Knees in motion
| September 1, 2006
In-Depth Report
Knees in motion
Knees suffer injury more often than any other joint. Between the ages of 25 and 75, your chance of having disabling knee pain or injury is about 50%. What makes the knee so vulnerable? One factor is anatomy. Often described as a simple hinge, the knee is actually a complicated network of bones, cartilage, muscles, tendons, and ligaments (see Figure 1).
Figure 1: Strong and flexible
The knee is more than a simple hinge. Along with the strength to raise and lower your body weight, this joint also has the supporting structures to allow you to twist and turn. |
Bones
The knee joint is the junction of three bones:
the thighbone, or femur
the shinbone, or tibia, the larger front bone of your calf
the kneecap (patella)
At its lower end, the femur divides into two rounded knobs called condyles that support the weight on the bone of the lower leg, the tibia. The top of the tibia is rather flat with a middle bump, and unlike the beautiful fit between bones found in many other joints, the knee's mismatch in shape allows for complex movement but is quite unstable, like two doorknobs balanced on an uneven plate.
The patella is the kneecap, a small, flat bone that floats in front of the knee joint. The patella moves within a groove between the two condyles of the femur. Your patella protects other knee structures and applies leverage to help straighten the joint.
Cartilage
Separating the bones of the knee are two rubbery cartilage pads known as menisci. Named for their crescent-moon shape, the menisci curve around each side of the tibia's top, serving as shock absorbers and helping the bones fit together. Menisci are made of tough, elastic cartilage but are susceptible to injury from the pressure of the thighbone and shinbone they cushion.
In addition, the ends of the bones themselves are coated with articular cartilage, slippery tissue that smoothes the movement of the joint.
Muscles
Muscles power the movement of your knees. These muscles include:
the quadriceps, a set of four muscles that run up the front of your thigh. Your "quads" contract when you straighten your knee, working hard when you get up from sitting or squatting.
the calf (gastrocnemius) muscle, which helps the knee bend and straighten.
the hamstrings, three muscles in back of your thighs that contract when you bend your knees, helping support your weight as you sit down.
Tendons
Tendons connect muscle to bone and transfer muscle power to the bone to create movement. For example, the quadriceps tendon connects the quadriceps muscle to the patella and provides the power to extend the leg.
Ligaments
Ligaments are tough fibrous tissues that connect bones or cartilage at a joint, allowing movement within a safe range. The medial collateral ligament, or MCL, connects the femur to the tibia on the inside (big-toe side) of the knee joint, limiting sideways motion. The lateral collateral ligament does the same on the outside (little-toe side), connecting the femur to the small bone of the calf, or fibula. Deep within the joint, the anterior cruciate ligament, or ACL, connects the femur to the tibia in the center of the knee; it keeps the joint from rotating too far or letting your shin get out in front of your thighbone. Crossing behind that ligament is the posterior cruciate ligament, or PCL, which keeps the shinbone from falling out of place behind the knee.
Other anatomical elements
The entire knee joint is located within a bag-like joint capsule with the consistency of thick plastic wrap. The synovium, a layer of cells lining the capsule, produces synovial fluid, a sticky, translucent liquid that lubricates the joint and minimizes friction. It also helps protect joints by forming a viscous seal that enables abutting bones to slide freely against each other but resist pulling apart. This seal breaks when a joint is moved quickly or forcefully and makes a popping sound.
Places where tendons, muscles, and bones cross paths are also subject to friction. These sites are protected by bursae, cushioning sacs containing a little oily lubricant.
Movement in the knee is like the hinge on a jewelry box: It opens in only one direction. Forcing it beyond a certain point causes damage. A healthy knee allows almost 150 degrees of movement; you can straighten your leg or bend it until your calf meets the back of your thigh, but you can't bend your knee in the other direction so your shin meets the front of your thigh. But unlike the jewelry box hinge, in which any wobble is undesirable, your knee can slightly rotate or move from side to side.
Click and clack: When to worry about noisy jointsDo your hips and knees click, snap, or pop? If there's no pain or swelling, the noises probably are not a sign of trouble. You may hear a tendon moving across a joint. Or you may have momentarily (and harmlessly) broken the seal of synovial fluid that fills the joint capsule. The sound could also be the release of nitrogen gas from a joint moved slightly out of position (like a cracking knuckle). It's a different story, however, if the noise occurs at the moment of injury, or if pain or swelling accompanies it, there may be joint damage that needs medical attention. |
Evaluating knees
Diagnosing knee problems can be complicated. In some situations, a physical examination and the information you provide is sufficient. But most diagnoses require at least an x-ray, and for others the doctor may need to use more sophisticated imaging techniques and laboratory tests to determine the cause and extent of damage (see "Testing for knee and hip problems").
Your medical history
During the exam, the doctor asks many questions about your pain and other symptoms.
Where does it hurt? Try to describe the location of the pain as precisely as possible. This is not always easy. In large joints your pain may be diffuse, radiate from one area to another, or seem to come from a nearby muscle.
How does the pain feel? Does it ache, stab, or burn? Have you had similar pain in other joints?
When did the pain start? Was there a fall, other injury, illness or fever, or a change in activity? If you were injured, did the knee pop or "give out"? Could you walk immediately afterward? Was there swelling? If you have injured that knee before, mention it. Even if it wasn't bothersome or got better, a previous injury might have caused significant damage — and a relatively trivial event could have worsened it enough to cause symptoms.
When does the pain occur? Is it "getting started" pain — worse when you first stand up and walk? Does it hurt more in the morning and then ease up? Is it worse after a certain activity? After you walk a certain distance?
What helps? Does it bother you in bed but ease up once you're up and about? Does pain with activity go away when you sit and rest?
Are there other symptoms? Do you have trouble straightening or bending your knee? Does it lock up or give out?
Expect also to answer questions about other illnesses and medications, which may increase the risk of certain joint problems.
Examining the knee
Your doctor looks for discoloration and swelling and assesses how your knees function. While you are in various positions — sitting with knees dangling, lying on your back, or lying on your stomach with knees flexed behind you — the doctor moves your legs to assess each knee's range of motion, muscle strength, abnormal movements within the joint, and telltale pain or sounds that occur with various maneuvers. Even if only one knee hurts, the doctor examines both for comparison. If the knee is too swollen to evaluate thoroughly, your doctor may schedule a follow-up appointment. Your doctor may want to assess the relationship of your knees to your hips by measuring your Q-angle (see Figure 2). The Q-angle is typically from 0 to 16 degrees, with men usually at the lower end. An abnormally high Q-angle places you at greater risk of patellofemoral pain syndrome (see "Knee pain syndrome") and certain injuries, such as tears of the anterior cruciate ligament. The doctor also evaluates nerve function and circulation in your legs, watches you walk, and follows up on any symptoms of general illness. He or she may schedule further tests at this point.
Women and knee vulnerabilitySome knee injuries — notably those of the anterior cruciate ligament — occur more than twice as often in women than in men (see "Ligament damage"). The explanation is a combination of anatomy, hormones, and differences in fitness training. As a group, women's knees are different from men's. Women's hips tend to be wider, so the thighbone reaches the knee at a larger angle, called the Q-angle, sometimes giving a slightly knock-kneed appearance. Of the four quadriceps muscles, the three extending to the outside of the hip are often stronger, tugging the kneecap in that direction — sometimes enough to cause pain (see "Knee pain syndrome"). Estrogen is an unproven suspect in women's knee vulnerability. Some (but not all) studies show that female athletes injure their knees more frequently at ovulation, when estrogen levels are high. Researchers speculate that high levels of estrogen and other hormones, which make ligaments more flexible during pregnancy, might also make knee ligaments more prone to injury. Ordinarily, flexibility is a good thing because it allows tissues to stretch farther without tearing. But if ligaments and muscles supporting the knee are overly flexible, they may absorb less of the stress of an impact. This forces the joint to absorb more of the impact, possibly rupturing the ACL. Other experts suggest that training techniques and muscle use among female athletes may be the culprit. Women tend to run in a more upright position, strongly contracting the quadriceps muscles on the front of their thighs (rather than their often-weaker hamstrings) and putting more strain on their ligaments. When jumping, women tend to land more on one leg or with straighter legs. What can women do to reduce the risk? If you have broader hips or a tendency toward knock-knees, you probably have a high Q-angle. Wearing the right shoes or arch supports can reduce it somewhat, lowering your risk of injury. When exercising, strengthen and stretch both your quadriceps and hamstrings. If you're involved in basketball or other jumping sports, find a knowledgeable coach and learn to land, stop (especially quick stops before shooting a basketball), and pivot safely. Figure 2: What's your Q-angle?
It's not obvious, but your thighbone (femur) and your shinbone (tibia) are not aligned in a straight line. The angle formed by the line of the femur and the line extending from the kneecap (patella) to the ankle form what is known as the Q-angle. Women usually have a more pronounced Q-angle than men and, as the result, are more susceptible to tears in the anterior cruciate ligament. |
Assessing the role of body weight
If you're overweight, your primary care physician will help assess the role your weight plays in your knee pain and recommend a plan of treatment accordingly. Most likely, a plan for weight loss will be part of your treatment. Many knee problems can be avoided by maintaining a healthy weight.
Carrying extra weight is directly related to knee pain. A 2003 study in Obesity Research of 5,700 Americans over age 60 found that the more obese a person was, the more likely he or she was to experience knee pain. About 56% of severely obese people had significant knee pain, compared to 15% of people who were not overweight. Another study found that severely obese men were 15 times as likely as normal weight people to have torn cartilage and severely obese women were 25 times as likely.
Such statistics are not surprising when you consider that with each step on level ground, you put 1 to 1.5 times your body weight on each knee. So a 200-pound person can put 300 pounds of pressure on each knee with each step. The burden is even higher when you go up and down stairs (2 or 3 times) or squat (4 or 5 times). So if you're 50 pounds overweight, the simple act of going downstairs and squatting to move clothes from the washer to the dryer puts hundreds of extra pounds of force on your knees.
Quick quiz: Do you know knees?Test your knee knowledge. Match these bones to their commonly used names: Quadriceps and hamstrings are types of _______: Severely obese people are ________ times as likely as normal weight individuals to experience torn cartilage in the knee. Painful inflammation of small fluid-sacs that cushion the bones of the knee is known as ___________: True or false: Women are more likely to damage their knee ligaments than are men. True or false: Arthroscopic surgery is a highly effective treatment for osteoarthritis of the knee. Which of the following statements about glucosamine and chondroitin supplements is true? The average age of a person undergoing a total knee replacement is _______. The average hospital stay for patients undergoing total knee replacements in the United States is ___________. Answers 1 = b, 2 = c, 3 = a B D A True False C C B |
Overuse injuries
The knee can be compared to an expensive sports car — a finely tuned machine that is capable of great power but also highly vulnerable to breakdown. Over time, many things can go awry as a result of illness, mishap, and misuse of the joint. Overuse injuries occur over a period of time rather than after a single injury or illness. They may result from repeated overwork or from doing too much in a single day. As we age, overuse injuries become more common. Even normal age-related changes, such as reduced muscle mass and bone density, can make you more prone to knee injury as you get older.
Bursitis
Small fluid-filled sacs called bursae cushion the movement of bones against muscle, skin, or tendons. Bursitis occurs when one or more of these sacs become inflamed.
Irritation from prolonged kneeling can result in bursitis involving either the sac that lies between the front of your kneecap and your skin (called prepatellar bursitis or "housemaid's knee") or the bursa just below the kneecap (called infrapatellar bursitis). People who kneel on the job or during prolonged gardening and housecleaning are susceptible to these forms of bursitis. You may also develop prepatellar bursitis if you hit the front of your knee in an accident or diving to the floor playing sports.
Pes anserine bursitis involves the lubricating sac between your shinbone and the hamstring tendons at the inside of your knee. Just walking may stress the pes anserine bursa if you are obese, have tight hamstring muscles, have knees with a natural turnout, or have changed how you walk in response to another type of joint damage (such as osteoarthritis). Runners are susceptible, particularly if they neglect to stretch and warm up properly, if they quickly increase their mileage, or if they train on hills. Repeatedly kicking a ball also irritates this bursa.
To check for bursitis, your doctor gently presses on the skin over the bursa to detect tenderness. He or she may inject a bit of local anesthetic into the sac. If the pain disappears, that's strong evidence of bursitis. You may need imaging tests to distinguish pes anserine bursitis from other conditions such as a stress fracture or meniscal tear. If you have symptoms of infection (fever, persistent redness, rash, or swelling) your doctor may withdraw a little fluid from the bursa to check for bacteria. Infection is very uncommon in the pes anserine bursa, but the prepatellar bursa can become infected in people who spend a lot of time on their knees.
Symptoms of bursitisSwelling in front of the kneecap (prepatellar) or underneath the kneecap (infrapatellar) Warmth and tenderness Pain when you bend or straighten your knee Pes anserine bursitis may cause distinctive pain as follows: Pain located a few inches below the kneecap, in the center, or behind Increase in pain when you climb stairs or exercise Pain that radiates to the back and inside of your thigh Pain when your knees touch as you lie on your side |
Treating bursitis. Bursitis is treated with rest, ice, and compression to reduce swelling (see "RICE"). To relieve pain, doctors typically recommend one of the common over-the-counter pain relievers known as nonsteroidal anti-inflammatory drugs (NSAIDs). These medications have a variety of side effects so it is important to discuss your personal health risks with your doctor when considering the long-term use of any NSAID. Doctors may also give a corticosteroid injection into the bursa to reduce inflammation.
You'll need to avoid activities that aggravate the condition during the healing process, which usually lasts two to six weeks. If the fluid in the bursa shows signs of infection, you'll need to take antibiotics, and the doctor may remove fluid daily. In extreme cases, the swollen bursa is removed surgically.
Your doctor may also recommend physical therapy. Physical therapy focuses on strengthening and stretching the quadriceps (see Figure 3) and inside hamstrings. A physical therapist can also show you how to protect your knee in sports and daily activities. If your normal stance puts pressure on the pes anserine bursa, using flexible, over-the-counter arch supports in your shoes may reduce it. To prevent prepatellar bursitis, wear protective kneepads (such as roofer's pads or gardening pads) while kneeling or while playing sports likely to involve hitting the knees. Bursitis can recur if you don't take preventive measures after it heals.
Figure 3: Knee-strengthening exercises
Straight-leg raise: To strengthen your quadriceps, the large muscles in the front of your thigh, lie on your back and tighten your thigh muscles with your knee fully straightened. Lift your leg several inches and hold for 10 seconds. Lower slowly. Repeat until your thigh feels fatigued, then switch to the other leg. Wall sit: This exercise also strengthens quadriceps. While standing with your back against the wall, bend your knees, lowering yourself into a sitting position. Do not lock your knees. Hold this position for 20 seconds. Repeat. |
Tendinitis
Tendinitis is inflammation in a tendon, usually because of overuse. The affected tendon continues to function, at least for a while, but there is recurrent pain. You may develop tendinitis if you engage in high-intensity activities such as running or basketball on the weekend but do little to maintain your conditioning during the week. With age, tendons become stiffer and more prone to tendinitis, while supporting muscles become weaker and less able to provide protection. Inflexible hamstrings and quadriceps make you more susceptible.
Tendinitis in the knee can occur in the patellar tendon (most common) or the quadriceps tendon. Dancers, runners who are training vigorously, and athletes who jump a lot are subject to patellar tendinitis, sometimes called "jumper's knee."
To diagnose tendinitis, the doctor gently stretches the tendon and probes for tenderness below and above the kneecap. Testing for characteristic muscle tightness (often in quadriceps, hamstrings, and heel cords) helps with the diagnosis and provides strategies for rehabilitation. X-rays usually aren't needed.
Symptoms of tendinitisPain above or below the kneecap where the tendons attach to bone Swelling Pain that recurs with particular activities and eases with rest In severe cases, pain that no longer improves with rest |
Treating tendinitis. For the first few days, tendinitis is treated with rest, ice, over-the-counter pain relievers, and often a knee support. After that, you can resume gentle activities that don't aggravate the area. If pain doesn't improve with rest, your doctor may apply a steroid solution over the area and use electrical stimulation to help the medication reach the tendon and reduce inflammation (see "Ultrasound, phonophoresis, and iontophoresis"). In many cases, tendinitis goes away in a few weeks or months. But if none of these remedies work and the pain persists for more than a year, surgery is sometimes performed to remove abnormal areas of the tendon.
Rehabilitation for tendinitis includes exercises to improve flexibility and address muscle imbalances that place extra stress on the tendons. Try this exercise:
Sit in a chair with your knees bent. Try to lift your right foot and shin while someone else holds it down. Press upward against the pressure for several seconds, then relax. You get the same effect by using weight-training machines that offer similar resistance. Using resistance to increase tension while a muscle is being lengthened is known as eccentric exercise.
You can usually resume normal activities in a few days and more demanding athletic activities in a few weeks, after the pain and swelling are gone and you have regained muscle strength.
Iliotibial band syndrome
The iliotibial (IT) band is a thick cord of tissue extending from the hipbone down the outside of the thigh to the tibia. When the knee bends, the IT band slides over the outside knob of the femur. If it becomes inflamed, the side of the knee hurts. In older people, IT band syndrome usually occurs when something else, such as a bad back or another joint problem, has thrown off your gait. In athletes, the condition is so common it is sometimes called "runner's knee." But IT band syndrome can occur in anyone who increases running mileage too rapidly or overdoes it while cycling, skiing, or playing soccer. The syndrome is more common in those who fail to warm up properly and those who have tight IT bands, unbalanced leg muscle strength, high or low arches, or unequal leg lengths.
To diagnose IT band syndrome, the doctor presses on the outside femur knob of your knee while you flex and extend your leg. If pain is greatest with the knee flexed about 30%, that's a telltale sign. The IT band may also be swollen or thicker where it passes over the femur.
Symptoms of iliotibial band syndromePain in the upper outside of the knee Pain along the IT band, from the hip to below the knee Dull, sharp, or stinging pain Pain that arises gradually or after a single intense workout |
Treating iliotibial band syndrome. The first line of treatment for IT band syndrome is resting the joint, applying ice, taking over-the-counter NSAID pain relievers, and reducing or eliminating the aggravating activity.
Women should avoid wearing shoes with heels higher than an inch. If pain occurs while you sleep, you can buy thin cushions made with a lightweight silicone gel for your bed that act as a comfortable shock absorber.
In physical therapy, you learn to stretch the IT band (see Figure 7) and improve the balance of flexibility and strength in your quadriceps muscles and hamstrings. While you are being treated, you can maintain conditioning by substituting other activities that don't stress the knee, such as swimming, aqua jogging, riding a stationary bike with little resistance, light walking, using an elliptical machine, and using cardiovascular fitness machines that involve only arm movements.
If symptoms do not improve, the doctor may inject a corticosteroid medication into the band to relieve pain and inflammation. Surgery is not usually required.
Depending on severity, IT band syndrome may take several weeks to heal. If you're overweight, losing weight can reduce the likelihood of the syndrome returning.
Tears in supporting tissues
Just as muscles can tear, the supporting tissues surrounding the knee can split under the pressure of injury or overuse.
Ruptured tendons
When you suddenly contract your quadriceps to their maximum capacity — say, if you stumble going down stairs and desperately try to stay upright — the force can be enough to tear the quadriceps tendon connecting your muscle to the kneecap. Bill Clinton suffered such an injury in 1997, and it's common in recreational athletes over age 40, particularly basketball players. Your risk is greater if you have diabetes, other hormonal disorders, or kidney failure. A ruptured tendon can be quite disabling temporarily and usually requires surgery. Recovery can take several months.
Less commonly ruptured is the patellar tendon, which connects the kneecap to the tibia (making it a ligament, even though it's commonly called a tendon). Although this usually occurs in athletes landing badly after a jump, occasionally a fall unrelated to sports is to blame. The same underlying conditions raise the risk, although most patellar tendon ruptures occur in people under age 40.
A tendon rupture needs immediate attention. To diagnose this injury, your doctor may feel the split in the quadriceps or patellar tendon by pressing the area just above or below your kneecap. X-rays won't show the tendon well, but may show that your kneecap is slightly out of place because it has lost connection with the muscle. The kneecap may sit abnormally low (called patella baja) in a quadriceps tendon rupture or too high (called patella alta) in a patellar tendon rupture. Magnetic resonance imaging (MRI), an imaging method that shows soft tissue (see "MRI"), can reveal a partial or complete tear. If both tendons rupture, an unlikely occurrence, the doctor tests for underlying diseases such as kidney failure and diabetes.
Symptoms of a ruptured knee tendonDisabling pain Swelling Difficulty or complete inability to straighten the knee Popping or snapping at the moment of injury |
Treating a ruptured tendon. At first, your doctor places your knee in a brace to immobilize it while you rest the leg and use ice to counter pain and swelling. If the tear is partial and you can extend your leg, surgery may be unnecessary and your doctor may place your leg in a cast for healing. For a complete rupture, you'll probably need surgery as soon as practical (within a week, before the muscle retracts and creates additional problems). During the procedure, the surgeon rejoins the tendon's torn ends and stitches them in place, often anchoring them to small holes drilled in the kneecap. The leg is held straight in a cast or brace for several weeks.
After being immobilized, a repaired tendon will be quite weak and you'll need crutches to get around. Under the direction of a physical therapist, you can start building up strength after about a week by gradually putting some weight on the leg. You should do this carefully and in small increments, however, to avoid re-rupturing the tendon. After three weeks, your physical therapist will show you exercises aimed at strengthening the quadriceps and calf muscles and help you slowly increase how much you bend the knee. It may be three months before you can run again and six months or longer before you can jump.
Meniscal tears
Among the most frequently injured parts of the knee are the shock absorbers called menisci, which provide cushioning between the thighbone (femur) and shinbone (tibia) (see Figure 4).
Figure 4: Meniscal tear
When the shock-absorbing cartilage in the knee is torn by injury or worn ragged by use, the result is called a meniscal tear. Stiffness and a vague sensation that the knee is not moving properly often result. |
Unfortunately, the menisci can tear. As you age, the menisci weaken and fray. Even such a simple motion as getting in and out of a squatting position or rising from a low chair can tear a meniscus. In younger people, tearing the menisci usually requires a strong, twisting force. This might occur as you round the bases in softball or pivot left to throw a basketball while your feet are facing right. Meniscus damage often accompanies a tear of the anterior cruciate ligament in the front of the knee. If you have osteoarthritis, meniscus damage may occur with no identifiable injury as part of the gradual cartilage degeneration process, because the same genetic predisposition for arthritis may also contribute to meniscal deterioration.
To diagnose a meniscal tear, the doctor asks about pain and movement. Is your knee most comfortable slightly flexed? Is it hard to straighten your leg? As you sit, lie on your stomach, and lie on your back, the doctor maneuvers your legs to observe any pain, popping, or grinding in the meniscal area.
MRI is 75% to 90% accurate in finding meniscal tears. It won't reveal whether a tear is new, however, or the cause of your symptoms — yours may have been torn for years and never bothered you. When Harvard researchers performed knee MRIs on people over age 45 with no knee complaints, one out of three was found to have meniscal tears. Because MRI is expensive, the test is reserved for times when the diagnosis is in doubt or the results will influence treatment.
A direct view inside the knee with arthroscopy is a reliable way to determine the significance of a tear. Because it is expensive and invasive, however, your doctor is likely to use arthroscopy only if all of the following conditions are met.
Your pain came on suddenly and is localized to the joint line where the meniscus commonly tears.
MRI and clinical examination both suggest there is a tear.
An x-ray or MRI indicates there is little or no arthritis in your knee.
Symptoms of a meniscal tearStiffness and swelling Pain and tenderness along the joint line or general knee pain Fluid accumulation Catching or locking of the knees |
Treating a meniscal tear. The goal is to relieve pain, restore normal motion, and preserve as much of the meniscus as possible. Initial treatment includes rest, ice, and compression, along with NSAID pain relievers. NSAID medications have a variety of side effects, so it's important to discuss your personal health risks with your doctor when considering the long-term use of any NSAID. Steroid injections may also be used. A definitive evaluation may be deferred a week or so until swelling subsides. At that point, if your knee is stable and doesn't lock, you may need no further treatment.
Whether a small tear heals depends on its location; the meniscus' outer rim is well-supplied with blood and should heal, while other portions have little or no blood supply and can't repair themselves. If pain persists, depending on the size and location of the tear, doctors may choose one of three surgical approaches: repair, removal, or replacement. Most surgeries can be performed arthroscopically on an outpatient basis and with a choice of anesthesia.
If possible, the surgeon sews up the tear, although most tears in people over age 45 cannot be repaired because there are fewer blood vessels in the menisci with age. If part of the ripped meniscus is blocking normal joint action, the surgeon removes that section. Before the shock-absorbing role of the menisci was fully appreciated, doctors used to remove the damaged meniscus entirely; now they remove as little as possible. Even if your menisci have weakened — after age 45, they may be softened and fat-filled — the tissue is worth keeping if possible. If a severely damaged meniscus can't be repaired, however, the surgeon may remove it since there is no value in keeping it in place and removing it may reduce pain and improve mobility. If you kept broken-down shock absorbers on your car, you'd still have a bumpy ride.
After surgery, you'll return home on crutches for a few days. You can resume normal activities after about a week and start more demanding activities such as sports in about four to six weeks. Rehabilitation includes exercises to improve the strength and flexibility of muscles surrounding the knee (hamstrings, quadriceps, and calf) and the range of motion of the joint.
After a meniscal tear, strengthening your quadriceps will help make up for lack of the knee's built-in shock absorber. Light exercise that does not put a lot of weight on the knee — such as swimming, riding a stationary bike, or using an elliptical machine — can help rebuild strength.
Ligament damage
Of the four major ligaments that support the knee joint and help control knee motion (see Figure 1), two are most easily ruptured or torn: the medial collateral ligament and the anterior cruciate ligament. Women are more than twice as likely as men to experience an ACL injury (see "Women and knee vulnerability").
Symptoms of ligament damageSymptoms of an MCL injury include: Pain and tenderness on the inside of the knee Swelling Wobbling of the knee or give to the side Sensation of the knee opening up with each step (in severe injuries) Symptoms of an ACL injury include: A popping sound at the time of injury Swelling, which may cause pain Instability, ranging from wobbling to an inability to get up |
Treating MCL damage. Your doctor will probably tell you to ice and elevate your knee, wrapping it in a bandage to reduce swelling. A brace may help you totally rest the joint. Surgery is rarely needed unless the ACL is also injured. Physical therapy can gradually improve your range of motion and the strength and flexibility of your quadriceps and hamstrings. Depending on the severity of the injury, it may take as little as a week or more than two months before you return to normal activities.
Treating ACL damage. Use ice and compression and elevate your knee whenever you sit or lie down. For pain relief, start with over-the-counter NSAID pain relievers such as ibuprofen or naproxen. To rest your knee, use a brace to keep it straight and crutches to keep weight off your leg. Although the ACL cannot heal, one in three people can regain enough strength in the knee to return to nondemanding activities without surgery. But this isn't easy. It may require a year of rehabilitation before muscles are strong enough to compensate for the loss of ACL-provided stability. Even so, your knee may sometimes pop out of joint. Your doctor may suggest an ACL brace to use during occasional strenuous activity. If you wish to return to activities involving jumping and pivoting, you will probably need surgery.
To determine whether you should have surgery, you and your doctor will need to consider your age, your activities, how unstable your knee is, and other injuries. Following surgery, rehabilitation is crucial and has a major impact on your outcome. If you don't have surgery, you must make an ongoing commitment to strengthening your knee muscles. If you do have surgery, you need to participate in physical therapy both before and after surgery to gain as much strength and range of movement as possible.
ACL surgery lasts about two hours and is usually done arthroscopically. After drilling holes in the bone where the ACL attaches, the surgeon puts a transplanted tendon from your patella or hamstring in place, fitting the bone-ends of the tendon into the holes and screwing them into place.
If you have multiple ligament injuries and there is not enough of your own tissue to make repairs, or if you are older than 45, your doctor may recommend the use of donor tissue, called an allograft. Surgery to implant an allograft is shorter and causes less discomfort because it doesn't disrupt healthy tissues. However, there can be a shortage of donor tissue, and you must accept a very small risk of disease transmission (see "Is donor tissue safe?").
Is donor tissue safe?Donor tissue from human cadavers is frequently used in orthopedic surgery, including meniscus and anterior cruciate ligament reconstruction. In 2001, 26 alarming cases of bacterial infection — fatal in one young knee patient — were linked to contaminated donor tissue. Several were traced to the same processing plant and the same donor, prompting the Centers for Disease Control and Prevention to recommend changes in plant sterilization procedures. As a result of stricter federal regulation since these cases, allografts (tissues from a donor) are now extremely safe, and infection is exceedingly rare. The risk of a meniscus allograft being contaminated with HIV or another virus is less than 1 in 1.6 million. Ask whether the provider of donor tissue is certified by the American Association of Tissue Banks. |
After surgery, you'll go home with crutches and may use a brace that holds your leg straight or lets it bend a set amount. Physical therapy will focus on improving your strength, stability, and movement. Your muscle strength dictates when you may reintroduce various activities, usually at least 10 weeks after surgery for normal activities and about 6 months for sports.
Lassie's ligamentsHumans aren't the only creatures whose knee ligaments are easily injured. Canine anatomy seems to make middle-aged dogs' knees especially prone to cruciate ligament injury. Each year in the United States pooches have more than 1.2 million procedures to repair ruptured ligaments, making it the most common canine surgery. The operation carries a steep price: Depending on the technique used, the cost ranges from $1,300 to $5,000 per dog knee! |
Kneecap problems
Kneecap problems involve the interface between your femur (thighbone) and patella (kneecap). As you bend and straighten your knee, the patella rides up and down a groove in the front of the femur called the trochlea. The patella is actually inside the quadriceps tendon and is firmly attached to the strong quadriceps muscles. At the bottom, it connects to the tibia (shinbone) via the patellar tendon. A variety of conditions can throw off the patella's position and movement, causing pain and other symptoms.
Knee pain syndrome
Patellofemoral pain syndrome, or anterior knee pain syndrome, is pain under and around the kneecap that can't be explained by other causes, such as tendinitis or bursitis. This syndrome also goes by other names. One is tracking disorder, because the patella tends to pull toward the outside. Another is chondromalacia patellae, meaning softening of the cartilage, because over time a rough-riding kneecap causes wear and tear on the cartilage beneath it, eventually leading to osteoarthritis. Patellofemoral pain syndrome is more common in women over 40 and in physically active teenage girls. Three major factors are involved, although their relative contributions can differ greatly from person to person:
Malalignment: People with a high Q-angle are at higher risk, as are people whose arches flatten with each step.
Muscle imbalance and tightness: Tight hamstrings, calves, and hip muscles increase the pressure between the kneecap and the thighbone. Of the four quadriceps muscles, three pull the kneecap toward the outside; if the innermost quadriceps muscle is relatively weak, this can create tracking problems.
Overuse: Bending the knee moves the patella tighter against the femur. Patellofemoral pain worsens with activities that put weight on the knee while it is bent, such as squatting or running on steps and hills.
During the exam, the doctor feels your kneecap to look for tender spots, abnormal movements, and grinding under the kneecap as it moves (called crepitus), and to determine how easily the kneecap moves out of regular alignment. The doctor assesses the alignment of both knees and legs. An examination of your shoes may reveal whether your feet and ankles fall inward (pronation) or your feet need more arch support. X-rays and other imaging tests are reserved for later, if you fail to see improvement after several weeks of treatment.
Symptoms of knee pain syndromePain in the front and center of the knee during and after physical activities, especially those that repeatedly put weight on a bent leg (running, step aerobics, basketball) Pain from prolonged sitting ("moviegoer's sign") Knee puffiness after activity |
Treating knee pain syndrome. Surgical treatment for knee pain syndrome is rarely recommended. Nonsurgical treatment involves self-help rehabilitation. Substitute low-impact activities, such as swimming and the use of elliptical trainers, for high-impact activities. After activity, ice the knee for 10–20 minutes. Exercise to strengthen your inner quadriceps muscles (see Figure 3), adding small ankle weights after two weeks. Stretch to increase the flexibility of your hamstrings, calves, and hip muscles. Your physical therapist can identify which areas need the most attention. Arch supports or better-fitting athletic shoes may be helpful. Custom-made orthotics (shoe inserts) aren't usually necessary.
It may take six weeks or more to notice an improvement. After you feel better, you may be able to gradually return to higher-impact sports. You should continue to do the exercises you learned during rehabilitation even after your condition improves.
Osteoarthritis of the knee
Osteoarthritis is a disease that causes the breakdown of articular cartilage, the tissue that covers and protects the ends of bones. Arthritis can appear in any joint, but the knee is particularly vulnerable because it is a weight-bearing joint that is subject to daily wear and tear as well as sudden injury. In people who are genetically predisposed, osteoarthritis of the knee can result from normal daily use, perhaps interspersed with minor injuries, or from one or more significant injuries (such as damaged ligaments) that may seem unrelated because they occurred so long ago.
Cartilage is about 75% water. It compresses under the pressure of each step and resumes its original thickness when the force is released, much like a very tough sponge. When articular cartilage breaks down (see Figure 5), the result is pain and disability. Osteoarthritis is rare in young adults, but one in three people over age 62 has some amount of osteoarthritis in one or both knees. In addition, genetic differences in bone and cartilage seem to make some people more susceptible to osteoarthritis.
Figure 5: Osteoarthritis of the knee
Age, mechanical wear and tear, genetics, and biochemical factors all contribute to the gradual degeneration of the cartilage and the meniscus. In this illustration, the articular cartilage of the condyles (knobs at the lower end of the thighbone) is degraded. Tenderness and morning pain that lasts less than 30 minutes are telltale signs of this condition. |
Early in the process of knee osteoarthritis, the space between your tibia and femur decreases as the cartilage wears away. Once the cartilage disappears, bone rubs on bone, causing intense pain and often the formation of bone spurs around the joint.
For many people with osteoarthritis, pain tends to worsen as muscles tire during the day. It's common for a person to feel fine and move about without discomfort for several hours in the morning. Pain may arise in the afternoon, steadily worsening to the point where, by evening, walking becomes impossible.
To diagnose your condition, the doctor will ask you about your symptoms and medical history and may suggest laboratory tests and x-rays. If the osteoarthritis has progressed far enough, x-rays may show a reduction in the joint space in the knee or the presence of bone spurs. There is no specific blood test for osteoarthritis. The results of blood tests that indicate general inflammation, such as the erythrocyte sedimentation rate and the level of C-reactive protein, are often normal in osteoarthritis patients, but may be elevated if you have rheumatoid arthritis, a different form of joint disease. If your knee is suddenly swollen for no apparent reason, the doctor may remove some of the synovial fluid in the joint to check for signs of infection or arthritis.
Symptoms of knee osteoarthritisIntermittent or steady pain Swelling or tenderness Stiffness when you get up from sitting or lying down Grinding or crunching sounds |
Treating osteoarthritis of the knee. So far, osteoarthritis has no cure. Although it is possible to regrow cartilage in the laboratory, doctors have not yet been able to get implanted cartilage to grow in an osteoarthritic knee. Like healthy plants in unhealthy soil, the implants eventually die. Doctors focus on three things when treating osteoarthritis: relieving pain, protecting joints, and improving muscle tone to help stabilize joints and prevent deformity.
For pain relief, acetaminophen (Tylenol) or NSAIDs can be effective. A combination of pain relievers, such as acetaminophen and ibuprofen, may bring more relief than using one of these medications alone. Since ibuprofen can cause stomach irritation, especially on an empty stomach, one option is to take ibuprofen with meals and acetaminophen between meals and before bed. Pain relievers have a variety of side effects, so it's important to discuss your personal health risks with your doctor when considering the regular use of these medications and to refrain from taking more than the recommended dose.
Occasionally, a doctor may inject a corticosteroid drug into a joint to ease pain. However, repeated injections may speed degeneration of cartilage.
Self-help for osteoarthritis of the knee. Exercise is a crucial component of osteoarthritis treatment. It can reduce pain and also improve your balance and your ability to walk and do everyday tasks. Regular exercise is important because the muscles surrounding the knee are prone to atrophy when not used. Swimming and cycling are usually good options. Walking is more problematic because it puts full weight-bearing stress on your knees, even while working the hip muscles harder than the knees. Using weight machines, such as Cybex or Nautilus, strengthens muscles surrounding the knee. The quadriceps are often weak, even before symptoms occur. Range-of-motion exercises help maintain joint function and relieve stiffness.
Because the knee bears the entire weight of your body, weight loss is particularly helpful in easing the discomfort of knee osteoarthritis. In addition, well-cushioned shoes can help reduce the impact on your knees as you walk. You can also take weight off the knee by using a cane or other walking device. If osteoarthritis affects the patellofemoral joint, a physical therapist can show you how to tape your knee to relieve pain and support your quadriceps. The therapist can also show you how to use walking aids such as crutches or canes, if needed, and devise an exercise plan that best suits your condition. Your local Arthritis Foundation chapter may have an arthritis self-management program including exercise, information, and support (see "Resources").
Surgery. Several surgical procedures are used for knee osteoarthritis, including arthroscopic surgery and knee replacement surgery.
Your orthopedic surgeon may recommend arthroscopic surgery to remove torn cartilage and small bone spurs (debridement) and to flush out the joint with a saline solution (lavage). While some studies have shown benefit from this frequently performed surgery, others have not. A 2002 study in the New England Journal of Medicine found that during two years of follow up, patients who had arthroscopic procedures reported no less pain or better function than the placebo group.
As a result of this and similar findings, arthroscopic surgery for osteoarthritis is now performed less often. However, some surgeons believe it can be effective in selected cases, such as when loose fragments of cartilage — also known as "joint mice" — are floating within the knee.
If knee osteoarthritis becomes severely limiting and nonsurgical means no longer control pain, you might consider total knee replacement. If the osteoarthritis affects only one compartment of the knee, partial knee replacement is an option.
Review Date: 2006-09-01
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