Biomedical subjects

R Huiskes

Publications and source records attributed to R Huiskes.

At least 127 records · Page 7Linked to original sources

PubMed1994

Effects of fit and bonding characteristics of femoral stems on adaptive bone remodeling.

Bone atrophy caused by stress-shielding may cause serious complications for the long-term fixation of hip stems. In particular, uncemented total hip arthroplasty is threatened by this problem, because the stems are usually larger and, as a consequence, stiffer than those of cemented implants. In the present study, the effects of fit and bonding characteristics of femoral hip stems were investigated, using the (nonlinear) finite element method in combination with adaptive bone remodeling theory to predict the bone density distribution in a bone or bone/implant configuration. Unknown parameters used in the theory, such as a reference equilibrium loading stimulus and a threshold (dead) zone of this stimulus, were established (triggered) by using the method to predict the density distributions in the natural femur and around fully coated uncemented implants. The computer simulation method can provide long term predictions of remodeling patterns around various implant configurations. Several cases were analyzed, whereby the coating conditions (fully, partly, or noncoated) and the fit characteristics (press fitted or overreamed) were varied. The computer predictions showed that partly coating can only significantly reduce bone atrophy relative to fully coated stems, when the coating is applied at a small region at the utmost proximal part of the stem. For smooth press-fit stems the predicted amount of bone loss (35 percent in the proximal medial region) was less than for a one-third proximally coated or a fully coated stem (50 to 54 percent predicted bone loss in the proximal medial region).(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗

PubMed1994

Morsellized allografts for fixation of the hip prosthesis femoral component. A mechanical and histological study in the goat.

To simulate femoral intramedullary bone stock loss in revision surgery of failed total hip arthroplasties, a method was developed using impacted trabecular bone grafts. In 14 goats a cemented total hip arthroplasty was performed, fixating the stem within a circumferential construction of bone allografts. After 6 or 12 weeks, 4 goats were used for mechanical tests and 3 for histology. The stability of the stems was determined in a loading experiment with roentgen-stereophotogrammetric analysis; loads of up to 1.44 times body weight were used. One aseptic loosening was seen with gross movements. In the other cases the most important movements were axial rotations (max. 0.24 degrees under 800 N) and axial translations (max. 0.16 mm under 800 N). After unloading some elastic recovery occurred. There were no differences between the 6 and 12-week groups. Histologically, revascularization and remodeling of the grafts were evident. Bone apposition and bone resorption of the grafts resulted in a mixture of graft and new bone. There was more new bone formation in the 12-week group, but the process was not yet completed. The use of impacted trabecular bone grafts in cases of severe intramedullary bone stock loss seems to be a promising revision technique.

Animals↗

PubMed1993

Adaptive bone remodeling around bonded noncemented total hip arthroplasty: a comparison between animal experiments and computer simulation.

Severe loss of bone related to stress-shielding is one problem threatening the long-term integrity of noncemented total hip arthroplasty. It is widely accepted that this phenomenon is caused by adaptive bone remodeling according to Wolff's law. Recently, quantitative bone-remodeling theories have been proposed, suitable for use in computer-simulation models in combination with finite-element codes, which can be applied to simulate the long-term effect of the remodeling process. In the present paper, the results of such a computer simulation are compared with those in an animal experiment. A three-dimensional finite-element model was constructed from an animal experimental configuration concerning the implantation of a fully coated femoral hip prosthesis in dogs. The simulation results of the adaptive bone-remodeling process (geometric adaptations at the periosteal surface and density adaptations within the cancellous bone) were compared with cross-sectional measurements of the canine femurs after 2 years of follow-up. The detailed comparison showed that long-term changes in the morphology of bone around femoral components of total hip replacements can be fully explained with the present quantitative adaptive bone-remodeling theory.

Adaptation, Physiological↗

PubMed1993

Method to determine collagen density distributions in fibrous tissues.

We present a method for the measurement of hydroxyproline density distributions, as an estimate for collagen density distributions, in fibrous tissues such as ligaments and tendons. To evaluate this method, a single flexor tendon of a human hand was divided into seven tissue locations. Triplicate determinations of the dry weight tissue mass, volume, and hydroxyproline mass were made at each location: two samples were analyzed at the same time (a and b) and one was analyzed later (c). The intralocation variation is an estimate for the measurement error variance, which indicates both the precision (a compared with b) and the repeatability (b compared with c) of the technique for determination of volume, dry weight tissue mass, hydroxyproline concentration, and hydroxyproline density. The precision was about 5% for all variables, and the repeatability ranged from 1.5-4.3%. In comparison with the interlocation variations, the error variances were small, except for collagen concentration. This indicates that despite the measurement errors, differences in hydroxyproline density can be detected within fibrous tissues with the proposed method. The use of only a single tendon is adequate to evaluate the measurement error of the method, but more tendons should be measured to generalize the absolute values of the variables.

Aged↗

PubMed1993

A clinical, radiological and biomechanical study of the TARA hip prosthesis.

We reviewed 60 patients with 72 TARA (total articular replacement arthroplasty) resurfacing hip prostheses. To analyse the behaviour of the femoral component a radiographic study was done and a two-dimensional finite element model was constructed. The stem of the femoral component plays a role in the load transfer mechanism. Stress shielding is seen in the proximal femur but depends on the interface conditions. When only the dome of the cup is assumed to be bonded to the bone, the stresses in the head increase dramatically and there is no more stress shielding. Five years after implantation radiographic signs of loosening of the femoral component were seen in 6.8% of the implants placed without notching in the femoral neck and in 28.6% of the components with notching (significant difference, P = 0.0005). Signs of loosening of the acetabular component were seen in 37.7% 5 years postoperatively. The cumulative survival rates of the femoral and acetabular components were 89.7% and 85.6% respectively 5 years after implantation. The overall clinical results are represented by an integration of the clinical results (Harris Hip Score System), the radiographic results and the survival analysis. This gave a success rate of only 72% 5 years after implantation.

Adult↗

PubMed1993

Carpal bone kinematics and ligament lengthening studied for the full range of joint movement.

Present data on carpal kinematics and carpal ligament behaviour are limited to flexion and deviation movements of the hand. These motions do not represent all the wrist-joint motions which are important for the activities of daily living. The goal of this project was to obtain insight into carpal kinematics and carpal ligament behaviour during motions of the hand covering the full range of motion of the wrist joint. The carpals and the ligaments of four wrist-joint specimens were provided with radiopaque markers. These joints were subjected to Röntgenstereophotogrammetric experimentation in a large number of hand positions to determine carpal positions and ligament lengths. The movements of the carpal bones were described by means of finite helical axes (FHA). It was found that the movements of the carpals in the distal row closely resemble those of the hand. Conversely, the motions of the carpals of the proximal row appeared not to be directly proportional to the hand motions and exhibited clear out-of-plane movements. Furthermore, it could be shown that movements of the hand into the ulnodorsal quadrant of the full range of hand motion corresponds to larger helical rotations and translations for most of the carpals than when the hand was moved into any other quadrant. The maximal ligament length changes determined did not exceed the length changes reported for pure flexion and pure deviation movements of the hand.

Aged↗

PubMed1993

Quantitative analysis of bone reactions to relative motions at implant-bone interfaces.

Connective soft tissues at the interface between implants and bone, such as in human joint replacements, can endanger the stability of the implant fixation. The potential of an implant to generate interface bone resorption and form soft tissue depends on many variables, including mechanical ones. These mechanical factors can be expressed in terms of relative motions between bone and implant at the interface or deformation of the interfacial material. The purpose of this investigation was to determine if interface debonding and subsequent relative interface motions can be responsible for interface degradation and soft tissue interposition as seen in experiments and clinical results. A finite element computer program was augmented with a mathematical description of interface debonding, dependent on interface stress criteria, and soft tissue interface interposition, dependent on relative interface motions. Three simplified models of orthopaedic implants were constructed: a cortical bone screw for fracture fixation plates, a femoral resurfacing prosthesis and a straight stem model, cemented in a bone. The predicted computer configurations were compared with clinical observations. The computer results showed how interface disruption and fibrous tissue interposition interrelate and possibly enhance each other, whereby a progressive development of the soft tissue layer can occur. Around the cortical bone screw, the predicted resorption patterns were relatively large directly under the screw head and showed a pivot point in the opposite cortex. The resurfacing cup model predicted some fibrous tissue formation under the medial and lateral cup rim, whereby the medial layer developed first because of higher initial interface stresses. The straight stem model predicted initial interface failure at the proximal parts. After proximal resorption and fibrous tissue interposition, the medial interface was completely disrupted and developed an interface layer. The distal and mid lateral side maintained within the strength criterion. Although the applied models were relatively simple, the results showed reasonable qualitative agreement with resorption patterns found in clinical studies concerning bone screws and the resurfacing cup. The hypothesis that interface debonding and subsequent relative (micro)motions could be responsible for bone resorption and fibrous tissue propagation is thereby sustained by the results.

Biomechanical Phenomena↗

PubMed1993

An indirect method to assess wrist ligament forces with particular regard to the effect of preconditioning.

A method has been developed to calculate the forces that are developed in the ligaments of a joint specimen during motions. This indirect method is needed since direct measurements fail in the case of small ligaments. As an example the small ligaments of the carpal joint are considered. The rationale of the method is that the force generated in a ligament depends on the amount of strain to which it is subjected and on its material characteristics. In the method presented the lengths of the ligaments are determined in vitro at several joint positions by means of röntgenstereophotogrammetry. The zero-force length and the force-elongation relationship are determined on the same ligaments isolated in a materials testing machine. Over a considerable part of the strain range the measurement errors are relatively small compared to the forces determined, less than 10%. The method is applicable to joints in situations where other measuring methods cannot be used. The present analysis shows, however, that the force values determined are susceptible to preconditioning of the ligaments. In preconditioned ligaments the forces could be up to 50% lower than in the non-preconditioned situation. This suggests that ligament forces may vary considerably in vivo, depending on the extent of preconditioning provoked by a particular function.

Biomechanical Phenomena↗

PubMed1993

From structure to process, from organ to cell: recent developments of FE-analysis in orthopaedic biomechanics.

The introduction of finite element analysis (FEA) into orthopaedic biomechanics allowed continuum structural analysis of bone and bone-implant composites of complicated shapes (Huiskes and Chao, J. Biomechanics, Vol. 16, 1983, pp. 385-409). However, besides having complicated shapes, musculoskeletal tissues are hierarchical composites with multiple structural levels that adapt to their mechanical environment. Mechanical adaptation influences the success of many orthopaedic treatments, especially total joint replacements. Recent advances in FEA applications have begun to address questions concerning the optimality of bone structure, the processes of bone remodeling, the mechanics of soft hydrated tissues, and the mechanics of tissues down to the microstructural and cell levels. Advances in each of these areas, which have brought FEA from a continuum stress analysis tool to a tool which plays an ever-increasing role in the scientific understanding of tissue structure, adaptation, and the optimal design of orthopaedic implants, are reviewed.

Adaptation, Physiological↗

PubMed1993

In vivo measurements of the loading conditions on the tibia of the goat.

In vivo strain measurements at 8 locations on the tibia of the goat were performed. Successive in vitro calibrations were used to determine the assumed linear relationship between the measured strain signals and the external loads (3 forces and 3 moments) at the tibia. For the reconstruction of the in vivo external loads from the strain data, a transformation matrix was created from the calibration experiments, using 'singular-value decomposition'. The method is a reliable technique for measuring in vivo loads during functional gait and gives reproducible results.

Animals↗

PubMed1993

Pre-clinical testing of hip prosthetic designs: a comparison of finite element calculations and laboratory tests.

To investigate the accuracy of finite element (FE) models for pre-clinical testing of unbounded hip prostheses, relative to aspects of load transfer and micromobility, two previously published laboratory experiments were simulated, using three-dimensional FE models. It was found for the load-transfer analyses that the experiment and the FE study revealed results that were very similar. The trends in the mobility experiments were also reproduced in the FE simulations, although quantitative differences were found. It is concluded that FE analysis can effectively be used for design evaluation of hip prostheses before prototypes are made.

Acrylic Resins↗

PubMed1993

Total hip reconstruction in acetabular dysplasia. A finite element study.

In acetabular dysplasia, fixation of the acetabular component of a cemented total hip prosthesis may be insecure and superolateral bone grafts are often used to augment the acetabular roof. We used finite element analysis to study the mechanical importance of the lateral acetabular roof and found that the lateral acetabular rim plays an important role in the load transfer of the pelvic bone. When the superlateral rim was lacking, the load shifted to the posterosuperior rim and to the area of pubic support, and the stresses in all materials, especially in the cement and in the trabecular bone, increased greatly. At the cement-bone interface the tilting component of the shear stress increased threefold. In a model in which the dysplastic acetabulum was augmented by a rigidly fixed, load-transmitting bone graft, the stresses were considerably diminished.

Acetabulum↗

PubMed1993

Failed innovation in total hip replacement. Diagnosis and proposals for a cure.

Many new hip prosthesis and fixation techniques have been introduced in orthopedics in recent years. Yet, none have provided superior total hip replacements (THR) in comparison to the traditional cemented Charnley concept, which nevertheless has limited long-term endurance. This review article investigates why the THR innovation process has failed. The predominant causes for long-term failure of THR are discussed. A framework of generic failure scenarios is proposed to provide guidelines for a scientifically-oriented approach to THR design, testing and clinical evaluation. It is shown that THR components are subject to incompatible design goals as regards prevention of the different failure scenarios. Neglect of those has been one important factor in the present innovation impasse. A second factor is the trial-and-error culture in orthopedic surgery, in which new devices run through the innovation cycle without proper testing or rigorous postoperative analysis. The third factor is ineffective regulation of marketing approval with respect to orthopedic implants. Scientific research in orthopedics and related sciences has produced new methods for systematic design evaluation, pre-clinical testing and clinical trials. These can provide a basis for self-regulation and self-control by the orthopedic community, in all stages of the innovation process.

Animals↗

PubMed1993

Stress shielding and bone resorption in THA: clinical versus computer-simulation studies.

"Stress shielding" of bone around noncemented prosthetic hip stems causes long-term adaptive bone resorption which threatens the integrity of the fixation. Recently, computer-simulation models based on adaptive bone-remodeling theory in combination with finite-element methods have been developed. These models can be used to predict the extent of long-term resorption. In this paper a comparison is presented between the results of these predictions and those of precise measurements in retrieval hip-replacement specimens reported by Engh and associates (1992). It is shown that certainly the predictions and the actual clinical findings are subject to the same trends. Under certain assumptions, these results even match precisely. It is also shown that both clinical results and simulation predictions can be approximated by a simple formula, in which the amount of bone loss is related to the ratio between stem stiffness and preoperative bone density.

Aged↗

PubMed1992

Effects of material properties of femoral hip components on bone remodeling.

Bone loss around femoral hip stems is one of the problems threatening the long-term fixation of uncemented stems. Many believe that this phenomenon is caused by reduced stresses in the bone (stress shielding). In the present study the mechanical consequences of different femoral stem materials were investigated using adaptive bone remodeling theory in combination with the finite element method. Bone-remodeling in the femur around the implant and interface stresses between bone and implant were investigated for fully bonded femoral stems. Cemented stems (cobalt-chrome or titanium alloy) caused less bone resorption and lower interface stresses than uncemented stems made from the same materials. The range of the bone resorption predicted in the simulation models was from 23% in the proximal medial cortex surrounding the cemented titanium alloy stem to 76% in the proximal medial cortex around the uncemented cobalt-chrome stem. Very little bone resorption was predicted around a flexible, uncemented "iso-elastic" stem, but the proximal interface stresses increased drastically relative to the stiffer uncemented stems composed of cobalt-chrome or titanium alloy. However, the proximal interface stress peak was reduced and shifted during the adaptive remodeling process. The latter was found particularly in the stiffer uncemented cobalt-chrome-molybdenum implant and less for the flexible iso-elastic implant.

Alloys↗

PubMed1992

Strains and forces in selected carpal ligaments during in vitro flexion and deviation movements of the hand.

The forces induced in tiny wrist joint ligaments must be estimated in order to understand their role in the mechanism of the joint. We estimated forces in a number of selected ligaments in seven human wrist joint specimens, using a noninvasive method. The method is based on the rationale that the force generated in a ligament depends on its change of length with the joint under load. In vitro length changes of the ligaments were determined during flexion and deviation movements of the hand, using a roentgenstereophotogrammetric analysis technique. Subsequently, bone-ligament-bone (BLB) preparations were dissected from the specimens. From these BLB preparations the zero-force length and the force-elongation relationship were determined in a material testing machine. The forces generated in the ligaments during flexion and deviation were calculated by combining results on the in vitro ligament length changes, the zero-force length, and the force-elongation relationship. Large interspecimen variations of the force patterns were found. Due to this variability, it is not possible to obtain quantitative models for the kinetic behavior of the ligaments. However, qualitative trends could be distilled from the strain and force patterns. It is clear that for most ligaments, the zero-force lengths were not equal to the lengths they possessed in the neutral position of the hand. Furthermore, it could be shown which motions of the hand would most likely strain a particular ligament. It could be shown that the variations in the force patterns originate mainly from variations in the zero-force lengths, and from variations in the force-strain relationship between specimens.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1992

The behavior of adaptive bone-remodeling simulation models.

The process of adaptive bone remodeling can be described mathematically and simulated in a computer model, integrated with the finite element method. In the model discussed here, cortical and trabecular bone are described as continuous materials with variable density. The remodeling rule applied to simulate the remodeling process in each element individually is, in fact, an objective function for an optimization process, relative to the external load. Its purpose is to obtain a constant, preset value for the strain energy per unit bone mass, by adapting the density. If an element in the structure cannot achieve that, it either turns to its maximal density (cortical bone) or resorbs completely. It is found that the solution obtained in generally a discontinuous patchwork. For a two-dimensional proximal femur model this patchwork shows a good resemblance with the density distribution of a real proximal femur. It is shown that the discontinuous end configuration is dictated by the nature of the differential equations describing the remodeling process. This process can be considered as a nonlinear dynamical system with many degrees of freedom, which behaves divergent relative to the objective, leading to many possible solutions. The precise solution is dependent on the parameters in the remodeling rule, the load and the initial conditions. The feedback mechanism in the process is self-enhancing, denser bone attracts more strain energy, whereby the bone becomes even more dense. It is suggested that this positive feedback of the attractor state (the strain energy field) creates order in the end configuration. In addition, the process ensures that the discontinuous end configuration is a structure with a relatively low mass, perhaps a minimal-mass structure, although this is no explicit objective in the optimization process. It is hypothesized that trabecular bone is a chaotically ordered structure which can be considered as a fractal with characteristics of optimal mechanical resistance and minimal mass, of which the actual morphology depends on the local (internal) loading characteristics, the sensor-cell density and the degree of mineralization.

Bone Density↗

PubMed1992

Stiffness of the ligaments of the human wrist joint.

In the present study the stiffness of the superficial ligaments of 14 human cadaver wrist joints have been determined. In these experiments the tested, fresh-frozen carpal joints are divided into a number of bone-ligament-bone complexes, which are loaded in a tensile testing machine at a rate of 66% of the ligaments' initial length per second to a maximal strain of 15%. From the force-elongation curves and ligament dimensions the tangent moduli for the ligament-bone strips are derived. The results show that, with regard to the tangent modulus, there is not a clear differentiation among ligament strips. Only the dorsal radiotriquetrum ligament (RTD) and the palmar radiocapitate ligament (RCP) appear to consist of a material of a relatively high tangent modulus, about 93 and 83 MPa, respectively. The other seven ligaments tested have similar tangent moduli, ranging from 25 to about 50 MPa.

Aged↗