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Biomedical subjects

S Gracovetsky

Publications and source records attributed to S Gracovetsky.

16 recordsLinked to original sources
PubMed1996

Can the computerized physical examination differentiate normal subjects from abnormal subjects with benign mechanical low back pain?

Inconsistencies among physicians in the evaluation of benign low back conditions make standardization desirable. A computerized physical examination device was used to evaluate low back pain patients and compare their results with a normative database obtained from a selection of healthy subjects. A high-resolution motion analysis system tracked the movement of skin markers placed on the midline and pelvis. Surface electromyography electrodes placed above L(5) collected data from multifidus. From the kinematics of skin markers during flexion extension with lifts up to 32 kg, and lateral bending with lifts up to 4.6 kg, the following parameters were estimated: lumbosacral angle and elongation, contribution of each lumbar segment to the lordosis reduction, relative pelvic/spine motion and trunk velocity. First, the average normal value for each estimated parameter was determined using 40 normal subjects. For each subject, the difference between his parameter and the normal was processed by an expert system generating a normality index varying from zero (perfect abnormal) to one (perfect normal). To develop the expert system's rules, a preliminary group of 20 very abnormal subjects were used, such that the normality index separated them from the normals. For validation, a set of 29 WCB sprain patients and another set of 42 discogram positive were selected. Each subject was tested and his computerized normality index calculated without any clinicians' input. The computerized normality index was compared with the clinicians' evaluation which was taken to be the gold standard. The Receiver Operating Characteristic technique was used to quantify the discrepancies. Results show that the expert system can detect clinically abnormal subjects with accuracy (sensitivity 83-91% and specificity >/=90%) while providing quantitative information on workers' functional capacities.

Journal Article↗
PubMed1995

A database for estimating normal spinal motion derived from noninvasive measurements.

STUDY DESIGN: A database for estimated normal spinal motion was derived using a noninvasive, high-resolution, computer-aided system, which tracks the motion of skin markers strategically placed on the spine. Forty normal subjects, selected from hundreds of possible subjects according to rigorous inclusion/exclusion criteria, were tested on the system. OBJECTIVES: Patterns of estimated spinal motion were analyzed as a function of load, age, and sex, confirming a correlation between the movement of spinal segments and the motion of skin markers. SUMMARY OF BACKGROUND DATA: The Workers Compensation Board of Quebec funded and supervised the experiments necessary to establish a normative reference database for a high-resolution motion analysis system that permits a noninvasive assessment of spinal function. A previous study examined the correlation between the movements of the skin markers and the underlying bony structures for trunk flexion. Skin movement cannot be random and contains information characterizing both the spine and its surrounding soft tissues. METHODS: A noninvasive dynamic imaging system was used to measure normal spinal function under free movement. A high-resolution three-dimensional camera system collected basic kinematic data from strategically placed skin markers over the lumbar spine while the activity of paraspinal muscles was being recorded with surface electromyography. The measurements were analyzed for consistent, specific patterns recognizable as normal lumbar spine skin motion and reflecting normal lumbar spine function. A comparison was made with previous radiographic studies to confirm the correlation between the motion of skin markers and lumbar spine function. RESULTS: Lumbar skin marker motion patterns in normal subjects were consistent and varied little with load; gender had no effect except in the initial phase of a movement. There was less mobility but similar coordination in older subjects. No inconsistencies with previous radiologic investigations were found for sagittal and lateral plane movement.

Adolescent↗
PubMed1990

Analysis of spinal and muscular activity during flexion/extension and free lifts.

Detailed measurements of the relative contributions of spine motion and pelvic motion during flexion-extension and free lifts (squat-type) are examined. The results are consistent with the conclusion that passive stretching of the ligamentous tissues transmits significant extensor moment in these activities, the power being supplied by the hip extensor complex acting on the pelvis. In addition, certain injuries result in measurable changes in the kinematic parameters that determine the ligamentous involvement, and these changes can be used to help evaluate spinal condition.

Biomechanical Phenomena↗
PubMed1989

The importance of pelvic tilt in reducing compressive stress in the spine during flexion-extension exercises.

An explanation for the importance of pelvic tilt exercises is proposed. This explanation derives from a mathematical model that predicts the existence of a relationship between lordosis (pelvic tilt) and the distribution of stresses within the spine. The model predicts that, for every angle of forward flexion, there is a unique degree of lordosis that will minimize and equalize the compressive stress within the spine. This stress-minimizing posture also is associated with the minimum muscular activity; the balance of the moment is supported by passive stretching of the connective tissues. These predictions were tested by comparing them with empirical values of spinal geometry and muscular activity, as measured simultaneously by an opto-electronic motion analysis and electromyographic (EMG) data collection system.

Exercise↗
PubMed1986

Function of the spine.

In spite of the considerable effort which has been invested in attempts to understand the mechanism of human spines, substantial controversy remains, particularly in connection with assumptions which have to be made by those engaged in biological modelling. The hypothesis presented here is that the living joint has stress sensors driving a feedback mechanism, an arrangement which could react to imposed loads by modifying muscular action in such a way as to minimize stress at the joints and therefore the risk of injury. A theory of this kind gives an image of the spine not in terms of a spatial picture, as would a CAT scan, but in terms of stresses, forces and moments acting at the intervertebral joints. Calculations show that the erectores spinae alone cannot support more than about 50 kg; there must be some other mechanism to explain man's ability substantially to exceed that load. It is suggested that the interaction between the erectores spinae and the abdominals are of fundamental importance in the function of the spine; how they are co-ordinated during the lifting of weights is examined in detail. The theory resulting from this hypothesis is used to relate spinal injury and an injured subject's posture and behaviour. A mathematical formulation permits an objective evaluation of the spine, and a procedure for determining an automatic diagnosis of lumbar spine disabilities is proposed.

Animals↗
PubMed1986

Determination of safe load.

The biomechanical criteria adopted by the National Institute for Occupational Safety and Health are shown to be based on considerations that are not consistent with current experimental data and theoretical principles. It is therefore suggested that these standards ought to be replaced, and a rationale for doing so is proposed.

Accidents, Occupational↗
PubMed1985

An hypothesis for the role of the spine in human locomotion: a challenge to current thinking.

Locomotion was first achieved by the motion of the spine. The limbs came after, as an improvement, not as a substitute; and yet, analysis of bipedal gait concentrates almost exclusively on the motion of the limbs. The requirements for land locomotion are examined from a general point of view and the evolution of the vertebrate spine is presented as a mechanism designed to move the animal. The necessary spinal movements are also analysed; the role of the musculoskeletal system is discussed and it is shown that the lumbar spine is a key structure in land locomotion, the pelvis being driven by the spine. The optimum control of motion demands that the stress at all the intervertebral joints should be minimized and equalized. This theory of locomotion requires the central nervous system to control the torque at those intervertebral joints and suggests that a breakdown of the control system would result in torsional failure of the spine. The theory is supported by EMG, force and torque data collected from several sources.

Animals↗
PubMed1985

The abdominal mechanism.

The abdominal mechanism, utilizing intraabdominal pressure, has been described and numericized. Simulations show that the lumbodorsal fascia under control of the abdominal muscles contributes to reduce the stress at the intervertebral joint. The musculature of the lumbar spine is of primary importance in the control of the efficiency of the spinal mechanism. The system of loading, which results in observable physiologic response, maintains the compressive load at virtually 90 degrees at the bisector of the disc for all weights and all angles of forward flexion.

Abdominal Muscles↗
PubMed1984

The nature of instability.

(Clinical) instability is that (symptomatic) condition where, in the absence of new injury, a physiologic load induces abnormally large deformations at the intervertebral joint.

Humans↗
PubMed1984

Tolerance of the human cervical spine to high acceleration: a modelling approach.

A sagittal plane mathematical model for the cervical spine has been used to simulate the neck's response to loads due to high acceleration. The model is capable of simulating the muscular response of the cervical spine and the stress distribution between the joint levels. In order to obtain conservative estimates of the maximum acceleration that the neck can support, the neck was simulated using the assumption that the inertial load is supported primarily by the muscles. It was found that accelerations of up to 30 g can be supported with the appropriate posture and direction of acceleration. Estimates were also obtained using experimental results to approximate the role that the ligaments of the spine play in supporting the load. It was found that accelerations of up to 40 g can be supported for the appropriate posture and acceleration direction.

Acceleration↗
PubMedDate not supplied

The mechanism of the lumbar spine.

The moments generated in the lumbar spine by a weight lifter are balanced by moments generated internally by muscles and by the intervertebral ligamentous structures including the disc. Unique real number solutions have been obtained by a optimization technique minimizing shear and penalizing excessive muscle power. The model faithfully reproduces the electromyographic responses and all known experimentally-determined values for muscle power and compression. The outputs can be used to calculate a realistic motion of the spine under various loads. The model suggests that in handling heavy loads, the stress at each intervertebral joint is identical and with maximal voluntary effort, the weight lifter does not exceed 67% of the ultimate strength of his tissues.

Adult↗
PubMedDate not supplied

The optimum spine.

System theory is used to describe the mechanism of the lumbar spine. The role of the spine in vertebrate evolution is presented. The importance of the intervertebral joint for the survival of the species is shown to be crucial. The mechanical behavior of the joint is derived, and from this the corresponding spinal motion and muscular responses is calculated. It is shown that physiologic behavior implies that the stress at the intervertebral joints is equalized and minimized. From this simple condition, the motion of the spine in the sagittal plane is calculated. From the analysis of sagittal plane motion together with a knowledge of the energy transfer through the intervertebral joint, a new theory of locomotion is derived. This theory of locomotion differs in important respects from current theories, but nevertheless explains available experimental data. This unified theory of the function of the human spine permits the determination of the level of safe loads that can be lifted and transported. It predicts the conditions of load transfer through a joint. It proposes a new approach to the mechanism of arthritis and to the repair of fractures.

Electromyography↗