anterior procedures are increasingly recognized as advantageous for multilevel cervical decompression in a compromised anterior spinal cord , having the ability for anterior release , durable reconstruction of physiological alignment and instrumented fusion through a less complicated approach compared to the posterior approach surgery . with anterior procedures , decompression of the neurologic structures
can be accomplished by means of segmental disectomy or corpectomy . however , in many cases , multilevel anterior disectomy or corpectomy and reconstruction is required . in such cases ,
the fusion and complication rates at the anterior cervical spine have been shown to have a direct correlation with the mechanical stability of fixation .
there are numerous reports of failure of instrumentation , especially in the weakened osteoporotic , neoplastic or infectious spine . in such cases ,
such surgeries are known to have more complications . to avoid the additional posterior surgery in such cases , without compromising the biomechanical stability of the cervical anterior screw - plate constructs , some authors introduced the concept of anterior transpedicular screw fixation and fusion .
successful placement of anterior transpedicular screws in the cervical spine requires accurate identification of the screw axis depending on a sufficient three - dimensional understanding of the anatomical morphology of the pedicle . as a result of the anatomical features of the cervical pedicle and its intimately close relationship to critical neural and vascular structures , navigation of this structure poses serious risks and
unfortunately little data exists on the anatomical morphologic character for cervical anterior transpedicular screw fixation .
the aim of the present study , was to investigate anatomical morphologic trends with respect to linear and angular parameters associated with anterior transpedicular screw fixation in the cervical spine .
morphological parameters for cervical anterior transpedicular screw fixation were measured using a helical computed tomography ( ct ) scan and reconstruction at the radiology imaging department of our university hospital .
informed consent was taken from all subjects and the institute ethics committee approved the study protocol .
there were 18 males and 18 females , ranging in age from 22 years to 75 years ( 43.80  8.02 ) .
subjects with evidence of infectious , neoplastic , traumatic or congenital spine anomalies and significant degenerative changes were excluded from the study .
cervical ct scans were performed with a general electric light speed helical ct scanner ( siemens , germany ) .
sagittal , oblique sagittal and coronal bony window reconstruction images of the cervical pedicles from c3 to c7 were obtained using 0.75 mm thickness slices .
the following left pedicle parameters were determined as diagrammatically shown in figure 1 , using the measuring tools of the centricity web imaging software .
( a ) maximal pedicle axial length ( the distance between a and b point ) , pedicle transverse angle (  , angle formed between pedicle axis and mid - sagittal line , distance transverse insertion point ( the distance between point a and c ) and outer pedicle width ( distance medial border of transverse foramen and medial border of pedicle ) . ( b ) out pedicle height ( distance upper to lower pedicle surface in the sagittal plane ) , distance of the insertion point to the upper end plate ( distance between point a and e ) and pedicle sagittal transverse angle (  , angle formed between plane of anterior vertebral body wall at mid - sagittal line and pedicle axis ) angle formed between transverse pedicle axis and mid - sagittal line
. angle formed between plane of anterior vertebral body wall at mid - sagittal line and pedicle axis , distance between the distance of the insertion point to the upper end plate ( diup ) in the sagittal plane .
distance between the transverse intersection point and mid - sagittal line at the anterior vertebral body wall .
( outer pedicle width [ opw ] , a distance medial border of transverse foramen to the medial border of pedicle ) .
distance upper to lower pedicle surface in the sagittal plane , maximal pedicle axis length ( mpal ) , distance from the posterior cortex of the lateral mass to the anterior wall of the vertebral body along the pedicle axis .
descriptive statistics including mean values , standard deviations and ranges were used to summarize data .
the independent t test was performed to analyze the difference of the parameters for cervical anterior transpedicular screws fixation between females and males p < 0.05 was considered statistically significant .
angle formed between plane of anterior vertebral body wall at mid - sagittal line and pedicle axis , distance between the distance of the insertion point to the upper end plate ( diup ) in the sagittal plane .
distance between the transverse intersection point and mid - sagittal line at the anterior vertebral body wall .
( outer pedicle width [ opw ] , a distance medial border of transverse foramen to the medial border of pedicle ) .
distance upper to lower pedicle surface in the sagittal plane , maximal pedicle axis length ( mpal ) , distance from the posterior cortex of the lateral mass to the anterior wall of the vertebral body along the pedicle axis .
descriptive statistics including mean values , standard deviations and ranges were used to summarize data .
the independent t test was performed to analyze the difference of the parameters for cervical anterior transpedicular screws fixation between females and males p < 0.05 was considered statistically significant .
the mean and standard deviations of linear and angular parameters were calculated at each level .
there were 36 opw ( 25 in females and 11 in males ) , less than 4.0 mm and only four oph in females less than 4.0 mm .
the overall average oph ranged from 5.8  0.9 mm to 7.3  1.4 mm in c3 - 7 .
the largest oph was found at c7 in both males ( 7.6  1.7 mm ) and females ( 7.1  1.6 mm ) .
the smallest average of oph was found at c5 in females and males ( 5.4  0.7 mm and 6.3  0.9 mm ) .
the average oph was significantly greater in males than in females at c3 - 6 , but there was no difference at c7 [ figure 2a ] .
( a ) average of out pedicle height was greater significantly in males than in females at c3 - 6 ( p<0.05 ) , but there was no difference at c7 ( p>0.05 ) ; ( b ) the average of outer pedicle width was greater significantly in males than in females at all levels p<0.05 the overall average opw ranged from 4.3  1.0 to 6.0  1.3 mm in c3 - 7 .
the smallest mean pw was found at c3 in both males ( 4.7  1.2 mm ) and females ( 3.9  0.5 mm ) ; the largest mean opw was at c7 in both males ( 5.8  1.5 mm ) and females ( 5.5  0.5 mm ) .
the average of opw was significantly greater in males than in females at all levels [ figure 2b ] .
the overall mean diup in c3 - 7 ranged from 4.0  0.8 to 4.4  1.2 mm .
the maximal mean value of diup was found at c7 and c3 in females ( 4.6  0.8 mm ) and males ( 4.8  1.4 mm ) .
the minimal mean value was observed at c6 and c4 in females ( 3.9  0.8 mm ) and males ( 3.8  1.0 mm ) .
the average of diup was significantly greater in males than in females in c3 , 4 , 6 , 7 levels , but there was no significant difference between females and males at c5 [ figure 3a ] .
( a ) average of distance of the insertion point to the upper end plate was significantly greater in males than in females in c3 , 4 , 6 , 7 levels , but it was no significant difference between females and males at c5 .
( b ) the average of maximal pedicle axis length was greater in males than in females at all levels , and this difference were statistically significant at all levels ( p < 0.05 ) the overall average mpal ranged from 31.8  2.0 mm to 33.3  2.4 mm .
the maximum mean mpal in females and males was found at c6 ( 3 2.4  1.8 mm ) and c7 ( 34.7  2.5 mm ) .
the minimum mean value of mpal was found at c4 in females ( 30.7  1.4 mm ) and c3 in males ( 32.5  2.4 mm ) .
the average mpal was greater in males than in females at all levels and the difference was statistically significant at all levels ( p < 0.05 ) [ figure 3b ] .
the overall mean dip in c3 - 7 ranged from 3.1  0.8 mm to 4.5  1.1 mm .
the largest mean value of dip was found at c5 in females ( 4.3  1.3 mm ) and c4 in males ( 4.9  1.1 mm ) .
the smallest value was at c 7 in both females ( 2.8  1.9 mm ) and males ( 2.8  1.9 mm ) .
the average of dip was greater in males than in females at c3 ( p < 0.05 ) , but there was no statistically significant difference between females and males at c4 - 7 levels [ figure 4a ] .
( a ) average of distance transverse insertion point was greater in males than in females at c3 ( p<0.05 ) , but there was no significant difference between females and males at c4 - 7 levels ( p>0.05 ) ; ( b ) the average of pedicle transverse angle was significantly greater in males than in females at c3 , but there were no statistically difference between females and males at c4 - 7 levels the overall mean pta ranged from 44.4  3.1 to 47.1  4.1. the smallest mean pta was found at c6 in both males ( 44.9  3.8 ) and females ( 43.9  4.8 ) .
the largest mean pta was observed at c3 in males ( 47.6  2.1 ) and at c5 in females ( 47.8  4.0 ) .
the average pta was significantly greater in males than in females at c3 , but there was no statistical difference between females and males at c4 - 7 levels [ figure 4b ] .
the overall mean psta ranged from 99.2  6.7 to 105.4  6.0. the smallest mean psta was found at c7 in both males ( 99.1  5.8 ) and females ( 99.3  7.6 ) .
the maximal mean value of psta was recorded at c6 in males ( 109.1  5.4 ) and at c4 in females ( 104.8  6.2 ) .
the mean value of psta showed no statistically significant differences at c3 - 4 and c7 level between genders , and was significantly greater in males than females at c5 - 6 [ figure 5 ] .
the mean value of pedicle sagittal transverse angle was no statistically significant differences at c3 - 4 and c7 level between gender and there was significant greater in males than n females at c5 - 6
the overall average oph ranged from 5.8  0.9 mm to 7.3  1.4 mm in c3 - 7 .
the largest oph was found at c7 in both males ( 7.6  1.7 mm ) and females ( 7.1  1.6 mm ) .
the smallest average of oph was found at c5 in females and males ( 5.4  0.7 mm and 6.3  0.9 mm ) .
the average oph was significantly greater in males than in females at c3 - 6 , but there was no difference at c7 [ figure 2a ] .
( a ) average of out pedicle height was greater significantly in males than in females at c3 - 6 ( p<0.05 ) , but there was no difference at c7 ( p>0.05 ) ; ( b ) the average of outer pedicle width was greater significantly in males than in females at all levels p<0.05
the overall average opw ranged from 4.3  1.0 to 6.0  1.3 mm in c3 - 7 .
the smallest mean pw was found at c3 in both males ( 4.7  1.2 mm ) and females ( 3.9  0.5 mm ) ; the largest mean opw was at c7 in both males ( 5.8  1.5 mm ) and females ( 5.5  0.5 mm ) .
the average of opw was significantly greater in males than in females at all levels [ figure 2b ] .
the overall mean diup in c3 - 7 ranged from 4.0  0.8 to 4.4  1.2 mm .
the maximal mean value of diup was found at c7 and c3 in females ( 4.6  0.8 mm ) and males ( 4.8  1.4 mm ) .
the minimal mean value was observed at c6 and c4 in females ( 3.9  0.8 mm ) and males ( 3.8  1.0 mm ) .
the average of diup was significantly greater in males than in females in c3 , 4 , 6 , 7 levels , but there was no significant difference between females and males at c5 [ figure 3a ] .
( a ) average of distance of the insertion point to the upper end plate was significantly greater in males than in females in c3 , 4 , 6 , 7 levels , but it was no significant difference between females and males at c5 .
( b ) the average of maximal pedicle axis length was greater in males than in females at all levels , and this difference were statistically significant at all levels ( p < 0.05 )
the overall average mpal ranged from 31.8  2.0 mm to 33.3  2.4 mm .
the maximum mean mpal in females and males was found at c6 ( 3 2.4  1.8 mm ) and c7 ( 34.7  2.5 mm ) .
the minimum mean value of mpal was found at c4 in females ( 30.7  1.4 mm ) and c3 in males ( 32.5  2.4 mm ) .
the average mpal was greater in males than in females at all levels and the difference was statistically significant at all levels ( p < 0.05 ) [ figure 3b ] .
the overall mean dip in c3 - 7 ranged from 3.1  0.8 mm to 4.5  1.1 mm .
the largest mean value of dip was found at c5 in females ( 4.3  1.3 mm ) and c4 in males ( 4.9  1.1 mm ) .
the smallest value was at c 7 in both females ( 2.8  1.9 mm ) and males ( 2.8  1.9 mm ) .
the average of dip was greater in males than in females at c3 ( p < 0.05 ) , but there was no statistically significant difference between females and males at c4 - 7 levels [ figure 4a ] .
( a ) average of distance transverse insertion point was greater in males than in females at c3 ( p<0.05 ) , but there was no significant difference between females and males at c4 - 7 levels ( p>0.05 ) ; ( b ) the average of pedicle transverse angle was significantly greater in males than in females at c3 , but there were no statistically difference between females and males at c4 - 7 levels
the overall mean pta ranged from 44.4  3.1 to 47.1  4.1. the smallest mean pta was found at c6 in both males ( 44.9  3.8 ) and females ( 43.9  4.8 ) .
the largest mean pta was observed at c3 in males ( 47.6  2.1 ) and at c5 in females ( 47.8  4.0 ) .
the average pta was significantly greater in males than in females at c3 , but there was no statistical difference between females and males at c4 - 7 levels [ figure 4b ] .
the overall mean psta ranged from 99.2  6.7 to 105.4  6.0. the smallest mean psta was found at c7 in both males ( 99.1  5.8 ) and females ( 99.3  7.6 ) .
the maximal mean value of psta was recorded at c6 in males ( 109.1  5.4 ) and at c4 in females ( 104.8  6.2 ) .
the mean value of psta showed no statistically significant differences at c3 - 4 and c7 level between genders , and was significantly greater in males than females at c5 - 6 [ figure 5 ] .
the mean value of pedicle sagittal transverse angle was no statistically significant differences at c3 - 4 and c7 level between gender and there was significant greater in males than n females at c5 - 6
transpedicular screw fixation provides greater strength to pull - out than does lateral mass screw fixation or screw fixation into the vertebral body .
however , due to the close proximity of the spinal cord , nerve roots and vertebral arteries , transpedicular cervical screw fixation has been considered inherently more risky than cervical vertebral body fixation and is supposed to be technically more demanding .
transpedicular fixation of the cervical spine is not widely performed because of its complex morphological structures .
there are numerous reports of screw penetrating the pedicle due to the variation of cervical pedicle morphology .
it is , therefore very important to sufficiently understand the three dimensional pedicle morphology for pedicle screw fixation .
recently , several studies have been aimed at describing the anatomical morphologic characteristics of the cervical pedicle for posterior transpedicular screw fixation .
koller et al . had reported that the morphologic character for cervical anterior transpedicular screw fixation was not different between left and right sides .
we had previously investigated the morphologic characters and clinical results for cervical anterior transpedicular screw fixation at c2 .
most right handed surgeons believed that the right side incision is more convenient and pedicle screws can only be implanted in the left pedicle . to measure the pedicle morphologic parameters ,
the helical ct scan is more accurate than artificial measure ( means manual measure in vitro ) . in vivo measurements of the cervical pedicle using ct images
are believed to provide more accurate linear and angular pedicular dimensions than similar measurements obtained manually in cadavers . in the present study
, we used helical ct scan and reconstruction imaging to evaluate the in vivo cervical pedicle parameters .
the measurements have been performed independently by three radiologists and the averages were analyzed . in this study ,
the orientation of pedicles was described as pta and psta and the insertion point was identified by the dip and diup .
the overall mean dip and diup ranged from 3.1  0.8 mm to 4.5  1.1 mm and 4.0  0.8 to 4.4  1.2 mm , respectively .
the overall mean pta and psta ranged from 40.6  3.1 to 47.1  4.1 and 99.2  6.7 to 105.4  5.0 in this study . as cervical posterior pedicle screw fixation ,
the opw and oph for anterior transpedicular fixation need to be larger than 4 mm to accept the smallest screw available today which has a diameter of 3.5 mm . in the present study ,
the overall average opw and oph were ranged from 4.3  1.0 mm to 6.0  1.3 mm and 5.8  0.9 mm to 7.3  1.4 mm in c3 - 7 .
there were 36 opw ( 25 in females and 11 in males ) was less than 4.0 mm , and only four oph in females were less than 4.0 mm .
furthermore , we found that the average of oph and opw were greater in males than in females at all levels ( p < 0.05 ) .
the data suggests that when compared with the male population , a smaller percentage of female cervical pedicles will be able to accommodate the smallest cervical pedicle screw available today .
diup should be sufficiently larger to accept the pedicle screws available today . however , there was no data of diup in present literature for the placement of anterior transpedicular screws in the cervical spine .
we a hypothesized that the diup>2.0 mm is feasibile for placement of anterior transpedicular screws in the cervical spine . in our study , diup ranged from 4.0  0.8 mm to 4.4  1.2 mm , and only four diup were less than 2.0 mm ( observed in females ) .
our data suggested that it was possible in most patients to do a cervical anterior transpedicular fixation . in our study , the mpal was larger than those reported in others studies , which investigated mpal for cervical posterior transpedicular fixation .
the mpal was lower in females than that in males at all levels and the difference was statistically significant ( p < 0.05 ) .
our data indicated that the anterior transpedicular screw fixation in the cervical spine , results in more strength and can provide longer pathway than in cervical posterior transpedicular fixation . thus longer
pedicle screws can be used in males than in females for anterior transpedicular screw fixation in the cervical spine . to conclude the results suggest that the placement of cervical anterior transpedicular screws should be individualized for each patient .
the preoperative helical ct scans and reconstructions for patients who would undergo cervical anterior transpedicular fixation should be thoroughly analyzed with attention to the pedicle size and its angulation .
 background : anterior cervical interbody grafts / cages combined with a plate were frequently used in multilevel discectomies / corpectomies . in order to avoid additional posterior stabilization in patients who undergo anterior reconstructive surgery , an anterior cervical transpedicular screw fixation , which offers higher stability is desirable . 
 we investigated in this study the anatomical ( morphologic ) characters for cervical anterior transpedicular screw fixation.materials and methods : left pedicle parameters were measured on computed tomography ( ct ) images based on 36 cervical spine ct scans from healthy subjects . 
 the parameters included outer pedicle width ( distance from lateral to medial pedicle surface in the coronal plane ) , outer pedicle height ( oph ) ( distance from upper to lower pedicle surface in the sagittal plane ) , maximal pedicle axis length ( mpal ) , distance transverse insertion point ( dip ) , distance of the insertion point to the upper end plate ( diup ) , pedicle sagittal transverse angle ( psta ) and pedicle transverse angle ( pta ) at c3 to c7.results:the values of outer pedicle width and mpal in males were larger than in females from c3 to c7 . 
 the oph in males was larger than in females at c3 to c6 , but there was no difference at c7 . 
 the dip and pta were significantly greater in males than in females at c3 , but there was no difference in the angle at c4 - 7 . 
 the psta was not statistically different between genders at c3 , 4 , 7 , but this value in males was larger than females at c5 , 6 . 
 the diup was significantly greater in males at c3 , 4 , 6 , 7 but was non significant at c5.conclusions:the placement of cervical anterior transpedicular screws should be individualized for each patient and based on a detailed preoperative planning . 