Hostile takeover attempts oftentimes signal that a target firm has an over-diversified and ineffective corporate strategy. What does this signal mean when takeover attempts fail? Drawing from agency ...theory, we argue that target firms managed by independent directory boards are likely to ignore the takeover attempt and not refocus their firms' strategy. Conversely, target firms managed by nonindependent boards are more likely to view the failed takeover attempt as a 'wake-up call' and will refocus their firms' strategy so as to preserve the firm's survival. These arguments are tested using a sample of 76 firms that were targets of failed hostile takeover attempts. Logistic regression analyses confirm the predictions. This study suggests that in the aftermath of a failed takeover attempt board of director characteristics can help predict changes in corporate strategies.
To evaluate a new 3-point bending type of cervical traction.
Nonrandomized controlled trial of prospective, consecutive patients compared with control subjects. Follow-up patient data were obtained ...at 3 and 15(1/2) months, and 8 1/10 months for controls.
Data were collected at a spine clinic in Nevada.
Volunteer subjects consisted of 30 patients and 24 controls. Subjects had cervicogenic pain (neck pain, headaches, arm pain, and/or numbness). Subjects were included if their Ruth Jackson radiographic stress lines measured less than 25 degrees but were excluded if they had suspected disk herniation or canal stenosis. All subjects completed the first follow-up examinations, and 25 of 30 patients completed the long-term follow-up examination.
Spinal manipulation for pain and a new form of 3-point bending cervical traction to improve lordosis. Cervical manipulation was provided for the first 3 to 4 weeks of treatment. Traction treatment consisted of 3 to 5 sessions per week for 9 +/- 1 weeks.
Besides pain visual analog scale (VAS) ratings, pre- and posttreatment lateral cervical radiographs were analyzed.
Control subjects reported no change in the pain VAS ratings and had no statistically significant change in segmental or global radiographic alignment. For the traction group, VAS ratings were 4.3 pretreatment and 1.6 posttreatment. Traction group radiographic measurements showed statistically significant improvements (P <.008 in all instances of statistical significance), including anterior head weight bearing (improved 6.2mm), Cobb angle at C2-7 (improved 12.1 degrees ), and angle between posterior tangents at C2-7 (improved 14.2 degrees ). For the treatment group, at 15(1/2)-month follow-up, only minimal loss of C2-7 lordosis (3.5 degrees ) was observed.
Sagittal cervical traction with transverse load at midneck (2-way cervical traction) combined with cervical manipulation can improve cervical lordosis in 8 to 10 weeks as indicated by increases in segmental and global cervical alignment. Magnitude of lordosis at C2-7 remained stable at long-term follow-up.
Previous study in human subjects has documented biomechanical and neurophysiological responses to impulsive spinal manipulative thrusts, but very little is known about the neuromechanical effects of ...varying thrust force–time profiles.
Ten adolescent Merino sheep were anesthetized and posteroanterior mechanical thrusts were applied to the L3 spinous process using a computer-controlled, mechanical testing apparatus. Three variable pulse durations (10, 100, 200
ms, force
=
80
N) and three variable force amplitudes (20, 40, 60
N, pulse duration
=
100
ms) were examined for their effect on lumbar motion response (L3 displacement, L1, L2 acceleration) and normalized multifidus electromyographic response (L3, L4) using a repeated measures analysis of variance.
Increasing L3 posteroanterior force amplitude resulted in a fourfold linear increase in L3 posteroanterior vertebral displacement (
p
<
0.001) and adjacent segment (L1, L2) posteroanterior acceleration response (
p
<
0.001). L3 displacement was linearly correlated (
p
<
0.001) to the acceleration response over the 20–80
N force range (100
ms). At constant force, 10
ms thrusts resulted in nearly fivefold lower L3 displacements and significantly increased segmental (L2) acceleration responses compared to the 100
ms (19%,
p
=
0.005) and 200
ms (16%,
p
=
0.023) thrusts. Normalized electromyographic responses increased linearly with increasing force amplitude at higher amplitudes and were appreciably affected by mechanical excitation pulse duration.
Changes in the biomechanical and neuromuscular response of the ovine lumbar spine were observed in response to changes in the force–time characteristics of the spinal manipulative thrusts and may be an underlying mechanism in related clinical outcomes.
Postinfarction ventricular septal defects (VSDs) are associated with high mortality and typically these are treated urgently with surgery for exclusion patch repair. Percutaneous closure of ...postinfarction VSDs using occlusion devices is feasible in some patients, but in some cases device deployment may not be possible due to VSD anatomy or valvular apparatus interference. We report the novel technique of deploying Amplatzer VSD devices in the operating room under direct vision through a right atriotomy with and without aortotomy in 2 patients with large inferobasal VSDs after myocardial infarction.
In the absence of external forces, the largest contributor to intervertebral disc (IVD) loads and stresses is trunk muscular activity. The relationship between trunk posture, spine geometry, extensor ...muscle activity, and the loads and stresses acting on the IVD is not well understood. The objective of this study was to characterize changes in thoracolumbar disc loads and extensor muscle forces following anterior translation of the thoracic spine in the upright posture. Vertebral body geometries (C2 to S1) and the location of the femoral head and acetabulum centroids were obtained by digitizing lateral, full-spine radiographs of 13 men and five women volunteers without previous history of back pain. Two standing, lateral, full-spine radiographic views were obtained for each subject: a neutral-posture lateral radiograph and a radiograph during anterior translation of the thorax relative to the pelvis (while keeping T1 aligned over T12). Extensor muscle loads, and compression and shear stresses acting on the IVDs, were calculated for each posture using a previously validated biomechanical model. Comparing vertebral centroids for the neutral posture to the anterior posture, subjects were able to anterior translate +101.5 mm+/-33.0 mm (C7-hip axis), +81.5 mm+/-39.2 mm (C7-S1) (vertebral centroid of C7 compared with a vertical line through the vertebral centroid of S1), and +58.9 mm+/-19.1 mm (T12-S1). In the anterior translated posture, disc loads and stresses were significantly increased for all levels below T9. Increases in IVD compressive loads and shear loads, and the corresponding stresses, were most marked at the L5-S1 level and L3-L4 level, respectively. The extensor muscle loads required to maintain static equilibrium in the upright posture increased from 147.2 N (mean, neutral posture) to 667.1 N (mean, translated posture) at L5-S1. Compressive loads on the anterior and posterior L5-S1 disc nearly doubled in the anterior translated posture. Anterior translation of the thorax resulted in significantly increased loads and stresses acting on the thoracolumbar spine. This posture is common in lumbar spinal disorders and could contribute to lumbar disc pathologies, progression of L5-S1 spondylolisthesis deformities, and poor outcomes after lumbar spine surgery. In conclusion, anterior trunk translation in the standing subject increases extensor muscle activity and loads and stresses acting on the intervertebral disc in the lower thoracic and lumbar regions.
Objective. To calculate and compare combined axial and flexural stresses in lordosis versus buckled configurations of the sagittal cervical curve.
Design. Digitized measurements from lateral cervical ...radiographs of four different shapes were used to calculate axial loads and bending moments on the vertebral bodies of C2–C7.
Background. Osteoarthritis and spinal degeneration are factors in neck and back pain. Calculations of stress in clinically occurring configurations of the sagittal cervical spine are rare.
Methods. Center of gravity of the head (inferior–posterior sella turcica) and vertebral body margins were digitized on four different lateral cervical radiographs: lordosis, kyphosis, and two “S”-shapes. Polynomials (seventh degree) and stress concentrations on the concave and convex margins were derived for the shape of the sagittal cervical curvatures from C1 to T1. Moments of inertia were determined from digitizing and the use of an elliptical shell model of cross-section. Moment arms from a vertical line through the center of gravity of the head to the atlas and scaled neck extensor moment arms from the literature were used to compute the vertical component of extensor muscle effort. Segmental lever arms were calculated from a vertical line through C1 to each vertebra.
Results. In lordosis, anterior and posterior stresses in the vertebral body are nearly uniform and minimal. In kyphotic areas, combined stresses changed from tension to compression at the anterior vertebral margins and were very large (6–10 times as large in magnitude) compared to lordosis. In kyphotic areas at the posterior vertebral body, the combined stresses changed from compression (in lordosis) to tension.
Conclusions. The stresses in kyphotic areas are very large and opposite in direction compared to a normal lordosis. This analysis provides the basis for the formation of osteophytes (Wolff's Law) on the anterior margins of vertebrae in kyphotic regions of the sagittal cervical curve. This indicates that any kyphosis is an undesirable configuration in the cervical spine.
Relevance
Osteophytes and osteoarthritis are found at areas of altered stress and strain. Axial and flexural stresses at kyphotic areas in the sagittal cervical spine are abnormally high.
To quantify the force-time and force-delivery characteristics of six commonly used handheld chiropractic adjusting devices.
Four spring-loaded instruments, the Activator Adjusting Instrument; ...Activator II Adjusting Instrument, Activator III Adjusting Instrument, and Activator IV Adjusting Instrument, and two electromechanical devices, the Harrison Handheld Adjusting Instrument and Neuromechanical Impulse Adjusting Instrument, were applied to a dynamic load cell. A total of 10 force-time histories were obtained at each of three force excursion settings (minimum to maximum) for each of the six adjusting instruments at preload of approximately 20 N.
The minimum-to-maximum force excursion settings for the spring-loaded mechanical adjusting instruments produced similar minimum-to-maximum peak forces that were not appreciably different for most excursion settings. The electromechanical adjusting instruments produced short duration (∼2-4 ms), with more linear minimum-to-maximum peak forces. The force-time profile of the electromechanical devices resulted in a more uniform and greater energy dynamic frequency response in comparison to the spring-loaded mechanical adjusting instruments.
The handheld, electromechanical instruments produced substantially larger peak forces and ranges of forces in comparison to the handheld, spring-loaded mechanical devices. The electromechanical instruments produced greater dynamic frequency area ratios than their mechanical counterparts. Knowledge of the force-time history and force-frequency response characteristics of spinal manipulative instruments may provide basic benchmarks and may assist in understanding mechanical responses in the clinical setting.
To determine if a new method of lumbar extension traction can increase lordosis in chronic low back pain (LBP) subjects with decreased lordosis.
Nonrandomized controlled trial with follow-up at 3 ...months and 1(1/2) years.
Primary care spine clinic in Nevada.
Beginning in mid-1998, the first 48 consecutive patients, who met the inclusion criteria of chronic LBP with decreased lordosis and who completed the treatment program were matched for sex, age, height, weight, and pain scores to 30 control subjects with chronic LBP, who received no treatment.
A new form of 3-point bending lumbar extension traction was provided in-office 3 to 4 times a week for 12+/-4 weeks. Per session, traction duration was started at 3 minutes and was increased to a maximum of 20 minutes. For short-term pain relief, torsion lumbar spinal manipulation was provided in the initial 3 weeks.
Pain as measured on a visual analog scale (VAS) and standing lateral lumbar radiographic measurements.
Pain scales and radiographic measurements did not change in the control subjects. In the traction group, VAS ratings decreased from mean +/- standard deviation of 4.4+/-1.9 pretreatment to 0.6+/-0.9 posttreatment (P<.001), and radiographic angles (except at T12-L1) showed statistically significant changes. Mean changes were 5.7 degrees at L4-5 (P<.001), 11.3 degrees between posterior tangents on L1 and L5 (P<.001), 9.1 degrees in Cobb angle at T12-S1 (P<.001), 4.6 degrees in pelvic tilt (P<.001), and 4.7 degrees in Ferguson's sacral base angle (P<.001). At long-term follow-up (17(1/2)mo), 34 of the 48 (71%) subjects returned. Improvements in lordosis were maintained in all 34.
This new method of lumbar extension traction is the first nonsurgical rehabilitative procedure to show increases in lumbar lordosis in chronic LBP subjects with hypolordosis. The fact that there was no change in control subjects' lumbar lordosis indicates the stability of the lumbar lordosis and the repeatability of x-ray procedures. Because, on average, chronic LBP patients have hypolordosis, additional randomized trials should be performed to evaluate the clinical significance of restoration of the lumbar lordosis in chronic LBP subjects.
Since thoracic cage posture affects lumbar spine coupling and loads on the spinal tissues and extremities, a scientific analysis of upright posture is needed. Common posture analyzers measure human ...posture as displacements from a plumb line, while the PosturePrint claims to measure head, rib cage, and pelvic postures as rotations and translations. In this study, it was decided to evaluate the validity of the PosturePrint Internet computer system's analysis of thoracic cage postures. In a university biomechanics laboratory, photographs of a mannequin thoracic cage were obtained in different postures on a stand in front of a digital camera. For each mannequin posture, three photographs were obtained (left lateral, right lateral, and AP). The mannequin thoracic cage was placed in 68 different single and combined postures (requiring 204 photographs) in five degrees of freedom: lateral translation (Tx), lateral flexion (Rz), axial rotation (Ry), flexion-extension (Rx), and anterior-posterior translation (Tz). The PosturePrint system requires 13 reflective markers to be placed on the subject (mannequin) during photography and 16 additional "click-on" markers via computer mouse before a set of three photographs is analyzed by the PosturePrint computer system over the Internet. Errors were the differences between the positioned mannequin and the calculated positions from the computer system. Average absolute value errors were obtained by comparing the exact inputted posture to the PosturePrint computed values. Mean and standard deviation of computational errors for sagittal displacements of the thoracic cage were Rx=0.3+/-0.1 degrees , Tz=1.6+/-0.7 mm, and for frontal view displacements were Ry=1.2+/-1.0 degrees , Rz=0.6+/-0.4 degrees , and Tx=1.5+/-0.6 mm. The PosturePrint system is sufficiently accurate in measuring thoracic cage postures in five degrees of freedom on a mannequin indicating the need for a further study on human subjects.
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