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Biomedical subjects

R Vanderby

Publications and source records attributed to R Vanderby.

At least 37 records · Page 2Linked to original sources
PubMed1998

In vitro effects of holmium. YAG laser on caprine stifle retinacular restraints.

This study was designed to evaluate the efficacy of the Holmium:YAG laser for performing lateral release and medial joint capsular tightening intracapsularly and to compare the efficacy of the laser versus a scalpel blade for performing a lateral release by performing arthroscopic surgery on 29 caprine patellofemoral joints. Specimens were divided into six treatment groups and treatments consisted of lateral release alone, medial capsular tightening alone, or both treatments, and the effect of each treatment on patellar tracking was evaluated using video analysis of optical markers. Each treatment caused significantly different magnitudes of medial patellar displacement throughout a 75 degrees range of motion: medial tightening followed by lateral release (1.5 +/- 0.10 mm, mean +/- standard error of the mean); lateral release followed by medial tightening (1.1 +/- 0.11 mm); medial tightening alone (0.73 +/- 0.10 mm); lateral release alone (0.36 +/- 0.09 mm); and sham (-0.15 +/- 0.05 mm). There were no significant differences between performing the lateral release using the laser (1.5 +/- 0.10 mm) versus a scalpel (1.4 +/- 0.11 mm). This study shows that lateral release can be performed as effectively with the laser as with a scalpel and that the laser is an effective tool for performing lateral release and medial joint capsular tightening procedures intracapsularly in this caprine model.

Analysis of Variance↗
PubMed1997

Interstitial fluid flow in tendons or ligaments: a porous medium finite element simulation.

The purpose of this study is to describe interstitial fluid flow in axisymmetric soft connective tissue (ligaments or tendons) when they are loaded in tension. Soft hydrated tissue was modelled as a porous medium (using Darcy's Law), and the finite element method was used to solve the resulting equations governing fluid flow. A commercially available computer program (FiDAP) was used to create an axisymmetric model of a biomechanically tested rat ligament. The unknown variables at element nodes were pressure and velocity of the interstitial fluid (Newtonian and incompressible). The effect of variations in fluid viscosity and permeability of the solid matrix was parametrically explored. A transient loading state mimicking a rat ligament mechanical experiment was used in all simulations. The magnitude and distribution of pressure, stream lines, shear (stress) rate, vorticity and velocity showed regular patterns consistent with extension flow. Parametric changes of permeability and viscosity strongly affected fluid flow behaviour. When the radial permeability was 1000 times less than the axial permeability, shear rate and vorticity increased (approximately 5-fold). These effects (especially shear stress and pressure) suggested a strong interaction with the solid matrix. Computed levels of fluid flow suggested a possible load transduction mechanism for cells in the tissue.

Animals↗
PubMed1997

Thermographic strain analysis of the proximal canine femur.

Thermographic strain analysis (TSA) was used to measure the surface strain distribution of cyclically loaded canine femora. Eleven canine femora were cyclically loaded at 20 Hz in compression at 600 N (+/-200 N). After calibration with measured local strain data, it was possible to quantify the full field patterns measured from the proximal, anterior and medial cortex. The average of each TSA signal normalized by the coincident strain data (0.996) was very near to 1.0 (p = 0.999). The thermographical scans iterate the maximum compressive strains carried by the femur within the region just distal to the femoral neck. Further understanding of the strain distribution in this region is critical in the design of components that attempt to mimic anatomical load transfer after total hip arthroplasty. TSA appears to offer a promising technology as a full field experimental strain analysis method for use with biomechanical issues.

Animals↗
PubMed1997

Ultrasonic wave velocity measurement in small polymeric and cortical bone specimens.

A system was refined for the determination of the bulk ultrasonic wave propagation velocity in small cortical bone specimens. Longitudinal and shear wave propagations were measured using ceramic, piezoelectric 20 and 5 MHz transducers, respectively. Results of the pulse transmission technique were refined via the measurement of the system delay time. The precision and accuracy of the system were quantified using small specimens of polyoxymethylene, polystyrene-butadiene, and high-density polyethylene. These polymeric materials had known acoustic properties, similarity of propagation velocities to cortical bone, and minimal sample inhomogeneity. Dependence of longitudinal and transverse specimen dimensions upon propagation times was quantified. To confirm the consistency of longitudinal wave propagation in small cortical bone specimens (< 1.0 mm), cut-down specimens were prepared from a normal rat femur. Finally, cortical samples were prepared from each of ten normal rat femora, and Young's moduli (Eii), shear moduli (Gij), and Poisson ratios (Vij) were measured. For all specimens (bone, polyoxymethylene, polystyrene-butadiene, and high-density polyethylene), strong linear correlations (R2 > 0.997) were maintained between propagation time and distance throughout the size ranges down to less than 0.4 mm. Results for polyoxymethylene, polystyrene-butadiene, and high-density polyethylene were accurate to within 5 percent of reported literature values. Measurement repeatability (precision) improved with an increase in the wave transmission distance (propagating dimension). No statistically significant effect due to the transverse dimension was detected.

Animals↗
PubMed1997

A structurally based stress-stretch relationship for tendon and ligament.

We propose a mechanical model for tendon or ligament stress-stretch behavior that includes both microstructural and tissue level aspects of the structural hierarchy in its formulation. At the microstructural scale, a constitutive law for collagen fibers is derived based on a strain-energy formulation. The three-dimensional orientation and deformation of the collagen fibrils that aggregate to form fibers are taken into consideration. Fibril orientation is represented by a probability distribution function that is axisymmetric with respect to the fiber. Fiber deformation is assumed to be incompressible and axisymmetric. The matrix is assumed to contribute to stress only through a constant hydrostatic pressure term. At the tissue level, an average stress versus stretch relation is computed by assuming a statistical distribution for fiber straightening during tissue loading. Fiber straightening stretch is assumed to be distributed according to a Weibull probability distribution function. The resulting comprehensive stress-stretch law includes seven parameters, which represent structural and microstructural organization, fibril elasticity, as well as a failure criterion. The failure criterion is stretch based. It is applied at the fibril level for disorganized tissues but can be applied more simply at a fiber level for well-organized tissues with effectively parallel fibrils. The influence of these seven parameters on tissue stress-stretch response is discussed and a simplified form of the model is shown to characterize the nonlinear experimentally determined response of healing medial collateral ligaments. In addition, microstructural fibril organizational data (Frank et al., 1991, 1992) are used to demonstrate how fibril organization affects material stiffness according to the formulation. A simplified form, assuming a linearly elastic fiber stress versus stretch relationship, is shown to be useful for quantifying experimentally determined nonlinear toe-in and failure behavior of tendons and ligaments. We believe this ligament and tendon stress-stretch law can be useful in the elucidation of the complex relationships between collagen structure, fibril elasticity, and mechanical response.

Animals↗
PubMed1997

Stability of proximal femoral grafts in canine hip arthroplasty.

In a canine model, the fixation stability of a prosthesis and proximal bone graft composite were measured relative to the distal femur. One group had the prosthesis graft composite cemented into the distal femur. The second group had the prosthesis graft composite press fit into the distal femur for biologic ingrowth. Displacements of the proximal femoral grafts relative to the host bone in each group were measured after ex vivo (acute with graft) implantation and 4 months after implantation. A third group with no osteotomy (acute intact) simulated perfect graft to host bone union. Relative displacements representing 6 degrees freedom (translation and rotation) were calculated from the displacement values measured by 9 eddy current transducers. Measurements of displacement were used to test the hypothesis that distal press fit fixation equals distal cement fixation at 4 months after implantation. In all cases the measured translations and rotations of the graft to implant construct were small and of a magnitude that should encourage bone ingrowth (< 0.05 mm and < 0.1 degree, respectively). The stability of the press fit group at 4 months was not significantly different from the cemented group in axial and transverse displacement during axial and transverse loading, respectively. There was no difference in stabilities at 4 months between distal press fit and cemented fixation in hip replacements requiring a proximal femoral graft.

Animals↗
PubMed1997

Finite elasticity formulations for evaluation of ligamentous tissue.

The variety of techniques used to measure the cross-sectional area of soft connective tissues during mechanical testing lead to inconsistencies in elastic descriptions. This study compares the numerical differences between finite elasticity (Eularian and Lagrangian formulations) and infinitesimal elasticity when considering stress, strain and elastic modulus of ligamentous tissue. Our results found stress differences (Cauchy versus Kirchhoff) of 22.4%, strain differences (engineering versus Green versus Almansi) as large as 14% and elastic modulus differences (Eularian versus Lagrangian) of 44% from ligament tissue sampled from rats. It is therefore critical to maintain consistent (energy conjugate) elastic formulations for reporting mechanical evaluation of soft hydrated tissue.

Algorithms↗
PubMed1996

Effect of a hypergravity environment on cortical bone elasticity in rats.

There is considerable interest in determining whether hypergravity can be used as a countermeasure for microgravity-induced bone loss. This study was conducted on 20 immature male rats in order to investigate possible elastic adaptations of cortical bone in rapidly growing rats exposed to chronic hypergravity. Ten rats were continuously centrifuged for 14 days at twice gravitational acceleration (2G) on a 12.75 foot radius centrifuge and 10 rats concurrently acted as stationary controls. The effect of hypergravity on the elastic characteristics of cortical bone was quantified via ultrasonic wave propagation. Propagation velocities of longitudinal and shear waves were measured through cubic cortical specimens from the posterior femoral diaphyses. Density was measured with an Archimedes' technique. The orthotropic elastic properties were calculated and used to compare the difference between groups. Results showed an average increase in both the Young's moduli (Eii, + 2.2%) and shear moduli (Gij, + 4.3%) with a statistically significant increase only in G12 (+15.7%, P = 0.046). The ratio of transverse to axial strain (Poisson's ratio, nuij) demonstrated statistically significant changes in nu12, nu21, nu13, and nu31 (P < 0.05). These findings suggest that although slight elastic changes were incurred via a hypergravity environment, the treatment level or duration in this study do not dramatically perturb the normal elastic behavior of cortical bone and that dramatic biomechanical differences noted in previous studies were due more to structural changes than material elasticity changes. Hypergravity applied post facto to a microgravity environment would offer further illucidation of this method as treatment for a degenerative spaceflight experience.

Animals↗
PubMed1996

Fixation of femoral allograft/prosthesis composites after 25%, 50% and 75% resection.

The relative linear and angular displacements of proximal femoral reconstructions were compared within six different replacement techniques during ex vivo axial compression, mediolateral bending, and axial torsion in dogs. Each femur was osteotomized at 25%, 50%, or 75% of its length and the proximal portion subsequently replaced using one of six techniques. The reconstruction techniques included various combinations of proximal and distal fixation methods (graft fixation/distal fixation): (1) an allograft/prosthesis composite (APC) press-fit proximally and cemented distally (press-fit/cement); (2) APC cemented proximally and distally (cement/cement); (3) APC cemented proximally and the host bone/graft interface double plated (cement/plates); (4) APC cemented proximally and secured distally with bicortical screws (cement/screws); (5) APC secured proximally and distally with bicortical screws (screws/screws); (6) Segmental proximal femoral replacement cemented into the distal femur without an allograft (no graft/cement). For axial compression and mediolateral bending, the combined resection lengths revealed no differences in linear and angular displacements, respectively, between reconstruction methods. During axial torsion, the cement/cement technique allowed larger angular displacements than all but the press-fit/cement technique which had larger displacements than the cement/screws, screws/screws, and no graft/cement groups (p < 0.0001). Overall, the measured implant stability was solid and consistent as evidenced by small amounts of relative displacement and small error values.

Animals↗
PubMed1996

Condylar failure of the Lacey Rotating-Hinge total knee.

The Lacey Rotating-Hinge (Wright Medical, Arlington, TN) total knee is a constrained device for reconstruction of knees without collateral ligaments or to replace resected bone. Problems have been described with hinged total knees such as stem fracture, particulate synovitis, and stem loosening. A different mode of failure is described here. Two case histories are provided in which similar fractures occurred in the lateral condyle of Lacey Rotating-Hinge total knees.

Aged↗
PubMed1996

Cortical bone growth and maturational changes in dwarf rats induced by recombinant human growth hormone.

The growth hormone (GH)-deficient dwarf rat was used to investigate recombinant human (rh) GH-induced bone formation and to determine whether rhGH facilitates simultaneous increases in bone formation and bone maturation during rapid growth. Twenty dwarf rats, 37 days of age, were randomly assigned to dwarf plus rhGH (GH; n = 10) and dwarf plus vehicle (n = 10) groups. The GH group received 1.25 mg rhGH/kg body wt two times daily for 14 days. Biochemical, morphological, and X-ray diffraction measurements were performed on the femur middiaphysis. rhGH stimulated new bone growth in the GH group, as demonstrated by significant increases (P < 0.05) in longitudinal bone length (6%), middiaphyseal cross-sectional area (20%), and the amount of newly accreted bone collagen (28%) in the total pool of middiaphyseal bone collagen. Cortical bone density, mean hydroxyapatite crystal size, and the calcium and collagen contents (microgram/mm3) were significantly smaller in the GH group (P < 0.05). Our findings suggest that the processes regulating new collagen accretion, bone collagen maturation, and mean hydroxyapatite crystal size may be independently regulated during rapid growth.

Animals↗
PubMed1995

Comparison of healing of allograft/endoprosthetic composites with three types of gluteus medius attachment.

This study compared three methods of gluteus medius tendon attachment to an allograft/endoprosthetic composite of the proximal 25% of the femur in a canine model. The three methods were bone to bone, tendon to bone, and tendon to tendon attachment. In an in vivo study, 24 dogs were assigned to three groups of eight dogs each, and serial radiography and weight-bearing analyses were performed throughout the study. The dogs were killed at 6 months, and the specimens were tested in tension to failure and were analyzed histologically. In an in vitro study, each repair was done on six limbs, with a contralateral limb serving as a control for each. In these specimens, the bone to bone attachments were significantly stronger (99.1% of the controls) than the tendon to bone attachments (71.8% of the controls) and the tendon to tendon attachments (40.0% of the controls); there were no differences in tensile stiffness among the three types of attachment. By 6 months, the tensile strength of the tendon to tendon attachments increased significantly and that of the tendon to bone attachments decreased significantly. There were no significant differences in tensile strength among the three types of attachment. The tensile stiffness of the bone to bone attachments (91.0% of the controls) was significantly greater than that of the tendon to bone attachments (40.8% of the controls) but not significantly different from that of the tendon to tendon attachments (63.2% of the controls). The bone to bone attachment was associated with increased bone resorption, bone remodeling, and bone porosity, accompanied by thinner allograft cortices, when compared with the other types of attachment. In dogs with a bone to bone attachment, weight-bearing increased more slowly than in dogs with either of the other two attachments. These changes associated with the bone to bone attachment may merely be secondary to healing of the bone to bone attachment to the greater trochanter; therefore, they may only be temporary phenomena or they may be the portents for long-term complications. Longer term studies of at least 1-2 years must be performed before these questions can be answered.

Animals↗
PubMed1995

Comparison of allograft/endoprosthetic composites with a step-cut or transverse osteotomy configuration.

This study was designed to compare the biomechanical and functional characteristics of allograft/endoprosthetic composites of the proximal 25% of the femur repaired with either a transverse or a step-cut osteotomy, using a canine model (10 dogs, five with each type of osteotomy). Serial radiography and weight-bearing studies were performed monthly, and mechanical testing was done 6 months after surgery. The femora were tested in torsion and compared with the contralateral control (insertion of a femoral component but no osteotomy). At 6 months, the composites with a step-cut osteotomy had 36% greater structural stiffness than the composites with a transverse osteotomy (p < 0.005) and 121% greater maximum torque at failure than the controls (p < 0.005), without greater structural stiffness. Evaluation of peak vertical ground reaction forces revealed significantly greater weight-bearing on the experimental limb in dogs with a transverse osteotomy. The results of this relatively short-term study were mixed. Despite the increased structural stiffness of the allograft/endoprosthetic composite with a step-cut osteotomy, the dogs with this type of reconstruction had decreased weight-bearing throughout the course of the study. The step-cut osteotomy may augment the stability of the allograft/endoprosthetic composite, allowing faster healing (as demonstrated by the results of mechanical testing), but in some way, not understood, may cause pain in the reconstructed limb. Longer term studies are needed to answer these questions and to determine whether alteration of the traditional transverse osteotomy has any advantage.

Animals↗
PubMed1995

The effects of elevated compartment pressure on tibial arteriovenous flow and relationship of mechanical and biochemical characteristics of fascia to genesis of chronic anterior compartment syndrome.

PURPOSE: The purpose of this study is to evaluate the effects of increased compartment pressure on anterior tibial arteriovenous flow patterns and to determine whether mechanical and biochemical properties of fascia are responsible for compartment pressure abnormalities. METHODS: Twenty patients with chronic anterior compartment syndrome (CACS) and 20 age-matched control subjects had compartment pressure measurements and analysis of tibial arterial and venous flow before and after fasciectomy. Fascia specimens were evaluated for thickness, stress failure, structural stiffness, and total collagen content and prevalence of collagen cross-linkage. RESULTS: Pressures were significantly elevated in patients with CACS versus control subjects (23.8 mm Hg vs 6 mm Hg). No significant difference in tibial arterial flow could be detected in either group (43 cm/sec mean vs 41.9 cm/sec mean). Venous drainage was severely impaired in patients with CACS but not in control subjects. CACS fascia was thicker and stiffer than control fascia specimens (0.35 mm +/- 0.12 mm, 109 +/- 65 MN/mm; versus 0.22 mm +/- 0.06 mm; 60.3 +/- 22 MN/mm). Fasciectomy normalized postoperative compartment pressures and improved venous drainage. Collagen content per unit mass was similar for both CACS and control fascia specimens, although collagen cross-linking was significantly lower in the CACS fascia than in the controls. CONCLUSIONS: Tibial venous drainage is impaired, but arterial flow is not in patients with CACS. Fascia thickness and structural stiffness can account for increased pressure in CACS compartments. Collagen content and cross-linkage are unrelated to fascia stiffness or thickness. Postoperative improvement in vascular hemodynamics and reduction in compartment pressure is caused by increased capacitance in the compartment after fasciectomy.

Anterior Compartment Syndrome↗
PubMed1995

Alterations in femoral strain, micromotion, cortical geometry, cortical porosity, and bony ingrowth in uncemented collared and collarless prostheses in the dog.

The effects of a collared femoral endoprosthesis in uncemented total hip arthroplasty were evaluated in 12 dogs. This experimental study compared the biomechanic and histologic responses between collared and collarless femoral prostheses 4 months after implantation. Implant stability (micromotion) and cortical surface strain were evaluated immediately and 4 months after implantation in a simulated postoperative condition, whereas bone ingrowth, cortical porosity, and cortical remodeling were assessed after 4 months only. There were no significant differences in implant stability or cortical surface strains when the collared and collarless groups were compared acutely or after 4 months (P > .05). There were also no significant differences in percent fill, bony ingrowth, or cortical geometry after 4 months (P > .05). There was a significant increase in cortical porosity measured from the proximal femur after 4 months for both the collared (P = .0002) and collarless groups (P = .009) and when both groups were compared (collarless, 8.2% and collared, 5.8%; P = .03). The results suggest that a collar may be beneficial in decreasing the cortical remodeling that occurs in the proximal femoral cortex after implantation of an uncemented total hip arthroplasty.

Animals↗
PubMed1995

An evaluation of instrumented tank rowing for objective assessment of rowing performance.

The aim of this study was to evaluate instrumented tank rowing for its ability to measure objectively the individual performance components of power output and rowing skill in a sample of collegiate rowers. The measuring system utilized strain gauges and a potentiometer to measure force on the oar and its angular position at each sampling interval. Power outputs were calculated for 13 collegiate rowers tested individually during a 30-s bout of maximal work. Results from this 'tank test' were compared with power measurements from both Concept II (CII) and Stanford rowing ergometers and from a Wingate test, using similar 30-s bouts of maximal work. Significant differences (P < 0.05) were found between the tank test and all other modes of testing except the Wingate test for average power. These differences can probably be attributed to the different methods of power measurement and to the different skill-dependence associated with the tests. For each subject, peak power and average power per stroke were measured from the rowing tests. The CII and Stanford test data for all subjects were correlated with their tank test data. Similar correlations were made between tank data and the peak and mean power from the Wingate test. The strongest correlation was in peak power measurements with the Wingate test (r = 0.92, P = 0.0001). Instrumented tank rowing provided objective information on individual power output unique from rowing and cycling ergometry. Of the various tests, the tank test appeared to provide better and more complete power data specific to rowing. This method also provided objective data for interpreting various aspects of rowing skill, including oar handling, technical efficiency, consistency, stroke frequency, stroke recovery ratio and stroke length. Instrumented tank rowing has substantial potential as a coaching tool or as a self-training device for improving rowing ability.

Adult↗
PubMed1995

Mechanical evaluation of transosseous wire rope configurations in a large animal external fixator.

By use of wire ropes as the transosseous component, an external skeletal fixator for the repair of long bone fractures in horses and cattle has been designed and tested in axial compression. Theoretical methods were used in the design process to size fixator components; however, our results suggest that conventional methods of analyzing the displacement of the transosseous component may not apply to wire ropes. Large pretensions in the wire ropes are necessary to obtain functional stiffnesses for fracture fixation. Therefore, a method was sought for terminating the ropes so that an appropriate pretension could be introduced into the rope through its interface with the fixator rings. Ropes were terminated by use of 5 methods and were tested in axial tension to failure. These methods included 3 copper sleeve arrangements, welded ends, and drum sockets. The drum sockets (57.6% of rope breaking strength) far exceeded the strengths provided by the copper sleeves (8.5 to 26.6%) and the welded ends (44.3%). Using the drum sockets, 5 rope configurations were assembled to the fixator, using wood blocks to simulate bones with a gap defect. The fixator was loaded in axial compression for each of the rope configurations, and stiffnesses were determined from measured axial displacement and applied load. The 4-ring fixator configuration, with 2 ropes at 60 degrees angular separation/ring, was the stiffest. In a worst case (gap) model, a mean axial compression load of 1,730 N was observed at 2 mm of displacement for a 4-ring fixator configuration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗