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At least 289 records · Page 16Linked to original sources
PubMed1987

Effect of material damping on bone remodelling.

This paper considers the effect of internal material damping on the stresses, strains, and surface and internal remodelling behaviour in a section of axisymmetrical bone with a force-fitted axially oriented medullary pin. The bone response to several loading situations is modelled using visco-elastic equations. An approximate method is developed to analyse the proposed mathematical model. By considering a numerical example, the effect of material damping on the remodelling stresses is quantified.

Adaptation, Physiological↗
PubMed1995

Stress protection due to external fixation.

Bone is sensitive to mechanical influences. The presence of an orthopaedic device will impose constraints on the mechanical environment that may influence subsequent remodelling and repair. An Oxford External Fixator was applied to six intact ovine tibiae. The strains engendered during normal walking were then recorded from strain gauges applied to the mid-shaft of the bone. The fixator configuration was then altered such that the intact fixator bar connecting the pins was replaced with a sectioned version that did not permit load transfer through the fixator, and the strain environment re-recorded. The peak strains recorded with the intact bar were significantly lower than those recorded with the sectioned bar. This showed that the use of a fixator with an intact bar resulted in significant stress protection of the underlying bone. A fixator was then applied to both the right and left tibiae of a further six animals and the resulting strain environment and corresponding remodelling response was observed over 16 weeks. In each case one fixator was configured with an intact bar (the stress protected limb), whilst the other utilised a sectioned bar (the unprotected limb). The results showed that over this period the bone mineral content fell by 9% in the stress protected limb compared to the unprotected limp. Quantitative assessment of the bones showed that this bone loss occurred as a direct consequence of resorption on the periosteal and endosteal surfaces. In addition, strain recordings at week 16 showed that the fixator was still stress protecting the tibia.

Animals↗
PubMed1994

Initial in vitro stability of the tibial component in a canine model of cementless total knee replacement.

The tibial component of a canine cementless total knee replacement model was used to determine the degree to which pegs and screws contributed to the initial in vitro stability of the device. Three implant designs were investigated: (1) a four-peg implant in which cortical bone screws passed through the pegs, (2) the four-peg implant without adjuvant screw fixation, and (3) a flat implant with screws placed in the same positions as in the first design. For measuring the interface motion, the tibial component and proximal tibia were modeled as rigid bodies and an experimental method was developed which permitted all six degrees of freedom of the motion between these two objects to be determined. In tests performed to validate this methodological approach, the potential confounding influences of tibial deformation and differential amounts of tibial deformation with the use of screws or pegs were shown to be minimal, supporting the use of the rigid-body method. In general, the areas of greatest motion were at the periphery of the bone-implant interface, regardless of whether or not screws or pegs were used. The components secured with screws had up to five-fold reductions in interface motion compared to components which had pegs but lacked screw fixation. Components with pegs and screws and components with screws only had the same amount of interface motion. Thus, in the presence of screw fixation, the addition of pegs did not increase the stability of the tibial component.

Alloys↗
PubMed1994

A spinal fixation device for in vivo load measurement.

An instrumented spinal fixation device has been developed that allows in vivo measurement of the forces and moments acting on the implant. The telemetry is inductively powered, hermetically sealed by electron beam welding and is active only during the measurements. The instrumented fixateur interne is similar in size to the original Dick internal fixator implant and has the strength of the original implant. Laboratory tests with paired implants mounted in plastic vertebrae show that small changes in the position of the implants have a strong influence on the distribution of the loads on the implants.

Activities of Daily Living↗
PubMed1994

Fixation pull-out response measurement of bone screws and porous-surfaced posts.

Screws and posts are used in various implant designs to contribute to the short- and long-term fixation stability of artificial joints. This study was undertaken to measure the detailed pull-out load-displacement response of bone screws, beaded porous coated posts, and smooth-surfaced posts in both proximal tibial cancellous bone and polyurethane material under monotonic static and repetitive cyclic loadings. The effect of a number of parameters such as insertion site on the proximal tibia, rate of displacement, insertion depth, outside diameter, drill size, repetitive loading and boundary conditions were studied. Bone screws resisted significantly larger loads than posts of the same size. Smooth-surfaced posts demonstrated much larger (about twice) pull-out forces than beaded porous coated posts of the same size. The pull-out force in the proximal tibia was markedly larger at the medial region followed by the lateral region. The central region exhibited the least force. The resistance of screws and posts diminished with repetitive cyclic loads/displacements, especially when these were larger than 50% of their respective values at pull-out force evaluated under monotonic static loading conditions. The smooth-surfaced posts showed superior performance in maintaining their resistance in fatigue than did the porous coated posts and bone screws. The pull-out force was found to also depend on the pull-out material arrangement and boundary conditions. Pull-out results measured with a specific test design should not, therefore, be compared with those performed using different design configurations.

Bone Nails↗
PubMed1989

Torsional moment to failure for carbon fibre polysulphone expandable rivets as compared with stainless steel screws for carbon fibre-reinforced epoxy fracture plate fixation.

A method of securing carbon fibre-reinforced epoxy bone plates with carbon fibre polysulphone expanding rivets was investigated. Six carbon fibre-reinforced epoxy bone plates were secured to rods with carbon fibre polysulphone rivets and six were secured with standard cortical stainless steel screws. These constructions were then subjected to pure torsional load to failure. The carbon fibre expandable rivets failed at a greater torsional moment.

Biocompatible Materials↗
PubMed1993

Hydrogels as an interface between bone and an implant.

The use of fully hydrated hydrogels in the body has been well established. The forces a hydrogel generates on swelling when it is placed in a constrained space were investigated with a view to providing a mechanism for fixing a prosthesis in the intramedullary cavity. A cross-linked poly(2-hydroxyethyl methacrylate) [p(HEMA)] hydrogel was investigated as a potential material. In vitro mechanical tests were carried out to determine the stresses generated in the p(HEMA) when it was placed in water and not allowed to swell. Pull out loads of up to 375 N indicated that the system could be used successfully in vivo. Consequently, the material was placed intraosseously at two sites in a rabbit animal model, in the mid-shaft (diaphysis) and the lower end (metaphysis) of the femur. Histological examination showed there was no adverse bone response; bone was growing from the endosteal surface up to and into the hydrogel in the diaphyseal implants and surrounded the hydrogel in the metaphysis. As a result of the shape and size variations in the rabbit femur, in vivo mechanical tests were found to give lower values than those obtained in vitro.

Animals↗
PubMed1995

Investigation of the torque-tension characteristics of a flanged external fixator pin.

The torque-tension characteristics of standard, conical and flanged external fixator pins and a cortical screw were compared using a commercially available testing apparatus. The flanged pin and the screw were similar in behaviour, and converted torque into tension more efficiently than conical and standard external fixator pins.

Biomechanical Phenomena↗
PubMed1989

A comparison of the use of external pin and transnasal Kirschner wire fixation for the unstable tripod malar fracture: a prospective trial.

A prospective study involving 54 patients was undertaken to compare external pin and transnasal Kirschner wire (K-wire) fixation of the unstable, non-comminuted, tripod malar fracture. The features assessed were: (1) The aesthetic result. (2) The ease and speed of both procedures. (3) Per-operative complications. (4) Post-operative complications. (5) Patient tolerance of the procedure.

Adult↗
PubMed1991

A technique for control of the condylar head during open reduction of the fractured mandibular condyle.

Open reduction of fractures of the neck of the mandibular condyle may be technically difficult. Control of the proximal fragment may be achieved by insertion of a Moule pin into the condylar neck. This facilitates retrieval of the condylar head and alignment of the bone fragments which are essential components of the technique. Accurate anatomical reduction and stabilisation of the fracture simplifies the technique of miniature plate fixation.

Adult↗
PubMed1994

The in-vivo effects of an intramedullary implant evoking a constant radial stress to bone. An animal study in the tibia of the goat.

Initial stability is essential for successful bone ingrowth into non-cemented prostheses. An entire new concept to increase the initial stability directly after implantation of intramedullary stems was developed (the tension rod prosthesis). The concept is based on a tension rod made out of memory metal that pulls a proximal stem of a prosthesis towards a distal anchor with a constant force. The stress generated along the long axis of the bone produces a radial stress around the prosthesis in the proximal femur. The main goal of this design is to increase the primary stability of the prosthesis during the ingrowth phase and to prevent stress shielding and bone resorption, as realized by the radial force applied to the proximal endosteum of the bone. To assess the efficacy of this concept and to collect data for the anchor design, an implant was developed for implantation into the tibia of the goat. Analyses of push-out strength and bone reactions were performed postoperatively. After 48 weeks the push-out strength of this implant was increased and the histological evaluation showed almost complete osseousintegration. Histomorphometrical analysis showed pronounced, permanent periosteal reactions, located around the anchor of the implant, which generates the radial stress. These first results showed that the bone can withstand the radial stress provoked by the anchor of the tension rod. It is concluded that the concept of a tension rod prosthesis is viable.

Animals↗
PubMed1985

The maxillary step osteotomy and Steinmann pin stabilization.

Use of the maxillary step osteotomy facilitates the transfer of information obtained by prediction tracing and model surgery to the patient at the time of surgery and allows for a well-visualized bone grafting area in cases of maxillary advancement. The use of Steinmann pin maxillary stabilization provides improved anteroposterior and vertical stabilization in indicated cases.

Bone Nails↗