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Biomedical subjects

J A Shaw

Publications and source records attributed to J A Shaw.

At least 55 records · Page 3Linked to original sources
PubMed1996

High tibial osteotomy: an operation based on a spurious mechanical concept. A theoretic treatise.

The biomechanical basis for high tibial osteotomy (HTO) is erroneously conceived, in that to unload the medial side of the knee, an osteotomy would have to be performed of sufficient magnitude to shift the lateral side of the knee joint far enough medially to intersect the dynamic axis, not the mechanical axis. The resulting angular deformity would be functionally and cosmetically unacceptable in the eyes of most patients and surgeons. To corroborate these theoretic considerations, and to define the angular deformity necessary to unload the medial side of the knee joint during the midstance phase of gait, a cadaver osteotomy model was used with compartmental loading defined by direct observation, as well as by load-sensitive film. As predicted, medial compartment unloading did not occur until the lateral side of the joint crossed the dynamic axis. In both cadavers tested, the extremity alignment necessary to unload the medial side was approximately 25 degrees valgus. The efficacy of HTO should be re-examined, as its biomechanical basis is fundamentally flawed.

Biomechanical Phenomena↗
PubMed1995

Hybrid fixation modular tibial prosthesis. Early clinical and radiographic results and retrieval analysis.

A prosthetic tibial component has been designed with features for fixation to bone using a combination of acrylic cement and ingrowth interfaces. This hybrid concept affords the component the immediate stability of cement fixation and the potential long-term stability of biologic fixation. The ingrowth interfaces (coupled with the central stem) are intended to shield the cement interface beneath the tibial tray from the tensile liftoff forces that result from eccentric loading, while avoiding the fretting and osteolysis associated with screw fixation. A disassembly capability allows the tray to be removed from the stemmed anchorage assembly, facilitating component extraction and limiting bone loss. A clinical and radiographic review of 50 consecutive primary total knee arthroplasties with a mean follow-up period of 35 months revealed stable interfaces with no progressive radiolucencies and minimal remodeling changes. The mean Knee Society knee score was 92.2. At final follow-up evaluation, 88.6% of patients noted no or mild (occasional) pain. Retrieval of three prosthetic knees with chronic sepsis showed extensive ingrowth into the porous interfaces and an osteointegrated bony sleave around the smooth central stem.

Adult↗
PubMed1995

Multiple myeloma. A differential consideration for osteolysis surrounding total hip arthroplasties.

A diagnosis of multiple myeloma was made in a 77-year-old man based on the presence of focal periprosthetic osteolytic lesions surrounding a noncemented femoral component. The radiographic appearance of these lesions was remarkably similar to that of focal osteolytic lesions seen around stable prosthetic femoral components resulting from the localized accumulation of particulate debris. Multiple myeloma should be included in the differential diagnosis of osteolytic lesions around prosthetic components.

Aged↗
PubMed1995

Psychological effects of Hurricane Andrew on an elementary school population.

OBJECTIVE: To explore the prevalence and progression of posttraumatic symptomatology (PTS), using emotional and behavioral indices of psychopathology in school-age children in the pathway of Hurricane Andrew (HI-IMPACT) and in a comparison group north of Miami (LO-IMPACT). METHOD: Pynoos' Posttraumatic Stress Disorder Reaction Index and Achenbach's Teacher's Report Form (TRF) were administered 8 weeks and 32 weeks after the hurricane. In addition, 21 measures of disruptive behavior cataloged by Dade County Public Schools were aggregated and compared by grading period between pre- and posthurricane school years. RESULTS: There were no statistically significant differences between the two schools in PTS at 8 weeks after the hurricane, although the children in the HI-IMPACT school were more likely to have severe PTS. TRF findings at 8 weeks revealed that children in the HI-IMPACT school evidenced lower means on the eight TRF scales and on the broader Internalizing and Externalizing measures. Analysis of the disruptive behavior revealed a drop in the marking period immediately after the hurricane in the HI-IMPACT area, but an opposite effect was observed in the LO-IMPACT area. CONCLUSIONS: After the hurricane there was an initial increase in PTS and a concomitant decrease in other measures of behavior and psychopathology. PTS remained relatively high throughout the school year, but there was a rebound and subsequent normalization of the measures of disruptive behavior.

Child↗
PubMed1994

Comparison of primate and canine models for bone ingrowth experimentation, with reference to the effect of ovarian function on bone ingrowth potential.

Bone growth into porous composite (mesh-bead) titanium plugs was compared in elderly (postmenopausal) female monkeys and female dogs as a means of validating the cross-species interpretations so often made between data from research on dogs and human applications. The effect of oophorectomy on bone ingrowth in the canine model was defined by the comparison of data on fractional ingrowth in animals that had had oophorectomy and in control animals that had had a sham operation. No significant difference in bone growth into the experimental plugs was identified between the two animal models, which lends credence to cross-species interpretation of existing data from dogs. The presence or absence of active ovaries did not affect the ingrowth fraction in the canine model; this suggests that existing data are not confounded by the lack of control of ovarian function. Estrogen depletion does not appear to influence bone ingrowth adversely.

Animals↗
PubMed1994

Segregation analysis of NIDDM in Caucasian families.

Non-insulin-dependent diabetes mellitus (NIDDM) has a substantial genetic component, but the mode of inheritance and the molecular basis are unknown. We have undertaken segregation analysis of NIDDM after studying 247 subjects in 59 Caucasian nuclear pedigrees ascertained without regard to family history of the disorder. The analyses were performed using POINTER and COMDS, which are computer programs which apply statistical models to the data. POINTER analysis was performed defining the phenotype as a presence or absence of hyperglycaemia. Among single locus hypothesis, the analyses rejected a recessive model and favoured a dominant model, but could not statistically show that this fitted better than a mixed model (a single locus against a polygenic background) or a polygenic model. COMDS analysis assumed a continuum of hyperglycaemia from normality to NIDDM, classified family members into a series of diathesis classes with increasing plasma glucose levels and compared the distribution with that found by screening the normal population. This analysis improved the likelihood of a dominant single locus model and suggested a gene frequency of 7.4%. It raised the possibility of a second locus, but cannot identify or exclude a polygenic model. In conclusion, two types of segregation analyses rejected a recessive model and favoured a dominant model of inheritance, although they could not statistically show that this fitted better than the polygenic model. The results raised the possibility of a common dominant gene with incomplete penetrance, but genetic analysis of NIDDM needs to take into account the likelihood of polygenic inheritance with genetic heterogeneity.

Adult↗
PubMed1994

MHC class II expression by microglia in tetanus toxin-induced experimental epilepsy in the rat.

Minute amounts of tetanus toxin injected into the hippocampus of rats results in an epileptiform syndrome. When the toxin injection is made unilaterally or bilaterally into the ventral hippocampus, about one-third of animals with seizures show bilateral neuronal loss in dorsal CA1 of the hippocampus after 1 week. In animals with seizures, microglia in hippocampus are found to be activated. The present work shows that during the acute phase, microglia in the substantia nigra become activated and express MHC class II antigens in the majority of animals with seizures. After the animals have recovered from the acute phase at 8 weeks, the MHC class II expression has largely disappeared from the substantia nigra but MHC class II-expressing microglia are found in the dorsal hippocampus of those rats with loss of cells from CA1. These results show that microglia are responsive to abnormal electrical activity in the central nervous system in the absence of degenerative changes. Further studies are required to determine how microglia may contribute to the neuropathology of epilepsy.

Animals↗
PubMed1993

Association of low birth weight with beta cell function in the adult first degree relatives of non-insulin dependent diabetic subjects.

OBJECTIVE: To examine the relation between birth weight and beta cell function in the first degree relatives of non-insulin dependent diabetic subjects. DESIGN: Cross sectional study of 101 adults of known birth weight from 47 families which had at least one member with non-insulin dependent diabetes. SUBJECTS: 101 white adults aged mean 43 (SD 7) years. SETTING: Oxfordshire, England. MAIN OUTCOME MEASURES: Glucose tolerance was measured by continuous infusion glucose tolerance test. beta cell function and insulin sensitivity were calculated from the fasting plasma glucose and insulin concentrations with homeostasis model assessment. beta cell function was standardised to allow for the confounding effects of age and obesity. RESULTS: Twenty seven subjects had non-insulin dependent diabetes, 32 had impaired glucose tolerance, and 42 were normoglycaemic. Birth weight correlated with the beta cell function of the complete cohort (rs = 0.29, p = 0.005), the non-insulin dependent diabetic subjects (rs = 0.50, p = 0.023), and the non-diabetic subjects (rs = 0.29, p = 0.013). The non-insulin dependent diabetic (n = 27) and the non-diabetic (n = 74) subjects had similar mean (inter-quartile range) centile birth weight 50% (19%-91%), and 53% (30%-75%) respectively. Non-insulin dependent diabetic subjects had significantly lower beta function than the non-diabetic subjects: 69% (48%-83%) v 97% (86%-120%), p < 0.001. CONCLUSIONS: The cause of the association between low birth weight and reduced beta cell function in adult life is uncertain. Impaired beta cell function in non-insulin dependent diabetic subjects was not accounted for by low birth weight, and genetic or environmental factors are likely to be necessary for development of diabetes.

Adult↗
PubMed1993

Young boys who commit serious sexual offenses: demographics, psychometrics, and phenomenology.

This study reports on a population of early adolescent male sexual offenders 9 to 14 years of age compared with a clinic control group matched for age, sex, ethnic status, and the presence of a DSM-III-R conduct disorder. The sex offenders were found to exhibit a significant history of nonsexual antisocial behavior, physical and sexual abuse, and psychiatric comorbidity. The two groups did not differ in number and category of comorbid psychiatric diagnoses, the number of nonsexual aggressive and nonaggressive symptoms of conduct disorder, symptoms of major depressive disorder or dysthymia, and symptoms of anxiety disorders. The EGTC group demonstrated significantly lower mathematic achievement. There is evidence that sexual offending behavior in this population is one aspect of a pattern of antisocial behavior. Sixty-five percent of the index group had a history of early sexual victimization.

Adolescent↗
PubMed1993

Biosynthesis of cell wall and septum during yeast growth.

The primary septum that forms in yeast cells at cytokinesis consists of the polysaccharide chitin. Three chitin synthetases (Chs1, Chs2 and Chs3) have been identified in Saccharomyces cerevisiae. Cloning and disruption of the respective genes showed that Chs3 is responsible for the formation of a chitin ring at the base of an emerging bud and of chitin dispersed in the cell wall, whereas Chs2 catalyzes the synthesis of a chitin disc that completes the primary septum. Chs1 acts as a repair enzyme, replenishing chitin lost through excessive action of a chitinase that facilitates cell separation by degrading part of the septum. The major structural polysaccharide of the yeast cell wall is beta(1->3)glucan. The glucan synthetase complex is bound to the plasma membrane. By differential extraction of the membranes with salt and detergents two solubilized fractions have been obtained which are required, in addition to GTP, for glucan synthesis. Further purification of one of these fractions led to results that indicate a role for other proteins in the modulation of GTP stimulation. A G-protein system appears to function in the regulation of beta(1->3) glucan and cell wall formation in vivo.

Cell Division↗
PubMed1993

Internal fixation of proximal femur fractures: a biomechanical comparison of the Gamma Locking Nail and the Omega Compression Hip Screw.

The fracture fixation capability of the Gamma Locking Nail was compared with the Omega Compression Hip Screw using cadaver femurs with simulated intertrochanteric and subtrochanteric fractures. Loading of the femurs was done on an Instron machine. Fracture fragment motion was recorded at 100-lb loading increments using standard roentgenograms. Both forms of hardware exhibited sufficient structural integrity to carry loads up to 600 lbs. Fracture motion was generally greater with the Gamma Locking Nail, which appeared to suspend the proximal fragments above a pivot point defined by the distal locking screws. Compression of the fracture site under loading did not occur with the Gamma Locking Nail. The potential for iatrogenic fracture generation appeared greater with the Gamma Locking Nail. Additionally, no clear mechanical advantage was documented in the fracture patterns tested. A limited discretionary use of the Gamma Locking Nail is advised.

Bone Nails↗
PubMed1992

Angled bearing inserts in total knee arthroplasty. A brief technical note.

Malalignment of total knee prosthetic components may lead to premature wear, loosening of components, or patellar instability. Unfortunately, removal of securely cemented or ingrown components is difficult and may be extremely destructive to the available bone stock. Angled bearing inserts provide a means to compensate for malpositioned components and should be considered an alternative to component removal in certain cases.

Aged↗
PubMed1992

Chitinase and chitin synthase 1: counterbalancing activities in cell separation of Saccharomyces cerevisiae.

Previous results [E. Cabib, A. Sburlati, B. Bowers & S. J. Silverman (1989) Journal of Cell Biology 108, 1665-1672] strongly suggested that the lysis observed in daughter cells of Saccharomyces cerevisiae defective in chitin synthase 1 (Chs1) was caused by a chitinase that partially degrades the chitin septum in the process of cell separation. Consequently, it was proposed that in wild-type cells, Chs1 acts as a repair enzyme by replenishing chitin during cytokinesis. The chitinase requirement for lysis has been confirmed in two different ways: (a) demethylallosamidin, a more powerful chitinase inhibitor than the previously used allosamidin, is also a much better protector against lysis and (b) disruption of the chitinase gene in chs1 cells eliminates lysis. Reintroduction of a normal chitinase gene, by transformation of those cells with a suitable plasmid, restores lysis. The percentage of lysed cells in strains lacking Chs1 was not increased by elevating the chitinase level with high-copy-number plasmids carrying the hydrolase gene. Furthermore, the degree of lysis varied in different chs1 strains; lysis was abolished in chs1 mutants containing the scs1 suppressor. These results indicate that, in addition to chitinase, lysis requires other gene products that may become limiting.

Cell Division↗
PubMed1992

Linkage analysis of glucokinase gene with NIDDM in Caucasian pedigrees.

NIDDM has a strong genetic component, as evidenced by the high level of concordance between identical twins. The nature of the genetic predisposition has remained largely unknown. Recently, the glucokinase gene locus on chromosome 7p has been shown to be linked to a subtype of NIDDM known as MODY in French and British pedigrees, and glucokinase mutations have been identified. To study the relationship between the glucokinase gene and NIDDM, we performed a linkage analysis in 12 Caucasian pedigrees ascertained through a proband with classical NIDDM. The LINKAGE program was used under four models, including autosomal dominant and recessive, with individuals with glucose intolerance counted as either affected or of unknown status. Linkage was significantly rejected with the dominant models (LOD scores -4.65, -4.25), and was unlikely with the recessive model when glucose intolerance was considered as affected (LOD score -1.38). These findings suggest that mutations in or near the glucokinase gene are unlikely to be the major cause of the inherited predisposition to NIDDM in Caucasian pedigrees, but do not exclude a role for this locus with a polygenic model, or a major role in some pedigrees.

Adult↗
PubMed1992

The influence of age, sex, and initial fit on bony ingrowth stabilization with the AML femoral component in primary THA.

A radiographic review of 178 consecutive primary total hip arthroplasties using the AML femoral component with a mean follow up of 40.1 months identified 92.3% to be stabilized by bony ingrowth and 7.7% by fibrous tissue. None were classified as loose. The quality of fit in the isthmus and calcar regions was identified as an important factor in achieving bony ingrowth stabilization. Bony ingrowth was achieved in all age groups with equal frequency. No relationship between sex and the type of stabilization was identified. A clinical correlation utilizing a subset of patients with identical prosthetic components identified equivalent clinical results across all age groups. Thirty-four percent of patients experienced some residual thigh pain. No statistically significant relationship between the presence of thigh pain and the type of femoral component stabilization (bony vs fibrous) could be identified. Ninety-eight percent of patients expressed unconditional satisfaction with their hip replacements.

Adult↗
PubMed1991

Proteinase B is, indeed, not required for chitin synthetase 1 function in Saccharomyces cerevisiae.

Previous genetic evidence led to the conclusion that proteinase B of yeast was not involved in the function of chitin synthetase 1 (Chs1), based on the demonstration of normal septum formation, cell division and chitin deposition in mutants devoid of the proteinase (Zubenko, G.S., Mitchell, A.P., and Jones, E.W. (1979) Proc. Natl. Acad. Sci. USA 76, 2395-2399). Later, however, it was found that the essential enzyme for septum formation is chitin synthetase 2, whereas Chs1 acts as an auxiliary enzyme, whose absence results in daughter cell lysis under acidic conditions (Cabib, E., Sburlati, A., Bowers, B. and Silverman, S.J. (1989) J. Cell Biol. 108, 1665-1672). By using the lytic behavior as a criterion, we have now found that prb1 strains are not defective in Chs1 function. Certain strains contain a recessive suppressor of lysis which could mask the Chs1 defect. However, appropriate crosses and transformation experiments showed that the prb1 mutants do not harbor the suppressor. It may now be concluded with confidence that proteinase B is not required for chitin synthetase 1 function.

Base Sequence↗
PubMed1991

Biomechanical comparison of cannulated small bone screws: a brief follow-up study.

The compressive forces generated by the ASIF and Herbert small bone cannulated screws were measured in the laboratory with the use of simulated bones and a custom-designed load washer as a means of quantifying their fixation capabilities. Comparative data were also generated for the Herbert scaphoid bone screw and the ASIF 4 mm cancellous screw. The cannulated Herbert bone screw and the ASIF 4 mm cancellous screw were found to have nearly identical compression capabilities. Both generated compression forces approximately five times those of the Herbert scaphoid bone screw. The ASIF small cannulated screw demonstrated a compressive capacity 2 1/2 times that of the Herbert screw.

Biomechanical Phenomena↗