In various fields of medicine—from cranial prostheses for skull defect reconstruction1,2 to titanium artificial jaw replacement3,4 to human earlobes5 to dermal skin grafts6 to tracheas7—3-dimensional (3D) printing has emerged as a clinically promising technology for rapid prototyping of graspable products. Recent advances in 3D printing have provided orthopedic surgeons with a new technology that has the potential to revolutionize preoperative planning, surgical instrument development, and custom orthopedic implant creation.
What Is Three-Dimensional Printing?
For more than 3 decades, 3D printers have been used to build custom-made objects by using computer software to build physical items from data. During the past decade, technological developments have lowered the cost of 3D printers, such that their use has expanded into areas not traditionally associated with rapid prototyping, such as patient education, surgical training, and research.8
To begin the process of 3D printing, an image portraying the desired object must be collected. This image is then converted into a format that the 3D printer software can use to template the object. For medical applications, this raw image can be acquired from computed tomography or magnetic resonance imaging scans. Advancements in medical imaging have resulted in scan resolution that far surpasses 3D printer resolution.8
The radiological scan data-set (often in the Digital Imaging and Communications in Medicine [DICOM] file format) must then be converted into a file format recognized by the 3D printer. The DICOM file is uploaded into a program (eg, OsiriX) that allows for 3D reconstruction of the image. The file is exported in the file format (stereolithography [STL]) that makes it readable to software (computer-aided design [CAD]) used to design the 3D objects. Defects or errors in the STL file can be corrected using readily available software (eg, MeshLab). The corrected STL file is then sent to the 3D printer.9
Three-dimensional printers use a variety of technologies to “additively manufacture” or construct objects layer by layer (Figure). Industrial-grade printers use lasers to precisely sinter granular substrates (eg, metal or plastic powders). Directed, localized fusion of certain regions on a bed of granular substrates results in the construction of a cross-section of the desired object. After each layer of the structure is completed, the printer adds a new layer of unfused powder on top of the old one, and the subsequent round of sintering builds the next cross-section fused to the previous one. The advantages of these printers are high print speeds, the ability to easily recycle unfused powder, and the ability to use stronger materials with higher melting points (eg, titanium, which had been difficult to sculpt by standard subtractive methods).10 The Table details commonly used materials.11
Steps in the 3-dimensional printing process. Computed tomography or magnetic resonance image. (Courtesy of Alan H. Daniels, MD.) (A). Three-dimensional image reconstruction and object design. (Courtesy of Alan H. Daniels, MD.) (B). Three-dimensional printer process. (“Extruder lemio” by Lemio: http://reprap.org/wiki/File:Extruder_lemio.svg. Licensed under GFDL via Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Extruder_lemio.svg#/media/File:Extruder_lemio.svg.) (C). Additive printing in layers. (“Printing with a 3D printer at Makers Party Bangalore 2013 11” by Subhashish Panigrahi. Licensed under CC BY-SA 3.0 via Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Printing_with_a_3D_printer_at_Makers_Party_Bangalore_2013_11.JPG#/media/File:Printing_with_a_3D_printer_at_Makers_Party_Bangalore_2013_11.JPG.) (D). Three-dimensional object. (Courtesy of Alan H. Daniels, MD.) (E).
Three-Dimensional Printing Materials Used in Orthopedics
Lower-throughput, commercially available printers use extrusion to print solids. These printers force feedstock material (eg, melted plastics) through mobile heads that lay down beads as little as 0.1 mm thick. After deposition, these beads quickly solidify onto the previous layer of material, and in this manner, the printer builds the structure from the bottom up. Printing itself takes from a few hours to days. Costs vary substantially for these types of printers—ranging from less than $1000 to more than $100,000.10 Three-dimensional printers are becoming less expensive and more accessible.
Three-Dimensional Printing in Orthopedics
Three-dimensional printing allows for anatomic model creation so surgeons can examine patient anatomy in a more concrete way compared with traditional 2-dimensional radiological images.10 The insight provided by a 3D printed model may be helpful to both patients and surgeons. Epps12 described how directly comparing normal anatomic models with custom printed models of complex deformities undergoing surgical correction can be used to deepen patients' insight into their condition as well as the surgical repair process. Bizzotto et al9 showed that the preoperative analysis of 3D printed models of patient bone fractures, compared with analysis of 2D and 3D reconstruction on screens alone, resulted in surgeons and residents reporting a major improvement in understanding fracture patterns. The model was able to accurately display features such as dislocation of the articular surface and joint fragmentation. These elements aided in the surgical planning, such as screw measurement and plate positioning.9 Additionally, intraoperative guidance with templates is possible with models printed with thermoplastics (eg, ULTEM 1010; Stratasys, Eden Prairie, Minnesota) that can be autoclave-sterilized.
Custom-made 3D printed implants have been used to repair a range of bone structures; they have been used in pelvic,13 femoral,14 and tibial15 hemiarthroplasty. Surgeons at the Mayo Clinic performed bilateral total hip arthroplasty using 3D printed implants for a patient with dwarfism, who was too small for conventional hip implants.16 The surgeons printed a model of her hip to perform a practice run of the surgery, then sent the model joint to a manufacturer who was able to fabricate a hip replacement implant to her specifications.
Chinese surgeons recently replaced a segment of cancerous cervical vertebrae in a 12-year-old patient with a 3D printed titanium implant.17 The theoretical advantage of the 3D printed implant is that its shape matches the excised bone site, lowering the pressure placed onto the existing bone compared with a conventional implant. Additionally, the implant can be created with osteoconductive pores to facilitate natural bone growth incorporation.18
A proof of concept for 3D printed casts has the potential to solve several problems posed by conventional plaster casts (eg, restricted access to the encased area, lack of breathability, heavy weight, and necessity to remain dry). Produced by a designer specializing in 3D printing, a new kind of 3D printed cast called the “cortex” has the potential to eliminate these problems. The cortex resembles a hardened mesh molded to encase the site of injury. If 3D printers become readily available to physicians, radiological scans could be used to quickly print customized, lightweight casts for patients on site to maximize immobilization of broken bones while minimizing inconvenience.19
As 3D printing technology advances and the cost of printing drops, the speed of printing increases, and the operation of printers becomes easier, the use of custom 3D printed models of patient bone may become standard in preoperative planning, surgical simulation, intraoperative guidance, and implant development.
Should 3D printer technology advance to the point that 3D printer use is widely accepted in a sterile hospital environment, one potential use of readily available 3D printers could be the on-demand manufacturing of customized surgical instruments that would otherwise be unavailable due to prohibitive costs or rare use.
Another possible application is in operations requiring reconstruction of large bone defects. A “negative” mold of the required implant would enable the surgeon to shape the implant to the proper dimensions for optimal fit even before the surgery is performed. Three-dimensional printed biologic and bone-like implants may be used to optimize restoration of original structure and function.20 Three-dimensional printers also have the potential to rapidly increase the number of tools available to surgeons. With the aid of a designer, surgeons could modify mass-produced instruments to suit their particular needs and preferences. The availability of rapid prototyping may spur instrument innovation because surgeons can easily produce novel tools to satisfy unmet needs during an operation.
The largest impediment to the implementation of 3D printers in orthopedics is the cost associated with the time it takes for medical staff to operate the machinery—the building material itself is relatively inexpensive, and printer prices are continually dropping. Three-dimensional printer technology may advance to the point that even an untrained user could operate a 3D printer efficiently, or better yet, the entire process of printing from image acquisition to rapid prototyping may become automated. A solution to the labor costs of printing may be the out-sourcing of medical 3D printing operations to a dedicated third-party company. That way, medical staff would not need 3D printing training, and economical advantages of scale could provide access to inexpensive, customized 3D printed products.
- Biomedical devices. http://www.oxfordpm.com/biomedical_parts.php. Accessed May 30, 2015.
- Eng J. Medical first: 3-D printed skull successfully implanted in woman. http://www.nbcnews.com/science/science-news/medical-first-3-d-printed-skull-successfully-implanted-woman-n65576. Accessed May 29, 2015.
- Richmond S. 3D printer builds new jaw bone for transplant: an 83-year-old woman has become the first person to have a 3D printer-created jaw fitted. The Telegraph. February7, 2012. http://www.telegraph.co.uk/technology/news/9066721/3D-printer-builds-new-jaw-bone-for-transplant.html. Accessed May 30, 2015.
- Singare S, Liu Y, Li D, Lu B, Wang J, He S. Individually prefabricated prosthesis for maxilla reconstruction. J Prosthodont. 2008; 17(2):135–140.
- Helsel S. Scientists use 3D printing and human cells to grow artificial earlobes. http://inside3dprinting.com/artificial-earlobes. Accessed May 29, 2015.
- Lee V, Singh G, Trasatti JP, et al. Design and fabrication of human skin by three-dimensional bioprinting. Tissue Eng Part C Methods. 2014; 20(6):473–484. doi:10.1089/ten.tec.2013.0335 [CrossRef]
- Zopf DA, Hollister SJ, Nelson ME, Ohye RG, Green GE. Bioresorbable airway splint created with a three-dimensional printer. N Engl J Med. 2013; 368(21):2043–2045. doi:10.1056/NEJMc1206319 [CrossRef]
- Rengier F, Mehndiratta A, von Tengg-Kobligk H, et al. 3D printing based on imaging data: review of medical applications. Int J Comput Assist Radiol Surg. 2010; 5(4):335–341. doi:10.1007/s11548-010-0476-x [CrossRef]
- Bizzotto N, Sandri A, Regis D, Romani D, Tami I, Magnan B. Three-dimensional printing of bone fractures: a new tangible realistic way for preoperative planning and education. Surg Innov. pii:1553350614547773. Epub ahead of print.
- Starosolski ZA, Kan JH, Rosenfeld SD, Krishnamurthy R, Annapragada A. Application of 3-D printing (rapid prototyping) for creating physical models of pediatric orthopedic disorders. Pediatr Radiol. 2014; 44(2):216–221. doi:10.1007/s00247-013-2788-9 [CrossRef]
- American Society of Mechanical Engineers. Top 10 materials for 3D printing. https://www.asme.org/engineering-topics/articles/manufacturing-processing/top-10-materials-3d-printing. Accessed May 29, 2015.
- Epps HR. 3-D printing helps with complex hip surgery: pediatric orthopaedists find it helpful for patient education too. AAOS Now. July2014. http://www.aaos.org/news/aaosnow/jul14/clinical4.asp.
- Dai KR, Yan MN, Zhu ZA, Sun YH. Computer-aided custom-made hemipelvic prosthesis used in extensive pelvic lesions. J Arthroplasty. 2007; 22(7):981–986. doi:10.1016/j.arth.2007.05.002 [CrossRef]
- Harrysson OL, Hosni YA, Nayfeh JF. Custom-designed orthopedic implants evaluated using finite element analysis of patient-specific computed tomography data: femoral-component case study. BMC Musculoskelet Disord. 2007; 8:91. doi:10.1186/1471-2474-8-91 [CrossRef]
- He J, Li D, Lu B, Wang Z, Tao Z. Custom fabrication of composite tibial hemi-knee joint combining CAD/CAE/CAM techniques. Proc Inst Mech Eng H. 2006; 220(8):823–830. doi:10.1243/09544119JEIM207 [CrossRef]
- Thobald S. Custom surgery creates normal hips for 30-year-old. http://sharing.mayoclinic.org/discussion/custom-surgery-creates-normal-hips-for-30-year-old. Accessed May 30, 2015.
- CBS News. 3D-printed vertebra used in spine surgery. http://www.cbsnews.com/news/3d-printed-vertebra-used-in-spine-surgery. Accessed June 7, 2015.
- Yang J, Cai H, Lv J, et al. In vivo study of a self-stabilizing artificial vertebral body fabricated by electron beam melting. Spine (Phila Pa 1976). 2014; 39(8):e486–e492. doi:10.1097/BRS.0000000000000211 [CrossRef]
- Evill J. Cortex. http://www.evilldesign.com/cortex. Accessed May 29, 2015.
- Meseguer-Olmo L, Vicente-Ortega V, Alcaraz-Baños M, et al. In-vivo behavior of Sihydroxyapatite/polycaprolactone/DMB scaffolds fabricated by 3D printing. J Biomed Mater Res A. 2013; 101(7):2038–2048. doi:10.1002/jbm.a.34511 [CrossRef]
Three-Dimensional Printing Materials Used in Orthopedicsa
|Sintered powdered metal|
|Bone-like (eg, CT-bone [Xilloc, Geleen, the Netherlands])|
|Plastics (eg, PolyJet [Stratasys, Eden Prairie, Minnesota], polyether ether ketone, polyether ketone ketone)|