As her son, the orthopedic surgeon, stood before the cameras and clutter of microphones, explaining how he had just accomplished the first replacement of part of a patient's spine, Dr. Charles C. Edwards' mother tried to supress her amusement.

"She said, 'I remember when you took your BSA bicycle apart,'" Edwards recalled during a recent interview. "'You were determined you were going to put it back together in better condition, but you never put it back together again.'"

Edwards, the inveterate tinkerer, progressed from bicycles to go-karts to cars and to old houses. And he learned how to put things back together.

It was the fortune of Jessie Thomas, a 33-year-old Baltimore woman, to be referred last May to this surgeon with a tinkerer's mind and a constant willingness to attempt things that no one ever tried before.

"People don't take me for being as really simple as I am," said the 37-year-old chairman of the University of Maryland's Department of Orthopedics. "Why would I take this case? There's no way I could function as a person, carry on, if I said: 'If I really work on this I could figure out how to do it, but frankly, it's never been done, it's terribly risky, it will take me about 50 or 60 hours . . . so I'm sorry, but you'll have to die.'"

When Edwards first examined Thomas, she was paralyzed from the waist down, the result -- she said -- of a fall at home.

X-rays "offered no suggestion of a possible cause," the surgeon said. But "things weren't looking as simple as a fall fracture."

At that point Thomas had failed to give the physicians some vital information. Edwards suspects she subconsciously supressed it, but eventually doctors learned she had undergone minor surgery and extensive radiation treatments in 1971 for a tumor near her spine.

"The next step," Edwards said, "was a CAT Scan, which showed a tumor bigger than anyone imagined." A CAT Scan is a series of cross-sectional pictures produced by a marriage of traditional X-ray technology and a computer, providing views never before possible of the body's interior.

The next step involved a biopsy -- the surgical removal of a small piece of the tumor -- to determine whether it was malignant and how to treat it.

Edwards said his goal is to do as little as necessary to achieve success. But in Jessie Thomas' case, he said, "The least intrusive thing we could do was one of the biggest that has ever been done."

Had Thomas been at practically any other hospital, dealing with almost any other orthopedic surgeon, she probably would have been sent home to die after biopsy showed her tumor was cancerous.

Doctors at that point knew she had a malignant tumor, the size of a canteloupe that engulfed her spine, aorta and other major blood vessels. She had already had a lifetime dose of radiation in 1971, so radiation was out, and it was determined that chemotherapy would be ineffective. Tumors like hers normally are considered inoperable.

Recognizing the magnitude of Jessie Thomas' dilemma did not constitute some grand moment of truth, Edwards said.

"It really wasn't a decision," he said, "because it represents my basic point of view that I had long before I met Jessie Thomas. That is, when confronted with a medical problem that is of great importance or urgency to some other human being, I first try to figure out, 'What is the nature of this problem?' Then I always ask myself: 'Can I think of any way to help this person overcome this problem?'

Edwards said he approached the Thomas case as he has approached about 10 other unique skeletal replacement cases he has performed, first carefully outlining the problem, then discussing it in a meeting of his department and eventually deciding if the enormous risks warrant the attempt.

"We actually try to develop numerical probabilities of risk and reward," Edwards said.

He said the brain-storming process has led him from a rule of thumb that he will not attempt surgety to improve or comfort patients expected to die within three months. Such operations, he said, ruin the quality of too much of the little time patients have left.

"With Jessie Thomas it is not a very difficult decision, even though it is so out of the ordinary, because she had almost inevitable mortality one way, and she was a person who had an enormous zeal to live, even to live a life with reduced capacity.

"Jessie's zeal to live and see her children grow up was a compelling force."

First, Edwards decided, the tumor had to be cut away from Thomas' spine and vital organs. Although he would have to remove four vertebrae, he decided he would make a unique attempt to leave the spinal cord intact, hoping some function might return to her lower body.

Edwards said he told Thomas after the first operation she would be held motionless in a frame until she was well enough for a second surgery.

"I said, 'I don't know how I'm going to reconstruct your spine, but I'll probably develop something that will at least give you limited mobility.'"

Edwards said he also told her all his previous reconstructions had been successful but that she had about three chances in 10 that she would die on the operating table.

The surgeon, who said his patient is a very religious woman, quoted her as telling him, "'I'm in your hands, and your hands are in God's.'"

But Edwards said he doesn't view himself as a healer or surrogate god: "The patient comes to me and contracts with me to use my ability, education, training," to solve a problem.

After the first operation in which the tumor was removed, Edwards redoubled his efforts to develop an artificial replacement for the six-inch section of spine he had taken out with the cancerous tumor.

The invention of such devices is an extremely logical process, he said. "I first look at what has been done, what can be done. If nothing has been done, then I contemplate the problem and try to think of existing materials" that can be used. "This development is just the logical next step. It's not something I do and then wait for a patient."

Edwards said it took him about two days to come up with an idea for a device, which he then had engineers reduce to mechanical drawings before ordering the part from a manufacturer who specializes in such orders.

The 16-hour operation two weeks ago to implant the resulting metal and plastic device will have been a success, Edwards said, if Jessie Thomas recovers enough to sit in a wheelchair. He said she could be well enough to do that in less than a week.

But even if she doesn't make it, he said, such operations still must be attempted.

Asked if he might be over-reaching in attempting the unknown for its own sake, Edwards replied:

"That isn't a danger for me. I have never to this date developed any new concept in surgery, or invented any applicance, before that innovation became clearly essential to solve a specific human being's problem better than existing means seemed able to solve it.

"My own driving force or philosophy or whatever you want to call it, goes very much along the order of: Here's a problem. Let's characterize it. Now, how can we solve it?

"Then, if you say, "Oh, my God! There is no appropriate treatment that we can find, we must develop it for this individual. If that's where you're coming from, then it's almost inconceivable to me that your own creativity is going to break out of responsible bounds and start creating monsters."