Remodeling of murine vaginal smooth muscle function with reproductive age and elastic fiber disruption

Advanced maternal age during pregnancy is associated with increased risk of vaginal tearing during delivery and maladaptive postpartum healing. Although the underlying mechanisms of age-related vaginal injuries are not fully elucidated, changes in vaginal microstructure may contribute. Smooth muscle cells promote the contractile nature of the vagina and contribute to pelvic floor stability. While menopause is associated with decreased vaginal smooth muscle content, whether contractile changes occur before the onset of menopause remains unknown. Therefore, the first objective of this study was to quantify the active mechanical behavior of the murine vagina with age. Further, aging is associated with decreased vaginal elastin content. As such, the second objective was to determine if elastic fiber disruption alters vaginal contractility. Vaginal samples from mice aged 2-14 months were used in maximum contractility experiments and biaxial extension-inflation protocols. To evaluate the role of elastic fibers with age, half of the vaginal samples were randomly allocated to enzymatic elastic fiber disruption. Contractile potential decreased and vaginal material stiffness increased with age. These age-related changes in smooth muscle function may be due, in part, to changes in microstructural composition or contractile gene expression. Furthermore, elastic fiber disruption had a diminished effect on smooth muscle contractility in older mice. This suggests a decreased functional role of elastic fibers with age. Quantifying the age-dependent mechanical contribution of smooth muscle cells and elastic fibers to vaginal properties provides a first step towards better understanding how age-related changes in vaginal structure may contribute to tissue integrity and healing. STATEMENT OF SIGNIFICANCE: Advanced maternal age at the time of pregnancy is linked to increased risks of vaginal tearing during delivery, postpartum hemorrhaging, and the development of pelvic floor disorders. While the underlying causes of increased vaginal injuries with age and associated pathologies remain unclear, changes in vaginal microstructure, such as elastic fibers and smooth muscle cells, may contribute. Menopause is associated with fragmented elastic fibers and decreased smooth muscle content; however, how reproductive aging affects changes in the vaginal composition and the mechanical properties remains unknown. Quantifying the mechanical contribution of smooth muscle cells and elastic fibers to vaginal properties with age will advance understanding of the potential structural causes of age-related changes to tissue integrity and healing.

Biaxial Murine Vaginal Remodeling With Reproductive Aging

Higher reproductive age is associated with an increased risk of gestational diabetes, pre-eclampsia, and severe vaginal tearing during delivery. Further, menopause is associated with vaginal stiffening. However, the mechanical properties of the vagina during reproductive aging before the onset of menopause are unknown. Therefore, the first objective of this study was to quantify the biaxial mechanical properties of the nulliparous murine vagina with reproductive aging. Menopause is further associated with a decrease in elastic fiber content, which may contribute to vaginal stiffening. Hence, our second objective was to determine the effect of elastic fiber disruption on the biaxial vaginal mechanical properties. To accomplish this, vaginal samples from CD-1 mice aged 2-14 months underwent extension-inflation testing protocols (n = 64 total; n = 16/age group). Then, half of the samples were randomly allocated to undergo elastic fiber fragmentation via elastase digestion (n = 32 total; 8/age group) to evaluate the role of elastic fibers. The material stiffness increased with reproductive age in both the circumferential and axial directions within the control and elastase-treated vaginas. The vagina demonstrated anisotropic mechanical behavior, and anisotropy increased with age. In summary, vaginal remodeling with reproductive age included increased direction-dependent material stiffness, which further increased following elastic fiber disruption. Further work is needed to quantify vaginal remodeling during pregnancy and postpartum with reproductive aging to better understand how age-related vaginal remodeling may contribute to an increased risk of vaginal tearing.

Biaxial Basal Tone and Passive Testing of the Murine Reproductive System Using a Pressure Myograph

The female reproductive organs, specifically the vagina and cervix, are composed of various cellular components and a unique extracellular matrix (ECM). Smooth muscle cells exhibit a contractile function within the vaginal and cervical walls. Depending on the biochemical environment and the mechanical distension of the organ walls, the smooth muscle cells alter the contractile conditions. The contribution of the smooth muscle cells under baseline physiological conditions is classified as a basal tone. More specifically, a basal tone is the baseline partial constriction of smooth muscle cells in the absence of hormonal and neural stimulation. Furthermore, the ECM provides structural support for the organ walls and functions as a reservoir for biochemical cues. These biochemical cues are vital to various organ functions, such as inciting growth and maintaining homeostasis. The ECM of each organ is composed primarily of collagen fibers (mostly collagen types I, III, and V), elastic fibers, and glycosaminoglycans/proteoglycans. The composition and organization of the ECM dictate the mechanical properties of each organ. A change in ECM composition may lead to the development of reproductive pathologies, such as pelvic organ prolapse or premature cervical remodeling. Furthermore, changes in ECM microstructure and stiffness may alter smooth muscle cell activity and phenotype, thus resulting in the loss of the contractile force. In this work, the reported protocols are used to assess the basal tone and passive mechanical properties of the nonpregnant murine vagina and cervix at 4-6 months of age in estrus. The organs were mounted in a commercially available pressure myograph and both pressure-diameter and force-length tests were performed. Sample data and data analysis techniques for the mechanical characterization of the reproductive organs are included. Such information may be useful for constructing mathematical models and rationally designing therapeutic interventions for women's health pathologies.

Backward walking measures are sensitive to age-related changes in mobility and balance

Many falls occur from backward perturbations or during transitional movements that require a person to turn and step backwards, suggesting that deficits in backward stepping may negatively impact mobility. Previous studies found significant declines in backward walking (BW) spatiotemporal measures in healthy elderly compared to young adults. No studies to date have examined BW performance in middle-aged adults and in elderly with impaired mobility. This study compared spatiotemporal measures of BW and forward walking (FW) in young, middle-aged, and elderly and in elderly fallers and non-fallers; and compared the strength of the relationship between age and BW and FW spatiotemporal measures to determine the utility of BW performance as a clinical tool for examining safety and mobility. BW measures were significantly more impaired in the elderly (n=62) compared to young (n=37) and middle-aged (n=31) adults and age effects were greater in BW than FW. No significant differences were found between young and middle-aged except for base of support in BW. Stronger correlations were found between age and BW measures than between age and FW measures, particularly correlations between age and BW velocity and stride length. Elderly fallers had greater deficits in BW performance than non-fallers. All elderly fallers had BW velocities<.6m/s. Clinicians are encouraged to assess BW, particularly BW velocity, as part of mobility examinations.

Clinical outcomes of a specialised inpatient unit for adults with mild to severe intellectual disability and mental illness

BACKGROUND

Limitations of general psychiatric services have led to the development of specialised psychiatric programmes for patients with intellectual disability (ID) and mental health needs. Few studies have examined treatment outcomes of specialised inpatient units, and no studies have explored how the effects of intervention may differ for individuals at varying levels of cognitive ability. The present study examined clinical outcomes of inpatients with mild ID in contrast to inpatients with moderate to severe ID within the same service.

METHOD

Thirty-three patients (17 with mild ID and 16 with moderate to severe ID) discharged between 2006 and 2008 from a specialised inpatient unit in Canada for adults with ID and mental illness were studied. In addition to examining change in scores on clinical measures, outcomes with regard to length of stay, diagnostic change, residential change and re-admission to hospital were explored.

RESULTS

Both groups demonstrated clinical improvement from admission to discharge. However, only patients with mild ID demonstrated improvements on the Global Assessment of Functioning.

CONCLUSIONS

This study is one of the first to consider outcomes of higher and lower functioning individuals with ID on a specialised inpatient unit. Results suggest that outcomes may be different for these groups, and some clinical measures may be more sensitive to changes in patients with more severe disabilities.

Integrating genetics and genomics to identify new leads for the control ofEimeriaspp

Eimerian parasites display a biologically interesting range of phenotypic variation. In addition to a wide spectrum of drug-resistance phenotypes that are expressed similarly by many other parasites, theEimeriaspp. present some unique phenotypes. For example, unique lines ofEimeriaspp. include those selected for growth in the chorioallantoic membrane of the embryonating hens egg or for faster growth (precocious development) in the mature host. The many laboratory-derived egg-adapted or precocious lines also share a phenotype of a marked attenuation of virulence, the basis of which is different as a consequence of thein ovoorin vivoselection procedures used. Of current interest is the fact that some wild-type populations ofEimeria maximaare characterized by an ability to induce protective immunity that is strain-specific. The molecular basis of phenotypes that defineEimeriaspp. is now increasingly amenable to investigation, both through technical improvements in genetic linkage studies and the availability of a comprehensive genome sequence for the caecal parasiteE. tenella. The most exciting phenotype in the context of vaccination and the development of new vaccines is the trait of strain-specific immunity associated withE. maxima. Recent work in this laboratory has shown that infection of two inbred lines of White Leghorn chickens with the W strain ofE. maximaleads to complete protection to challenge with the homologous parasite, but to complete escape of the heterologous H strain, i.e. the W strain induces an exquisitely strain-specific protective immune response with respect to the H strain. This dichotomy of survival in the face of immune-mediated killing has been examined further and, notably, mating between a drug-resistant W strain and a drug-sensitive H strain leads to recombination between the genetic loci responsible for the specificity of protective immunity and resistance to the anticoccidial drug robenidine. Such a finding opens the way forward for genetic mapping of the loci responsible for the induction of protective immunity and integration with the genome sequencing efforts.

Sagittal sinus blood flow in the ovine fetus as a continuous measure of cerebral blood flow: relationship to behavioural state activity

Superior sagittal sinus blood flow (Q(ss)) was studied over a 6-h period in nine chronically catheterized fetal sheep as a continuous measure of cerebral blood flow to determine the change in blood flow values and in measures of blood flow variability in relation to behavioural state activity. Mean Q(ss) was increased during the low voltage (LV)/rapid eye movement (REM) state compared to the high voltage (HV)/NREM state by approximately 25%, and was further increased during periods of LV/REM with fetal breathing movements. The increase in Q(ss) was abrupt and began at the transition to LV/REM, with the rate of change 2-fold greater than that during transition to HV/NREM, where the decrease in Q(ss) was gradual and began prior to the evident state change. Q(ss) showed considerable fluctuation, which tended to be greater during the HV/NREM state compared to the LV/REM state when analyzed using measures of longer term variability. Q(ss) thus provides for a continuous measure of cerebral blood flow in the ovine fetus, with the approximately 25% increase with change from the HV/NREM to LV/REM state similar to that previously reported using radioactive microspheres. The abrupt increase in Q(ss) at the transition to LV/REM versus the gradual decrease in Q(ss) before transition to HV/NREM would suggest that the state-related change in brain blood flow is better linked to the presence of the LV electrocorticogram and favours its active generation.

Adaptation of cardiovascular responses to repetitive umbilical cord occlusion in the late gestation ovine fetus

1. The impact of repeated umbilical cord occlusion on the normal maturation of fetal heart rate (FHR) and mean arterial pressure (MAP) and the cardiovascular responses to successive umbilical cord occlusion was investigated over a 21 day period in the latter part of gestation. 2. Fifteen chronically instrumented sheep (control group n = 6; occlusion group n = 9) were studied for 21 days (113-133 days of gestation, term = 145 days) with umbilical cord occlusions (90 s duration) performed every 30 min for 1-4 h each day. On days 1, 9 and 18, FHR, FHR variation and MAP were monitored continuously and fetal arterial blood gases, pH and metabolites were measured at predetermined intervals. The baroreflex response to 75-100 microg phenylephrine (I.V.) was tested on days 1 and 18. 3. Basal FHR decreased (DeltaFHR: control, 34.6 +/- 3.6 beats x min(-1); occlusion, 36.9 +/- 2.7 beats x min(-1)) and MAP increased (DeltaMAP: control, 3.1 +/- 1.7 mmHg; occlusion, 5.2 +/- 2.1 mmHg) to a similar extent in control and occlusion groups between days 1 and 21 of the study. There was a small decline in FHR variation over the 21 day study in occlusion, but not control, group fetuses. 4. The magnitude of the fall in FHR decreased and the rise in MAP increased, despite similar changes in blood gases in response to umbilical cord occlusion, over the course of the 21 day study. Despite a significant decline in the ratio of DeltaFHR to DeltaMAP on days 9 and 18 compared to day 1, there was no difference between control and occlusion groups in baroreflex sensitivity. However DeltaFHR/DeltaPO2, an index of chemoreceptor sensitivity, had decreased by day 9 and 18 compared to day 1. 5. The cardiovascular responses to umbilical cord occlusion are altered with repetitive occlusions during the latter part of gestation, with a decrease in DeltaFHR/DeltaMAP, which does not involve changes in baroreflex sensitivity, but may involve changes in chemoreceptor sensitivity. However, repeated umbilical cord occlusion appears to have no impact on baseline cardiovascular control since there was no change in the normal maturational decrease in FHR and rise in MAP.

In vivo and in vitro development of the protist Helicosporidium sp

We describe the discovery and developmental features of a Helicosporidium sp. isolated from the black fly Simulium jonesi. Morphologically, the helicosporidia are characterized by a distinct cyst stage that encloses three ovoid cells and a single elongate filamentous cell. Bioassays have demonstrated that the cysts of this isolate infect various insect species, including the lepidopterans, Helicoverpa zea, Galleria mellonella, and Manduca sexta, and the dipterans, Musca domestica, Aedes taeniorhynchus, Anopheles albimanus, and An. quadrimaculatus. The cysts attach to the insect peritrophic matrix prior to dehiscence, which releases the filamentous cell and the three ovoid cells. The ovoid cells are short-lived in the insect gut with infection mediated by the penetration of the filamentous cell into the host. Furthermore, these filamentous cells are covered with projections that anchor them to the midgut lining. Unlike most entomopathogenic protozoa, this Helicosporidium sp. can be propagated in simple nutritional media under defined in vitro conditions, providing a system to conduct detailed analysis of the developmental biology of this poorly known taxon. The morphology and development of the in vitro produced cells are similar to that reported for the achorophyllic algae belonging to the genus Prototheca.

Effects of trendelenburg position and positive intrathoracic pressure on internal jugular vein cross-sectional area in anesthetized children

STUDY OBJECTIVE

To compare the cross-sectional area (in cm(2)) of the left internal jugular vein (LIJV) and right internal jugular vein (RIJV) in anesthetized children, and measure the response to the Trendelenburg tilt position (TBRG) and a positive inspiratory pressure hold.

DESIGN

Prospective, nonrandomized study.

SETTING

University medical center.

PATIENTS

45 ASA physical status I and II children, ages 6 months to 8 years, undergoing general anesthesia and mechanical ventilation.

INTERVENTIONS

The cross-sectional area of both internal jugular veins was measured with a 5-MHz, two-dimensional surface transducer, at the level of the cricoid cartilage. Three measurements were obtained: 1) with the patient supine, 2) during a 10-second breath-hold with a positive inspiratory pressure (PIP) of 20 cm H(2)O, and 3) with the patient at 20 degrees TBRG. Data were analyzed with two-way analysis of variance (ANOVA) and Student-Newman-Keuls test, with a p < 0.05 considered significant.

MEASUREMENTS AND MAIN RESULTS

In supine patients, the cross-sectional area of the RIJV was larger than the LIJV in 31 patients (69%), and equal or smaller in 14 patients (31%) (0.80 +/- 0.38 vs. 0.59 +/- 0.22; p = 0.002). A PIP hold, but not TBRG, significantly dilated the RIJV (0.8 +/- 0.38 at baseline vs. 0.93 +/- 0.42 with TBRG; p = not significant vs. 1.1 +/- 0.46 with PIP; p < 0.05), whereas neither maneuver was effective with the LIJV.

CONCLUSION

The cross-sectional area of the RIJV is often greater than the LIJV; the TBRG was not effective to increase the cross-sectional area of the internal jugular veins, and only a PIP hold increased significantly the cross-sectional area of the RIJV. In this study, the LIJV appeared of smaller size and less compliant compared with the RIJV.

The molecular evolution of terminal ear1, a regulatory gene in the genus Zea

Nucleotide diversity in the terminal ear1 (te1) gene, a regulatory locus hypothesized to be involved in the morphological evolution of maize (Zea mays ssp. mays), was investigated for evidence of past selection. Nucleotide polymorphism in a 1.4-kb region of te1 was analyzed for a sample of 26 sequences isolated from 12 maize lines, five populations of the maize progenitor, Z. mays ssp. parviglumis, six other Zea populations, and two Tripsacum species. Although nucleotide diversity in te1 in maize is reduced relative to ssp. parviglumis, phylogenetic and statistical analyses of the pattern of polymorphism among these sequences provided no evidence of past selection, indicating that the region of the gene studied was probably not involved in maize evolution. The level of reduction in genetic diversity in te1 in maize relative to its progenitor is comparable to that found in previous reports for isozymes and other neutrally evolving maize genes and is consistent with a genome-wide reduction of genetic diversity resulting from a domestication bottleneck. An estimate of the age (1.2-1.4 million yr) of the maize gene pool based on te1 is roughly consistent with previous estimates based on other neutral genes, but may be biased by the apparently slow synonymous substitution rate at te1.

The adenosine A(1)-receptor antagonist 8-CPT reverses ethanol-induced inhibition of fetal breathing movements

Administration of either ethanol or adenosine inhibits fetal breathing movements (FBM), eye movements, and low-voltage electrocortical activity (LV ECoG). The concentration of adenosine in ovine fetal cerebral extracellular fluid increases during ethanol-induced inhibition of FBM. The purpose of this study was to determine the effect of a selective adenosine A(1)-receptor antagonist, 8-cyclopentyltheophylline (8-CPT) on the incidence of FBM during ethanol exposure. After a 2-h control period, seven pregnant ewes received a 1-h intravenous infusion of ethanol (1 g/kg maternal body wt), followed 1 h later by a 2-h fetal intravenous infusion of either 8-CPT (3.78 +/- 0.08 microg. kg(-1). min(-1)) or vehicle. Ethanol reduced the incidence of FBM from 44.0 +/- 10.4 to 2.7 +/- 1.3% (P < 0.05) and 51.2 +/- 7.6 to 11.9 +/- 5.0% (P < 0.05) in fetuses destined to receive 8-CPT or vehicle, respectively. In the vehicle group, FBM remained suppressed for 7 h. In contrast, during the first hour of 8-CPT infusion, FBM returned to baseline (31 +/- 11%) and was not different from control throughout the rest of the experiment. Ethanol also decreased the incidence of both low-voltage electrocortical activity and eye movements, but there were no differences in the incidences of these behavioral parameters between the 8-CPT and vehicle groups throughout the experiment. These data are consistent with the hypothesis that adenosine, acting via A(1) receptors, may play a role in the mechanism of ethanol-induced inhibition of FBM.

Evaluation of tibial component fixation in specimens retrieved at autopsy

Fixation of the tibial component was evaluated in eight knees retrieved at autopsy by comparing their radiographs with measurements of micromovement between the component and the tibial plateau. Micromovement in the one cemented Miller-Galante and seven cementless Ortholoc components, which had been implanted for a range of 3 days to 57 months, was measured with linearly variable differential transducers under anteroposterior shear and axial compressive loads. Micromovement between the tibial component and the screws and between the tibial component and the bone after the screws were removed also was measured in the cementless specimens. Minimal micromovement in most of the implants suggests that the tibial components were well fixed. Micromovement between the tibial tray and the screws also was minimal in the cementless components. Removing the screws did not significantly affect micromovement, except in the specimen retrieved 3 days after surgery and in the specimen with a complete radiolucent line under the component. The cementless tibial components fixed with screws, pegs, and stem were as stable as the component secured with cement. Partial radiolucencies were not associated with greater micromotion than that of bone ingrown areas, but the component with complete radiolucency did have greater micromotion than that of all of the other specimens.

Increased cerebral extracellular adenosine and decreased PGE2 during ethanol-induced inhibition of FBM

Adenosine and PGE2 are neuromodulators, both of which inhibit fetal breathing movements (FBM). Although circulating PGE2 has been implicated as a mediator of ethanol-induced inhibition of FBM in the late-gestation ovine fetus, a role for adenosine has not been examined. The objective of this study was to determine the effect of maternal ethanol infusion on ovine fetal cerebral extracellular fluid adenosine and PGE2 concentrations by using in utero microdialysis and to relate any changes to ethanol-induced inhibition of FBM. Dialysate samples were obtained from the fetal parietal cortex over 70 h after surgery to determine steady-state extracellular fluid adenosine and PGE2 concentrations. On each of postoperative days 3 and 4, after a 2-h baseline period, ewes received a 1-h infusion of ethanol (1 g/kg maternal body wt) or an equivalent volume of saline, and the fetus was monitored for a further 11 h with 30-min dialysate samples collected throughout. Immediately after surgery, dialysate PGE2 and adenosine concentrations were 3.7 +/- 0.7 and 296 +/- 127 nM, respectively. PGE2 did not change over the 70 h, whereas adenosine decreased to 59 +/- 14 nM (P < 0.05) at 4 h and then remained unchanged. Ethanol decreased dialysate PGE2 concentration for 2 h (3.3 +/- 0.3 to 1.9 +/- 0.4 nM; P < 0.05) and increased adenosine concentration for 6 h (87 +/- 13 to a maximum of 252 +/- 59 nM, P < 0.05). Ethanol decreased FBM incidence from 47 +/- 7 to 16 +/- 5% (P < 0.01) for 8 h. Saline infusion did not change dialysate adenosine or PGE2 concentrations or FBM incidence. These data are consistent with the hypothesis that fetal cerebral adenosine, and not PGE2, is the primary mediator of ethanol-induced inhibition of FBM at 123 days of gestation in sheep.

Cardiovascular and metabolic responses to intermittent umbilical cord occlusion in the preterm ovine fetus

OBJECTIVE

To determine the cardiovascular and metabolic responses to umbilical cord occlusion in the preterm ovine fetus and the impact of repetitive intermittent insults over a 4-day period.

METHODS

Repetitive umbilical cord occlusions (experimental group, n = 7; control group, n = 7) were performed daily (112-115 days' gestation, term = 147 days). Mean arterial pressure (MAP), fetal heart rate (FHR), and FHR variation were monitored, and arterial blood was sampled at predetermined intervals.

RESULTS

During umbilical cord occlusions, arterial oxygen pressure (PaO2) (approximately 17 mmHg) and glucose (approximately 0.3) millimoles per liter (mmol/L) fell and arterial carbon dioxide pressure (approximately 8 mmHg) rose (P < .01) to a similar extent on days 1 and 4. Umbilical cord occlusion produced a rise in lactate over the course of successive umbilical cord occlusions each day, the magnitude of which tended to be reduced by day 4 (0.3 +/- 0.1 versus 0.6 +/- 0.1 mmol/L). Control hour FHR and MAP were unaltered over the 4 days, but the delta (delta) FHR to delta PaO2 ratio during umbilical cord occlusions was less on day 4 than on day 1 (6.0 +/- 0.4 versus 10.9 +/- 1.5 beats per minute/mmHg; P < .01). During occlusion hours, high FHR variation episodes, as a measure of fetal activity, were reduced (14.6 +/- 1.5 versus 4.2 +/- 1.3 min/h; P < .01), whereas the reduction in short-term (7.4 +/- 0.7 to 5.8 +/- 0.6 milliseconds; P < .05) and long-term (34.9 +/- 2.7 to 30.0 +/- 0.6 milliseconds; P < .05) FHR variation reached significance only on day 4.

CONCLUSION

The increase in lactate and reduced high-FHR variation episodes over successive umbilical cord occlusions may affect fetal growth and development. Furthermore, repeated umbilical cord occlusions over several days alter the preterm FHR response to subsequent stresses, suggesting an altered chemoreflex response.

The effect of varus tilt on contact stresses in total knee arthroplasty: a biomechanical study

The contact stress produced in the tibiofemoral joint from a varus-tilted tibial component was tested in five total knee prostheses. Peak and mean stresses were measured with a digital electronic sensor under compressive load at 15 degrees and 90 degrees flexion. Stresses were measured with the tibial component tilted 0 degrees and 5 degrees in the mediolateral direction. At a 5 degree tilt, the Advantim, the Miller-Galante II, and the Omnifit prostheses, which have a flat configuration on the femoral and tibial surfaces in the coronal plane, had significantly greater stresses than the LCS and the Profix prostheses, which have tibial and femoral components with matching curved surfaces in the coronal plane. These results suggest that the femoral component surface should have a radius of curvature that matches that of the tibial articular surface in the coronal plane to achieve a large contact area even in varus-valgus tilting.

Altered fetal cardiovascular responses to prolonged hypoxia after sinoaortic denervation

This study examines the role of the peripheral chemoreceptors in mediating fetal cardiovascular responses to prolonged hypoxia secondary to reduced uterine blood flow (RUBF). Fetal sheep were chronically instrumented for continuous heart rate (FHR), blood pressure (FBP), and carotid blood flow (CBF) measurements after bilateral sectioning of the carotid sinus and vagus nerves (denervated, n = 7) or sham denervation (intact, n = 7). Four days postoperatively, uterine blood flow was mechanically restricted, reducing fetal arterial oxygen saturation by 47.3% (P < 0.01). An initial bradycardia was observed in intact (184.0 +/- 10.7 to 160.5 +/- 10.7 beats/min, not significant) but not denervated fetuses, followed by a tachycardia (180.0 +/- 2.2 to 193.7 +/- 2.7 beats/min, P < 0.05). FHR increased in denervated fetuses (175.5 +/- 8.7 to 203. 0 +/- 17.9 beats/min, P < 0.05). FBP increased transiently in intact fetuses from 45.1 +/- 1.0 to 55.4 +/- 3.0 mmHg at 2 h (P < 0.01), whereas denervated fetuses demonstrated a decrease in FBP from 47.1 +/- 4.2 to 37.2 +/- 3.7 mmHg (not significant). CBF increased (P < 0. 05) in both intact and denervated fetuses from 39.3 +/- 2.8 and 29.7 +/- 3.8 ml. min-1. kg-1 to 47.7 +/- 0.4 and 39.1 +/- 0.3 ml. min-1. kg-1, respectively, whereas carotid vascular resistance decreased only in denervated fetuses (1.7 +/- 0.1 to 1.1 +/- 0.02 mmHg. ml-1. min. kg-1, P < 0.05). We conclude that the peripheral chemoreceptors play an important role in mediating fetal cardiovascular responses to prolonged RUBF.

Knee stability in meniscal bearing total knee arthroplasty

The effect of a meniscal bearing on knee laxity in anterior cruciate ligament-sacrificing total knee arthroplasty was evaluated in 7 cadaver knees using a knee testing device that measured knee flexion angle as well as laxity to medial-lateral, anterior-posterior [AP], and rotational loads. A standard fixed tibial component and mobile tibial components (AP sliding, rotationally sliding, and AP and rotationally sliding) were used to evaluate AP, rotational, and varus-valgus stability and maximal flexion and extension with the neutrally positioned and malrotated tibial tray. The AP movable components increased AP laxity, and the fixed component decreased rotational laxity significantly when compared with the normal knees. The rotationally movable components did not change knee laxities significantly even when the tibial tray was malrotated. No significant difference among the components was detected when the maximal flexion and extension angles were compared in the neutrally positioned tibial tray. Malrotation of the tibial tray decreased the maximal extension angle in the fixed component. This study showed that the rotationally movable component can achieve near-normal laxity regardless of tibial tray rotation, but AP mobility of the bearing produces AP laxity that could lead to implant failure.

Prostaglandin E2 inhibition of fetal breathing movements is not sustained during prolonged reduced uterine blood flow in sheep

Fetal breathing movements (FBM) are inhibited by both exogenous prostaglandin E2 (PGE2) and ethanol in sheep. Maternal ethanol exposure in late-gestation sheep also increases fetal [PGE2]. However, during prolonged reduced uterine blood flow (RUBF) when [PGE2] in fetal plasma is already elevated, FBM are not inhibited by ethanol. These experiments were designed, therefore, to test the hypothesis that the FBM response to PGE2 is also diminished during RUBF. PGE2 (594+/-19 ng.min(-1).kg(-1) fetal body weight) was infused for 6 h into the jugular vein of RUBF (PO2 = 14+/-1 mmHg (1 mmHg = 133.3 Pa); n = 7) and control (PO2 = 22+/-1 mmHg (p < 0.01); n = 7) ovine fetuses, and the effect on FBM, electrocortical (ECoG), and electroocular activities was determined. The infusion of PGE2 increased plasma [PGE2] from 881+/-162 to 1189+/-114 pg.mL(-1) in RUBF fetuses and from 334+/-72 to 616+/-118 pg.mL(-1) (p < 0.05) in control fetuses. FBM were initially inhibited by PGE2 from 22.5+/-9.4 and 17.9+/-6.5% of the time to 6.9+/-2.4 and 0.5+/-0.4% (p < 0.01) in RUBF and control fetuses, respectively. FBM remained inhibited in control fetuses throughout the infusion but returned to baseline incidence in RUBF fetuses in the last 2 h of the infusion. These results are consistent with the hypothesis that one component of the adaptative mechanisms of the fetus to prolonged RUBF is an altered response of FBM to exogenous PGE2. We speculate that the lack of a sustained inhibition in FBM during RUBF with infusion of PGE2 may be a result of an alteration in brainstem receptor function or number or local PGE2 removal.

Multivariate prediction of skeletal Class II growth

Prediction of craniofacial growth is one of the keys to successful orthodontic treatment and stability. Despite numerous attempts at growth forecasting, our ability to accurately predict growth is limited. The present study outlines a possible new approach to prediction of craniofacial growth that differs from any previous attempt because of both the methods used and type of patients studied. The purpose of this study is to create and test prediction equations for forecasting favorable or unfavorable patterns of growth in skeletal Class II preadolescents. The subjects for this study include 19 females and 12 males from the Bolton growth center in Cleveland, Ohio. The patients were all untreated orthodontically, had lateral cephalometric headfilms taken biannually from the ages of 6 through 18 and had a Class II skeletal relationship at age 8. Twenty-six skeletal and dental landmarks were identified and digitized, and 48 linear, angular, and proportional measurements were calculated. The subjects were divided into two groups based on anterior-posterior changes in the relationship between the maxilla and mandible. Eleven patients were in the favorable growth group, with an average improvement of 4.13 degrees in the ANB angle; 20 patients were in the unfavorable growth group with an average increase of 0.16 degrees in the ANB angle. The following prediction formula was created with Bayes theorem and assuming a multivariate Gaussian distribution: P(Good¿Fn) = ke (-(0.5)) ¿Fn - mu(ng)¿sigma(g)(-1)¿Fn - mu(ng)¿T. The equation's sensitivity and specificity was calculated from serial cephalometric data from ages 6, 8, 10, and 12. The results obtained with this equation indicate 82.2% sensitivity, 95% specificity with a overall positive predictive value of 91%. This corresponds to 17.8% of patients being incorrectly identified as Poor Growers and only 5% of our patients were incorrectly identified as Good Growers. We conclude that this prediction formula improves the ability to predict favorable or unfavorable patterns of growth in this sample of skeletal Class II preadolescents.

Contact stress analysis in meniscal bearing total knee arthroplasty

The effect of a mobile meniscal bearing on tibiofemoral contact stress was tested with a standard fixed tibial component and with movable tibial components (anteroposterior sliding, rotationally sliding, and anteroposterior and rotationally sliding). A digital electronic sensor was used to detect tibiofemoral contact location in five cadaver knees, then the location was reproduced while peak and mean stresses were measured under compressive load at 0 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion. Stresses were measured when the tibial component was normally aligned and at 15 degrees internal and 15 degrees external rotation. To evaluate the effect of excessive overhang of the polyethylene articular surface, undersurface stress of the rotationally sliding component was also measured with a 30 degrees and a 45 degrees malrotated tibial tray. Uppersurface stresses of the fixed-bearing components were significantly higher at full extension than those recorded in components with rotational mobility. Undersurface stresses were always lower than uppersurface stresses, but correlated with uppersurface stresses. Undersurface stresses of the rotationally sliding component gradually increased as the malrotation angle of the tray increased. A mobile meniscal bearing surface appears to offer an advantage over a standard fixed component when rotational malalignment of the tibial component occurs. However, with severe rotational malalignment, edge contact markedly increases undersurface stresses, which could cause deformity and subluxation.

Effect of partial release of the posterior cruciate ligament in total knee arthroplasty

Appropriate tension of the posterior cruciate ligament, which often is tight in deep flexion, is difficult to achieve after posterior cruciate ligament retaining total knee arthroplasty. Kinematics and maximum flexion after partial release of the posterior cruciate ligament were evaluated in this study. A partial release improved the maximum flexion angle and maintained anteroposterior stability without causing undesirable changes in kinematics, whereas full resection of the posterior cruciate ligament caused unfavorable anteroposterior instability. Partial posterior cruciate ligament release eliminated excessive rollback movement caused by a tight posterior cruciate ligament and also shifted the point of articular surface contact anteriorly. These results indicate that partial release of the posterior cruciate ligament may improve knee function in patients with a tight posterior cruciate ligament after total knee arthroplasty.

Fetal endocrine responses to prolonged reduced uterine blood flow are altered following bilateral sectioning of the carotid sinus and vagus nerves

The present study examines the effect of carotid sinus/vagosympathetic denervation on fetal endocrine responses to prolonged reduced uterine blood flow (RUBF). Fetal sheep had vascular catheters inserted following bilateral sectioning of the carotid sinus and vagus nerves (denervated, n = 7) or sham denervation (intact, n = 7). Uterine blood flow was mechanically restricted at 126.1 +/- 0.7 days (mean +/- S.E.M.) for 24 h, decreasing arterial oxygen saturation by 47.3 +/- 2.6% (P < 0.01). Fetal plasma samples were obtained at -1, 3, 6, 12 and 24 h for subsequent analyses of arginine vasopressin (AVP), angiotensin II and catecholamines. The AVP response to prolonged RUBF was markedly attenuated in denervated fetuses (15.6 +/- 3.6 to 34.9 +/- 6.0 pg/ml) when compared with intact (10.0 +/- 1.4 to 127.3 +/- 28.4 pg/ml). In contrast, intact fetuses demonstrated no change in plasma angiotensin II concentrations with RUBF whereas denervated fetuses demonstrated a marked increase from 47.5 +/- 18.9 to 128.7 +/- 34.2 pg/ml. The norepinephrine and epinephrine responses to prolonged RUBF were attenuated in denervated fetuses (950.1 +/- 308.9 and 155.8 +/- 58.5 to 1268.3 +/- 474.6 and 290.6 +/- 160.2 pg/ml respectively) when compared with intact (1558.3 +/- 384.4 and 547.3 +/- 304.7 pg/ml to 3289.2 +/- 1219.8 and 896.8 +/- 467.8 pg/ml respectively). These results support a role for the peripheral chemoreceptors in mediating fetal endocrine responses to prolonged RUBF, which may in part lead to the altered cardiovascular responses observed in denervated fetuses under these conditions.

Patellofemoral joint after total knee arthroplasty. Effect on contact area and contact stress

Compressive contact stress between the patella and the anterior femur and between the quadriceps tendon and anterior femur was measured before and after total knee arthroplasty in 5 cadaver knee specimens using a digital electronic sensor. Contact stresses were measured in the normal knee and after total knee arthroplasty with an unresurfaced patella, a dome-shaped patella, and a conforming patella. Patellofemoral contact stresses did not change significantly after total knee arthroplasty when the patella was not resurfaced, but they increased significantly after the patella was resurfaced with both the dome-shaped and the conforming components. The conforming patella had the highest contact stresses because it tilted at flexion angles greater than 90 degrees and applied load to a small area on the superior portion of the patellar component. The conforming patella markedly decreased tendofemoral contact force because the thicker superior pole of the patella tented the quadriceps tendon at flexion angles greater than 120 degrees. This further increased patellofemoral contact force in deep knee flexion.

Knee kinematics of posterior cruciate ligament sacrificed total knee arthroplasty

Two different posterior stabilizing mechanisms in posterior cruciate ligament sacrificing total knee arthroplasty were evaluated to test knee kinematics, tibiofemoral contact location, and the quadriceps force needed to extend the knee. A posterior stabilizing post and a deeply dished polyethylene with a high anterior lip (anterior buildup stabilizing tibial articular surface) were tested in four anatomic specimen knees with a knee kinematics testing device. Both posterior stabilizing mechanisms partially restored anteroposterior stability, but the knees were still more lax than were the normal knees in the anteroposterior direction. The anterior buildup stabilizing tibial articular surface decreased rotational laxity in early flexion. Tibiofemoral contact location in the knees with the anterior buildup stabilizing tibial articular surface did not move posteriorly as the knee flexed, and the knees with this articular surface required significantly more quadriceps force to extend the knee than did the knees with a stabilizing post.

Failure of magnesium sulfate infusion to inhibit uterine activity in pregnant sheep

OBJECTIVES

Our purpose was to determine the effect of magnesium sulfate infusion on nonlabor uterine contractures and corticotropin-induced preterm uterine contractions in pregnant sheep.

STUDY DESIGN

Fetal and maternal vascular catheters and uterine electromyographic electrodes were surgically placed in 15 pregnant sheep between 118 and 125 days' gestation. After 3 to 5 days of recovery, magnesium sulfate was infused into 7 ewes with a 0.11 gm/kg bolus over 20 minutes, followed by 0.08 gm/kg/hr. In 8 animals labor was induced with use of an intrafetal corticotropin infusion, after which 4 ewes received magnesium sulfate and 4 received saline solution. Continuous recordings of uterine electromyographic activity, amniotic pressure, fetal heart rate, blood pressure, and tracheal pressure were made. Maternal and fetal magnesium, calcium, albumin concentrations, and blood gases were determined before and during the infusion.

RESULTS

Maternal magnesium concentrations increased from an average of 0.94 +/- 0.03 mmol/L to 2.73 +/- 0.1 mmol/L at the end of the bolus, remaining elevated (2.44 +/- 0.17 mmol/L) for 8 hours. Fetal magnesium concentrations (0.89 +/- 0.03 mmol/L before the bolus) did not change with the maternal infusion. In ewes not in labor, uterine contractures occurred 3.7 +/- 0.7 times per 2 hours before and did not change significantly with the infusion of magnesium sulfate. During corticotropin-induced preterm labor uterine contractions were present 13 +/- 3.2 times per hour before infusions and were unchanged by infusion of magnesium sulfate to the ewes.

CONCLUSIONS

Magnesium sulfate infusion in pregnant sheep has no effect on either nonlabor uterine contractures or on corticotropin-induced preterm uterine contractions.

Sarcoidosis in a pregnant woman

Sarcoidosis, a rare multisystem disease, often occurs in women of childbearing age. The disease, which may be improved or exacerbated by pregnancy, presents unique considerations to the anesthesiologist. These considerations are illustrated by the case presented here of complicated sarcoidosis in a parturient who underwent cesarean section.

Intramuscular atropine sulfate in children: comparison of injection sites

In children undergoing inhaled induction of anesthesia with halothane who suffer bradycardia, submental glossal injection of atropine may result in more rapid onset of vagolysis than traditional intramuscular sites. We compared the intervals between injection and onset of heart rate acceleration (tHR increases) after intramuscular injection of atropine into the deltoid, vastus lateralis, and glossa in children between 1 mo and 10 yr of age scheduled for elective surgery. The tHR increases was determined by measuring the interval between atropine injection and the time point at which the slope of the heart rate curve initially became positive. To ensure that the drug had taken effect before surgical stimulation, heart rate observation was continued until it increased at least 5% above baseline with evidence of continuing acceleration. Anesthesia was induced in all subjects by mask with nitrous oxide and halothane. After tracheal intubation, constant inspired concentrations of the anesthetics were administered for 3 min. While heart rate was monitored, atropine (0.02 mg/kg) was injected into one of the three sites. Each patient's end-tidal anesthetic concentrations were recorded, and minimum alveolar anesthetic concentrations (MAC) were subsequently calculated and adjusted for age. The tHR increases was recorded and averaged for each group. The study groups did not differ by age, weight, end-tidal anesthetic concentrations, age-adjusted MAC, or heart rate at the time atropine was administered. After submental glossal injection (n = 11), tHR increases increase was fastest (3.0 +/- 1.1 min) and was significantly faster than that found with deltoid injection (n = 16; 4.4 +/- 1.1 min) or vastus lateralis injection (n = 8; 6.4 +/- 2.4 min) (P < 0.05 compared with both). The tHR increases also differed significantly between the deltoid and the vastus lateralis (P < 0.05). We conclude that submental glossal injection of atropine results in a more rapid onset of vagolysis than injection at traditional intramuscular sites.

Fixation of ultrahigh-molecular-weight polyethylene liners to metal-backed acetabular cups

Locking mechanisms and metal-liner interface surfaces of six modular acetabular systems were evaluated to determine their effect on micromotion and backside wear of the polyethylene liner. Rotational and axial motion between the metal shell and polyethylene liner was measured in the Duraloc (DePuy, Warsaw, IN), Harris-Galante (Zimmer, Warsaw, IN), Impact (Biomet, Warsaw, IN), Lip Loc (Biomet), Precision Osteoloc (Howmedica, Rutherford, NJ), and Reflection (Smith & Nephew Orthopaedics, Memphis, TN) designs at the start of each test, and at 1 million, 5 million, and 10 million cycles. At 10 million cycles, the Lip Loc and Reflection cups had significantly lower rim micromotion than the Duraloc and Harris-Galante cups (F < .0010). The Impact, Precision Osteoloc, and Reflection cups had significantly lower rim subsidence than the Harris-Galante cup (F < .0025). The Harris-Galante cup had significantly greater rotational micromotion than the Lip Loc cup (F < .0074), and had significantly greater interface slippage than the Impact and Reflection cups (F < .0070). The Lip Loc produced significantly lower dome micromotion than the Harris-Galante (F < .0300). The Lip Loc and Reflection cups had significantly less backside wear than the Duraloc and Harris-Galante cups (P < .0001), the Impact cup (P < .0243), and the Precision Osteoloc (P < .0027) cup.

Egg production by Strelkovimermis spiculatus (Nematoda:Mermithidae)

Egg production by the mermithid nematode Strelkovimermis spiculatus, a parasite of mosquitoes, was examined over a period of 34 days. Oviposition did not occur in the absence of males. Egg production was best when males were continuously present (6.4 x 10(3) +/- 0.9 x 10(3) eggs/female). Fewer eggs were produced when males were removed after 7 days (2.8 x 10(3) +/- 0.2 x 10(3) eggs/female) and oviposition partially recovered after males were returned 11 days later (4.4 x 10(3) +/- 0.5 x 10(3) eggs/female). The nematodes deposited substantially more eggs in sand (6.4 x 10(3) +/- 0.9 x 10(3)/female) than in water (1.9 x 10(3) +/- 0.3 x 10(3)/(female).

Effects of sterilization on wear in total knee arthroplasty

Twenty-nine Ortholoc II ultrahigh molecular weight polyethylene tibial components were retrieved from 27 patients at revision surgery from the same hospital. The polyethylene material grade, method of sterilization, and sterilization dosage for 26 of the tibial components were determined by tracing the material lot number for each component. Each tibial surface was scored for wear using a qualitative scoring system that evaluated delamination, pitting, scratching, cold flow, abrasion, and burnishing. After the wear score analysis, 14 of the 26 components were analyzed to determine the physical and mechanical properties of the polyethylene including toughness and elongation. Seven of these 14 components were sterilized using ethylene oxide and 7 were sterilized using gamma radiation. Tibial components sterilized with gamma radiation had significantly higher wear rates than those sterilized with ethylene oxide. Thirteen of the 18 components sterilized with gamma radiation had delamination of the articular surface compared with 2 of 8 components sterilized with ethylene oxide. Mechanical properties were significantly affected by the sterilization method. Components sterilized with ethylene oxide had significantly higher toughness and percent elongation than those sterilized with gamma radiation. These findings suggest that ethylene oxide sterilization caused less microstructural damage to the polyethylene and resulted in significantly less wear than was found in those components sterilized with gamma radiation.

Fetal breathing is not inhibited by ethanol exposure during prolonged reduced uterine blood flow

When prolonged hypoxemia is induced in fetal sheep by reducing uterine blood flow, fetal breathing movements (FBM) return to normal incidence after their initial decrease. Ethanol also inhibits FBM. These experiments were designed to determine the role of fetal oxygenation status in affecting ethanol-induced inhibition of FBM. A 1-h maternal infusion of 1 g ethanol/kg maternal body weight was given to animals following 20 h of reduced uterine blood flow (RUBF; n = 9), as well as to normoxemic (n = 9) fetal sheep, and the effect on FBM, electrocortical activity (ECoG), and electroocular activity (EOG) was determined. In normoxemic fetuses, the incidence of FBM decreased from 26.1 +/- 5.5% to 2.8 +/- 1.6% (p < 0.05) with ethanol, subsequently returning to baseline values over 6 h, but there was no effect of ethanol on FBM incidence in RUBF fetuses (32.8 +/- 9.1%). Ethanol increased the incidence of intermediate ECoG from 16.6 +/- 2.9% to 49.0 +/- 9.8% (p < 0.01) in normoxemic fetuses, but there was no change in RUBF fetuses. We conclude that the adaptive mechanism(s) invoked by fetal sheep during prolonged RUBF abolishes its ability to respond behaviourally to ethanol.

Rotational stability of noncemented total hip femoral components

Achieving torsional fixation of the femoral component in total hip arthroplasty is an important factor in success of the implant, so design features that improve fixation are likely to improve clinical results. Four femoral stem designs that allow different levels of femoral neck resection and use different distal fixation techniques were mechanically tested in cadaveric femurs to determine resistance to torsional loads. Five specimens for each stem design were implanted according to the standard procedure, and each was axially and torsionally loaded in a servohydraulic testing machine. Rotational interface micromotion and interface slippage were measured at the bone-implant interface. Decreased micromotion and interface slippage were associated with a distal scratch fit and neck retaining design, and the combination of distal scratch fit and neck retention had the least micromotion and smallest standard deviation of the four designs.

Effect of medial displacement of the tibial tubercle on patellar position after rotational malposition of the femoral component in total knee arthroplasty

A large Q angle induced by technical error such as an internally rotated femoral component causes patellar failure after total knee arthroplasty. The effect of medial displacement of the tibial tubercle to decrease the Q angle for patellar tracking was studied by evaluating the patellar position relative to the patellar groove on the femoral component in cadaver specimens. A 5 degrees internally rotated femoral component caused the patella to shift medially about 5 mm, and also caused the tibia to rotate internally about 3 degrees at full extension. With a 5 degrees externally rotated femoral component, normal patellar tracking occurred. The distance of medial displacement was determined so that the patellar tendon was parallel to the longitudinal axis of the tibia at full extension. This allowed the quadriceps tendon, the patella, and the patellar tendon to form a straight line. The average distance of medial transposition of the tibial tubercle was 9.32 mm. Medialization of the tibial tubercle caused the patella to shift about 2 mm medially from the patellar groove. The transfer also caused an external rotation of the tibia (2 degrees-5 degrees). Medial transfer of the tibial tubercle changes patellar kinematics and corrects the tendency toward lateral patellar dislocation caused by internally rotating the femoral component; however, it also creates minor patellar and tibial kinematic changes that may have a clinical effect.

Effect of prolonged catecholamine infusion on heart rate, blood pressure, breathing, and growth in fetal sheep

Norepinephrine and epinephrine were infused into fetal sheep for 24 h to compare the effects on fetal heart rate, blood pressure, breathing movements, and tissue growth with those of prolonged reductions in uterine blood flow. Norepinephrine concentrations increased (p < 0.01) from 871 +/- 71 to 6831 +/- 1090 pg/mL (2 h) with norepinephrine infusion, and epinephrine concentrations increased from 310 +/- 95 to 1424 +/- 288 pg/mL (2 h) with epinephrine infusion. Fetal pH decreased (p < 0.01) from 7.37 +/- 0.01 to 7.29 +/- 0.02 at 0.5 h of the norepinephrine infusion and returned to control values by 2 h, whereas fetal lactate concentrations increased (p < 0.05) from 1.6 +/- 0.2 to 4.6 +/- 1.0 mmol/L at 2 h and remained elevated for 12 h. Lactate concentrations also increased with epinephrine infusion. Fetal heart rate increased (p < 0.05) from 176 +/- 5 to 246 +/- 6 and 220 +/- 6 beats/min in the 1st h of norepinephrine and epinephrine infusions, respectively, with a subsequent decline. Fetal blood pressure increased (p < 0.05) from 43 +/- 3 and 40 +/- 2 to 53 +/- 3 and 47 +/- 2 mmHg (1 mmHg = 133.3 Pa) during the 1st h of norepinephrine and epinephrine infusions, respectively, remaining elevated for 24 h. Fetal body weights were not different between the groups of animals, although liver/body weight ratio was less (p < 0.05) in epinephrine-infused fetuses (0.030 +/- 0.001) compared with vehicle-infused animals (0.036 +/- 0.002). There was no change in DNA synthesis rate in any of the fetal organs, despite changes in organ-specific DNA and protein content. Our results indicate that the changes in fetal cardiovascular and behavioural function, as well as tissue growth, that occur with prolonged reductions in uterine blood flow are not mediated solely by elevated circulating catecholamine concentrations.

LTR-retrotransposons and MITEs: important players in the evolution of plant genomes

Retrotransposons are an abundant and ancient component of plant genomes, yet recent evidence indicates that element activity in many modern plants is restricted to times of stress. Stress activation of plant retrotransposons may be a significant factor in somaclonal variation, in addition to providing an important means to isolate new active elements. Long terminal repeat retrotransposons and a second class of elements we have called miniature inverted-repeat transposable elements (MITEs) have recently been found to be associated with the genes of diverse plants where some contribute regulatory sequences. Because of their sequence diversity and small size, MITEs may be a valuable evolutionary tool for altering patterns of gene expression.

Effect of neck resection on torsional stability of cementless total hip replacement

Loosening of the femoral component in total hip arthroplasty commonly results from inadequate resistance to torsional loads. We evaluated 20 adult human cadaver femora to determine the effect of different neck-resection levels on torsional resistance of the femoral component. All specimens were prepared for fixation with the Impact modular total hip replacement. Each femoral diaphysis was overreamed 2 mm to achieve only proximal fixation. The specimens were then divided into groups of five and implants were inserted with the precision press-fit technique. Each specimen was loaded in an Instron stress-testing device. A linearly variable differential transducer was then attached to the specimen to measure micromotion at the medial interface between the implant and bone. Each specimen was loaded until failure occurred. When all of the neck was preserved, torsional load to failure was significantly better than in the 50%, 15%, and 0% neck-preservation specimens. At a 20 N-m torsional load, the 100% and 50% neck preservation specimens had similar micromotion, but the 15% and 0% specimens had gross motion and a large standard deviation at this load level. Without distal fixation, the femoral component is highly dependent on proximal geometry for resistance to torsional loading. Preserving the femoral neck provides an effective means of resistance. Maintaining the entire femoral neck most effectively reduces miromotion at low loads, but maintaining the midshaft area of the femoral neck appears to most effectively control micromotion at higher torsional loads. Resection below the midshaft of the neck markedly decreases the torsional load-bearing capacity of the proximal femur.

Femoral rotational alignment, based on the anteroposterior axis, in total knee arthroplasty in a valgus knee. A technical note

The landmarks used to achieve correct rotational alignment of the femoral component in total knee arthroplasty may be indistinguishable or unreliable in the distal architecture of a valgus knee. Five observers identified the anteroposterior axis, the posterior condylar axis, and the transepicondylar axis in thirty cadaveric femora to determine the reliability of the use of each axis in the operative setting. In addition, radiographs were made of the distal aspect of each femur, the axes were constructed, and the angles were measured and compared with the visual measurements made by the observers. A line drawn perpendicular to the anteroposterior axis consistently approximated 4 degrees of external rotation relative to the posterior condylar surfaces. The transepicondylar axis was more difficult to define and was not as accurate. The radiographic results were similar to the visual results, but the standard deviations for the former were less than those for the latter. The anteroposterior axis appears to be a reliable landmark for rotational alignment of the femoral component in a valgus knee.

Effect of polyethylene quality on wear in total knee arthroplasty

During evaluation of 29 Ortholoc II tibial polyethylene components retrieved at revision surgery, the authors noticed that components with a lot number prefix of CP (Custom Product) consistently had minimal wear and those with a standard lot number had severe wear, regardless of patient age, weight, gender, and activity level. Non-CP components had earlier and more severe wear than CP components in service for the same amount of time. Microscopic evaluation of the polyethylene revealed major differences in the material. Large subsurface cracks, fusion defects, and intergranular cracks were present in the non-CP components, but these defects were minimal or nonexistent in the CP components. The components with defects had a significantly greater delamination rate than those without defects. Gamma irradiation did not seem to accelerate wear or delamination, because irradiated components that had minimal microscopic signs of fusion defects performed as well as nonirradiated components with a similar microscopic appearance. The manufacturing details disclosed that different materials and processing methods were used for the 2 groups. The results from this study suggest that improved quality control of polyethylene material would greatly decrease wear and delamination of total knee arthroplasty components.

Effect of rotational malposition of the femoral component on knee stability kinematics after total knee arthroplasty

Excessive external rotation of the femoral component can cause an abnormally tight popliteus tendon complex, which induces loss of rotational laxity of the knee in the late phase of knee flexion after total knee arthroplasty. This study evaluated the effect of popliteus tendon release on rotational and varus-valgus laxity of implanted knees with an excessively externally rotated femoral component. Rotational and varus-valgus laxity was measured with a knee kinematics testing device before and after total knee arthroplasty. External rotational positions of the femoral component of 5 degrees and 8 degrees were compared, and the effects of popliteus tendon release on rotational and varus-valgus laxity were evaluated. To further investigate this question, the effect of a conforming articular design was compared with that of a flat tibial surface. External rotational position of 5 degrees did not change rotational or varus-valgus laxity of the knee. With an 8 degrees external rotational position, however, external rotational laxity significantly decreased in knees with a conforming surface at angles of 30 degrees, 45 degrees, 60 degrees, and 90 degrees. After popliteus tendon release, external rotational laxity significantly improved at 90 degrees flexion and was identical to that of the normal knee. Internal rotational range was similar before and after popliteus tendon release. Popliteus tendon release did not affect the varus-valgus laxity (stability) with either articular surface.

Reaming technique of the femoral diaphysis in cementless total hip arthroplasty

Distal fixation enhances initial torsional stability of cementless femoral components in primary and revision total hip arthroplasty. Surgical technique affects the quality of distal fixation, and too aggressive a technique can cause femoral fracture during insertion of the stem. Thirty-five adult human cadaveric femoral specimens were implanted with either a standard or long femoral stem. Control specimens were reamed 0.5 mm less than the diameter of the distal cylindrical portion of the stem and were broached line to line proximally. The proximal femur was removed from the remaining specimens to allow assessment of distal fixation. The controls outperformed the distal-only fixation groups in all testing modes, illustrating that proximal and distal fixation work in concert to resist torsional load. The average failure torque in underreamed specimens with only distal fixation was 23.6 Nm for standard length stem specimens and 41.3 Nm for long stem specimens, whereas the average failure torque for specimens with only distal fixation prepared by a line-to-line reaming technique was only 6 Nm. The estimated length of tight distal fit should be 10 to 40 mm to obtain sufficient initial torsional stability of the stem and still avoid intraoperative femoral fracture.

Placental and fetal hepatic growth are selectively inhibited by prolonged reductions of uterine blood flow in pregnant sheep

Experiments were conducted in eight pregnant sheep to determine the effect on fetal growth of mechanical restriction of uterine blood flow (RUBF) between 120 days and 134 days gestation. Uterine blood flow measured in the middle uterine arteries was 40% less in RUBF animals compared with control animals at the end of the experimental period. There was no change in fetal blood gases, bodyweights, or organ weights between the two groups of animals. The rate of DNA synthesis in the right lobe of the liver was significantly less in RUBF animals (581 +/- 34 dpm micrograms-1 DNA) compared with control animals (845 +/- 44 dpm microgram-1 DNA). There was no difference in the rate of DNA synthesis in the left lobe of the liver or in any of the other organs examined. Autoradiographic examination of the placental cotyledons demonstrated that most DNA synthesis in the placenta was occurring in fetal trophoblastic cells and there was a 40% reduction in the nuclear-labelling index of placental trophoblast cells. These studies show that mild mechanical reductions in uterine blood flow in pregnant sheep results in the selective inhibition of growth in the right lobe of the fetal liver and the placental trophoblastic cells. The mechanism underlying this close association remains to be determined.

Patellar tracking measurement in the normal knee

Eleven fresh frozen cadaveric knee specimens were mounted in a knee kinematics test device, and normal patellar movements were evaluated with use of an external device for direct measurement of patellar movements. The effects of four different measurement conditions were assessed through alteration of one condition and determination of its effect on patellar kinematics with the use of six specimens. The four conditions included (a) change of the measuring axis from an axis parallel to the central axis of the femur (femoral axis) to one parallel to the central axis of the tibia (tibial axis), (b) rotation of the femoral axis internally 6 degrees, (c) change of the direction of the quadriceps force from parallel to the mechanical line of the lower extremity to a direction parallel to the femoral shaft, and (d) increase of the magnitude of the quadriceps force from 111 to 500 N. During knee flexion, the patella shifted laterally after a slight initial medial shift, tilted laterally from midflexion to 90 degrees, and gradually rotated medially. The patellar shift relative to the tibial axis appeared to be more medial than the shift measured relative to the femoral axis; the discrepancy was caused by the valgus position of the tibia relative to the femur. Changing the rotational angle of the femoral axis artificially changed the patellar position. Varying the direction of the quadriceps within the narrow range and increasing the quadriceps force did not affect patellar movements.(ABSTRACT TRUNCATED AT 250 WORDS)

Retrotransposons in the flanking regions of normal plant genes: a role for copia-like elements in the evolution of gene structure and expression

The wx-K mutation results from the insertion of a copia-like retrotransposon into exon 12 of the maize waxy gene. This retrotransposon, named Hopscotch, has one long open reading frame encoding all of the domains required for transposition. Computer-assisted database searches using Hopscotch and other plant copia-like retroelements as query sequences have revealed that ancient, degenerate retrotransposon insertions are found in close proximity to 21 previously sequenced plant genes. The data suggest that these elements may be involved in gene duplication and the regulation of gene expression. Similar searches using the Drosophila retrotransposon copia did not reveal any retrotransposon-like sequences in the flanking regions of animal genes. These results, together with the recent finding that reverse-transcriptase sequences characteristic of copia-like elements are ubiquitous and diverse in plants, suggest that copia-like retrotransposons are an ancient component of plant genomes.