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PubMed1994

Advance directives. Stability of patients' treatment choices.

BACKGROUND: Advance directives are intended to extend patient autonomy into periods of mental incompetence. However, for advance directives to fulfill this objective, patients' choices must be reasonably consistent over time. Thus, we assessed the stability of the advance treatment decisions of patients and members of the public. METHODS: In a prospective cohort study of 495 outpatients and 102 members of the public, we studied the stability of scenario- and treatment-specific choices. Subjects completed an advance directive, which included four illness scenarios with 11 treatment choices in each, as part of a questionnaire. A second interview was completed by 296 patients and 78 members of the public after 6 to 12 months; 154 patients completed a third interview after a further 6 to 12 months. We assessed stability by comparing each choice between interviews. RESULTS: Stability of choices was moderately high among patients (pooled kappa = 0.39) and members of the public (pooled kappa = 0.48). Stability improved with repeat interview (pooled kappa = 0.47 among patients). Patients who had discussions with their physicians showed more improvement (kappa = 0.57) than others. Patients had a wide range of personal stability levels (0% to 100%), but individuals starting out stable rarely became less so (93% of the patients with 85% to 100% stability maintained this level of stability on the third interview). Hospitalized patients showed no significant difference in stability at the second interview, but their stability was not improved at the third interview. CONCLUSIONS: Our findings generally support the use of advance directives. Most people made moderately stable decisions when using scenario- and treatment-specific directives, and stability improved after they reviewed the decisions, especially among those who had discussions with their physicians. Recent hospitalization did not decrease stability, although it appeared to reduce the improvement that others achieved with repeat interview. These findings suggest that advance directives can be relied on 1 to 2 years after completion to reflect a patient's choices.

Adult↗
PubMed2001

Animal flight dynamics I. Stability in gliding flight.

Stability is as essential to flying as lift itself, but previous discussions of how flying animals maintain stability have been limited in both number and scope. By developing the pitching moment equations for gliding animals and by discussing potential sources of roll and yaw stability, we consider the various sources of static stability used by gliding animals. We find that gliding animals differ markedly from aircraft in how they maintain stability. In particular, the pendulum stability provided when the centre of gravity lies below the wings is a much more important source of stability in flying animals than in most conventional aircraft. Drag-based stability also appears to be important for many gliding animals, whereas in aircraft, drag is usually kept to a minimum. One unexpected consequence of these differences is that the golden measure of static pitching stability in aircraft--the static margin--can only strictly be applied to flying animals if the equilibrium angle of attack is specified. We also derive several rules of thumb by which stable fliers can be identified. Stable fliers are expected to exhibit one or more of the following features: (1) Wings that are swept forward in slow flight. (2) Wings that are twisted down at the tips when swept back (wash-out) and twisted up at the tips when swept forwards (wash-in). (3) Additional lifting surfaces (canard, hindwings or a tail) inclined nose-up to the main wing if they lie forward of it, and nose-down if they lie behind it (longitudinal dihedral). Each of these predictions is directional--the opposite is expected to apply in unstable animals. In addition, animals with reduced stability are expected to display direct flight patterns in turbulent conditions, in contrast to the erratic flight patterns predicted for stable animals, in which large restoring forces are generated. Using these predictions, we find that flying animals possess a far higher degree of inherent stability than has generally been recognized. This conclusion is reinforced by measurements of the relative positions of the centres of gravity and lift in birds, which suggest that the wings alone may be sufficient to provide longitudinal static stability. Birds may therefore resemble tailless aircraft more closely than conventional aircraft with a tailplane.

Animals↗
PubMed1993

Direct evidence for selective modulation of psbA, rpoA, rbcL and 16S RNA stability during barley chloroplast development.

The turnover of RNAs encoded by seven different barley chloroplast genes was analyzed after treatment of barley shoots with tagetitoxin, a selective inhibitor of chloroplast transcription. Changes in RNA stability were examined during chloroplast development using basal and apical leaf sections of 4.5-day-old dark-grown seedlings and apical leaf sections of 4.0-day-old dark-grown seedlings which had been illuminated for 12 h. Of the RNAs examined, a 2.6 kb unspliced precursor of tRNA(lys) exhibited the shortest half-life, which was estimated to be 3 h. The 16S rRNA and psbA mRNA had the longest estimated half-lives, which were greater than 40 h. Among mRNAs, half-lives were estimated to range from 6 h for psaA mRNA, to over 40 h for psbA mRNA. Therefore, barley chloroplast mRNAs have long half-lives relative to bacterial mRNAs. The stability of atpB mRNA and the unspliced precursor of tRNA-lys was not altered during chloroplast development, while the stability of psaA mRNA decreased 2-fold. In contrast, the stability of the 16S rRNA and mRNAs for rpoA, psbA and rbcL increased during chloroplast development. The stability of 16S rRNA increased markedly during chloroplast development in the dark and this increase was maintained in illuminated seedlings. The stability of rbcL mRNA increased 2.5-fold during chloroplast development in the dark, and then decreased 2-fold in chloroplasts of light-grown plants. The initial increase in rpoA and psbA mRNA stability was also light-independent, with total increases in stability of at least 5-fold. In the case of rpoA, the stability of 2 of the 13 polycistronic rpoA transcripts that were detected in dark-grown plants was selectively increased during chloroplast development. In conclusion, the stability of some transcripts is selectively increased and further modulated during chloroplast development in barley. We propose that the selective stabilization of chloroplast mRNA, which occurred independent of light, is an indication that non-light regulated developmental signals are involved in barley chloroplast mRNA stability.

Base Sequence↗
PubMed2005

An evaluation of the colloidal stability of metal working fluid.

The effect of calcium on the stability of a commercial MWF is characterized through the experimental determination of the stability ratio, W. Three experimental methods of stability ratio evaluation are investigated. (1) The initial slope of the absorbance versus time curve is used to estimate the rate of coagulation. (2) Absorbance measurements are used to estimate N(0)/N with time. The stability ratio is determined from the slope of N(0)/N versus time. (3) Photon correlation spectroscopy (PCS) measurements of the volume distribution with time are used to estimate N(0)/N with time. Electrophoretic mobility was also measured and used to determine the fast coagulation concentration of the MWF. The accuracy of the experimentally determined stability ratios is evaluated using a population balance coagulation model. The model predicts the population distribution of a coagulating dispersion with time based on an initial particle size distribution and stability ratio. The model results were compared with the PCS-measured distributions to determine which stability ratio evaluation method best describes the stability of the MWF emulsion studied. Using the initial slope of the absorbance versus time curve to determine the fast coagulation concentration correlates well with electrophoretic mobility measurements. However, using absorbance measurements to determine the rate of coagulation underestimates the stability ratio of the MWF studied by orders of magnitude. N(0)/N values calculated from absorbance measurements provide a reasonable estimate of the stability ratio but inconsistencies in the method decrease its reliability. The stability ratio derived from PCS measurements appears to provide the most accurate, reliable description of MWF stability.

Journal Article↗
PubMedDate not supplied

Stability and instability of the glenohumeral joint: the role of shoulder muscles.

Shoulder muscles contribute to both mobility and stability of the glenohumeral joint. To improve treatments for shoulder instability, we focused on the contribution of the shoulder muscles to glenohumeral joint stability in clinically relevant positions. Both computational and experimental models were used. A computational model of the glenohumeral joint quantified stability provided by active muscle forces in both mid-range and end-range glenohumeral joint positions. Compared with mid-range positions, the resultant joint force at end-range positions was more anteriorly directed, indicating that its contribution to glenohumeral joint stability was diminished. In end-range positions, simulated increases in rotator cuff muscle forces tended to improve stability whereas increases in deltoid or pectoralis major muscle forces tended to further decrease stability. To validate these results, a cadaveric model, simulating relevant shoulder muscles, was used to quantify glenohumeral joint stability. When infraspinatus muscle activity was decreased, compressive forces decreased. When pectoralis major muscle activity was increased, anteriorly directed forces increased. If anteriorly directed forces increase or compressive forces decrease, stability of the glenohumeral joint decreases. This cadaveric model was then used to evaluate the effect of placing the joint in the apprehension position of abduction, external rotation, and horizontal abduction. Consistent with the results of our computational model, apprehension positioning increased anteriorly directed forces. Knowledge gained from these models was then used to develop a cadaveric model of glenohumeral joint dislocation. Dislocation resulted from the mechanism of forcible apprehension positioning when the appropriate shoulder muscles were simulated and a passive pectoralis major muscle was included. Capsulolabral lesions resulted that were similar to those observed in vivo. Shoulder muscle forces are usually powerful stabilizers of the glenohumeral joint, especially in mid-range positions when the passive stabilizers are lax. However, muscle forces can contribute to instability as well. Certain muscle forces decrease glenohumeral joint stability in end-range positions. We found this to be the case with both active and passive pectoralis major forces. Improved understanding of the contribution of muscle forces not only toward stability but also toward instability will improve rehabilitation protocols for the shoulder and prove useful in the treatment of joint instability throughout the body.

Biomechanical Phenomena↗
PubMed2003

The relationship between sitting stability and functional performance in patients with paraplegia.

OBJECTIVES: To compare sitting stability between patients with high and low thoracic spinal cord injury (SCI), to determine the factors that can predict sitting stability, and to examine the relationship between sitting stability and functional performance. DESIGN: Cross-sectional assessment was performed on subjects with paraplegia. SETTING: Rehabilitation hospital affiliated with a medical university. PARTICIPANTS: Convenience sample of 30 adults with complete chronic thoracic SCI. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: (1) Postural sway during quiet sitting over 30 seconds was recorded as static sitting stability, and composite maximal weight-shift during leaning tasks over 30 seconds was measured as dynamic sitting stability; (2) age, body weight, trunk length, trunk strength, postonset duration, injury level, and presence of spasticity were examined as predictive variables for sitting stability; and (3) the time for completion of upper- and lower-body dressing and undressing and transfer was measured as functional performance. RESULTS: A significant difference in composite maximal weight-shift was found between high and low thoracic SCI subjects (t=2.90, P<.01). Injury level and trunk length were 2 important predictive factors for dynamic sitting stability, and they explained 43.5% of the variance. Only the completion time of upper-body dressing and undressing correlated significantly with static (r=.465, P=.01) and dynamic (r=-.377, P<.05) sitting stability. CONCLUSIONS: The subjects with low thoracic SCI showed better dynamic sitting stability than those with high thoracic SCI. Injury level and trunk length, not trunk flexion or extension strength, predicted the outcome of dynamic sitting stability. Measures were not precise enough to predict functional performance from the viewpoint of injury level and sitting stability. The underlying premise that a reduction or increase in trunk strength is indicative of poorer or better sitting stability in SCI individuals is questioned, and implications for problem identification and treatment planning are discussed.

Activities of Daily Living↗
PubMed1996

Contribution of the intramolecular disulfide bridge to the folding stability of REIv, the variable domain of a human immunoglobulin kappa light chain.

BACKGROUND: Immunoglobulin domains contain about 100 amino acid residues folded into two beta-sheets and stabilized in a sandwich by a conserved central disulfide bridge. Whether antibodies actually require disulfide bonds for stability has long been a matter of debate. The contribution made by the central disulfide bridge to the overall folding stability of the immunoglobulin REIv, the variable domain of a human kappa light chain, was investigated by introducing stabilizing amino acid replacements followed by removal of the disulfide bridge via chemical reduction or genetic substitution of the cysteine residues. RESULTS: Nine REIv variants were constructed by methods of protein engineering that have folding stabilities elevated relative wild-type REIv by (up to) 16.0 kJ mol-1. Eight of these variants can be cooperatively refolded after unfolding and chemical reduction of the disulfide bridge-in contrast to wildtype REIv. The stabilizing effect of one of these residue replacements (T39K) was rationalized by determining the structure of the respective REIv variant at 1.7 A. The loss of folding stability caused by reduction of the intramolecular disulfide bond is on average 19 kJ mol-1. Removal of the disulfide bridge by genetic substitution of C23 for valine resulted in a stable immunoglobulin domain in the context of the stabilizing Y32H amino acid exchange; again, REIv-C23V/Y32H has 18 kJ mol-1 less folding stability than REIv-Y32H. The data are consistent with the notion that all variants studied have the same overall three-dimensional structure with the disulfide bridge opened or closed. CONCLUSIONS: A comparison of the magnitude of the stabilizing effect exerted by the disulfide bond and the length of the mainchain loop framed by it suggests lowering of the entropy of the unfolded state as the sole source of the effect. Disulfide bonds are not necessary for proper folding of immunoglobulin variable domains and can be removed, provided the loss of folding stability is at least partly compensated by stabilizing amino acid exchanges.

Disulfides↗
PubMed1995

Prolyl isomerase as a probe of stability of slow-folding intermediates.

Catalysis of slow folding reactions by peptidyl prolyl cis-trans isomerase (PPI) provides estimates of stabilities of intermediates in folding of normal and mutational variants of yeast iso-2 cytochrome c. A two-state model postulating a rapid preequilibration of intermediates with the unfolded protein is employed to calculate the stabilization free energy of the intermediate from the catalytic efficiency (kcat/Km) of PPI toward slow folding species. Stability measurements have been made for two distinct slow-folding intermediates: the absorbance-detected (IIS) and fluorescence-detected (IIIS) intermediates. Mutation-induced changes in the stability of the intermediates and in the activation free energy for slow folding are compared to changes in equilibrium thermodynamic stability. The results show that (1) for iso-2 the absorbance-detected intermediates (IIS) are slightly more stable than the fluorescence-detected intermediates (IIIS), (2) most mutations have different effects on equilibrium stability and the stability of the IIS or IIIS intermediates, and (3) for both slow folding reactions the mutation-induced changes in the activation free energy are small compared to the magnitude of the activation free energy barrier. Differential effects of mutations on equilibrium stability and the stability of intermediates provides a means of assessing the sequence-encoded structural specificity for folding. Mutations with different effects on intermediate stability and equilibrium stability change the encoded folding information and may alter folding pathways and/or lead to different three-dimensional structures. Identification of mutations which stabilize a folding intermediate relative to the native conformation provides an empirical approach to the design of thermodynamically stable forms of folding intermediates.

Amino Acid Isomerases↗
PubMed2003

The contribution of polar group burial to protein stability is strongly context-dependent.

We previously suggested that proteins gain more stability from the burial and hydrogen bonding of polar groups than from the burial of nonpolar groups (Pace, C. N. (2001) Biochemistry 40, 310-313). To study this further, we prepared eight Thr-to-Val mutants of RNase Sa, four in which the Thr side chain is hydrogen-bonded and four in which it is not. We measured the stability of these mutants by analyzing their thermal denaturation curves. The four hydrogen-bonded Thr side chains contribute 1.3 +/- 0.9 kcal/mol to the stability; those that are not still contribute 0.4 +/- 0.9 kcal/mol to the stability. For 40 Thr-to-Val mutants of 11 proteins, the average decrease in stability is 1.0 +/- 1.0 kcal/mol when the Thr side chain is hydrogen-bonded and 0.0 +/- 0.5 kcal/mol when it is not. This is clear evidence that hydrogen bonds contribute favorably to protein stability. In addition, we prepared four Val-to-Thr mutants of RNase Sa, measured their stability, and determined their crystal structures. In all cases, the mutants are less stable than the wild-type protein, with the decreases in stability ranging from 0.5 to 4.4 kcal/mol. For 41 Val-to-Thr mutants of 11 proteins, the average decrease in stability is 1.8 +/- 1.3 kcal/mol and is unfavorable for 40 of 41 mutants. This shows that placing an [bond]OH group at a site designed for a [bond]CH3 group is very unfavorable. So, [bond]OH groups can contribute favorably to protein stability, even if they are not hydrogen-bonded, if the site was selected for an [bond]OH group, but they will make an unfavorable contribution to stability, even if they are hydrogen-bonded, when they are placed at a site selected for a [bond]CH3 group. The contribution that polar groups make to protein stability depends strongly on their environment.

Crystallography, X-Ray↗
PubMed2005

Stability constraints and protein evolution: the role of chain length, composition and disulfide bonds.

Stability of the native state is an essential requirement in protein evolution and design. Here we investigated the interplay between chain length and stability constraints using a simple model of protein folding and a statistical study of the Protein Data Bank. We distinguish two types of stability of the native state: with respect to the unfolded state (unfolding stability) and with respect to misfolded configurations (misfolding stability). Several contributions to stability are evaluated and their correlations are disentangled through principal components analysis, with the following main results. (1) We show that longer proteins can fulfil more easily the requirements of unfolding and misfolding stability, because they have a higher number of native interactions per residue. Consistently, in longer proteins native interactions are weaker and they are less optimized with respect to non-native interactions. (2) Stability against misfolding is negatively correlated with the strength of native interactions, which is related to hydrophobicity. Hence there is a trade-off between unfolding and misfolding stability. This trade-off is influenced by protein length: less hydrophobic sequences are observed in very long proteins. (3) The number of disulfide bonds is positively correlated with the deficit of free energy stabilizing the native state. Chain length and the number of disulfide bonds per residue are negatively correlated in proteins with short chains and uncorrelated in proteins with long chains. (4) The number of salt bridges per residue and per native contact increases with chain length. We interpret these observations as an indication that the constraints imposed by unfolding stability are less demanding in long proteins and they are further reduced by the competing requirement for stability against misfolding. In particular, disulfide bonds appear to be positively selected in short proteins, whereas they evolve in an effectively neutral way in long proteins.

Amino Acids↗
PubMed2004

Determining the stabilizing role of individual torso muscles during rehabilitation exercises.

STUDY DESIGN: A systematic biomechanical analysis involving an artificial perturbation applied to individual lumbar muscles in order to assess their potential stabilizing role. OBJECTIVES: To identify which torso muscles stabilize the spine during different loading conditions and to identify possible mechanisms of function. SUMMARY OF BACKGROUND DATA.: Stabilization exercises are thought to train muscle patterns that ensure spine stability; however, little quantification and no consensus exists as to which muscles contribute to stability. METHODS: Spine kinematics, external forces, and 14 channels of torso electromyography were recorded for seven stabilization exercises in order to capture the individual motor control strategies adopted by different people. Data were input into a detailed model of the lumbar spine to quantify spine joint forces and stability. The EMG signal for a particular muscle was replaced either unilaterally or bilaterally by a sinusoid, and the resultant change in the stability index was quantified. RESULTS: A direction-dependent-stabilizing role was noticed in the larger, multisegmental muscles, whereas a specific subtle efficiency to generate stability was observed for the smaller, intersegmental spinal muscles. CONCLUSIONS: No single muscle dominated in the enhancement of spine stability, and their individual roles were continuously changing across tasks. Clinically, if the goal is to train for stability, enhancing motor patterns that incorporate many muscles rather than targeting just a few is justifiable.

Adult↗
PubMed2006

Evaluation of stability of k-means cluster ensembles with respect to random initialization.

Many clustering algorithms, including cluster ensembles, rely on a random component. Stability of the results across different runs is considered to be an asset of the algorithm. The cluster ensembles considered here are based on k-means clusterers. Each clusterer is assigned a random target number of clusters, k and is started from a random initialization. Here, we use 10 artificial and 10 real data sets to study ensemble stability with respect to random k, and random initialization. The data sets were chosen to have a small number of clusters (two to seven) and a moderate number of data points (up to a few hundred). Pairwise stability is defined as the adjusted Rand index between pairs of clusterers in the ensemble, averaged across all pairs. Nonpairwise stability is defined as the entropy of the consensus matrix of the ensemble. An experimental comparison with the stability of the standard k-means algorithm was carried out for k from 2 to 20. The results revealed that ensembles are generally more stable, markedly so for larger k. To establish whether stability can serve as a cluster validity index, we first looked at the relationship between stability and accuracy with respect to the number of clusters, k. We found that such a relationship strongly depends on the data set, varying from almost perfect positive correlation (0.97, for the glass data) to almost perfect negative correlation (-0.93, for the crabs data). We propose a new combined stability index to be the sum of the pairwise individual and ensemble stabilities. This index was found to correlate better with the ensemble accuracy. Following the hypothesis that a point of stability of a clustering algorithm corresponds to a structure found in the data, we used the stability measures to pick the number of clusters. The combined stability index gave best results.

Algorithms↗
PubMed2003

Stability analysis of an acoustically levitated disk.

In this paper, a model is developed for the stability analysis of an acoustically levitated disk on the basis of analyzing eddy acoustic streaming and acoustic viscous stress. In the model, the effect of the acoustic streaming outside the boundary layer that is on the surface of the levitated disk is properly taken into account. Also, the calculation of sound field and acoustic viscous stress is limited to the range that has a dominant effect on the stability. By this method, we obtain a quite accurate solution of the stability coefficient. For the small horizontal shift of a large levitated disk, the model is verified by the good agreement between the experimental and theoretical results. By means of this model and relevant experiments, some factors that affect the stability of the levitated disk are investigated, and useful guidelines for design and application are obtained. It is found that the range from the edge to the outermost nodal circle of the disk-shaped vibrator has a large effect on the stability of the levitated disk. To stabilize the levitated disk by acoustic viscous force, the distance between the edge and the outermost nodal circle of the vibrator must be larger than a critical value, which is determined by the driving frequency and the sound velocity of the fluid between the levitated disk and the vibrator. When this condition is satisfied, increasing the distance between the edge and the outermost nodal circle leads to a decrease in the stability. It is also found that the property of the fluid between the levitated disk and the vibrator has a large effect on the stability. It is easier to stabilize the levitated disk in steam than in air, but more difficult to do so in carbon dioxide and hydrogen. In addition, theoretical results show that increasing the weight per unit area of the levitated object increases the stability for a given vibrator velocity. The distribution of the acoustic viscous stress and the dependence of the stability coefficient and the holding force on the horizontal shift of the levitated disk, which are obtained by this study, also are useful to a better understanding of the stability of the levitated disk.

Journal Article↗
PubMed2004

Defining the minimum size of a hydrophobic cluster in two-stranded alpha-helical coiled-coils: effects on protein stability.

The alpha-helical coiled-coil motif is characterized by a heptad repeat pattern (abcdefg)(n) in which residues a and d form the hydrophobic core. Long coiled-coils (e.g., tropomyosin, 284 residues per polypeptide chain) typically do not have a continuous hydrophobic core of stabilizing residues, but rather one that consists of alternating clusters of stabilizing and destabilizing residues. We have arbitrarily defined a cluster as a minimum of three consecutive stabilizing or destabilizing residues in the hydrophobic core. We report here on a series of two-stranded, disulfide-bridged parallel alpha-helical coiled-coils that contain a central cassette of three consecutive hydrophobic core positions (d, a, and d) with a destabilizing cluster of three consecutive Ala residues in the hydrophobic core on each side of the cassette. The effect of adding one to three stabilizing hydrophobes in these positions (Leu or Ile; denoted as [see text]) was investigated. Alanine residues (denoted as [see text]) are used to represent destabilizing residues. The peptide with three Ala residues in the d a d cassette positions ([see text]) was among the least stable coiled-coil (T(m) = 39.3 degrees C and Urea(1/2) = 1.9 M). Surprisingly, the addition of one stabilizing hydrophobe (Leu) to the cassette or two stabilizing hydrophobes (Leu), still interspersed by an Ala in the cassette ([see text]), also did not lead to any gain in stability. However, peptides with two adjacent hydrophobes in the cassette ([see text])([see text]) did show a gain in stability of 0.9 kcal/mole over the peptide with two interspersed hydrophobes ([see text]). Because the latter three peptides have the same inherent hydrophobicity, the juxtaposition of stabilizing hydrophobes leads to a synergistic effect, and thus a clustering effect. The addition of a third stabilizing hydrophobe to the cassette ([see text]) resulted in a further synergistic gain in stability of 1.7 kcal/mole (T(m) = 54.1 degrees C and Urea(1/2) = 3.3M). Therefore, the role of hydrophobicity in the hydrophobic core of coiled-coils is extremely context dependent and clustering is an important aspect of protein folding and stability.

Alanine↗
PubMed2003

Multivariate stabilizing selection and pleiotropy in the maintenance of quantitative genetic variation.

We investigate maintenance of quantitative genetic variation at mutation-selection balance for multiple traits. The intrinsic strength of real stabilizing selection on one of these traits denoted the "target trait" and the observed strength of apparent stabilizing selection on the target trait can be quite different: the latter, which is estimable, is much smaller (i.e., implying stronger selection) than the former. Distinguishing them may enable the mutation load to be relaxed when considering multivariate stabilizing selection. It is shown that both correlations among mutational effects and among strengths of real stabilizing selection on the traits are not important unless they are high. The analysis for independent situations thus provides a good approximation to the case where mutant and stabilizing selection effects are correlated. Multivariate stabilizing selection can be regarded as a combination of stabilizing selection on the target trait and the pleiotropic direct selection on fitness that is solely due to the effects of real stabilizing selection on the hidden traits. As the overall fitness approaches a constant value as the number of traits increases, multivariate stabilizing selection can maintain abundant genetic variance only under quite weak selection. The common observations of high polygenic variance and strong stabilizing selection thus imply that if the mutation-selection balance is the true mechanism of maintenance of genetic variation, the apparent stabilizing selection cannot arise solely by real stabilizing selection simultaneously on many metric traits.

Genetic Variation↗
PubMed2004

Neuromuscular training improves single-limb stability in young female athletes.

STUDY DESIGN: Controlled single-group pretest/posttest design. OBJECTIVE: The purpose of this study was to determine if a 6-week neuromuscular training program designed to decrease the incidence of anterior cruciate ligament (ACL) injuries would improve single-limb postural stability in young female athletes. We hypothesized neuromuscular training would result in an improvement in postural stability, with the greatest improvement taking place in the medial-lateral direction. BACKGROUND: Balance training has become a common component of programs designed to prevent ACL injury. Rehabilitation programs can improve postural stability following ACL injury and reconstruction; however, there is limited information available which quantifies improvement of postural stability following neuromuscular training designed to prevent ACL injuries in a healthy population. METHODS AND MEASURES: Forty-one healthy female high school athletes (mean age, 15.3 years; age range, 13-17 years) participated in this study. Single-limb postural stability for both lower extremities was assessed with a Biodex Stability System. The neuromuscular training program consisted of three 90-minute training sessions per week for 6 weeks. Following the completion of the training program, each subject was re-evaluated to determine change in total, anterior-posterior, and medial-lateral single-limb stability. Two-way analysis of variance models were used to determine differences between pretraining and posttraining and between limbs. RESULTS: The subjects showed a significant improvement in single-limb total stability (P = .004) and anterior-posterior stability (P = .001), but not medial-lateral stability (P = .650) for both the right and left lower extremity following training. In addition, the subjects demonstrated significantly better total postural stability on the right side as compared to the left (P = .026). CONCLUSIONS: A 6-week neuromuscular training program designed to decrease the incidence of ACL injuries improves objective measures of total and anterior-posterior single-limb postural stability in high school female athletes.

Adolescent↗
PubMed2003

Comparison of stabilities between obliquely and conventionally inserted Bagby and Kuslich cages as posterior lumbar interbody fusion in a cadaver model.

BACKGROUND: The Bagby and Kuslich (BAK) cage as posterior lumbar interbody fusion (PLIF) is reported to give satisfactory results in restoring spinal stability. Moreover, correction by obliquely inserting a single BAK cage has the advantages of reducing exposure, precise implantation, and lower cost. However, biomechanical data on this procedure are not abundant. This study was designed to compare the stability imparted by the cages placed using an oblique and posterior approaches and to determine the effects of supplementary posterior instrumentation. METHODS: After affixing nine human cadaveric spines (L2-S1) within a testing frame, load testing in several clinically relevant modes was performed sequentially for the intact and the following procedures across the L4-5 segments: posterior destabilization, stabilization using 2 parallel BAK cages (CBAK group) or 1 oblique BAK cage (OBAK group), and additional stabilization with posterior instrumentation. Spatial locations of vertebral bodies were recorded after each loading step using a 3-D motion measurement system. RESULTS: Except the OBAK group that had a lower stability in left axial rotation, there were no significant differences in the stability between both groups in all loading modes for the stabilization using cages alone. Compared with the intact cases, CBAK cages provide significant improvement in the stability in 5 displacement modes and OBAK cage may restore the stabilities of the specimens to the intact state in 5 modes and provide significant improvement in flexion. Addition of supplementary posterior instrumentation significantly reduced the angular displacements in both groups. CONCLUSIONS: Both methods of cage insertion have similar stability. Both implantations, alone or with posterior instrumentation, may improve the stability of the spine, although posterior instrumentation may further strengthen the stability. The oblique insertion is more favorable since it requires less exposure, enables precise implantation, and is less expensive.

Cadaver↗
PubMed1992

[Synovectomy in the realignment-stabilization of the rheumatoid wrist. Apropos of a series of 104 cases with average follow-up of 5 years].

The authors studied a series of 104 rheumatoid wrists, stages II, III or IV according modified Larsen's grading, treated between 1980-1988 by synovectomy realignment stabilization. The mean follow-up period was 5 years. The operation presents different steps which have an additive effect and must be associated in order long term clinical and radiological stability. They associated: extensor tendons and articular synovectomy stabilization of the distal radio ulnar complex by Sauve-Kapandji's operation, tendon transfert: the extensor carpis radialis longus is transferred on the extensor carpi radialis brevis the extensor carpi ulnaris is relocated with posterior annular dorsal ligament plasty. Results concerning relief of pain were very clear because the patients presented either complete relief of pain (73%) or only intermittent occasional pain. The overall active range of motion is nearly the same, when compared pre- and post-operative ratings. In general the patients who presented good pre-operative mobility usually improved them and the others preserved them. Larsen's radiological grading was modified by the authors to include instability's criteria in frontal and sagittal plane. Carpal height remained stable (75% less than or equal to 1 mm), ulnar deviation has never overreached 3 mm, radial deviation was not modified in 50% of cases. They found only 4 wrists presenting a stage II radiological grading with an evolution to the stage III and 12 of the stage III grading became stage IV. The instable type of the stage IV was stabilized by a surgical radiolunate arthrodesis. The stabilized type was nearly not modified. The different steps of operation (articular and tenosynovectomy, carpus stabilization and realignment with stabilization by stabilization of the radio ulnar complex joint using Sauve-Kapandji operation, tendons transfers and dorsal retinacular plasty) have an additive effect in achieving relief of pain with preservation of the pre-existing mobility. The stabilization of the radio ulnar complex by the Sauve-Kapandji operation constitutes a new approach in rheumatoid arthritis published by the author in 1985 and in our opinion appears to be simple and is very efficient in stabilizing wrist immediately, thus allowing early rehabilitation of these patients. Long term stability is affirmed by clinical and roentgenologic follow-up and globally a painless wrist, a preservation of the pre-operative motion and a stabilization in frontal and sagittal plane is obtained.

Adult↗