Mass production to mass customization

Departments - Features

A new era in knee implant manufacturing brings accompanying customization of implants and surgical instrumentation, leading to rapid innovation in designs.

May 29, 2014

knee implantsJust like fingerprints, every knee is different. Knee shape and size can differ widely between people, and even in the same person, the left and right knee can be distinctly different from one another.

The anatomy of our knee is a key factor in the alignment of our leg and the level of comfort and flexibility we feel when we walk, climb stairs, or perform many other common functions. The fact that no knee is the same presents a challenge for manufacturers of total and partial knee implants to deliver a successful outcome with a limited number of implant shapes and sizes.

A recent survey showed that the rate of knee replacement surgeries has more than tripled among people aged 45 to 64 throughout the last decade. According to the American Academy of Orthopedic Surgeons, more than 600,000 total knee replacement surgeries are now performed in the United States each year, and that number is projected to grow to 3.5 million by 2030. While the demand for knee replacements has rapidly increased, patient results have been mixed. The current industry standard for manufacturing knee implants may be to blame.

Implants used in knee replacement surgeries are generally mass-produced in a limited range of sizes. The final products are shipped to hospitals and surgical practices where they are stored in inventory until they are needed, often for many months or even years. Surgeons choose the off-the-shelf implant that appears to most closely match each patient’s anatomy, and during the procedure must remove enough bone and tissue to achieve the best fit possible.

For many patients, the results of total or partial knee replacement surgery are not what they expect, and the reason is often based on how the implant fits or does not fit. Studies show that 1 in 5 patients with a total knee replacement are not satisfied with the result. 1 Leading complaints include pain following surgery, poor function, and unnatural feel. These problems may be attributable, at least in part, to the use of implants that do not fit well with that patient’s anatomy.

In an effort to address these challenges and improve outcomes, researchers at ConforMIS concluded that implants that resemble a patient’s natural knee have the potential to remove less bone, eliminate pain, and improve recovery and function. Using a proprietary process, ConforMIS manufactures customized knee implants that are developed based on 3D digital models of a patient’s own knee. Using a just-in-time (JIT) manufacturing and delivery, each implant is designed, produced, and shipped to the surgeon just before the procedure, eliminating the need for hospitals to store multiple implants in inventory.

Innovative manufacturing process

Not even mass produced implants available in a range of sizes can match a patient’s own anatomy. Following years of research, the product design and engineering teams at ConforMIS successfully developed a proprietary manufacturing process involving advanced image-to-implant technology that addresses these challenges without any loss in quality or significant increases in production costs.

A key element in this manufacturing process involves advanced digital imaging technology and 3D printing. ConforMIS is the first orthopedics company to use 3D technology as part of the process to produce a complete line of patient-specific metal knee implants. The production process starts with a CT scan of the patient’s hip, affected knee, and ankle to ensure that the leg is realigned to the neutral mechanical axis before the implant is designed. Called iFit technology, ConforMIS uses a series of proprietary algorithms to convert the two dimensional CT scan of the patient’s knee into a 3D model that maps the articular surface of the joint and clearly defines the area of disease. The software then designs each customized femoral and tibial implant as well as all the instrumentation from the 3D model.

Image-to-implant process
iFit image-to-implant software is the technology platform that allows for the design of patient-specific implants and instrumentation.

iFit design
ConforMIS implants and instruments are designed based on the patient’s CT scan. An automated design process uses proprietary algorithms to map the articular surface of the joint in three dimensions. The software uses that information to design the implants and instrumentation that will match precisely to the 3D model of the knee, correcting the data for any underlying deformity such as bone spurs, cysts, or flattening of the joint.

iFit 3D additive printing
Disposable, patient-specific iJig instrumentation is manufactured using 3D printing technology, allowing engineers to develop patient-specific instruments for every step of the procedure.

iFit Just-in-Time delivery
ConforMIS’ single-use kit is delivered a few days before surgery, removing the inventory from hospital shelves while allowing for design improvements that can be implemented immediately.

While the availability of a precise 3D model is an important advantage, the manufacturing process used to produce customized products of any kind, and especially those associated with complex surgical procedures, is often riddled with unique challenges. In the case of knee implants, the manufacturing process must be able to produce each implant rapidly to avoid delays in scheduling a patient’s surgery. The process also has to be scalable to accommodate increases in demand, which is anticipated as more surgeons adopt the use of customized knee implants. Speed and scalability also have to be achievable with no negative impact on the quality or precision of the implant.

In the manufacturing process for the ConforMIS iTotal knee replacement, 3D technology is used to print a precise wax mold that is then used to form the metal femoral component of the knee. The implants are manufactured in cobalt-chromium-molybdenum – an industry standard for decades. The implant is then packaged and shipped directly from ConforMIS to the hospital.

Customized surgical instrumentation

Crucial to the successful implantation of a customized knee replacement is instrumentation matched to that implant and patient. Each ConforMIS implant is designed and manufactured with a full set of customized iJig instrumentation designed for use in just one patient. This represents a landmark shift in standard operating procedure in knee replacement, where the same reusable instruments are used in hundreds of surgeries, requiring ongoing storage, cleaning, and sterilization.

iJig instrumentation is manufactured using 3D printing and each set is pre-navigated specifically for use with one customized implant. The automated manufacturing employs a precise layer-by-layer process that enables rapid customization. iJig instruments are shipped with the ConforMIS knee and arrive fully sterilized. They are discarded after use, eliminating the need for repeat sterilization.

Pre-sterilized and pre-navigated instruments designed for one-time use have many advantages for surgeons and surgical practices. Many OR teams often must sterilize and prepare up to nine different trays of instruments for each implant surgery. Re-using instruments also can increase the risk of infection.

Opportunities for rapid innovation

Customized knee implants enable more rapid innovation in implant design. With mass-manufactured, off-the-shelf knee implants, important and sometimes essential innovations in implant or instrument design can take years to reach the market. When new or more advanced implants do come out, hospitals typically do not adopt them until older inventories are depleted.

In a customized manufacturing model where products are developed as needed for each patient, new implant designs can be incorporated into production immediately. Improvements in design and applications of new materials and technologies can reach both surgeons and patients faster. Since 2008, ConforMIS has introduced a new product iteration every year. In a mass production model new product iterations can take as long as a decade.




About the author:
Matthew Scott is senior vice president of operations at ConforMIS and can be reached at 781.345.9001.


1 Bourne, R.B., et al; “Patient Satisfaction After Total Knee Arthroplasty. Who is Satisfied and Who is Not?” Clinical Orthopaedics and Related Research: 2010.