Where engineering meets medicine

DN Staff

November 20, 1995

6 Min Read
Where engineering meets medicine

Warsaw, IN--What do Pope John Paul II, Elizabeth Taylor, and Liza Minnelli have in common?

Like tens of thousands of people worldwide, they enjoy a more active and pain-free lifestyle, thanks to hip implants designed by engineers at DePuy, Inc., which this year celebrates its 100th anniversary.

DePuy, along with two rival companies--Zimmer and Biomet--account for 40% of all the artificial joints manufactured worldwide, making this unassuming North Central Indiana town of 12,000 the "orthopedic capital of the world."

Splints to implants. It all started a century ago when Revra DePuy began making wire mesh splints to replace the wooden barrel staves commonly used for fractures. Now DePuy's annual sales total $680 million. From 1985 through 1994, the company grew at a compounded annual rate of 20%. Long the leader in hip implants, Depuy has broadened its scope to include implants for knees, shoulders, and other joints, as well as surgical tools, protective clothing for surgeons, and other medical products.

It also has become a mecca for a special breed of engineers drawn to a field that allows them to push the limits of technology, while at the same time giving people a much better quality of life.

Take Frank Bono, an ex-aerospace engineer with Hughes. Where he once worked on missiles used in the Gulf War, Bono now develops hip implants like the Replicaa, which incorporates many of the core technologies that have made DePuy an industry pacesetter.

Developed over a 20-month period and approved by the FDA in December of 1994, the Replica marries several materials technologies. It is constructed mainly of cobalt chrome alloy, machined in a 42-step process to meet tolerances as tight as 1/1000 of an inch. A round ceramic head fits over the top section of the implant. This ball-like head in turn fits into a cobalt chrome alloy socket lined with a wear-resistant grade of polyethylene developed through a partnership with DuPont. The surgeon needs no cement to hold the implant in place; a patented porous metal coating applied to certain sections of the device promotes a natural bonding through the ingrowth of tissue.

A great deal of engineering, including 3D CAD modeling and finite element analysis, goes into shaping the implant to insure structural strength and patient comfort. For example, the bottom or distal section of the implant is fluted to reduce rotational forces as the individual moves about. There's also a slot, cut into the stem of the implant by a wire EDM process, to reduce stiffness in the device and create some natural "give" during movement.

These and other design subtleties develop from close contact with surgeons and others in the medical community. "There's not a single product engineer who hasn't been in the operating room at least a dozen times," says Tony Cutshall, who is in charge of new venture projects. "We always ask ourselves, 'How can I make it easier for the surgeon?' "

Engineers routinely visit with surgeons, listening to their suggestions and answering their questions about both the implants and the surgical instruments that DePuy designs in conjunction with the devices. DePuy engineers often address meetings attended by top orthopedic surgeons from all over the world.

"I think just about every engineer here wanted to be a doctor at some time or other," notes Michael Esch, who develops knee implants. "The work demands engineers who are very people oriented."

DePuy has been manufacturing artificial knees for more than 16 years. Its LCS(R) (low contact stress) total knee system uses a polyethylene bearing material to simulate the movement of the human knee. Here, too, sections of its cobalt chrome alloy components are covered with a porous coating to achieve natural adhesion without the need for cement.

Says Esch: "I've got a picture of a 48-year-old fireman who has the LCS knee, and he's carrying someone out of a building. He's also a referee."

Recipe for success. Engineers at DePuy agree that the field of bioengineering demands broad-based, outgoing engineers who can blend the technical precision demanded in their designs with the individual needs and preferences of surgeons. Most have master's degrees in bioengineering or biomechanics, with undergraduate training in mechanical engineering or materials science.

DePuy engineers also work very closely with marketing to promote and sell the company's broad line of standard products and to customize, where necessary, to meet the special needs of surgeons and patients. For example, the company has developed special proprietary software that can transform readings from a patient's X-ray into a CAD model in minutes--then transfer the data to a CNC machine for actual production of a hip implant.

Most of the product development and design staff use Intergraph TD 30 workstations. They create their 3-D drawings primarily with Intergraph's EMS software. Intergraph's FEA package is used for structural analysis.

And very few companies rely more heavily on stereolithography. The company owns three SLA 250 prototyping machines from 3D Systems. Dan Anderson, who heads the Engineering Services department, says this equipment has cut months from the product development cycle and saved thousands of dollars in tooling costs. It's also given engineers and model builders the time to pursue other projects, such as development of a new shoulder implant system.

The fact that the company is a technological leader and gives its engineers wide freedom to pursue their interests in an "entrepreneurial environment" more than makes up for Warsaw's sleepy small town image, notes Stacey Milionis, a group product development manager who left a job in Los Angeles to join DePuy five years ago. She worked initially in implant development but now heads development of an entirely different product line--Sterile View(R), a complete system for protecting surgeons and other operating personnel from blood-borne viruses. Looking very much like a lightweight space suit, it consists of such items as disposable hood and gown, helmet and face shield, and portable blower and air filter connected to a belt around the doctor's waste.

New horizons. Other ventures to broaden the company's mission include the DePuy DuPont Orthopaedics alliance. It has yielded products ranging from the enhanced Hylamer(R) polyethylene for implants to special surgical glove liners made from Kevlar(R) and Lycra(R) that protect against cuts and punctures.

Longer term, the company is pursuing research projects with several universities. For example, DePuy is working with Purdue University to investigate the use of pig intestines as a biological replacement for damaged human tissue, such as tendons and ligaments. Clinical tests on humans using this small intestine submucosa, or SIS, will begin in 1996, says DePuy Research Director Todd Smith.

For Smith and DePuy's technical staff, developing future generations of implant systems and other medical products will be tougher in this new era of increased government controls and curbs on Medicare reimbursement. "The regulatory environment is now very unfriendly to new product development," says Smith. "And that means that controlling costs have become more important than ever." As a result, development has been slowed on new types of implants that patients need to relieve serious pain in such areas as finger and jaw joints.

While the sky is no longer the limit when it comes to developing new medical devices, most engineers at DePuy wouldn't think of turning away from their speciality. "Surgeons introduce me to patients as the engineer who designed your implant," says Frank Bono. "They smile and tell me how much better they feel. That really makes your day."

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