Review Article on Three-dimensional Print Spine

Abstract

This article highlights the significance of three-dimensional-print spine in delicate and complex surgery of the spine. It includes computer techniques and software used in three-dimensional print spine and steps involved in three-dimensional print spine. We have also discussed the materials used in three-dimensional printing techniques. It also signifies the three-dimensional print spine preoperatively and its role in the planning of procedure.  This review article also provides an insight into the anatomical variances in different participants. The use of three- dimensional prints in complex procedures such as Spinal Orthoses, Spine Bio models, Craniocervical Surgery, Disc substitution Surgery, Slightly Invasive Spine Surgery is also discussed. The authors, in this review article, have also shed light on precision of  the three-dimensional printing techniques as well as its limitations three-dimensional

Introduction: In the last 10 to 20 years, spine surgery has improved immensely by through the use of three-dimensional printing. Each individual has a unique and varied anatomical structure of spine due to which we have to follow a slightly different approach for spine surgery for a particular person. Tissue engineering and three-dimensional (3D) open up a new gate for research and development in the vital fields of medicine and orthopedics. The role of spine surgeryhas been found to be very useful. In this particular review, we have revised the recent articles that emphasize the emerging role of the three-dimensional printing in medicine in multiple ways like inorthopedics, spine surgery etc. and abridged the usage of three-dimensional printing. The usage of the three-dimensional spine surgery has shown vital results in numerous aspects. It is a very important instrument for neurosurgeons. The increasing interest in the studied topics like tissue engineering has discovered a great vitality for tissue engineering and in the remedy of different spinal deformities.





This is a unique method that involves mainframe-aided design to produce physical entities in the form of layers (Michalski MH, 2014).  Though the three-dimensional printing has been vital since the 1980s,but the gradual improvements and advancement in it have made it possible that one can create anything imaginable from the prototype models of small gadgets to house (TT, 2008).The use of three-dimensional printing in medical sciences has proliferated very rapidly in the last ten years, largely due to its cost-effectiveness, computer engineering, and vast advancement. 
Since there are individual to individual changes in human makeup, thethree-dimensional printing has made it possible for surgeons to design highly personalized surgeries. This emerging field makes it easy to understand the human anatomy, its variations and its multiple dimensions more effectively and easily (Rengier F, 2010). Though the old-style method in medicine is limited to use time trial procedure, the current tendencies include the use of patient-oriented care. This article provides an overview of application of this technique in the treatment of spinal diseases and spine surgeries.

Techniques to design objects by use of 3-Dimensional printing
In order to design physical objects using 3-Dimensional printing, the three-dimensional Computer Aided Design files are used. First, an image is taken using multi detectors computed tomography scan machine. Second step involves three-dimensional image simulation which allows us to get required object as a computer image. By using the computer software, digital cross sections are converted to Computer Aided Design folder. This copy is then conveyed to 3-Dimensional printers to produce the object in distinct coating by putting polyurethane powder without the use of molds. Multiple substances, such as ceramics, resins, metaloplastic polymers, glass are widely used to create three-dimensional models (MB, 2013) . These produced layers are joined together by the use of numerous techniques, for instance, sintering along with laser and electronic beams which compacts the material to get a base for forming new body. 


This highly significant step entirely depends on the digital conditions of three-dimensional printing procedures. It also depends on the nature of required end product. Other 3-dimensional printing procedure includes many methods such as laser sintering, stereo lithography, and laminated object manufacturing. (Sun W, 2005).
The inherent technical limitations in three-dimensional printing technology may cause further complications However, with the help of enhanced technology and dexterity, such errors and limitation can be overcome and minimized. 
One of the restrictive factors is typically the support material used in sealing empty spaces that will persist inside the spaces because of present incapability to remove the solid. Despite many breakthroughs in the production of replicas of soft tissues and implants, bones, such as neurons and arteries and veins, we still require more development and delicacy. Additionally, mixture texture or consistency should be improved to look like the unique tissue for improved reproduction. (Kim K, 2010).

Uses of three-dimensional print techniques

Three-dimensional printing can be used for practical purposes such as learning and understanding the difficult anatomical parts of body, teaching, and surgical planning in complicated surgeries. Neurosurgeons often encounter complex anatomical structures such as nerves and ganglion . The sophisticated and slightly vague morphological relationships between cranial nerves, vasculature, and other complicated structures of pons and medulla cannot be shown clearly in the two dimensional computer tomography scans. If we apply any procedure without completely understanding the anatomy, there will be disappointing results and complications. Thus, for complete understanding, teaching, planning and designing step by step surgery, we need to understand the delicate parts completely and preoperatively. For that purpose, we need to use three-dimensional printing techniques (Klein GT, 2013).
The use of three-dimensional printing in medicine is multi-faceted and includes listening aids, patient precise rehabilitation equipment, complicated neural, orthopedic surgeries, and modified grafts for each specific person. Three-dimensional printing also used to produce personalized bone prosthetics with the use of very delicate computed tomography scans. And another very significant use of three-dimensional printing is in maxillary and facial surgeries. Maxillofacial surgery is a very complicated and delicate surgery due to its variance in various patients. The first completely fruitful personalized three-dimensional procedure which is done by the aid of titanium is of mandibular a This procedure was first done in Belgium on an eighty-six year old woman. (M, 2017).
The developing technique used in this case a laser is used to melt down very thin coatings of titanium sequentially to form personalized prosthesis by the use of  a computer-based three-dimensional image. Food and Drug Administration in the United States of America allowed for the development of Polyetheretherketone skull implants (Bonda DJ, 2015). Polyetheretherketone has two major benefits of possessing a nearly equivalent structure to that of titanium and a unique flexibility and resistance much more like that of cancellous bone (Kurtz SM, 2007).

The application of typically made spongy titanium or Polyetheretherketone prosthetics is mainly specific to spine surgery as it acts as a support for bone ingrowth. Tracheobronchomalacia is a very rare ailment of middle airways caused by softening or damage of cartilaginous anatomical structures of bronchioles walls in bronchi and trachea. Food and drug administration also allowed the use of the three-dimensional tracheal splint in infants, having ailment of tracheobronchomalacia (Zopf DA, 2013) (Gonfiotti A, 2014).

The most exciting and improved advancement of Three-Dimensional printing in the medical field is tissue engineering. In tissue engineering, we form inert frameworks for organic ingrowth of small compartments called cells in living organisms to do the replacement. Bioprinting involves the development of three-dimensional printing of whole individual constituents to develop a whole tissue. There is an extensive usage of coalescing degradable scaffolding with tissue bio printing to establish personalized biological. These prosthetics bioprinting technique proved very useful for tissue engineering as it enables very precise and specific placement of the cells and other biomaterials such as carbohydrates, lipids and proteins to form a tissue that is very much similar in morphology as an originally grown tissue (Murphy SV, 2014).
Research has showed the development of whole performing kidneys by the application of the three-dimensional bioprinting.  Kidneys were grown with a combination of human cells and a gel-like biodegradable framework. Researchers also established bio printers, which enable us to produce various cell kinds such as vascular cells and stem cells etc. (Leberfinger AN, 2017) (Xu T, 2013).Researchers also developed a technique for bioprinting of adipose containing tissues with anticipation to use in breast cancer female patients in case of fractional mastectomy and breast lumpectomy.
Surgeons and physicians of hepatic and biliary systems use three-dimensional printing technique to design hepatic transplants. Copy of a body part is used to define the extent of model essential to replace the benefactor's liver into receiver's abdomen. The three-dimensional models used were made of partly translucent cheap materials such as acrylic resins and polyvinyl alcohol etc. It also has water as a constituent and consistency comparable to living tissues, that allow operating blades to expurgate into  replicas more practically (Zein NN, 2013).
   
Cardiothoracic surgeons of Professor Jeffery L and his team at  Port at Presbyterian Weill Cornell Medical Center in New York(United States of America) performed a very first operation to substitute the sternum and some parts of rib cage by use of three-dimensional printed implants (H, 2017. Oct 19).

Preoperative Designing of procedure

A big benefit of using three-dimensional spine printing replicas is the realistic and applicable operating imitation in the preoperative arrangement, which has  proved beneficial to mitigating complicated spinal malfunctioning (Xiao JR, 2016). The use of three-dimensional printed spine replicas has made us capable to effectively do multipart en bloc resections of main cervical tumors  In one more case, three-dimensional replicas were cast off in multifaceted craniovertebral procedures to understand the leaning of joints, false expressions, and pedicles sizes courses preoperatively. Information and calculations from the previous models are permissible for preoperative calculation and designing of screw and plate dimensions and direction of screw enclosure (Goel A, 2016). For improvement of spinal malformation in infants and children with meningomyelocele, custom-made three-dimensional printing was used in the past to produce medical planning prototypes and patient particular spinal instrumentations (Karlin L, 2017).The preoperative three-dimensional modeling for operating preparation is now vastly used in procedure of a thoracolumbar fractures with displacement of the sagittal curves and triangulation patterns for pedicle screws. This technique resulted in benefits such asless time taken during operation, less blood wastage, much improved retrieval of thoracolumbar displacement, and improved Frankel organization when finalized with a three-dimensional model (Wu C, 2015) .
Speedy prototyping of three-dimensional replicas have been used in procedural preparation for reconsideration of  lumbar discectomy, resultant in abridged operation time and perioperative blood and tissue wastage (Li C, 2015) .A revision on posterior remedial procedure for Lenke 1 teenage without any known cause scoliosis using preoperative preparation with three-dimensional printed spine replicas set up considerably smaller operation time,dramatically  reduced blood wastage and transfusion volume. It is also observed that higher postoperative hemoglobin is found as compared to the same procedure without the three-dimensional printing model. Nevertheless, no noteworthy variances were detected in difficulty rate, length of clinic stay, postoperative radiological results, or pedicle screw misalignments in the middle of two groups (Yang M, 2015)
.Some restrictions occur in the use of three-dimensional printing in respective site before operation. Research has demonstrated numerous benefits in application of three-dimensional printed models in before-operation planning, including in case of Lenke1 AIS. Granting the replicas may deliver smaller operation time and one must ponder the extra time obligatory to scheme and build the model preoperatively. However, it is being used in circumstances of preoperative planning for acetabula rebuilding following shock (Duncan JM, 2015).Developments in the swiftness and readiness of fast prototyping expertise may permit us to more extensive use in the shock site. Consequently, researchers reflect that the three-dimensional printer will be more beneficial in more multifaceted cases.


Application of three-Dimensional Printing in Spinal Care
This technique also helps a lot in keeping the diagnostic process healthy. It also found its application in spine surgery, which is considered highly complicated and most difficult of all the surgeries. The latest research has discovered its usability in several vital procedures such as planning patient precise spinal orthoses. This technique helps in making personalized spinal implants.  The three-dimensional printed tissue engineering has lately expanded the interest and attention of the scientific community  and provided outstanding benefits in complicated procedures. Additive engineering is now extensively used to create personalized spinal grafts. After many failed attempts, the first successful developed titanium spinal implant was  produced by the use of electron beam fused three-dimensional printers at Peking University Hospital, Beijing, Xiu in 2009. It was illustrated that the three-dimensional printed implants were of superior quality to the unprinted implants because of their capacity to print precise structurally based configurations. Due to relative effortlessness of producing porous material,  the three-dimensional printed implants can aid as a framework for the ingrowth of bone. Many researchers are now working on three-dimensional printing and getting positive results (Xiu P, 2016).
Spinal Orthoses
Spinal orthosis is a back brace that is planned to grip your spine in place and greatly reduce the chances that the curve in your spine will develop poorer as you develop and reach high age. By using that technique, 8 out of 10 people have had their curves remain the same size. Researchers also found the utility of three-dimensional printing in scheming personalized orthoses with spinal malformations. They thought that the orthodox brackets that were made of casts had reported a major nonconformity.due to numerous causes. Computer aided design software was used to produce a patient precise template, over which the brace was prepared into layers. It provides us patient compliance. Global improvement in technology would let us extensive use of this technique in whole social fabric (Bagaria V, 3D printing and developing patient optimized rehabilitation tools (PORT): a technological leap, 2015).
Spine Bio models
Researchers have proposed the usage of bio modeling as a help to spinal equipment. Acrylate bio models were considered by fast prototyping by three-dimensional computed tomography images of patients. Pins were inserted in these bio models before the technique feigns the procedure. Drills monitors were created by use of these trajectory pins and bio models that were cast off while the procedure is carried out to fix the actual pedicle screws. Since bio models and drill guides are composed of acrylate, these were disinfected and used during an operation to provide surgeons a visual sign for placing the pedicle screw. Computed tomography scans were carried out in patients for post-procedure settling the location of screws. Researchers also found that the use of bio models before operation enhanced the content provided in well-versed agreement for patients. Many medical setups are using the three-dimensional printed precise drill guides that compose of polyurethane in ailments of malformation and improvement for drilling pedicle screws, chiefly on the hollow on the side of the curve (D'Urso PS, 1976).

Craniocervical Surgery
 Thethree-dimensional printed replicas are used in large numbers to provide satisfactory bar mold into a specific mold in fifteen to twenty patients with hypersensitivity rheumatoid arthritis who go through craniocervical fusion procedure (Mizutani J, 2008).  Thethree-dimensional polyurethane replicas were invented using quick prototyping procedures from 1millimeter slice width individual Computed tomography scan. Use of replicas as patterns, suitable forms of plate rods were designed and produced in development. Radiance vest is mostly used before operation to regulate the occipitocervical angle. A computed tomography scan was done in comfort position to get the copy from which the three-dimensional replicas were made. The chances of dysphagia are very rare. In modern clinical practice and research, the personalized three-dimensional printed replicas are extensively used in the controlling and operating the preparation of complex spinal pathologies. For instance, the use of three-dimensional printed replicas is aimed at planning complex surgeries of atlantoaxial displacement with fixed kyphosis and an inconsistent vertebral artery. By use of axial computed tomography scans, the three-dimensional rebuilding of innate structure is shaped in Future, an arterial inclination was extra to recreate the innate morphology of the vertebral arteries .Such information and calculation are then further used to make computer aided design files and finally to print a three-dimensional model. This prototypical was used as a substitute for definite surgery before operation for planning the course and extents of screws.
Disc substitution Surgery
The use of additive and tissue engineering has roused the attention and curiosity of researchers in the build-up to bioengineered whole disc substitution prostheses.  (Moriguchi et al).  The complete disc replacement is created by using stem cell instilled into bio ink printers (having cellular organic material) in Cornell University in Ithaca, New York. These three-dimensional printed builds control erudite ovine nucleus pulposus cells in a central hydrogel that later reproduce itself, while the circumferentially located annulus fibrosus cells extend the collagen matrix. In an experiment of more than one hundred rodents, disc tallness and biomechanical purpose were supported for the complete life span of all rodents in a crowd that established the tissue engineered discs (Moriguchi Y, 2017).
Slightly Invasive Spine Surgery
In slightly invasive spine procedure, the three-dimensional printed bio models are very vital for defining whether the screws can be placed in the margins of tubular retractor. It is feasible to compute the space from the midline where the routes meet, if we measure the soft tissue superficial to the spine correctly. Though the technique is still in a its infancy, it is likely that it will not be also extended before the implant making companies develops customized patient-specific screw addition sleeves for use in slightly invasive spine surgery (Bagaria V, 3D printing and developing patient optimized rehabilitation tools (PORT): a technological leap, 2015).
Precision of Three-dimensional Printing technique
The accuracy and exactness of the three-dimensional models that demonstrate true anatomic structures is essential for its medical application in spine surgery.  Research has authenticated the possibility for three-dimensional printed replicas to precisely represent the complicated anatomical sorts of the spine. Researcher Wu et al equated commuted tomography images of fit cervical, thoracic, and lumbar vertebrae against their corresponding three-dimensional printed replicas and establish the three-dimensional models had strong structural correspondence (Wu AM, 2015). One more study evaluated the accurateness of three-dimensional printed replicas expressive cadaveric pelvises and detected no important difference amid them (Wu XB, 2015).
Another researcher McMenamin et al. establish that three-dimensional printed models not only precisely signified physical radiologic data but also precisely signified air and liquid full negative spaces (McMenamin PG, 2014). Contemporary printing methods permit for formation of replicas with great calcium concentration to precisely mimic the true thickness of bone (West SJ, 2014)


Limitation in Use of 3D printing in medical procedure
Though there is rapid advancement in the technique of three-dimensional printing, it is still not available in all regions and countries of world due to multiple reasons such as lack of research, lack of facilities, low quality and capacity of healthcare system. The price of the whole developing procedure for these three-dimensional replicas depends on the substance being used. During commuted tomography scanning, the person must be rightly put out of action to stop motion relics, which disturb the continuity in the spinal model (Van Dijk M, 2001).
To attain a maximum degree of reproducibility, the space among the commuted tomography cuts should not surpass 1.5 millimeter (Woolson ST, 1985). Pseudo foramina’s are the flaws in the duplicate due to low commuted tomography values formed by thin bone. The pseudo foramina and metal relics produced by in situ inserts must be amended and removed by dexterity and by following all described protocols (Solar P, 1992). Sometime it is not likely to yield real size spinal replicas in single part. Therefore, lesser portions are arranged by three-dimensional printing and then accumulated together by introducing negligible extra inconsistencies comparative to real human anatomy. These replicas show only the vertebral column and not nearby soft tissue. It is worth noting that the neuronal and vessels structure as well as the soft living tissues must be taken as conclusive preparation of osteotomies and rebuilding. A new limit in three-dimensional printing techniques is that the whole making period is about six to eight weeks (Yang Z, 2016). Creating a spinal prototypical may require about twelve days, and producing personalized spinal grafts may possibly need roughly four weeks.

Conclusion
Despite speedy advancement and improvements, the technique of three-dimensional printing is still in its nascent stage. Though a lot of study is being carried out worldwide to fund its benefits and feasibility, it will still take many decades for three-dimensional printing to become an extensive and noteworthy medical modality. The actual size three-dimensional printed bio models composed of polyurethane froth can be manipulated to deliver an outstanding studying of complicated spinal ailments that are otherwise impossible using the present imaging procedures for extremely particular patients with stark complicated spinal ailments. These replicas also deliver a graphic and demonstrative response. The nonstop and increasing study on tissue bio engineering and its use in combination with additive development has provided novel prospects for the management of deteriorating disc disease. Three-dimensional printing techniques in spine surgery are presently being used for preoperative preparation, apprentice and patient awareness, intraoperative direction systems, intraoperative grafts. It has also transformed, if not entirely, the field of tissue engineering. The ongoing developments in printing techniques have encouraged optimistic results as well as room for further research. 



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