For a couple of months, ever since she stumbled on a stone in a parking lot, Margery Brockway had been suffering chronic pain and swelling in her left knee.

As a machine operator in the Folding Room of the House of Representatives, Brockway, 40, of Gaithersburg, was on her feet most of the day. She walked with a limp, and "if I put any weight on it, it hurt."

Finally, she sought medical help and was referred to Dr. J. Richard Wells, an orthopedic surgeon. He suggested an operation called arthroscopy, by which he could look inside her knee without cutting it open.

Brockway was unconscious under general anesthesia when Wells walked into Georgetown University Hospital's Operating Room 12, masked and scrubbed. The only part of her body not covered with sterile sheets was her left knee, which had been scrubbed with a yellowish iodine-based solution as a precaution against infection.

A tourniquet was applied to her thigh to minimize the blood flow in her knee during the operation.

Wells made three tiny incisions or portals in Brockway's knee. One was for insertion of the arthroscope itself, a thin, lighted tube attached to a video camera smaller than a cigarette pack. Another was to drain water from the knee (a stream of water flowed from the scope through the knee during the operation, to flush out bacteria and improve the camera's visibility). The third was for insertion of long narrow instruments for probing, snipping, shaving and removing damaged tissue inside the knee.

Once the scope was inserted under the kneecap, a remarkably clear color image of the inside of Brockway's knee appeared in a six-inch circle on the television screen opposite Wells on the far side of the operating table.

With his right hand Wells manipulated the scope, aiming its tip up against the tissues of the knee. With his left he guided a probe, testing the surface of the kneecap and the cartilage in the joint. All the while, his eyes scanned the "Fantastic Voyage" image on the screen. The scope's powerful light glowed red inside Brockway's knee.

Wells was searching for fragments of bone or cartilage floating loose inside the knee -- a possible cause of Brockway's pain. He found just one piece of cartilage.

But he found two other problems: inflammation and scarring of the inside of the kneecap, probably due to arthritis; and two tears in the menisci, or the crescents of cartilage that act as shock absorbers in the center of the knee.

With his left hand, Wells inserted a probe tipped with a tiny clipper that snipped off loose or ragged tissue and captured it in a specimen trap. On the television screen, the frayed cartilage showed up on the screen as whitish cottony swirls, and the clipper looked like Pac-Man picking off bits of injured tissue.

Besides trimming torn and frayed tissue, Wells also used a miniature shaver to smooth some rough patches on the inside of the kneecap, scarred by arthritis. Those bits of tissue -- about a teaspoonful of material resembling crabmeat -- were retrieved in a tiny trap and sent to the pathology lab for testing.

"The surface of the kneecap is very rough along here," Wells said. "The shaver smooths it down. It will bleed and grow back in -- not as smooth as it originally was, but better than she has now."

An hour after it had begun, the operation was over. Wells withdrew the probe and the scope and flushed the remaining water from Brockway's swollen knee. Each of the three tiny incisions in her knee was closed with a single stitch. The tourniquet was loosened, and the anesthesiologist began to bring her back to consciousness.

Less than three hours after her operation, Brockway left the hospital on crutches.

By contrast, her husband, Mark, underwent open-knee surgery six years ago to repair a single tear in one ligament. He was in the hospital four days, on crutches six weeks, and has an eight-inch scar to show for it.

Margery Brockway missed only two days of work. Three days after arthroscopy, she felt only mild soreness in the knee -- "nowhere near as painful as it was before."