Although they are rare, joint infections do occur sometimes. It is important to know about this potential complication for two reasons. First, among all of the many types of arthritis, arthritis caused by infections results in the most rapid destruction of joints. In some cases, a joint can be totally destroyed after only a few days of untreated infection. Second, joint infections are often misdiagnosed, even by experienced doctors.
A joint infection is referred to as septic arthritis. Doctors suspect septic arthritis when they see intense inflammation of a joint along with cloudy fluid inside the joint. A diagnosis of septic arthritis usually requires special tests of joint fluid to determine whether microorganisms, such as bacteria, are present in the joint fluid. While bacteria cause the majority of infections, viruses, tuberculosis, and fungi can also cause this problem.
A joint that has been previously damaged by injury or arthritis is more likely to become infected than an undamaged joint. In the general population, joint infections occur at a rate of 10 cases in every 100,000 people. Among individuals with RA, this rate jumps to 70 cases in every 100,000 people.
Although septic arthritis can occur in any joint, the knee is the most common site of infection, accounting for approximately 50% of cases. The hip is the next most common site of infection, accounting for 20% of cases. The shoulders, elbows, ankles, and wrists account for the majority of the remaining cases.
Infectious agents can enter the joint from many sources, though the most common route of infection is via the blood. Bacteria from an infection in a distant location, such as the heart or lungs, can be carried to the joint by the bloodstream. Joints may also become infected during a surgical procedure, such as a joint replacement, arthroscopy, or even the injection of steroids into the joint. Fortunately, these complications, while serious, are very rare. Direct trauma to the joint, such as an open fracture, stepping on a nail, or having a bite wound to a knuckle can also lead to infection of a joint.
Arthroscopy
A diagnostic and surgical technique that uses a thin tube with a light and a tiny video camera at one end to view the inside of a joint.
In its earliest stages, septic arthritis can be difficult to diagnose. The joint may be sore and swollen. As the infection progresses, the symptoms become more severe. Typically, a person with a septic joint presents with fever and a joint that is hot, red, painful, and bulging. The joint is very painful to flex or extend and may even be too painful to touch. Given that this doesn't sound different from a worse-than-average flare of RA, you can see why your physician might have difficulty making this diagnosis. The following clues should point your doctor to a diagnosis of septic arthritis:
- History of fever
- An inability to bear weight on the affected joint
- An elevation in your “sed rate” (sedimentation rate—specifically, an erythrocyte sedimentation rate higher than 40 mm/hour) or C-reactive protein (CRP)
- An elevated white blood cell count (WBC count higher than 12,000/liter)
Septic arthritis is diagnosed by placing a needle into the joint and aspirating the fluid for analysis. The joint fluid is then examined under a microscope. The presence of bacteria or other infectious organisms confirms the diagnosis.
The treatment of an infected joint starts with the administration of intravenous antibiotics. The joint itself needs to be drained of the excess fluid that contributes to joint destruction. This fluid is drained with a needle as often as is necessary—sometimes daily. Sometimes, the joint has to be opened and drained surgically.
Untreated infections can rapidly destroy a joint and lead to more widespread infection; in turn, widespread infection can result in hospitalization and even death. Therefore, any severely inflamed joint should be examined by your doctor, especially if you also have a fever. Early treatment of an infected joint will prevent joint damage and hospitalization.
Any severely inflamed joint should be examined by your doctor, especially if you also have a fever. Early treatment of an infected joint will prevent joint damage and hospitalization.