Septic arthritis


Acute septic arthritis, infectious arthritis, suppurative arthritis, pyogenic arthritis, osteomyelitis, or joint infection is the invasion of a joint by an infectious agent resulting in joint inflammation. Generally speaking, 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, especially in neonates, younger children and immunocompromised individuals. In neonates, infants during the first year of life, and toddlers, the signs and symptoms of septic arthritis can be deceptive and mimic other infectious and non-infectious disorders.
In children, septic arthritis is usually caused by non-specific bacterial infection and commonly hematogenous, i.e., spread through the bloodstream. Septic arthritis and/or acute hematogenous osteomyelitis usually occurs in children with no co-occurring health problems. Other routes of infection include direct trauma and spread from a nearby abscess. Other less common cause include specific bacteria as mycobacterium tuberculosis, viruses, fungi and parasites. In children, however, there are certain groups that are specifically vulnerable to such infections, namely preterm infants, neonates in general, children and adolescents with hematologic disorders, renal osteodystrophy, and immune-compromised status. In adults, vulnerable groups include those with an artificial joint, prior arthritis, diabetes and poor immune function. Diagnosis is generally based on accurate correlation between history-taking and clinical examination findings, and basic laboratory and imaging findings like joint ultrasound.
In children, septic arthritis can have serious consequences if not treated appropriately and timely. Initial treatment typically includes antibiotics such as vancomycin, ceftriaxone or ceftazidime. Surgery in the form of joint drainage is the gold standard management in large joints like the hip and shoulder. Without early treatment, long-term joint problems may occur, such as irreversible joint destruction and dislocation.

Signs and symptoms

Children

In children septic arthritis usually affects the larger joints like the hips, knees and shoulders. The early signs and symptoms of septic arthritis in children and adolescents can be confused with limb injury. Among the signs and symptoms of septic arthritis are: acutely swollen, red, painful joint with fever. Kocher criteria have been suggested to predict the diagnosis of septic arthritis in children.
Importantly, observation of active limb motion or kicking in the lower limb can provide valuable clues to septic arthritis of hip or knee. In neonates/new born and infants the hip joint is characteristically held in abduction flexion and external rotation. This position helps the infant accommodate maximum amount of septic joint fluid with the least tension possible. The tendency to have multiple joint involvements in septic arthritis of neonates and young children should be closely considered.

Adults

In adults, 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 people. In adults the most common joint affected is the knee. Hip, shoulder, wrist and elbow joints are less commonly affected. Spine, sternoclavicular and sacroiliac joints can also be involved. The most common cause of arthritis in these joints is intravenous drug use. Usually, only one joint is affected. More than one joint can be involved if bacteria are spread through the bloodstream.

Prosthetic joint

For those with artificial joint implants, there is a chance of 0.86 to 1.1% of getting infected in a knee joint and 0.3 to 1.7% of getting infected in a hip joint.
There are three phases of artificial joint infection: early, delayed and late.
  • Early – infection occurs in less than 3 months. Usual signs and symptoms are fever and joint pain, with redness and warmth over the joint operation site. The mode of infection is during the joint implant surgery. The usual bacteria involved are Staphylococcus aureus and gram negative bacilli.
  • Delayed – infection occurs between 3 and 24 months. There would be persistent joint pain, due to loosening of the implant. The mode of infection is during the implant surgery. Common bacteria are coagulase-negative Staphylococcus and Cutibacterium acnes.
  • Late – more than 24 months. It is usually presented with a sudden onset of joint pain and fever. The mode of infection is through the bloodstream. The bacteria involved are the same as those in septic arthritis of a normal joint.

    Cause

Septic arthritis is most commonly caused by a bacterial infection. Bacteria can enter the joint by:
  • The bloodstream from an infection elsewhere
  • Direct penetration into the joint
  • A surrounding infection in the bone or tissue
Microorganisms in the blood may come from infections elsewhere in the body such as wound infections, 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 spread through the blood. In addition, some treatments for rheumatoid arthritis can also increase a person's risk by causing an immunocompromised state. Intravenous drug use can cause endocarditis that spreads bacteria in the bloodstream and subsequently causes septic arthritis. Bacteria can enter the joint directly from prior surgery, intraarticular injection, trauma or joint prosthesis.

Risk factors

In children, although septic arthritis occurs in healthy children and adolescents with no co-occurring health issues, there are certain risk factors that may increase the likelihood of acquiring septic arthritis. For example, children with renal osteodystrophy or renal bone disease, certain hematological disorders and diseases causing immune suppression are risk factors for childhood septic arthritis.
The rate of septic arthritis varies from 4 to 29 cases per 100,000 person-years, depending on the underlying medical condition and the joint characteristics. For those with a septic joint, 85% of the cases have an underlying medical condition while 59% of them had a previous joint disorder. Having more than one risk factor greatly increases risk of septic arthritis.
Most cases of septic arthritis involve only one organism; however, polymicrobial infections can occur, especially after large open injuries to the joint. Septic arthritis is usually caused by bacteria, but may be caused by viral, mycobacterial, and fungal pathogens as well. It can be broadly classified into three groups: non-gonococcal arthritis, gonococcal arthritis, and others.
  • Non-gonococcal arthritis – These bacteria account for over 80% of septic arthritis cases and are usually staphylococci or streptococci. Such infections most commonly come from drug abuse, cellulitis, abscesses, endocarditis, and chronic osteomyelitis. Methicillin-resistant Staphylococcus aureus may affect 5 to 25% of the cases while gram negative bacilli affects 14 to 19% of the septic arthritis cases. Gram negative infections are usually acquired through urinary tract infections, drug abuse, and skin infections. Older people who are immunocompromised are also prone to get gram negative infections. Common gram negative organisms are: Pseudomonas aeruginosa and Escherichia coli. Both gram positive and gram negative infections are commonly spread through the blood from an infective source; but can be introduced directly into the joint or from surrounding tissue. It often affects older people, and often happens suddenly, involving only one joint. Joint aspiration cultures are positive in 90% of cases, while only 50% of blood cultures yield any organisms.
  • Gonococcal arthritis – Neisseria gonorrhoeae is a common cause of septic arthritis in people who are sexually active and 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 migration of joint pain, tenosynovitis and dermatitis. Synovial fluid cultures are positive in 25 to 70% of the cases while blood cultures are seldom positive. Apart from blood and joint cultures, swabs from urethra, rectum, pharynx, and cervix should also be taken. Polymerase chain reaction is another useful way of identifying gonococcal infections if diagnosis is difficult and clinical presentation is similar to reactive arthritis.
  • Others – Fungal and mycobacterial infections are rare causes of septic arthritis and usually have a slow onset of joint symptoms. Mycobacterial joint infection most commonly affects hip and knee joints, caused by reactivation of past mycobacterial infections, with or without signs and symptoms of tuberculosis in lungs. Synovial fluid cultures will be positive in 80% of the cases. However, acid fast smears are not useful. Histology is not specific to myocobacterial infection as there are other granulomatous diseases that can show similar histology. Borrelia burgdorferi, a bacterium that causes lyme disease, can affect multiple large joints such as the knee. Confirmation of Lyme disease is done through enzyme-linked immunosorbent assay followed by confirmation using Western Blot test. It cannot be cultured from synovial fluid. However, PCR testing yields 85% positive result from synovial fluid. Viruses such as rubella, parvovirus B19, chikungunya, and HIV infection can also cause septic arthritis.
  • Prosthetic joint infection – Artificial joint infection are usually caused by coagulase negative Staphylococci, Staphylococcus aureus, and gram negative bacilli. Concurrent infections by multiple organisms is also reported in 20% of the cases. The risk factors of prosthetic joint infections are: previous fracture, seropositive rheumatoid arthritis, obesity, revision arthroplasty, and surgical site infections.