Three-Dimensional Printing: A Catalyst

Three-Dimensional Printing: A Catalyst
for a Changing Orthopaedic Landscape
Jonathan Minto, BA
Xuan Zhou, PhD
Jenna Osborn, MS
Lijie Grace Zhang, PhD
Kausik Sarkar, PhD
Raj D. Rao, MD
Investigation performed at the
Department of Orthopaedic Surgery,
George Washington University,
Washington, DC
COPYRIGHT © 2020 BY THE
JOURNAL OF BONE AND JOINT
SURGERY, INCORPORATED
Abstract
» Three-dimensional (3D) printing is an emerging tool in provider and
patient education, surgical planning, and the design and implementation of medical devices and implants.
» Recent decreases in the cost of 3D printers along with advances in
and cost reduction of printable materials have elevated 3D printing
within the medical device industry.
» The advantages of 3D printing over traditional means of implant
manufacturing lie in its ability to use a wide array of materials, its fine
control of the macro- and microarchitecture, and its unprecedented
customizability.
» Barriers to the widespread adoption of 3D-printed implants include
questions of implant durability, U.S. Food and Drug Administration
(FDA) approval for patient-specific implants, and insurance coverage of
those implants.
Orthopaedics is primed to
take advantage of technologic advances in threedimensional (3D) printing.
Surgical instruments that have been developed with the latest technology, including
patient-specific cutting jigs, guides, and
templates, are currently in use, and initial
data promise improved surgical accuracy
and a reduction in operating room time.
Three-dimensional-printed models tailored to patient-specific pathology
improve surgical planning. Most exciting
is the current research on and use of
patient-specific implants and advancements in tissue engineering. Threedimensional printing has an advantage
over traditional means of manufacturing
because of its ability to use a wide array of
materials, its fine control of the macroand microarchitecture, and its unprecedented customizability.
Three-dimensional printing, also
known as additive manufacturing, has
transformed segments of the medical
device industry. Used originally for
rapid prototype development, 3D printing is now making inroads into the
manufacturing world. The hearing aid
industry converted from conventional
manufacturing techniques to 3D printing in ,500 days, while firms that
maintained traditional processes were
unable to survive1
. The expiration of
several key patents has decreased the cost
of 3D printers, and advances in and cost
reduction of printable materials have
driven much of the recent interest. In
orthopaedic surgery, 3D printing is
being studied and used for a variety of
surgical applications2 (Table I). Surgical
instruments (e.g., patient-customized
cutting jigs, templates, and guides) for
knee arthroplasty, spinal surgery, and
tumor resection currently are being
used, and patient-specific implants
and advancements in tissue engineering that are being investigated show
Disclosure: The authors indicated that no external funding was received for any aspect of this work.
The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the
article (http://links.lww.com/JBJSREV/A541).
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JBJS REVIEWS 2020;8(2):e0076 · h t tp: / /dx.doi.org /10.2106 / JB JS.RVW.19.00076 1
promise and the likelihood of immediate applicability2-8.
Traditional implant manufacturing occurs through subtraction processes
(e.g., milling, turning, and cutting),
where a larger block of material is cut
down to the desired shape and size, or
through forming methods, where the
material is reshaped (e.g., rolling,
extrusion, and forging) without adding or removing material. Threedimensional printing allows instruments and implants of predesigned
shapes to be manufactured by sequential
layered deposition of the selected material. While traditional manufacturing
techniques generate randomly organized macropores9
, 3D printing allows
for an intentional organization of
implant microarchitecture with intentional design of pore size, pore number,
and pore interconnectivity9,10, regulating the elastic modulus and facilitating
biointegration.
Bioprinting utilizes 3D-printing
technologies to manufacture and
assemble scaffolds, tissues, and cells in
a precise layer-by-layer fashion to
replace or repair native tissue11. Scaffold matrices that are created from
natural or synthetic materials are
seeded or directly printed with factors
or cells that will drive tissue growth and
regeneration12. In vitro and in vivo
studies have shown the efficacy of bioprinted scaffolds for facilitating
chondrogenesis and repair13. Cellladen matrices have been constructed
to induce cartilage regrowth and subchondral repair, but the zonal distribution of cartilage has been difficult to
replicate13,14. Three-dimensional bioprinting utilizing precise control of
microarchitecture has shown the
potential to better replicate some of the
complexity of native cartilage13. The
primary difficulty faced in the development of this technology is vascularizing implanted tissue5,11. Tissue that
is .200 mm thick is beyond the diffusion depth of oxygen and requires a
vascular network to survive5,11.
This review article aims to provide
a scientific overview of 3D printing,
including the manufacturing process,
the biologic and nonbiologic materials
that are used and their relative benefits,
implant architecture and durability, and
the current clinical applications of 3D
printing in orthopaedics.
Three-Dimensional Printing
Three-dimensional printing is a group of
processes that creates objects from 3D
modeling layer by layer. The first step is
to produce a 3D image. Computed
tomography (CT) is the most common
imaging modality that is used to construct the 3D model15,16. Threedimensional printers require the target
object to have a discrete region that is
enclosed by defined surfaces, something that DICOM (Digital Imaging
and Communications in Medicine)
images from CT scans do not provide16. Raw DICOM images are
used to create a standard tessellation
language (STL) file or an additive
manufacturing file (AMF) that defines
regions for the 3D printer16. The STL
format does this by encompassing the
“region” in interlocking triangular
facets16. The newer AMF format was
created to provide a more complete
format by integrating more granular
details such as color, texture, or differences in material16. The slice
thickness of the image is critical for
constructing appropriate spatial resolution, and 1.25 mm is the cutoff for
creating a smooth construct15.
TABLE I Commercially Available Three-Dimensional-Printed Implants*
Company Implant (Year of FDA Approval) Method Material
Stryker119-123 Tritanium PL (2016), Tritanium C (2017),
Triath