In some ways, Von Ferber and Kirk Arnold are mirror images of each other.

Both are big, physically active men. Both love to ride motorcycles. And both are missing their right hands and use prosthetics as substitutes.

They also typify most Americans who have had hand or upper arm amputations in two other significant ways. They are male, as almost all upper-extremity amputees are, and they lost their hands in a work accident and a traffic accident.

"Most of these amputations occur for two reasons," explained Dr. Joseph Imbriglia, a hand surgeon based at the Hand & UpperEx Center in Pine. "They come from work injuries, working with saws, box cutters, log splitters and heavy equipment, or they come from automobile accidents or motorcycle accidents, and both are overwhelmingly among males."

Earlier this month, UPMC announced it had performed the region's first hand transplant on a 24-year-old Marine whose right hand was blown off in a training accident.

While hand transplants are the most dramatic solution for victims of these accidents, prostheses will probably always be the first-line treatment for people with amputations because they are less expensive and don't carry the risks that accompany a lifetime of taking immunosuppressive drugs.

Mr. Ferber, 49, of Shaler, is one of 630 people in the world using the iLimb myoelectric hand prosthesis made by Touch Bionics, of Scotland.

Like other myoelectric devices, it has a sleeve that fits over the person's stump, with electrical contacts on the inside that can pick up signals from the person's muscles and use them to control the hand. Unlike many other prosthetics, the iLimb's hand has individually moveable fingers, wrist and thumb.

Mr. Ferber lost his right hand and half of his forearm in a horrific motorcycle accident two years ago on Route 8 in Shaler when a van doing a U-turn pinned him against a guardrail and dragged him along the metal railing for 230 feet.

Overwhelmed by shock and pain, Mr. Ferber would not let paramedics near him for several minutes. He eventually got off his motorcycle and walked to a nearby gurney before being rushed to a hospital.

Mr. Arnold, 52, of Clinton, lost his hand and most of his forearm in a work accident 14 years ago. While he was operating a printing press at Herbick & Held in Weirton, W.Va., his arm was pulled into the moving rollers on the press. Within seconds, it looked as though the rest of his body would follow.

"I figured I had one last chance," he recalled, "so I just pulled as hard as I could and I guess I bent my arm back and snapped the bones off and it just tore my arm off."

Mr. Arnold also relies primarily on a myoelectric prosthesis, although he occasionally wears an older-style prosthesis operated by a harness that goes around his shoulders. He can operate the prosthetic hands on that device by hunching or pulling back his shoulders.

Over the years, he has amassed an array of prosthetic hands to attach to the wrist of his false forearm. They range from a two-piece gripper known as a Greifer to a lifelike hand encased in a brown glove to an old-fashioned hook.

After attaching the hook and rhythmically opening and closing its two curved extensions, he asked with a twinkle in his eye: "You know what this is? It's a $7,000 windshield wiper motion."

Mr. Arnold even has a custom-made hand-arm prosthesis for motorcycle riding that is based on a World War II-era design, in which the fingers and thumb are made of springs, so they can easily be pulled off the bike handle in an emergency.

"I ride a stock Harley," he said with a grin. "I ride good, and I ride long." His wife sits behind him on the cycle, he said, and he pulls a trailer as well.

Mr. Ferber would dearly love to ride again himself -- in fact, he thinks his desire to climb back on a motorcycle might be one reason UPMC turned him down when he applied for its hand transplant program -- but he has not mastered his prosthetic hand well enough to attempt that yet.

While the sleek black iLimb he wears has individual motors for each finger and the thumb, it is not yet equipped with sensors to control each digit.

Technically, that should mean Mr. Ferber can only open and close the fingers and thumb all at once. In fact, he is sometimes able to control the fingers individually, even though his myoelectric sensors only touch his forearm at two spots -- on the top for opening the hand and on the bottom for closing it.

Neither he nor the experts know exactly how he accomplishes that. But it could be that by thinking about moving different fingers, he alters electrical signals to the sensors just enough to provide individual digit control, said his professional adviser, Drew Buffat, the director of prosthetics for De La Torre Orthotics and Prosthetics Inc., in Harmar.

"I feel that with the iLimb, the sky's the limit," Mr. Ferber said."It's up to Drew and myself to get the technology to work with my body.

"It gives me hope that I possibly could ride a motorcycle, that I might be able to put my hair in a ponytail without asking for help, or that I could tie a shoe versus wearing slip-on boots or shoes -- there's a chance to do the things I used to do, maybe a little slower, but there are possibilities."

But even though the iLimb is advancing the state of the art, prosthetics also have limitations, Dr. Imbriglia said.

At the hand transplant press conference three weeks ago, doctors said that 40 percent of men in their 20s and 30s who have amputations refuse to use prosthetics. The primary reason: the devices lack a sense of touch, Dr. Imbriglia said.

"If you think in terms of your hand function and break it down as basically as you can, what does your hand do?" he said. "It has to, No. 1, open, and No. 2, it has to close around an object, whether you're gripping or pinching, and No. 3, it has to be able to discern things like texture and pressure. If you wanted to close it around an egg, it has to know how hard to push; otherwise you lose the egg.

"What we have been unable to do thus far with prosthetics is to create that ability to feel, and that's why if someone amputates his hand, it's much better to sew it back on if you can because that hand has a chance to feel."

But if that can't be done, prosthetics users can become very skilled at working with what doctors and engineers have given them.

At Dr. Imbriglia's office last week, Mr. Arnold used his two-piece Greifer to delicately pinch and lift a penny.

Still, he was quick to acknowledge that his prosthetic is not truly a replacement for his missing arm and hand. Even with all his varied attachments, Mr. Arnold said, he probably uses his prosthetic only about 30 percent of the time.

"I wear it to do what I have to do and then I take it off," he said. "It's a tool."

"In other words," Dr. Imbrig-lia interjected, "no one could be better at using his prosthetic than this man, and yet he only wears it 30 percent of the time."

Mr. Arnold and Mr. Ferber will need a lifetime of medical care, and that puts them smack up against a major societal issue -- health insurance.

Mr. Ferber said he would love to work again, to feel productive and have a sense of purpose. But he not only has to find a job that can be adapted to his disability, but one that provides ample health benefits. In the meantime, he has applied for Social Security disability. Mr. Arnold lives on workers compensation, which paid for his prosthetics.

Another necessity for both men: A sense of humor.

After demonstrating how he wears a sleeve with a locking pin to secure the prosthetic arm to his stump, Mr. Arnold remembered an earlier prosthetic arm that didn't attach so firmly.

"I'd be standing at the store ready to check out and my arm would just fall on the ground, and I'd just look up and say, 'Geez, I hate when that happens.' "