Little more than three years ago, Don Aase's right arm was in a sling. He couldn't lob a baseball without pain flaring through his elbow -- let alone uncork the 90 mph fastball that had been his ticket to the major leagues.

Aase, a professional pitcher since 1972, sat out the entire 1983 season, wondering if his career was over at age 28.

Today, he's not only throwing hard again as a relief pitcher for the Baltimore Orioles. He's having an All-Star season and leads the majors in saves.

The difference between the sidelined Don Aase of 1983 and the All-Star Don Aase of 1986 is a radical surgical operation on his elbow.

Or what was left of his elbow.

Years of trying to fire a baseball past batters had taken their toll. At the end of the 1982 season, when Aase was playing for the California Angels, he decided to undergo surgery.

When Dr. Lewis A. Yocum, orthopedic surgeon for the Angels, opened up Aase's elbow for exploratory surgery, he hoped to find minor damage that could be easily repaired -- such as a small tear or scar tissue that could be trimmed away to restore the joint's smooth motion.

But as he probed beneath the arm muscles to inspect the medial collateral ligament, which binds and supports the elbow, Yocum found something quite different.

"In Don's case," said the surgeon, "there was no collateral ligament. Just some fibers, but nothing to provide the stability he needed. His elbow was being held together only by muscles."

The main ligament was so badly torn and worn away, Yocum said, that trying to stitch it back together would have been "like trying to sew scrambled eggs together."

Instead, Yocum decided to rebuild Aase's elbow, using a technique pioneered eight years earlier by his colleague, Dr. Frank Jobe, on another top pitcher, Tommy John. That operation, which salvaged John's career, is now known by Yocum and his colleagues as "the full Tommy John" or "the full T.J."

The "full T.J." replaces the injured elbow ligament with a section of tendon taken from the wrist.

"When you're looking at something totally gone," Yocum said, "you have no choice but to reconstruct the ligament."

The tendon Yocum used is the palmaris longus, an expendable tendon in the wrist. It is not crucial to wrist motion; in fact, about 15 percent of people are born without it.

"Fortunately, Don did have it," said Yocum.

The first step in the operation was to "harvest" a six- or seven-inch section of the wrist tendon, which one doctor described as "a thick shoelace." Then Yocum drilled holes in the ends of two bones that connect at the elbow: the humerus, or upper arm bone, and the ulna, the long bone on the little-finger side of the forearm.

"Then you basket-weave the tendon through those holes and double it back in a kind of figure-eight and sew it to itself," Yocum said.

The trickiest challenge of the surgery, he added, is to place the "points of attachment" -- the holes in the bone -- so that the new "ligament" will bind the joint and maintain a relatively constant tension throughout the pitching motion. The ligament must support and stabilize the elbow both when it is fully flexed (when the pitcher cocks his arm back to throw) and when it is completely extended (during the follow-through after the ball leaves the pitcher's hand).

"You have to get it tight enough but not too tight," Yocum said.

The surgery itself was only the beginning of Aase's recovery. The elbow was immobilized for about 10 days, after which only limited motion was allowed, to protect the new "ligament" while it secured itself to the bone. It took months of physical therapy and gentle weightlifting before Aase even threw a baseball, and he went more than a year between pitching assignments.

"You're looking for that tendon to turn into something stronger and attach itself to the bone," Yocum said. "It's nine months to a year before that tendon turns into a ligament."

Yocum and his partners at the Kerlan-Jobe Orthopedic Clinic in Inglewood, Calif., have performed the "T.J." surgery on about 25 people, mainly professional athletes.

"It's not the sort of thing you want to do on your weekend warrior," Yocum said. "There are very few people who throw a baseball 92 mph."

Aase's injury was much more serious than "tennis elbow," the bane of the weekend tennis player. Tennis elbow is an inflammation of the muscles or tendons on the outside of the elbow joint, but Aase's injury was structural. It destroyed the elbow's support system, its main ligament.

For Aase (pronounced "Ossie"), the pain started early in the 1982 season, when he was pitching for the California Angels, and forced him onto the disabled list twice that summer. He tried cortisone shots, physical therapy and rest -- at one point he didn't throw for six weeks -- but nothing stopped the pain.

The official diagnosis was chronic medial elbow pain, the result of years of wear and tear from throwing a baseball at high speed.

Caught early, Yocum said, the damage can be limited to inflammation of the joint and its supporting tissue. But over a period of years, it can wear down the joint "like metal fatigue in an airplane, setting the stage for disaster."

The medial collateral ligament, said Dr. Louis Levitt, an orthopedic surgeon and clinical instructor at Georgetown University Medical Center, "is the guardian of the elbow, just as the anterior cruciate ligament is the guardian of the knee."

"Pitching is not a natural motion," said Dr. Charles Epps, chief of orthopedic surgery at Howard University Hospital. "It's particularly hard on the shoulder and the elbow. With pitchers, elbow and shoulder injuries are an occupational hazard."

The "T.J." operation carries no guarantee of success, Yocum warned, particularly for a professional athlete whose career depends on exquisite physical fitness.

"You're really stacking the odds against him," Yocum said. "The tolerances are so close.

"A difference of 5 mph in the speed of his fastball can mean the difference between Triple-A for life and the major leagues , especially for a power pitcher like Aase."

A hard-throwing pitcher such as Aase is putting about four or five times the normal stress on his elbow, said Dr. John Cohen, an orthopedic surgeon who works with the Sports Medicine Center at Capitol Hill Hospital.

"The same thing that caused the original injury could happen again," Cohen said. "Every time he rears back to throw a pitch, he's stretching that ligament. Nobody can tell you how long it will last."

"Anytime you have an operation like that," Yocum said, "I don't think you ever get completely back to normal. But Don is about as close to normal as possible. He actually picked up a couple of degrees of motion in the flexion-extension of the elbow.

"I can't explain that."