Septic arthritis, also known as joint infection or infectious arthritis, is the invasion of a joint by an infectious agent resulting in joint inflammation. [2][4] Symptoms typically include redness, heat, and pain in a single joint associated with a decreased ability to move the joint. [2][4] Onset is usually rapid. [5] Other symptoms may include fever, weakness, and headache. [5][4] Occasionally more than one joint may be involved.[4] The knee is the most commonly affected joint. [6]
Initial treatment typically include antibiotics such as vancomycin, ceftriaxone, or ceftazidime.[2][5] Surgery may also be done to clean out the joint.[2] Without early treatment long term joint problems may occur.[2] Septic arthritis occurs in about 5 out of every 100,000 people each year. [3] It occurs more commonly in elderly people. [5] Mortality is about 15% with treatment and 66% without treatment. [2][9][5]
These bacteria account for over 80% of septic arthritis cases and are usually staphyloccoci or streptococci. [2] It is commonly spread through the blood from an infection site elsewhere, but can be introduced directly into the joint or from surrounding tissue.[4]
Septic arthritis most commonly causes pain, swelling, and warmth at the affected joint. [2][4] 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. [6]
The most common joint affected is the knee. [6] Hip, shoulder, wrist, or elbow joints are less commonly affected. [5] Spine, sternoclavicular, and sacroiliac joints can also be involved; however, the most common cause of arthritis in these joints is intravenous drug use. [4]
Usually only one joint is effected. More than one joint can be involved if bacteria are seeded through the bloodstream.[4]
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)
Having more than one risk factor greatly increases risk of septic arthritis. [5]
Organisms
Most cases of septic arthritis involve only one organism; however, polymicrobial infections can occur, especially after large open injuries to the joint. [7]
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. [5][7]
Neisseria gonorrhoeae - the most common cause of septic arthritis in young, sexually active adults. [11] Multiple macules or vesicles seen over the trunk are a pathognomonic feature. [12]
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. [6][4][2]
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. [4][7]
In children, the Kocher criteria is used for diagnosis of septic arthritis.[14]
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). [15] 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.[15][5]
The Gram stain can rule in the diagnosis of septic arthritis, however, cannot exclude it. [5]
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. [5][4] Cultures are usually negative in gonoccocal arthritis or if fastidious organisms are involved. [4][5]
If the culture is negative or if a gonococcal cause is suspected, NAAT testing of the synovial fluid should be done. [4]
Positive crystal studies do not rule out septic arthritis. Crystal induced arthritis such as gout can occur at the same time as septic arthritis. [2]
A lactate level in the synovial fluid of greater than 10 mmol/l makes the diagnosis very likely. [8]
Blood cultures can be positive in up to half of patients with septic arthritis. [2][5]
Imaging
Imaging such as x-ray, CT, MRI, or ultrasound are nonspecific. They can help determine areas of inflammation but cannot confirm septic arthritis. [9]
When septic arthritis is suspected, x-rays should generally be taken. [5] This is used to assess for involvement of surrounding structures such as bone and also for comparison purposes when future x-rays are taken. [5] While x-rays may not be helpful early in the diagnosis/treatment, they may show subtle increase in joint space and tissue swelling.[4] Later findings include joint space narrowing due to destruction of the joint. [9]
Ultrasound can be done and is effective at detecting joint effusions. [9]
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. sacroiliac or hip joints). They can can help assess for inflammation/infection in or about the joint (ie. osteomyeltis). [5][9]
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. [2][4] General guidelines are as follows:
Once cultures are available, antibiotics can be changed to target the specific organism. [5][4]
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. [2][4][5]
In infection of a prosthetic joint, a biofilm is often created on the surface of the prosthesis which is resistant to antibiotics.[17]Surgical debridement is usually indicated in these cases.[18][2] A replacement prosthesis is usually not inserted at the time of removal to allow antibiotics to clear infection of the region.[9][18] Patients that cannot have surgery may try long-term antibiotic therapy in order to suppress the infection. [9]
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. [5][2]
Outcomes
Risk of permanent impairment of the joint varies greatly.[5] 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.[9] Gonococcal arthritis generally does not cause long term impairment. [4][5][9]
Mortality rates generally range from 10-20%.[9] These rates increase depending on the offending organism, older age, and comorbidities such as rheumatoid arthritis[5][7][9]
References
^Hagino, Tetsuo; Wako, Masanori; Ochiai, Satoshi (1 October 2011). "Arthroscopic washout of the ankle for septic arthritis in a three-month-old boy". Sports Medicine, Arthroscopy, Rehabilitation, Therapy & Technology. 3 (1). doi:10.1186/1758-2555-3-21.((cite journal)): CS1 maint: unflagged free DOI (link)
^ abcd"Arthritis, Infectious". NORD (National Organization for Rare Disorders). 2009. Archived from the original on 21 February 2017. Retrieved 19 July 2017. ((cite web)): Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^Malik S, Chiampas G, Leonard H (November 2010). "Emergent evaluation of injuries to the shoulder, clavicle, and humerus". Emerg Med Clin North Am. 28 (4): 739–63. doi:10.1016/j.emc.2010.06.006. PMID20971390.
^Zhao, J; Zhang, S; Zhang, L; Dong, X; Li, J; Wang, Y; Yao, Y (August 2017). "Serum procalcitonin levels as a diagnostic marker for septic arthritis: A meta-analysis". The American journal of emergency medicine. 35 (8): 1166–1171. doi:10.1016/j.ajem.2017.06.014. PMID28623003.
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