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Biomedical subjects

R Vanderby

Publications and source records attributed to R Vanderby.

At least 73 records · Page 4Linked to original sources
PubMed1990

Acute modification of biomechanical properties of the bone-ligament insertion to rat limb unweighting.

We investigated the acute adaptation of the rat femur-medial collateral ligament-tibia (FMT) complex to 7 days of limb unweighting by means of a hind-limb suspension protocol. Male, young adult, Harlan Sprague-Dawley rats were randomly assigned to either control or suspended groups. Rats deprived of hind limb-to-ground contact forces had a 42% decrease in soleus muscle mass compared with the control group. Medial collateral ligament (MCL) length and cross-sectional area were measured, and each FMT complex was tension tested to failure. All failed at their tibia-MCL insertion. The ultimate load in the FMT and the peak Kirchhoff stress in the MCL (occurring immediately before insertion site failure) were significantly reduced in the suspended group. The suspended MCLs were 9.7% larger in area and 5.7% shorter in length than the controls under the same preload (0.25 N). We found no significant differences between the control and suspended MCLs in Green strain, stretch, or deformation immediately before insertion site failure, nor did we find a significant difference in the MCL tangent modulus. This study indicates that even acute periods of limb unweighting can structurally compromise bone-ligament insertions. Further, this study implies that the adaptations responsible for this structural compromise must involve acute changes in the intrinsic zone (or zones) of the bone-ligament insertion.

Animals↗
PubMed1990

Biomechanical and histological evaluation of the Herbert screw.

The Herbert screw has been demonstrated to have widespread clinical applicability. A biomechanical and histological evaluation of the Herbert screw was conducted to better define its applications. When subjected to pull-out, toggle, and compression testing, in a cancellous bone calf model, it was demonstrated to be biomechanically inferior to the 4.0 mm ASIF cancellous screw. The use of two Herbert screws minimized but did not eliminate this difference. Articular cartilage healing in a rabbit model was consistently demonstrated if the Herbert screw was buried deep to the osteochondral junction. However, toluidine blue histochemical staining showed that the hyaline-like repair cartilage differed qualitatively from normal cartilage. Utilization of the Herbert screw should include an understanding of the limitations of its fixation potential and a recognition of the repair response after intraarticular applications.

Animals↗
PubMed1990

Femoral strain adaptation after total hip replacement: a comparison of cemented and porous ingrowth components in canines.

The purpose of this study was to investigate if experimental strain analysis is predictive of femoral adaptation after total hip replacement (THR). Ten large adult dogs underwent unilateral THR with identical implants. Five implants were press fit for porous ingrowth fixation, and five were cemented. Four months after surgery femora were harvested. Strain gauge rosettes were applied to the femora at eight proximal locations. Femora were compressively loaded on the head of the femur or femoral component. Strain data represented three conditions: preoperative, acutely postoperative, and four-month postoperative. The unoperated femur of each dog was used to simulate preoperative and acutely postoperative behavior of the contralateral implanted femur. Strains from each condition were compared. Transverse femoral sections were obtained through the levels of the strain gauges. Fine detailed radiographs were used to quantify morphological changes. Results showed cemented and uncemented implantations produce similar trends but different amounts of bone adaptation. Adaptations were generally consistent in direction with strain perturbations caused by implantation, but the extent of adaptation did not strongly correlate with the magnitude of perturbations. Also, there was no consistent trend towards normalization of altered strains. Results suggest that strain perturbations after THR may be mechanical triggers for morphological changes, but caution is required when predicting the extent of these changes or the autoregulatory role of strain.

Adaptation, Physiological↗
PubMed1989

Significance of acute posttraumatic bony encroachment of the neural canal.

Neurologic status (NS) of 80 consecutive patients with acute, traumatic thoracic, thoracolumbar, or lumbar fractures was correlated with the amount of neural canal impingement (NCI) demonstrated by computerized axial tomography (CT). Average NCI was significantly higher in the 34 patients with neurologic deficits, but the range of NCI was similar to that observed in the 46 patients with no deficits. Burst fractures and fractures in the lumbar spine had the highest average NCI but the lowest percentage of patients with neurologic deficits. The immediate, posttraumatic NS of the 80 patients studied did not directly correlate with the percent of NCI demonstrated on their CT scans.

Adult↗
PubMed1987

Elastic moduli, yield stress, and ultimate stress of cancellous bone in the canine proximal femur.

Elastic moduli, yield stress and ultimate compressive stress were determined for cancellous bone from the femoral head and neck regions of the canine femur. Unconfined compression tests were performed on 5 mm cubic samples which were cut from two femurs. Elastic moduli were measured in three orthogonal directions, and the yield stress and ultimate stress were measured along the proximal-distal axis. The results from this investigation support previous assumptions that the mechanical behavior of canine cancellous bone is qualitatively similar to human cancellous bone. The canine cancellous bone was observed to be anisotropic in elastic modulus. For two thirds of the cubic specimens tested, the elastic modulus was largest in the load-bearing, proximal-distal direction. A linear relationship between yield stress and elastic modulus was observed for canine bone, as is typical of human bone. A similar linear relationship between ultimate stress and elastic modulus was observed. Thus, for canine bone as well as for human bone, failure appears to be governed by a strain level which is position independent. The yield strain of 0.0259 and ultimate strain of 0.0288 for canine bone were both less than the yield strain of 0.0395 reported for human bone.

Animals↗
PubMed1986

A biomechanical analog of curve progression and orthotic stabilization in idiopathic scoliosis.

A biomechanical analog of curve progression and orthotic stabilization in idiopathic scoliosis has been developed using the classical theory of curved beam-columns. The interaction of the spinal musculature and other supporting structures is incorporated in the model using an equivalent flexural rigidity. The stability of a given scoliotic curve relative to a normal spine is described in terms of the so-called critical load ratio (Pc/Pe). This dimensionless quantity appears in the exact solution of the governing differential equation and boundary conditions. It is defined as the ratio of the load bearing capacity of a scoliotic spine (Pc) to that of a normal spine where the load bearing capacity of a normal spine is defined as Euler's buckling load (Pe). The computation of Pc/Pe is based upon a maximum allowable moment criterion. This model is used to study the effect of the degree of initial curvature and curve pattern in the frontal plane on the stability of untreated idiopathic scoliosis. Although restricted to two-dimensions, the model appears to demonstrate the synergistic effects of end support, transverse loading, and curve correction on improvement in relative stability of an orthotically supported scoliotic curve. The results of this study are in qualitative agreement with clinical findings that are based on long-term studies of natural history of idiopathic scoliosis and of patients undergoing orthotic management for scoliosis.

Biomechanical Phenomena↗
PubMed1986

A method for the identification of in-vivo segmental stiffness properties of the spine.

A numerical algorithm is used to estimate in-vivo segmental stiffness properties of individual spine segments based upon existing load-displacement data. A static nonlinear finite element model stimulates a pathological spine and corrective instrumentation system. A systematic procedure for establishing the model's stiffness parameters is described, in the form of a nonlinear constrained optimal design problem. The numerical method is demonstrated using as an example a case of adolescent idiopathic scoliosis requiring corrective surgery.

Adolescent↗
PubMed1983

Load-bearing characteristics of lumbar facets in normal and surgically altered spinal segments.

An in-vitro experimental study was carried out to measure the induced loading on human lumbar facets due to varying amounts of compressive axial load. Testing was done on L2-L3 and L4-L5 spinal motion segments obtained from cadavers at autopsy. The compressive loading was applied to the spinal specimens in first a neutral position and then in an extended position. The motion segments were tested in a normal state and after facetectomy of the left facet. Contact pressures were quantified using pressure-sensitive film. This film was inserted between the articulating surfaces of the two facet joints prior to placing axial loads on the motion segments. In addition to recording pressure, the film was also used to quantify contact area. This provided sufficient information to compute the total facet loadings for all cases studied. Results of this study show how facet loads, peak pressures and contact areas change with respect to the various loads, positions and states studied. In particular this study shows that the absolute facet loads remain relatively constant with increasing segmental compressive loads such that the facet load expressed as a percent of load applied to the segment decreases with increasing axial loads. It also shows that the contact area moves cranially at L2-L3 and caudally at L4-L5 with increasing loads in extension. Furthermore, this study indicates that the load on the remaining facet is reduced substantially after a facetectomy although peak pressure increases. Finally, this study demonstrates the substantial difference in facet loadings between L2-L3 segments and L4-L5 segments.

Biomechanical Phenomena↗
PubMed1980

Force systems from orthodontic appliances: an analytical and experimental comparison.

Experimental data is compared with the simulated displacements from a computer program for the clinical activations of two separate orthodontic appliances undergoing a total of four separate loading conditions. Good agreement is shown over the entire range of activation. Suggestions for future strengthening of both the analytical and the experimental methods are given. An interactive design graphics system is shown to be imminently available to the research orthodontist.

Biomechanical Phenomena↗
PubMed1977

Reduction in the modulus of elasticity in orthodontic wires.

The modulus of elasticity of stainless steel orthodontic wires was found to be 20% below the normally assumed range of 19.3 to 20.0 x 10(4) MPa (28.0 to 29.0 x 10(6) psi). Use of the latter value can result in significant computational errors in orthodontic applicance mechanics. The lower modulus was attributed to severe cold drawing.

Crystallography↗
PubMedDate not supplied

Mechanical and biochemical analyses of tibial compartment fascia in chronic compartment syndrome.

Increases in compartment pressure associated with chronic compartment syndrome (CCS) may be due to changes in the mechanical properties and/or thickness of fascia (4,22). To explore this possibility, we compared the mechanical and biochemical characteristics (stiffness, thickness, time-dependent response, collagen content, and collagen crosslinking) of fascia from patients with symptomatic anterior compartment syndrome to fascia from adjacent collateral compartments. We tested 43 specimens harvested from 20 individuals during surgical fasciectomy. Properties of normal (lateral)-compartment (NC) and pathological (anterior)-compartment (PC) fascia were mechanically tested in the axial and transverse directions forming four groups. An external control group (EX) of six specimens of anterior and lateral-compartment fascia harvested from amputated legs was also included in the study. PC fascia was found to be thicker and structurally stiffer (elastic modulus times thickness) in the axial direction than was NC fascia (p < or = 0.05). No significant differences were found between NC and PC time-dependent response, although significant differences between percent relaxation in the pooled axial and transverse direction specimens were observed. No differences were found in the collagen content, as measured by hydroxyproline (Hyp) concentration, between NC and PC fascia. PC fascia was found to have less collagen crosslinking by hydroxylyslpyridinoline (HP) concentration. In conclusion, although this study does not elucidate etiological factors in CCS, the changes found in PC fascia suggest that fascial mechanical properties contribute to the pathology.

Adolescent↗
PubMedDate not supplied

Effect of a growth hormone treatment on bone orthotropic elasticity in dwarf rats.

A refinement of the current ultrasonic elasticity technique was used to measure the orthotropic elastic properties of rat cortical bone as well as to quantify changes in elastic properties, density, and porosity of the dwarf rat cortex after a treatment with recombinant human growth hormone (rhGH). The ultrasonic elasticity technique was refined via optimized signal management of high-frequency wave propagation through cubic cortical specimens. Twenty dwarf rats (37 days old) were randomly assigned to two groups (10 rats each). The dwarf rat model (5-10% of normal GH) was given subcutaneous injections of either rhGH or saline over a 14-day treatment period. Density was measured using Archimedes technique. Porosity and other microstructural characteristics were also explored via scanning electron microscopy and image analysis. Statistical tests verified significant decreases in cortical orthotropic Young's (-26.7%) and shear (-16.7%) moduli and density (-2.42%) concomitant with an increase in porosity (+125%) after rhGH treatments to the dwarf model (p < 0.05). A change in material symmetry from orthotropy toward planar isotropy within the radial-circumferential plane after GH treatments was also noted. These results demonstrate some alteration in bone properties at this time interval. Structural implications of these changes throughout physiological loading regimens should be explored.

Animals↗
PubMedDate not supplied

A fiber matrix model for interstitial fluid flow and permeability in ligaments and tendons.

Collagen fibrils in ligaments and tendons are highly organized into parallel arrays which influence interstitial fluid transport. Finite element (FE) models were developed analogous to the fibrillar arrays in ligaments and tendons to investigate interstitial fluid flow and tissue permeability as a function of interfibrillar spacing and fluid properties. Collagen fibrils were assumed to be a periodic square array of impermeable cylinders. A two-dimensional FE model was used to study transverse fluid flow and a three-dimensional model was used to study flow parallel to the collagen fibrils. Parametric FE analysis provided data to formulate empirical expressions for permeability (kappa) as a function of porosity (phi). Results show that longitudinal permeability (kappa = 1.1.10(-15)phi 2.5[1 - phi]-0.333) can be up to 50 times higher than transverse permeability (kappa = 1.2.10(-15)phi 0.5[phi - phi min]2.5) in a compact array. Maximum fluid shear stresses occur at the narrowest zones of adjacent fibrils (1.21 Pa or 12.1 dyn/cm2 at 10 microns/s of average transverse influx). If interstitial fluid is highly non-Newtonian, the permeability should be considered as flow (shear)-dependent. The computational results suggest that tissue permeability in ligaments and tendons is highly anisotropic, porosity-dependent, and can be estimated by analytic expressions.

Extracellular Space↗
PubMedDate not supplied

The mechanical consequence of failure of ossified union in attempted posterior spinal fusion. A canine model.

The mechanical behavior of pseudarthrosis in posterior spinal fusion was investigated. A canine model was developed in which an incompletely ossified posterior fusion mass was consistently produced. The spines were excised, and the motion segments were mechanically tested using a specially developed loading apparatus. Tests were performed to evaluate stiffness of the segments to loading with compression, torsion, and anterioposterior and lateral bending shear stiffness. Changes in other modes of loading were less consistent. The motion characteristics of the pseudarthrosis could not be predicted from the extent of the osseous defect noted on roentgenograms. These findings correlate clinically with the progression of curvature seen with pseudarthrosis in scoliosis surgery and the unpredictable results of pseudarthrosis in posterior fusion performed in treatment of degenerative disc disease.

Animals↗
PubMedDate not supplied

Progression of unsupported curves in adolescent idiopathic scoliosis.

Stability of three types of double scoliotic curves of 10-40 degrees was analyzed using a biomechanical model: double primary (Type I), primary thoracic with compensatory lumbar (Type II), and primary lumbar with compensatory thoracic (Type III). The load-carrying capacity of each curve was analyzed as a function of magnitude of the curve, its location and flexibility. Curve magnitude was found to be the most influential parameter governing the stability of a scoliotic curve up to 30 degrees. Results suggest that in evaluating curves of comparable magnitudes, Type I and II curves are more likely to progress and, therefore, should be braced at an earlier stage than Type III curves.

Adolescent↗
PubMedDate not supplied

Ex vivo biomechanics of Kirschner-Ehmer external skeletal fixation applied to canine tibiae.

The purpose of this study was to determine the respective contribution of each of the following parameters to the compressive, bending, and torsional rigidity of the Kirschner-Ehmer (KE) external fixation splint as applied to canine tibiae with an osteotomy gap: bilateral versus unilateral splints; increasing the number of fixation pins; altering the diameter of fixation pins and side bars; decreasing side bar distances from the bone; increasing pin separation distances in each pin group; decreasing distances between pin groups; altering pin clamp orientation; and altering side bar conformation. Bilateral splints were 100% (mean) stiffer than unilateral splints, with stiffness enhanced to the greatest extent in mediolateral bending and torsion. Increasing pin numbers stiffened both bilateral (mean, 41%; 8 versus 4) and unilateral splints (mean, 14%; 8 versus 4). Medium KE splints were 85% (mean) stiffer than small KE splints. Decreasing side bar distances to the bone from 1.5 cm to 1.0 cm to 0.5 cm increased stiffness of both bilateral and unilateral splints by a mean of 13% to 35%. Widening pin spacing from 1.67 cm to 2.5 cm increased stiffness in craniocaudal bending only (56% increase, bilateral splints; 73% increase, unilateral splints). Decreasing the distance between pin groups from 5.84 cm to 2.5 cm increased stiffness in torsion between 23% (unilateral splints) and 45% (bilateral splints) and decreased stiffness of unilateral splints by 29% in craniocaudal bending. Altering pin clamp configuration so that the bolts of the clamp were inside the side bar rather than outside the side bar increased stiffness in axial compression only (73% increase, bilateral splints; 54% increase, unilateral splints). Conforming the lateral side bar to the tibiae increased only axial compressive stiffness by 77% but was no different than placing the clamps inside the side bars of an unconformed bilateral splint. These results quantify the relative importance of specific parameters affecting KE splint rigidity as applied to unstable fractures in the dog.

Animals↗