Biomedical subjects

R Vanderby

Publications and source records attributed to R Vanderby.

At least 55 records · Page 3Linked to original sources

PubMed1995

Diaphyseal structural properties of equine long bones.

We evaluated the single-cycle structural properties for axial compression, torsion, and 4-point bending with a central load applied to the caudal or lateral surface of a diaphyseal segment from the normal adult equine humerus, radius, third metacarpal bone, femur, tibia, and third metatarsal bone. Stiffness values were determined from load-deformation curves for each bone and test mode. Compressive stiffness ranged from a low of 2,690 N/mm for the humerus to a high of 5,670 N/mm for the femur. Torsional stiffness ranged from 558 N.m/rad for the third metacarpal bone to 2,080 N.m/rad for the femur. Nondestructive 4-point bending stiffness ranged from 3,540 N.m/rad for the radius to 11,500 N.m/rad for the third metatarsal bone. For the humerus, radius, and tibia, there was no significant difference in stiffness between having the central load applied to the caudal or lateral surface. For the third metacarpal and metatarsal bones, stiffness was significantly (P < 0.05) greater with the central load applied to the lateral surface than the palmar or plantar surface. For the femur, bones were significantly (P < 0.05) stiffer with the central load applied to the caudal surface than the lateral surface. Four-point bending to failure load-deformation curves had a bilinear pattern in some instances, consisting of a linear region at lower bending moments that corresponded to stiffness values from the nondestructive tests and a second linear region at higher bending moments that had greater stiffness values.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1994

The use of generalized cell-survival data in a physiologically based objective function for hyperthermia treatment planning: a sensitivity study with a simple tissue model implanted with an array of ferromagnetic thermoseeds.

PURPOSE: A physiologically based objective function for identifying a combination of ferromagnetic seed temperatures and locations that maximizes the fraction of tumor cells killed in pretreatment planning of local hyperthermia. METHODS AND MATERIALS: An objective-function is developed and coupled to finite element software that solves the bioheat transfer equation. The sensitivity of the objective function is studied in the optimization of a ferromagnetic hyperthermia treatment. The objective function has several salient features including (a) a physiological basis that considers increasing the fraction of cells killed with increasing temperatures above a minimum therapeutic temperature (Tmin,thera), (b) a term to penalize for heating of normal tissues above Tmin,thera, and (c) a scalar weighting factor (gamma) that has treatment implications. Reasonable estimates for gamma are provided and their influence on the objective function is demonstrated. The cell-kill algorithm formulated in the objective function is based empirically upon the behavior of published hyperthermic cell-survival data. The objective function is shown to be independent of normal tissue size and shape when subjected to a known outer-surface, thermal boundary condition. Therefore, fractions of cells killed in tumors of different shapes and sizes can be compared to determine the relative performance of thermoseed arrays to heat different tumors. RESULTS: In simulations with an idealized tissue model perfused by blood at various rates, maxima of the objective function are unique and identify seed spacings and Curie-point temperatures that maximize the fraction of tumor cells killed. In ferromagnetic hyperthermia treatment planning, seed spacing can be based on maximizing the minimum tumor temperature and minimizing the maximum normal tissue temperature. It is shown that this treatment plan is less effective than a plan based on seed spacings that maximize the objective function. CONCLUSIONS: It is shown that under the assumptions of the model and based on a desired therapeutic goal, the objective function identifies a combination of thermoseed temperatures and locations that maximizes the fraction of tumor cells killed.

Cell Survival↗

PubMed1994

Ingrowth reduces implant-to-bone relative displacements in canine acetabular prostheses.

We examined bone-to-implant relative displacement of acetabular prostheses acutely and after ingrowth in a canine model. Uncemented hemispherical acetabular cups with titanium mesh pads comprising approximately 26% of the surface of the cup were inserted in eight adult canine hemipelves ex vivo. The acetabular prostheses were fixed with 13 mm titanium screws. Zero, one, and two-screw configurations were tested, with the order of testing randomly assigned. A load simulating 1,000 cycles of canine gait as applied to the acetabular component, and relative displacements were measured at three locations between implant and bone to determine acute fixation. A repeated measures analysis of variance showed that two screws produced only 42% of the average relative displacement of one screw and 14% that of zero screws. Eight adult mixed-breed dogs then underwent unilateral total hip arthroplasty. All acetabula were biologically fixed with two cancellous screws. The results at 4 months showed significantly less relative displacement between the implant and bone than was measured in ex vivo implantations (p = 0.014). Bone ingrowth filled 20 +/- 6% (mean +/- SD) of the available space. The relative displacements of these implants were small in all cases (12 +/- 13 microns) and did not correlate with the amount of bone ingrowth. These data suggest that acetabular fixation with two screws can lead to bone ingrowth and reduced relative motion of the prosthesis under functional loading.

Acetabulum↗

PubMed1994

Mechanical evaluation of six types of reconstruction following 25, 50, and 75% resection of the proximal femur.

The structural stiffness and the stiffness of the osteotomy site after six types of reconstruction of the proximal femur were compared by testing in axial compression, mediolateral bending, and axial torsion in a canine model. An osteotomy was carried out for 25, 50, or 75% of the length of each femur, and the proximal portion was replaced by one of five allograft/endoprosthetic composites or a segmental replacement. The reconstructions included (a) a composite press-fit proximally and cemented distally, (b) a composite cemented proximally and distally, (c) a composite cemented proximally and fixed with two plates at the allograft-host bone interface, (d) a composite cemented proximally and secured distally with bicortical screws, (e) a composite secured proximally and distally with bicortical screws, and (f) a segmental prosthesis cemented into the distal femur. The results showed that the segmental reconstruction and the reconstruction with double-plate fixation and a cemented endoprosthesis were structurally stiffer and had greater stiffness of the osteotomy site than the other reconstructions. In comparison, reconstructions that involved cement alone or cement and press-fit techniques generally were more compliant than the others, both structurally and at the osteotomy site.

Animals↗

PubMed1994

Ultrasonically determined elasticity and cortical density in canine femora after hip arthroplasty.

Effects of canine hip replacement (with a porous-coated femoral component) on the material properties of surrounding cortical bone were evaluated. The hypotheses were: (1) after four months of implantation, mechanical properties of the cortex would change, and (2) a collared implant would be associated with smaller changes than a collarless design. Unilateral total hip arthroplasty was performed in 15 mixed-breed dogs. Nine received a collared and six received a collarless femoral component. Four months after implantation, longitudinal ultrasonic wave propagation velocities and bone mineral densities (from dual energy X-ray absorptiometry) were measured in harvested femora and used to calculate the axial elastic constitutive coefficients for the cortex surrounding the implants. Results showed no difference in bone elasticity or bone density between collared and collarless designs. Significant velocity decreases from control values (p < 0.0001) were noted in all implanted femora at four months. Bone mineral densities also displayed decreased values after four months of implantation (p < 0.0145). Elastic coefficients were consistently less after four months of implantation when compared to control values (p < 0.0001). This alteration in material properties would affect load transfer into the implanted femur via the increased disparity between implant and bone stiffnesses regardless of the component design. Significant differences in the elastic coefficients between implanted and control femora support hypothesis 1. However, no group differences were found between collared and collarless implantations; thus, the study does not support hypothesis 2.

Alloys↗

PubMed1994

Effect of preconditioning on the viscoelastic response of primate patellar tendon.

Current techniques for anterior cruciate ligament reconstruction with patellar tendon (PT) allow a measurable tension to be applied to the graft at the time of fixation. The viscoelastic nature of the PT, however, ensures that relaxation will cause the graft tension to decrease over time. To better understand this process, a primate model was used to evaluate acute viscoelastic relaxation in the PT. Thirty-five patella-patellar tendon-tibia (P-PT-T) complexes were harvested from normal primate knees (Cynomolgus monkeys), and were divided into five groups for mechanical comparison. Specimens were subjected to two 10-min relaxation tests separated by a 1-30-min unloaded interval. The first test provided baseline relaxation data as well as serving as preconditioning for the second test. Results indicate that preconditioning significantly reduces the tension lost in a graft due to viscoelastic relaxation. The effect of preconditioning is reduced with increasing recovery time (the time between preconditioning and the second relaxation test), but the effect is still significant after 30 min of unloading. No differences were observed in the relaxation behavior of specimens that were cyclicly or isometrically preconditioned, nor were differences observed between irradiated and nonirradiated specimens. These results suggest that preconditioning can reduce acute tension loss in a graft due to viscoelastic relaxation and that simple isometric preconditioning is just as effective as cyclic stretching.

Animals↗

PubMed1994

Effect of interseed spacing, tissue perfusion, thermoseed temperatures and catheters in ferromagnetic hyperthermia: results from simulations using finite element models of thermoseeds and catheters.

Finite element heat-transfer models of ferromagnetic thermoseeds and catheters are developed for simulating ferromagnetic hyperthermia. These models are implemented into a general purpose, finite element computer program to solve the bioheat transfer equation. The seed and catheter models are unique in that they have fewer modeling constraints than other previously developed thermal models. Simulations are conducted with a 4 x 4 array of seeds in a multicompartment tissue model. The heat transfer model predicts that fractions of tumor greater than 43 degrees C are between 8 and 40% lower when seed temperatures depend on power versus models which assume a constant seed temperature. Fractions of tumor greater than 42 degrees C, in simulations using seed and catheter models, are between 3.3 and 25% lower than in simulations with bare seeds. It is demonstrated that an array of seeds with Curie points of 62.6 degrees C heats the tumor very well over nearly all blood perfusion cases studied. In summary, results herein suggest that thermal models simulating ferromagnetic hyperthermia should consider the power-temperature dependence of seeds and include explicit models of catheters.

Catheterization↗

PubMed1994

A multi-degree of freedom system for biomechanical testing.

A system is described that allows axial, torsional, and bending testing of biomechanical specimens. The system uses electric motors under closed loop control in its grips allowing application of pure bending moments. These grips attach to an axial/torsional testing system. Thus, it provides simultaneous closed loop control of all three degrees of freedom (D.O.F), so that under any given test condition either the loads or the displacements for each D.O.F. can be maintained at zero, selected constant values, or simultaneously controlled. This enables the expedient evaluation of the mechanical behavior of biological structures under complex loadings or simple loadings (one D.O.F.) with no artificially induced constraints in the other two D.O.F.'s due to specimen mounting.

Biomechanical Phenomena↗

PubMed1994

A biomechanical analysis of prophylactic fixation for pathological fractures of the distal third of the humerus.

Twenty-four matched pairs of fresh-frozen humeri from human cadavera were divided randomly into four groups, in order to determine the most biomechanically desirable construct for the prophylactic fixation of impending fractures of the distal third of the humerus. Group I comprised intact humeri and matched humeri in which a 50 per cent lateral, semicylindrical cortical defect of the distal third had been created, resulting in a reproducible model of an impending fracture due to a lytic defect involving 50 per cent cortical disruption at the distal end of the humeral medullary canal. In Group II, such a lateral defect was created in both the right and the left, matched humeri. Group III was composed of humeri in which the defect had been fixed prophylactically with a single plate and the contralateral humeri, which had been treated with double-plating. Group IV comprised specimens in which the defect had been fixed with double-plating as well as those fixed with Rush rods. The fixation of each specimen in Groups III and IV was supplemented with bone cement. Each specimen was tested in torsion to failure, and the resulting peak torque, torsional stiffness, and total energy absorbed were analyzed for each group. The Group-I specimens that had a defect had a significantly lower (p < 0.05) peak torque, torsional stiffness, and total energy absorbed than the intact specimens; all of the specimens with a defect failed at the defect, and all of the intact specimens failed proximally. In Group II, there was a high side-to-side association with respect to peak torque, torsional stiffness, and total energy absorbed.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗

PubMed1993

A mechanical comparison of gluteus medius attachment methods in a canine model.

Seven techniques of gluteus medius attachment were compared in vitro in a canine model. Four methods were used for tendon to tendon attachment: (a) two modified Bunnell-Mayer sutures, (b) two Kessler locking loop sutures, (c) two horizontal mattress sutures, and (d) two sutures with a looped suture technique. The two methods of tendon to bone attachment were repair with a 1 cm spiked staple and repair with a spiked washer and screw, and the method of bone to bone attachment involved two figure-eight cerclage wires. The contralateral limb served as a control. Compared with the bone to bone attachment, the four tendon to tendon attachments and the two tendon to bone attachments had significantly less strength (31 and 30% of the ultimate load for bone to bone repair, respectively) and tensile stiffness (24 and 39% of the tensile stiffness for bone to bone attachment, respectively) (p < 0.0001). The control specimens were significantly stronger and stiffer than all specimens (p < 0.05) except those that had bone to bone fixation. There were no significant differences among the four tendon to tendon suture repairs with regard to either strength or stiffness; the values ranged from 28-45% of those of the controls. Among the tendon to bone repairs, fixation with a spiked washer and screw was significantly stronger than that with a spiked staple (p = 0.032), but there was no difference between these two techniques with regard to stiffness.

Analysis of Variance↗

PubMed1993

Biomechanical analysis of mallet finger fracture fixation techniques.

A biomechanical study was conducted to determine the best fixation technique for mallet finger fracture among four commonly used methods. Considerations were technical complications, biomechanical properties, and maintenance of reduction. Techniques tested included Kirshner wire, figure-of-eight wire, tension band wire, and tension band suture. Technical complications were frequent with both the Kirschner wire and tension band wire techniques. Biomechanical testing yielded significantly greater energy absorbed to failure and a trend toward greater peak loads to failure for both the figure-of-eight wire and tension band suture techniques. Irreversible loss of reduction during testing occurred in all of the Kirschner wire-fixed fractures, in 60% of the tension band wire-fixed fractures, and in 50% of the figure-of-eight wire-fixed fractures. No irreversible failure occurred in the tension band suture group.

Aged↗

PubMed1992

Fixation stability of femoral components in a canine hip replacement model.

A canine hip replacement model was used to compare fixation stability in cemented and cementless femoral components. Parameters of comparison were the load-induced positional changes of each prosthesis relative to its proximal femoral cortex, hereafter called relative displacements. Identical femoral components, with the proximal third of their stem porous-coated, were implanted in the right femurs of 10 large, mixed-breed dogs. Five were tightly fit to allow porous ingrowth, and five were cemented into the medullary canal. Four months after implantation, all femurs were harvested. A prosthesis was implanted in the left (normal) femur of each dog ex vivo with fixation identical to the contralateral limb to simulate acute postoperative fixation. Eddy current transducers measured relative displacements under application of static loads, serially applied in the axial, mediolateral, and craniocaudal directions. Thereafter, the femurs were transversely sectioned and morphologically analyzed to correlate bony apposition at the implant surface with relative displacements. We observed no difference in relative displacements between acute and 4-month-cemented groups (e.g., 0.0059 +/- 0.0021 vs. 0.0060 +/- 0.0048 mm, respectively, for 100-N axial loading measured at midstem). With cementless implantation, relative displacements of the acute group were significantly larger (p = 0.007) than those of the 4-month group (e.g., 0.236 +/- 0.257 vs. 0.097 +/- 0.129 mm, respectively, for 100-N axial loading measured at midstem). Cementless components implanted for 4 months were not significantly different than cemented components, but a trend suggested that they were still not as stable as cemented components, particularly for craniocaudal loads. Relative displacements of the 4-month, porous ingrowth group were approximately proportional to the percentage of bony apposition raised to the -1.44 power (r = 0.94).

Animals↗

PubMed1992

Anterior cervical discectomy and fusion. A comparison of techniques in an animal model.

An animal model for three-level anterior cervical discectomy and fusion was established in the goat. Twenty-one goats underwent surgery, with seven goats in each of three experimental groups. In Group I, all seven goats underwent three-level anterior cervical discectomy without fusion. In Group II, each of the seven goats had a three-level discectomy with autogenous bone performed according to the Smith-Robinson technique. In Group III, fresh-frozen allograft bone was used for each of the three-level discectomy and fusion. Each goat was then killed after 12 weeks. Analysis consisted of radiographic review, fluorochrome labeling, biomechanical rigidity and flexion and extension, axial compressive load, and torsion. Histologic analysis was also performed for evidence of fusion and vertebral body histomorphometric analysis. The analysis of results showed that radiographic union was judged to have occurred in 0 of 21 Group I disc spaces, 10 of 21 Group II disc spaces, and 8 of 21 Group III disc spaces. Histologic fusion was judged to have occurred in 0 of 21 Group I goats, 10 of 21 Group II goats, and 0 of 21 Group III goats. The histologic fusion rate was significantly higher in Group II than either Group I or Group III. Biomechanically, the spines that had autogenous bone grafting (Group II) were significantly stiffer in compressive axial load and in extension. Both Group II and Group III were stiffer in flexion than Group I. An evaluation of the peri-endplate vascularity showed that the vascularity measured 10.4% in Group I, 16.7% in Group II, and 8.5% in Group III.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Adaptations of young adult rat cortical bone to 14 days of spaceflight.

To determine whether mature humeral cortical bone would be modified significantly by an acute exposure to weightlessness, adult rats (110 days old) were subjected to 14 days of microgravity on the COSMOS 2044 biosatellite. There were no significant changes in peak force, stiffness, energy to failure, and displacement at failure in the flight rats compared with ground-based controls. Concentrations and contents of hydroxyproline, calcium, and mature stable hydroxylysylpyridinoline and lysylpyridinoline collagen cross-links remained unchanged after spaceflight. Bone lengths, cortical and endosteal areas, and regional thicknesses showed no significant differences between flight animals and ground controls. Our findings suggest that responsiveness of cortical bone to microgravity is less pronounced in adult rats than in previous spaceflight experiments in which young growing animals were used. We hypothesize that 14 days of spaceflight may not be sufficient to impact the biochemical and biomechanical properties of cortical bone in the mature rat skeleton.

Adaptation, Physiological↗

PubMed1992

Cervical stability after foraminotomy. A biomechanical in vitro analysis.

Laminectomy or facetectomy of the cervical spine, or both, may be needed for decompression of the spinal cord or of the nerve-roots. Acute stability of the cervical spine was tested after laminectomy and progressive staged foraminotomies in an in vitro model. Twelve cervical spines from human cadavera were used in the experiment. Biomechanical testing included the application of an axial load, the application of a flexion and extension moment, and the application of a torsional moment. Each specimen was tested intact, after laminectomy of the fifth cervical vertebra, and after progressive foraminotomy of the sixth cervical root. Foraminotomy was performed by resection of 25, 50, 75, and 100 per cent of the facet joint and capsule. Torsional stiffness decreased dramatically when more than 50 per cent of the facet had been resected. Statistically equivalent subsets were the intact specimen, laminectomy, 25 per cent facetectomy, and 50 per cent facetectomy in one subset, and 75 and 100 per cent facetectomy in the least-stiff subset. Flexion-moment testing showed that the posterior strain did not differ among three groups: the intact specimens, those that had been treated with laminectomy, and those that had been treated with a 25 per cent facetectomy. The 50 per cent facetectomy resulted in a 2.5 per cent increase in posterior strain, and the 75 or 100 per cent facetectomy, in a 25 per cent increase in posterior strain compared with the intact specimen. Segmental hypermobility of the cervical spine results if a foraminotomy involves resection of more than 50 per cent of the facet.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Canine intersegmental hip joint forces and moments before and after cemented total hip replacement.

Intersegmental forces and moments (i.e. resultant free body forces and moments computed at the joint centers) were studied in canine hindlimbs before and after cemented total hip replacement (THR). Five large, adult, mixed-breed dogs were selected. Their gait was recorded (while leash-walked) before surgery using high-speed cinematography and a force plate. Cemented total hip replacement was unilaterally performed on each dog. Gait was again recorded at one and four months after surgery. Segmental properties (mass, center of mass, and mass moment of inertia) of the hindlimbs were experimentally determined, and an inverse dynamics approach was used to compute intersegmental forces and moments in the sagittal plane. Significant reductions in intersegmental joint forces and moments were observed in the operated hindlimb one month after surgery, although kinematic gait parameters were unaltered. Decreases of 77.0% for vertical forces, 61.9% for craniocaudal forces, and 66.2% for extension moments were determined. Four months after surgery, the joint forces and moments had returned to their preoperative values. This experiment demonstrates that the dynamics of normal walking can be restored in a canine model by four months after THR. It also shows that kinetic (rather than kinematic) parameters are more descriptive of antalgic gait in the canine.

Animals↗

PubMed1991

A device to measure the cross-sectional area of soft connective tissues.

A device has been designed and fabricated to measure the cross-sectional area of soft connective tissues ex vivo. It consists of two displacement transducers; one sensing tissue thickness and the other sensing width. Outputs are recorded (via an analog to digital interface) using a personal computer. Numerical integration of a thickness versus width plot computes cross-sectional area. This plot also provides a quality check of acquired data. This device has been successfully used in biomechanical studies of rabbit patellar tendons, rat medial collateral ligaments, and dissected specimens of human fascia.

Anthropometry↗

PubMed1991

Thermographic stress analysis in cortical bone.

Under adiabatic (or near adiabatic) conditions a volumetric change in an elastic material will produce a corresponding change in temperature. Based upon this principle, thermographic stress analysis (TSA) measures changes in surface heat flux (which are related to changes in surface temperature) and relates them to a coupled form of strains or stresses. To demonstrate the feasibility of using this technique for biomechanical applications, we thermographically measured heat flux from loaded specimens of cortical bone and correlated the results with strain gage data. Regular parallelepipeds were cut from the cortex of bovine femora and loaded sinusoidally at 20 Hz. At this rate of loading, mechanically induced changes in surface temperature could be sampled (via heat flux) prior to a measureable attenuation of the thermoelastic effect. Correlation coefficients demonstrated a significant linear relationship between TSA and measured and computed mechanical parameters (stress, strain, first strain invariant, and strain energy density). TSA therefore appears to be a promising technology for experimental stress analysis in cortical bone.

Animals↗