Falling linemen rolled up the left knee of the Washington Redskins' Joe Jacoby during a field goal attempt in Philadelphia last year, dislocating his kneecap and ending his season. The game before, teammate Mark May blew out his right knee during a home game against the Cowboys.

In the third game this season, tumbling players bent Redskins quarterback Mark Rypien's left knee backward, knocking him out of that and subsequent games. Three games later, Eagles defensive end Reggie White took down backup Redskins quarterback Stan Humphries, spraining his right knee in the process.

Some of the carnage even comes in the offseason. A. J. Johnson, who had a successful season last year as a rookie defensive back, locked up his right knee just getting up off the floor at home, ultimately leading to surgery.

"Knee injuries are the biggest injury that we have," said Redskins Coach Joe Gibbs. "It is a major problem for us all the time."

Small wonder. Unlike hips and shoulders, where ball-shaped ends on the bones fit into sockets to form a solid joint, the knees are like two abutting broomsticks, with rubber pads between the ends, held together by four ropes. When a player runs, the forces flowing through the knees exceed five times body weight; when a blow or a sudden direction change stretches one of the four cable-like ligaments by more than 10 or 15 percent, that ligament can tear, causing extreme pain and joint instability.

Damaged knees make up between 20 and 25 percent of the injuries that cause football players to miss games, said Redskins trainer Bubba Tyer. "And that's compared to everything else: fingers, hands, wrists, shoulders, necks, backs, hamstrings, {quadriceps} and ankles."

But players are coming back from major knee injuries faster and more frequently than ever. All five key Redskins recently felled by serious knee problems are either back on the field or physically ready to resume playing.

"These players are neuromuscular geniuses," Tyer said. "They are highly motivated. Strong. Tough. They have all the qualities you want in a patient. That is one reason we get them back."

Technical advances also have made a difference, including a new approach to reconstructive knee surgery, the widespread use of the arthroscope, a viewing device that allows doctors to see inside the knee without cutting it open, and more aggressive rehabilitation programs to restore strength and flexibility.

The arthroscope has made the biggest impact, said Redskins orthopedic surgeon Charles Jackson. The device has a hollow steel barrel, not much thicker than a pen, that can be poked through the skin. Inside the barrel are glass fibers for viewing the knee's internal anatomy, hollow tubes for squirting in fluids and flushing out bone chips and other debris, and tiny cutters for trimming rough cartilage.

"We used to feel that we had only one crack at a knee," Jackson said. "The arthroscope makes it possible to look at the knee repeatedly, do what you have to do, and get out. Before that, washing out a knee or trimming cartilage would have been a major procedure."

Because the knee is not cut wide during an arthroscopic exam, healing takes less time. Rypien is a classic example.

"I had a partial tear of the posterior cruciate ligament and the capsule of the joint," Rypien said.

The posterior cruciate is the strongest ligament in the knee and rarely torn. Rupturing the sac that encases the knee joint caused blood to leak down into Rypien's calf, painfully swelling the muscle.

In the past, this would have looked serious enough to open the knee. Instead Jackson used the arthroscope the next day and found it wasn't all that bad.

"It was just a basic tear," Rypien said. "There wasn't any cartilage tearing. They did not have to clean any of that out."

Jackson decided that the tear could heal on its own without reconstructive surgery, but that would take a month or so. Two days after the exam, Rypien was back at Redskin Park, icing the joint and starting rehabilitation.

The injury to Humphries was so minor, Tyer said, that "we didn't scope Stan." He sprained a ligament on the inner portion of the knee that recovered on its own. "Stan has been well for a good while," Tyer said.

Too often, however, the injuries are not so minor.

Late in his rookie season last year, A. J. Johnson sprained his knee, primarily stretching the anterior cruciate ligament (ACL). The anterior cruciate and the posterior cruciate, which Rypien injured, crisscross inside the knee joint, giving it rotation, as well as backward and forward stability. If knee injuries are the most common killer of football careers, destruction of the anterior cruciate ligament is the most common kind of serious knee injury.

For a 23-year-old player with a promising career, the idea of a knee injury was terrifying, and Johnson wanted to have nothing to do with it. But the injury had loosened his joint, allowing the meniscus, a cartilage pad that keeps the ends of the bones from rubbing together, to slip out of place.

"A couple of time my meniscus popped out and got lodged between my two bones, so I couldn't straighten my knee out," Johnson said. "It hurt."

Jackson scoped the knee and recommended reconstructive surgery on the anterior cruciate ligament. Johnson refused. "I know other people who had played with stretched ligaments," said Johnson. "Some people don't ever have" surgery.

But the knee locked up again, and a second surgeon also urged reconstructive surgery. Johnson relented and was operated on last June.

Until recently, said Jackson, "we did not have a good operation" for the anterior cruciate. The revolution has been a sort of transplant: Surgeon's take about one-third of the long tendon that holds the kneecap in place, complete with wedges of bone where the kneecap tendon originally was attached. Holes are drilled in the leg bones where the transplanted tendon will be situated. The bone wedges on the tendon are then jammed into the holes and held in place by screws.

Recovery can begin immediately. "I was moving when I woke up," said Johnson. In his hospital bed, he immediately began working with a machine that helps restore flexibility in the knee. "I was real aggressive," he said. "I was not holding back." A month and a half after surgery, he was jogging.

Offensive lineman Mark May, 31, had the same surgery as Johnson, but his recovery was slower, Tyer said, in part because the transplanted tendon began rubbing over a bony prominence.

"It was clicking when he moved," Tyer said. "It didn't hurt him, but it was irritating. So we scoped him {to grind down the bone} and that set us back about a month." Still, May, who has declined to talk about his injury, has been practicing since November.

Sometimes injuries that look the worst are not so difficult to repair.

Jacoby missed the final six weeks of last season after a pile up of bodies -- with him on the bottom -- ruptured the tough sac that surrounds the knee. His kneecap was pushed off to the side of his leg.

"I knew it was major because I could feel everything going," Jacoby said. "My first reaction was yelling for them to get off. After that, you just lay there. I couldn't move."

When they got Jacoby off the field, the doctor "had to push the kneecap back over," Jacoby said. "It felt fine after that."

It wasn't fine. It took reconstructive surgery and five weeks in a cast just to put Jacoby's knee back together again. It took months of determined rehabilitation to make it function.

Aggressive rehabilitation after reconstruction has become as sophisticated as surgery. Tyer and his trainers start the rehab programs with a host of machines sooner than ever before, attempting to quickly restore joint flexibility and to prevent the muscles from weakening.

Still, rehab in the weight room and workouts on the practice field are not the same as being in the game.

"Playing," said Tyer, "is the final stage of rehabilitation. They have to play to reach full confidence."

The players agree.

"I think my worst concern was how would it would feel like after taking a shot," Rypien said. After the first hit, "you kind of like just pop up and wiggle it a little bit, see if everything is still connected." He laughed, a little nervously. "And then get back to work."

Even with the advances, reconstructed knees are not as good as the original equipment. "I still cannot get full flexion," Rypien said. "To do a deep knee bend is probably going to take awhile."

Although Jacoby denies that players worry about their knees at age 55 or 60, defensive line coach Torgy Torgeson is a constant reminder that years in the football trenches can leave lasting damage. Torgeson, a former linebacker and center for the Detroit Lions, plans to have artificial knees implanted in both legs during the offseason.

Still, for Gibbs, all the improvements in sports medicine have been good news. "We are doing a lot better job getting the players back," he said. "I can remember in the early '70s that the guys rarely came back from a major {knee} reconstruction. Today, it is rare that a guy doesn't come back."

The anterior cruciate ligament can stretch about 10 to 15 percent before beginning to tear. Small incomplete tears can heal by themselves, but complete breaks leave the torn ends looking like a severed cable with individual fibers pointing in many different directions. Physicians are unable to stitch such breaks back together.

Instead, orthopedic surgeons now replace the torn anterior cruciate ligament with part of the patella tendon. Bone wedges still attached to the tendon are inserted into holes drilled into the upper and lower leg and held in place with screws. The tendon follows the same course taken by the original anterior cruciate ligament, stabilizing the knee. After rehabilitation to restore strength and flexibility, the player can return to active competiton.