Knee pain is a common complaint that affects people of all ages. Knee pain may be the result of an injury, such as a ruptured ligament or torn cartilage. Medical conditions including arthritis, gout and infections also can cause knee pain.
Many types of minor knee pain respond well to self-care measures. Physical therapy and knee braces also can help relieve knee pain. In some cases, however, your knee may require surgical repair.
The location and severity of knee pain may vary, depending on the cause of the problem. Signs and symptoms that sometimes accompany knee pain include:
- Swelling and stiffness
- Redness and warmth to the touch
- Weakness or instability
- Popping or crunching noises
- “Locking,” or inability to fully straighten the knee
When to see a doctor
Call your doctor if you:
- Can’t bear weight on your knee
- Have marked knee swelling
- Are unable to fully extend or flex your knee
- See an obvious deformity in your leg or knee
- Have a fever, in addition to redness, pain and swelling in your knee
- Fall because your knee “gives out”
Knee pain can be caused by injuries, mechanical problems, types of arthritis and other problems.
A knee injury can affect any of the ligaments, tendons or fluid-filled sacs (bursae) that surround your knee joint as well as the bones, cartilage and ligaments that form the joint itself. Some of the more common knee injuries include:
- ACL injury. An ACL injury is the tearing of the anterior cruciate ligament (ACL) — one of four ligaments that connect your shinbone to your thighbone. An ACL injury is particularly common in people who play basketball or go downhill skiing, because it’s linked to sudden changes in direction.
- Torn meniscus. The meniscus is formed of tough, rubbery cartilage and acts as a shock absorber between your shinbone and thighbone. It can be torn if you suddenly twist your knee while bearing weight on it.
- Knee bursitis. Some knee injuries cause inflammation in the bursae, the small sacs of fluid that cushion the outside of your knee joint so that tendons and ligaments glide smoothly over the joint.
- Patellar tendinitis. Tendinitis is irritation and inflammation of one or more tendons — the thick, fibrous cords that attach muscles to bones. Runners, skiers and cyclists are prone to develop inflammation in the patellar tendon, which connects the quadriceps muscle on the front of the thigh to the shinbone.
- Loose body. Sometimes injury or degeneration of bone or cartilage can cause a piece of bone or cartilage to break off and float in the joint space. This may not create any problems unless the loose body interferes with knee joint movement — the effect is something like a pencil caught in a door hinge.
- Knee ‘locking.’ This can occur from a cartilage tear. When a portion of cartilage from the tear flips inside the knee joint, you may not be able to fully straighten your knee.
- Dislocated kneecap. This occurs when the triangular bone (patella) that covers the front of your knee slips out of place, usually to the outside of your knee. You’ll be able to see the dislocation, and your kneecap is likely to move excessively from side to side.
- Hip or foot pain. If you have hip or foot pain, you may change the way you walk to spare these painful joints. But this altered gait can interfere with the alignment of your kneecap and place more stress on your knee joint. In some cases, problems in the hip or foot can refer pain to the knee.
Types of arthritis
- Osteoarthritis. Sometimes called degenerative arthritis, osteoarthritis is the most common type of arthritis. It’s a wear-and-tear condition that occurs when the cartilage in your knee deteriorates with use and age.
- Rheumatoid arthritis. The most debilitating form of arthritis, rheumatoid arthritis is an autoimmune condition that can affect almost any joint in your body, including your knees. Although rheumatoid arthritis is a chronic disease, it tends to vary in severity and may even come and go.
- Gout. This type of arthritis occurs when uric acid crystals build up in the joint. While gout most commonly affects the big toe, it can also occur in the knee.
- Pseudogout. Often mistaken for gout, pseudogout is caused by calcium pyrophosphate crystals that develop in the joint fluid. Knees are the most common joint affected by pseudogout.
- Septic arthritis. Sometimes your knee joint can become infected, leading to swelling, pain and redness. There’s usually no trauma before the onset of pain. Septic arthritis often occurs with a fever.
- Iliotibial band syndrome. This occurs when the ligament that extends from the outside of your pelvic bone to the outside of your tibia (iliotibial band) becomes so tight that it rubs against the outer portion of your femur. Distance runners are especially susceptible to iliotibial band syndrome.
- Chondromalacia patellae (patellofemoral pain syndrome). This is a general term that refers to pain arising between your patella and the underlying thighbone (femur). It’s common in young adults, especially those who have a slight misalignment of the kneecap; in athletes; and in older adults, who usually develop the condition as a result of arthritis of the kneecap.
- Osgood-Schlatter disease. This condition affects the softer area of bone near the top of the shinbone, where bone growth occurs. It’s most common in boys who play games or sports that involve running or jumping. The discomfort can last a few months and may continue to recur until the child’s bones stop growing.
- Osteochondritis dissecans. Caused by reduced blood flow to the end of a bone, osteochondritis dissecans is a joint condition in which a piece of cartilage, along with a thin layer of the bone beneath it, comes loose from the end of a bone. It occurs most often in young men, particularly after an injury to the knee.
A number of factors can increase your risk of having knee problems, including:
- Age. Certain types of knee problems are more common in young people — Osgood-Schlatter disease and patellar tendinitis, for example. Others, such as osteoarthritis, gout and pseudogout, tend to affect older adults.
- Sex. Teenage girls are more likely than are boys to experience an ACL tear or a dislocated kneecap. Boys, on the other hand, are at greater risk of Osgood-Schlatter disease and patellar tendinitis than girls are.
- Excess weight. Being overweight or obese increases stress on your knee joints, even during ordinary activities such as walking or going up and down stairs. It also puts you at increased risk of osteoarthritis by accelerating the breakdown of joint cartilage.
- Mechanical problems. Certain structural abnormalities, such as having one leg shorter than the other, misaligned knees and even flat feet, can make you more prone to knee problems.
- Lack of muscle flexibility or strength. A lack of strength and flexibility are among the leading causes of knee injuries. Tight or weak muscles offer less support for your knee because they don’t absorb enough of the stress exerted on the joint.
- Certain sports. Some sports put greater stress on your knees than do others. Alpine skiing with its sharp twists and turns and potential for falls, basketball’s jumps and pivots, and the repeated pounding your knees take when you run or jog all increase your risk of knee injury.
- Previous injury. Having a previous knee injury makes it more likely that you’ll injure your knee again.
Not all knee pain is serious. But some knee injuries and medical conditions, such as osteoarthritis, can lead to increasing pain, joint damage and even disability if left untreated. And having a knee injury even a minor one makes it more likely that you’ll have similar injuries in the future.
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