3D-printed patient-specific applications in orthopedics

Abstract

With advances in both medical imaging and computer programming, two-dimensional axial images can be processed into other reformatted views (sagittal and coronal) and three-dimensional (3D) virtual models that represent a patients' own anatomy. This processed digital information can be analyzed in detail by orthopedic surgeons to perform patient-specific orthopedic procedures. The use of 3D printing is rising and has become more prevalent in medical applications over the last decade as surgeons and researchers are increasingly utilizing the technology's flexibility in manufacturing objects. 3D printing is a type of manufacturing process in which materials such as plastic or metal are deposited in layers to create a 3D object from a digital model. This additive manufacturing method has the advantage of fabricating objects with complex freeform geometry, which is impossible using traditional subtractive manufacturing methods. Specifically in surgical applications, the 3D printing techniques can not only generate models that give a better understanding of the complex anatomy and pathology of the patients and aid in education and surgical training, but can also produce patient-specific surgical guides or even custom implants that are tailor-made to the surgical requirements. As the clinical workflow of the 3D printing technology continues to evolve, orthopedic surgeons should embrace the latest knowledge of the technology and incorporate it into their clinical practice for patient-specific orthopedic applications. This paper is written to help orthopedic surgeons stay up-to-date on the emerging 3D technology, starting from the acquisition of clinical imaging to 3D printing for patient-specific applications in orthopedics. It 1) presents the necessary steps to prepare the medical images that are required for 3D printing, 2) reviews the current applications of 3D printing in patient-specific orthopedic procedures, 3) discusses the potential advantages and limitations of 3D-printed custom orthopedic implants, and 4) suggests the directions for future development. The 3D printing technology has been reported to be beneficial in patient-specific orthopedics, such as in the creation of anatomic models for surgical planning, education and surgical training, patient-specific instruments, and 3D-printed custom implants. Besides being anatomically conformed to a patient's surgical requirement, 3D-printed implants can be fabricated with scaffold lattices that may facilitate osteointegration and reduce implant stiffness. However, limitations including high cost of the implants, the lead time in manufacturing, and lack of intraoperative flexibility need to be addressed. New biomimetic materials have been investigated for use in 3D printing. To increase utilization of 3D printing technology in orthopedics, an all-in-one computer platform should be developed for easy planning and seamless communications among different care providers. Further studies are needed to investigate the real clinical efficacy of 3D printings in orthopedic applications.

Keywords: 3D printing; custom implants; image processing; patient-specific instrument; patient-specific orthopedics.

Figure 1

This image summarizes the clinical workflow of patient-specific orthopedics from image acquisition to 3D-printed models and implants. Notes: The workflow requires close collaboration between surgeons and engineers to achieve the surgery that is customized to the patient’s anatomy and surgical requirement. Abbreviations: CT, computer tomography; MR, magnetic resonance; FEA, finite element analysis.

Figure 2

Axial CT images were acquired in a patient with low-grade osteosarcoma involving the sacrum (red arrows). Notes: The CT images in DICOM format were imported into a CAD engineering program. As the sacrum was at a tilted position during CT scanning, the image data set could be resliced to allow better visualization of sacrum in its anatomical alignment. The extent of the tumor could also be segmented manually from the images. The reformatted axial (A), coronal (B), and sagittal (C) views, and the 3D bone-tumor model (D) enabled surgeons to analyze the patient’s anatomy and pathology accurately for customized surgical planning. Abbreviations: CT, computer tomography; CAD, computer-aided design; DICOM, digital imaging and communications in medicine.

Figure 3

Summary of the steps in patient-specific orthopedics in a patient with low-grade chondrosarcoma involving the anterior acetabulum of pelvis and a partial acetabular tumor resection and reconstruction with a 3D-printed custom implant was planned. Notes: The steps consist of image acquisition (A), image postprocessing (B), and 3D printing (C). Abbreviations: DICOM, digital imaging and communications in medicine; CAD, computer-aided design; CT, computer tomography; MR, magnetic resonance; 3D, three-dimensional.

Figure 4

(A) This image shows surgical exposure in a patient with humeral shaft bone sarcoma undergoing intercalary tumor resection. The 3D-printed PSM with planned resections (red arrows) could be used for easy intraoperative reference of the surgical plan. 3D-printed PSIs and bone models (B) were fabricated preoperatively for a joint-saving tumor resection in a 9-year-old patient with femur osteosarcoma. Abbreviations: 3D, three-dimensional; PSM, patient-specific model; PSI, patient-specific instrument.

Figure 5

(A) and (B) The figures show a 3D-printed custom implant for acetabular reconstruction in the patient with low-grade chondrosarcoma. The implant has a solid plate, flanges, and an acetabular cup with screw holes for fixation. The scaffold lattice (C) contains an interconnected network of pores with an average porosity of 70%. Notes: The pores have an average size of 720 µm and the thickness of the solid struts is about 350 µm. The porous construct can facilitate the bone ingrowth at the bone–implant interface for better implant longevity. In addition, it is highly resistant to mechanical compression, while its elastic modulus is similar to that of bone to minimize the stress-shielding problem around the implant. Abbreviation: 3D, three-dimensional.