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Biomedical subjects

S Stevenson

Publications and source records attributed to S Stevenson.

At least 55 records · Page 3Linked to original sources
PubMed1995

Evaluation of three fixation techniques for repair of mandibular fractures in dogs.

Bilateral midbody hemimandibular osteotomies were performed between premolars 3 and 4 in 18 adult dogs. Hemimandibles were repaired by use of monocortically applied bone plates (n = 6), an interdental fixator composed of an Erich arch bar and acrylic (n = 6), or a type I external skeletal fixator (n = 6). At the immediate postoperative evaluation, hemimandibles stabilized with interdental fixators had an osteotomy gap distance (mean +/- SEM, 1.6 +/- 0.2 mm) that was significantly (P < 0.05) greater than for hemimandibles stabilized with external skeletal fixators (1.2 +/- 0.3 mm). Osteotomy gap distance of hemimandibles stabilized with external skeletal fixators (1.5 +/- 0.2 mm) was significantly (P < 0.05) greater at weeks 4 (1.1 +/- 0.2 mm) and 8 (0.8 +/- 0.3 mm) after surgery than the osteotomy gap distance of hemimandibles stabilized by application of bone plates. By week 16, significant differences in osteotomy gap distance were not detected between groups. Immediately after surgery, mandibular alignment measurements were not significantly different for dogs with bone plates (0.3 +/- 0.1 mm), interdental fixators (0.3 +/- 0.1 mm), and external skeletal fixators (0.9 +/- 0.5 mm). Mandibular alignment scores were not significantly different between treatment groups during the remaining postoperative period. Occlusal measurements were not significantly different between evaluations performed before surgery and 16 weeks after surgery, regardless of treatment group. Radiographic evidence of healing in hemimandibles stabilized with external skeletal fixators was significantly (P < 0.05) less at 4 and 8 weeks, compared with hemimandibles stabilized with bone plates and interdental fixators; however, radiographic evidence of bone healing was not significantly different between fixation groups at 16 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Induction of bone by a demineralized bone matrix gel: a study in a rat femoral defect model.

Demineralized bone matrix contains osteoinductive factors and stimulates filling of gaps and defects with bone; however, it is difficult to handle by itself and various preparations have been tested. Demineralized bone matrix with a gel consistency now is available for clinical use. We studied, in a femoral segment defect in the rat, the effects of rat demineralized bone matrix gel with and without a ceramic substratum. This preparation is analogous to the human demineralized bone matrix in the same carrier, used clinically for humans. One hundred adult male Fischer rats were divided into 10 experimental groups. Independent variables included the presence or absence of hydroxyapatite ceramic cylinders, the presence of demineralized bone matrix in carrier or carrier alone (glycerol), and the duration of observation (1, 2, and 4 months). Defects filled with the gel alone had significantly higher radiographic scores for host-graft union at 4 months compared with ceramic with the gel, ceramic alone, or carrier alone. Demineralized bone matrix gel significantly increased the total histologic score for host-graft union, whether ceramic was present or not, and a three-way interaction occurred among ceramic, the gel, and time. Demineralized bone matrix gel was an effective inducer of bone formation in this model. An additional substratum was not required; in fact, significantly more bone was formed in the absence of the ceramic cylinder. Neither the gel nor the ceramic were impediments to revascularization of the defect. Host-graft union was enhanced by demineralized bone matrix gel but not by the ceramic cylinder.

Analysis of Variance↗
PubMed1995

Effects of hydroxyapatite tricalcium phosphate coating and intracancellous placement on bone ingrowth in titanium fibermetal implants.

The purpose of this study was to compare the host-bone response to hydroxyapatite/tricalcium phosphate (HA/TCP)-coated and noncoated titanium fibermetal implants placed in a load-sharing cancellous bone environment of the distal femurs of rabbits. The influence of implantation site was also investigated by comparing these intracancellous implants with intramedullary implants evaluated in a previous study. Three parameters were measured: percentage implant perimeter surface length in contact with new bone, percentage internal fibermetal surface length in contact with ingrown bone, and percentage of available pore space filled with bone. The HA/TCP coating significantly accelerated and increased bone ongrowth, new bone formation on the perimeter and internal surface of the implants. This effect was evident as early as 2 weeks after implantation. In contrast, there was no difference between HA/TCP-coated and noncoated implants in the bone ingrowth parameter, percentage of available pore space filled with bone, or pull-out strength. Scanning electron microscopy in the backscatter mode demonstrated that new bone formed directly onto the HA/TCP-coated fibers and did not usually form directly on noncoated fibers. Analysis of fluorochrome labeling revealed that bone formation in weeks 1 through 4 was primarily woven and thereafter lamellar. Compared with intramedullary placement, intracancellous placement significantly accelerated the apposition of bone to the perimeter and internal surface of HA/TCP-coated implants and both accelerated and increased bone ingrowth as a percentage of available pore volume. These data show that the host response to titanium fibermetal implants is influenced both by HA/TCP coating and by the implantation site.

Animals↗
PubMed1995

Repair of chronic tympanic membrane perforations with long-term epidermal growth factor.

Chronic tympanic membrane (TM) perforation is a common problem worldwide. Recent reports have shown epidermal growth factor (EGF) to stimulate healing in approximately 80% of chronic TM perforations in chinchillas when applied in three doses over 1 week. The objective of this controlled study is to evaluate the efficacy of long-term EGF in the closure of TM perforations. Chronic chinchilla TM perforations were treated with EGF for up to 6 weeks. One hundred percent (17 of 17) of treatment group perforations completely healed. However, two new findings with this long dosing scheme were reperforation on long-term follow-up and three TMs with cholesteatomas. It is likely that reperforation was due to a progressive thinning seen with prolonged EGF application. Long-term EGF use is not recommended for the treatment of TM perforations because of possible wound healing impairment and possible cholesteatoma induction.

Animals↗
PubMed1995

The influence of surface-blasting on the incorporation of titanium-alloy implants in a rabbit intramedullary model.

The apposition of new bone to polished solid implants and to implants with surfaces that had been blasted with one of three methods of grit-blasting was studied in a rabbit intramedullary model to test the hypothesis that blasted implant surfaces support osseous integration. Intramedullary titanium-alloy (Ti-6Al-4V) plugs, press-fit into the distal aspect of the femoral canal, were implanted bilaterally in fifty-six rabbits. Four surface treatments were studied: polished (a surface roughness of 0.4 to 0.6 micrometer) and blasted with stainless-steel shot (a surface roughness of five to seven micrometers), with thirty-six-grit aluminum oxide (a surface roughness of five to seven micrometers), or with sixty-grit aluminum oxide (a surface roughness of three to five micrometers). Localized attachment of new bone to the surfaces of the blasted implants was present radiographically at twelve weeks. The total bone area was significantly affected by the level of the section (the diaphysis had a greater bone area than the proximal part of the metaphysis and the proximal part of the metaphysis had a greater bone area than the distal part of the metaphysis; p < 0.001) and the quadrant within each section (the posterior and anterior quadrants had greater bone area than the medial and lateral quadrants; p < 0.00001). The length of the bone-implant interface was significantly affected by the surface treatment (the length of the bone-implant interface for the implants that had been blasted with sixty-grit aluminum oxide was greater than the length for the polished implants; p = 0.02), the time after implantation (the interface was longer at six and twelve weeks than at three weeks; p < 0.00001), and the level of the section (the interface was longer at the diaphysis than at the proximal part of the metaphysis and longer at the proximal part of the metaphysis than at the distal part of the metaphysis; p = 0.004). Blasting of the surface of titanium-alloy implants did not have an effect on the area of bone formation around the implants, but it did significantly affect the area of bone formation on the implant and the shear strength at the bone-implant interface. The two effects were not necessarily parallel, as significantly less (p < 0.05) bone formed on implants that had been blasted with stainless-steel shot than on those blasted with aluminum grit, whereas their interface shear strengths were similar.

Alloys↗
PubMed1995

Early post-tonsillectomy morbidity following hospital discharge: do patients and GPs know what to expect?

Tonsillectomy is a commonly performed operation; like many others there is increasing pressure for it to be performed as a day-case procedure, with no follow-up for the majority of patients. This paper presents the results of a prospective study of the incidence of post-tonsillectomy morbidity, the recognition of these symptoms by patients, and their management by general practitioners. The results indicate: a lack of awareness by patients of symptoms they might expect post-operatively, despite written and verbal information given; an over-prescription of antibiotics by general practitioners for normal post-operative symptoms such as throat pain, temporary voice changes and referred otalgia; and a failure by patients to recognise the importance of the potentially life-threatening complication of secondary haemorrhage from the tonsillar bed.

Adult↗
PubMed1995

Biology of grit-blasted titanium alloy implants.

This study describes the biologic integration of grit-blasted titanium alloy (Ti-6A1-4V) implants that were press fit into the distal femoral canal of young adult rabbits and evaluated by histologic, histomorphometric, and biomechanical methods. Polished and aluminum oxide grit-blasted (4.2 +/- 0.7 microns surface roughness) solid implants were compared with titanium fibermetal implants. Nondecalcified cross sections were studied by histology, histomorphometry, and electron microscopy in the backscatter mode at 3, 6, and 12 weeks after implantation. Pullout strength was measured at 12 weeks. Data were analyzed by analysis of variance and post-hoc Student-Newman-Keuls and Scheffe's tests. The blasted implants had significantly more bone intimately in contact with the implant surface (31%) than the fibermetal (17%), or solid polished implants (15%). By 3 weeks, woven bone had formed directly on the surface of the blasted implants, whereas there was a discrete space between woven bone and the other implants. Active remodeling of bone was shown by fluorochrome uptake at the surface of the blasted implants at 12 weeks after implantation. The strength of fixation of blasted and fiber-metal implants was significantly greater than polished implants at 12 weeks after implantation. Direct attachment of newly formed bone onto the blasted implant surface was confirmed by backscatter electron microscopy. The results of this study indicate that grit-blasted titanium surfaces provide an excellent surface for bone implant integration.

Alloys↗
PubMed1994

Effects of irradiation on posterior spinal fusions. A rabbit model.

STUDY DESIGN: The biological and biomechanical effects of irradiation on posterior bone graft healing in the lumbar spine of rabbits were investigated. Twenty-seven New Zealand white rabbits were divided into four groups. Each rabbit underwent a posterior lumbar spine fusion with autogenous iliac crest bone graft, and three of the experimental groups received perioperative irradiation. OBJECTIVES: This study evaluated the histologic and biomechanical effects of perioperative irradiation on posterior spinal fusions using a rabbit model. SUMMARY OF BACKGROUND DATA: Treatment of metastatic disease of the spine depends on the neurologic status of the patient, stability of the spine, location of the tumor, and the tissue of origin. Some patients require surgical decompression and stabilization. The response of a posterior spinal bone graft to irradiation has not been studied previously. METHODS: Group 1 (n = 7), the control group, did not receive irradiation. Group 2 (n = 6) received preoperative irradiation. Group 3 (n = 7) received immediate (day 3) postoperative irradiation, and Group 4 (n = 7) received delayed (day 21) postoperative irradiation. The radiation protocol consisted of 480 centigrade/fraction for 5 consecutive days. At 3 months, the rabbits were euthanatized. Nondestructive biomechanical testing was performed, followed by histologic evaluation of the fusion mass. RESULTS: Compared with the control group, Group 3 (immediate postoperative irradiation) specimens were less stiff in extension (P = .0001), flexion (P = .0006), compression (P = .018), and left lateral bending (P = .018). The preoperatively irradiated spines (Group 2) were less stiff in extension (P = .0008) and in compression (P = .035) than controls. The control group and the delayed irradiation group had the highest histologic scores and more mature fusion mass. The immediate postoperative irradiation group had the worst results, with consistent fibrous union of the graft. CONCLUSION: Healing of a posterior spinal fusion is influenced by the timing of radiation therapy. Adjuvant radiation therapy for patients with spinal neoplasm requiring a posterior fusion should, if possible, be delayed for 3 to 6 weeks postoperatively to maximize the probability of successful arthrodesis.

Animals↗
PubMed1994

Primary structure and function of a second essential member of the heterooligomeric TCP1 chaperonin complex of yeast, TCP1 beta.

A role for heterooligomeric TCP1 complex as a chaperonin in the eukaryotic cytosol has recently been suggested both by structural similarities with other chaperonins and by in vitro experiments showing it to mediate ATP-dependent folding of actin, tubulin, and luciferase. Here we present the primary structure of a second subunit of the complex and present genetic and functional analyses. The TCP1 beta amino acid sequence, predicted from the cloned gene, bears 35% identity to TCP1, termed here TCP1 alpha, containing the same highly conserved residues found in the collective sequence of chaperonins. The predicted product was identified as the fastest-migrating species of the TCP1 complex purified from soluble extracts of yeast. The TCP1 beta gene, like TCP1 alpha, is essential. Strains containing lethal disruptions of either gene could not be rescued by additional copies of the other. Spores bearing disruption of either gene germinated as single, large-budded cells. Similarly, large-budded cells were observed following shift to 37 degrees C of strains carrying temperature-sensitive mutations in either TCP1 alpha or TCP1 beta. The arrested cells contained replicated DNA present in single nuclear masses, associated with abnormal tubulin staining patterns, supporting the assertion that mitotic spindle formation and function are impaired. We conclude that TCP1 beta supplies an essential function that partially overlaps with that of TCP1 alpha in acting as a molecular chaperone in tubulin and spindle biogenesis.

Alleles↗
PubMed1994

Histomorphometric analysis of the repair of a segmental diaphyseal defect with ceramic and titanium fibermetal implants: effects of bone marrow.

We used a rat femoral diaphyseal defect/implant model to quantify the ingrowth of bone, cartilage, and fibrous connective tissue in a comparative study of woven sintered titanium fibermetal and porous hydroxyapatite/tricalcium phosphate ceramic implanted with and without the addition of syngeneic bone marrow cells. The patterns of tissue growth into the implants were analyzed with respect to time, type of implant, and the presence or absence of syngeneic marrow. Significantly more bone was found in ceramic implants than in fibermetal implants, with the addition of syngeneic marrow than without it, and at 4 months than at 2 months. Significantly more bone was found at both time periods in ceramic implants with bone marrow than in any other combination studied. We hypothesize that these findings resulted from interactions between the implanted material and its surroundings, specifically its ability to serve as a substratum for cell attachment, and cells in and around the defect, whether surgically implanted or arising from the soft-tissue bed.

Animals↗
PubMed1994

Demonstration of HLA and ABH antigens in fresh and frozen human menisci by immunohistochemistry.

The expression of HLA and ABH antigens in fresh, frozen, and twice-frozen normal human meniscal tissue was evaluated with use of immunohistochemistry. A generalized expression of Class-I and Class-II HLA antigens was found in the endothelial and synovial cells of all three forms of tissue. Fibrochondrocytes were Class-I positive and Class-II negative. ABH antigens were expressed by endothelial cells in relationship to the blood group of the patient. Freezing preserved most of the HLA and ABH molecular structure. Although the normal meniscus consists of a relatively few chondrocytes embedded in an extracellular matrix, it also contains Class-II and ABH-positive endothelial cells and Class-II-positive synovial cells. These antigens are present at the moment of transplantation and could evoke an immune response in the host that would modulate the results of meniscal allografting.

ABO Blood-Group System↗
PubMed1994

The proteoglycan synthesis repertoire of rabbit chondrocytes maintained in type II collagen gels.

Repair of experimental articular cartilage lesions employing cultured rabbit articular chondrocytes requires a detailed knowledge of the phenotypic stability of these cells. A suitable matrix vehicle for use in chondrocyte transplantation is a much sought-after component of any transplantation paradigm. We studied the proteoglycan synthesis repertoire of young immature rabbit articular chondrocytes maintained in chick type II collagen gels or collagen gels supplemented with recombinant human transforming growth factor-beta 1 (rhTGF beta 1). Maintenance of chondrocytes in type II collagen gels increased the percentage 35SO4-labeled proteoglycans reaching equilibrium in the A1D1 or D1 fraction of CsCl density gradient when compared to chondrocytes maintained in polystyrene microwell cultures. Although rhTGF beta 1 supplementation increased the percentage of A1D1/D1 proteoglycan by chondrocytes grown on polystyrene, rhTGF beta 1 did not augment this percentage increase in A1D1/D1 when added to collagen II gels. Rabbit chondrocytes synthesized two core proteins derived from the high-density aggregatable proteoglycans. LI and LII have apparent molecular sizes of 480 kDa and 390 kDa, respectively. Both core protein forms were found in the medium fraction, but the predominant core protein form associated with the cell fraction was LI. Maintenance of chondrocytes in collagen II gels increased synthesis of both core proteins. In addition to the large core proteins, three other core proteins with properties on SDS PAGE characteristic of the small dermatan sulfate proteoglycans, biglycan and decorin, were identified. Synthesis of these core proteins was stimulated by maintenance in collagen gels. Furthermore, they were preferentially retained in the gel matrix. Chondrocytes maintained on glass or in type II collagen gels stained with monoclonal antibodies specific for chondroitin-6-sulfate, chondroitin-4-sulfate and keratan sulfate. However, while chondrocytes grown on glass slides failed to stain with monoclonal antibody 3B3 in the absence of chondroitinase ABC digestion, chondrocytes grown in collagen II gels stained intensely in the absence of enzyme pretreatment. These results were confirmed by Western blots.

Animals↗
PubMed1994

The influence of a hydroxyapatite and tricalcium-phosphate coating on bone growth into titanium fiber-metal implants.

A study was done in rabbits to determine the effect of a hydroxyapatite and tricalcium-phosphate coating on bone growth into titanium fiber-metal implants. Titanium fiber rods with a solid titanium core were implanted bilaterally into the distal aspect of the femora of fifty-five New Zealand White rabbits. One rod was uncoated and the other rod was surface-coated with hydroxyapatite and tricalcium phosphate by the plasma-spray technique. Thirty-five rabbits were labeled sequentially with fluorochromes; killed at one, two, three, four, six, twelve, or twenty-four weeks after the operation; and studied histologically and histomorphometrically. The implants in the remaining twenty rabbits were subjected to pull-out testing to determine the shear strength at the implant-bone interface at three, six, twelve, and twenty-four weeks after the operation. Histomorphometry revealed significant effects of the hydroxyapatite and tricalcium-phosphate coating. When whole-group means (which included all time-points) were compared, it was found that 44 per cent of the perimeter of the hydroxyapatite and tricalcium-phosphate-coated implants was covered with bone compared with 12 per cent of the perimeter of the uncoated implants. The percentage of the internal surface of the implant that was covered with bone was also significantly higher in the hydroxyapatite and tricalcium-phosphate-coated implants: 27 per cent of the internal surface of the coated implants was covered compared with 8 per cent in the uncoated implants. The amount of bone in the pores of the implants was also higher in the hydroxyapatite and tricalcium-phosphate-coated implants: 12 per cent of the available pore space in the hydroxyapatite and tricalcium-phosphate-coated implants was filled with bone compared with 4 per cent in the uncoated implants. Scanning electron microscopy of the implants, done in backscatter mode, demonstrated apposition of new bone directly on the hydroxyapatite and tricalcium-phosphate coating, with variable degrees (amounts) of hydroxyapatite and tricalcium-phosphate resorption and new-bone replacement over time. Bone was never directly apposed to uncoated titanium fiber-metal. The pull-out strength of the hydroxyapatite and tricalcium-phosphate-coated implants was consistently greater than that of the uncoated implants, at all time-periods.

Animals↗
PubMed1994

The biological and biomechanical effects of irradiation on anterior spinal bone grafts in a canine model.

We evaluated the effects of irradiation on the healing of anterior vertebral strut grafts with use of a canine model. Through a left thoracotomy, a partial corpectomy of the seventh thoracic vertebra and autogenous iliac strut-grafting from the sixth to the eighth thoracic levels were performed in twenty-two adult beagles. Four groups were established: Group I (control) received no irradiation, Group II received preoperative irradiation, Group III received postoperative irradiation that began on the third postoperative day, and Group IV received postoperative irradiation that began on the twenty-first postoperative day. The irradiation protocol was five treatments of 500 centigray three times a week for a total of 2500 centigray. Fluorochromes were administered at regular intervals postoperatively. The beagles were killed three months postoperatively, and non-destructive biomechanical testing was done to evaluate the stiffness of the construct. The quality of healing at the junctions of the graft with the sixth and eighth thoracic vertebrae, the degree of revascularization of the graft, and the amount of new-bone formation were evaluated histologically. Statistical evaluation of the biomechanical data revealed no significant difference in the stiffness of the construct between Groups I, II, and IV. The specimens from Group III were significantly less stiff than those from Group I (the control group) in torsion (p = 0.03) and left lateral bending (p = 0.04) and than those from Group II in flexion (p = 0.02) and left lateral bending (p = 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

The effect of osteogenin (a bone morphogenetic protein) on the formation of bone in orthotopic segmental defects in rats.

We studied the effects of partially purified, natural osteogenin, a bone morphogenetic protein, on the formation of bone in rats. An osteoperiosteal segmental defect, eight millimeters wide, in the middle of the femoral diaphysis was created bilaterally in thirty-six adult male Fischer rats and stabilized with a polyacetyl plate and threaded Kirschner wires. One defect was filled with a cylinder of 60 per cent hydroxyapatite and 40 per cent tricalcium phosphate ceramic (pore diameter, 250 to 400 micrometers) containing 100 micrograms of partially purified bovine osteogenin, and the contralateral defect was filled with a hydroxyapatite-tricalcium ceramic cylinder without osteogenin. Eighteen animals (six animals each at one, two, and four months after the operation) were studied histologically and histomorphometrically. The implants from eighteen additional animals (six animals each at one, two, and four months after the operation) were subjected to biomechanical testing. Histomorphometry revealed that the total area of bone, the area of bone outside of the implant, and the amount of bone within the pores of the implant were all significantly (p < or = 0.05) greater in the femora that had an implant with osteogenin than in those that had an implant without osteogenin at most time-periods. The presence of osteogenin had no significant effect on the biomechanical parameters measured in this study.

Animals↗
PubMed1993

The effects of cisplatin on the incorporation of fresh syngeneic and frozen allogeneic cortical bone grafts.

Allograft transplantation with concomitant chemotherapy has proven successful in the treatment of malignant bone tumors. However, these chemotherapeutic agents may delay tissue healing, resulting in clinical complications. To clarify the effects of cisplatin on the healing of bone grafts, we studied the incorporation of stably fixed massive diaphyseal femoral syngeneic and allogeneic grafts in rats treated with cisplatin. These data were compared with those of historical controls from animals that did not receive cisplatin. Rats that were to receive a fresh syngeneic graft or frozen allogeneic graft were given cisplatin every 4 weeks starting 9 weeks preoperatively and continuing until the time of death. The total bone area of the graft in animals that received cisplatin was smaller than that of the graft in untreated control rats that did not receive cisplatin. The area of the frozen allograft did not increase between 2 and 4 months. Revascularization was incomplete in cisplatin-treated groups at 2 months, but by 4 months, vessel ingrowth in fresh syngeneic grafts approached control values. Frozen allografts remained poorly revascularized at 4 months. Host-graft union was poor at 2 months in cisplatin-treated rats compared with controls. In cisplatin-treated rats, the host-graft union of the frozen allograft remained inferior at 4 months while that of the syngeneic graft improved. Allogeneic cortical bone grafts are incorporated more slowly and incompletely than syngeneic grafts, and this handicap is exacerbated by the administration of cisplatin.

Animals↗