symptoms

A knee injury can affect any of the ligaments, tendons or fluid-filled sacs (bursa) that surround your knee joint as well as the bones, cartilage and ligaments that form the joint itself. Because of the knee's complexity, the number of structures involved, the amount of use it gets over a lifetime, and the range of injuries and diseases that can cause knee pain, the signs and symptoms of knee problems can vary widely.

Acute knee pain
Severe knee pain that comes on suddenly (acute pain) is often the result of injury. Some of the more common knee injuries and their signs and symptoms include the following:

• Ligament injuries. Your knee contains four ligaments — tough bands of tissue that connect your thighbone (femur) to your lower leg bones (tibia and fibula). You have two collateral ligaments — one on the inside (medial collateral ligament) and one on the outside (lateral collateral ligament) of each knee. A tear in one of these ligaments is usually the result of a fall or contact trauma, especially in sports like football, and is likely to cause immediate pain in the injured area. The discomfort, which can range from mild to severe, is usually worse when you walk or bend your knee. If the collateral ligament on the inside of your knee sprains or tears, you may feel a ripping sensation. In some cases, this ligament may become calcified after repeated injuries (Pellegrini-Stieda syndrome).

  The other two ligaments are inside your knee and cross each other as they stretch diagonally from the bottom of your thighbone to the top of your shinbone (tibia). The posterior cruciate ligament (PCL) connects to the back of your shinbone, and the anterior cruciate ligament (ACL) connects near the front of your shinbone. If you tear the ACL, either partially or completely, you're likely to know it right away. You may feel or hear a pop in your knee and have intense pain and immediate swelling. When you try to stand and put weight on your injured leg, your knee may "buckle" or at least feel as if it might give way. In most cases, you'll have to stop all activity, either because the pain is too severe or because your knee isn't stable enough to support your weight.

  PCL tears aren't usually as dramatic or painful. Most often, you'll experience pain and swelling in the space behind your knee (popliteal fossa) and a feeling of instability, as if your knee might give way.

• Tendon injuries (tendinitis). Tendinitis is irritation and inflammation of one or more tendons — the thick, fibrous cords that attach muscles to bone. Athletes — especially 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 larger lower leg bone (tibia). Tendinitis can occur in one or both knees and often causes pain and swelling at the front of your knee and just below your kneecap. The discomfort usually isn't constant but tends to occur when you jump, run, squat or climb stairs. The quadriceps or patellar tendons may also rupture, either partially or completely. In that case, the pain is likely to be most intense when you try to extend your knee. If the tendon is completely ruptured, you won't be able to extend or straighten your knee at all.
• Meniscus injuries. The meniscus is a C-shaped cartilage that curves within your knee joint. Meniscus injuries involve tears in the cartilage, which can occur in various places and configurations. For example, the cartilage may tear lengthwise or from the inside to the outside rim of the meniscus (radial tear). Although you may not notice small tears, in most cases, you'll have pain and mild to moderate swelling that develops over 24 to 48 hours. Occasionally, a lengthwise tear flips into the knee joint instead of staying around the joint's edge, an injury called a bucket-handle tear. A flap of the torn cartilage can interfere with knee movement and cause your knee joint to lock so that you can't straighten it completely. Meniscal injuries that cause locking of your knee should be surgically treated. Meniscal tears that don't cause locking, including those of a degenerative nature, can usually be managed nonsurgically.
• 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. Bursitis can lead to warmth, swelling and redness over the inflamed area, aching or stiffness when you walk, and considerable pain when you kneel. Sometimes the bursa located over your kneecap bone (prepatellar bursa) can become infected, leading to fever, pain and swelling. When the pes anserine bursa on the lower inner side of your knee is affected, you're likely to have pain when you go up or down stairs.
• 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 — leading to pain and a locked joint.
• Dislocated kneecap. This occurs when the triangular bone that covers the front of your knee (patella) 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. You're also likely to have intense pain and swelling in the affected area and difficulty walking or straightening your knee. Unfortunately, once you've had a dislocated kneecap, you're at increased risk of having it happen again. Although you may not experience as much swelling or discomfort with subsequent episodes, repeated dislocations can lead to chronic knee pain. But good rehabilitation, with a focus on strength training of the muscles that control your kneecap, can help prevent dislocation.
• Osgood-Schlatter disease. Primarily affecting athletic teens and preteens, this overuse syndrome causes pain, swelling and tenderness at the bony prominence (tibial tuberosity) just below the kneecap. The pain, which can range from mild to debilitating, is usually worse with activity, especially running and jumping, and improves with rest. Osgood-Schlatter disease frequently affects just one knee, but sometimes develops in both knees. The discomfort can last from weeks to months and may continue to recur until your child stops growing.
• 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, which generally causes a sharp, burning pain in the knee that often begins 10 to 15 minutes into a run. Initially, the pain goes away with rest, but in time it may persist when you walk or go up and down stairs.
• Hyperextended knee. In this injury, your knee extends beyond its normally straightened position so that it bends back on itself. Sometimes the damage is relatively minor, with pain and swelling when you try to extend your knee. But a hyperextended knee may also lead to a partial or complete ligament tear, especially in your ACL.
• Septic arthritis. Sometimes your knee joint can become infected, leading to swelling, pain and redness. Septic arthritis often occurs with a fever.

Chronic knee pain
Sometimes an injury can lead to ongoing (chronic) knee pain. Often, chronic pain results from a medical condition such as:

• Rheumatoid arthritis. The most debilitating of the more than 100 types of arthritis, rheumatoid arthritis can affect almost any joint in your body, including your knees. In addition to pain and swelling, you're likely to have aching and stiffness, especially when you get up in the morning or after periods of inactivity; loss of motion in your knees and eventually deformity of the knee joints; and sometimes a low-grade fever and a general sense of not feeling well (malaise). Rheumatoid arthritis usually affects both knees at the same time. And although it's a chronic disease, it tends to vary in severity and may even come and go. Periods of increased disease activity — called flare-ups or flares — often alternate with periods of remission.
• Osteoarthritis. Sometimes called degenerative arthritis, this 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. Osteoarthritis usually develops gradually and tends to cause varying degrees of pain and swelling when you stand or walk and before a change in the weather. It also can lead to stiffness, especially in the morning and after you've been active, and to a loss of flexibility in your knee joints.
• Gout. With this type of arthritis, you're likely to experience redness, swelling and intense pain in your knee that comes on suddenly — often at night — and without warning. The pain typically lasts five to 10 days and then stops. The discomfort subsides gradually over one to two weeks, leaving your knee joints apparently normal and pain-free. Another condition, pseudogout (chondrocalcinosis), which mainly occurs in older adults, can cause severe inflammation and intermittent attacks of pain and swelling in large joints, especially the knees.
• Chondromalacia of the patella, or patellofemoral pain. This is a general term that refers to pain arising between your patella and the underlying thighbone (femur). It's common in young women, 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. Chondromalacia of the patella causes pain and tenderness in the front of your knee that's worse when you sit for long periods, when you get up from a chair and when you climb stairs. You may also notice a grating or grinding sensation when you extend your knee.