Search PubMed⌕ Search

Biomedical subjects

D R Carter

Publications and source records attributed to D R Carter.

At least 127 records · Page 7Linked to original sources
PubMed1982

Strain-controlled fatigue of acrylic bone cement.

Monotonic tensile tests and tension-compression fatigue tests were conducted of wet acrylic bone cement specimens at 37 degrees C. All testing was conducted in strain control at a strain rate of 0.02/s. Weibull analysis of the tensile tests indicated that monotonic fracture was governed more strongly by strain than stress. The number of cycles to fatigue failure was also more strongly controlled by strain amplitude than stress amplitude. Specimen porosity distribution played a major role in determining the tensile and fatigue strengths. The degree of data scatter suggests that Weibull analysis of fatigue data may be useful in developing design criteria for the surgical use of bone cement.

Acrylic Resins↗
PubMed1982

Experimental determination of whole long bone sectional properties.

A strain gage based experimental method is presented which provides an alternative to use of area sectional properties for obtaining the cross sectional centroids, flexural rigidities and axial stiffness of whole bone specimens. While area sectional property computations require detailed records on the geometry of cross sections, the experimental method presented here requires only gage locations plus the applied loads and recorded strains. Both techniques are used to analyze the midshaft sectional properties of canine radii. The results demonstrate the advantage of the experimental method for the analysis of heterogeneous cross sections with an unknown distribution of bone elastic modulus. By applying the experimental and area methods together, effective elastic modulus values for the sections were obtained.

Animals↗
PubMed1982

Stress distributions in the acetabular region--I. Before and after total joint replacement.

Two-dimensional finite element analyses of the acetabular region before and after hip replacement were conducted. The distribution of pressure at the acetabular surface for the single limb stance phase of gait was transformed to nodal loads to stimulate in vivo loading conditions. A nonhomogeneous distribution of bone elastic properties was incorporated in the models. The results demonstrated that the principal stresses in the normal acetabulum were aligned with the principal orientations of the trabeculae. Total joint replacement increased the von Mises' equivalent stresses in the cancellous bone immediately superior to the acetabular cup, and increased stresses in the medial wall of the ilium. Biaxial, tension-compression stresses were created in the layer of bone cement and introduced in the medial wall of the ilium. Tensile stresses in the bone cement were greatest at the superior roof and at the inferior margin of the cup. Tensile stresses in the cup were more pronounced at the margins, particularly near the inferior lip. The cup tended to close in such a manner as to grip the head of the femoral component as it was pressed between the medial and lateral walls of the ilium.

Acetabulum↗
PubMed1982

Stress distributions in the acetabular region--II. Effects of cement thickness and metal backing of the total hip acetabular component.

A two-dimensional finite element study was undertaken to establish the stresses in the acetabular region after total joint replacement. The influence of cement thickness and the effect of metal backing on the polyethylene cup were explored. Increasing cement thickness (from 1 to 3 to 5 mm) caused a decrease in the von Mises' equivalent stresses in the cement and surrounding cancellous bone. A more dramatic reduction in these stresses was found when a 2 mm thick cobalt-chromium alloy backing was added to the cup. The results indicate that increasing the stiffness of the composite implant by either method is helpful but that the metal backing causes a more efficient transfer of the stresses to the walls of the ilium. The finding strongly suggests that the use of a metal-backed acetabular component will help to delay or prevent cup loosening and migration in total hip replacement patients.

Acetabulum↗
PubMed1982

Accuracy enhancement of in-vivo bone strain measurements and analysis.

A numerical technique is presented to evaluate and correct the zero-strain reference points determined experimentally for certain in-vivo strain rosette applications on long bones. The method is used to determine whether significant transverse stresses are present at the gage site during in-vivo activities. If transverse stresses are shown to be negligible, the experimentally determined zeroes can be appropriately adjusted to provide an increased accuracy of the strain measurements. In addition, the transverse Poisson's ratio is calculated and can be incorporated in subsequent in-vivo stress calculations.

Animals↗
PubMed1982

The relationship between in vivo strains and cortical bone remodeling.

Bone has the capacity to remodel in response to the mechanical demands which are made on it during in vivo activities. It has long been assumed that mathematical laws exist which can describe the relationship between bone stress or strain histories and the remodeling activity of the bone tissue. Despite extensive research into bone stress/remodeling relationships, these mathematical laws have not yet been formulated. Research into this important area of bone physiology will be reviewed and the current state of knowledge assessed. Promising new directions in this research area will be discussed.

Animals↗
PubMed1981

Positive middle ear pressure shown by tympanometry.

The incidence and implications of positive middle ear pressure shown by tympanometry have been sparsely reported in the literature. A series of 13 patients (16 ears) exhibited middle ear pressures that exceeded +49 mm H2O. Clinical, otoscopic, audiologic, and pathologic findings are reviewed. Otalgia or fullness and pharyngitis were the most commonly reported symptoms. Acute middle ear pathologic conditions were otoscopically confirmed in 13 ears. Effusion was present in five of six ears that were selected for myringotomy. The clinical implications of positive middle ear pressure would be particularly important when screening in a nonmedical setting and in the examination of infants. These findings are also important for considering the role of positive middle ear pressure in the pathogenesis of otitis media.

Acoustic Impedance Tests↗
PubMed1981

Fatigue behavior of adult cortical bone: the influence of mean strain and strain range.

Uniaxial fatigue tests were conducted of devitalized cortical bone specimens machined from human femora. Specimens were tested at strain ranges from 0.005 to 0.010 under physiologic loading rates. The influence of compressive, zero, and tensile mean strains on fatigue life and on the stress/strain histories during fatigue were examined. Results showed that bone fatigue is a gradual damage process accompanied by a progressive increase in hysteresis and a loss of bone stiffness. The total number of cycles to fatigue failure was influenced only by the total strain range and was not affected by mean strain. Bone was shown to have extremely poor fatigue resistance. Fully reversed cyclic loading to one half of the yield strain caused fatigue fracture in 1000 cycles. Biological implications. The bone regions which experience the highest strain ranges in vivo generally have a compressive mean strain. The results of this study indicate that mechanical fatigue damage accumulates more rapidly in these "compressive" areas than in "tensile" areas of bone.

Aged↗
PubMed1981

The plated femur: relationships between the changes in bone stresses and bone loss.

Calculations were made of the alterations in the in vivo cyclic bone stresses due to the application of various plates on the canine femoral shaft. The plate configurations analyzed were those used by previous investigators when studying the influence of plating on bone remodeling. The magnitude of the reduction in the loads borne by the bone tissue and the degree of shift in the bone stress neutral axis during the stance phase of gait was influenced by the geometry of the plate, the plate elastic modulus, and the location of plate application. From a correlation of the calculated alterations in bone stresses with the resulting measured changes in bone mass, it appears that bone remodeling is very sensitive to small changes in cyclic bone stresses. Changes in cyclic bone stresses of 1 MPa (less than 1 percent of the ultimate strength) can cause measurable differences in bone remodeling after a period of a few months.

Animals↗
PubMed1981

In vitro evaluation of the loosening characteristics of self-tapped and non-self-tapped cortical bone screws.

The heads of self-tapping and non-self-tapping screws in dog femurs were exposed to a cyclic shearing force of 110 N for 200 loading cycles. This cyclic shear loading created a decrease in pull-out strength for both screw types of approximately 11% (p less than 0.01). No statistically significant difference in pull-out strength was found between screw types either before or after cyclic loading. A linear relationship between pull-out force and cortical thickness was observed for both screw types. These tests corroborated past work which showed equal holding power for the self-tapping and non-self-tapping screw. The progressive loosening of the screws with cyclic shear loading was accompanied by increasing load-displacement hysteresis and screw head migration. Greater hysteresis suggested that the non-self-tapping screw might have loosened more than the self-tapping screw from this applied loading schedule. Bone microcracking around screw threads before and after cyclic loading was observed by scanning electron microscopy. Photomicrographs of one non-self-tapping screw type and two self-tapping screw types showed microcracks at the tip of the outer diameter of the screw thread. More microcracks were observed after application of cyclic shear loading.

Bone Screws↗