When Zina Bethune's arthritic hips had deteriorated so badly she was told to abandon her ballet career, she hit upon some luck: She found orthopedist Charles Anderson Engh of Arlington, Va., who replaced both her hips.

A year afterward, she was dancing again.

Seven years later, Bethune, 45, still dances, and she runs Bethune Theatredanse in Los Angeles to bring dance to children, including those with cerebral palsy. And she is one of Engh's greatest champions.

The story of Zina Bethune and Charles Engh is part of this week's installment of "The Infinite Voyage" (Wednesday at 8 on PBS), which features a look at advancements in materials science both for medical and industrial advances.

Leonard Nimoy narrates producer Richard J. Wells' special, called "Miracles by Design."

Other segments focus on artificial skin for burn victims, high-speed auto racing, super-strong alloys, biodegradable plastics, "smart materials" that react to external stresses or stimuli, ceramics so strong they can be used for car engines and magnets so powerful they can lift a train to allow friction-free travel. There's also a look back at the early days of synthetics, plastics and Bakelite.

What makes Zina Bethune's hip replacement interesting is that Engh used a new alloy implant with a porous cobalt-chrome coating, an adhesive made of thousands of tiny metal beads that fooled her own bones into making the implant part of her body.

Earlier, Charles Engh had done hip replacements using the then-standard acrylic cement. Most of his patients were elderly and weren't bothered that the cement itself had a limited life. They were looking for comfort for their own last years.

But Engh knew that for his younger patients -- people with degenerative arthritis, people injured in accidents -- the replacement surgery would be only stop-gap: When the cement gave out, they'd need surgery again. One 34-year-old man came to Engh for his sixth hip replacement.

Biomedical engineers at the University of Toronto had developed a new procedure for tooth implants, using a porous-coated metal stem to be bonded into bone. In 1977, Engh began to use the new material in hip replacements, he said, "but the little company in Canada that made them went bankrupt in 1978. I bought about 40 or 50 of the ones left, their entire stock."

Engh said he was the only orthopedist using the coated metal in 1979, '80 and '81, when he began to run out of supplies. "Then Depuy, an international company located in Warsaw, Ind., became interested in it," he said, gaining approval from the Federal Food and Drug Administration to to market the replacement hips in 1983 by presenting the cases Engh had worked on.

The Depuy implants were coated through a metallurgical process called sintering, in which metal particles are partially fused at high temperatures, but below the melting point, to produce a bonded mass.

"The outside of the implant looks like sandpaper," said Engh, "but there's a lot of porosity there extending right down to the metal core. You drill the inside of the bone out, which makes it bleed and act like it's broken, and you drive in the implant. The normal response is to fool the intentionally damaged bone into trying to repair itself by building more bone."

About the same time, Zina Bethune was searching for help. Engh said he believes she had read a newspaper article about the new porous implant that had been approved, and contacted him.

Bethune, who had been dancing since she was 7, had been told that her arthritic joints meant an end to her dancing career. A Danish surgeon repaired her right hip, and she danced for another decade until pain from her dysplastic hips and deteriorating cartilage sent her on another search.

True, Bethune could have given up dancing and concentrated on her acting career. At 17, she had starred in CBS' "The Nurses," a medical drama that aired in prime time from September 1962 to September 1965, switching to daytime until March 1967. Bethune played Gail Lucas, a student nurse, with co-star Shirl Conway as Liz Thorpe, the more experienced head nurse on the show.

But her first love had always been dancing, and she had refused to quit, despite the pain. "She's an exceptional person," said Engh.

Last year, returning to the Anderson Clinic for the yearly check-up that Engh requires, she also danced at the Kennedy Center's special arts program, he said.

Engh is both enthusiastic and cautious when he talks about the technique. His practice is still predominantly older people, but he said that "I do more young people than most people who do hip surgery." He also uses the porous-coated protheses with middle-aged and older people who have active lifestyles.

"But after 14 years of experience with this, and thinking that this would solve all the problems that I thought cement had caused, there are problems with this too," he said. "I have some concerns -- they may be unfounded -- for about 5 percent. In a small percentage, the polyethylene plastic {lining the metal prosthesis} begins to wear a little bit, starting as early as seven years, so I worry that I may have a problem. But if I take all the people under 50 I've done that are between 5 to 10 years {after surgery}, the number is about 5 percent, and none of those patients have any symptoms. But that's not anywhere near the magnitude of the problem before.

"This technique has worked absolutely beautifully," he said. "And after 15 years of doing this, I am just as enthusiastic as before."