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Biomedical subjects

J R Parsons

Publications and source records attributed to J R Parsons.

At least 19 recordsLinked to original sources
PubMed1992

The mechanical properties of the canine lumbar disc and motion segment.

A study was initiated to measure the mechanical properties of the canine lumbar spine disc and motion segment at two specific levels. Compressive stiffness was determined to be 717.8 N/mm at L2-3 and 949.0 N/mm at L5-6. Torsional stiffness was found to be 1.04 Nm/deg at L2-3 and 1.72 Nm/deg at L5-6. These data were then compared to human lumbar spine disc and motion segment properties that have been reported in the literature. After normalizing for size differences, the canine lumbar disc showed a similar axial modulus (14.03 MPa for L2-3 and 16.30 MPa for L5-6) and a significantly higher torsional modulus (30.80 MPa for L2-3 and 26.17 MPa for L5-6) when compared to human values. The relative contributions of ligaments, posterior elements, and intervertebral disc to overall stability of the motion segment was found to be similar in canines and humans. As has been shown in human spine research, the posterior elements including the facet joints were found to be significant structures in providing torsional rigidity of the canine spine.

Animals↗
PubMed1992

Shear stability of an elastomeric disk spacer within an intervertebral joint: a parametric study.

A parametric study was conducted to compare the resistance to shear force provided by three surgical implantation techniques and three endplate designs for use with a polymeric lumbar intervertebral disk spacer. While under an axial load, the implant was pushed out laterally through the surgical window created for implantation. Force at 0.3 mm displacement, slope of the initial portion of the force-displacement graph, and maximum force were measured. The results indicate that implants with pegs, inclined planes, or domes on the surfaces of the disk will add significantly to the shear stability of the implant while maintaining the simplicity of a single part device.

Animals↗
PubMed1991

Enhanced osseointegration of hydroxylapatite implant material.

This study was undertaken to determine whether the addition of calcium sulfate to hydroxylapatite (HA) implant material would improve its working properties without adversely affecting its osseointegration. The clinical and histologic examinations of bone response of three implant materials, hard tissue replacement (HTR), HA, and HA composite (HA plus calcium sulfate), were performed after 2-, 4-, and 6-week implantation in tibia and mandible of rabbits. No sign of extensive chronic inflammatory response was detected. The highest rate of bone ingrowth occurred with the HA composite, followed by HA, with HTR showing the least ingrowth. Bone was deposited directly on the surface of HA and HA composite implant materials. In contrast, HTR particles had a thin layer of fibrous tissue encapsulation with the normal bony investment.

Analysis of Variance↗
PubMed1991

QSARs and PARs for biodegradation of PCBs.

Relationships between the biodegradation rate constants of a number of polychlorinated biphenyls (PCBs) and hydrophobic and electronic structural parameters are compared. There is no simple relationship with octanol-water partition coefficients, indicating that the biodegradation rates of PCBs are probably not determined by their rates of permeation through the bacterial membranes. Biodegradation rate constants correlated much better with both the electronic and hydrophobic properties of the chlorine substituents, which suggests that the reactivity and possibly enzyme binding of PCBs control their biodegradation rates.

Acinetobacter↗
PubMed1991

Effects of environmental exposure on carbon polysulphone composites.

In vivo and in vitro studies were designed to characterize the material degradation associated with implantation of carbon fibre-reinforced polysulphone (C/PS). Composite plates were compression moulded for both studies, and a fibre orientation of 0 degrees with the long axis and a fibre volume fraction of approximately 55% were used. The in vitro experiment involved soaking three groups of four plates each at 4, 12 and 26 wk in 0.9% saline solution at 37 degrees C. The plates were measured for weight gain after each time period and mechanically tested non-destructively in four-point bending to determine modulus. The in vivo experiment involved implanting three groups of eight composite plates (24 total) subcutaneously in the abdomens of 12 rabbits (two implants/animal). Implants were harvested at 4, 12 and 26 wk after implantation and evaluated for changes in weight or modulus of elasticity. In vitro results showed a statistically significant (P less than 0.05 paired t-test) increase in weight for all time periods: 0.41, 1.25 and 0.93% weight gain for the 4, 12 and 26 wk periods respectively. In vivo results were similar to those in vitro: 0.66, 1.06 and 1.15% weight gain for the 4, 12 and 26 wk periods respectively (P less than 0.05 paired t-test). There was no statistically significant difference between the pre- and post-implantation modulus of elasticity for any time period in vivo or in vitro. However, in both studies, on average, the modulus tended to increase with environmental exposure.

Animals↗
PubMed1991

Biomechanical comparison of fixation devices in experimental scaphoid osteotomies.

This study determined the force, bending rigidity, and bending moment at failure of three types of internal fixation systems for the scaphoid bone. A pair of parallel, 0.045-inch Kirschner wires were compared on a paired, bilateral basis with either a Herbert screw or a 3.5 millimeter cannulated screw in repairing a transverse waist osteotomy in cadaver scaphoids. The mean values at failure of the Herbert screw and the cannulated screw versus the paired, parallel Kirschner wires for force (65 N and 77 N versus 23.7 N), rigidity (0.47 Nm2 and 0.54 Nm2 versus 0.16 Nm2) and bending (0.98 Nm and 1.15 Nm versus 0.36 Nm) were approximately three times greater. These differences were statistically significant when compared on a paired basis. This experiment demonstrates that the Herbert screw and cannulated screw are significantly stronger in resisting bending forces than paired, parallel Kirschner wires.

Biomechanical Phenomena↗
PubMed1991

A preliminary study of mechanically stress-induced changes in the extracellular matrix of the canine intervertebral disc.

The intervertebral discs of a young (age, 3 years) and an old (age, 8 years) dog were isolated as motion segments and cyclically stressed in physiologic nondestructive axial compression loads. Chemical analysis of the matrix of the annulus fibrosus revealed a shift in proteoglycan molecular size from larger to smaller moieties for the older dog but not for the younger. These preliminary results may indicate an age-related inability of the disc to tolerate cyclic stress.

Aging↗
PubMed1991

Development of a prosthetic intervertebral disc.

This article is a preliminary report of a 10-year investigation of the development of an intervertebral disc prosthesis. Spinal fusion is a method for the treatment of chronic, disabling low-back pain that does not respond to nonoperative treatments. Spinal fusion, however, has various adverse effects, and the results of spinal fusion are often unpredictable. The goal of this research project was to develop disc prostheses that have mechanical properties very similar to those of natural, normal discs. Two types of disc prosthesis, one with fiber-reinforced polyurethane and the other with multicomponent, non-fiber-reinforced polymers (C-Flex), have been designed and manufactured. The fiber-reinforced disc was made of polyurethane end-plates with A100 hardness, a homogenous nucleus with A40, and 12 layers of multidirectional (0, +45 degrees), fiber-reinforced anulus with A40 polyurethane. The design and modeling of the multicomponent polymers (non-fiber-reinforced) was made of C-Flex endplates with A90 hardness, a nucleus with A35 occupying 35% of the volume, and an anulus with 70A. Mechanical testing of these disc prostheses demonstrated similar mechanical properties to those of natural, normal discs.

Biocompatible Materials↗
PubMed1991

Gunshot wounds to the extremities. Experience of a level I trauma center.

Gunshot wounds to the extremities are more common today, largely because civilian handgun injuries have increased. Such injuries, which are usually caused by low-velocity missiles, should be treated differently from those caused by high-velocity (military) missiles. Bone involvement, including fractures and joint injuries, necessitates orthopaedic management. At the University of Medicine and Dentistry of New Jersey-New Jersey Medical School's (UMDNJ-NJMS) University Hospital, a level I trauma center, 44 gunshot wounds (32 lower-extremity and 12 upper-extremity) with orthopaedic complications were treated between January 1986 and December 1988. The protocol/questionnaire used by the UMDNJ-NJMS is presented here to assist the orthopaedic surgeon in the evaluation and treatment of these problematic injuries.

Adolescent↗
PubMed1991

Comparison of bovine collagen xenografts to autografts in the rabbit.

The use of bovine tendon as a xenograft material in humans is attractive because of its ready availability and favorable mechanical characteristics. Previous research has shown that the fibroblasts and some extracellular proteoglycans and glycoproteins, not the collagen matrix itself, in bovine tendon are primarily responsible for its antigenicity. Various attempts have been made to decrease the antigenicity of these grafts. A chloroform/methanol (CM) extraction procedure has been developed that selectively removes the fibroblasts from bovine tendon without destroying the collagen matrix. The mechanical, immunologic, and local host tissue responses to these grafts were compared to autografts and to untreated and glutaraldehyde-treated bovine tendon xenografts. The humoral immune response to a purified bovine Type I collagen product was also studied. The central two-thirds of a rabbit Achilles tendon were replaced with a reversed autograft or an experimental graft. Histologic examination of one- and two- week specimens showed an acute inflammatory response to all grafts. Untreated grafts stimulated a severe inflammatory response and were almost completely resorbed by two weeks. Glutaraldehyde-treated grafts were encapsulated. Cellular repopulation was minimal and inflammatory response was more persistent than in the autograft and CM groups. Inflammatory response to CM-treated grafts was similar to that of autografts. The CM grafts repopulated rapidly with host cells. The mechanical strength of CM grafts was equal to autograft controls at 12 weeks. The mechanical strength of untreated and glutaraldehyde-treated grafts was significantly lower. Measurement of the humoral immune response to these grafts was conducted in an independent group of animals using an enzyme-linked immunosorbent assay. A significant antibody response to untreated, glutaraldehyde-fixed, and CM-treated grafts was detected at 30 days. Antibody titers to glutaraldehyde-fixed and untreated grafts remained elevated at 60 and 90 days. In the CM group, antibody titers decreased to the level of autograft controls by 90 days. No significant antibody response was detected toward purified bovine Type I collagen.

Achilles Tendon↗
PubMed1990

Investigation of a hydroxyapatite and calcium sulfate composite supplemented with an osteoinductive factor.

In the search for a suitable bone graft substitute, a study was conducted using a material that combined a proven osteoconductive composite, hydroxyapatite-calcium sulfate (HA/CS), with an osteoinductive factor, bovine osteogenic factor (OF). The initial study demonstrated the osteoinductive potential of OF in the rabbit muscle model. Once satisfied that the OF was active, it was added to the HA/CS composite and placed in 8-mm trephine defects in the rabbit cranium. This HA/CS/OF was directly compared to HA/CS augmented with a control protein, rabbit serum albumin (RSA). Animals were sacrificed at 4 and 8 weeks. Results demonstrated increased bone formation with the addition of the OF to the composite with bridging of the defects, in most cases, by 4 weeks. No bridging was seen, at this time period, in the other defects left unfilled or filled with HA/CS/RSA. Osteogenic factor, with the appropriate delivery system, can induce bone formation in the rabbit muscle. It may also increase the rate of bone formation at early time periods in a bony defect site when the delivery system is the osteoconductive composite HA/CS.

Animals↗
PubMed1990

Preliminary characterization of bioresorbable and nonresorbable synthetic fibers for the repair of soft tissue injuries.

Preliminary characterizations of two new synthetic fibers were performed to determine their potentials for use in soft tissue scaffolding devices. A slowly bioresorbing random copolymer of dimethyltrimethylene carbonate (DMTMC) and trimethylene carbonate (TMC) was the first fiber evaluated. The second was a nonresorbable high-strength synthetic fiber of highly oriented polyethylene. Their in vitro mechanical behavior was evaluated by loading fibers in uniaxial tension to determine mechanical properties in dry and wet (saline) environments. The polyethylene fiber had a dry strength of approximately 2.0 GPa, an ultimate strain of 3 to 4%, a tangent modulus of 57 GPa, and was not affected by the saline environment. The bioresorbable fiber had a dry strength of approximately 500 MPa, an ultimate strain of 35%, and tangent modulus of 5.4 GPa. The in vitro resorption of the bioresorbable fibers produced a 15% loss in strength over a 10-week period. In vitro cell-fiber compatibility studies were conducted to assay material biocompatibility and fiber substrate efficacy. Fibroblasts proliferated and migrated on both the polyethylene and bioresorbable fibers at rates similar to those previously found for other compatible fibers, thus demonstrating the new materials to be similar in their in vitro biocompatibility profiles. Morphological assessment with SEM also confirmed that these materials were suitable substrates for cell attachment. A rabbit Achilles tendon repair model using oriented polyethylene or bioresorbable fiber tows was evaluated after 12 and 26 weeks of implantation. The mechanical performances of both types of tendon repairs were similar to those found in previous studies using carbon or PET fibers. The polyethylene fibers elicited a low-grade chronic inflammatory tissue response. The bioresorbable fibers were still intact at 26 weeks and remained relatively inert in the host tissue, eliciting a minimal foreign body response.

Animals↗
PubMed1990

Degradation of halogenated aromatic compounds.

Due to their persistence, haloaromatics are compounds of environmental concern. Aerobically, bacteria degrade these compounds by mono- or dioxygenation of the aromatic ring. The common intermediate of these reactions is (halo)catechol. Halocatechol is cleaved either intradiol (ortho-cleavage) or extradiol (meta-cleavage). In contrast to ortho-cleavage, meta-cleavage of halocatechols yields toxic metabolites. Dehalogenation may occur fortuitously during oxygenation. Specific dehalogenation of aromatic compounds is performed by hydroxylases, in which the halo-substituent is replaced by a hydroxyl group. During reductive dehalogenation, haloaromatic compounds may act as electron-acceptors. Herewith, the halosubstituent is replaced by a hydrogen atom.

Bacteria↗
PubMed1990

Quantitative structure-activity relationships for biodegradation.

Quantitative structure-activity relationships (QSARs) between biodegradation rates of organic compounds and chemical structure parameters are reviewed. Although a number of such relationships have been developed, they in general only apply to restricted ranges of compounds, limiting their value as predictors of biodegradation rates. For many of these classes of chemicals relationships have been reported with different structural descriptors, varying from macroscopic physical properties to molecular structure parameters. More information on the mechanism and rate-determining steps of biodegradation, which can lead to a better-founded choice of descriptors, and more biodegradation rate data are required to further develop QSARs for biodegradation.

Biodegradation, Environmental↗
PubMed1990

The influence of growth hormone on the reversibility of articular cartilage degeneration in rabbits.

Growth hormone has chondrogenic affects on normal as well as on damaged articular cartilage. In this study, the influence of growth hormone is investigated on early degenerative changes in the articular cartilage in 72 New Zealand white rabbits. Cartilage lesions were created in femoral condyles using an immobilization model. Cartilage damage was assessed using biochemical, histologic, and biomechanical criteria. Growth hormone had no influence on prevention of immobilization abnormalities but had a significant affect on healing of established lesions.

Animals↗
PubMed1990

Perioperative blood loss associated with total knee arthroplasty. A comparison of procedures performed with and without cementing.

We reviewed the cases of thirty-four patients (thirty-eight knees) in whom prostheses with an identical design were used for primary total knee arthroplasty, and we compared the perioperative blood loss between the eleven knees in which cement was used and the twenty-seven knees in which cement was not used. The patients who had an uncemented prosthesis had a significantly greater mean blood loss, both intraoperatively (p less than or equal to 0.05) and during each subsequent eight-hour interval on the first postoperative day (p less than or equal to 0.05). The total for the forty-eight-hour postoperative collection also was greater (p less than or equal to 0.01), as was the cumulative loss for the entire study (p less than or equal to 0.01). When patients who had rheumatoid arthritis and osteoarthrosis were considered separately, the results were similar; that is, there was a significantly greater total postoperative blood loss in each of the two groups when cement was not used (p less than or equal to 0.025). A minimum postoperative hemoglobin concentration of ninety-five grams per liter was maintained; a greater percentage of patients (sixteen of twenty-seven) in whom cement was not used needed a transfusion as compared with two of eleven in the group in whom cement was not used (p less than or equal to 0.025), and they also needed more packed red-blood cells (1062 compared with 750 milliliters) (p less than or equal to 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

An evaluation of purified reconstituted type 1 collagen fibers.

Collagen fibers composed of type I collagen molecules were studied for biocompatibility and mechanical properties. These fibers were crosslinked using two different processes: 1) glutaraldehyde, 2) dehydration followed by exposure to cyanamide (DHT/C); the latter method produces only urea as a by-product of the crosslinking process and is postulated to be more biocompatible. An in vitro model using rat tendon fibroblasts growing on individual fibers was used to evaluate outgrowth rates, cell/fiber interactions, and cell morphology. These studies showed an advantage with DHT/C crosslinking, relative to glutaraldehyde crosslinking, in promoting fibroblast growth. In vivo intramuscular implantation in rats showed excellent biocompatibility for both kinds of collagen implants. In addition, aligned ingrowth into the implant from the medial collateral ligament when applied in that location was demonstrated. Mechanical testing demonstrated the higher strength of dry fibers; however, upon hydration, there was a marked decrease in stress to failure. This reduction in strength was due principally to an increase in cross section due to swelling. These collagen fibers appear to be very biocompatible even in the presence of low concentrations of glutaraldehyde. They promote fibrous aligned ingrowth in a setting of ligament healing. Thus, they represent a strong candidate as a scaffold ligament or tendon prosthesis if crosslink density can be increased.

Animals↗