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V C Mow

Publications and source records attributed to V C Mow.

At least 73 records · Page 4Linked to original sources
PubMed1994

Compressive stress-relaxation behavior of bovine growth plate may be described by the nonlinear biphasic theory.

The compressive behavior of the bovine distal femoral growth plate was studied in vitro. Strain-rate controlled, compression stress-relaxation experiments were performed on cylindrical bone-growth plate-bone specimens from the interior and periphery of the growth plate. The questions addressed in this study were (a) Can the nonlinear biphasic theory, one with strain-dependent permeability, be used to represent the compressive stress-relaxation behavior of bovine growth plate? (b) How do different assumptions concerning the permeabilities of the chondro-osseous interfaces influence the inferred material properties of the growth plate? and (c) Are there any differences in these properties between the periphery and the interior of the growth plate? Intrinsic biphasic material properties--aggregate modulus (HA), Poisson's ratio (v), and nonlinear strain-dependent permeability coefficients (ko and M)--were calculated from the compression stress-relaxation data with use of a finite element model and a least squares curve-fitting procedure. To verify this constitutive model for the growth plate, an independent set of finite element analyses was performed with use of the determined intrinsic biphasic properties, and comparisons were made between these finite element predictions and two additional sets of experimental data subsequently obtained for the same specimens with use of two slower rates of compression. Excellent agreement was achieved between these finite element predictions and the latter two sets of data. The aggregate modulus was found to be insensitive to the permeability of the chondro-osseous interface. The permeability coefficients were very sensitive to, and the Poisson's ratio was only slightly sensitive to the interface permeability condition. Therefore, the periphery of the growth plate is more compliant and permeable than the interior.

Animals↗
PubMed1994

A stereophotogrammetric method for determining in situ contact areas in diarthrodial joints, and a comparison with other methods.

Determination of contact areas in diarthrodial joints is necessary for understanding the state of stress within the articular cartilage layers and the supporting bony structures. The present study describes the use of a stereophotogrammetry (SPG) system [Huiskes et al., J. Biomechanics 18, 559-570 (1985) and Ateshian et al., J. Biomechanics 24, 761-776 (1991)] for determining contact areas in diarthrodial joints, using a surface proximity concept similar to the one used by Scherrer et al. [ASME J. biomech. Engng 101, 271-278 (1979)]. This method consists of evaluating the proximity of the articular surfaces to determine joint contact areas using precise geometric models of the joint surfaces obtained from the SPG system, and precise kinematic data, also obtained from SPG. In this study, the SPG method for determining contact areas is compared to other commonly used methods such as dye staining, silicone rubber casting and Fuji film contact measurement techniques which have been often used and reported by other investigators. The bovine glenohumeral joint and the bovine lateral tibiofemoral articulation (without the meniscus) were used to represent congruent and incongruent joints, respectively. While all the methods yielded consistent contact patterns for the incongruent tibiofemoral articulations, the results for the congruent bovine glenohumeral joints showed that the SPG and Fuji film methods were in better agreement than those obtained from the dye staining and silicone rubber casting methods. The advantages of the new SPG method are that it can be used for intact joints, and used repeatedly and quickly thus making contact-area movement analyses possible [Soslowsky et al., J. orthop. Res. 10, 524-534 (1992)]. The results of this comparison study show that the SPG technique is a reliable and versatile method for determining contact areas in diarthrodial joints.

Animals↗
PubMed1994

An asymptotic solution for the contact of two biphasic cartilage layers.

This study addresses the hypothesis that interstitial fluid plays a major role in the load support mechanism of articular cartilage. An asymptotic solution is presented for two contacting biphasic cartilage layers under compression. This solution is valid for identical thin (i.e. epsilon = h'/a'0 << 1), frictionless cartilage layers, and for the 'early' time response (i.e. t' << (h')2/HAk) after the application of a step load. An equilibrium asymptotic solution is also presented (i.e.t'-->infinity). Here h' is the thickness, a'0 is a characteristic contact radius, HA is the aggregate modulus and k is the permeability of the cartilage layer. A main conclusion from this analysis is that the fluid phase of cartilage plays a major role in providing load support during the first 100-200 s after contact loading. Further, the largest component of stress in cartilage is the hydrostatic pressure developed in the interstitial fluid. For tissue fluid volume fraction (porosity) in the range 0.6 < or = phi f < or = 0.8, k = O(10(-15) m4/Ns) and HA = O(1 MPa), the peak magnitude of the principal effective (or elastic) stress may be as low as 14% of the peak hydrostatic pressure within the tissue, or the contact stress at the surface. In effect, the interstitial fluid shields the solid matrix from high normal stresses and strains. The asymptotic solution also shows that pressure-sensitive film measurements of intra-articular contact stress do not measure the elastic stress at the surface, but they rather provide a measure of the interstitial fluid pressure. Finally, this analysis provides strong support for the hypothesis that, if sudden loading causes shear failure within the cartilage-bone layer structure, this failure would take place at the cartilage-bone interface, and the plane of failure would be either parallel or perpendicular to this interface.

Adhesiveness↗
PubMed1994

Determination of kinetic changes of aggrecan-hyaluronan interactions in solution from its rheological properties.

The kinetics of interactions between aggregating cartilage proteoglycan (aggrecan) and hyaluronan was examined through their rheological flow behavior using a cone on plate viscometer. The mixing of the two types of molecules was carried out directly on the plate of the viscometer, and aggregation process was monitored through the changes of the sample's steady-shear viscosity and/or dynamic shear modulus as a function of time. The effect of flow conditions on the aggrecan-hyaluronan interaction rates was examined by subjecting samples to steady-shearing motions at specified shear rates, and to oscillatory shear motions of specified frequencies and amplitudes. The characteristics of the kinetics of interaction between aggrecan and hyaluronan molecules depended not only on the flow conditions under which proteoglycan aggregation took place, but also on the concentration of the components in the solution. At high shear rates (> 10 s-1), viscosity of the mixture solution increased monotonically, starting near the viscosity of the aggrecan solution, and reaching the viscosity of the aggregate solution in approximately 35 min. Surprisingly, under slow shearing motions (< 10 s-1), the viscosities of the mixture solutions exceeded those of control aggregate solutions at identical hyaluronan: aggrecan ratios and concentrations. In addition, the aggregation under oscillatory motions took place near physiologic frequency (10 rad s-1) although the rate of aggregation process was much slower than under steady-shearing motion (> 100 min). However, the high-frequency oscillatory shearing (62.8 rad s-1) tended to impede aggregation resulting in a reduction of dynamic modulus over time.(ABSTRACT TRUNCATED AT 250 WORDS)

Aggrecans↗
PubMed1994

The effects of matrix compression on proteoglycan metabolism in articular cartilage explants.

The effects of compressive stress on the rate of proteoglycan synthesis and release were determined in bovine articular cartilage from 4-5-month-old animals. Full depth cartilage explants were compressed in an unconfined configuration at various stresses ranging up to 1.0 MPa. At mechanical equilibrium (after 24 h), no significant changes were detected in the rate of [35S]-sulfate (35SO4) incorporation at the low level of compressive stresses used (less than 0.057 MPa). At an intermediate level of compressive stress (0.057, 0.1, 0.5 MPa), 35SO4 incorporation rates were reduced to approximately 60% of control values. At the highest level compressive stress (1.0 MPa) studied, 35SO4 incorporation rates were further reduced to approximately 20% that of controls. Recovery experiments at intermediate stress levels showed increased rates of 35SO4 incorporation at 24 h after compression. In explants loaded for 24 h at stresses of 0.1 MPa or higher, there was a stress-dose dependent inhibition of proteoglycan release into the media (up to 61% at 1.0 MPa), and proteoglycan release rates did not return to control values following a 24 h recovery period. While cartilage composition and biosynthetic activity were found to vary significantly with depth in control cartilage, the observed suppression (% change) in biosynthetic activity was relatively uniform with depth in both loading and recovery experiments. The study indicates that compression of the tissue to physiological strain magnitudes serves as a signal to modulate chondrocyte biosynthetic and catabolic responses through the depth of cartilage, while prolonged compression at higher strains may be responsible for tissue and cell damage.

Animals↗
PubMed1994

Computer simulation of glenohumeral and patellofemoral subluxation. Estimating pathological articular contact.

Analytic stereophotogrammetry and an interactive computer graphics program were used to obtain first order assessments of joint contact patterns in patellofemoral and glenohumeral joints, simulating normal and abnormal articulations. Precise (90 microns accuracy) computer graphic representations of the humeral head, glenoid, patella, and femoral articular surfaces were obtained from cadaver knees and shoulders. These surface representations were then manipulated into an articulated position, and joint contact areas computed by a proximity criterion. Pathologic states were then simulated, and contact recomputed. Simulated glenohumeral subluxations dramatically reduced contact area, and focused it eccentrically on the glenoid rim. Simulated size mismatch of humeral heads to glenoids reduced contact area, producing a pattern of peripheral contact on the glenoid if the humeral head had a larger radius of curvature, and central contact on the glenoid if the humeral head had a smaller radius of curvature. At 30 degrees knee flexion, the patellofemoral joint demonstrated a broad distribution of contact along the distal aspect of the patella and proximal aspect of the trochlea. Simulated lateral tilt (5 degrees) and translation (5 mm) of the patella resulted in shift of the predominant contact area laterally, along with a drastic decrease in the contact area. These results have implications for prosthetic sizing and biomechanical modeling of the glenohumeral and patellofemoral joints, and in selecting models for more rigorous empiric studies of joint contact. Furthermore, this technique allows a first order assessment of the effects of specific surgical reconstructions on articular mechanics.

Computer Graphics↗
PubMed1994

Anisotropic viscoelastic shear properties of bovine meniscus.

The objectives of this study were to determine the viscoelastic shear properties of bovine menisci and to examine those variations with respect to the structural organization of the tissue. Disc shaped meniscal specimens were subjected to: (1) oscillatory shear deformation over a physiological range of frequencies (1-100 rads per second), and (2) shear deformation in the range of infinitesimal strains (0.005-0.05 rad). The dynamic shear modulus and the transient shear stress relaxation function were determined from the experiments. The dynamic shear modulus was measured at 3 levels of compressive strain (7%, 10%, 13%). Directional variations in shear properties were examined by testing axially, radially, and circumferentially oriented specimens. The experiment showed that meniscal tissue exhibits intrinsic viscoelastic behavior in shear that depends on frequency, shear strain, and compressive strain. Shear anisotropy is evident and is dependent upon compression. At low compressive strains (< or = 10%), the circumferentially oriented specimens were found to be stiffer in shear than the axially and radially oriented specimens. At high compressive strains (> 10%), no statistically significant difference was found between the circumferentially and axially oriented specimens. These results suggest that the anisotropic shear properties of the meniscus are related to the collagen fiber orientation within the meniscus.

Analysis of Variance↗
PubMed1993

In vivo effects of naproxen on composition, proteoglycan metabolism, and matrix metalloproteinase activities in canine articular cartilage.

Naproxen is a nonsteroidal anti-inflammatory drug commonly used in the clinical treatment of joint disease. In this study, its effect in vivo on the biochemical composition, metabolic activities, and metalloproteinase activities of normal canine articular cartilage was analyzed. The articular cartilage from the knee joints of dogs who had been given naproxen for 4 weeks to maintain a serum level of 40-50 micrograms/ml was examined. Control animals were given a placebo. Treatment with naproxen was not found to change the composition (water, collagen, and proteoglycan) of the articular cartilage. The culture studies of cartilage explants indicated that proteoglycan synthesis rates were unaffected by the treatment with naproxen but that proteoglycan release from the tissue was suppressed. Analysis of the cartilage for matrix metalloproteinase activities showed reduced activity of neutral matrix metalloproteinase by 80%, of collagenase by 40%, and of gelatinase by 87%, with no change in activity of acid metalloproteinase or of tissue inhibitor for metalloproteinase. These findings indicate that in vivo treatment with naproxen has the capacity to modulate catabolic activities in articular cartilage.

Animals↗
PubMed1993

Compressive properties of the cartilaginous end-plate of the baboon lumbar spine.

The viscoelastic behavior of the cartilaginous end-plate of the baboon (Papio anubis) was studied in an experiment on compressive creep. Data were analyzed with the biphasic poroviscoelastic constitutive theory to assess the relative contributions of flow-dependent and flow-independent viscoelastic mechanisms to the observed creep behavior. Material coefficients describing the equilibrium compressive behavior (HA) and both flow-independent (c, tau 1, and tau 2) and flow-dependent (k) viscoelastic effects were determined for the end-plate by the curve-fitting of the theoretical solution to the experimental creep data. Biochemical analyses were performed to test for potential relationships between material properties and composition which may give rise to the viscoelastic behavior of the end-plate. The results indicate that the cartilaginous end-plate has a hydraulic permeability of 14.3 x 10(-14) m4/N-s, which is associated with rapid transport and pressurization of the interstitial fluid in response to loading and an increased emphasis on flow-independent viscoelastic effects. Biochemical analyses for water, sulfated glycosaminoglycan content, and hydroxyproline indicate that the end-plate of the baboon is compositionally similar to the cartilaginous end-plate in humans. Interpretation of the mechanical and compositional data suggests that fluid pressurization in the cartilaginous end-plate may be important in the maintenance of a uniform stress distribution across the boundary between vertebral body and intervertebral disc.

Animals↗
PubMed1993

Viscoelastic shear properties of articular cartilage and the effects of glycosidase treatments.

The objectives of this study were to determine the viscoelastic shear properties of articular cartilage and to investigate the effects of the alteration of proteoglycan structure on these shear properties. Glycosidase treatments (chondroitinase ABC and Streptomyces hyaluronidase) were used to alter the proteoglycan structure and content of the tissue. The dynamic viscoelastic shear properties of control and treated tissues were measured and statistically compared. Specifically, cylindrical bovine cartilage specimens were subjected to oscillatory shear deformation of small amplitude (gamma degrees = 0.001 radian) over a physiological range of frequencies (0.01-20 Hz) and at various compressive strains (5, 9, 12, and 16%). The dynamic complex shear modulus was calculated from the measurements. The experimental results show that the solid matrix of normal articular cartilage exhibits intrinsic viscoelastic properties in shear over the range of frequencies tested. These viscoelastic shear properties were found to be dependent on compressive strains. Our data also provide significant insights into the structure-function relationships for articular cartilage. Significant correlations were found between the material properties (the magnitude of dynamic shear modulus, the phase shift angle, and the equilibrium compressive modulus), and the biochemical compositions of the cartilage (collagen, proteoglycan, and water contents). The shear modulus was greatly reduced when the proteoglycans were degraded by either chondroitinase ABC or Streptomyces hyaluronidase. The results suggest that the ability of collagen to resist tension elastically provides the stiffness of the cartilage matrix in shear and its elastic energy storage capability. Proteoglycans enmeshed in the collagen matrix inflate the collagen network and induce a tensile prestress in the collagen fibrils. This interaction of the collagen and proteoglycan within the cartilage matrix provides the complex mechanism that allows the tissue to resist shear deformation.

Animals↗
PubMed1993

The in vivo effects of naproxen on canine experimental osteoarthritic articular cartilage: composition, metalloproteinase activities and metabolism.

A canine experimental model of osteoarthritis (OA), generated by arthroscopic transection of the anterior cruciate ligament (ACL) of the knee, was used to investigate the in vivo effects of the NSAID naproxen on the course of cartilage degeneration. The drug was given at the time of surgery, or from before surgery, and for 16 weeks after surgery. Analysis of the articular cartilage showed the naproxen was able to significantly suppress the decrease in proteoglycan content and metalloproteinase activities. The results indicate that pharmaceutical agents have the potential to modulate the progression of degenerative joint disease.

Animals↗
PubMed1993

Altered structure-function relationships for articular cartilage in human osteoarthritis and an experimental canine model.

A review of the structure-function relationships for normal articular cartilage is provided. This provides the foundation for understanding the roles played by collagen, proteoglycan and water in determining the material properties of the tissue. A summary of biomechanical and compositional changes in human osteoarthritic cartilage is also presented. Finally, the results from our recent interdisciplinary study on an experimental osteoarthritis model is described, and new hypotheses are proposed on the initiating factors responsible for the increase of tissue hydration. At present, it appears that microstructural alterations, rather than compositional changes, of the collagen-proteoglycan solid matrix are responsible for the early increase of hydration and the deterioration of biomechanical properties of articular cartilage.

Animals↗
PubMed1993

Transport of fluid and ions through a porous-permeable charged-hydrated tissue, and streaming potential data on normal bovine articular cartilage.

Using the triphasic mechano-electrochemical theory [Lai et al., J. biomech. Engng 113, 245-258 (1991)], we analyzed the transport of water and ions through a finite-thickness layer of charged, hydrated soft tissue (e.g. articular cartilage) in a one-dimensional steady permeation experiment. For this problem, we obtained numerically the concentrations of the ions, the strain field and the fluid and ion velocities inside when the specimen is subject to an applied mechanical pressure and/or osmotic pressure across the layer. The relationships giving the dependence of streaming potential and permeability on the negative fixed charge density (FCD) of the tissue were derived analytically for the linear case, and calculated for the nonlinear case. Among the results obtained were: (1) at a fluid pressure difference of 0.1 MPa across the specimen layer, there is a 10% flow-induced compaction at the downstream boundary; (2) the flow-induced compaction causes the FCD to increase and the neutral salt concentration to decrease in the downstream direction; (3) while both ions move downstream, relative to the solvent (water), the anions (Cl-) move with the flow whereas cations (Na+) move against the flow. The difference in ion velocities depends on the FCD, and this difference attained a maximum at a physiological FCD of around 0.2 meq ml-1; (4) the apparent permeability decreases nonlinearly with FCD, and the apparent stiffness of the tissue increases with FCD; and (5) the streaming potential is not a monotonic function of the FCD but rather it has a maximum value within the physiological range of FCD for articular cartilage. Finally, experimental data on streaming potential were obtained from bovine femoral cartilage. These data support the triphasic theoretical prediction of non-monotonicity of streaming potential as a function of the FCD.

Animals↗
PubMed1993

Biomechanics of diarthrodial joints: a review of twenty years of progress.

A survey of some of the advances made over the past twenty years in understanding diarthrodial joint biomechanics is presented. Topics covered in this review include: biotribology (i.e., friction, lubrication and wear of diarthrodial joints); contact area determinations; stereophotogrammetric rendering of articular surfaces; deformational field analysis using canonical problems; and finite element formulations for both infinitesimal and finite deformations of biphasic materials and precise anatomic surfaces. Suggestions are made for future research directions as well.

Animals↗
PubMed1992

Tensile properties of the inferior glenohumeral ligament.

The tensile properties of the inferior glenohumeral ligament have been determined in 16 freshly frozen cadaver shoulders. The inferior glenohumeral ligament was divided into three anatomical regions: a superior band, an anterior axillary pouch, and a posterior axillary pouch. This yielded 48 bone-ligament-bone specimens, which were tested to failure in uniaxial tension. The superior band was consistently the thickest region, averaging 2.79 mm. The thickness of the inferior glenohumeral ligament decreased from antero-superiorly to postero-inferiorly. The resting length of all three anatomical regions was not statistically different. Total specimen strain to failure for all bone-ligament-bone specimens averaged 27%. Variations occurred between the three regions, with the anterior pouch specimens failing at a higher strain (34%) than those from the superior band (24%) or the posterior pouch (23%). Strain to failure for the ligament midsubstance (11%) was found to be significantly less than that for the entire specimen (27%). Thus, larger strain must occur near the insertion sites of the inferior glenohumeral ligament. Stress at failure was found to be nearly identical for the three regions of the ligament, averaging 5.5 MPa. These values are lower than those reported for other soft tissues, such as the anterior cruciate ligament and patellar tendon. The anterior pouch was found to be less stiff than the other two regions, perhaps suggesting that it is composed of more highly crimped collagen fibers. Three failure sites were seen for the inferior glenohumeral ligament: the glenoid insertion (40%), the ligament substance (35%), and the humeral insertion (25%). In addition, significant capsular stretching occurred before failure, regardless of the failure mode.

Aged↗
PubMed1992

The microstructural tensile properties and biochemical composition of the bovine distal femoral growth plate.

The tensile properties of distal femoral growth plates from 12-month-old cows were determined on uniformly prepared straight bone-growth plate-bone specimens (7 x 7 mm2 in cross-section) from predetermined anatomical sites on the physis. Each specimen was distracted to failure using a computer-controlled servo-hydraulic testing machine at a strain rate of 0.004 s-1. It was found that the exponential constitutive law, using finite deformation formulation for strain, provides an excellent description of the stress-strain behavior of all the specimens up to the point of failure. The ultimate stress and both tangent moduli (i.e., the toe region tangent modulus and the tangent modulus calculated at 75% of ultimate strain) varied with anatomical site. The anterior region was the strongest, followed by the posterior/lateral. The anterior and posterior/lateral regions were also the stiffest, whereas the posterior/medial and center regions were the weakest and most compliant. The bone-growth plate-bone specimen exhibited a low ultimate strain (13.8% +/- 6%) that did not vary significantly throughout the growth plate. This result suggests that disruption of the physis may occur in vivo even at the lower distractions currently recommended for the clinical chondrodiatasis procedure for leg lengthening. The biochemical composition of the growth plate in the anatomical regions correlated well with the tensile properties. There was a greater collagen content in the regions that were the stiffest and strongest. The gross morphology of the growth plate of the bovine distal femur is also described in this study. There is a regular pattern to the undulations of the physis at several dimensional levels. Histologic findings showed that orientation of the hypertrophic cell columns and transphyseal septa are aligned nearly parallel to the longitudinal axis of the diaphyseal shaft. This column orientation is not affected by the undulation of the primary contour of the physis, which at certain locations may be inclined as much as 60 degrees relative to the diaphyseal axis. The orientation of the hypertrophic cell columns appears to be one of the dominant microstructural features influencing the tensile behavior of the bone-growth plate-bone specimens.

Animals↗
PubMed1992

Quantitation of in situ contact areas at the glenohumeral joint: a biomechanical study.

Glenohumeral arthritis may result from abnormal articular mechanics, and shoulder reconstructive procedures often rely implicitly on the belief that the restoration of normal articular mechanics is required to obtain satisfactory clinical results. Despite this, limited knowledge of normal or pathologic glenohumeral joint articular mechanics and contact is available. This study uses a stereophotogrammetry technique to determine contact areas in normal cadaver glenohumeral joints with intact ligaments and capsule through a large range of motion using simulated forces of the four rotator cuff muscles and three deltoid heads. All shoulders were first elevated to their maximum elevation in the scapular plane at an external rotation (starting rotation = 40 +/- 8 degrees), which allowed each shoulder to attain its maximal elevation in the scapular plane, and then repeated at 20 degrees internal to this rotation. Contact areas consistently increased with increasing elevation until 120 degrees to an average of 5.07 cm2 before decreasing with further increased elevation to an average of 2.59 cm2 at 180 degrees of total arm elevation. At 20 degrees internal to the starting rotation, contact areas reached high values 60 degrees earlier (averaged 4.56 cm2 at 60 degrees of total arm elevation) and then remained fairly constant through 120 degrees before decreasing with further increased elevation to 2.51 cm2 at 180 degrees total arm elevation. With increasing elevation in the external starting rotation, humeral head contact dramatically migrates from an inferior region to a superocentral-posterior region while glenoid contact shifts posteriorly. When the humeral shaft is positioned 20 degrees internal to the starting rotation, humeral head contact shifts from inferocentral-anterior to superocentral-posterior regions. Simultaneously, a similar posterior shift in glenoid contact is observed. Furthermore, whereas only a small portion of the humeral head surface area is in contact in any given position, contact on the glenoid surface is much more uniformly distributed over its entire articulating surface.

Aged↗