BACKGROUND
cervical spondylomyelopathy  is characterized by dynamic and static compressions of the neural components caused by developmental abnormalities and secondary degenerative changes of the cervical vertebral column, leading to variable degrees of neurologic deficits and neck pain .
the pathogenesis of csm is not well understood, but it is believed to be multifactorial  <cit> .
among the factors involved, it has been suggested that intervertebral foraminal stenosis is implicated in the pathogenesis of csm  <cit> .
it is also known that normal and csm-affected dobermans and great danes have foraminal stenosis, however, the number of sites and severity is higher in the csm-affected dogs  <cit> .
it is nonetheless interesting to note that a high proportion of normal dogs have foraminal stenosis without clinical signs.
the exact role of foraminal stenosis in the pathogenesis of csm is still open to debate  <cit> .
cervical spondylomyelopathy in dogs bears considerable similarities to, and has been proposed as the natural study model for the most common cause of chronic spinal cord dysfunction in humans, called cervical spondylotic myelopathy  <cit> .
in humans, an in vivo study with healthy volunteers, measured the dimension of the cervical intervertebral foramina at various positions, showing that flexion significantly increased the foraminal dimensions and extension significantly decreased the foraminal dimensions  <cit> .
these results may explain the clinical observation that cervical extension aggravates symptoms in patients with cervical radiculopathy and that flexion often relieves them  <cit> .
although the diagnosis and treatment of csm have been described in the literature, few studies have aimed at understanding the pathogenesis of this disease .
experimental studies in dogs have shown that ischemia of the radicular arteries cause severe spinal cord degeneration and necrotic changes  <cit> .
the combination of spinal cord ischemia with compression leads to more severe neurologic deficits than spinal cord compression or ischemia alone  <cit> .
in humans with cervical spondylotic myelopathy, foraminal stenosis is well known to be one of the main causes of cervical pain and ischemic spinal cord injury  <cit> .
it is possible that dynamic foraminal stenosis contributes to the pathogenesis of ischemic injury to the nerve roots and spinal cord in dogs.
extension movements in the cervical vertebral column of dogs causes severe vertebral canal stenosis  <cit> .
currently, there is no data in the veterinary literature that demonstrates the movement-associated morphological changes of the cervical intervertebral foramina.
the dimensions of the cervical intervertebral foramina may change during neck movements and could be implied in the pathogenesis of diseases associated with cervical radiculopathy such as csm and intervertebral disc disease.
the hypothesis of this investigation was that the dimensions of the intervertebral foramina would increase with flexion and decrease with extension.
the objective of this study was to determine the changes in cervical intervertebral foraminal width and height as a result of traction-compression forces and flexion, extension movements in cervical vertebral column specimens of cadaveric dogs.
additionally, we aimed to compare the foraminal changes between normal vertebral columns with vertebral columns with intervertebral disc degeneration or protrusion.
RESULTS
there were no significant differences in the foraminal height and width between different intervertebral levels, and there were no significant differences between groups  <dig> and  <dig> either .
since location and groups had no significant influence on the measured intervertebral levels and groups, we will report the results combining the data from both groups and the three intervertebral levels.
comparison of neutral vs neutral with compression, and neutral vs neutral with traction
in neutral position under no load mean width was  <dig>  mm .
under compression, the mean width decreased to  <dig>  mm , .
with traction, the mean width increased to  <dig>  mm, however, this was not significantly different .
moving from neutral position with traction to compression, resulted in a net change of  <dig>  mm,  .table  <dig> mean foraminal width  of the cervical foramina , of dogs divided according to movement and load
aforaminal width and ci in millimeters
fig.
<dig> graph representation of the foraminal width and height changes in neutral, compression, traction, flexion and extension movements.
data represents combined data from all  <dig> levels  and all dogs from both groups.
data shown as bar graphs with standard error in millimeters
in neutral position under no load, the mean height was  <dig>  mm .
under compression, the mean height decreased to  <dig>  mm ,  .
with traction, the mean height increased to  <dig>  mm , .
moving from neutral position with traction to compression resulted in a net change of  <dig>  mm .table  <dig> mean foraminal height  of the cervical foramina , of dogs divided according to movement and load
aforaminal height and ci in millimeters
p-valueb
adifference and ci in millimeters
b
p-values adjusted by the holm’s procedure to conserve the overall type i error at  <dig>
comparison of neutral vs flexion, and neutral vs extension
in neutral position with no load, mean width was  <dig>  mm .
in an extended position, the mean width decreased to  <dig>  mm ,  , whereas in flexion the mean width increased to  <dig>  mm ,  .
in neutral position with no load, mean height was  <dig>  mm .
in an extended position, the mean height decreased to  <dig>  mm , , whereas in flexion the mean height increased to  <dig>  mm ,  .
comparison of flexion vs extension
with regards to comparison between flexion and extension, the mean width changed  <dig>  mm , .
in terms of comparison between flexion and extension, the mean height changed  <dig>  mm ,  .
intraobserver agreement
the intraobserver agreement  for the height and width ratios was  <dig>  and  <dig> , respectively.
these results indicate fair to good agreement for the measurement of all dimensions.
discussion
the primary goal of our study was to examine the morphological changes in the intervertebral foramina during flexion, extension, traction, and compression of the cervical vertebral column , and to compare these changes between normal vertebral columns and those with intervertebral disc degeneration.
as no differences were seen between groups, the data for all dogs was combined, thus the changes observed seem to affect equally dogs with or without degenerative changes.
disc degeneration and dorsal disc protrusion per se does not seem to affect the foramen size, although they could alter the biomechanics of the spine.
in flexion, the cervical foramina width increased  <dig>  % and the height increased  <dig>  %, when compared with neutral position.
in extension, the foraminal width decreased  <dig>  % and the height decreased  <dig>  % when compared with neutral position.
with regards to comparison between flexion and extension, the foraminal width decreased  <dig>  %, and the height decreased  <dig>  %.
these results likely have implications on the pathogenesis of cervical myelopathies because the intervertebral foramina changes were significant in flexion and extension.
studies in vitro and in vivo with human cervical vertebral column have shown that flexion significantly increases the width and height dimension of the foramina by 8-16 % and foraminal area by 28 %, whereas extension significantly decreases foraminal dimensions by width and height 10-22 % and foraminal area by 17 %  <cit> .
in general, our results are in agreement with the aforementioned studies.
we found a reduction in the foraminal size ranging from  <dig>  % to  <dig>  %  going from flexion to extension, respectively.
although dynamic intervertebral foraminal stenosis has been discussed in recent papers investigating the dynamic component of csm in dogs,  <cit>  we are the first to document these dynamic intervertebral foraminal changes.
our study shows unequivocally that dynamic movements of the canine cervical vertebral column cause intervertebral foraminal narrowing in extension.
this could cause repetitive compression of the radicular arteries and nerves roots, primarily in dogs with intervertebral foraminal stenosis.
this dynamic narrowing may be important in the pathogenesis of cervical myelopathies, such as canine csm, primarily because of the high incidence of foraminal stenosis in csm-affected dogs  <cit> .
the blood supply to the spinal cord is provided by the radicular arteries that enter the vertebral canal via the intervertebral foramen .
intervertebral foraminal stenosis can cause ischemic changes in the spinal cord of dogs.
experimental studies in dogs have shown that the bilateral interruption of the 5th pair of cervical radicular arteries produced spinal cord degeneration in all cervical segments  <cit> .
other studies have also shown that the effects of spinal cord compression and spinal cord ischemia are additive and cause more neurologic deficits than spinal cord compression or ischemia alone .
studies in humans have shown that the local pressure of the intervertebral foramen is significantly higher during extension, of the lumbar vertebral column  <cit> .
mechanical pressure has the potential to disturb the blood supply and nutrition of the nerve root such that a pressure as low as 10 mmhg was sufficient to decrease the blood supply to the nerve roots, in experimental studies with pigs .
others studies suggest that the symptoms of lumbar spinal stenosis, including pain and neurologic deficits, may be the result of ischemia caused by mechanical stress to the spinal nerve root .
a recent report described  <dig> cases of cervical intervertebral foraminal disc extrusions.
the most common location was c5- <dig> and c6- <dig>  and signs were cervical hyperesthesia and lameness.
interestingly, even though the acute disc extrusion caused acute severe foraminal stenosis, most dogs recovered with medical treatment, without surgical decompression of the foramen  <cit> .
a study in humans correlated nerve root compression and decreased foraminal width and area in the cervical vertebral column  <cit> .
this study showed a significant correlation between disc degeneration and reduced foraminal width and foraminal area, but not with foraminal height  <cit> .
in other studies of the lumbar vertebral column, the results showed that narrowing of the disc space significantly reduces the height of the intervertebral foramen but has no significant effects on its width  <cit> .
it is important to remember that humans are bipeds, and foraminal height is equivalent to the width of the foramen in dogs, and the foraminal width in humans equals the height in dogs.
we probably did not detect differences in the spines with and without degenerative changes because the number and severity of the degenerative changes in the dogs of group  <dig> was not sufficiently different from group  <dig>  the incidence of nerve root compression in lumbar vertebral columns was 21 % in when patients had their columns in neutral position,  <dig>  % in flexion, and  <dig>  % in the extension  <cit> .
in dogs, lumbar foraminal areas were significantly smaller when the vertebral column was extended versus flexed  <cit> .
in humans, degenerative changes of the anatomic structures forming the walls of the intervertebral foramen may affect its dimension and shape causing narrowing or stenosis of the foramen  <cit> .
in a study with  <dig> normal and  <dig> csm-affected dobermans, foraminal stenosis was detected in  <dig> clinically normal and  <dig> csm-affected dogs  <cit> .
a similar study of  <dig> clinically normal and  <dig> csm-affected great danes , found foraminal stenosis present in  <dig> normal and  <dig> csm-gds  <cit> .
although many normal dobermans and great danes had foraminal stenosis, the number of sites and severity was significantly greater in csm affected dogs  <cit> .
in our study, there was no significant difference between groups.
it is possible that we did not detect differences between groups because even though group  <dig> had degenerative changes, they probably were less severe than those seen with csm cases.
most dogs also only had degenerative changes at a single site, whereas dogs with csm frequently have multiple levels affected.
the application of traction forces is used to treat dogs with vertebral canal stenosis  <cit> .
the goal of these techniques is decompression, by increasing vertebral canal and intervertebral foramen dimensions, by means of traction and stabilization  <cit> .
in the present study, traction forces increased the foraminal height in  <dig>  %, which was significant, but the foraminal changes in width were not significant.
this finding could partially explain why these techniques lead to clinical improvement in dogs with csm.
molds from vertebral column, vertebral canal, and foramina have been used in morphological and biomechanics studies in humans and dogs .
oil based clay  was adopted in this study because it is malleable at room temperature, and becomes rigid when it is frozen.
this method was used in a recent study  <cit> .
vertebral canal and foraminal dimension have been measured by ct, mri, computer software and caliper .
in our study, a digital precision caliper was used to measure the foraminal dimensions.
this technique has been previously reported to be reliable, with low interobserver and intraobserver variability  <cit> .
a single investigator performed all measurements in a non-blinded manner, which could have biased the observations.
further studies with larger sample sizes, primarily of dogs confirmed to have csm with mri are needed to examine these dynamic changes in affected dogs, and to clarify differences in characteristics and amounts of dynamic change in neural foraminal dimensions between patients with and without cervical radiculopathy.
CONCLUSIONS
our findings suggest that extension and compressive forces decrease the foraminal height and width.
flexion and traction forces increase the foraminal dimensions.
dynamic foraminal stenosis may play a role in the pathogenesis of cervical myelopathies such as csm by causing intermittent compression of the radicular arteries, resulting in decreased blood supply to the nerve roots and spinal cord and signs of cervical myelopathy and radiculopathy.

 cervical spondylomyelopathy is characterized by dynamic and static compressions of the neural components caused by developmental abnormalities and secondary degenerative changes of the cervical vertebral column, leading to variable degrees of neurologic deficits and neck pain. the pathogenesis of csm is not well understood, but it is believed to be multifactorial. among the factors involved, it has been suggested that intervertebral foraminal stenosis is implicated in the pathogenesis of csm. it is also known that normal and csm-affected dobermans and great danes have foraminal stenosis, however, the number of sites and severity is higher in the csm-affected dogs. it is nonetheless interesting to note that a high proportion of normal dogs have foraminal stenosis without clinical signs. the exact role of foraminal stenosis in the pathogenesis of csm is still open to debate. cervical spondylomyelopathy in dogs bears considerable similarities to, and has been proposed as the natural study model for the most common cause of chronic spinal cord dysfunction in humans, called cervical spondylotic myelopathy. in humans, an in vivo study with healthy volunteers, measured the dimension of the cervical intervertebral foramina at various positions, showing that flexion significantly increased the foraminal dimensions and extension significantly decreased the foraminal dimensions. these results may explain the clinical observation that cervical extension aggravates symptoms in patients with cervical radiculopathy and that flexion often relieves them. although the diagnosis and treatment of csm have been described in the literature, few studies have aimed at understanding the pathogenesis of this disease. experimental studies in dogs have shown that ischemia of the radicular arteries cause severe spinal cord degeneration and necrotic changes. the combination of spinal cord ischemia with compression leads to more severe neurologic deficits than spinal cord compression or ischemia alone. in humans with cervical spondylotic myelopathy, foraminal stenosis is well known to be one of the main causes of cervical pain and ischemic spinal cord injury. it is possible that dynamic foraminal stenosis contributes to the pathogenesis of ischemic injury to the nerve roots and spinal cord in dogs. extension movements in the cervical vertebral column of dogs causes severe vertebral canal stenosis. currently, there is no data in the veterinary literature that demonstrates the movement-associated morphological changes of the cervical intervertebral foramina. the dimensions of the cervical intervertebral foramina may change during neck movements and could be implied in the pathogenesis of diseases associated with cervical radiculopathy such as csm and intervertebral disc disease. the hypothesis of this investigation was that the dimensions of the intervertebral foramina would increase with flexion and decrease with extension. the objective of this study was to determine the changes in cervical intervertebral foraminal width and height as a result of traction-compression forces and flexion, extension movements in cervical vertebral column specimens of cadaveric dogs. additionally, we aimed to compare the foraminal changes between normal vertebral columns with vertebral columns with intervertebral disc degeneration or protrusion.  there were no significant differences in the foraminal height and width between different intervertebral levels, and there were no significant differences between groups and either. since location and groups had no significant influence on the measured intervertebral levels and groups, we will report the results combining the data from both groups and the three intervertebral levels. comparison of neutral vs neutral with compression, and neutral vs neutral with traction in neutral position under no load mean width was  mm. under compression, the mean width decreased to  mm,. with traction, the mean width increased to  mm, however, this was not significantly different. moving from neutral position with traction to compression, resulted in a net change of  mm,.table mean foraminal width of the cervical foramina, of dogs divided according to movement and load aforaminal width and ci in millimeters fig. graph representation of the foraminal width and height changes in neutral, compression, traction, flexion and extension movements. data represents combined data from all levels and all dogs from both groups. data shown as bar graphs with standard error in millimeters in neutral position under no load, the mean height was  mm. under compression, the mean height decreased to  mm,. with traction, the mean height increased to  mm,. moving from neutral position with traction to compression resulted in a net change of  mm.table mean foraminal height of the cervical foramina, of dogs divided according to movement and load aforaminal height and ci in millimeters p-valueb adifference and ci in millimeters b p-values adjusted by the holm’s procedure to conserve the overall type i error at comparison of neutral vs flexion, and neutral vs extension in neutral position with no load, mean width was  mm. in an extended position, the mean width decreased to  mm,, whereas in flexion the mean width increased to  mm,. in neutral position with no load, mean height was  mm. in an extended position, the mean height decreased to  mm,, whereas in flexion the mean height increased to  mm,. comparison of flexion vs extension with regards to comparison between flexion and extension, the mean width changed  mm,. in terms of comparison between flexion and extension, the mean height changed  mm,. intraobserver agreement the intraobserver agreement for the height and width ratios was and, respectively. these results indicate fair to good agreement for the measurement of all dimensions. discussion the primary goal of our study was to examine the morphological changes in the intervertebral foramina during flexion, extension, traction, and compression of the cervical vertebral column, and to compare these changes between normal vertebral columns and those with intervertebral disc degeneration. as no differences were seen between groups, the data for all dogs was combined, thus the changes observed seem to affect equally dogs with or without degenerative changes. disc degeneration and dorsal disc protrusion per se does not seem to affect the foramen size, although they could alter the biomechanics of the spine. in flexion, the cervical foramina width increased  % and the height increased  %, when compared with neutral position. in extension, the foraminal width decreased  % and the height decreased  % when compared with neutral position. with regards to comparison between flexion and extension, the foraminal width decreased  %, and the height decreased  %. these results likely have implications on the pathogenesis of cervical myelopathies because the intervertebral foramina changes were significant in flexion and extension. studies in vitro and in vivo with human cervical vertebral column have shown that flexion significantly increases the width and height dimension of the foramina by 8-16 % and foraminal area by 28 %, whereas extension significantly decreases foraminal dimensions by width and height 10-22 % and foraminal area by 17 %. in general, our results are in agreement with the aforementioned studies. we found a reduction in the foraminal size ranging from  % to  % going from flexion to extension, respectively. although dynamic intervertebral foraminal stenosis has been discussed in recent papers investigating the dynamic component of csm in dogs, we are the first to document these dynamic intervertebral foraminal changes. our study shows unequivocally that dynamic movements of the canine cervical vertebral column cause intervertebral foraminal narrowing in extension. this could cause repetitive compression of the radicular arteries and nerves roots, primarily in dogs with intervertebral foraminal stenosis. this dynamic narrowing may be important in the pathogenesis of cervical myelopathies, such as canine csm, primarily because of the high incidence of foraminal stenosis in csm-affected dogs. the blood supply to the spinal cord is provided by the radicular arteries that enter the vertebral canal via the intervertebral foramen. intervertebral foraminal stenosis can cause ischemic changes in the spinal cord of dogs. experimental studies in dogs have shown that the bilateral interruption of the 5th pair of cervical radicular arteries produced spinal cord degeneration in all cervical segments. other studies have also shown that the effects of spinal cord compression and spinal cord ischemia are additive and cause more neurologic deficits than spinal cord compression or ischemia alone. studies in humans have shown that the local pressure of the intervertebral foramen is significantly higher during extension, of the lumbar vertebral column. mechanical pressure has the potential to disturb the blood supply and nutrition of the nerve root such that a pressure as low as 10 mmhg was sufficient to decrease the blood supply to the nerve roots, in experimental studies with pigs. others studies suggest that the symptoms of lumbar spinal stenosis, including pain and neurologic deficits, may be the result of ischemia caused by mechanical stress to the spinal nerve root. a recent report described cases of cervical intervertebral foraminal disc extrusions. the most common location was c5- and c6- and signs were cervical hyperesthesia and lameness. interestingly, even though the acute disc extrusion caused acute severe foraminal stenosis, most dogs recovered with medical treatment, without surgical decompression of the foramen. a study in humans correlated nerve root compression and decreased foraminal width and area in the cervical vertebral column. this study showed a significant correlation between disc degeneration and reduced foraminal width and foraminal area, but not with foraminal height. in other studies of the lumbar vertebral column, the results showed that narrowing of the disc space significantly reduces the height of the intervertebral foramen but has no significant effects on its width. it is important to remember that humans are bipeds, and foraminal height is equivalent to the width of the foramen in dogs, and the foraminal width in humans equals the height in dogs. we probably did not detect differences in the spines with and without degenerative changes because the number and severity of the degenerative changes in the dogs of group was not sufficiently different from group the incidence of nerve root compression in lumbar vertebral columns was 21 % in when patients had their columns in neutral position,  % in flexion, and  % in the extension. in dogs, lumbar foraminal areas were significantly smaller when the vertebral column was extended versus flexed. in humans, degenerative changes of the anatomic structures forming the walls of the intervertebral foramen may affect its dimension and shape causing narrowing or stenosis of the foramen. in a study with normal and csm-affected dobermans, foraminal stenosis was detected in clinically normal and csm-affected dogs. a similar study of clinically normal and csm-affected great danes, found foraminal stenosis present in normal and csm-gds. although many normal dobermans and great danes had foraminal stenosis, the number of sites and severity was significantly greater in csm affected dogs. in our study, there was no significant difference between groups. it is possible that we did not detect differences between groups because even though group had degenerative changes, they probably were less severe than those seen with csm cases. most dogs also only had degenerative changes at a single site, whereas dogs with csm frequently have multiple levels affected. the application of traction forces is used to treat dogs with vertebral canal stenosis. the goal of these techniques is decompression, by increasing vertebral canal and intervertebral foramen dimensions, by means of traction and stabilization. in the present study, traction forces increased the foraminal height in  %, which was significant, but the foraminal changes in width were not significant. this finding could partially explain why these techniques lead to clinical improvement in dogs with csm. molds from vertebral column, vertebral canal, and foramina have been used in morphological and biomechanics studies in humans and dogs. oil based clay was adopted in this study because it is malleable at room temperature, and becomes rigid when it is frozen. this method was used in a recent study. vertebral canal and foraminal dimension have been measured by ct, mri, computer software and caliper. in our study, a digital precision caliper was used to measure the foraminal dimensions. this technique has been previously reported to be reliable, with low interobserver and intraobserver variability. a single investigator performed all measurements in a non-blinded manner, which could have biased the observations. further studies with larger sample sizes, primarily of dogs confirmed to have csm with mri are needed to examine these dynamic changes in affected dogs, and to clarify differences in characteristics and amounts of dynamic change in neural foraminal dimensions between patients with and without cervical radiculopathy.  our findings suggest that extension and compressive forces decrease the foraminal height and width. flexion and traction forces increase the foraminal dimensions. dynamic foraminal stenosis may play a role in the pathogenesis of cervical myelopathies such as csm by causing intermittent compression of the radicular arteries, resulting in decreased blood supply to the nerve roots and spinal cord and signs of cervical myelopathy and radiculopathy. 
cervical spondylomyelopathy in dogs is characterized by dynamic and static compressions of the neural components, leading to variable degrees of neurologic deficits and neck pain. extension decreased all the foraminal dimensions significantly, whereas flexion increased all the foraminal dimensions significantly. compression decreased all the foraminal dimensions significantly, and traction increased the foraminal height, but did not significantly change the foraminal width. all vertebral columns were examined with magnetic resonance imaging prior to biomechanic testing. eight normal vertebral columns were placed in group and eight vertebral columns with intervertebral disc degeneration or/and protrusion were assigned to group molds of the left and right intervertebral foramina from c4- c5- and c6- were taken during all positions and loading modes. this could have implication in the pathogenesis of csm and other diseases associated with radiculopathy such as intervertebral disc disease. our results show movement-related changes in the dimensions of the intervertebral foramina, with significant foraminal narrowing in extension and compression. the dimensions of the cervical intervertebral foramina may significantly change during neck movements. studies suggest that intervertebral foraminal stenosis has implications in the pathogenesis of csm. previous studies in humans have reported that the dimensions of the intervertebral foramina change significantly with movement of the spine. the purpose of this study was to quantify the morphological changes in the intervertebral foramina of dogs during flexion, extension, traction, and compression of the canine cervical vertebral column. comparisons were made between neutral to flexion and extension, flexion to extension, and traction to compression in neutral position. cervical spondylomyelopathydisc degenerationdogspinal cordwobbler syndromeissue-copyright-statement© the author 2015
 previous studies in humans have reported that the dimensions of the intervertebral foramina change significantly with movement of the spine. cervical spondylomyelopathy in dogs is characterized by dynamic and static compressions of the neural components, leading to variable degrees of neurologic deficits and neck pain. studies suggest that intervertebral foraminal stenosis has implications in the pathogenesis of csm. the dimensions of the cervical intervertebral foramina may significantly change during neck movements. this could have implication in the pathogenesis of csm and other diseases associated with radiculopathy such as intervertebral disc disease. the purpose of this study was to quantify the morphological changes in the intervertebral foramina of dogs during flexion, extension, traction, and compression of the canine cervical vertebral column. all vertebral columns were examined with magnetic resonance imaging prior to biomechanic testing. eight normal vertebral columns were placed in group and eight vertebral columns with intervertebral disc degeneration or/and protrusion were assigned to group molds of the left and right intervertebral foramina from c4- c5- and c6- were taken during all positions and loading modes. molds were frozen and vertical and horizontal dimensions of the foramina were measured. comparisons were made between neutral to flexion and extension, flexion to extension, and traction to compression in neutral position.  extension decreased all the foraminal dimensions significantly, whereas flexion increased all the foraminal dimensions significantly. compression decreased all the foraminal dimensions significantly, and traction increased the foraminal height, but did not significantly change the foraminal width. no differences in measurements were seen between groups.  our results show movement-related changes in the dimensions of the intervertebral foramina, with significant foraminal narrowing in extension and compression. keywords cervical spondylomyelopathydisc degenerationdogspinal cordwobbler syndromeissue-copyright-statement© the author 2015 