| The Surgical Technologist | APRIL 2022 166 the depth of osteotomy is difficult and can lead to cartilage damage.41 Patient-specific Custom Implants Although standard implants are made to fit most of the general population, a personalized fit is required in cases with variations in anatomy and cases in which no already produced implant would suffice (eg, severe bone loss for trauma, cancer, and infection). Custom implants are arguably themost ground-breaking aspect of 3Dprinting for orthopaedic surgery; surgeons can now design and implant custom devices. Although this technology has the potential to revolutionize patient care, we must also exercise caution and obey the mantra“just because you can, doesn’t mean you should.” Understanding the indications and contraindications of using custom implants is important. The primary indication is cases in which currently available implants will not adequately treat the patient. General contraindications include active infection, vascular compromise, poor bone quality, and a poor soft tissue envelope. Further contraindications are region and subspecialty specific. Once a patient has been identified for a 3D-printed custom implant, a prescription form is required to describe the pathology and document the unique need for a custom implant. In addition, preoperative imaging is needed. Typically, a CT scan and radiographs are submitted for the engineering team to create a 3D model of the patient’s anatomy. Next, the surgeon and company representatives meet to discuss the patient’s problem and implant design considerations, typically via a webinar. The surgeon should be ready to describe the goals and function of the implant. From the initial design meeting, one or more designs are created, which the surgeon approves or modifies. After the final design is approved by the engineering team and the primary surgeon, the process of fabricating the implant via 3D printing begins. This process is summarized in Figure 5. Custom implants are granted FDA approval through Section 520(b) of the Food, Drug, and Cosmetic Act.42 Several terms must apply for these implants to fall within this category of custom devices. First, each implant is designed for a specific patient at the prescription of a physician. Furthermore, the anatomy or pathology indicated must necessitate the use of a custom implant and cannot be treated with an implant already commercially available in the United States. Thus, the custom implants apply only on a case-by-case basis to manage unique and patient-specific pathology. Three-dimensional printing has played a major role in the production of these patient-specific implants with growing evidence of its clinical success. An example of a patient receiving a custom 3D-printed implant for a large bony defect sustained in a motor vehicle collision is shown in Figure 6. For large bone defects arising from traumatic bone loss, deformities, and nonunions, currently used strategies include allograft bone reconstruction, vascularized bone grafts, noncustom metal augments, and bone transport.43 Each of these treatment modalities has its own drawbacks (Table 2), with the literature showing mixed clinical outcomes. Studies of 3D-printed patient-specific implants have demonstrated early promising results in cases of segmental bone defects.44 Fifteen patients underwent treatment with a 3D-printed custom implant for severe bone loss, deformity correction, and/or arthrodesis Figure 5 Design process of a custom three-dimensional printed implant. Figure 4 Designing of ankle-foot orthosis (left). The ankle-foot orthosis being fitted to the patient (right). 6 Journal of the AAOS Global Research & Reviews® ----- April 2021, Vol 5, No 4 ----- © American Academy of Orthopaedic Surgeons Three-dimensional Printing in Orthopaedic Surgery
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