Septic arthritis, also known as joint infection or infectious arthritis, is the invasion of a joint by an infectious agent resulting in joint inflammation. Symptoms typically include redness, heat, and pain in a single joint associated with a decreased ability to move the joint. Onset is usually rapid. Other symptoms may include fever, weakness, and headache. Occasionally more than one joint may be involved.
Causes include bacteria, viruses, fungi, and parasites. Risk factors include an artificial joint, prior arthritis, diabetes, and poor immune function. Most commonly joints becomes infected via the blood but may also become infected via trauma or an infection around the joint. Diagnosis is generally based on aspirating joint fluid and culturing it. White blood cells of greater than 50,000 mm3 or lactate greater than 10 mmol/l in the joint fluid also makes the diagnosis likely.
Initial treatment typically include antibiotics such as vancomycin, ceftriaxone, or ceftazidime. Surgery may also be done to clean out the joint. Without early treatment long term joint problems may occur. Septic arthritis occurs in about 5 people per 100,000 each year. It occurs more commonly in older people. With treatment about 15% of people die while without 66% die.
Video Septic arthritis
Signs and symptoms
Septic arthritis most commonly causes pain, swelling, and warmth at the affected joint. Therefore, those affected by septic arthritis will often refuse to use the extremity and prefer to hold the joint rigidly. Fever is also a symptom; however, it is less likely in older patients.
The most common joint affected is the knee. Hip, shoulder, wrist, or elbow joints are less commonly affected. Spine, sternoclavicular, and sacroiliac joints can also be involved; however, the most common cause of arthritis in these joints is intravenous drug use.
Usually only one joint is effected. More than one joint can be involved if bacteria are seeded through the bloodstream.
Maps Septic arthritis
Cause
Septic arthritis is most commonly caused by bacteria reaching the synovial membrane of a joint. Bacteria can enter the joint by:
- The bloodstream from an infection elsewhere (most common)
- Direct penetration into the joint
- A surrounding infection in the bone or tissue (uncommon).
Micro-organisms in the blood may come from infections elsewhere in the body such as abscesses, wound infections, osteomyelitis, urinary tract infections, meningitis , or endocarditis. Sometimes the infection comes from an unknown location. Joints with preexisting arthritis, such as rheumatoid arthritis, are especially prone to bacterial arthritis seeded through the blood stream. In addition, some treatments for rheumatoid arthritis can also increase a patient's risk by causing an immunocompromised state. Intravenous drug use can cause endocarditis that seeds bacteria into the bloodstream and subsequently causes septic arthritis.
Bacteria can enter the joint directly from prior surgery, intraarticular injection, trauma, or joint prosthesis.
Risk factors
- Age over 80 years
- Diabetes mellitus
- Osteoarthritis
- Rheumatoid arthritis
- Immunosuppressive medication
- Intravenous drug abuse
- Recent joint surgery
- Hip or knee prosthesis and skin infection
- HIV infection
- Other causes of sepsis
Having more than one risk factor greatly increases risk of septic arthritis.
Organisms
Most cases of septic arthritis involve only one organism; however, polymicrobial infections can occur, especially after large open injuries to the joint.
- Staphyloccoci
- Staphylococcus aureus - the most common cause in most age groups. Can be caused by skin infection, previously damaged joint, prosthetic joint, or intravenous drug use.
- coagulase-negative staphylococci - usually due to prosthetic joint
- Streptococci - the second most common cause
- Streptococcus pyogenes - a common cause in children under 5
- Streptococcus pneumoniae
- Group B streptococci - a common cause in infants
- Haemophilus influenzae
- Neisseria gonorrhoeae - the most common cause of septic arthritis in young, sexually active adults. Multiple macules or vesicles seen over the trunk are a pathognomonic feature.
- Neisseria meningitidis
- Escherichia coli - in the elderly, IV drug users and the seriously ill
- Pseudomonas aeruginosa - IV drug users or penetrating trauma through the shoe
- M. tuberculosis, Salmonella spp. and Brucella spp. - cause septic spinal arthritis
- Eikenella corrodens - human bites
- Pasteurella multocida, bartonella henselae - animal bites or scratches
- Fungal species - immunocompromised state
- Borrelia burgodorferi - ticks, causes lyme disease
Diagnosis
Septic arthritis should be considered whenever a person has rapid onset pain in a swollen joint, regardless of fever. One or multiple joints can be affected at the same time.
The diagnosis of septic arthritis is based on physical exam and prompt arthrocentesis which yields synovial fluid from within the affected joint. This fluid should be collected before the administration of antibiotics and should be sent for gram stain, culture, leukocyte count with differential, and crystal studies. This can include NAAT testing for N. gonorrhoeae if suspected in a sexually active patient.
Other studies such as blood cultures, white blood cell count with differential, ESR, and CRP should also be included. However, these tests are nonspecific and could be elevated due to infection elsewhere in the body. Serologic studies should be done if lyme disease is suspected.
In children, the Kocher criteria is used for diagnosis of septic arthritis.
Classification
Septic arthritis is usually caused by bacteria, but may be caused by viral, mycobacterial, and fungal pathogens as well.
Nongonoccocal Arthritis
Thesebacteriaaccount for over 80% of septic arthritis cases and are usuallystaphyloccoci or streptococci. It is commonly spread through the blood from an infection site elsewhere, but can be introduced directly into the joint or from surrounding tissue.
Gonococcal Arthritis
Neisseria gonorrhoeaeis a common cause of septic arthritis in sexually active patients under 40 years old. The bacteria is spread through the blood to the joint following sexual transmission. Other symptoms of disseminated gonococcal infection can include tenosynovitis and dermatitis.
Other
Fungal and mycobacterial infections are rare causes of septic arthritis and usually have a slow onset of joint symptoms.
Borrelia burgodorferi, a bacteria that causes lyme disease, can affect multiple joints.
Viruses such as rubella, parvovirus B19, chikungunya, and HIV infection can also cause arthritis.
Joint aspiration
In the joint fluid, the typical white blood cell count in septic arthritis is over 50,000-100,000 cells per 10-6/l (50,000-100,000 cell/mm3). However, septic synovial fluid can have white blood cell counts as low as a few thousand in the early stages. Therefore, differentiation of septic arthritis from other causes is not always possible based on cell counts alone.
The Gram stain can rule in the diagnosis of septic arthritis, however, cannot exclude it.
Synovial fluid cultures are positive in over 90% of nongonoccocal arthritis; however, it is possible for the culture to be negative if the patient received antibiotics prior to the joint aspiration. Cultures are usually negative in gonoccocal arthritis or if fastidious organisms are involved.
If the culture is negative or if a gonococcal cause is suspected, NAAT testing of the synovial fluid should be done.
Positive crystal studies do not rule out septic arthritis. Crystal induced arthritis such as gout can occur at the same time as septic arthritis.
A lactate level in the synovial fluid of greater than 10 mmol/l makes the diagnosis very likely.
Blood tests
Laboratory testing includes white blood cell count, ESR, and CRP. These values are usually elevated in those with septic arthritis; however, these can be elevated by other infections or inflammatory conditions and are, therefore, nonspecific. Procalcitonin may be more useful than CRP.
Blood cultures can be positive in up to half of patients with septic arthritis.
Imaging
Imaging such as x-ray, CT, MRI, or ultrasoundarenonspecific. They can help determine areas of inflammation but cannot confirm septic arthritis.
When septic arthritis is suspected, x-raysshould generally be taken. This is used to assess for involvement of surrounding structures such as bone and also for comparison purposes when future x-rays are taken.While x-rays may not be helpful early in the diagnosis/treatment, they may show subtle increase in joint space and tissue swelling. Later findings include joint space narrowing due to destruction of the joint.
Ultrasound can be done and is effective at detecting joint effusions.
CT and MRI are not required for diagnosis but can be used if diagnosis is unclear or in joints that are hard to examine (ie.sacroiliacor hip joints). They can can help assess for inflammation/infection in or about the joint (ie.osteomyeltis).
Differential diagnosis
- Crystal induced arthritis such as gout or pseudogout
- Inflammatory arthritis
- Rheumatoid arthritis
- Seronegative spondyloarthropathy such as ankylosing spondylitis or reactive arthritis
- Traumatic arthritis due to hemarthrosis, fracture, or foreign body
- Osteoarthritis
Treatment
Treatment is usually with intravenous antibiotics, analgesia and washout and/or aspiration of the joint. Draining the pus from the joint is important and can be done either by needle (arthrocentesis) or opening the joint surgically (arthrotomy).
Empiric antibiotics for suspected bacteria should be started. This should be based on gram stain of the synovial fluid as well as other clinical findings. General guidelines are as follows:
- Gram positive cocci - vancomycin
- Gram negative cocci - Ceftriaxone
- Gram negative bacilli - Ceftrioxone, cefotaxime, or ceftazidime
- Gram stain negative and immunocompetent - vancomycin
- Gram stain negative and immunocompromised - vancomycin + third generation cephalosphorin
- IV drug use (possible pseudomonas aeruginosa) - ceftazidime +/- an aminoglycoside
Once cultures are available, antibiotics can be changed to target the specific organism.
After a good response to intravenous antibiotics, patients can be switched to oral antibiotics. The duration of oral antibiotics varies, but is generally for 1-4 weeks depending on the offending organism.
In infection of a prosthetic joint, a biofilm is often created on the surface of the prosthesis which is resistant to antibiotics. Surgical debridement is usually indicated in these cases. A replacement prosthesis is usually not inserted at the time of removal to allow antibiotics to clear infection of the region. Patients that cannot have surgery may try long-term antibiotic therapy in order to suppress the infection.
Close follow up with physical exam & labs must be done to make sure patient is no longer feverish, pain has resolved, has improved range of motion, and lab values are normalized.
Outcomes
Risk of permanent impairment of the joint varies greatly. This usually depends on how quickly treatment is started after symptoms occur as longer lasting infections cause more destruction to the joint. The involved organism, age, preexisting arthritis, and other comorbidities can also increase this risk. Gonococcal arthritis generally does not cause long term impairment.
Mortality rates generally range from 10-20%. These rates increase depending on the offending organism, older age, and comorbidities such as rheumatoid arthritis
References
External links
Source of the article : Wikipedia
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