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- Ekström, Lars, 1959, et al.
(författare)
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Intervertebral disc response to cyclic loading--an animal model.
- 1996
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Ingår i: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine. - 0954-4119. ; 210:4, s. 249-58
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Tidskriftsartikel (refereegranskat)abstract
- The viscoelastic response of a lumbar motion segment loaded in cyclic compression was studied in an in vivo porcine model (N = 7). Using surgical techniques, a miniaturized servohydraulic exciter was attached to the L2-L3 motion segment via pedicle fixation. A dynamic loading scheme was implemented, which consisted of one hour of sinusoidal vibration at 5 Hz, 50 N peak load, followed by one hour of restitution at zero load and one hour of sinusoidal vibration at 5 Hz, 100 N peak load. The force and displacement responses of the motion segment were sampled at 25 Hz. The experimental data were used for evaluating the parameters of two viscoelastic models: a standard linear solid model (three-parameter) and a linear Burger's fluid model (four-parameter). In this study, the creep behaviour under sinusoidal vibration at 5 Hz closely resembled the creep behaviour under static loading observed in previous studies. Expanding the three-parameter solid model into a four-parameter fluid model made it possible to separate out a progressive linear displacement term. This deformation was not fully recovered during restitution and is therefore an indication of a specific effect caused by the cyclic loading. High variability was observed in the parameters determined from the 50 N experimental data, particularly for the elastic modulus E1. However, at the 100 N load level, significant differences between the models were found. Both models accurately predicted the creep response under the first 800 s of 100 N loading, as displayed by mean absolute errors for the calculated deformation data from the experimental data of 1.26 and 0.97 percent for the solid and fluid models respectively. The linear Burger's fluid model, however, yielded superior predictions particularly for the initial elastic response.
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| 2. |
- Hult, E, et al.
(författare)
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In vivo measurement of spinal column viscoelasticity--an animal model.
- 1995
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Ingår i: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine. - 0954-4119. ; 209:2
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Tidskriftsartikel (refereegranskat)abstract
- The goal of this study was to measure the in vivo viscoelastic response of spinal motion segments loaded in compression using a porcine model. Nine pigs were used in the study. The animals were anaesthetized and, using surgical techniques, four intrapedicular screws were inserted into the vertebrae of the L2-L3 motion segment. A miniaturized servohydraulic exciter capable of compressing the motion segment was mounted on to the screws. In six animals, a loading scheme consisting of 50 N and 100 N of compression, each applied for 10 min, was used. Each loading period was followed by 10 min restitution with zero load. The loading scheme was repeated four times. Three animals were examined for stiffening effects by consecutively repeating eight times 50 N loading for 5 min followed by 5 min restitution with zero load. This loading scheme was repeated using a 100 N load level. The creep-recovery behavior of the motion segment was recorded continuously. Using non-linear regression techniques, the experimental data were used for evaluating the parameters of a three-parameter standard linear solid model. Correlation coefficients of the order of 0.85 or higher were obtained for the three independent parameters of the model. A survey of the data shows that the viscous deformation rate was a function of the load level. Also, repeated loading at 100 N seemed to induce long-lasting changes in the viscoelastic properties of the porcine lumbar motion segment.
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| 3. |
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| 4. |
- Indahl, A, et al.
(författare)
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Sacroiliac joint involvement in activation of the porcine spinal and gluteal musculature.
- 1999
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Ingår i: Journal of spinal disorders. - 0895-0385. ; 12:4, s. 325-30
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Tidskriftsartikel (refereegranskat)abstract
- In the search for causes of low back pain, the sacroiliac joint has gained renewed interest as a possible pain generator. There is reason to believe that the sacroiliac joint plays a regulatory role involving reflex muscle activation, which controls trunk mobility and stability, as well as locomotion. The aim of this experimental study was to determine whether stimulation of nerves in the sacroiliac joint and joint capsule could elicit contractions in porcine gluteal or lumbar spinal muscles. Via a lateral retroperitoneal approach and using hypodermic needles, bipolar stimulating wire electrodes were inserted into the ventral area of the sacroiliac joint and directly under the surface of the capsular membrane, in 10 adolescent pigs (45 kg). This procedure was performed bilaterally, thus establishing two bilateral stimulation sites in the joints. Six electromyographic electrodes were unilaterally inserted into the following muscles: multifidus, gluteus medius, gluteus maximus, and quadratus lumborum. On stimulation within the ventral area of the joint, predominant responses occurred in both the gluteus maximus and quadratus lumborum muscles. However, when stimulating the capsule, the greatest muscular responses were detected in the multifidus muscles. This study addressed the possible regulatory function of the sacroiliac joint, namely, its involvement in activation of the spinal and gluteal muscles, which help control locomotion and body posture, as well as provide stability on the segmental level in the lumbar spine.
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| 5. |
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| 6. |
- Kaigle Holm, Allison, 1964, et al.
(författare)
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Experimental instability in the lumbar spine.
- 1995
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Ingår i: Spine. - 0362-2436. ; 20:4, s. 421-30
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Tidskriftsartikel (refereegranskat)abstract
- An in vivo animal model of lumbar segmental instability, involving both passive and active stabilizing components of the spine, was developed.
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| 7. |
- 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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