3D Printing Is a Promising Alternative for Manufacturing Orthopaedic Implants

Editor’s note: This article is part one of a two-part series on 3D printing in orthopaedics. Part two covers novel and innovative uses of 3D printing in orthopaedics.

Orthopaedic implants have traditionally been manufactured with techniques such as casting, stamping, and machining. These manufacturing processes involve removing material, referred to as subtractive manufacturing. Although these processes are often ideal for manufacturing multiple identical devices, the costs of constructing molds and machining instruments for only a few (or one) implants can be prohibitive. Furthermore, creating highly irregular implants with subtractive manufacturing can be impossible. To solve these problems, 3D printing, or additive manufacturing, has become a ready solution. It can be done in a variety of ways. Material is deposited, joined, or solidified under computer control, with the material being added together (such as plastics, liquids, or powder grains being fused), typically layer by layer. However, the start-up cost of equipment needed for high-quality additive implant fabrication can make one-of-a-kind output extremely expensive.

The first patents for this technology appeared in the 1950s. Application of 3D printing to medical devices began in the early 2000s. Established orthopaedic applications include anatomic models, 3D-printed surgical guides, prosthetics, and both custom and non-custom implants. The market size for orthopaedic 3D-printed devices is expected to grow by $1.35 billion USD from 2023 to 2028, with North America accounting for 40 percent of market growth.

Benefits and production
Additive manufacturing is widely used for non-custom implants. Additively manufactured implants result in much less waste of raw materials than traditional subtractive manufacturing, which can significantly decrease costs. 3D-printed acetabular cups can be manufactured thinner and at lower expense than those made with subtractive manufacturing. Bone ingrowth porous metal implants are now routinely additively manufactured for a wide range of orthopaedic products, such as joint replacement implants, interbody lumbar cages, and other devices, to accelerate bone fusion. These devices would be difficult if not impossible to manufacture with subtractive manufacturing.

Once a physician decides that a patient-specific implant is in the best interest of the patient, a device manufacturer with 3D-printing capacity is contacted. Virtually all custom-printed devices are currently constructed with data from CT imaging. The manufacturer’s engineering team works with the physician on the design of the custom device. Once the final design is agreed upon by the team, the final device is printed and processed.

Regulatory considerations
The real benefit of 3D printing comes with the creation of unique implants for patients with issues requiring special devices not currently cleared or approved by the FDA. The FDA is responsible for protecting public health by ensuring the safety, efficacy, and security of human and veterinary drugs, biologic products, and medical devices. However, the FDA mandate extends only to regulation of interstate commerce, which creates unique issues with “point-of-care” devices manufactured and distributed completely within a single state. Despite this issue, the FDA has stated that if a product is composed of ingredients from out of state, then it is considered “interstate commerce,” even if the product was created and consumed within a state. This rule means that healthcare facilities must comply with all federal regulations regarding manufacturing medical devices and cannot distribute devices not approved by the FDA without risking a warning letter and potential prosecution. The American College of Radiology has petitioned the FDA for enforcement discretion for 3D-manufactured anatomic models, as they are of very low risk as an exception to this regulatory requirement.

The FDA offers two potential pathways to permit the use of devices not yet legally marketed: the Compassionate Use Program and the Custom Device Program. The FDA guidance on custom devices states that they must not be generally available in finished form. Under this program, a manufacturer may make such a device on the order of a physician. The Custom Device Exemption allows for the creation of no more than five devices per year. Devices that do not meet all elements of the custom device definition described in section 520(b) of the Federal Food, Drug, and Cosmetic Act may qualify, under appropriate circumstances, for compassionate use. An unapproved and uncleared medical device may be used on human subjects if a clinical trial is not available and the use complies with all applicable requirements. Compassionate use or expanded access of an unapproved or uncleared device may occur when a device is the only option available to a patient with a serious condition. All compassionate uses require, among other things, prior FDA approval. As these unique implants have not been rigorously evaluated, patients must be informed about the lack of information available and the potential risks associated.

Potential drawbacks
Although offering unique solutions to complex orthopaedic problems, 3D printing is not without its problems. In theory, 3D printing can increase the accuracy of execution of the patient’s surgery; however, this is not always the case, and at least some studies involving patient-specific surgical guides have shown significant deviations between planned and achieved radiographic measurements at final outcome. In these situations, the surgeon may find that the custom-made implant does not properly fit into its designated recipient site. Surgeons must work closely with the manufacturer to ensure that the final product can, in fact, be used in the patient’s surgery, because once the implant is printed, the cost incurred must be borne by someone. Custom implants accrue significant costs over traditional off-the-shelf devices, and the financial burden of these costs must be discussed in advance with the patient and hospital, in the event that these costs are not covered by insurance. Increasing concerns about CT and the associated radiation risks must also be considered.

In summary, the advent of 3D printing has resulted in multiple established uses for this technology in orthopaedic surgery. Part two of the series discusses novel and innovative uses of 3D printing in orthopaedic applications.

Stephen Weber, MD, FAAOS, is an orthopaedic surgeon who is an assistant professor of orthopaedics at the Johns Hopkins School of Medicine. He is a former FDA medical officer and a member of the AAOS Devices, Biologics, and Technology Committee.

Reference

1. Technavio: Orthopedic 3D Printed Devices Market Analysis North America, Europe, Asia, Rest of World (ROW) – US, Canada, Germany, UK, China – Size and Forecast 2024–2028. Available at: https://www.technavio.com/report/orthopedic-3d-printed-devices-market-industry-analysis. Accessed Dec. 3, 2024.
2. U.S. FDA: Custom Device Exemption. Guidance for Industry and Food and Drug Administration. Available at: https://www.fda.gov/media/89897/download. Accessed Aug. 17, 2024.