PubMed Health⌕ Search

Biomedical subjects

M H Pope

Publications and source records attributed to M H Pope.

At least 109 records · Page 6Linked to original sources
PubMed1989

The design and use of a microcomputerized real-time muscle fatigue monitor based on the medial frequency shift in the electromyographic signal.

We have designed a real-time microcomputerized muscle fatigue monitor based on the median frequency shift of the electromyographic signal, computed via the fast Fourier transform. For the ten subjects performing an isotonic and isometric trunk extension task on two separate days, preliminary results suggest a repeatable linear decrease in median frequency as a function of time.

Electromyography↗
PubMed1989

Biomechanics of the lumbar spine.

The magnitude of low back pain in terms of its occurrence and cost is reviewed. The biomechanics of the lumbar spine are related to the functional anatomy. The disparate functional mechanical requirements of the spine, support, mobility, housing, protection and control are reviewed. Typical forces one applies to the spine in activities of daily living as well as in mechanical overloads are discussed. The loads are broken down into tensile, compressive, shear and torsional loads. The posterior elements, the vertebral body and the intervertebral disc are reviewed separately and some implication in terms of the aetiology of low back pain is given. Finally, the behavior of the unit (the functional spinal unit) is discussed.

Back Pain↗
PubMed1989

Risk indicators in low back pain.

Injuries leading to low back pain can occur by direct trauma, overexertion or repetitive trauma. Overexertion is claimed by 60% of low back pain patients as the cause of injury. Of these patients with overexertion injuries, 66% implicated lifting and 20% pushing or pulling. It is, however, difficult to relate the workplace to the complaint of low back pain in a specific worker, and low back pain is found quite often in those with sedentary occupations. The incidence, severity and potential disability are all related to the demands on the individual in the workplace. Among the factors implicated are the requirements for lifting (particularly when compared to the worker's lifting capacity), pushing and pulling, posture, and cyclic loading. Drivers of heavy vehicles have two to four times the average incidence of serious low back pain. This is probably due to the cyclic loading environment. The general psychosocial environment (including that at work) is an important risk factor. The first attack of low back pain occurs in the teens or twenties. Low back pain is as frequent in females as males, although women in manual materials handling jobs are at greater risk. Posture, anthropometry and mobility measures have limited prognostic value. Muscle strength and physical fitness probably have some value. Radiographic findings have little pragmatic value.

Age Factors↗
PubMed1989

The balance point of the intervertebral motion segment: an experimental study.

A loading or "balance" point was sought that could serve as a functional reference for mechanically testing spinal motion segments. This point is located above the in-vitro motion segment where, when an axial compressive load is applied, the segment exhibits minimal coupled rotation. The balance point is a reliable indicator of the mechanical characteristics of the segment. Segments exhibited increasing rotation as axial compressive loads were applied further and further away from the balance point. The location of the balance point was significantly affected by sustained static or cyclic flexion-compression loading and by brief flexion-compression overloads.

Biomechanical Phenomena↗
PubMed1988

Total knee arthroplasty kinematics. An in vivo evaluation of four different designs.

Thirty-four patients who had 42 total knee arthroplasties during the past 5 years were examined. Four types of total knee arthroplasties (Tricon-M, PCA, Variable Axis, and Anametric) were evaluated, using a computerized knee evaluation system. The patients and 10 controls with normal knees were tested for anteroposterior stability with the Lachman test, medial/lateral stability at 20 degrees, varus/valgus stability at 20 degrees, internal/external rotation at 80 degrees and 20 degrees of flexion, and internal/lateral rotation (screw home) over the active range of motion. At 30 degrees of flexion, the Variable Axis prosthesis was 54% more constrained than the normal knee to anterior/posterior shear. The Anametric and the Variable Axis were more lax under varus/valgus stress than the normal knee by 85% and 71%, respectively. There were no statistical differences for any of the other tests.

Aged↗
PubMed1988

Depth of insertion of transpedicular vertebral screws into human vertebrae: effect upon screw-vertebra interface strength.

Improvement in the strength of the transpedicular screw-vertebra interface by increasing the depth of screw insertion may provide improved performance of spinal implants using such screws. Within human cadaveric vertebrae, we measured the failure strength of Vermont Spinal Fixator (VSF) screws under flexion or torsion loads and of Schanz screws under pull-out loads (along the screw axis). Comparisons between opposite pedicles of vertebral specimens were made at 50 vs. 80% and 80 vs. 100% of maximum available insertion depth. Mean failure strength of VSF screws at 50% depth was 75-77% (depending upon load type) of that at 80% depth; strength for screws at 100% ("to-cortex") depth was 124-154% of that at 80%. Reanalysis of the data from Lavaste shows, contrary to his conclusion, a 26% increase in strength from a 5-mm increase in screw depth of insertion. All these differences were significant (p less than 0.05) by the matched-pairs t test. Benefit from the increased strength of deeper screw placement must be balanced against possible increased operative risk. A "near-approach" x-ray view is suggested here to decrease that presumed operative risk.

Bone Screws↗
PubMed1988

Repeatability of four clinical methods for assessment of lumbar spinal motion.

Spinal motion usually is recorded from subjective observation of the fully flexed trunk using a goniometer or the distance from the fingertips to the floor. To quantify functional improvement in the low-back pain patient, the repeatability of four clinical techniques was studied: the common fingertip-to-floor distance; the modified Schober; the two-inclinometer method, and a photometric technique. Ten normal subjects (five men, five women), ages 24 to 34 years old, were examined in full flexion, full extension, and the erect position, both standing and sitting. Repeatability was poor for the fingertip-to-floor method in all postures and for the two-inclinometer method in full flexion. Although other methods for various postures had good repeatability, the modified Schober method of determining lumbar spinal motion was the most repeatable and is recommended for a routine, noninvasive, clinical evaluation of lumbar spinal motion.

Adult↗
PubMed1988

The biomechanics of lumbar disc herniation and the effect of overload and instability.

A multipart study has been performed to provide a mechanical explanation for the epidemiologic association between sitting in static (e.g., factory or office) or vibration (e.g., car or truck driving) environments and acute herniated lumbar discs. It was shown that a 1 h exposure to sitting environments caused significant changes in the mechanical properties of the lumbar intervertebral disc. During many of the latter tests, specimens were unstable (exhibited by a sudden, large flexion and/or lateral bend rotation response to an axially applied load). This showed that a motion segment in the lumbar spine could suddenly buckle and apply a tensile impact loading to the posterolateral region of the disc. We also demonstrated that a combined lateral bend, flexion, and axial rotation vibration loading could cause tracking tears proceeding from the nucleus through the posterolateral region of the anulus. It suggests that a mechanism for disc herniation is mechanical changes leading to instability of the motion segment. These experiments complete the argument that lumbar disc herniations can be a direct mechanical consequence of prolonged sitting in static or vibration environments.

Aged↗
PubMed1987

A mechanical model for the human intervertebral disc.

Stress relaxation experiments were performed on specimens from a human intervertebral disc. Specimens were made from the nucleus pulposus and from the external lamellae of the anulus fibrosus in two different orientations. Tests were run with varying moisture content so as to develop a relaxation master curve. A model was developed based on the experimental data. It was found that the short term master curve for the lamellae of the anulus and nucleus are similar, whereas the long term rubbery plateau is different between the lamellae and the nucleus. It was also established that the master curves for different lamellae and the nucleus were shifted relative to each other in the time domain due to changes in water content. The average relaxation modulus of the whole disc was obtained by averaging the properties between the anulus and nucleus. This model was then used for studies of Schmorl's nodes, of degenerated discs and for circumstances in which hydration is considered to be important.

Body Water↗
PubMed1987

The relationship between trunk muscle electromyography and lifting moments in the sagittal and frontal planes.

In this study, we explore the relationship between moments in the frontal and sagittal planes, generated by a lifting task, vs the electromyographic (EMG) activity of right and left trunk muscle groups. In particular, we postulate that the functional dependence between erector spinae muscle activity and the applied lifting moments about the spine is as follows: the sum of left and right erector spinae processed EMG depends on the sagittal plane moment, and the difference of left and right erector spinae processed EMG depends on the frontal plane moment. A simple out-of-sagittal plane physical model, treating the lumbar spine as a two degree-of-freedom pivot point is discussed to justify these hypotheses. To validate this model, we collected surface EMG and lifting moment data for ten males performing a grid of frontal and sagittal plane lifting tasks. A digital RMS-to-DC algorithm was developed for processing raw EMG. For these tests, we measured EMG for the left and right erector spinae and for the left and right external oblique muscles. The processed EMG signals of the left and right erector spinae muscles are summed and differenced for comparison to the measured sagittal and frontal plane moments. A linear correlation (r2) of 0.96 was obtained for the sum of erector spinae EMG vs the sagittal plane moment; a corresponding value of r2 = 0.95 was obtained for the difference vs the frontal plane moment. No correlations (r2 less than 0.004) was found for the sagittal plane moment and the difference of the left and right erector spinae EMG, and the frontal plane moment and the sum of the left and right erector spinae EMG.

Back↗
PubMed1987

Water content in human intervertebral discs. Part I. Measurement by magnetic resonance imaging.

Tension-relaxation experiments were performed on human disc lamellae specimens. The water content was found to affect the viscoelastic behavior and a master relaxation curve was constructed from the experimental data. The water content of disc phantoms is measured by magnetic resonance imaging (MRI) techniques. MRI was used to compare the discs of patients of different ages. The possibility of obtaining cross-sectional water distribution in human intervertebral disc material using MRI techniques and its relation to the disc's mechanical properties was explored, with the goal of constructing a realistic mathematical model of the disc which takes into account the water content of the disc.

Body Water↗
PubMed1987

Water content in human intervertebral discs. Part II. Viscoelastic behavior.

Water content of intervertebral discs is a significant aspect of both viscoelastic behavior and age-related degenerative changes. Using water content as a dependent variable, stress-relaxation was measured using standardized anulus fibrosus specimens strained at various levels of strain. Synthesis of experimental data into a master relaxation curve allows prediction of specimen response over time intervals not readily accessible experimentally. A quantitative understanding of the role of water content may have important clinical application, since magnetic resonance imaging is a tool which should allow water content determination in vivo.

Biomechanical Phenomena↗
PubMed1987

Internal displacement distribution from in vitro loading of human thoracic and lumbar spinal motion segments: experimental results and theoretical predictions.

Small metal markers are implanted within intervertebral discs and their displacements in response to a complex load (flexion, compression, and anterior shear) are measured radiographically. These are contrasted to the displacements predicted by a finite element model (FEM) that uses 20 constant-strain triangular elements and is based upon a linear elastic isotropic material. The central portion of the disc (nucleus pulposus) moves posteriorly and oppositely to the FEM prediction. The anterior and posterior portions of the disc agree more closely with the FEM than the central portions of the disc. In general, the FEM predicts much more accurately the up-down displacement components than it does the anterior-posterior components. The measured displacements provide a new class of information concerning the function of the interior of the disc, and also provide a new basis for validation of FEMs that attempt to mimic real intervertebral disc behavior. Implications for understanding of disc function and pathology are discussed.

Aging↗
PubMed1987

The role of prerotation of the trunk in axial twisting efforts.

The myoelectric activity of selected trunk muscles was recorded during the development of controlled isometric axial torques. Muscle activity was measured bilaterally over the erector spinae, the rectus abdominus, the oblique external and the oblique internal abdominal muscles at the L3 level. Subjects first applied graded isometric torque efforts over a 10 second ramp up to maximum voluntary contraction with the trunk in neutral rotation. They then repeated the effort with the trunk twisted to the left and right. The largest electromyographic activities were found in the agonistic oblique muscles, but considerable antagonistic activity was present also. While the activity of the internal oblique and rectus were bilaterally similar in symmetric standing a difference occurred between the two sides when the trunk was twisted to the right or left. Axial prerotation of the trunk by 30 degrees in the direction of torque development marginally decreased the maximal developed torque, whereas prerotation in the opposite direction increased the developed torque.

Abdominal Muscles↗
PubMed1987

The response of the seated human to sinusoidal vibration and impact.

Low back pain has been shown to occur more frequently among vehicle drivers than in representative control groups. Thus the response of the human to vibration and impact is of interest. This study investigated the response of the spine to both impact and sinusoidal excitation in either a relaxed or erect seated posture. The sinusoidal testing apparatus used was a resonating system consisting of two parallel wooden beams, simply supported, and the impact testing apparatus a bearing-guided, spring-suspended platform, struck from below. Ten subjects (5 males, 5 females) were evaluated using both methods. Transfer functions were compared at 2-4 Hz, 4-8 Hz and 8-16 Hz intervals using a sign test. Although in 24 comparisons of either test method (vibration or impact) or posture (erect or relaxed) where eleven showed differences significant at the p less than .05 level, only 2 out of 24 comparisons were the differences distinct enough to be significant (at the p less than .01 level). Both of these latter differences were due to test method while the subjects were sitting erect. In those instances where there were no significant differences due to test method, the impact method may be a viable replacement for the vibration test method. Where the levels of significance are higher (p less than .01 or p less than .05), further study of the magnitude of the differences is indicated and may reveal further insight into the seated individual as a system.

Adolescent↗
PubMed1987

Stability of fixation in femoral neck fractures. Comparison of four fixation devices in vivo and in cadavers.

On human cadaveric femora, internal fixation of cervical osteotomies was performed with four different devices. With the use of a lever, a static force was applied through the acetabulum to the osteotomy site. Motion at the osteotomy site was measured by two strain gauges. The compression force necessary to inhibit motion at the osteotomy site during the fixation procedure was measured. This force was lower with a hook pin than with the other devices. During surgery in 12 patients with displaced femoral neck fractures, the forces holding the fracture surfaces together were measured with a dynamometer. The force at which widening of the fracture gap was observed by fluoroscopy was recorded. In seven fractures, the mean compression force was 110 (60-170) N. The remaining five fractures did not open up when pressures of up to 200 N were applied. These forces were always greater than the hook pin forces measured in the cadaver experiments, but often less than the forces obtained with the other devices.

Aged↗
PubMed1987

A comparison of ankle taping methods.

Four different types of ankle tapings were applied to a model of the human ankle joint. The model was constructed so that it contained a hinge to represent the ankle joint and had an external shape identical to a real ankle and foot. A mechanical testing machine was used to apply moments to the model at a controlled loading rate. From these tests, the deflection and torque to failure and the tangent stiffness were determined. Loadings of an ankle joint in vivo revealed that the angular deflection to initiate pain was approximately 8 degrees. Only the figure eight and full tapings could withstand 8 degrees of angular displacement on the ankle model prior to failure. Analysis of athletic trauma revealed that torques of 420 Nm could be applied to the ankle joint. Only the figure eight taping with three or more wraps has adequate strength to withstand this moment, and thus this taping is recommended. In practice, tapings failed by shearing away from the surface of the foot of shrinking rather than by rupture of the tape.

Ankle Injuries↗