with development of thoracic diseases and thoracic surgery skills , spinal posterior pedicle internal fixation has been clinically used to treat thoracic fractures and tumors , according to the spinal 3-column theory of denis .
it has become an important spinal fixation operation due to its slight operational trauma , short fixed segments , and high fixed strength .
boucher   first reported a successful pedicle internal fixation in 1959 , but it has not been applied widely until 1986 , after roy - camille   reported excellent clinical efficacy of pedicle fixation in treating spinal fractures .
however , the vertebral arch in the mid - upper thoracic vertebrates is relatively thinner and has more malformations , making screw placement difficult high risk .
complications of failed placement , such as spinal cord damage , injuries of great vessels around the vertebral bodies , fracture of pedicles , and thoracic nerve root injury , happen occasionally , posing a technical difficulty that needs to be solved .
although intra - operative imaging positioning and screw placement under navigation have been popular research topics in recent years , and accuracy of screw placement has been improved , the high expense , complex process , and increased radiation risks during the operation have limited its adoption .
this article was based on , and made some improvements of , lu s method , which applied 3-d printing technique   in thoracic pedicle screw placement .
medical mimics software , combined with 3-d laser printing technique , was used in manufacturing individualized thoracic pedicle screw guide plates , which could assist in accurate insertions .
there were 2 males and 1 female , with han ethnicity and an average death age of 52.3 years ( all provided by the anatomy dept .
the t1 to t12 vertebral bodies were taken out of each body , with peripheral soft tissues wiped out and intervertebral discs preserved . a thin - layer 3-d ct scan was performed ( siemens , germany ) to exclude the samples with bone - structure damage such as fractures , occupation , or malformation of vertebral pedicles .
samples were scanned with 3-d ct , and images with a dicom format were obtained ( the layer and scan thickness were all < 1.25 mm ) .
3-d images of spines were produced by medical mimics software and corresponding 3-d images of each vertebral body were designed with 3-d data from ptc creo 3.0 ( http://www.ptc.com/product/creo ) and geomagic ( http://www.geomagic.com/en/products/design/overview ) software .
ptc creo was used to design models and geomagic was used in reverse engineering technique .
a virtual screw panel was established on a vertebral model by medcad , which was parallel with the long axis of the pedicle ( figure 1 ) .
after the virtual screw was placed , an entry point and an axial leaning angle and sagittal dip angle of the screw were confirmed on 3-d reconstructive images .
the screw panels were hollowed out and a 3.04.0 cylindrical panel formed reversely , which made a guide plate leading channel ( figure 2 ) . in the manufacture of guide plates ,
the inner sides of guide plates and the bony structures of the backsides of vertebral bodies were made to completely fit with each other .
then the models were saved in stl format and transmitted to a sps600 3-d printer ( provided by xian jiaotong university ) .
posterior soft tissues of vertebral bodies were cleared , and normal bony structure damage was avoided .
the operator held the corresponding individualized guide plate in one hand , matched it up with the vertebral body , and kept it stable while the surgeon held the screw panel alongside the leading panel on the plate with the pedicle instrument open in the other hand .
after the guide plate was removed , screws were placed alongside bilateral panels ( figure 5 ) .
x - ray assistance or screw panels correction by exploration during placement should be avoided to reflect true assistant effects of guide plates .
after placement of screws , the positional relation between the screw and the neighboring structures , such as vertebral body and spinal canal ( figure 6 ) , were first directly observed , then all the samples for examination were dissected to assess the positional relationship between the screw and the neighboring structures ( figure 7 ) .
there were 2 males and 1 female , with han ethnicity and an average death age of 52.3 years ( all provided by the anatomy dept .
the t1 to t12 vertebral bodies were taken out of each body , with peripheral soft tissues wiped out and intervertebral discs preserved . a thin - layer 3-d ct scan was performed ( siemens , germany ) to exclude the samples with bone - structure damage such as fractures , occupation , or malformation of vertebral pedicles .
samples were scanned with 3-d ct , and images with a dicom format were obtained ( the layer and scan thickness were all < 1.25 mm ) .
3-d images of spines were produced by medical mimics software and corresponding 3-d images of each vertebral body were designed with 3-d data from ptc creo 3.0 ( http://www.ptc.com/product/creo ) and geomagic ( http://www.geomagic.com/en/products/design/overview ) software .
ptc creo was used to design models and geomagic was used in reverse engineering technique .
a virtual screw panel was established on a vertebral model by medcad , which was parallel with the long axis of the pedicle ( figure 1 ) .
after the virtual screw was placed , an entry point and an axial leaning angle and sagittal dip angle of the screw were confirmed on 3-d reconstructive images .
the screw panels were hollowed out and a 3.04.0 cylindrical panel formed reversely , which made a guide plate leading channel ( figure 2 ) . in the manufacture of guide plates ,
the inner sides of guide plates and the bony structures of the backsides of vertebral bodies were made to completely fit with each other .
then the models were saved in stl format and transmitted to a sps600 3-d printer ( provided by xian jiaotong university ) .
posterior soft tissues of vertebral bodies were cleared , and normal bony structure damage was avoided .
the operator held the corresponding individualized guide plate in one hand , matched it up with the vertebral body , and kept it stable while the surgeon held the screw panel alongside the leading panel on the plate with the pedicle instrument open in the other hand .
after the guide plate was removed , screws were placed alongside bilateral panels ( figure 5 ) .
x - ray assistance or screw panels correction by exploration during placement should be avoided to reflect true assistant effects of guide plates .
after placement of screws , the positional relation between the screw and the neighboring structures , such as vertebral body and spinal canal ( figure 6 ) , were first directly observed , then all the samples for examination were dissected to assess the positional relationship between the screw and the neighboring structures ( figure 7 ) .
we measured 25 vertebral samples through 3-d ct scans and precisely rebuilt them into 3-d models using medical mimics software .
the corresponding individualized guide plates were established by medical mimics software . under assistance of guide plates ,
the operative time of placement was 50 to 62 seconds , with an average time of 56.2 seconds .
post - operative direct observation showed a good positional relationship between screws and neighboring structures , such as vertebral bodies and vertebral canals , and no bony cortex was penetrated ( figure 6 ) .
the dissection showed that the 50 screws were all in pedicles and vertebral bodies , with proper length and angles ( figure 7 ) .
with development of spinal surgery , internal fixation of posterior thoracic pedicle screw has grown increasingly important . a key point of this operation is the one - time accurate placement of pedicle screw , but this has been very difficult and has safety concerns because of anatomic characteristics of thoracic pedicles . according to the spinal 3-column theory , placement of thoracic pedicle screw through pedicle bony channel better complied with the thoracic anatomic mechanical properties , which could improve spine stability compared with other internal fixations . with less trauma and a shorter fixed segment , a maximum number of active segments of spine can be maintained .
however , according to kothe , thoracic pedicles were thin , short , and narrow , and the cortex was thin and fragile ; therefore , thoracic pedicles easily broke .
in addition , the angles of thoracic pedicles were often different from each other , which made the error rate of one - time placement of thoracic pedicle screws very high , thereby damaging peripheral tissues and leading to severe consequences . in complex thoracic fractures or vertebral malformation ,
. the penetration rate of free - hand insertion of thoracic pedicle screw   can be 30% to 40% .
physicians started to consider safety of screw insertion as the most important factor in this operation .
some experts thought that thoracic pedicle screw fixation must be limited to spinal posterior column damage and 3-column damage with complete spinal cord injury .
some even thought that other thoracic screw fixations must replace thoracic pedicle screw placement . in order to remedy a lack of precision ,
many researches relied on imaging techniques in spinal surgeries , using intra - operative c - arm or ct imaging navigation   to assist accurate placement of pedicle screw placement , and achieved great improvement .
the intra - operative imaging navigation screw placement technique played an important role in accurate placement of thoracic pedicle screws , which was considered as the best way to assess accuracy of pedicle screw placement . but with errors brought by intra - operative position changes and spinal instability , and disadvantages such as a lack of real - time navigation , operating complexity , and high cost , this technique was not suitable for wide use .
therefore , a practical , less - expensive , and easy - spreading assistant screw placement method is necessary for clinical work . with application of 3-d printing in orthopedic spinal surgeries , individualized production of guide plates
the relatively simpler operation processes and higher safety of guide plates remedied limitations of imaging navigation .
some researchers have applied this technique in assisting cervical pedicle or vertebral plate screw placement , and proved that it could ensure accurate placement of screws .
this study aimed to improve lu s   method : to select experimental thoracic samples , to design and produce individualized thoracic pedicle screw guide plates , and perform assistant screw placement .
the pilot study showed that 3-d models of thoracic pedicle screw placement guide plates built using medical mimics software could be used for establishing screw placement parameters by a surgeon on the basis of accurate assessment of thoracic pedicle - related anatomic structures .
the individualized screw placement guide plates could be used for assisting screw placement and to ensure accurate insertion of screws .
medical mimics software used for guide plate designation could set accurate parameters and reduce data lost during process exchange between software , through which models had a higher compliance .
the process of guide plate designation has been used in daily education and research , which more closely resembled clinical work , and could be used in demonstrative teaching . while producing the guide plate , a 3-d printer could print melted materials into formation layer by layer , with shorter time and lower cost , making it possible to use guide plates in emergent surgeries .
printing materials are made of medical biodegradable polylactic acid , which could be used in operations after sterilization by ethylene oxide at a low temperature , making it more convenient and less risky for clinical application .
radiation damage by c - arm or ct imaging navigation in traditional operations and high expense were reduced .
data transformation between 3-d ct scans and printing might have some errors or defects , which make models different from actual structures .
materials for printing are still limited and might have morphological changes from formation to usage , which could lead to small errors when plates are applied to vertebral bodies . but with development and perfection of 3-d printing technique and material science , these limitations could be overcome and clinical advantages would be predominant . in this study , vertebral bodies were removed from corpses , followed by thoracic pedicle screw placement , which might cause deviations when compared with placement during surgeries in real life . however , crew placement should also be done after complete exposure of vertebral plate in lumbar posterior approaches , which is not significantly different from the method of this study .
another limitation is that there was no comparison between actual surgeries and experiments on corpses in this study .
with development of spinal surgery , internal fixation of posterior thoracic pedicle screw has grown increasingly important . a key point of this operation is the one - time accurate placement of pedicle screw , but this has been very difficult and has safety concerns because of anatomic characteristics of thoracic pedicles . according to the spinal 3-column theory , placement of thoracic pedicle screw through pedicle bony channel better complied with the thoracic anatomic mechanical properties , which could improve spine stability compared with other internal fixations . with less trauma and a shorter fixed segment , a maximum number of active segments of spine can be maintained .
however , according to kothe , thoracic pedicles were thin , short , and narrow , and the cortex was thin and fragile ; therefore , thoracic pedicles easily broke .
in addition , the angles of thoracic pedicles were often different from each other , which made the error rate of one - time placement of thoracic pedicle screws very high , thereby damaging peripheral tissues and leading to severe consequences . in complex thoracic fractures or vertebral malformation ,
. the penetration rate of free - hand insertion of thoracic pedicle screw   can be 30% to 40% .
physicians started to consider safety of screw insertion as the most important factor in this operation .
some experts thought that thoracic pedicle screw fixation must be limited to spinal posterior column damage and 3-column damage with complete spinal cord injury .
some even thought that other thoracic screw fixations must replace thoracic pedicle screw placement . in order to remedy a lack of precision ,
many researches relied on imaging techniques in spinal surgeries , using intra - operative c - arm or ct imaging navigation   to assist accurate placement of pedicle screw placement , and achieved great improvement .
the intra - operative imaging navigation screw placement technique played an important role in accurate placement of thoracic pedicle screws , which was considered as the best way to assess accuracy of pedicle screw placement . but with errors brought by intra - operative position changes and spinal instability , and disadvantages such as a lack of real - time navigation , operating complexity , and high cost , this technique was not suitable for wide use .
therefore , a practical , less - expensive , and easy - spreading assistant screw placement method is necessary for clinical work .
with application of 3-d printing in orthopedic spinal surgeries , individualized production of guide plates improved accuracy of operations . the relatively simpler operation processes and higher safety of guide plates remedied limitations of imaging navigation .
some researchers have applied this technique in assisting cervical pedicle or vertebral plate screw placement , and proved that it could ensure accurate placement of screws .
this study aimed to improve lu s   method : to select experimental thoracic samples , to design and produce individualized thoracic pedicle screw guide plates , and perform assistant screw placement .
the pilot study showed that 3-d models of thoracic pedicle screw placement guide plates built using medical mimics software could be used for establishing screw placement parameters by a surgeon on the basis of accurate assessment of thoracic pedicle - related anatomic structures .
the individualized screw placement guide plates could be used for assisting screw placement and to ensure accurate insertion of screws .
medical mimics software used for guide plate designation could set accurate parameters and reduce data lost during process exchange between software , through which models had a higher compliance .
the process of guide plate designation has been used in daily education and research , which more closely resembled clinical work , and could be used in demonstrative teaching . while producing the guide plate , a 3-d printer could print melted materials into formation layer by layer , with shorter time and lower cost , making it possible to use guide plates in emergent surgeries .
printing materials are made of medical biodegradable polylactic acid , which could be used in operations after sterilization by ethylene oxide at a low temperature , making it more convenient and less risky for clinical application .
radiation damage by c - arm or ct imaging navigation in traditional operations and high expense were reduced .
data transformation between 3-d ct scans and printing might have some errors or defects , which make models different from actual structures .
materials for printing are still limited and might have morphological changes from formation to usage , which could lead to small errors when plates are applied to vertebral bodies . but with development and perfection of 3-d printing technique and material science , these limitations could be overcome and clinical advantages would be predominant . in this study ,
vertebral bodies were removed from corpses , followed by thoracic pedicle screw placement , which might cause deviations when compared with placement during surgeries in real life . however , crew placement should also be done after complete exposure of vertebral plate in lumbar posterior approaches , which is not significantly different from the method of this study .
another limitation is that there was no comparison between actual surgeries and experiments on corpses in this study .
thoracic pedicle screw placement guide plates can be produced by 3-d printing . with high accuracy in placement and convenient operation , it provides a new method for accurate placement of thoracic pedicle screws .
 backgroundthe aim of this study was to evaluate the accuracy and feasibility of an individualized thoracic pedicle screw placement guide plate produced by 3-d laser printing.material/methodsthoracic pedicle samples of 3 adult cadavers were randomly assigned for 3-d ct scans . 
 the 3-d thoracic models were established by using medical mimics software , and a screw path was designed with scanned data . then the individualized thoracic pedicle screw placement guide plate models , matched to the backside of thoracic vertebral plates , were produced with a 3-d laser printer . 
 screws were placed with assistance of a guide plate . 
 then , the placement was assessed.resultswith the data provided by ct scans , 27 individualized guide plates were produced by 3-d printing . 
 there was no significant difference in sex and relevant parameters of left and right sides among individuals ( p>0.05 ) . 
 screws were placed with assistance of guide plates , and all screws were in the correct positions without penetration of pedicles , under direct observation and anatomic evaluation post-operatively.conclusionsa thoracic pedicle screw placement guide plate can be produced by 3-d printing . with a high accuracy in placement and convenient operation , it provides a new method for accurate placement of thoracic pedicle screws . 