A Percutaneous Technique for Reduction and Internal Fixation of Displaced Intra-Articular Calcaneal Fractures.

INTRODUCTION: A retrospective cohort study demonstrated that, in comparison with open reduction and internal fixation through an extensile lateral approach, our percutaneous technique for reduction and internal fixation of displaced intra-articular calcaneal fractures decreases the rate of complications and achieves and maintains extra-articular fracture reductions just as well. STEP 1 PATIENT POSITIONING AND IMAGING: Position the patient correctly to obtain excellent fluoroscopic views, which are key to the procedure. STEP 2 FRACTURE REDUCTION: The techniques for reducing and fixing joint depression and tongue-type calcaneal fractures differ and will be described separately. STEP 3 SCREW FIXATION: Identify screw entry points and paths using fluoroscopic images, and confirm the final positions with c-arm imaging. STEP 4 POSTOPERATIVE MANAGEMENT: Apply a splint; then obtain postoperative images to confirm fracture reduction and screw placement. RESULTS & PREOP/POSTOP IMAGES: The results of percutaneous reduction of displaced intra-articular calcaneal fractures in seventy-nine patients with a total of eighty-three fractures were compared with those obtained by another surgeon using the extensile lateral approach. WHAT TO WATCH FOR: IndicationsContraindicationsPitfalls & Challenges.

Grain yields with limited water.

Plant reproduction is sensitive to water deficits, especially during the early phases when development may cease irreversibly even though the parent remains alive. Grain numbers decrease because of several developmental changes, especially ovary abortion in maize (Zea mays L.) or pollen sterility in small grains. In maize, the water deficits inhibit photosynthesis, and the decrease in photosynthate flux to the developing organs appears to trigger abortion. Abscisic acid also increases in the parent and may play a role, perhaps by inhibiting photosynthesis through stomatal closure. Recent work indicates that invertase activity is inhibited and starch is diminished in the ovaries or affected pollen. Also, sucrose fed to the stems rescues many of the ovaries otherwise destined to abort. The feeding restores some of the ovary starch and invertase activity. These studies implicate invertase as a limiting enzyme step for grain yields during a water deficit, and transcript profiling with microarrays has identified genes that are up- or down-regulated during water deficit-induced abortion in maize. However, profiling studies to date have not reported changes in invertase or starch synthesizing genes in water-deficient ovaries, perhaps because there were too few sampling times. The ovary rescue with sucrose feeding indicates either that the changes identified in the profiling are of no consequence for inhibiting ovary development or that gene expression reverts to control levels when the sugar stream recovers. Careful documentation of tissue- and developmentally specific gene expression are needed to resolve these issues and link metabolic changes to the decreased sugar flux affecting the reproductive organs.

Growth-induced water potentials originate from wall yielding during growth.

Multicellular plants display growth-induced water potentials that generate tensions on water in the apoplast and move water into the growing cells. The potentials are sometimes assumed to arise from wall yielding, keeping the turgor pressure below what otherwise would occur. There has been no direct test of this theory, and therefore whole plants or growing regions of stems (hypocotyls) of dark-grown soybean (Glycine max L. Merr.) seedlings were sealed in a pressure chamber, and wall yielding was decreased by applying external pressure. In whole plants, external pressure had little effect because the plants and water supply were uniformly exposed to the pressure. If pressure was applied to the stem while the roots were outside in water, stem elongation was markedly inhibited because the pressure raised the water potential of the growing region and decreased water entry, reducing wall yielding. Further increasing the pressure prevented water entry completely and measured the tensions in the apoplast in the same growing regions. Tensions were about 0.19 MPa at low external pressure, but diminished as wall yielding was inhibited. At external pressures of about 0.63 MPa, wall yielding was abolished and tensions approached zero. There was a linear relation between wall yielding and tension, supporting the theory that wall yielding lowers the turgor thus causing most of the growth-induced water potential.

Turgor, temperature and the growth of plant cells: using Chara corallina as a model system.

Rapid changes in turgor pressure (P:) and temperature (T:) are giving new information about the mechanisms of plant growth. In the present work, single internode cells of the large-celled alga Chara corallina were used as a model for plant growth. P was changed without altering the chemical environment of the wall while observing growth without elastic changes. When P: was measured before any changes, the original growth rate bore no relationship to the original P. However, if P of growing cells was decreased, growth responded immediately without evidence for rapid changes in wall physical properties. Growth occurred only above a 0.3 MPa threshold, and increasing P caused small increases in growth that became progressively larger as P rose, resulting in a curvilinear response overall. The small changes in growth close to the threshold may explain early failures to detect these responses. When T was lowered, the elastic properties of the cell were unaffected, but growth was immediately inhibited. The lower T caused P to decrease, but returning P to its original value did not return growth to its original rate. The decreased P at low T occurred because of T effects on the osmotic potential of the cell. At above-normal P, growth partially resumed at low T Therefore, growth required a P-sensitive process that was also T-sensitive. Because elastic properties were little affected by T, but growth was markedly affected, the process is likely to involve metabolism. The rapidity of its response to P and T probably excludes the participation of changes in gene expression.

Photosynthesis during desiccation in an intertidal alga and a land plant.

This study was undertaken to determine how photosynthesis tolerates desiccation in an intertidal alga Fucus vesiculosus L. and a terrestrial sunflower Helianthus annuus L. Photosynthetic O2 evolution generally was inhibited at low water potentials (psiw) but more in sunflower leaves than in Fucus fronds at the same psiw. As psiw decreased, less carbon accumulated in an organic carbon store in Fucus. The inhibition of photosynthesis appeared to be mostly biochemical because it could not be prevented by supplying additional CO2 or by supplying CO2 from the internal organic carbon store. The inhibition of photosynthesis and carbon storage occurred after turgor disappeared and thus when solute concentrations were increasing in the cells. Solute concentrations were much higher in Fucus than in sunflower. After desiccation to the air-dry state (psiw below - 10 MPa), photosynthesis could not recover in sunflower but it recovered rapidly when Fucus was exposed to seawater. The lack of recovery in sunflower was associated with inability to recover turgor probably because of breaks in cell membranes. The ability to recover in Fucus was gradually lost during 1.5 d of desiccation at 45% relative humidity. At lower humidities, recovery was lost sooner as small amounts of water were removed. We conclude that photosynthesis tolerated desiccation more in Fucus than in sunflower because of differences in the molecular environment around the photosynthetic enzymes. Important aspects of this environment were features that prevented membrane breakage but promoted the retention of small amounts of water that were critical for viability.

Starch and the control of kernel number in maize at low water potentials.

After reproduction is initiated in plants, subsequent reproductive development is sometimes interrupted, which decreases the final number of seeds and fruits. We subjected maize (Zea mays L.) to low water potentials (psi(w)) that frequently cause this kind of failure. We observed metabolite pools and enzyme activities in the developing ovaries while we manipulated the sugar stream by feeding sucrose (Suc) to the stems. Low psi(w) imposed for 5 d around pollination allowed embryos to form, but abortion occurred and kernel number decreased markedly. The ovary contained starch that nearly disappeared during this abortion. Analyses showed that all of the intermediates in starch synthesis were depleted. However, when labeled Suc was fed to the stems, label arrived at the ovaries. Solute accumulated and caused osmotic adjustment. Suc accumulated, but other intermediates did not, showing that a partial block in starch synthesis occurred at the first step in Suc utilization. This step was mediated by invertase, which had low activity. Because of the block, Suc feeding only partially prevented starch disappearance and abortion. These results indicate that young embryos abort when the sugar stream is interrupted sufficiently to deplete starch during early ovary development, and this abortion results in a loss of mature seeds and fruits. At low psi(w), maintaining the sugar stream partially prevented the abortion, but invertase regulated the synthesis of ovary starch and partially prevented full recovery.

Sex differences in discriminative stimulus and diuretic effects of the kappa opioid agonist U69,593 in the rat.

Female and male rats were trained to discriminate the kappa opioid agonist (5alpha,7alpha,8beta)-(-)-N-methyl-[7-(1-pyrrolidinyl) -1-oxaspiro(4,5)dec-8-yl]benzeneacetamide (U69,593, 0.13 mg/kg SC) from vehicle using a FR-10 schedule of food reinforcement. Female rats took significantly longer than males to acquire the discrimination (66.9 vs. 44.1 sessions, respectively), and the ED50 for U69,593 discrimination was significantly higher in females than in males (0.074 vs. 0.025 mg/kg). The time course of U69,593 discrimination also differed between the sexes: peak and offset occurred earlier in females than in males. The ED50 for bremazocine substitution was significantly higher in females than in males (0.0039 vs. 0.0006 mg/kg), whereas ethylketazocine substituted for U69,593 in all males and five of seven females, with no sex difference in substitution ED50. Morphine and BW373U86 did not substitute for U69,593 in a majority of rats of either sex. U69,593 also produced significantly less urine output/dose in females compared to males (e.g., 5.92 vs. 14.83 ml urine/kg body weight after 1.0 mg/kg U69,593), but was equipotent between the sexes in producing hot-plate antinociception. There was no sex difference in response rate-decreasing effect of any opioid agonist tested, and no sex difference in brain/blood ratio of [3H]U69,593 measured in a separate group of rats, suggesting that sex differences observed in some effects of U69,593 probably are not due to sex differences in U69,593 pharmacokinetics. When retested at the end of the study, U69,593 and bremazocine were no longer differentially potent as discriminative stimuli in females and males, suggesting that factors that change over time (e.g., additional training, age, hormonal status) may contribute to initial sex differences in discriminability of U69,593.

Microinjection of morphine into the rostral ventromedial medulla produces greater antinociception in male compared to female rats.

The antinociceptive and locomotor effects of microinjecting morphine into the rostral ventromedial medulla (RVM) of male and female rats was assessed. Male rats showed greater antinociception than female rats at all doses and times following morphine administration. Male, but not female rats, also showed a dose dependent decrease in locomotion. These data demonstrate that sex differences in antinociception are mediated at least in part by the RVM.

An automated measurement system for characterization of RF and gradient coil parameters.

A fully automated laboratory-based measurement system for characterization of coil system parameters is presented. This method uses an inexpensive personal computer (PC)-controlled stepper motor positioning system in conjunction with a network/spectrum analyzer and an analog-to-digital converter (A/D) board that allows high resolution data acquisition in an unattended manner. A graphical interface was created for complete control of stepper motor movement, measurement, and data acquisition. The system is capable of performing a wide range of measurements that can, either individually or combined, characterize radiofrequency (RF) and gradient coils used in MRI. Measurement methods, theory, and results for conductor and shield current distributions, mutual impedance, and magnetic fields are given. Comparisons with theoretical calculations are included to validate the accuracy and utility of the system.

Decreased Growth-Induced Water Potential (A Primary Cause of Growth Inhibition at Low Water Potentials).

Cell enlargement depends on a growth-induced difference in water potential to move water into the cells. Water deficits decrease this potential difference and inhibit growth. To investigate whether the decrease causes the growth inhibition, pressure was applied to the roots of soybean (Glycine max L. Merr.) seedlings and the growth and potential difference were monitored in the stems. In water-limited plants, the inhibited stem growth increased when the roots were pressurized and it reverted to the previous rate when the pressure was released. The pressure around the roots was perceived as an increased turgor in the stem in small cells next to the xylem, but not in outlying cortical cells. This local effect implied that water transport was impeded by the small cells. The diffusivity for water was much less in the small cells than in the outlying cells. The small cells thus were a barrier that caused the growth-induced potential difference to be large during rapid growth, but to reverse locally during the early part of a water deficit. Such a barrier may be a frequent property of meristems. Because stem growth responded to the pressure-induced recovery of the potential difference across this barrier, we conclude that a decrease in the growth-induced potential difference was a primary cause of the inhibition.

CO2 and Water Vapor Exchange across Leaf Cuticle (Epidermis) at Various Water Potentials.

Cuticular properties affect the gas exchange of leaves, but little is known about how much CO2 and water vapor cross the cuticular barrier or whether low water potentials affect the process. Therefore, we measured the cuticular conductances for CO2 and water vapor in grape (Vitis vinifera L.) leaves having various water potentials. The lower leaf surface was sealed to force all gas exchange through the upper surface, which was stoma-free. In this condition both gases passed through the cuticle, and the CO2 conductance could be directly determined from the internal mole fraction of CO2 near the compensation point, the external mole fraction of CO2, and the CO2 flux. The cuticle allowed small amounts of CO2 and water vapor to pass through, indicating that gas exchange occurs in grape leaves no matter how tightly the stomata are closed. However, the CO2 conductance was only 5.7% of that for water vapor. This discrimination against CO2 markedly affected calculations of the mole fraction of CO2 in leaves as stomatal apertures decreased. When the leaf dehydrated, the cuticular conductance to water vapor decreased, and transpiration and assimilation diminished. This dehydration effect was largest when turgor decreased, which suggests that cuticular gas exchange may have been influenced by epidermal stretching.

Direct Demonstration of a Growth-Induced Water Potential Gradient.

When transpiration is negligible, water potentials in growing tissues are less than those in mature tissues and have been predicted to form gradients that move water into the enlarging cells. To determine directly whether the gradients exist, we measured water potentials along the radius of stems of intact soybean (Glycine max [L.] Merr.) seedlings growing in vermiculite in a water-saturated atmosphere. The measurements were made in individual cells by first determining the turgor with a miniature pressure probe, then determining the osmotic potential of solution from the same cell, and finally summing the two potentials. The osmotic potentials were corrected for sample mixing in the probe. The measurements were checked with a thermocouple psychrometer that gave average tissue water potentials. In the elongating region, the water potential was highest near the xylem and lowest near the epidermis and in the center of the pith. In the basal, more mature region of the same stems, water potentials were near zero next to the xylem and throughout the tissue. These basal potentials reflected mostly the potential of the xylem, which extended into the elongating tissues. Thus, the high basal potential confirmed the high potential near the xylem in the elongating tissues. The psychrometer measurements for each tissue gave average potentials that agreed with the average of the cell potentials from the pressure probe. We conclude that a radial gradient was present in the elongating region that formed a water potential field in three dimensions around the xylem and that confirmed the predictions of Molz and Boyer (F.J. Molz and J.S. Boyer [1978] Plant Physiol 62: 423-429).

Enlargement in chara studied with a turgor clamp : growth rate is not determined by turgor.

A new method, the turgor clamp, was developed to test the effects of turgor on cell enlargement. The method used a pressure probe to remove or inject cell solution and change the turgor without altering the external environment of the cell walls. After the injections, the cells were permanently at the new turgor and required no further manipulation. Internode cells of Chara corallina grew rapidly with the pressure probe in place when growth was monitored with a position transducer. Growth-induced water potentials were negligible and turgor effects could be studied simply. As turgor was decreased, there was a threshold below which no growth occurred, and only reversible elastic/viscoelastic changes could be seen. Above the threshold, growth was superimposed on the elastic/viscoelastic effects. The rate of growth did not depend on turgor. Instead, the rate was highly dependent on energy metabolism as shown by inhibitors that rapidly abolished growth without changing the turgor. However, turgors could be driven above the maximum normally attainable by the cell, and these caused growth to respond as though plastic deformation of the walls was beginning, but the deformation caused wounding. Growth was inhibited when turgor was changed with osmotica but not inhibited when similar changes were made with the turgor clamp. It was concluded that osmotica caused side effects that could be mistaken for turgor effects. The presence of a turgor threshold indicates that turgor was required for growth. However, because turgor did not control the rate, it appears incorrect to consider the rate to be determined by a turgor-dependent plastic deformation of wall polymers. Instead, above the turgor threshold, the rapid response to energy inhibitors suggests a control by metabolic reactions causing synthesis and/or extension of wall polymers.

Internal CO(2) Measured Directly in Leaves : Abscisic Acid and Low Leaf Water Potential Cause Opposing Effects.

Observations of nonuniform photosynthesis across leaves cast doubt on internal CO(2) partial pressures (p(i)) calculated on the assumption of uniformity and can lead to incorrect conclusions about the stomatal control of photosynthesis. The problem can be avoided by measuring p(i) directly because the assumptions of uniformity are not necessary. We therefore developed a method that allowed p(i) to be measured continuously in situ for days at a time under growth conditions and used it to investigate intact leaves of sunflower (Helianthus annuus L.), soybean (Glycine max L. Merr.), and bush bean (Phaseolus vulgaris L.) subjected to high or low leaf water potentials (psi(w)) or high concentrations of abscisic acid (ABA). The leaves maintained a relatively constant differential (Deltap) between ambient CO(2) and measured p(i) throughout the light period when water was supplied. When water was withheld, psi(w) decreased and the stomata began to close, but measured p(i) increased until the leaf reached a psi(w) of -1.76 (bush bean), -2.12 (sunflower) or -3.10 (soybean) megapascals, at which point Deltap = 0. The increasing p(i) indicated that stomata did not inhibit CO(2) uptake and a Deltap of zero indicated that CO(2) uptake became zero despite the high availability of CO(2) inside the leaf. In contrast, when sunflower leaves at high psi(w) were treated with ABA, p(i) did not increase and instead decreased rapidly and steadily for up to 8 hours even as psi(w) increased, as expected if ABA treatment primarily affected stomatal conductance. The accumulating CO(2) at low psi(w) and contrasting response to ABA indicates that photosynthetic biochemistry limited photosynthesis at low psi(w) but not at high ABA.

Photophosphorylation in Attached Leaves of Helianthus annuus at Low Water Potentials.

The in situ response of photophosphorylation and coupling factor activity to low leaf water potential (psi(L)) was investigated using kinetic spectroscopy to measure the flash-induced electrochromic absorption change in attached sunflower (Helianthus annuus L. cv IS894) leaves. The electrochromic change is caused by the formation of an electric potential across the thylakoid membrane associated with proton uptake. Since depolarization of the thylakoid membrane following flash excitation is normally dominated by proton efflux through the coupling factor during ATP formation, this measurement can provide direct information about the catalytic activity of the coupling factor. Under low psi(L) conditions in which a clear nonstomatal limitation of net photosynthesis could be demonstrated, we found a strong inhibition of coupling factor activity in dark-adapted leaves which was probably caused by an increase in the energetic threshold for the activation of the enzyme at low psi(L). While this result supported earlier in vitro findings, we further discovered that the light-dependent reduction of coupling factor reversed any observable effect of low psi(L) on the energetics of activation or on photophosphorylation competence. Furthermore, coupling factor was reduced, even in severely droughted sunflower, almost immediately upon illumination. Based on these measurements, we conclude that the nonstomatal limitation of photosynthesis observed by us and others in droughted plants cannot be explained by impaired coupling factor activity.

Low water potentials affect expression of genes encoding vegetative storage proteins and plasma membrane proton ATPase in soybean.

We have examined growth, water status and gene expression in dark-grown soybean (Glycine max L. Merr.) seedlings in response to water deficit (low water potentials) during the first days following germination. The genes encoded the plasma membrane proton ATPase and two proteins of 28 kDa and 31 kDa putatively involved in vegetative storage. Water potentials of stems and roots decreased when 2-day-old seedlings were transferred to water-saturated air. Stem growth was inhibited immediately. Root growth continued at control rates for one day and then was totally inhibited when the normal root-stem water potential gradient was reversed. Expression of mRNA for the 28 kDa and 31 kDa proteins, measured independently using specific 3'-end probes, occurred about equally in stems. However, only the mRNA for the 31 kDa protein was detected in roots and at a lower abundance than in stems. Low water potentials increased the mRNA only for the 28 kDa protein in stems and the 31 kDa protein in roots. This differential expression followed the inhibition of stem growth but preceded the inhibition of root growth. The expression of the message for the ATPase, measured using a probe synthesized from a partial oat ATPase clone, was low in stems and roots but there was a 6-fold increase at low water potentials in roots. The increase followed the inhibition of root growth. This appears to be the first instance of regulation of ATPase gene expression in plants and the first demonstration of differential expression of the 28 kDa, 31 kDa, and ATPase messages. The correlation with the differential growth responses of the stems and roots raises the possibility that the differential gene expression could be involved in the growth response to low water potentials.

Primary events regulating stem growth at low water potentials.

Cell enlargement is inhibited by inadequate water. As a first step toward understanding the mechanism, all the physical parameters affecting enlargement were monitored to identify those that changed first, particularly in coincidence with the inhibition. The osmotic potential, turgor, yield threshold turgor, growth-induced water potential, wall extensibility, and conductance to water were measured in the elongating region, and the water potential was measured in the xylem of stems of dark-grown soybean (Glycine max [L.] Merr.) seedlings. A stepdown in water potential was achieved around the roots by transplanting the seedlings to vermiculite of low water content, and each of the parameters was measured simultaneously in the same plants while intact or within a few minutes of being intact using a newly developed guillotine psychrometer. The gradient of decreasing water potential from the xylem to the enlarging cells (growth-induced water potential) was the first of the parameters to decrease to a growth-limiting level. The kinetics were the same as for the inhibition of growth. The decreased gradient was caused mostly by a decreased water potential of the xylem. This was followed after 5 to 10 hours by a similar decrease in cell wall extensibility and tissue conductance for water. Later, the growth-induced water potential recovered as a result of osmotic adjustment and a rise in the water potential of the xylem. Still later, moderate growth resumed at a rate apparently determined by the low wall extensibility and tissue conductance for water. The turgor did not change significantly during the experiment. These results indicate that the primary event during the growth inhibition was the change in the growth-induced water potential. Because the growth limitation subsequently shifted to the low wall extensibility and tissue conductance for water, the initial change in potential may have set in motion subsequent metabolic changes that altered the characteristics of the wall and cell membranes.