Knee sprains, meniscal injuries, and runner's knee are common knee injuries.
Knee Sprains and Meniscal Injuries
Sprains of the external (medial and lateral collateral) or internal (anterior and posterior cruciate) knee ligaments usually result from twisting injuries while weight-bearing.
Knee ligaments are often injured by a weight-bearing, twisting motion of the knee that occurs when the foot is planted on the ground and a force is applied to the outside of the knee, as when tackled in football (clipping injury). This motion often damages the anterior cruciate ligament inside the knee joint. Hyperextension of the knee (forceful straightening of the joint), if severe, typically damages the posterior cruciate ligament inside the joint. Weight-bearing and rotation at the time of injury can also injure the rubbery shock absorbers (menisci) inside the knee.
Symptoms depend on the severity of the injury. Swelling and pain can occur over the first few hours after a severe ligament injury or more than 24 hours later with a less severe injury. Sometimes, an athlete hears or feels a “pop” in the knee as the injury occurs. This pop usually indicates a ligament or meniscal tear.
A severe injury may cause muscle spasm, swelling, and stiffness within hours. After a severe ligament injury, the person may feel the knee is unstable and be reluctant to put weight on it, fearing that the knee will give way. Sometimes the knee becomes locked and cannot bend if a torn meniscus blocks knee movement.
Doctors try and move the knee certain ways to determine whether ligaments are torn. However, muscle stiffness makes the knees stiff, preventing testing of normal joint motion. Sometimes, magnetic resonance imaging (MRI), arthroscopy (looking inside the joint with a flexible viewing tube), or both are needed. Sometimes just reexamining the person in 2 or 3 days, after muscle spasm has resolved, is all that is needed.
If a large amount of fluid has built up in the knee, doctors can drain the fluid to help relieve pain. Most mild or moderate injuries can be treated initially with rest, ice, compression, and elevation (RICE) and immobilization of the knee. Severe injuries of ligaments or menisci usually require surgical repair.
Pain in the Front of the Knee
The kneecap (patella) is a circular bone that is attached to ligaments and tendons around the knee and normally moves up and down the thigh bone during running.
Pain in the front of the knee (anterior knee pain) may be caused by
Weak thigh muscles are a common cause of runner's knee, a treatable cause of anterior knee pain. Weak thigh muscles allow the kneecap to move sideways and rub abnormally against the thigh bone. Runner's knee usually starts out with knee pain when running downhill. Later, any running or walking, especially down steps, is painful.
Excessive pronation of the foot when walking or running (rolling of the foot inward) can cause knee pain. Pronation forces the thigh muscles (quadriceps) to pull the kneecap outward and rub abnormally against the end of the thigh bone.
Doctors ask about symptoms and examine the person. Sometimes MRI, arthroscopy (looking inside the joint with a flexible viewing tube), or both are needed.
Running is avoided until it can be done without pain. Ice applied to the affected area, nonsteroidal anti-inflammatory drugs, and temporary use of a knee sleeve or elastic support also help. Other exercises, such as riding an exercise bike (with high seat position, low repetition, and low resistance) or swimming, can be done to protect the knee and maintain physical fitness during recovery. Exercises to strengthen and balance the muscles in the back (hamstrings) and front (quadriceps) of the thigh are helpful.
In runner's knee, stretching before exercise can help balance the abnormal forces caused by tight muscles and reduce injury.
A shoe insert can help correct excessive pronation.
Last full review/revision February 2009 by Paul L. Liebert, MD