Jumping - Daily Functioning of the Knee

Jumping
It’s hard not to feel a twinge of envy when you watch your favorite six-year-old leap off the furniture, knowing the only damage she’s likely to cause is to Mom’s favorite breakable. As we get older, the impact of jumping is likely to have far more painful consequences than paying for repairs out of our allowance money. The harsh impact combined with the potential for twisting and tearing, makes jumping a risky business indeed. Still, some of us can’t resist. We rise into the air on driveway basketball courts and in funk-music-driven aerobics classes. Sometimes we land easily, sometimes we don’t.

When you jump, even a good landing may compromise your knee joint. Those strong quadriceps muscles contract on landing and pull hard at the patellar tendon’s insertion on the tibial tuberosity (the little bump at the top of the tibia). This may cause jumper’s knee (inflammation of the patellar tendon). Of course, if you land off your intended, balanced course, you will strain all elements of your knee joint. The correct shoes and corrective knee bands can reduce knee injury when jumping.

Stair Climbing - Daily Functioning of the Knee

Stair Climbing
Once used primarily by athletes in training, stair climbing has become popular with exercisers who take step classes in gyms and with aerobic enthusiasts who use the outdoor stairs at beaches, hills, and high school or college stadiums. A lot of them end up limping into the doctor’s office with knees that just can’t take the strain. With stair climbing, the knee moves quite a bit and is under a great deal of pressure. The more the knee is flexed, the tighter the patellar tendon is stretched, pushing on the patella. When the tendon stretches out, the area where it attaches becomes inflamed, and tracking of the patella goes off course. It drifts, slips, and tilts, resulting in patellofemoral syndrome (runner’s knee) or, in more extreme cases, chondromalacia patellae (wearing out of the cartilage on the back of the patella). Extreme wear and tear on the cartilage and menisci (the cushioning discs between the femur and the tibia), over time, roughen the glassy cartilage surface and decrease the protection it and the menisci offer. Eventually, bone may meet bone, causing painful arthritis. Stair climbing may increase the force of the patella on the femur up to four times body weight. To help keep the exercise as safe for your knees as it is good for your metabolism and cardiac function, take care to give your knees a rest (don’t do the same exercise two days in a row), alternate stair climbing with other types of exercise, reduce your speed while climbing, and pay immediate heed when your knees start to ache or swell.

Squatting - Daily Functioning of the Knee

Squatting
In some cultures squatting is the preferred method of sitting and is practically an art form. People in those cultures can sustain the posture for lengthy periods of time—astonishing to the average American. Squatting is sometimes advocated for pregnant women as a way to ease the eventual difficulties of labor. When regular squatting is practiced from childhood, the knee suffers no ill effects. However, if you use this motion only occasionally—or incorporate it suddenly into your daily routine—it can cause problems. Certainly you may occasionally squat to pick up an errant sock or a sleeping child from the floor. Mostly, though, squatting in this country occurs during exercise. A well-executed squat is an excellent muscle-toner and muscle stabilizer, but a poorly executed one can create problems. Deep knee bends to a squatting position—once the cornerstone of military inspired exercise regimes—have now been determined to do more harm than good by jamming the patella into the femur, and subluxing (partially dislocating) the femur from the tibia—in this case, slipping the femur over the tibia, outside its normal anatomical placement. Squatting may increase the forces on the knee joint up to eight times body weight.

Jogging and Running - Daily Functioning of the Knee

Jogging and Running
Jogging and running have benefits for both body and mind. Great calorie burners, they also clear your mind and renew your spirit, offering the much vaunted “runner’s high.” They can, however, take a real toll on the knees unless you take precautions. As discussed in the preceding section, good shoes are a must, and you should replace them regularly if you are a frequent or long-distance runner. Carefully consider your running surface—a dirt track is better than a concrete one, and flat or uphill running is preferable to downhill. Most runners do pay attention to these factors.

Another predictor of potential knee problems as a runner is your physical build. Q angle (quadriceps angle) is measured by drawing a line from your anterior iliac spine (the bump on your pelvis above and in front of your hip joint) to the center of your kneecap, and a second line from your kneecap to the tibial tuberosity (the little bump at the top of the tibia where the patellar tendon attaches to your tibia). A wide Q angle would be more than 15 degrees and might be found on extremely broad-hipped women. Such an angle may increase the likelihood of “runner’s knee” (patellofemoral syndrome), because it predisposes a person to run with the knees pushed inward (knock kneed). The resultant strain loosens the patellar tendon and its collagenous attachments and weakens their hold on the patella. The patella may then move off its track on the femur, resulting in pain and inflammation. A wide Q angle does not always cause pain and is not a reason to stop running, however; its effects can be adjusted by the use of orthotics or braces.

Shoes - Daily Functioning of the Knee

Shoes
The common shoe offender to knee health is, of course, high heels. Their negative impact is compound. First, they position the foot so that its usefulness as a shock absorber is greatly diminished. This problem is exacerbated by the fact that the shoes themselves are often thin-soled and unpadded, offering no cushion between the foot and the pavement. Second, they create stress for the knee by causing prolonged muscle contraction and fatigue. Third, over the long haul, constant wearing of high heels can create a permanent tightening and shortening of the Achilles tendons, so that any shoes other than high heels become difficult and painful to wear.

Another source of problems is worn-out or improperly fitted athletic shoes. Designed to compensate for the impact caused by running, jogging, or jumping, shoes that become worn down create problems in two ways. First, a reduction in the cushion increases the impact on the knees. Second, soles worn down on their sides, heel, or toe may magnify the slight imperfection in gait that caused uneven wear in the first place. A shoe that fits poorly may cause poor toe-off (the beginning of a step) or excess muscle strain.

Irregular Gait - Daily Functioning of the Knee

Irregular Gait
Gait is simply the way in which a person walks. In a perfect gait cycle, the pushing off and landing motions of the heel and toe are in balance, contributing to an even stride. Many people, however, unconsciously favor the heel or toe when they walk, contributing to an uneven and uncomfortable gait cycle. Plantar flexion, favoring the toe, occurs when the foot is angled down at the ankle from heel to toes (at its most extreme, walking on tiptoe). This causes the knee to hyperextend (literally straighten too far), putting extreme pressure on the joint itself as well as its individual anatomical parts. The tendons, ligaments, and joint capsule are stretched so that they move out of place, resulting in a sprain or strain. Dorsiflexion, favoring the heel, occurs when the foot is angled up from the ankle (at its most extreme, walking on the heels alone) so that the person falls forward, straining the quadriceps (thigh) muscles. Excess dorsiflexion keeps the quadriceps contracted in order to keep the individual from falling over and inhibits normal straightening of the knee. Both of these gait deviations are commonly seen in people who have had a stroke, brain injury, or spinal cord injury and in children with cerebral palsy

Walking - Daily Functioning of the Knee

Walking
No movement or exercise is easier on the knees than a well-paced, well-executed walk in good, comfortable shoes. Some factors, however, can make this most natural of motions hazardous to knee health, and I discuss those next.

Anatomy Of The Knee

The knee is made up of bones, ligaments, tendons, cartilage, and a joint capsule, all of which are composed of collagen. Ligaments connect bone to bone. Tendons attach muscle to bone. Cartilage is the smooth, fibrous connective tissue covering bones that allows easy, gliding movement.



Collagen is the fibrous protein constituent of connective tissue present throughout the body. As we age, the most obvious sign of collagen breakdown is in the face, where it leads to the sagging that keeps plastic surgeons in business. Less obviously, however, collagen breaks down throughout the body and contributes to a variety of age-related injuries and conditions. These keep orthopedic surgeons in business. However, treatments and methods other than surgery may do a better job of preserving and rejuvenating the knee.

The knee joint is a link between the thighbone—the femur—and the two bones of the lower leg—the tibia (large and on the inside) and the fibula (small and on the outside). The attaching ligaments on the outer surfaces of the knee are the medial collateral ligament (connecting the tibia to the femur) and the lateral collateral ligament (connecting the fibula to the femur). The patellar tendon attaches the quadriceps muscles of the thigh to the tibia, enabling extension of the knee. Inside the knee joint, two ligaments stretch between the femur and tibia—the anterior cruciate ligament and, behind it, the posterior cruciate ligament. Covering the ends of the bones is articular cartilage, which provides a smooth surface to facilitate motion. Articular cartilage is so named because when bones move against each other, they are said to articulate. In the knee, auricular cartilage covers the end of the femur, the top of the tibia, and the back of the patella (the kneecap). In the middle of the knee joint are the menisci, which are collagenous disc-shaped cushions that act as shock absorbers.

Unlike a ball joint, such as the hip, which sits in a deep pocket (the acetabulum of the pelvis), the knee doesn’t have much protection from trauma and stress. It is designed to move mostly in one plane like a hinge. Because of this inherent limitation of movement, strong knee ligaments are extremely important for knee health.

Side-to-side stresses are controlled by the medial and lateral collateral ligaments; front-to-back motion is handled by the anterior and posterior cruciate ligaments, which ensure that the tibia doesn’t slide backward or forward in relation to the femur. When these ligaments become lax, or are torn, bone movement may become excessive and damaging, and painful arthritis can begin.

HOW THE KNEE WORKS (AND DOESN’T)

The skeletal structure has two primary types of joints—the ball joint, exemplified by the shoulder, which allows free rotation (a freedom that comes with its own set of problems and injuries, by the way); and the hinge joint, illustrated by the knee, which operates primarily in a single plane (bent to straight) with only a slight rotational or pivoting motion. This restriction of movement is what makes the knee so vulnerable to traumatic injury. Additionally, the knee is regularly subjected to the stress of both supporting body weight and absorbing shock from intermittent impacts such as jumping, walking, and running. Over time these stresses cause a loosening of the connective ligaments, the tendons, and the joint capsule that holds the knee together. Along with a wearing away of cushioning cartilage and collagen, this loosening leads to the pain and dysfunction of bone meeting bone. At its worst, this condition manifests as arthritis.