| 1. |
- Ekström, Lars, 1959, et al.
(författare)
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In vivo porcine intradiscal pressure as a function of external loading
- 2004
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Ingår i: J Spinal Disord Tech. - 1536-0652. ; 17:4, s. 312-6
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Spinal loading during daily activity as it relates to the ability of the intervertebral disc to sustain its integrity has been a major issue in spinal research. The purpose of this investigation was to establish the relationship between the intervertebral disc pressure in the nucleus and the load applied to the motion segment in an in vivo porcine model. METHODS: Nine domestic pigs were used in this study. A miniaturized servohydraulic testing machine was affixed to the lumbar spine via four intrapedicular screws, which were inserted bilaterally into the L2 and L3 vertebrae. A pressure needle was inserted through the lateral part of the L2-L3 disc annulus and into the nucleus pulposus. Force, deformation, and intradiscal pressure data were collected during a loading scheme that consisted of applying a set of constant loads in increasing order, that is, 50, 100, 150, 200, and 250 N. Each load was applied for 30 seconds followed by 30-second restitution. RESULTS: Intradiscal nucleus pressure was found to correlate to the applied load in all cases. Linear regression analyses resulted in the following equation: intradiscal pressure (MPa) = 0.08 + 1.25E(-3)(load, N), r(2) = 0.81, n = 8. Intradiscal pressure was also highly linearly dependent on the stress. The intrinsic intradiscal pressure was found to be 81 +/- 5 kPa. The results also indicated that the pressure within the disc exhibited a creep behavior. CONCLUSION: In conclusion, pressure in the nucleus of the porcine intervertebral disc was linearly related to the applied load and stress.
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| 2. |
- 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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| 3. |
- Hodges, P., et al.
(författare)
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Rapid atrophy of the lumbar multifidus follows experimental disc or nerve root injury
- 2006
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Ingår i: Spine. - 1528-1159. ; 31:25, s. 2926-33
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Tidskriftsartikel (refereegranskat)abstract
- STUDY DESIGN: Experimental study of muscle changes after lumbar spinal injury. OBJECTIVES: To investigate effects of intervertebral disc and nerve root lesions on cross-sectional area, histology and chemistry of porcine lumbar multifidus. SUMMARY OF BACKGROUND DATA: The multifidus cross-sectional area is reduced in acute and chronic low back pain. Although chronic changes are widespread, acute changes at 1 segment are identified within days of injury. It is uncertain whether changes precede or follow injury, or what is the mechanism. METHODS: The multifidus cross-sectional area was measured in 21 pigs from L1 to S1 with ultrasound before and 3 or 6 days after lesions: incision into L3-L4 disc, medial branch transection of the L3 dorsal ramus, and a sham procedure. Samples from L3 to L5 were studied histologically and chemically. RESULTS: The multifidus cross-sectional area was reduced at L4 ipsilateral to disc lesion but at L4-L6 after nerve lesion. There was no change after sham or on the opposite side. Water and lactate were reduced bilaterally after disc lesion and ipsilateral to nerve lesion. Histology revealed enlargement of adipocytes and clustering of myofibers at multiple levels after disc and nerve lesions. CONCLUSIONS: These data resolve the controversy that the multifidus cross-sectional area reduces rapidly after lumbar injury. Changes after disc lesion affect 1 level with a different distribution to denervation. Such changes may be due to disuse following reflex inhibitory mechanisms.
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| 4. |
- Holm, Sten, 1948, et al.
(författare)
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Experimental disc degeneration due to endplate injury
- 2004
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Ingår i: J Spinal Disord Tech. - 1536-0652. ; 17:1, s. 64-71
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to create an experimental model of disc degeneration that closely mimicked human disc degeneration. In six domestic pigs, an L4 cranial endplate perforation into the nucleus pulposus was made. Three months postoperatively, compressive testing was performed on the L2-L4 motion segments, and intradiscal pressure was measured in the intervening discs. Histochemical and morphologic examinations were made on the excised degenerated and adjacent discs. A significant reduction in water content was observed in the outer anterior annulus of the degenerated disc. In the nucleus, the proteoglycan content was significantly reduced, as well as the cellularity, although not significantly. The nucleus lost its gel-like structure and was discolored, and there was delamination of annular layers. Intradiscal pressure in the nucleus was significantly lower in the degenerated disc. In conclusion, experimental degeneration of the intervertebral disc induced by endplate penetration resembled human disc degeneration, as exemplified by biochemical and structural changes.
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| 5. |
- Holm, Sten, 1948, et al.
(författare)
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Intradiscal pressure in the degenerated porcine intervertebral disc
- 2007
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Ingår i: Vet Comp Orthop Traumatol. - 0932-0814. ; 20:1, s. 29-33
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Tidskriftsartikel (refereegranskat)abstract
- Measuring intradiscal pressure is one way of mechanically assessing the discs degenerative state. In this study, the load-bearing capacity of degenerated and their adjacent lumbar intervertebral discs was evaluated using two different injury models. Seventeen adolescent pigs were divided into two groups, an annulus injury group and an endplate injury group. The annulus injury group was subjected to a stab incision in the L3-L4 disc, whereas the endplate injury group received a cranial endplate perforation of the L4 vertebral body. Both groups were biomechanically evaluated three months later using a miniaturized servohydraulic testing machine across L2-L4 and with two pressure needles inserted into the nucleus pulposus of the L2-L3 and L3-L4 discs. Linear relationships between the intradiscal pressure and the applied load were determined within the load range studied. When comparing the ratio of the injured to the adjacent disc pressure, the endplate injury was lower (mean value 0.31) than the annulus injury (mean value 0.51). The pressures in the discs adjacent to the degenerated level were found to be slightly higher. This increase can be expected due to a redistribution in mobility demands in segments adjacent to those with increased stiffness, i.e. degenerated intervertebral discs.
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| 6. |
- Holm, Sten, 1948, et al.
(författare)
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Reactive changes in the adolescent porcine spine with disc degeneration due to endplate injury
- 2007
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Ingår i: Vet Comp Orthop Traumatol. - 0932-0814. ; 20:1, s. 12-7
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Tidskriftsartikel (refereegranskat)abstract
- Degenerative and reactive structural alterations occurring after experimentally-induced disc degeneration were evaluated using a porcine model. A cranial perforation was made through the L4 vertebral endplate into the nucleus pulposus. Three months later, the lumbar intervertebral disc and adjacent vertebrae were dissected, fixed in formalin and further processed for histopathological analyses. The results showed that there were nucleus pulposus fragments, rather than a distinct border between the nucleus and annulus fibrosus. The central lamellae were distorted and delamination of the outer anterior layers was observed. Blood vessels emerged from the adjacent tissue, penetrated the annulus and branched into the residues of the nucleus. Nerve fibres accompanying the blood vessels could be recognized in the disc within the connective scar tissue. The epiphyseal cartilage plates in the vertebrae were hypertrophic in several areas and there was bone formation directed towards the centre of the vertebral body and the disc. Hypertrophic hyaline cartilage, newly formed bone and scar tissue filled the injury canal. A slight chronic inflammatory reaction was evident along vascular buds. The reactive changes dominated over the degenerated features in the operated disc. Physiological loading enhanced the infiltration of various tissue types characterizing immature cartilage formation. Prominent neovascularisation of the central parts of the disc is likely to be of key importance in turning the degenerative features of the remaining tissue into reactive healthy structures.
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| 7. |
- 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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| 8. |
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| 9. |
- 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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| 10. |
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| 11. |
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| 12. |
- 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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| 13. |
- 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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| 14. |
- Kawchuk, G. N., et al.
(författare)
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Bulging of the inner and outer annulus during in vivo axial loading of normal and degenerated discs
- 2009
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Ingår i: Journal of Spinal Disorders & Techniques. - 1539-2465. ; 22:3, s. 214-8
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Tidskriftsartikel (refereegranskat)abstract
- STUDY DESIGN: Comparison of in vivo biomechanical outcomes between experimental and control group animals. OBJECTIVE: To quantify the in vivo bulging response of the inner and outer annulus in animals with and without disc degeneration. SUMMARY OF BACKGROUND DATA: Prior attempts to quantify the load-deformation response of the inner annulus have most often relied on in vitro preparations. Unfortunately, to visualize the inner annulus, these in vitro approaches rely on disc modifications that may result in nonphysiologic behaviors. In response to this problem, in vivo techniques were developed to quantify regional bulging of the inner and outer annulus during applied axial loading. METHODS: Two groups of pigs were tested: a normal group and a group having disc degeneration that was induced surgically 3 months earlier. Eight adolescent pigs were evaluated and for each animal, a miniature servohydraulic actuator was attached to the third and fourth lumbar vertebrae to deliver a cyclic axial loading protocol (300 N, 1 Hz, 10 cycles) whereas regional deformations of the annulus were visualized ultrasonically via retroperitoneal access. RESULTS: For the normal animals, image analysis demonstrated a significantly greater bulging of the inner annular region when compared with the outer annular region. In animals with disc degeneration, the inner and outer annular regions were equal in their bulging response, which ranged from 0 bulging to 37% greater than the average response of the normal animals. CONCLUSIONS: This work supports prior in vitro studies that observed maximal disc bulging in the inner annulus and minimal bulging in the external annulus. Results for this in vivo study suggest that this normal bulging gradient is lost with degenerative disc disease. Compared with in vitro approaches, this new in vivo technique has the potential to demonstrate disc behavior in a variety of loading conditions and/or with a variety of induced disc pathologies.
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| 15. |
- Baranto, Adad, 1966, et al.
(författare)
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Fracture patterns of the adolescent porcine spine: an experimental loading study in bending-compression
- 2005
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Ingår i: Spine. - 1528-1159. ; 30:1, s. 75-82
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Tidskriftsartikel (refereegranskat)abstract
- STUDY DESIGN: To expose functional spinal units from adolescent porcine to mechanical flexion-compression and extension-compression to failure. The biomechanical, radiologic, magnetic resonance imaging, and histologic characteristics are described. OBJECTIVES: The aim of the present study was to investigate the fracture pattern of functional spinal units from adolescent porcine lumbar spines in in vitro compression loading and bending. SUMMARY OF BACKGROUND DATA: In several studies, it has been shown that the adolescent spine, especially the vertebral growth zones, is vulnerable to trauma. A high frequency of abnormalities affecting the spine has been found among athletes participating in sports with high demands on the back. The etiology of these abnormalities is still a controversial issue. METHODS: Sixteen functional spinal units obtained from eight adolescent male pigs were used. Eight functional spinal units were exposed to flexion-compression and eight functional spinal units to extension-compression loading to failure. They were examined with plain radiography and magnetic resonance imaging before and after the loading. The functional spinal units were finally examined macroscopically and histologically. RESULTS: Fractures/separations were seen in the growth zone anteriorly and more frequently, posteriorly in functional spinal units exposed to flexion-compression. In the extension-compression group, such injuries occurred only anteriorly. Only large fractures could be seen on plain radiographs and on magnetic resonance imaging. Macroscopically, a fracture/separation could be seen in 15 cases and histologically in all 16 cases. The median angle at failure for the flexion group was 17 degrees (range, 12-19) and for the extension group 17 degrees (range, 13-19 degrees). The median ultimate compression load in the flexion-compression group was 1894 N (range, 1607-3138 N) and in the extension-compression group 1801 N (range, 1158-2368 N). CONCLUSIONS: The weakest part of the growing porcine lumbar spine, when compressed into flexion- or extension-compression, was the growth zone. The injury was more extensive in extension loading than during flexion loading. Growth zone injuries of the adolescent spine may go undetected on plain radiographs and magnetic resonance imaging.
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| 16. |
- Baranto, Adad, 1966, et al.
(författare)
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Vertebral fractures and separations of endplates after traumatic loading of adolescent porcine spines with experimentally-induced disc degeneration
- 2005
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Ingår i: Clin Biomech (Bristol, Avon). - : Elsevier BV. - 0268-0033. ; 20:10, s. 1046-54
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Abnormalities of the intervertebral discs have been found in a high frequency among young elite athletes. Several studies have also reported that the adolescent spine, especially the vertebral growth zones, is vulnerable to trauma. However, there is incomplete knowledge regarding the injury mechanism of the growing spine. In this study, the injury patterns of the adolescent porcine spine with disc degeneration were examined. METHODS: Twenty-four male pigs were used. A degenerative disc was created by drilling a hole through the cranial endplate of a lumbar vertebra into the disc. Two months later the animals were sacrificed and the degenerative functional spinal units (segments) were harvested. The segments were divided into three groups and exposed to axial compression, flexion compression or extension compression to failure. The load and angle at failure were measured for each group. The segments were examined with magnetic resonance imaging and plain radiography before and after the loading and finally examined macroscopically and histologically. FINDINGS: The degenerated segments required considerably more compressive load to failure than non-degenerated segments. Creating a flexion injury required significantly more load than an extension injury. Fractures and/or separations of the endplates from the vertebral bodies were seen at the margins of the endplates and in the growth zone. Only severe separations and fractures could be seen on plain radiography and magnetic resonance imaging. INTERPRETATION: The weakest part of the adolescent porcine lumbar spine with experimentally-induced degeneration, when loaded in axial compression, flexion compression or extension compression, was the growth zone, and, to a lesser extent, the endplate. Degenerated discs seem to withstand higher mechanical loads than non-degenerated discs, probably due to altered stress distribution.
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| 17. |
- Hebelka, Hanna, 1977, et al.
(författare)
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The transfer of disc pressure to adjacent discs in discography: a specificity problem?
- 2010
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Ingår i: Spine. - 0362-2436. ; 35:20
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Tidskriftsartikel (refereegranskat)abstract
- STUDY DESIGN: In vivo experimental study. OBJECTIVE: The primary objective of the study was to investigate pressure transmission to adjacent discs during discography. A secondary objective was to quantify the transmitted pressure, both in contrast injected and noninjected porcine intervertebral discs. SUMMARY OF BACKGROUND DATA: Discography is used to before surgery identify painful discs. A pain response during discography that is concordant with the patient's experienced back pain is regarded as an indication that the injected disc is the source of pain. However, the sensitivity and specificity of discography are matters of debate. Pressure-controlled discographies have been reported to reduce the number of false-positive discs using low pressure criteria. Preliminary data indicated a transfer of pressure from an injected to an adjacent disc during discography. Pressure transmission in vivo during lumbar discography, not reported before might, if clinically present, contribute to a false-positive diagnosis. METHODS: Thirty-six lumbar discs in 9 adolescent pigs were investigated. Intradiscal pressure was recorded during contrast injection, using a 0.36/0.25 mm fiber-optic pressure transducer inserted into the nucleus pulposus via a 22 G needle. The pressure was measured simultaneously in 2 adjacent discs during contrast injection into 1 of the discs at pressures up to 8 bar. Transmitted pressure was recorded both in noninjected discs and in discs that were prefilled with contrast. RESULTS: Thirty-three discs were successfully examined. During contrast injection, there was an intradiscal pressure rise in the adjacent disc with a median value of 16.0% (range, 3.2-37.0) over baseline pressure. There was no significant difference in pressure increase between the noninjected and prefilled discs (P < 0.68). CONCLUSION: Discography of porcine discs induces a pressure increase in adjacent discs. A similar pressure transfer during human clinical discography might elicit false-positive pain reactions.
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| 18. |
- Ihlebaek, C., et al.
(författare)
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Prevalence of low back pain and sickness absence: a "borderline" study in Norway and Sweden
- 2006
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Ingår i: Scand J Public Health. - 1403-4948. ; 34:5, s. 555-8
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Tidskriftsartikel (refereegranskat)abstract
- AIMS: Low back pain (LBP) is a major public health problem in both Norway and Sweden. The aim of the study was to estimate the prevalence of LBP and sickness absence due to LBP in two neighbouring regions in Norway and Sweden. The two areas have similar socioeconomic status, but differ in health benefit systems. METHODS: A representative sample of 1,988 adults in Norway and 2,006 in Sweden completed questionnaires concerning LBP during 1999 and 2000. For this study only individuals in part or full time jobs, (n = 1,158 in Norway and n = 1,129 in Sweden) were included. RESULTS: In Norway the lifetime prevalence was 60.7% and in Sweden 69.6%, the one-year prevalence was 40.5% and 47.2%, and the point prevalence 13.4% and 18.2% respectively. There was a significantly higher risk of reporting LBP in Sweden, even after controlling for gender, age, education, and physical workload. There was no difference in risk of self-certified short-term sickness absence (1-3 days), but it was a 40% lower risk of sickness absence with medical sickness certification in Sweden compared with Norway. CONCLUSION: The prevalence of LBP was higher in the Swedish area than in the Norwegian. The risk of self-certified sickness absence, however, showed no differences and the risk of medically certified sickness absence was lower in the Swedish area. This contradiction might partly be explained by the economical "disincentives" in the Swedish health compensation system.
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| 19. |
- Thoreson, Olof, 1981, et al.
(författare)
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The immediate effect of repeated loading on the compressive strength of young porcine lumbar spine
- 2010
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Ingår i: Knee Surgery, Sports Traumatology, Arthroscopy. - : Springer Science and Business Media LLC. - 1433-7347 .- 0942-2056. ; 18:5, s. 694-701
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Tidskriftsartikel (refereegranskat)abstract
- The human spine is exposed to repeated loading during daily activities and more extremely during sports. Despite this, there remains a lack of knowledge regarding the immediate effects on the spine due to this mode of loading. Age-specific spinal injury patterns has been demonstrated and this implies differences in reaction to load mode and load history The purpose of the present study was to investigate the impact of cyclic pre-loading on the biomechanical properties and fracture patterns of the adolescent spine in an experimental model. Eight functional spinal units from four young porcine spines were harvested. The functional spinal units were cyclic loaded with 20,000 cycles and then axially compressed to failure. The compression load at failure, ultimate stress and viscoelastic parameters were calculated. The functional spinal units were examined with plain radiography, computer tomography and MRI before and after the loading, and finally macroscopically and histologically. The median compression load at failure in this study was 8.3 kN (range 5.6-8.7 kN). The median deformation for all cases was 2.24 mm (range 2.30-2.7 mm) and stiffness was 3.45 N/mm (range 3.5-4.5 N/mm). A fracture was seen on radiograph in one case, on CT and macroscopically in seven, and on MRI and histologically in all eight cases. The cyclic loaded functional spinal units in the present study were not more sensitive to axial compression than non-cyclic loaded functional spinal units from young porcine. The endplate and the growth zone were the weakest part in the cyclic loaded functional spinal units. Disc signal reduction and disc height reduction was found on MRI. The E-modulus value found in this study was of the same order of magnitude as found by others using a porcine animal model.
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