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- Kaigle Holm, Allison, 1964, et al.
(författare)
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In vivo dynamic stiffness of the porcine lumbar spine exposed to cyclic loading: influence of load and degeneration.
- 1998
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Ingår i: Journal of spinal disorders. - 0895-0385. ; 11:1, s. 65-70
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic axial stiffness of the L2-3 motion segment subjected to vibratory loading under intact and injured states of the intervertebral disc was studied using an in vivo porcine model. Three groups of animals with the following states of the intervertebral discs were studied: intact disc, acutely injured disc, and degenerated disc. A miniaturized servo-hydraulic exciter was used to sinusoidally vibrate the motion segment from 0.05 to 25 Hz under a compressive load with a peak value of either 100 or 200 N. The dynamic axial stiffness of the intervertebral disc was calculated at 1-Hz intervals over the frequency range. The results showed that the dynamic axial stiffness was frequency dependent. A positive relationship was found between an increase in mean dynamic stiffness and load magnitude. An increase in mean stiffness with successive exposures at the same load magnitude was observed, despite the allowance of a recovery period between loading. The greatest difference was noted between the first and second load sets. No significant change in stiffness was found due to an acute disc injury, whereas a significant increase in mean stiffness was found for the degenerated disc group as compared with the intact group. The form of the frequency response curve, however, remained relatively unaltered regardless of the degenerated state of the disc. With heavier loads, repeated loading, and/or disc degeneration, the stiffness of the intervertebral disc increases. An increase in stiffness can mean a reduction in the amount of allowable motion within the motion segment or a potentially harmful increase in force to obtain the desired motion. This may locally result in greater stresses due to an altered ability of the disc to distribute loads.
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| 2. |
- Kaigle Holm, Allison, 1964, et al.
(författare)
-
Muscular and kinematic behavior of the lumbar spine during flexion-extension.
- 1998
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Ingår i: Journal of spinal disorders. - 0895-0385. ; 11:2, s. 163-74
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Tidskriftsartikel (refereegranskat)abstract
- Reduction in lumbar muscular activity at full body flexion, known as flexion relaxation, has been studied in relation to overall trunk, lumbar spine, and hip flexion, but has not been evaluated in conjunction with motion on the segmental level. In this study, intervertebral motion in a lumbar motion segment, trunk flexion, and the electromyographic activity in the lumbar erector spinae muscles were simultaneously measured during dynamic flexion-extension in seven patients with chronic low back pain with symptoms suggesting segmental instability and in six asymptomatic controls. A linkage system, which attached directly to the spinous processes of a lumbar motion segment, was used to continuously measure the sagittal plane intervertebral motion, while a potentiometric goniometer measured trunk flexion; myoelectric activity was measured using surface electrodes. It was found that intervertebral motions, as well as trunk mobility, were significantly less in the patients, both in terms of range and pattern of motion. Flexion relaxation was demonstrated in the controls by a 78% decrease in myoelectric activity at full flexion, whereas in the patients, only a 13% reduction was found, with most of the patients experiencing no reduction at all. Flexion relaxation occurred only in subjects in whom intervertebral rotation had reached a stage of completion considerably before full trunk flexion was achieved. These findings suggest that persistent muscle activation, which restricts intervertebral motion, is a means by which the neuromuscular system provides stability to help protect diseased passive spinal structures from movements that may cause pain.
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