In the radiological examination of the spine one frequently sees in association with kyphoses very varied contours of the upper and lower vertebral margins. Mechanical Compression and Nucleus Pulposus Application on Dorsal Root the disc core is presumed to contribute to intervertebral disc hernia-related pain. This report examines 18 surgically proven L3/4 herniated nucleus pulposus ( HNP), all having myelogram, CT and adequate neurological evaluation. It will focus.
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A combination of mechanical compression caused by a protruding disc and leakage of nucleus pulposus NP from the disc core is presumed to contribute to intervertebral disc hernia-related pain. Experimental models of disc hernia including both components have resulted in changes in neuronal activity at the level of the dorsal root ganglion DRG and spinal cord, but changes within the brain have been less well studied.
However, acute application of NP to a DRG without mechanical compression rapidly increases neuronal activity in the thalamus, a major brain relay nucleus processing information from sensory pathways including ascending nociceptive tracts. The combination of mechanical compression and NP might therefore result in further increases in central neuronal activity. Using an experimental disc herniation rat model including both mechanical compression and NP the present study aimed to investigate changes in neuronal activity in the contralateral thalamic ventral posterior lateral nucleus in vivo.
In all animals, light mechanical compression of the DRG depressed the number of evoked neuronal responses. The contribution of acute DRG compression and disc material leakage to changes in transmission in central neuronal networks is likely to be complex and to involve both short-term and long-term effects.
Since a light mechanical compression may reduce transmission in nociceptive pathways, it is possible that the presence or absence of NP is crucial for pain development in the acute phase of disc herniation.
Nucleus pulposus | Radiology Reference Article |
I ntervertebral disc hernia was first described by Mixter and Barr, 1 and the ensuing pain has been suggested to arise as a result of the mechanical compression that a ruptured disc exerts on adjacent nerves. While mechanical compression nkuleus still presumed to be of major importance, 2 — 4 leakage of nucleus pulposus NP from the disc core onto nervous tissue may also contribute to the experience of pain by causing a local inflammatory response and inducing both structural and functional changes in nerve roots.
Experimental models nukleuss to explore the origin of disc hernia-related pain often include both a mechanical and an inflammatory component. The results have suggested that the presence of both these components increases the pulpsous in terms of behavior 1415 and in neuronal activity by resulting in more pronounced changes in dorsal root conduction velocity than when either of these interventions are applied alone.
The thalamus is the major brain relay nucleus for sensory information, including transmission in nociceptive pathways from the spinal cord en route to cortical regions where the information hednia processed further. A recent study reported that NP applied to a DRG results in increased neuronal activity in the thalamus.
However, the questions of whether similar or more potent changes may be induced by the combination of mechanical compression and NP exposure, as suggested by behavior studies, 15 as well as whether exposure to NP prior to the mechanical compression would have resulted in further changes in central neuronal activity were not investigated. The aim of the present study was to investigate nukleis changes in neuronal thalamic activity using an acute experimental disc hernia model in the rodent.
We included both light mechanical compression of the DRG and exposure to NP, mimicking the clinical situation hfrnia which a disc protrusion may be followed by a rupture of the annulus fibrosus with subsequent NP leakage. This model has previously been shown lulposus induce behavioral changes as determined by von Frey withdrawal tests 15 and video analysis of changes in spontaneous behavior 14 as well as morphological changes in the peripheral nervous system, such as changes in the capsule surrounding the Pulposks.
All experimental procedures were approved by the regional animal ethics committee. The aims of the present study were addressed in four different experimental series Fig. Study design for series 1—4.
The boxes in the left panel indicate the intervention performed on day 1 for each group of animals. An experimental flow chart for the acute electrophysiological and behavioral experiments performed on day 2 is shown on the right. Anesthesia was induced with isoflurane Baxter Medical AB. Following a midline incision, the left facet joint between the fourth puplosus fifth lumbar vertebrae L4—L5 was removed to expose the L4 DRG. In 28 rats, a syringe connected to a G injection needle was used to incise the disc and inject small hernis of air until NP leaked out and could be applied to the exposed DRG.
Twenty-six sham-operated animals were subjected to the same surgical procedures with the exception of the disc incision. The animals were tracheotomized and attached to a respirator with neuromuscular transmission blocked by intravenous pancronium bromide Pavulon, total dose 0.
The left sciatic nerve was transected at knee level and mounted on a pair of silver-ball stimulating electrodes in a pool of paraffin created by skin flaps. At this stage, no remnants of the previously applied NP were visible on macroscopic inspection. Light mechanical compression was induced by gently dislocating the L4 DRG with a G needle and was maintained by inserting the needle in the underlying bone, as previously described by Omarker and Myers.
A laminectomy was performed at Th11—12, exposing the spinal cord, and used for transdural cord dorsum recordings via a silver-ball electrode in nukleuss with the surface of the spinal cord. A herni was performed, nukpeus the dura mater was removed to insert a recording electrode into the VPL nucleus of the thalamus Fig.
Experimental gernia with stimulation and recording sites. A Schematic drawing with a sciatic nerve and stimulation electrode; b dorsal root ganglion DRG for exposure to nucleus pulposus NP and light mechanical compression; c recording electrode at the surface of the spinal cord; d recording site in the ventral posterior lateral VPL nucleus.
Dotted horizontal lines represent discrimination lines used for spike counting. The electrode track and recording site corresponding to d in the schematic drawing in A is indicated pilposus a dotted vertical line and a filled circle.
D Representative cresyl violet—stained histological section of lesion, corresponding to the drawing in C. The sciatic nerve was stimulated 50— times at each recording point by a short train of impulses three stimuli, 0. One group of animals subjected to the same surgical procedures as in series 2 and 3 were tested for changes in paw withdrawal thresholds series 4; see Fig.
The investigator performing the test was blinded with regard to the surgical intervention. The von Frey monofilaments were applied in order of increasing stiffness, starting with 0. A positive withdrawal was scored when the animal responded to two out of three stimuli presented. Original data records from the electrophysiological experiments were stored online using a software system designed by E. Pihlgren University of Gothenburg. After positioning the recording electrode in the contralateral VPL nucleus a series of baseline records were obtained while stimulating the ipsilateral sciatic nerve.
Kruskal—Wallis test was used to compare the number of evoked responses at different time points in between groups, and paired t -test was used to compare changes in the number of evoked responses between baseline and each separate time point within the individual groups. Behavioral test data were analyzed with paired-samples t -test before and after intervention surgery for both the left hind paw and the right hind paw, and for differences between groups with Mann—Whitney test.
HERNIA NUKLEUS PULPOSUS EBOOK
P values less than 0. Following the addition of NP an increased number of evoked responses were observed, irrespective of whether the mechanical compression remained or was removed. The mean number of evoked responses is presented as a percentage of baseline records. Effects of application of NP in disc-punctured and sham-operated animals. Furthermore, no differences were found when comparing the disc-punctured and sham-operated animals.
Spinal disc herniation
Experimental models designed to study the origin of disc hernia-related pain often include both a mechanical and an inflammatory component, and the results obtained have suggested that these two components may mutually enhance each other in terms of effects on behavior 141520 and neuronal activity. For this purpose, we used an experimental model simulating two hypothetical clinical situations, in which the disc protrusion may or may not be preceded by a small continuous leakage of NP from the interior of the disc due to ruptures in the annulus fibrosus.
Since disc herniation surgery includes a mechanical decompression while the possible chemical effect of the disc material may remain, series 1 included subgroups in which the effects of applied NP were investigated at the level of the thalamus with and without remaining compression.
The results suggest that in the acute phase, light mechanical compression results in reduced evoked neuronal activity in the thalamus that is rapidly reversed following decompression. Thus, it cannot be determined whether the recovery observed in series 1 and 3 at later time points and in the presence of NP only reflects the natural time course of changes in central neuronal activity following DRG compression per se and is due to a recovery of nerve function, or whether the recovery is at least in part due to the application of NP.
In addition, nerve compression has been demonstrated to reduce or completely abolish neuronal firing and more often results puulposus paresthesia and muscle weakness than in pain. Taken together, these results may therefore indicate that a single episode of NP leakage does not result in lasting changes in neuronal activity, but that any such effects are restricted to acute and short-lasting events.
The cellular mechanisms behind the observed effects of light mechanical compression and NP pulosus are not addressed in this study. Mechanical compression may cause a block in action potentials propagating toward the spinal cord, resulting in a reduced number of evoked responses, 23 — 25 which would be consistent with the findings in the present study.
Importantly, the observed decrease was not likely to be due to irreversible fiber damage because the addition of NP herniia only reversed the decrease in neuronal activity herjia also resulted in an increased activity while the mechanical compression still remained. In addition, removal of the compression resulted in immediate recovery, further suggesting that the decrease induced by light mechanical compression is transient in the acute phase.
The model used in the present work, however, includes extensive surgery and therefore does not allow recordings in vivo to be taken other than at the terminal experiment. It therefore cannot be excluded that the NP leakage onto the DRG introduced on day 1 might already have altered the activity before baseline records were obtained on day 2. However, a statistical comparison of the raw data obtained as baseline records failed to reveal any significant differences between the experimental groups Kruskal—Wallis test; nonsignificant.
Several ascending tracts carrying nociceptive information from the spinal cord to the brain are relayed in the thalamus 31 — 33 and changes in evoked neuronal responses in the VPL nucleus may thus reflect changes in activity in a number of nociceptive pathways. Graded nociceptive stimuli to the rat plantar surface were recently reported to result in increases in firing rate and in the number of activated neurons in the VPL nucleus and to be associated with increased neuronal activity in cortical areas involved in nociceptive processing.
Taken together, the findings in the present study using an experimental acute disc hernia model including light mechanical compression and application of NP to the DRG suggest that any ensuing changes in transmission in central neuronal networks are likely to hsrnia complex.
As a light mechanical compression may reduce pulposjs in nociceptive pathways it is possible that the presence or absence of NP is crucial for the development of pain development in the acute phase of disc herniation. This study was supported by grants from the Dr. National Center pulposux Biotechnology InformationU. Journal List Biores Open Access v. Find articles by Elin Nilsson.
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CopyrightMary Ann Liebert, Inc. This article has been cited by other articles in PMC. Abstract A combination of mechanical compression caused by a protruding disc and leakage numleus nucleus pulposus NP from the disc core is presumed to contribute to intervertebral disc hernia-related pain.
Introduction I ntervertebral disc hernia was first described by Mixter and Pulpowus, 1 and the ensuing pain has been suggested to arise as a result of the mechanical compression that a ruptured disc exerts on adjacent nerves.
Methods All experimental procedures were approved by the regional animal ethics committee. Study design The hrrnia of the present study were addressed in four different experimental series Fig. Open in a separate window. Stimulation and recording The sciatic nerve was stimulated 50— times at each recording point by a short train of impulses three stimuli, 0.
Behavioral test One group of animals subjected to the same surgical procedures as in series 2 and 3 were tested for changes in paw withdrawal thresholds series 4; see Fig.
Analysis Original data records from the electrophysiological experiments were stored online using a software system designed by E.
Discussion Experimental models designed to study the origin of disc hernia-related pain often include both a mechanical and an inflammatory component, and the results obtained have suggested that these two components may mutually enhance each other in terms of effects on behavior 141520 and pulposux activity.
Author Disclosure Statement No competing financial interests exist. Rupture of the intervertebral disc with involvement of the spinal canal. N Engl J Med. An experimental model for chronic compression of dorsal root ganglion produced by intervertebral foramen stenosis in the rat.
Pathoanatomy and pathophysiology of nerve root compression. Spine Phila Nuleus Sciatica and the intervertebral disc; an experimental study. J Bone Joint Surg Am.