The success of a surgical replantation depends on a lot more than the technical skill of the surgeons. It's a team effort -- from emergency room to rehabilitation -- involving paramedics, nurses, doctors, therapists and the patients themselves.

The first key decision is whether to operate at all.

Not every patient with a severed body part is a sound risk for replantation surgery. The microsurgery team at Bellevue Hospital in New York sees nearly 400 trauma patients a year with amputated or severely injured extremities, but only about 100 undergo replantation surgery.

In assessing an amputation injury in the emergency room, says Dr. William Shaw, director of the Bellevue microsurgery team, "you have to look ahead one or two years to see what will happen over the long haul. And in the meantime, you have to get back down to earth and ask, 'What do I have to do tonight?' "

Replantation surgery is risky, expensive and time-consuming, with a long, tedious period of recovery and rehabilitation. Even in the best medical centers, a finger replant has only an 80 percent chance of "taking."

The patient, often in shock and with little time to think through the long-term potential complications, usually favors an operation.

"You're dealing with a patient and family sitting in the ER with a finger in a basin beside them," says Dr. Mary H. McGrath, director of plastic and reconstruction surgery at George Washington University Medical Center. "It would be amazing if the patient refused."

Doctors consider many factors before deciding whether to try to reattach a severed part:

*Age. The younger the patient, the more reason to operate. Nerve recovery is better in children than in adults. The success rate slips after age 40 and plummets after 65.

*Occupation. The ring and little fingers could be more important to, say, a carpenter or a musician than to a business executive. And patients who undergo replantation surgery usually are out of work for a couple of months longer than if they had forgone the surgery -- a financial consideration for many families.

*General physicial condition. A replantation patient must be strong enough to endure many hours of anesthesia. And recovery is quicker and more complete in those who are otherwise healthy. Ryan Kahn, for example, was in excellent physical shape from running, weightlifting and rock climbing.

*Psychological condition. Motivation is crucial. Some amputations result from suicide attempts or self-mutilation. Patients must be prepared for a long and difficult recovery and the frustration of limited function from the reattached part.

*The injury itself. A clean knife cut is much easier to repair than a crush injury. Hand surgery is usually attempted if the injury is to the patient's dominant hand, or if it involves more than one finger, or a thumb. If only one finger has been lost, says McGrath, it's a judgment call.

The tip of a finger is the most difficult to restore, because the blood vessels are too tiny to be found.