On Your Knees

Once the knee was considered little more than a basic hinge; like a garden gate, it swung open and closed. This reductionist view was eagerly embraced by the medical profession, which had enough problems to contend with without worrying about a joint that seemed to be simplicity in motion. However, it offered little comfort to patients who were in agonizing pain.

Today we recognize that the knee doesn’t just flex; it also glides, Q slides, twists, rocks, and rolls. The demands placed upon the modern knee would be a challenge to the best-designed machine, but the knee is the most poorly constructed joint in the body, with little intrinsic stability. Cons quently, almost everything people do for recreation is tough on the knee. In fact, much of what the knee faces in simple day-to-day living—kneeling, walking, climbing, and being crossed while at rest—can take a toll over time.

At its most fundamental, the knee is indeed a hinge that connects the thighbone (femur) and the leg bone (tibia). While seated, the bones barely touch, but stand up and they lock together, providing a strong, unified structure.

Holding these two bones together are four major ligaments: the two collateral ligaments, which run up the inside and outside of the leg, and the two cruciate (as in “excruciating pain”) ligaments, which cross within the joint. The former provide side-to-side stability, while the latter prevent the bones from slipping backward or forward out of the joint. No matter how powerful the muscles around the knee, without most of its strong, resilient ligaments, the joint would be useless.

The anterior (front-to-back) cruciate ligament (ACL) is often torn in contact sports or sprained during activity. Like its partner, the posterior (back-to-front) cruciate ligament (PCL), it should look like a good strong rope. However, when it’s tom completely, it becomes a frayed mass swaying in the currents. Some athletes can get by without it, others need as knee brace or surgery.

The primary problem with ligaments is that they are tough but not particularly ?exible. Once, stretched, a ligament tends to stay stretched, and it stretched beyond 6 percent of its length, it snaps, leaving the knee vulnerable to further injury. 

If an audible “pop” is noted upon injury, the odds are that the ACL has been damaged. A classic ACL rupture involves an athlete who is running and trying to change directions quickly. He plants his left foot and cuts over it with his right, thus screwing the left leg as he rotates his body until he feels excruciating pain and hears the knee pop. In this situation the athlete generally hits the ground before the ball does.

In basketball the player may be coming down from a jump when he or she is thrown off balance by landing on someone’s foot. The femur externally rotates and extends as he or she tries to prevent falling, causing an ACL rupture.

Bones are soft enough to wear away with the least bit of rubbing, so to alleviate bone-on-bone wear and tear nature covers the ends of the most active bones with a natural shock absorber called cartilage. There are no blood vessels or nerves in this white, gristle-like substance and, to keep this cartilage from just wearing away, the whole area is enclosed in a sac containing a thick fluid substance that looks like the white of an egg. This synovial fluid further protects and lubricates the joint. The sac itself is known as the bursa, and when irritated over time, the end result is called bursitis.

The cartilage between the bones in the knee is called the menisci. What is commonly called a torn cartilage is more accurately a tear of one of the menisci of the knee joint. The menisci are two thin, crescent-shaped structures that fact as shock absorbers between the thigh and leg bones. By pushing synovial fluid around, they also contribute to the lubrication of the knee and to the nourishment of the cartilage. A child’s ability to jump for joy, a professional athlete’s career, and an elderly person’s general mobility all largely depend on the way the cartilage crumbles.

There are two basic types of meniscal tears: acute tears and degenerative tears. Originally, orthopedic surgeons felt that any tom meniscus must be totally removed. Indeed, during the sixties and seventies meniscectomy was the most common orthopedic surgical procedure. Now we realize that he who hesitates is saved. Looking back on all those meniscectomies, we discovered that people who have a torn meniscus removed in their twenties have a greatly increased risk of developing arthritis by the time they’re forty-five or fifty. In fact, studies have found evidence of degenerative changes within the knee in up to 85 percent of meniscectomy patients at a ten-year follow-up. What this means for all those athletes who had meniscectomies during the 1950s, 1960s, and early 1970s remains to be seen. Unfortunately, the feeling in the sports medicine community is that, due to those meniscectomies, the number of former athletes who will need total knee replacement will increase steadily during the next couple of decades.

This is because without the meniscus acting as a buffer, the two joint bones rub against each other. In time the bones can wear away at the ends, leaving nerves painfully exposed. The result is osteoarthritis, or degenerative arthritis, which can spread to the entire joint.

Researchers estimate that the medial meniscus and anterior cruciate ligament absorb 90 percent of all knee injuries. Once they were a primary cause of lifelong limps. Today if the injured is lucky and the injury is accurately diagnosed, he or she will be left with little more than a dot of a scar and an heroic tale of medical trauma to entertain the masses or at least the folks at the next cocktail party.

The mode of injury for the meniscus is similar to that of the ACL. Often they are injured together and that can confuse all concerned. If one problem and not the other is corrected, the knee is still damaged and very susceptible to reinjury.

Moving on, the front shield of the knee is the ever-popular kneecap or patella. When you knee a piece of furniture or open a door without getting out of the way, it is the kneecap that lets you know you’ve made a mistake. The patella moves within a track near the end of the thighbone. A severe sudden twist or constant stress can throw the kneecap off track. Although it takes some powerful abuse, when it is seriously injured it can take much of the future with it.

That’s because the kneecap is the fulcrum that gives power to the muscles of the leg. It also absorbs a lot of the stress of daily activities, like climbing stairs. You don’t realize it, but when you simply walk up a few stairs the pressures across your knees are approximately four times your body weight! This massive load is largely due to forces that are generated by muscles being worked. Furthermore, damage to any major muscle in the leg will mean more work for the patella and could begin to wear it clown.

The major muscles and bones of the knee and legs

Tying all this together is a thick and powerful system of muscles and tendons that flex, drive, and support the knee. The front thigh (quadriceps), hamstring, and calf muscles are the three major muscle groups involved and the only supporting structures that can be strengthened. The patella tendon connects the kneecap to the front thigh muscle and shinbone. A tear here is called “jumper’s knee” and is common among basketball and volleyball players, hurdlers, and male dancers.

Injury to any of these structures, which provide stability at the knee joint, represents a major cause of disability, loss of playing time, and the beginning of the t degenerative arthritic changes that may befall an active individual.

If all of this makes you feel like wearing designer armor the next time you’re heading out for a little recreation, do remember that probably 70 percent of all knee injuries are of a relatively minor nature. And you’ll be much better equipped to both prevent and pinpoint your own knee problems now that you know what’s where!