Personalizing Orthopedic ImplantsPersonalizing Orthopedic Implants

ORTHOPEDICS DESIGN

The U.S. market for reconstructive joint replacements and spinal hardware is valued at $17.3 billion.¹ As it grows, the market seems to be getting more personal, with an increase in the use of patient-specific implants. New technology is enabling quick, cost-effective creation of exactly the right hip, knee, shoulder, or spinal section for an individual patient in a matter of weeks, not months. Contract manufacturers that specialize in digital manufacturing technologies are playing a key role in driving this change. Innovations in new business processes provide lessons for orthopedic industry players on the evolving WDB: all-digital work flow. Orthopedics companies need to understand how best to leverage outside contract manufacturing resources to complement internal expertise.

In the past, replacement hips, knees, and sections of spinal columns came in a small range of sizes primarily because manufacturing processes were too costly and labor-intensive to support low-volume or custom projects. Today, aging baby boomers receive repeat implants, and surgeons strive to preserve the patient's own bone structure in case replacements are needed. Although many more sizes of off-the-shelf implants are available in modular designs that can be used together, off-the-shelf implants are not always the best answer for a number of cases.

Barriers to Customization

Although the technology exists, the current processes employed to create patient-specific implants are often flawed for a variety of reasons. Customization requires a switch in thinking, and orthopedic product manufacturers should consider whether their processes are hindering the ability to move to personalization.

Volume Manufacturing. Orthopedic product manufacturers often gear their operations for volume manufacturing, for which they design once, and then manufacture efficiently in volume. They generally refine designs for simplicity and cost, not necessarily custom patient fit, and they stay with a single design for many years. They may view deviations from standard processing techniques, such as those required for custom implant creation, as unprofitable. And companies that do create patient-specific implants often do so as a favor to a valued client, without tailoring the work flow for efficiency.

Lead Times. For a custom orthopedic implant, design technicians may need up to three months of lead time. The work flow includes interpreting the CT scans, making rough prototypes of the component in clay or wax, shipping it to the surgeon, and awaiting approval or input. This process is often repeated two or three times before a final design is achieved.

Required Technical Skills. Customizing implant design to achieve a perfect fit requires that technicians have a rare blend of skills. Designers must understand the specific target anatomy and the mechanical aspects of joint components, and they must have a working knowledge of manufacturing processes. They should also be able to communicate with a surgeon. Without such skills, producing a customized device is difficult if not impossible.

Design Process Efficiency. Regardless of whether the orthopedic company uses clay, 3-D modeling, or computer-aided design (CAD) tools to design the implant, the traditional design process involves iterations done on prototype versions of the proposed design. These prototypes often move back and forth between collaborators with iterative improvements. Surgeons mark changes onto the model itself, and the model is then sent back for modification. The process is fraught with delays. Of the three-month lead time, a significant portion of it is lost to shipment or other unusable time. Because a patient for a replacement or customized implant is usually more uncomfortable or more ill than a typical case, such delays can be a hardship for the patient.

Suitable Modeling Tools. The traditional CAD 3-D modeling tools used to design other types of implants may not be able to support the irregular shapes and organic curves required in most patient-specific implants. In addition, the skills needed may be difficult to acquire, resulting in only a few trained technicians. Creating 3-D models may take several days as the hardware and software computes the math behind the organic graphics.

Such delays often lead designers to explore nondigital workarounds. For example, designers may receive a surgeon's marked-up prototype, and then either carve the model out by hand or place real putty or clay over the area to be revised to create a physical copy of the desired implant. If the physical copy appears to be accurate, the designer then scans it. Stepping in and out of the digital work flow introduces imprecision for which the patient may suffer.

Manufacturing Equipment and Techniques. New, specialized rapid-manufacturing equipment and techniques provide far greater efficiency in small-volume or one-off runs for producing a finished custom implant in a high-strength material such as titanium (the material of choice for many orthopedic devices). Few hospitals or research institutions can afford to invest in high-end manufacturing-related equipment.

Contract Manufacturing. The rise of rapid manufacturing technologies means that contract manufacturing is now available for one-off or short-run projects, not just mass production. Contract manufacturers may be better able to justify the cost of dedicated, expensive tools and manufacturing options, because they are getting such custom work from many sources, including teaching hospitals and pioneering surgeons. They are able to support investments in the specialized people, software, and output methods for customized implants.

Orthopedic surgeons and device companies may find that outsourcing part or all of the process for patient-specific implants gives them the most flexibility. The company can retain client contact and coordination, but enable others with better economies of scale to provide services that address selected parts of the process.

Rise of Custom Technologies

Advances in imaging, design, and manufacturing technologies are enabling increased availability of customization options. Modeling technologies, sophisticated imaging, and advanced manufacturing each play a role. In addition, interoperability between these processes is crucial to the creation of successful implants that ultimately lead to improved patient outcomes.

3-D Modeling versus CAD. Traditional 3-D modeling packages are best suited for designing sleek, geometric, and prismatic products that can be readily calculated mathematically. They can also be used for highly procedural work flows. However, these modeling systems are limited when it comes to rapidly producing the complex, organic shapes of the human body.

Additionally, once an organic-shaped model is created, the time it takes to render an image of that model is often prohibitive. It's not uncommon for technicians to report waiting 12 hours for the image of a newly designed new hip joint to render. When a change is made, that 12-hour time lag begins again. In addition, custom implants designed to mend broken bones have irregular shapes, which makes traditional 3-D modeling packages inefficient.

A better option for custom implants is a sculptural CAD approach. For example, one system called FreeForm offers modeling with virtual clay. The flexibility of sculptural CAD enables designers to quickly and intuitively create multiple versions of models by inflating, tugging, smoothing, and carving. The system should also enable sharing of digital files, perhaps via annotated 3-D PDFs, to speed the design and approval cycles. Such a system must also enable the import and export of STL files (commonly used for data exchange in working with scan data, rapid manufacturing, and milling).

Medical Imaging. The availability of sophisticated medical imaging technology in most clinical settings makes design of customized products possible. To quickly capture and submit patient data, clinicians must have on-site magnetic resonance or computed tomography scanning, as well as the ability to electronically transfer scans.

Manufacturing. Advanced manufacturing processes, such as inexpensive plastic rapid prototypes for approvals, and advanced rapid manufacturing techniques such as electron-beam melting (EBM), emphasize efficiencies in several ways. EBM plays a role in increasing on-demand manufacturing capabilities for small-to-medium-sized quantities and is suitable for customized components. It enables manufacturing of complex, free-form shapes and allows material with more-sophisticated properties compared with traditional manufacturing via investment casting. EBM is suitable for use with commercially pure titanium along with titanium and cobalt-chrome–based alloys that meet the mechanical requirements of applicable American Society for Testing and Materials (ASTM) standards.

Interoperability. As more patient data are captured digitally, the industry is moving to more interoperability between file formats. This can be done either directly or via programs such as Mimics (Materialise; Leuven, Belgium) or 3D Doctor (Able Software; Lexington, MA), which can take slice data and turn them into an STL file that can be brought into a 3-D modeling package. These products are increasingly supporting the ability to import and export STL files.

Example: Design for a Revision Hip Implant

A designer and manufacturer of orthopedic medical devices was assigned to provide a custom acetabular (hip) revision component for a 70-year-old female patient. The patient's existing off-the-shelf hip implant was dislocating into her pelvic cavity. She reported increasing levels of pain to her orthopedic surgeon and was unable to bear weight on her hips without the use of crutches.

The patient had a portion of her hip intact, but the acetabular implant had been revised before, and while the stem was part of her original implant, it showed some sign of bone resorption. The surgeon needed to create an implant that was slightly bigger than the present, damaged implant in place. He concluded that an off-the-shelf implant was unlikely to be effective in a case this extreme and requested a custom part from an orthopedic manufacturer.

The manufacturer had recently partnered with a contract manufacturing company to create portions of the implants for unusual cases. The manufacturer specialized in all-digital work flows for creating custom body parts. The process used by the contract manufacturing company exemplifies how new technologies can be employed.

CT Scan Conversion to 3-D Model. The patient had recently obtained a CT scan as part of the diagnostic process. The company used a software program to convert the medical imaging files into a file compatible with the FreeForm 3-D modeling system. It also cleaned up the image to remove scatter artifacts present in the scan because of the existing metallic implants in place.

Predesign Surgeon Input. After the scan was put into FreeForm, both the orthopedic firm and the contract manufacturer discussed key factors with the surgeon, including surgical objectives, the patient's challenges, patient-specific design issues such as age and weight, and bone condition. The team also discussed other requirements for the final implant, such as the surgical approach, associated implants to be used along with this custom implant, expected outcome, and other special tools.

Design Refinement. Extensive effort went into refining the 3-D model to suit the patient's needs. This typically requires one to three weeks, depending on the review process required by surgeons and other parties. In the hip revision case, the design needed to enlarge the size of the patient-specific implant compared with the patient's existing implant. This is because the new implant would be replacing slightly more of the patient's existing bone structure. However, the resulting shape of the implant it defined was asymmetrical, and not typical of the normal hip bone structure. A technician modified the model to ensure the most beneficial implant design.

The team used a sculptural CAD modeling system because it provided modeling speed and flexibility. The system is based on voxel technology (think of voxels as 3-D pixels) instead of mathematics. Unlike traditional CAD, this approach has no topology restrictions and the order of operation does not matter. Additionally, the system uses haptics or virtual touch technology to mimic physical modeling. The designer held what is called a phantom device instead of a computer mouse to work the model. Force feedback is applied as the designer pushes, pulls, deforms, and extrudes virtual clay or putty to create an implant on the computer screen.

The design work required extreme precision and skill from the technician. As is typical of hip, knee, spine, and even cranial implant design, the work on the computer was to create mesh structures that follow an unusual, irregular shape. Creating them requires a deep understanding of anatomy as well as fluency with the design system.

Online Design Review. The team used e-mail and uploaded images of the 3-D model of the implant, rather than wait for overnight shipments to arrive. In some cases, discussion of the design took place via conference call or Web-based review. This way, the surgeon received expedited delivery and was able to make edits to the digital copy, instead of to a less precise, physical one. As the team discussed changes, the designer in charge rotated the model, made minor adjustments quickly, and let the surgeon immediately see his requests on the model.

Although most people are comfortable with an all-digital work flow, some surgeons feel more comfortable seeing a physical model of the proposed implant before moving forward with manufacturing preparations. By reserving this step only for the end, however, the team saved significant time while still ensuring that the physical creation met the patient's requirements.

Manufacturing. Once the surgeon authorized the implant design, the contract manufacturer created machine-specific instructions for the EBM manufacturing technique. As mentioned before, short-run or one-off creations of implants are achievable using EBM manufacturing. The EBM process is capable of producing components in commercially pure titanium, titanium alloy, and cobalt chrome alloys. In the process, a high-power electron beam is used to melt successive layers of metal from powdered raw material, thus forming a solid, metallic part in an additive fashion. In addition to supporting extremely complex, organic shapes, EBM is less expensive and faster than forging or machining, both of which are better suited for larger-volume runs.

Finishing, Sterilization, and Final Delivery. The manufacturer delivered the custom implant to the orthopedics company, which then machined the outer surface that comes into contact with the surrounding tissues. The under­surface of the implant was left in the rough, as-produced state to allow for tissue integration behind the implant. The final finishing steps of the implant development included threading fixed-angle screw holes to accommodate locking-screw fixation. The device was cleaned, sterilized, and packaged in-house.

The optimal fit of the implant allowed surgeons to complete the surgery in three hours—­half the anticipated surgical time. Implant design and production took place in two weeks from CT scan transmission to delivery of the finished implant to the surgeon, which is also about half the time usually required. Total costs for this case were comparable to a traditional off-the-shelf implant.

The Case for Customization

Although patient data on outcomes from custom approaches are new and still limited, it is logical to assume better patient outcomes with such personalization. Researchers are also studying whether there is increased longevity for personalized implants.

Beyond these assumptions, using external contract manufacturing resources for customized implants makes business sense for ensuring optimal delivery time to the patient, as demonstrated by the example in this article. However, working with a contract manufacturer is not without challenges. Surgery dates are always uncomfortably close, communication between partners can be difficult, and expectations are high. These challenges can be overcome by structuring the relationship to create a partnership in which each company focuses on deploying its unique expertise in service of the surgeon and, most importantly, the patient.

Reference

1. The 2007–2008 Orthopaedic Industry Annual Report, Knowledge Enterprises Inc. (Chagrin Falls, OH), July 2008.

Copyright ©2008 Medical Device & Diagnostic Industry