Biomedical subjects

D L van Deursen

Publications and source records attributed to D L van Deursen.

6 recordsLinked to original sources

PubMed2001

In vitro torsion-induced stress distribution changes in porcine intervertebral discs.

STUDY DESIGN: A cadaveric porcine spine motion segment experiment was conducted. OBJECTIVE: To test the hypothesis that small vertebral rotations cause increased stress in the anulus while decreasing stress in the nucleus through stiffening of the anulus. SUMMARY OF BACKGROUND DATA: Stress profiles of the intervertebral disc reportedly depend on degeneration grade and external loading. Increased stress in the anulus was found during asymmetric loading. In addition, depressurization of the nucleus combined with an instantaneous disc height increase was found when small (<2 degrees ) axial vertebral rotations were applied. METHODS: Seven lumbar porcine cadaveric motion segments consisting of two vertebrae and the intervening disc with ligaments were loaded in the neutral position with 340 N of compression. Stress profiles were obtained in the neutral position, then after 0.5 degrees and 1 degrees axial rotation of the bottom vertebral body. The distribution of compressive stress in the disc matrix was measured by pulling a miniature pressure transducer through the disc along a straight path in the midfrontal plane. Stress profiles were measured in vertical (0 degrees ) and horizontal (90 degrees ) orientation. RESULTS: Deformation of the anulus by small axial rotations of the lower vertebra instantaneously decreased the horizontally and vertically measured stress in the nucleus while increasing stress in the anulus. A 1-hour period of creep loading decreased the stresses in the nucleus and the anulus 20% to 30%, depending on the orientation, but the effect of an increasing stress in the anular region after axial rotation persisted. CONCLUSIONS: The compressive Young's modulus of the composite anulus tissue increases instantaneously when small axial rotations are applied to porcine spine motion segments. This is accompanied by decreased stress in the nucleus pulposus, increased stress in the anulus fibrosus, changes in the stress profile superimposed on and independent of prolonged viscoelastic creep and dehydration, and changes in stress distribution independent of horizontal and vertical orientation.

Animals↗

PubMed2001

The effect of passive vertebral rotation on pressure in the nucleus pulposus.

To study the immediate effects of axial rotation on the intervertebral disc, six pig cadaver lumbar functional spinal units were exposed to rotations of up to 2 degrees, while disc height and intradiscal pressure were measured. The results showed that rotary movements are capable of causing an immediate increase in disc height and drop in nucleus pressure. However, the long-term effects were opposite in direction.

Analysis of Variance↗

PubMed2000

Length of the spine while sitting on a new concept for an office chair.

Changes in spinal length were used to evaluate a new concept for an office chair. This so-called dynamic chair imparts passive forced motion to the seated subject. The passive forced motion is a rotary movement about an axis, perpendicular to the seat with amplitude of 0.6 degrees and a frequency of 0.08 Hz. Change of stature is assumed to provide a measure for spinal load. Eight subjects were measured in two situations: static (without motion) and dynamic. In both situations the same office tasks were performed and the duration of the sitting period was 1 h. To allow for the normal shrinkage curve the starting time was the same on each of the measurement days. The results indicated a significant difference: when sitting on the dynamic chair the average spinal length increased in comparison to the spinal length in the static chair, where average spinal length decreased. It was concluded that there is spinal distress relief due to the passive motion of the chair.

Adult↗

PubMed2000

Mechanical effects of continuous passive motion on the lumbar spine in seating.

The aim of this study was to develop a model which describes the mechanical spinal response to small alternating pelvic stimulation induced by an active rotational movement of a normal chair. The rotary continuous passive motion (RCPM) of the seat about a vertical axis of only 0.6 degrees resulted in an increased in spinal length as opposed to the normal daily shrinkage, and back patients experienced pain relief. Passive and active exercies have been broadly applied for treating and healing spinal disorders. A rigid body package (ADAMS Android) was used to translate the stimulation of the ischial tubersoity in caudo-cranial handing-over visualisation. The parameters of the model were set so that the values of the global stiffness and geometry of the intervertebral discs could be changed. In vivo validation of the model was based on force and moment measurements using an internal AO fixator. The predicitons of the model concerning natural frequency (4.5Hz) in vertical direction and the axial torsion response on small pelvic torsion are comparable with experimental data.

Algorithms↗

PubMed2000

Spinal load changes during rotatory dynamic sitting.

OBJECTIVE: To measure load and moment changes acting on the lumbar spine during rotatory sitting. BACKGROUND: A new chair concept generating dynamic stimuli by alternating rotations in the horizontal plane of the chair's seat was recently developed. METHODS: Load and moment changes were measured telemetrically with a spinal fixator device in vivo. RESULTS: A rotatory frequency of 0.22 Hz with an amplitude of 1.8 degrees to the right and left side showed maximum axial force changes in the fixator of 23 N and maximum bending moment changes of 0.52 Nm. CONCLUSIONS: Lumbar force and moment changes during dynamic sitting occur, although only one patient was included in the study. Reasons could be temporary muscular activation in order to adapt the body's equilibrium conditions at the end-point rotation. RelevanceOur measurements suggest that a rotatory chair does have an effect on lumbar spine forces. It becomes more likely that this concept could improve the discs' nutrition and may prevent low back pain.

Adult↗

PubMed2000

Lumbar spine curvature during office chair sitting.

Prolonged sitting is generally accepted as a high risk factor in low back pain and it is frequently suggested that a lordotic posture of the lumbar spine should be maintained during sitting. We asked whether the sagittal curvature of the lumbar spine during sitting is affected by the seat tilt, backrest and the direction of the synchronised mechanism of the back and seat tilt (synchro tilt). Two office chairs were tested by multibody analysis interfacing a human model with a chair model. Results indicate that a synchronised mechanism of an office chair representing a posterior tilt of the seat while the backrest is reclined maintains an evenly distributed lumbar lordosis. The segmental angles are between 3.1 and 3.6 degrees at the lumbar vertebrae 1/2-4/5 (L1/2-L4/5). These lumbar spine segmental angles are not sensitive to the backrest height. In contrast, a synchro tilt concept with a reduction of the seat's posterior tilt while the backrest is reclined causes a strong reduction of the lumbar lordosis in backrest recline with a maximum reduction from 11.7 to 2.8 degrees in L4/5. As a consequence of these results, a synchro tilt concept with a posterior tilt of the seat while the backrest is reclined is preferable from the lumbar spine kinematics point of view.

Ergonomics↗