Search PubMed⌕ Search

Biomedical subjects

I A Stokes

Publications and source records attributed to I A Stokes.

At least 55 records · Page 3Linked to original sources
PubMed1989

Rib cage asymmetry in idiopathic scoliosis.

Seventy-one patients attending a scoliosis clinic and 10 control subjects were studied by a stereoradiographic three-dimensional reconstruction of the spine and rib cage. The symmetry of each rib pair (at each anatomic level) was described by measurements of rib arc length, chord length, enclosed area, maximum curvature, and frontal and lateral angulations. Patients were divided into four groups: 19 with a single right thoracic curve, 15 with a single left lumbar or thoracolumbar curve, 22 with double curves, and 15 with a curve with less than 10 degrees Cobb angle. In the control group and the group with minimal scoliosis, there was no statistically significant rib asymmetry. Among the patients with scoliosis, 11 of 19 patients with right single thoracic curves had rib arc lengths greater on the right side at the curve apex, and nine of 15 patients with left lumbar scoliosis had longer ribs on the left side in the corresponding region of the thoracic spine. Eleven of 22 patients with double curves had symmetrical rib lengths (within +/- 3%), the other 11 had ribs longer on the left. These proportions should not have occurred by chance (p less than 0.001). The mean rib length difference in patients with single thoracic curves was 1.39% (right longer than left), in single lumbar curves it was 3.57% (left longer than right), and in double curves 3.18% (left longer than right). These differences between the groups of patients and control subjects were statistically significant (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Axial rotation component of thoracic scoliosis.

The axial rotation (rotation about a vertical axis) of the vertebrae, of the ribs, and of the back surface are components of the deformity recognized clinically as the "rib hump" in thoracic scoliosis. Relationships of these rotations to the lateral deviation and lateral curvature of the spine were studied in 40 patients with idiopathic scoliosis. Stereoradiographs of the spine and rib cage were used to measure three components of axial rotation: rotation of the vertebrae, of the rib cage, and of the plane of maximum curvature of the spine. Stereotopographs of the back surface were digitized to measure the axial rotation of the back surface. In individual patients, there were high correlations of all components of axial rotation at each spinal level with the corresponding vertebral lateral deviation from the spinal axis. By regression analyses of the maximum values of each rotation in each curve, the rotation of the apex vertebra was found to be generally of lesser magnitude than the rotation of the plane of maximum curvature of the spine and in an opposite sense in kyphotic curves. The rib cage rotation was generally of lesser magnitude than the vertebra rotation, and the back surface rotation was less than both of these skeletal rotations. Vertebra rotation correlated most closely with lateral deviation of the spine. Simple segmental coupling of axial rotation and lateral bending could not be responsible for this axial rotation.

Humans↗
PubMed1989

Experimental instability in the rabbit lumbar spine.

The authors performed mechanical, biochemical, and histologic analyses of changes in the rabbit lumbar spine occurring after instability had been induced by facet removal to find whether this intervention produced an experimental model for intervertebral disc degeneration. Sham operated animals and an unoperated control group were used for comparison. Half of the operated animals were housed under conditions to promote higher physical activity than the other animals housed individually in small cages. Acutely, the removal of facet joints increased the flexibility of intervertebral joints. Over the following year, this increase in flexibility was reduced to close to control levels in all groups of animals. Within the intervertebral discs, there was no significant change in proportions or solubility of collagen or proteoglycans after surgery, nor was there microscopic or macroscopic evidence of disc degeneration. The surgical procedure produced hypermobility of the spine, but there was a subsequent restabilization, and the intended disc degeneration was not produced. These findings indicate that some as yet unidentified soft tissue repair process, facilitated by activity, overcame the hypermobility created at surgery, so degenerative changes in the intervertebral discs did not result. We suggest that other animal models of disc degeneration may represent a failure of reparative response to acute injury.

Animals↗
PubMed1989

Concordance of back surface asymmetry and spine shape in idiopathic scoliosis.

In order to determine why topographic methods have shown a poor correlation with radiographically measured scoliosis in clinical studies, the accuracy of detection of the presence, side, apex, and magnitude of a scoliosis curve was determined topographically (by moiré fringe photography and by projected raster photography) in 104 patients attending a scoliosis clinic. The presence or absence of thoracic curves was correctly shown by the topograms in 77% of cases, and in the lower region (lumbar and thoracolumbar curves) in 79% of cases. For correctly identified curves, the greatest back surface rotation was, on average, 1.0 vertebral levels below the skeletal curve apex in the thoracic region and 0.5 levels below the apex in the lower region. The moiré fringe with the greatest asymmetry occurred on average at 1.5 and 1.8 vertebral levels above the spinal apex in upper and lower regions, respectively. The magnitude of the Cobb angle was determined to within +/- 5 degrees in 24% of cases by moiré measurements, and in 27% by the raster technique. The side of the scoliosis was incorrectly diagnosed by topography in ten patients with minimal or 'nonstandard' vertebral rotation. It was concluded that the presence, level, and side of a scoliosis curvature is well demonstrated by back surface topography in patients with 'standard' rotation, but the magnitude of the scoliosis cannot be determined from topograms sufficiently accurately for most clinical purposes.

Adolescent↗
PubMed1989

EMG to torque relationship in rectus abdominis muscle. Results with repeated testing.

Rectus abdominis muscles of young healthy female volunteers were studied to determine both the maximum strength in isometric flexion and the relation between the surface electromyogram (RMS EMG) and torque. Both the upper and lower portions of the abdominal muscle were studied during graded increase and decrease of torque. Repeated testing was performed over 6 weeks. The form of the relation between torque and EMG was better described by a quadratic than by a linear regression relationship, but with considerable variability about the best-fit line. The torque-increasing and torque-decreasing parts of each test were different and were analyzed separately. After 6 weeks of repeated testing, maximum voluntary isometric flexion torque increased 16.8% (P less than 0.01). There was a decrease in the ratio of electromyographic activity to torque production, which was statistically significant in the torque-increasing recordings. These changes in maximum torque and in the EMG-torque relation were attributed to learning through a test-retest effect, rather than to a true change in muscle characteristics. These findings, which show changes in normal subjects undergoing repeated testing, do not support the reliability of isometric strength measurements, or measurements based on RMS EMG recordings, for quantifying abdominal muscle function in patients with back pain, or those undergoing strengthening exercises.

Abdominal Muscles↗
PubMed1988

Spinal deformity and back surface asymmetry in idiopathic scoliosis.

Stereo radiography and stereotopography were used to record simultaneously the three-dimensional spinal and back surface shape of 141 patients with a clinical diagnosis of adolescent onset idiopathic scoliosis. Radiography confirmed 80 patients with single lateral curves (Cobb angle 5-87 degrees); 59 with double curves (Cobb angle 5-61 degrees), and two patients with triple curves. Orientation of each vertebra was measured by the lateral deviation from the spinal axis and the axial rotation. For each curve detected, the Cobb angle, the maximum deviation, the maximum axial rotation, and the sagittal plane curvature was measured. Topographic data were used to generate a profile of a cross-section through the back of each vertebral level. This section was characterized by its axial rotation, deviation of its midpoint from the spinal axis, and area symmetry about the midpoint. Maximum values of these measurements in the region of each radiographic scoliosis curve were noted. Regression and correlation analysis showed (for each curve) a high correlation of apical vertebral lateral deviation with back surface axial rotation (r = 0.79) and with vertebral axial rotation (r = 0.79). The back surface rotation was less than vertebral rotation in magnitude, however, by a mean factor of 0.55. The measurement of the back surface asymmetry that gave the highest correlation with the skeletal deformity was the axial rotation. Relationships between skeletal and surface measures were similar for curves in thoracic and lumbar regions and for patients with single and double curves. There is potential for clinical application of surface measurement techniques to prescription of orthoses and monitoring of changes due to progression or treatment.

Adolescent↗
PubMed1988

Comparison of acoustic and electrical signals from erectores spinae muscles.

Comparison was made between simultaneous recordings of the electromyogram (EMG) and acoustic myogram (AMG) signals and the torque produced by the lumbar erectores spinae muscles of three healthy subjects while they performed isometric contractions. Repeatability of each signal was studied. The AMG had a relationship to the torque which was more quadratic than linear, whereas that of the EMG was more linear. The coefficient of variability of residuals about a "best-fit" line was 8.55% for torque-increasing EMG recordings and 19.2% for torque-increasing AMG recordings. At the same torque, the EMG was on average about 10% greater for increasing-torque recordings than for decreasing-torque parts of the recordings, but the magnitude of the AMG signal was about 10% less. With repeated testing on the same day, the coefficient of variability of the signal/torque relationship (torque-increasing) was 9% for EMG and 23% for AMG signals. With long-term testing over 2 weeks these coefficients were 23 and 39%, respectively. Correlation analysis showed that the two signal/torque relationships varied independently of each other.

Electromyography↗
PubMed1988

Measurements of the three-dimensional shape of the rib cage.

A stereoradiographic method was developed to measure the three-dimensional shape of the rib cage in vivo in order to provide descriptive data and to study symmetry in the normal population. The method is also intended for use in description of rib asymmetry in scoliosis. Rib midlines were reconstructed from digitized points on lines drawn through the middle of each rib image in stereo-radiographs of the rib cage. The method relied on pairing points in one image with a corresponding point found in the second image. The error term obtained from a Direct Linear Transformation (DLT) reconstruction program was used for optimizing this correspondence. The method was used on test objects of known shape where the standard deviation of measurement errors was found to be 0.72 mm. Studies in which different sets of points on the rib midlines were selected for digitizing showed that the precision of the method was 1.04 mm (S.D.). Rib shape was described by intrinsic measurements (arc and chord length, maximum curvature and enclosed area) and rib orientation by extrinsic measurements (frontal and lateral angulations and posterior rib cage rotation). No statistically significant rib shape asymmetry was found among ten subjects without spinal or thoracic abnormalities, although a trend of inequality of rib angulation at all anatomical levels was observed.

Biomechanical Phenomena↗
PubMed1988

Bulging of lumbar intervertebral discs: non-contacting measurements of anatomical specimens.

A noncontacting photogrammetric method was used to measure intervertebral disc bulge (deformation perpendicular to the disc surface) at an anterior site and a posterolateral site of 17 human lumbar discs. Specimens were tested in constructs consisting of two lumbar vertebrae and the intervening disc. The posterior elements were removed to give unobstructed visibility of the posterolateral aspects. Stereophotogrammetry was used to record the motion of target points attached to the disc and vertebral body surfaces. In axial loading, the bulging increased linearly with disc compression, which in turn had a nonlinear relationship with the applied load. Axial loads and offset compression loads of physiologic magnitude caused disc bulge that was generally less than 1 mm. Axial torsion of an otherwise unloaded specimen produced minimal change in disc bulge. The disc bulging measured in this study is generally less than that previously reported, especially for angular motions between the vertebrae. This is probably because the photogrammetric method used here is independent of motion of the vertebrae, which can corrupt mechanical, contacting methods of measurement.

Biomechanical Phenomena↗
PubMed1988

Dimensional changes of the feet in pregnancy.

Serial measurements of the volume, length, and width of the feet of seventeen pregnant women were made at, or close to, the thirteenth and thirty-fifth weeks of pregnancy and eight weeks postpartum. The same measurements were made twice on a control group of sixteen nulliparous women at intervals that ranged from sixteen to twenty weeks. There was no change in the length or width of the feet in either group. The mean volume of the feet increased 57.2 milliliters between early and late pregnancy (p less than 0.001) and decreased by only 8.42 milliliters between late pregnancy and eight weeks postpartum. These changes were attributed to retention of fluid or to an increase in soft tissue and not to stretching or relaxation of the ligaments.

Adult↗
PubMed1988

Spine and back-shape changes in scoliosis.

Thirty-five untreated patients with scoliosis were studied by Cobb radiography and back-surface photogrammetry on each of at least two clinic visits. Also, the maximum vertebral axial rotation was measured. Each pair of patient visits was classified as showing either a progression, improvement, or no change in the scoliosis using a threshold of 5 degrees change in the Cobb angle. The computer Cobb measurement was the most precise measurement, and the back-surface measurements were the least precise. The Cobb measurement of scoliosis is the most precise for detecting small changes, but can be improved by a computerized analysis of digitized radiographs.

Adolescent↗
PubMed1987

Three-dimensional spinal curvature in idiopathic scoliosis.

Scoliosis is usually considered as a deformity of the spine in the frontal plane, without reference to curvatures in other planes. In this study, the three-dimensional shape of the spine of 104 patients with untreated idiopathic scoliosis (5-55 degrees Cobb) was studied by means of stereo radiographs to determine relationships between curvature of the spine in the frontal plane view, in the lateral view, and in the intermediate views. There was a weak but statistically significant correlation (r = 0.2) relating greater scoliosis with lesser kyphosis or greater lordosis. In the thoracic region, the sagittal plane spinal curvature was less than that measured in a population without scoliosis (mean difference, 7.72 +/- 9.9 degrees). Seventy-four of 76 scolioses in the upper region of the spine with lateral curvature greater than 5 degrees Cobb were kyphotic. Sixty-four of 84 curves greater than 5 degrees Cobb in the lower region were lordotic. Measuring curvatures in the plane of symmetry of the rotated apical vertebra altered these ratios to 69 of 76 kyphotic in the upper region and 68 of 84 lordotic in the lower region. The plane of maximum curvature of sections of the spine with scoliosis was not related to the plane of symmetry of the rotated apical vertebra, for in kyphotic regions of the spine the rotations of these two planes were in opposite directions. In all cases, the magnitudes of the rotations were quite different, i.e., by a factor of -0.22 for curves in thoracic region and by a factor of 0.24 for curves in the lumbar region. This implies that mechanical measures to correct this spinal deformity or to prevent progression should apply different rotations to the apex from those applied to the curve as a whole and, in opposite senses, in curves in kyphotic regions. There was no evidence of an abnormality of sagittal curvature of a magnitude to implicate it in the etiology or in the treatment.

Adolescent↗
PubMed1987

Surface strain on human intervertebral discs.

The biomechanical functions of the internal components of the intervertebral disc are not well understood. The surface deformation of 17 human cadaveric lumbar intervertebral discs was studied by photogrammetry by adhering small optical targets to the disc surface and thereby recording the length, bulge, and vertical height of lines on the disc surface representing annular fibers. Discs were studied in pure compression, flexion and extension, axial rotation, and shear. Two definitions of a fiber were investigated: first with the end-points of the fiber on the vertebra ("bone-to-bone" definition), second, where the end points of the fiber were just before the disc vertebra junction (the "disc-only" definition). Measurements were compared with a "constant-volume" physical model and with a mathematical model of the intervertebral disc. Fiber strains were 6% or less under physiological conditions. Comparison of results from the two definitions of fiber length showed greater strains for the disc-only definition in compressive loading. Fiber strains were less than in the constant-volume model of comparable dimensions in compressive loading by a factor of about two, thus suggesting fluid loss or end-plate deformations in the physiologic conditions. The mathematical model indicated that the surface strain for intervertebral discs is very sensitive to the disc-height: diameter ratio and to fluid loss from the disc but is less sensitive to the helix angle of the fibers.

Adult↗
PubMed1987

Axis for dynamic measurement of flexion and extension torques about the lumbar spine. A computer simulation.

Most reports of trunk testing with an isokinetic dynamometer describe the axis of the machine aligned with the lumbosacral junction. A computerized mathematical simulation of motion of the lumbar spine under three conditions was performed, representing variations on the physiologic motion of the lumbar spine. The instantaneous center of rotation of the T12 vertebral body moving about a fixed pelvis was calculated and displayed. Under normal conditions, the center of rotation started close to the center of the L3 vertebral body and moved in an arc similar to that of L3 during flexion and extension. Dynamic testing of the trunk musculature in the lumbar region, therefore, should be performed with the axis of the isokinetic dynamometer aligned with the L3 vertebral body, and motion of the pelvis and thoracic spine should be minimized. This position of the axis provides the best approximation of the fixed axis of the testing machine to the physiologic axis. Failure to observe these precautions would tend to make the motion of the lumbar spine nonisokinetic and, thus, interfere with angular measurement of the spinal motion.

Adult↗
PubMed1987

Back surface curvature and measurement of lumbar spinal motion.

Lumbar spinal flexion and extension motion was measured radiographically and from the back surface curvature in 42 patients with low-back pain to determine whether the surface measurements provided accurate measurement of the total lumbar spinal motion and its distribution by vertebral level. Also, a biomechanical model of motion of the lumbar spine was used to predict the changes in the back surface as a function of varying amount of flexion and extension at the intervertebral articulations. Surface measurements provided reasonably accurate (+/- 11.2 degrees or +/- 25.5%) measurement of the total lumbar motion with a correlation coefficient of 0.58 between surface and radiographic measures. However, there was a poor correlation (varying between -.08 and .54 at different levels) between segmental motion measured radiographically and at the surface. Detection of the most mobile and least mobile intervertebral levels was done successfully by the surface curvature method in no more cases than would be expected by chance. Measurements of intersegmental motion are inherently error prone since they involve calculating differences between small angles which in turn are difficult to measure accurately. Surface measurements based on changes in back curvature are further complicated since the back surface has a variable relationship with spine shape and accurate measurement of curvature is very difficult.

Biomechanical Phenomena↗