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Biomedical subjects

W R Walsh

Publications and source records attributed to W R Walsh.

At least 73 records · Page 4Linked to original sources
PubMed1995

Effects of local injection of corticosteroids on the healing of ligaments. A follow-up report.

One hundred and one skeletally mature New Zealand White rabbits were used to study the long-term effects of a single injection of corticosteroid on the biomechanical, histological, and biochemical properties of ligament-healing. Two steroid doses were studied, as previously described. The injections were made into a fascial pocket immediately after transection of the ligament. The animals were killed forty-two and eighty-four days after the injury. In our previous investigation, in which we examined the early (inflammatory and proliferative) phases of ligament-healing, the specimens that had been injected with a dose of steroids equivalent to that given to humans demonstrated significantly inferior biomechanical properties and histological organization relative to controls that had not received an injection. In the current study, we examined the later (remodeling and maturation) phases of ligament-healing and found that the tensile strength (the ultimate stress) of the specimens that had been injected with the steroids returned to a value that was equal to that of the controls that had not received an injection; however, the peak load of the specimens that had been injected with steroids remained inferior to that of the controls. This was accompanied by a lag in the histological maturation.

Animals↗
PubMed1995

Remodeling of articular step-offs. Is osteoarthrosis dependent on defect size?

One of the major unresolved questions in trauma repair concerns the degree of step-off that can be accepted in a joint surface. In answer to this question, a new rabbit model of femoral step-off was developed. Osteoarthrotic changes in cartilage and bone and the failure of repair responses were seen at 20 weeks in the presence of a 3-mm wide sagittal defect displaced 5 mm from the joint surface and spanning the anteroposterior extent of the medial femoral condyle. This study examined the effects of a similar defect, displaced 2 mm from the joint surface, to determine whether the development of osteoarthrosis is dependent on the size of the step-off. Defects were created in 18 New Zealand white rabbits. In a second group, the medial joint surface was osteotomized, but was not displaced. In contrast to th first study, cartilaginous and bony repair resulted in closure of the surgical defect and restoration of femoral congruity. Histologic and biochemical parameters did not differ significantly between groups. The results indicate that cartilage and bone possess the ability to remodel small articular step-offs and to restore joint congruity. Furthermore, the combined data suggest that the development of osteoarthrosis requires significant articular incongruity.

Analysis of Variance↗
PubMed1994

Mechanism of initial attachment of cells derived from human bone to commonly used prosthetic materials during cell culture.

The suitability of polymeric biomaterials as surfaces for the attachment and growth of cells has often been investigated in cell culture. In this study the contribution that serum fibronectin (Fn) or vitronectin (Vn) make to the attachment and spreading of cells cultured from explanted human bone (bone-derived cells) during the first 90 min of culture was determined for metallic and ceramic surfaces. The requirement for Fn or Vn for attachment and spreading of bone-derived cells onto stainless steel 316 (SS), titanium (Ti) and alumina (Al2O3) and to polyethyleneterephthalate (PET) was directly tested by selective removal of Fn or Vn from the serum prior to addition to the culture medium. Attachment and spreading of bone-derived cells onto SS, Ti and Al2O3 surfaces were reduced by 73-83% when the cells were seeded in medium containing serum from which the Vn had been removed. Cell attachment and spreading on these surfaces when seeded in medium containing Fn-depleted serum (which contained Vn) were not reduced to the same extent as in the medium containing Vn-depleted serum. The bone-derived cells failed to attach to the surfaces to the same extent when seeded in medium containing serum depleted of both Vn and Fn. Our results show that for human bone-derived cells, the attachment and spreading of cells onto SS, Ti and Al2O3 as well as PET during the first 90 min of a cell culture attachment assay are a function of adsorption of serum Vn onto the surface.

Aluminum Oxide↗
PubMed1994

Compressive properties of cortical bone: mineral-organic interfacial bonding.

Bone tissue is an anisotropic non-homogeneous composite material composed of inorganic, bone mineral fibres (hydroxyapatite) embedded in an organic matrix (type I collagen and non-collagenous proteins). Factors contributing to the overall mechanical behaviour include constituent volume fraction, mechanical properties, orientation and interfacial bonding interactions. Interfacial bonding between the mineral and organic constituents is based, in part, on electrostatic interactions between negatively charged organic domains and the positively charged mineral surface. Phosphate and fluoride ions have been demonstrated to alter mineral-organic interactions, thereby influencing the mechanical properties of bone in tension. The present study explores the effects of phosphate and fluoride ions on the compressive properties of cortical bone.

Analysis of Variance↗
PubMed1994

Human osteoblast response to PTFE surfaces.

Recently, expanded polytetrafluoroethylene (ePTFE, Gortex) vascular grafts have been rolled and used for interpositional arthroplasties of the carpus in the wrist. Little data, however, are available on the response of human osteoblasts to ePTFE. In-vitro cell culture is a useful method to determine initial cell-biomaterial interactions. The present study explores the morphological and mitogenic response of human bone cells cultured on vascular grade ePTFE grafts. The present findings suggest that neither the inner nor the outer surface of ePTFE, in its present form, support osteoblast growth. PTFE may be a suitable material to act as a space filler for carpal bone interpositional arthroplasties.

Arthroplasty↗
PubMed1994

Biomechanical and physical properties of lengthened bone in a canine model.

Reports on the mechanical and physical properties of lengthened bone after completion of the lengthening process remain scarce. Varied results of torsional testing of lengthened bone have been reported. Furthermore, torsional testing provides information on the shear properties of the tissue but does not reflect the elastic properties obtained from tensile, compressive, or bending tests. The present study evaluated the mechanical properties of lengthened bone at various time points, using a uniaxial tension test. Physical properties (density and ash weight) were determined as well. Results indicate that the tensile properties of the lengthened bone increase with time after the completion of lengthening, but they remain significantly weaker than controls (50%) even after 12 weeks. Density and ash weight measurements also increased with time, correlating with the increase in the tensile mechanical properties.

Analysis of Variance↗
PubMed1993

Ion concentration effects on bone streaming potentials and zeta potentials.

Electrical potentials are dependent on the properties of the solid and fluid phases of bone. The solid phase in bone is composed of an organic matrix and inorganic bone mineral fibre, while the fluid phase is separated into compartments associated with the vascular channel system and mineralized matrix. Recently, a piezoelectric and electrokinetic response following mechanical deformation was demonstrated in fully hydrated bone. However, alterations in the fluid phase and the effects on streaming potentials where flow through the sample due to pressure on the fluid phase without prior solid matrix mechanical deformation have not been examined. Streaming potentials in high ionic strength solutions reveal a flow-dependent streaming potential in the absence of mechanical deformation not previously observed in stress-generated potentials. Streaming potentials in high ionic strength sodium chloride solutions (0.75 M) of control and deproteinized samples suggest that organic molecules and ions in the electrical double layer may be susceptible to flow-induced alterations which can modify the streaming potentials generated. Alterations in properties of the fluid phase can modify the streaming and zeta potentials and may play a role in the biofeedback response to bone tissue.

Animals↗
PubMed1993

Biomechanical evaluation of interference screw fixation in a bovine patellar bone-tendon-bone autograft complex for anterior cruciate ligament reconstruction.

A bovine model was developed for biomechanical evaluation of anterior cruciate ligament (ACL) reconstruction using patellar bone-tendon-bone (b-t-b) autograft to examine the differences in time zero fixation mechanical properties of different interference screw lengths and diameters. The surgical technique of interference screw fixation of the b-t-b complex performed clinically was reproduced in a controlled animal model. The femur-patellar tendon graft-tibia complex was tested with anterior displacement of the tibia in 30 degrees of knee flexion to allow examination of the femoral and tibial fixation properties simultaneously. The statistical model concurrently explored differences between screw length and diameter while accounting for variations between graft properties. No statistically significant differences were found between the 7- and 9-mm screws with respect to peak load or energy to failure when using a 10-mm triangular graft in a 10-mm tunnel. The 7- and 9-mm screws were superior to the 5.5-mm screws with respect to these same parameters. Based on our results, the 7-mm interference screws can be used with equal confidence as the 9-mm screw, and the 20-mm length can be similarly exchanged for 30-mm length for patellar b-t-b graft fixation.

Animals↗
PubMed1993

An experimental model of femoral condylar defect leading to osteoarthrosis.

The acute treatment of articular step-off injuries is based largely on reduction criteria, because the presence of residual incongruity has been correlated with the development of posttraumatic arthrosis (PTA). However, this association has not been demonstrated on a prospective basis. Using the rabbit femoral condyle, we developed a surgical model of articular condylar defect without sacrificing the axial alignment or inherent stability of the knee joint. Twenty weeks after the creation of 5-mm femoral condylar defects, progressive osteoarthritic changes were confirmed by radiographic, histological, and biochemical parameters. Osteophytes were observed on the medial aspect of operated knee joints in 67% of cases. Femoral and tibial articular cartilage at the site of the condylar defect exhibited fibrillation, hypocellularity, and severe loss of safranin-O staining. Focal areas of cartilage were denuded or replaced by pannus. In no case was femoral congruity restored by cartilage repair. Statistically significant decreases in proteoglycan content were demonstrated for cartilage sampled from the weight-bearing region of the condylar defect and from the tibial surface directly beneath it. These changes resemble those arising from previously reported models of osteoarthrosis. We present the model as a valid tool for the study of articular condylar defect and its role in the development of PTA.

Animals↗
PubMed1993

The role of ions and mineral-organic interfacial bonding on the compressive properties of cortical bone.

Bone tissue is a composite material composed of an inorganic stiff mineral phase embedded in a compliant organic matrix. Similar to other composites, the mechanical properties of bone depend upon the properties, volume fraction, and orientation of its constituents as well as the bonding interactions. Interfacial bonding between the mineral and organic constituents are based, in part, on electrostatic interactions between negatively charged organic domains and positively charged mineral surface. Phosphate and fluoride ions can alter mineral-organic interfacial causing a permutation in the mechanical properties. Partial debonding between the mineral and organic constituents of bone may play an important role in the mechanical properties of aged and diseased bone. The present study examines the effects of phosphate and fluoride ion treatment on the compression properties of cortical bone and the reversibility of the effect.

Animals↗
PubMed1991

Electrokinetic behavior of intact wet bone: compartmental model.

Streaming potential experiments were performed on chemically-treated intact wet bone plugs equilibrated in potential-determining ion buffers. Comparison of calculated zeta (zeta) potentials from intact wet bone streaming potentials and bone particle electrophoresis indicates different values. Intact streaming potential experiments, where fluid is forced through the samples, represents flow, primarily through the vascular channel system, and contribution of the organically-lined channels to the electrokinetic zeta potential. Bone particle electrophoresis represents mainly the electrokinetic contribution of exposed mineralized matrix. The organic linings present in the vascular channel system limit potential-determining ions' access to the mineralized matrix. These linings may have an important role in mineral homeostasis and control of ion fluxes between bone compartments.

Animals↗
PubMed1990

Streaming potential of intact wet bone.

The conversion of mechanical loads to bioelectrical signals in bone have been suggested to control repair and remodeling. These signals in wet bone are attributed to the electrokinetic behavior where mechanical forces cause electrical signals due to motion of an ion carrying extracellular fluid in the bone matrix (streaming potentials). Streaming potential experiments were performed on control and chemically treated intact wet bone plugs in aphosphate and phosphate buffers to examine the contribution of bone constituents to the electrokinetic behavior of bone tissue. Data indicate that the organic constituents of bone dominate streaming potentials. Slopes of streaming potential vs pressure are related to the electrokinetic (zeta) potential. The slopes should be analyzed in the low pressure region where data is mainly linear. Comparisons of estimated zeta potentials from streaming potentials with existing data obtained by particle electrophoresis showed similar trends.

Animals↗
PubMed1988

Trimetrexate: predictors of severe or life-threatening toxic effects.

In four phase II trials of trimetrexate given iv daily for 5 days, we noted marked variability among patients in the development of severe or life-threatening toxic effects. In an effort to define which of 15 patient characteristics were associated with toxic effects of this degree, we have carried out single-factor and multifactor analyses on toxic effects during the first cycle of therapy in 68 patients. The final logistic regression model identified both low pretreatment serum protein levels and metastatic liver disease as significant correlates of severe toxic effects (P = .02 and P = .0005, respectively). While drug dose was an important element of the best logistic model, its statistical significance was only borderline. Trimetrexate is extensively protein bound and is cleared primarily by hepatic metabolism, so it is not unreasonable to believe that alteration in protein binding of the drug or in metabolic capacity of the liver could produce enhanced toxic effects. Although the validity of these predictors should be confirmed, it seems prudent to recommend lower starting doses of trimetrexate for patients with metastatic liver disease and/or low protein levels and dose escalation if toxic effects allow it.

Antineoplastic Agents↗
PubMedDate not supplied

The effect of in vitro fluoride ion treatment on the ultrasonic properties of cortical bone.

The mechanical properties of composites are influenced, in part, by the volume fraction, orientation, constituent mechanical properties, and interfacial bonding. Cortical bone tissue represents a short-fibered biological composite where the hydroxyapatite phase is embedded in an organic matrix composed of type I collagen and other noncollagenous proteins. Destructive mechanical testing has revealed that fluoride ion treatment significantly lowers the Z-axis tensile and compressive properties of cortical bone through a constituent interfacial debonding mechanism. The present ultrasonic data indicates that fluoride ion treatment significantly alters the longitudinal velocity in the Z-axis as well as the circumferential and radial axes of cortical bone. This suggests that the distribution of constituents and interfacial bonding amongst them may contribute to the anisotropic nature of bone tissue.

Animals↗
PubMedDate not supplied

Type 2 fractures of the distal clavicle: a new surgical technique.

Neer type 2 fractures of the distal clavicle have a high rate of nonunion and delayed union. In this series nine cases of coracoclavicular ligament reconstruction with Dacron graft material led to union at the fracture site. All patients had no symptoms and returned to full activity. This technique allows for stable fixation with early mobilization and return to work and sports.

Activities of Daily Living↗
PubMedDate not supplied

Laminated tears of the human rotator cuff: a histologic and immunochemical study.

Laminated tears of the rotator cuff are often lined by a cellular layer that has an appearance suggestive of synovium. This study demonstrates, by histologic and immunohistochemical means, that the lining cells are synovial. It remains unclear whether these cells arise by synovial extension from the joint or bursa, or by metaplasia in the presence of synovial fluid, and this has implications for surgical repair of laminated cuff defects. We suggest that these defects be curetted, to remove at least some of this synovial lining, before suture repair.

Adult↗
PubMedDate not supplied

A novel, resorbable suture anchor: pullout strength from the human cadaver greater tuberosity.

The pullout strength of a collagen bone anchor that creates interference fixation as the result of radial swelling on hydration was compared with a Mitek rotator cuff anchor after insertion into the greater tuberosity of human cadaver humeri. Bones were fully hydrated at 37 degrees C. Stiffness, peak load, and the mode of failure were recorded. Real and apparent bone densities were measured. Peak load for the collagen anchor at 15 minutes (121.0N +/- 81.3N) was greater than at 2 minutes (60.5N +/- 38.5N) after insertion (P <.05). At between 5 and 60 minutes after insertion, peak loads for the Mitek and the collagen anchors did not differ. After 30 minutes from insertion, the mode of failure of the collagen anchor changed from pullout with minor body damage to pullout with major body damage. Peak load at pullout correlated with bone density for the Mitek (P <.05, r = 0.516) but for the collagen bone anchor appeared unaffected by bone density.

Aged↗