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Biomedical subjects

B Sim

Publications and source records attributed to B Sim.

6 recordsLinked to original sources
PubMed2001

In vitro genesis of subaxial cervical unilateral facet dislocations through sequential soft tissue ablation.

STUDY DESIGN: In vitro anatomic study investigating the degree of soft tissue disruption required to produce a subaxial cervical unilateral facet dislocation. OBJECTIVES: To develop an understanding of the relative contributions to stability of the subaxial cervical soft tissues and to define an anatomic threshold of injury necessary to produce a unilateral cervical facet dislocation. SUMMARY OF BACKGROUND DATA: The literature at this time is unclear regarding the precise pathomechanics of a cervical unilateral facet dislocation and the required threshold of soft tissue injury necessary for its genesis. Published clinical reports do not make any specific reference to these factors or are unclear in their objectivity. METHODS: Two adjacent vertebra at a time in 10 fresh-frozen subaxial cervical spine specimens (C2-C3 to C6-C7) were transfixed in the coronal plane with 3.5-mm Schanz screws. A steady unilateral vertical distraction force resulting in lateral cervical flexion was applied to these screws as the surrounding cervical soft tissue structures were sequentially ablated. Four experimental models were developed, varying the order of soft tissue disruption. RESULTS: The physiologic coupling of subaxial cervical unilateral distraction and rotation, because of the spatial orientation or inclination of the cervical facet joints, allowed the creation of a unilateral facet dislocation without an additional flexion moment. Disruption of the ipsilateral articular capsule, ligamentum flavum, and more than half of the anulus fibrosus was necessary for the genesis of a unilateral facet dislocation. Disruption of the supraspinous and interspinous ligaments was not necessary but appeared to facilitate or lessen the force required to dislocate a unilateral facet. Disruption of the anterior and posterior longitudinal ligaments and intertransverse ligaments was not necessary to create a unilateral facet dislocation. CONCLUSION: This anatomic study further supports the theory that discontinuity of the anterior and posterior longitudinal ligaments is not necessary for a unilateral facet dislocation to occur. The ipsilateral facet capsule, anulus fibrosus, and ligamentum flavum appear to be the physical soft tissue restraints that need to be disrupted to produce a unilateral facet dislocation.

Adolescent↗
PubMed1999

Influence of packaging conditions on the properties of gamma-irradiated UHMWPE following accelerated ageing and shelf ageing.

The ageing behaviour of ultra-high molecular weight polyethylene (UHMWPE) has been studied following gamma irradiation (25 or 40 kGy) in air or in inert atmosphere (vacuum packed). Accelerated ageing procedures used elevated temperature (70 degrees C) and/or pressurised oxygen (5 bar). Shelf ageing for up to six months was also performed. The variation in polymer properties with depth into the polymer was determined using density measurements, infra-red spectroscopy and differential scanning calorimetry. Tensile properties of the irradiated polymer after accelerated ageing were also determined. Accelerated ageing in air for 20 days or pressurised oxygen for 4 days resulted in peaks in polymer density, crystallinity and degree of oxidation at the polymer surface. Accelerated ageing in pressurised oxygen for 8 days resulted in peaks in these properties 500 microns below the polymer surface. Where gamma irradiation was performed in inert atmosphere the amount of polymer degradation following accelerated ageing (in oxidising conditions) was generally lower but still significant. Differences were also observed in tensile properties between material gamma-irradiated in air and in vacuum. This study indicated that performing gamma sterilisation procedures under inert conditions can reduce the level of UHMWPE degradation when exposed to an oxidising environment.

Biocompatible Materials↗
PubMed1995

Blends of synthetic and natural polymers as drug delivery systems for growth hormone.

In order to overcome the biological deficiencies of synthetic polymers and to enhance the mechanical characteristics of natural polymers, two synthetic polymers, poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) were blended, in different ratios, with two biological polymers, collagen (C) and hyaluronic acid (HA). These blends were used to prepare films, sponges and hydrogels which were loaded with growth hormone (GH) to investigate their potential use as drug delivery systems. The GH release was monitored in vitro using a specific enzyme-linked immunosorbent assay. The results show that GH can be released from HA/PAA sponges and from HA/PVA and C/PVA hydrogels. The initial GH concentration used for sample loading affected the total quantity of GH released but not the pattern of release. The rate and quantity of GH released was significantly dependent on the HA or C content of the polymers.

Acrylic Resins↗
PubMed1994

Inhibition of crevicular fluid neutrophil elastase by alpha 1-antitrypsin in periodontal health and disease.

Gingival crevicular fluid (GCF) was collected from two healthy, two gingivitis and two periodontitis sites of two groups of individuals presenting for treatment of chronic adult periodontitis (group 1, 25 subjects; group 2, seven subjects) and from distal approximal sites of two incisors and one molar of 10 subjects with periodontal health. GCF eluates of periodontitis group 1 and controls, prepared by a technique that lysed polymorphonuclear leucocytes (PMN) in the samples, were assayed for functional neutrophil elastase (NE) and immunoreactive alpha 1-antitrypsin (alpha 1-AT) and alpha 1-antitrypsin-neutrophil elastase complex (alpha 1-AT-NE). Periodontitis group 2 GCF eluates, generated by a method that did not disrupt PMNs, were assayed for functional NE in the presence and absence of a specific NE inhibitor. A greater amount of NE (ng/5-s sample) was found in eluates of GCF from diseased sites irrespective of whether or not the eluates contained products of lysed PMNs. However, the GCF eluates prepared without disrupting PMNs contained only about one-tenth as much NE as eluates of corresponding sites that included constituents of lysed PMNs. The amount of alpha-AT in GCF was insufficient to inactivate most of the NE available for release into the gingival sulcus at either healthy or diseased sites. In addition, much of the alpha 1-AT in GCF was not complexed with NE under conditions of excess NE. More than 90% of the NE in GCF from each site category was inactivated by the NE specific inhibitor. It is concluded, because of the large quantity of NE available in PMNs compared to the amount of NE inhibitors in GCF, that at least locally transient free NE occurs, which contributes to tissue destruction in chronic adult periodontitis.

Adult↗