Updated December 16, 2014.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Infections of the knee joint can be a serious problem. Symptoms of an infection include redness, swelling, and fevers. The treatment of a knee infection depends on the type and location of the infection. The most serious infections occur inside the knee joint where the body's immune system has a difficult time fighting the infection. Learn about some of the more common types of knee infections and what treatments are recommended to cure these infections.

Septic Joint:

A septic joint means that infection has entered into the joint space. A normal joint is where two bones connect. The bones are covered with cartilage, and the joint space is defined by an envelope of tissue called synovium. The synovium makes a fluid called synovial fluid that lubricates the joint space. This synovial fluid has little immune defense, and when infection enters this space it can be difficult to treat.

Bacteria can enter a joint either by a penetrating injury or through the bloodstream. When the joint is infected, typical symptoms include swelling, warmth, and pain with any movement of the joint. Most patients with a septic joint require a surgery to clean the knee joint, although it is possible in some cases to treat a septic joint with antibiotics alone. The appropriate treatment depends most significantly on exactly what type of bacteria have infected the joint.

Infection After Surgery:

Any time there is a surgical procedure, there is a chance of developing an infection.

Infections after most knee surgical procedures, including knee arthroscopy are rare, but they do occur. Infections are particularly troublesome after reconstructive knee surgery, such as ACL reconstruction, because of the presence of tissue grafts.

Infections after surgery have the same symptoms as a septic joint, and often require a second surgical procedure to clean the infection. If the surgical procedure involves the placement of either a tissue graft or any foreign material (screws, implants, etc.), these may ultimately have to be removed to cure the infection.

Infected Knee Replacement:

Knee replacement surgery is a very successful procedure that most often relieves pain and allows patients to resume many activities. Unfortunately, there are possible risks of joint replacement, and one of the most serious is an infection of a knee replacement.

Infections of a knee replacement are generally divided into early infections (within 6 weeks from the time of surgery) and late infections. Early infections may be treated in some cases by surgically cleaning the replacement, and administering antibiotic treatment.

Late infections, and some difficult early infections, require more aggressive treatment. This includes removal of the replacement implants, following by a period of time of antibiotic administration with no implants in the joint, followed by a revision knee replacement.

Bursal Infection:

Knee bursitis can cause swelling over the top of the kneecap. The bursa of the knee is not located within the joint, but rather in front of the joint. If there is an abrasion or cut, the kneecap bursa can become infected. Typical symptoms include pain, redness, and increasing swelling over the kneecap.

When identified early, kneecap bursitis may respond to antibiotic treatment. In more advanced cases, the bursa may have to be drained through a needle or a surgical incision.

Soft-Tissue Infection/Cellulitis:

Cellulitis is the condition that occurs when infection is in the deep layers of the skin. Cellulitis typically causes redness and swelling of the legs. Often there is an injury such as a cut, scrape, or insect bite that causes the infection to enter the deep layers of the skin. In other situations, there is no preceding injury. In most patients who have cellulitis with no preceding injury there is some type of immune deficiency, such as diabetes, that allowed the infection the occur.

It is important to recognize the signs and symptoms of cellulitis early, and the condition is usually treated with antibiotics. In patients who allow symptoms to persist, there is a chance of the infection worsening and even spreading by entering the bloodstream.