dynamic factors have a significant role in causing cervical spondylotic myelopathy ( csm ) . in patients with cervical ossification of the posterior longitudinal ligament ( c - opll ) , mild symptoms of myelopathy
the pathomechanism of cervical myelopathy caused by c - opll remains unknown . despite spinal stenosis ( 6 mm < space available for the spinal cord < 14 mm )
, myelopathy may not develop in patients with severe range limitations of the cervical spine .
this possibility indicates that not only static factors but also dynamic factors , such as listhesis or hypermobility at the discontinuity of the ossified lesion , have important roles in the development of myelopathy , especially in mixed and segmental oplls .
multidetector - row computed tomography ( mdct ) has given a better understanding of spinal ligament ossification .
unlike the tsuyama classification based on lateral radiographs , ossification morphology and bone continuity between each vertebrae are shown more clearly by mdct .
previously , we reported that ossification morphology at each disc segment was divided into 3 groups : the connection department , coating part , and non - connection department of opll .
we previously used mdct to measure spinal cord cross - sectional areas ( sccsas ) during flexion and extension . in that report
it is the possible that myelopathy is aggravated by dynamic factors , even in the connection department of opll .
however , we did not investigate the sagittal range of motion ( rom ) and ossification of the anterior longitudinal ligaments .
previously , we reported that the incidence of spinal cord injury in the stoppage department of ossification was 64%
the purpose of this study was to measure rom by mdct , to investigate the influence of dynamic factors on the spinal cord of patients with c - opll . and
the roms of adjacent intervertebral disc in connected vertebrae and those of others were investigated for each morphology .
from january 2006 to august 2010 , a total , of 110 patients ( 80 men and 30 women ) with c - opll were enrolled in this study .
in addition , 99 patients ( 64 men and 35 women ) who had lumbar disc herniation determined by mdct were defined as normal controls .
patients with opll , fused vertebrae , and spinal instability were excluded from this normal control .
the aims of this study were explained to all patients before myelography and ct scanning , and all patients gave informed consent to their participation .
preoperative ct scans after myelography were performed in all subjects in maximum neck flexion and extension .
ct scans were obtained ( 1-mm - thick axial helical ) with sagittal and coronal reconstruction using 64-line , multi - slice unit ( light speed vct ; ge healthcare bio - sciences , piscataway , nj , usa ) .
the rom at each disc level between c2/3 and c7/t1 in sagittal view was measured using synapse enterprise - pacs ( fujifilm medical co. , ltd . ,
ossification morphology at each disc segment was divided into 6 groups : covered disc , covered vertebra , unconnected vertebra , connected vertebra ( continuous ) , connected vertebra ( localized ) , and others ( fig .
the covered disc group was defined as comprising either cranial or caudal vertebra connected by ossification , with the other intervertebral disc not completely covered by ossification .
the covered vertebra group was defined as comprising either cranial or caudal vertebra connected by ossification , with the other intervertebral disc completely covered by ossification .
the unconnected vertebra group was defined as coprising either cranial or caudal vertebra connected by ossification , with ossification completely covering the vertebra , including other cranial and caudal intervertebral discs or vertebrae .
the connected vertebra ( continuous ) group was defined as comprising both cranial and caudal vertebrae connected by ossification , of the continuous type according to the tsuyama classification .
in addition , the connected vertebra ( localized ) group was defined as comprising both cranial and caudal vertebrae connected by ossification , that was the localized type according to the tsuyama classification .
the others group was defined as vertebrae with osteophytes , disc ossification , or no problematic features .
the ossification morphology was defined at the biggest and longest place in much mdct slice .
ossification morphology at each disc segment was divided into 6 groups : covered disc , covered vertebra , unconnected vertebra , connected vertebra ( continuous ) , connected vertebra ( localized ) , and others .
in addition , the roms of adjacent intervertebral disc in connected vertebrae ( continuous and localized ) and those of others were investigated for each group .
roms during neck flexion and extension were measured once on two different days by a spinal surgeon , and average values were adopted . the stat view 5.0 software ( abacus , berkeley , ca )
analysis of variance with a post hoc test ( kruskal -wallis test ) was used to perform comparisons between the groups . a p - value < 0.05 was considered to be statistically significant .
the rom of the patients with c - opll was significantly smaller than that of the normal controls .
there were 122 disc levels in the covered disc group , 114 disc levels in the covered vertebra group , 12 disc levels in the unconnected vertebra group , 40 disc levels in the connected vertebra ( continuous ) group , 20 disc levels in the connected vertebra ( localized ) group , and 340 disc levels in the others group ( fig .
2 ) . number of intervertebral disc according to each classification the average roms were 6.4  4.6 in the covered disc group , 4.8  4.3 in the covered vertebra group , 4.8  3.8 in the unconnected vertebra group , 2.9  2.3 in the connected vertebra ( continuous ) group , 2.8  2.4 in the connected vertebra ( localized ) group , 6.0  4.3 in the others group , and 8.1  4.2 in the normal control .
the average rom of the covered disc group was significantly higher than that of the connected vertebra ( continuous ) group and connected vertebra ( localized ) group .
in addition , the average rom of the normal control was significantly higher than those of the covered disc group , covered vertebra group , connected vertebra ( continuous ) , and connected vertebra ( localized ) groups .
the average rom of the connected vertebra ( continuous ) group was significantly lower than those of the covered disc group , others group , and normal control group ( fig .
the average rom according to each classification the average roms of the roms of adjacent intervertebral disc in connected vertebrae ( continuous and localized ) and those of others were investigated for each group shown in table 2 and fig .
4 , were 5.9  4.8 and , 6.5  4.6 in the covered disc group , 5.5  4.3 and , 4.5  4.3 in the covered vertebra group , 3.8  1.7 and , 5.3  4.5 in the unconnected vertebra group , 2.9  2.5 and , 2.9  2.2 in the connected vertebra ( continuous ) group , 3.0  2.5 and , 2.5  2.3 in the connected vertebra ( localized ) group , and 4.8  4.7 and , 6.0  4.3 in the others group , respectively . there were no significant differences between the adjacent intervertebral disc in connected vertebrae and others .
the average rom of adjacent connected vertebra ( continuous and localized ) and that of except adjacent connected vertebra ( continuous and localized )
the tsuyama classification is the most widely used criteria for classifying c - opll . on the basis of lateral radiographs alone , c - opll can be roughly classified into 4 types : ( 1 ) continuous type , which is a continuous ossified mass extending over several vertebrae ; ( 2 ) segmental type , which is a segmental ossification behind each vertebral body ; ( 3 ) mixed type , which is a mixture of these 2 types ; and ( 4 ) localized type , which includes other types , ( e.g. , circumscribed ossification of the ligament corresponding to the level of the intervertebral disc ) .
in addition , mdct has enabled better understanding of ossification of spinal ligaments than provided by lateral radiographs , because the ossification morphology and bone continuity between each vertebrae have become clear .
previously , we had described ossification morphology at each disc segment that had been divided into 3 groups : the connection department , coating part , and non - connection department of opll .
we had used mdct to measure sccsa during flexion and extension , and sccsa did not show statistically significant differences in ossification morphology .
it is possible that myelopathy is aggravated by dynamic factors , even in the connection department of opll .
therefore , we reclassified these groups more finely , and examined rom at each segment using a new classification .
ossification morphology at each disc segment was divided into 6 groups : covered disc , covered vertebra , unconnected vertebra , connected vertebra ( continuous ) , connected vertebra ( localized ) , and others .
the average rom in the covered vertebra group was quite similar to that in the unconnected vertebra group .
the average rom in the connected vertebra ( continuous ) was quite similar to that in the connected vertebra ( localized ) group .
we used the former classification to classify the covered vertebra group and unconnected vertebra group as the coating part .
similarly , we had classified the connected vertebra ( continuous ) group and connected vertebra ( localized ) group as the connection department .
it is not necessary to each distribute , re - classification that we increase cases is desirable .
the influence of dynamic factors on the cervical spine has been investigated by flexion  extension magnetic resonance imaging ( mri ) .
matsunaga et al . showed that in patients with c - opll , involvement of not only chronic pathological compressive factors caused by opll but also of circulatory and dynamic factors were thought to be important in the development and aggravation of myelopathy .
morio et al.suggested that important factors in the onset or aggravation of myelopathy are related to pathological compression by opll , cervical soft disc herniation , a developmentally narrow spinal canal , and a local or non - proportional hypermobility .
previously , we reported that sccsa by mdct was measured to elucidate the influence of dynamic factors .
there were no significant differences in the dynamic changes of sccsa between the connection department , coating part , and non - connection department of opll .
it has also been suggested that the influence of dynamic factors is less in patients with mature continuous opll .
acute spinal cord injury associated with c - opll can be induced by minor cervical trauma , and there is often radiographic evidence of trauma , termed cervical spinal cord injuries without radiographic evidence of trauma ( sciworet ) .
described the pathogenesis of central cord injury in the cervical spine as the result of a hyperextension mechanism , with subsequent compression of bony spur , a herniated disc , or a buckled ligamentum flavum .  
onishi et al . reported that sciworet with c - opll occurred at the edge of opll or oall .
previously , we reported that the incidence of spinal cord injury in the stoppage department of ossification was 64%
there were no significant differences between the adjacent intervertebral disc in connected vertebrae and others for each group , but the average rom of the connected vertebra ( continuous and localized ) group was significantly lower than that of the covered disc group and normal control group .
dynamic factors were reduced at the continuous segment : therefore , frequency of sciworet at the continuous segment may be less likely to happen from other segments .  
the limitations of this study were that the examination of the spinal cord changes relied on mri signal intensities .
second , it will be necessary to examine the differences between rom based on mdct and rom based on x - ray .
we should closely observe the natural course of patients with c - opll from dynamic factors even in patients with mature c - opll , and it will be necessary to consider sciworet with respect to dynamic factors .
this study was performed to measure rom in patients with c - opll by mdct , and to investigate the influence of dynamic factors on the spinal cord . and
rom of adjacent intervertebral disc in connected vertebrae ( continuous and localized ) and those of others were investigated for each group .
ossification morphology at each disc segment was divided into 6 groups : covered disc , covered vertebra , unconnected vertebra , connected vertebra ( continuous ) , connected vertebra ( localized ) , and others .
the average rom of covered disc group was significantly higher than that of connected vertebra ( continuous , localized ) .
the average rom of connected vertebra ( continuous ) group was significantly lower than that of covered disc group , others group , and normal control .
there was no significant difference between rom of adjacent intervertebral disc in connected vertebrae and others , but the average rom of the connected vertebra group was significantly lower than that of the covered disc group and normal control group .
dynamic factor was reduced at continuous segment , but it was not increased in adjacent intervertebral disc .
each author certifies that they had no commercial associations ( e.g. , consultancies , stock ownership , equity interest / licensing arrangement , etc . ) that might pose a conflict of interest in connection with the submitted article .
 abstractthe purpose of this study was to measure range of motion ( rom ) in patients with cervical ossification of posterior longitudinal ligament ( c - opll ) by multidetector - row computed tomography ( mdct ) , and to investigate the influence of dynamic factors . 
 the study included 101 patients with c - opll and 99 normal control patients . 
 preoperative mdct were taken in all subjects in maximum neck flexion and extension . 
 rom at each disc level between c2/3 and c7/t1 in sagittal view was measured . 
 ossification morphology at each disc segment was divided into 6 groups : covered disc , covered vertebra , unconnected vertebra , connected vertebra ( continuous ) , connected vertebra ( localized ) , and others . 
 the relationship between rom and the group of ossification morphology was also investigated . 
 rom of adjacent intervertebral disc in connected vertebrae ( continuous and localized ) and those of others were investigated for each group . 
 the average rom of covered disc group was significantly higher than that of connected vertebra ( continuous , localized ) . 
 the average rom of connected vertebra ( continuous ) group was significantly lower than that of covered disc group , others group , and normal control . 
 there was no significant difference between rom of adjacent intervertebral disc in connected vertebrae and others , but the average rom of the connected vertebra group was significantly lower than that of the covered disc group and normal control group . 
 dynamic factor was reduced at continuous segment , but it was not increased in adjacent intervertebral disc . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS
CONFLICT OF INTEREST