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Biomechanical comparison of the stability provided by four pedicle screw systems and facet screw fixation
742
Abstracts
BIOMECHANICAL COMPARISON OF THE STABILITY PROVIDED BY FOUR PEDICLE SCREW SYSTEMS AND FACET SCREW FIXATION M. Panjabi*, I. Yamamoto+, T. Oxland*, J. Crisco*, & D. Freedman* *Dept. of Orthopaedics and Rehabilitation, Yale University Medical School, New Haven, CT 06501 +Dept. of Orthopaedic Surgery, Hokkaido University School of Medicine. Sapporo, Japan Pedicle screw fixation systems are becoming increasingly important as an option for spinal stabilization. This biomechanical study evaluated the three-dimensional stability provided by four such devices: Wiltse Spine Fixation System (with I and 2 rods), A0 Fixation Device, Steffee Plate System and CD Fixation System. In addition, the stability provided by bone screws through the facets was determined. The instability test involved applying pure moments to Ll and measuring the relative motion of each vertebra in terms of Neutral Zones (NZ) and Ranges of Motion (ROM). All devices and facet screws reduced the motion of an injured specimen to less than 50% of the intact value in flexion loading. In axial rotation, only the Wiltse system reduced both NZ and ROM to below the intact values while in lateral bending, the AO, Steffee Plate, and CD systems reduced both motion parameters below the intact levels.
THE SAGITTAL THORACOLUMBAR
CENTROID CURVE WITH RESPECT TO THE LINE OF GRAVITY
D.J. Pearsall & J.G. Reid School of Physical and Health Education, Queen’s University,
Canada
The purpose of this study was to collect normative data measures of the sagittal thoracolumbar posture of the vertebral body centroids and to identify their relative position to the line of gravity. A non-invasive means of calculating the thoracolumbar vertebral body centroid curve within the sagittal plane from back profiles was utilized. A normal population sample of adolescents (28 males, 15 females) between ages 15 and 16 years, were evaluated. The centroid curves indicate that for females the line of gravity lay significantly more posterior than for the males. As well, the extent of kyphosis was significantly greater in the females with respect to the males. The passage of the line of gravity, in general, passed anterior to the vertebral centroids; yet, would remain within the vertebral bodies in the lumbar and upper thoracic and slightly anterior of the mid-thoracic vertebral bodies. This suggests that the gravitational moments created about the spine in the sagittal plane for upright stance are minimal.
Abstracts
BIOMECHANICAL COMPARISON OF THE STABILITY PROVIDED BY FOUR PEDICLE SCREW SYSTEMS AND FACET SCREW FIXATION M. Panjabi*, I. Yamamoto+, T. Oxland*, J. Crisco*, & D. Freedman* *Dept. of Orthopaedics and Rehabilitation, Yale University Medical School, New Haven, CT 06501 +Dept. of Orthopaedic Surgery, Hokkaido University School of Medicine. Sapporo, Japan Pedicle screw fixation systems are becoming increasingly important as an option for spinal stabilization. This biomechanical study evaluated the three-dimensional stability provided by four such devices: Wiltse Spine Fixation System (with I and 2 rods), A0 Fixation Device, Steffee Plate System and CD Fixation System. In addition, the stability provided by bone screws through the facets was determined. The instability test involved applying pure moments to Ll and measuring the relative motion of each vertebra in terms of Neutral Zones (NZ) and Ranges of Motion (ROM). All devices and facet screws reduced the motion of an injured specimen to less than 50% of the intact value in flexion loading. In axial rotation, only the Wiltse system reduced both NZ and ROM to below the intact values while in lateral bending, the AO, Steffee Plate, and CD systems reduced both motion parameters below the intact levels.
THE SAGITTAL THORACOLUMBAR
CENTROID CURVE WITH RESPECT TO THE LINE OF GRAVITY
D.J. Pearsall & J.G. Reid School of Physical and Health Education, Queen’s University,
Canada
The purpose of this study was to collect normative data measures of the sagittal thoracolumbar posture of the vertebral body centroids and to identify their relative position to the line of gravity. A non-invasive means of calculating the thoracolumbar vertebral body centroid curve within the sagittal plane from back profiles was utilized. A normal population sample of adolescents (28 males, 15 females) between ages 15 and 16 years, were evaluated. The centroid curves indicate that for females the line of gravity lay significantly more posterior than for the males. As well, the extent of kyphosis was significantly greater in the females with respect to the males. The passage of the line of gravity, in general, passed anterior to the vertebral centroids; yet, would remain within the vertebral bodies in the lumbar and upper thoracic and slightly anterior of the mid-thoracic vertebral bodies. This suggests that the gravitational moments created about the spine in the sagittal plane for upright stance are minimal.