Effect of pegs and screws on bone ingrowth in cementless total knee arthroplasty.
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Humans↗
Biomedical subjects
J Vander Sloten
Publications and source records attributed to J Vander Sloten.
Interactive simulation of cranial surgery in a computer aided design environment.
Accurate pre-surgical planning is a prerequisite for successful craniofacial surgery. This paper introduces a simulation system developed in a computer aided design (CAD) environment, where a 3-D mathematical model of the skull is entered. The architecture of the program yields a flexible and easy-to-use system that allows the simulation of surgery on the wire frame image of the model. Possible actions simulated are osteotomy, bending, rotation, translation and removal. Numerical values for anatomical distances and the intracranial volume are easily calculated. Information on the techniques used and the numerical data resulting from the simulation can be stored. Plots of intermediate steps of the simulation or of contours of separate pieces permit feed-back to the operating theatre.
Computer Simulation↗
Internal fixation of the spine in traumatic and scoliotic cases. The potential of pedicle screws.
Internal fixation techniques are in common used to stabilize vertebral fractures and correct severe scoliosis. Consolidation of injured vertebrae with neighbouring intact vertebra is the goal in the former case whilst fusion of the vertebrae in a corrected position is aimed at in the latter case. Degenerative spine diseases are not considered in this paper. Classical instrumentation consists of rods (e.g., Cotrel-Dubousset, Harrington, Luque-Galveston) attached to the bone by means of hooks or wires. More recently, transpedicular screws are introduced as an alternative bone/implant interface. Comparing the results of several studies, the posterior pedicle screw based devices demonstrate the ability to produce the most rigid constructs. However, the insertion of pedicle screws implicates a relatively high complication risk and its success strongly depends on the experience of the surgeon. Incorrect drilled holes or malplacement of the screws can result in nerve root injuries and fracture of the pedicle. Studies reported complication ratios up to 30% with substantial neurological implications. A certain degree of automation of the critical actions may be necessary to enhance the safety of pedicle screw insertion. Two techniques of computer assisted spine surgery are compared. Both techniques permit a computer assisted surgical planning based on CT images. During operation the first system permanently observes the position of the drill relative to the spine and informs the surgeon on the deviation of the actual drill path to the planned drill path. The second system uses a pre-operative surgical planning to design and construct a mechanical drill guide, fitting perfectly on the patient's spine.
Bone Screws↗
The influence of geometrical distortions of three-dimensional finite elements, used to model proximal femoral bone.
A realistic three-dimensional finite element model of the proximal femur requires the use of irregularly shaped elements to represent this geometry, unless the geometry is considerably simplified. The authors have investigated the influence of different types of element distortions upon the accuracy of two stresses which are relevant in the proximal femur: the bending stress and the tangential (hoop) stress. While most angular and geometric distortions did not influence the bending stress significantly, the position of the middle node on the edge of a quadratic element was very critical, as were some types of element skewness. The hoop stresses can only be calculated accurately if the geometry is modelled as well as possible by a cylinder, and not by a cone.
Femur↗
The development of a physiological hip prosthesis: evaluation of the strains after implantation of a prototype of hip implant: experiment in a dry femur.
Based upon previous research on the relation between hip prosthesis designs and strain distributions in a proximal femur model, a prototype of a "physiological" hip prosthesis was designed and manufactured. Strain gauge measurements on a dry femur before and after implantation of this prosthesis were made in different loading conditions simulating one-legged stance with and without torsional loading and two-legged stance. The strains in the outer cortex were within 10% of the physiological values along the whole medial side in all measurement conditions.
Biomechanical Phenomena↗
Development of an above-knee prosthesis equipped with a microcomputer-controlled knee joint: first test results.
The shortcomings of conventional above-knee prostheses are due to their lack of adaptive control. Implementation of a microcomputer controlling the knee joint in a passive way has been suggested to enhance the patient's gait comfort, safety and cosmesis. This approach was used in the design of a new prosthetic system for the above-knee amputee, and tested on one patient. The knee joint of a conventional, modular prosthesis was replaced by a knee joint mechanism, equipped with a controllable brake on the knee joint axis. Sensors and a microcomputer were added, keeping the system self-contained. The modularity of the design permits the use of an alternative, external, PC-based control unit, emulating the self-contained one, and offering extended data monitoring and storage facilities. For both units an operating environment was written, including sensor/actuator interfacing and the implementation of a real-time interrupt, executing the control algorithm. A double finite state approach was used in the design of the control algorithm. On a higher level, the mode identification algorithm reveals the patient's intent. Within a specific mode (lower level), the relevant mode control algorithm looks for the current phase within the gait cycle. Within a particular phase, a specific simple control action with the brake replaces normal knee muscle activity. Tests were carried out with one prosthetic patient using a basic control algorithm for level walking, allowing controlled knee flexion during stance phase. The technical feasibility of such a concept is illustrated by the test results, even though only flexion during early stance phase was controlled during the trials.(ABSTRACT TRUNCATED AT 250 WORDS)
Artificial Limbs↗
Trabecular structure compared to stress trajectories in the proximal femur and the calcaneus.
The theory that the trabecular structure within bones follows the principal stress trajectories, is investigated by two-dimensional finite element models of increasing complexity. This is done for the proximal femur of the human and for the calcaneus of the horse. In both cases, a simple model with well-chosen loading and boundary conditions gives good agreement between the observed trabecular structure and the calculated stress trajectories. It is shown that this stress trajectory theory has a mechanically founded explanation.
Adaptation, Biological↗
Assessment of mechanobiological models for the numerical simulation of tissue differentiation around immediately loaded implants.
Nowadays, there is a growing consensus on the impact of mechanical loading on bone biology. A bone chamber provides a mechanically isolated in vivo environment in which the influence of different parameters on the tissue response around loaded implants can be investigated. This also provides data to assess the feasibility of different mechanobiological models that mathematically describe the mechanoregulation of tissue differentiation. Before comparing numerical results to animal experimental results, it is necessary to investigate the influence of the different model parameters on the outcome of the simulations. A 2D finite element model of the tissue inside the bone chamber was created. The differentiation models developed by Prendergast, et al. ["Biophysical stimuli on cells during tissue differentiation at implant interfaces", Journal of Biomechanics, 30(6), (1997), 539-548], Huiskes et al. ["A biomechanical regulatory model for periprosthetic fibrous-tissue differentiation", Journal of Material Science: Materials in Medicine, 8 (1997) 785-788] and by Claes and Heigele ["Magnitudes of local stress and strain along bony surfaces predict the course and type of fracture healing", Journal of Biomechanics, 32(3), (1999) 255-266] were implemented and integrated in the finite element code. The fluid component in the first model has an important effect on the predicted differentiation patterns. It has a direct effect on the predicted degree of maturation of bone and a substantial indirect effect on the simulated deformations and hence the predicted phenotypes of the tissue in the chamber. Finally, the presence of fluid also causes time-dependent behavior. Both models lead to qualitative and quantitative differences in predicted differentiation patterns. Because of the different nature of the tissue phenotypes used to describe the differentiation processes, it is however hard to compare both models in terms of their validity.
Animals↗