mathematical model of the human knee-joint. In particular the effect of articular contact on the passive motion characteristics is assessed in relation to experimentally obtained joint kinematics. Two basically different mathematical contact descriptions were compared for this purpose. One description was for rigid contact and one for deformable contact. The description of deformable contact is based on a simplified theory for contact of a thin elastic layer on a rigid foundation. The articular cartilage was described either as a linear elastic material or as a non-linear elastic material. The contact descriptions were introduced in a mathematical model of the knee. The locations of the ligament insertions and the geometry of the articular surfaces were obtained from a joint specimen of which experimentally determined kinematic data were available, and were used as input for the model. The ligaments were described by non-linear elastic line elements. The mechanical properties of the ligaments and the articular cartilage were derived from literature data. Parametric model evaluations showed that, relative to rigid articular contact, the incorporation of deformable contact did not alter the motion characteristics in a qualitative sense, and that the quantitative changes were small. Variation of the elasticity of the elastic layer revealed that decreasing the surface stiffness caused the ligaments to relax and, as a consequence, increased the joint laxity, particularly for axial rotation. The difference between the linear and the non-linear deformable contact in the knee model was very small for moderate loading conditions. The motion characteristics simulated with the knee model compared very well with the experiments. It is concluded that for simulation of the passive motion characteristics of the knee, the simplified description for contact of a thin linear elastic layer on a rigid foundation is a valid approach when aiming at the study of the motion characteristics for moderate loading conditions. With deformable contact in the knee model, geometric conformity between the surfaces can be modelled as opposed to rigid contact which assumed only point contact.

Elasticity↗
PubMed1991

Recruitment of knee joint ligaments.

On the basis of earlier reported data on the in vitro kinematics of passive knee-joint motions of four knee specimens, the length changes of ligament fiber bundles were determined by using the points of insertion on the tibia and femur. The kinematic data and the insertions of the ligaments were obtained by using Roentgenstereophotogrammetry. Different fiber bundles of the anterior and posterior cruciate ligaments and the medial and lateral collateral ligaments were identified. On the basis of an assumption for the maximal strain of each ligament fiber bundle during the experiments, the minimal recruitment length and the probability of recruitment were defined and determined. The motions covered the range from extension to 95 degrees flexion and the loading conditions included internal or external moments of 3 Nm and anterior or posterior forces of 30 N. The ligament length and recruitment patterns were found to be consistent for some ligament bundles and less consistent for other ligament bundles. The most posterior bundle of each ligament was recruited in extension and the lower flexion angles, whereas the anterior bundle was recruited for the higher flexion angles. External rotation generally recruited the collateral ligaments, while internal rotation recruited the cruciate ligaments. However, the anterior bundle of the posterior cruciate ligament was recruited with external rotation at the higher flexion angles. At the lower flexion angles, the anterior cruciate and the lateral collateral ligaments were recruited with an anterior force. The recruitment of the posterior cruciate ligament with a posterior force showed that neither its most anterior nor its most posterior bundle was recruited at the lower flexion angles. Hence, the posterior restraint must have been provided by the intermediate fiber bundles, which were not considered in the experiment. At the higher flexion angles, the anterior bundles of the anterior cruciate ligament and the posterior cruciate ligament were found to be recruited with anterior and posterior forces, respectively. The minimal recruitment length and the recruitment probability of ligament fiber bundles are useful parameters for the evaluation of ligament length changes in those experiments where no other method can be used to determine the zero strain lengths, ligament strains and tensions.

Adult↗
PubMed1991

Ligament-bone interaction in a three-dimensional model of the knee.

In mathematical knee-joint models, the ligaments are usually represented by straight-line elements, connecting the insertions of the femur and tibia. Such a model may not be valid if a ligament is bent in its course over bony-surfaces, particularly not if the resulting redirection of the ligament force has a considerable effect on the laxity or motion characteristics of the knee-joint model. In the present study, a model for wrapping of a ligament around bone was incorporated in a three-dimensional mathematical model of the human knee. The bony edge was described by a curved line on which the contact point of the line element representing a ligament bundle was located. Frictionless contact between the ligament bundle and the bone was assumed. This model was applied to the medial collateral ligament (MCL) interacting with the bony edge of the tibia. It was found that, in comparison with the original model without bony interactions, the bony edge redirected the ligament force of the MCL in such a way that it counterbalanced valgus moments on the tibia more effectively. The effect of the bony interaction with the MCL on the internal-external rotation laxity, however, was negligible.

Biomechanical Phenomena↗
PubMed1990

The three-dimensional tracking pattern of the human patella.

A study was undertaken to provide data on the three-dimensional tracking pattern of the patella, relative to the femur, in human knee-joint specimens. For this purpose, a highly accurate roentgen stereophotogrammetric analysis (RSA) method was applied. The three-dimensional motion patterns of the tibia and the patella were measured and represented in terms of three translations and three rotations each, during knee flexion in neutral (unloaded), endorotated, and exorotated pathways. We found that the patella displays complex but consistent three-dimensional motion patterns during flexion, which include flexion rotation, medial rotation, wavering tilt, and a lateral shift relative to the femur. The motion patterns are very much affected by tibial rotations accompanying flexion.

Humans↗
PubMed1990

Wrist-joint ligament length changes in flexion and deviation of the hand: an experimental study.

A method to study ligament-length patterns in situ with roentgen-stereophotogrammetry, using strings of glued tantalum markers, was developed. The method was tested against a bone-to-bone marking method in five carpal ligaments in three specimens, whereby the hand was moved through dorsopalmar flexion and radioulnar deviation. The "glued-string" marking method was found to be superior to the bone-to-bone marking method. The length patterns obtained were found to be reproducible in the specimens and different from earlier expectations presented in the literature. The radiocapitate ligament seems to limit the displacements of the capitate in both radial and ulnar deviation, and dorsal flexion. The radiolunate ligament has the same effect for the lunate. Both the dorsal radiotriquetrum and the palmar triquetrocapitate ligaments seem to play a stabilizing role in the neutral position of the hand, whereas the radiotriquetrum ligament also has a function in palmar flexion and the triquetrocapitate ligament functions in dorsal flexion, ultimately resisting these excursions. These findings require confirmation in more extensive experiments, whereby the relationship between ligament length patterns and carpal motion axes is investigated.

Adult↗
PubMed1990

Measurement errors in roentgen-stereophotogrammetric joint-motion analysis.

In many biomechanical motion studies, kinematic parameters are estimated from position measurements on a number of landmarks. In the present investigation, dummy motion experiments are performed in order to study the error dependence of kinematic parameters on geometric factors (number of markers, isotropic vs anisotropic landmark distributions, landmark distribution size), on kinematic factors (rotation step magnitude, the presence of translational displacements, the distance of the landmarks' mean position to the rotation axis), and on anisotropically distributed measurement errors. The experimental results are compared with theoretical predictions of a previous error analysis assuming isotropic conditions for the measurement errors and for the spatial landmark distribution. In general, the experimental findings agree with the predictions of the error model. The kinematic parameters such as translations and rotations are well-determined by the model. In the helical motion description, the same applies for the finite rotation angle about and the finite shift along the helical axis. However, the direction and position of the helical axis are ill-determined. An anisotropic landmark distribution with relatively few markers located in the direction of the rotation axis will even aggravate the ill-posed nature of the finite helical axis estimation.

Biomechanical Phenomena↗
PubMed1990

Trends of mechanical consequences and modeling of a fibrous membrane around femoral hip prostheses.

In the present study, the effects of a fibrous membrane between cement and bone in a femoral total hip replacement were investigated. The study involved the problem of modeling this fibrous membrane in finite-element analyses, and its global consequences for the load-transfer mechanism and its resulting stress patterns. A finite-element model was developed, suitable to describe nonlinear contact conditions in combination with nonlinear material properties of the fibrous membrane. The fibrous tissue layer was described as a highly compliant material with little resistance against tension and shear. The analysis showed that the load transfer mechanism from stem to bone changes drastically when such a membrane is present. These effects are predominantly caused by tensile loosening and slip at the interface, and are enhanced by the nonlinear membrane characteristics. Using parametric analysis, it was shown that these effects on the load-transfer mechanism cannot be described satisfactorily with linear elastic models. Most importantly, the fibrous tissue interposition causes excessive stress concentrations in bone and cement, and relatively high relative displacements between these materials.

Biomechanical Phenomena↗
PubMed1990

Helical axes of passive knee joint motions.

The purpose of this study was to determine finite helical axes for passive knee joint motions in vitro and to evaluate the descriptive value of the finite helical axes for step-by-step flexion motions, with respect to consistency and reproducibility. An accurate Roentgenstereophotogrammetric system was used for motion measurements. Four knees were tested in a motion and loading rig with one and the same experimental protocol. A fifth specimen was used to study the effects of some of the experimental conditions on the axis parameters. On the basis of earlier reported motion characteristics in terms of Euler rotations and translations, two motion pathways were chosen to be reported here: a flexion motion with an internal torque of 3 Nm and one with an external torque of 3 Nm on the tibia. The positions and orientations of the axes were described relative to the insertions of the four major ligaments and the geometry of the articular surfaces of the femur, and also as intersections with a medial and a lateral sagittal plane. The three-dimensional patterns of the helical axes of the four knee specimens were found to be highly reproducible and consistent for each of the two motion pathways. The axis patterns were not unique, but reflected the particular combination of flexion and axial rotation for each particular motion pathway. Although small, the helical translations indicated medial motions of the tibia relative to the femur. This medial helical translation was more pronounced for the internal pathway compared with the external pathway. Above 70 degrees flexion, the axes move posteriorly relative to the femur.

Biomechanical Phenomena↗
PubMed1990

Post-loosening mechanical behavior of femoral resurfacing prostheses.

The survival rate of femoral surface replacements has been low relative to conventional total hip replacements. The purpose of this investigation was to determine whether the early clinical loosening can be explained by mechanical causes. Using linear and nonlinear finite element methods, the pre- and post-failure load-transfer characteristics of the femoral surface replacement were analysed, and stress patterns and relative motions at the implant/bone interface were evaluated for a particular hip-loading cycle. Using histology of revision material as a guideline, implant loosening, bone resorption and fibrous interface formation were introduced in the model and their mechanical consequences analysed. The results suggest that the high failure rates are not correlated directly with the chances for primary mechanical failure of the implant-bone interface, but rather indirectly with the sensitivity of the implant design to implant loosening and the propagation of bone resorption and fibrous tissue formation. This mechanism appears to be governed by the proliferation of relative motions between implant and bone. We conclude that the 'secondary stability' of implants in general and their capacity to obtain a stable post-loosening configuration is an important design criterion for long-term survival.

Bone Cements↗
PubMed1990

Effects of data smoothing on the reconstruction of helical axis parameters in human joint kinematics.

In biomechanical joint-motion analyses, the continuous motion to be studied is often approximated by a sequence of finite displacements, and the Finite Helical Axis (FHA) or "screw axis" for each displacement is estimated from position measurements on a number of anatomical or artificial landmarks. When FHA parameters are directly determined from raw (noisy) displacement data, both the position and the direction of the FHA are ill-determined, in particular when the sequential displacement steps are small. This implies, that under certain conditions, the continuous pathways of joint motions cannot be adequately described. The purpose of the present experimental study is to investigate the applicability of smoothing (or filtering) techniques, in those cases where FHA parameters are ill-determined. Two different quintic-spline smoothing methods were used to analyze the motion data obtained with Roentgenstereophotogrammetry in two experiments. One concerning carpal motions in a wrist-joint specimen, and one relative to a kinematic laboratory model, in which the axis positions are a priori known. The smoothed and non-smoothed FHA parameter errors were compared. The influences of the number of samples and the size of the sampling interval (displacement step) were investigated, as were the effects of equidistant and nonequidistant sampling conditions and noise invariance.

Adult↗
PubMed1990

The various stress patterns of press-fit, ingrown, and cemented femoral stems.

Finite-element analysis was used to study the general differences in load-transfer mechanisms and stress patterns of cemented, fully ingrown, proximally ingrown, and smooth press-fitted femoral stems in total hip arthroplasty (THA). Identical stems were used for the noncemented configurations and a similar stem shape for the cemented configurations. In each model, bone properties and loading characteristics were equal. Stem elastic moduli were varied so that the effects of cobalt-chromium-molybdenum (CoCrMo) and titanium as different stem materials could be assessed. The load-transfer mechanism is similar for all bonded configurations but differs dramatically for unbonded stems, e.g., press-fit designs. In the bonded configurations, interface stress concentrations occur on the proximal and distal sides. Stress value depends on stem rigidity, with higher proximal stress occurring in cemented stems and higher distal stress in noncemented stems. In the press-fit stem, the interface stresses are affected more by stem shape as a geometric entity and less by stem rigidity. Considering possible postoperative failure mechanisms, such as interface loosening and cortical bone loss, titanium is expected to produce better results in noncemented stems and CoCrMo in cemented stems. Cortical stress shielding as a qualitative phenomenon is caused by all stems, particularly in the calcar region. Quantitatively, stress-shielding effects differ with each type of fixation used. Stress-shielding effects are severe in fully ingrown stems and milder in cemented stems because of the differences in stem rigidity. The proximally ingrown stem falls between the fully ingrown and cemented stems in regard to stress shielding because stress transfer is more evenly distributed along the stem and concentrated at the lower coated edge. The press-fit stem provokes calcar stress shielding only. In the midstem region the stresses in the cortex are even greater than in the natural case.

Bone Cements↗
PubMed1989

A stereophotogrammetric method for measurements of ligament structure.

A stereophotogrammetric method is presented to reconstruct the course of a curve in the three-dimensional space. This method is exclusively suitable as a non-destructive tool to determine the surface fiberstructure of ligaments, tendons and other organised collagenous structures. In addition, it is a convenient tool to measure the geometry of articular surfaces and other complicated surface shapes.

Hip Prosthesis↗
PubMed1989

Mathematical shape optimization of hip prosthesis design.

The long-term success of artificial-joint replacement depends partly on the chances for acrylic cement failure and interface disruption. These chances can be diminished by an optimal load-transfer mechanism, whereby stress concentrations are avoided. The present paper introduces a method for numerical shape optimization, whereby the finite element method is used iteratively to determine optimal prosthetic designs, which minimize interface stresses. The method is first applied in a simplified one-dimensional model of a cemented femoral stem fixation, using acrylic cement. The results show that 30-70% cement and interface stress reductions can be obtained in principle with an optimized design. Although the actual optimal shape is susceptible to the characteristics of the joint load, the stem length, stem modulus, cement modulus and bone properties, its general geometrical characteristics are consistent, featuring proximal and distal tapers, and a belly-shaped middle region. These general characteristics are confirmed in a more realistic two-dimensional FEM model. It is concluded that this method of shape optimization can provide a meaningful basis for prosthetic design and analysis activities in general.

Bone Cements↗