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Biomedical subjects

M H Krag

Publications and source records attributed to M H Krag.

42 records · Page 3Linked to original sources
PubMed1984

Effects of disc injury on mechanical behavior of the human spine.

The effects of injury to the intervertebral disc were investigated using three-dimensional flexibility and creep measurements of functional spinal units from fresh cadaver lumbar spines. The techniques utilized were accurate and the data had a high degree of reproducibility. An injury to the annulus and a removal of the nucleus significantly altered the mechanical properties of the spinal unit. Not only were the main motions affected but also the coupled motions. Sagittal plane symmetry was disturbed, resulting in asymmetric facet joint movements. These effects of injury could be measured because of the three-dimensionality of the experiments. Previous studies, utilizing only axial compression loading, claimed to observe no changes due to the disc injuries and are, therefore, in conflict with the present findings.

Adult↗
PubMed1982

Cervical spine motion in the sagittal plane: kinematic and geometric parameters.

The kinematic function of the cervical spine has been examined previously by means of cineradiography or a sequence of lateral X-rays, usually of a flexion-extension range of motion. Interpretation of these studies, however, presents difficulties. One of the major problems is how to extract information from the X-ray images which is not only explicit, quantitative and accurate, but which is also diagnostically useful. Another problem is that as one increases the number of steps of motion between full flexion and full extension to obtain a more detailed examination, one also increases the amount of radiation exposure and the bulk of the data. Reported here is a technique which uses one lateral-view X-ray for each of five neck positions: full flexion, full extension, and three intermediate positions. From each set of X-rays, various parameters are derived to describe two types of data: kinematic (angles and centers of rotation), and geometric (pattern of curvature). This technique has been shown capable of identifying functional abnormalities in patients with neck pain who have no structural abnormalities detectable by X-ray. Further experience will be useful in better defining various types of functional abnormalities.

Adult↗
PubMed1977

Effects of preload on load displacement curves of the lumbar spine.

Elastic mechanical properties of the spine are a function of the axial preload as well as the physiologic loads. The published literature does not take into account the effect of the preload. In this study we have presented a new technique for applying large preloads together with 12 physiologic loads and for measuring the resulting three dimensional motion. Some of the conclusions regarding the elastic behavior of the lumbar spine are: (1) The application of any one of the 12 physiologic loads produces a three dimensional motion consisting of three translations and three rotations. (2) The main as well as the coupled motion curve is affected by the inclusion of preloads. (3) As represented by the main motion curves, the spine becomes more flexible in the presence of preloads with the physiologic forces directed laterally or anteriorly, or moments producing lateral bending or flexion. (4) The spine becomes less flexible in the presence of preload when it is subjected to axial tension or axial torsion. (5) No appreciable change due to the preloads is noticed in the load displacement curves when axial compression, posteriorly directed force, or extension moment is applied.

Biomechanical Phenomena↗