What Is the Most Common Cause of Septic Arthritis in Kids?

What is pediatric septic arthritis?

Septic arthritis can be caused by bacterial, fungal or viral infections. Staphylococcus aureus, a type of bacteria, is the most common cause of septic arthritis in infants. Septic arthritis is a general term for any joint pain caused by infection of the joint.

Pediatric septic arthritis is a painful infection that can affect a child’s joint tissues and synovial fluid which lubricates the joints. Septic arthritis is more common in children than adults, and most often affects large joints in the lower body, though it can affect any joint.

What is the most common cause of septic arthritis?

Septic arthritis can be caused by bacterial, fungal or viral infections. Staphylococcus aureus, a type of bacteria which normally inhabits the human skin, is the most common cause of septic arthritis in infants.

Haemophilus influenzae type B was the most common cause of septic arthritis in children, before the development and widespread use of vaccines to prevent this bacterial infection.

Some of the other bacterial causes include:

Neisseria gonorrhoeae, which commonly causes gonococcal arthritis in adolescents
Streptococcus pneumoniae
Community-acquired methicillin-resistant S aureus (MRSA-CA)
Escherichia coli
Kingella kingae
Group A and B streptococci

How does a child get septic arthritis?

A child may develop septic arthritis when microorganisms from infection in other parts of the body travel through the blood and infect the joint space. Septic arthritis in the hip and shoulder joints is very often consequent to osteomyelitis, a bone infection, in the adjoining long bones such as femur or humerus. Infection may also develop from direct injury to the joint or after a surgery.

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Is septic arthritis an emergency?

Septic arthritis in infants and children is an emergency that requires immediate treatment. Delay in diagnosis and treatment can result in irreversible damage to the joint. Septic arthritis can:

Destroy the cartilage in the joint
Affect growth of the bone
Cause dislocation of the joint
Lead to sepsis, which can be fatal

How is septic arthritis diagnosed?

Symptoms of septic arthritis include:

Joint pain
Joint swelling
Redness and warmth in the joint
Fever and chills

Symptoms in an infant may be subtle and may also be diagnostic of certain other conditions that affect the joints, such as:

Transient synovitis: Inflammation of a joint from viral infection
Lyme arthritis: Caused by Lyme disease
Legg-Calvé-Perthes disease: Hip disorder from disrupted blood flow

Septic arthritis is considered a 99.6% possibility if all four of the following clinical factors are positive:

Fever
Inability to bear weight on the joint
Erythrocyte sedimentation rate (ESR) of 40 mm/hour
Serum white blood cell (WBC) count above 12,000/microliter

Following are the tests a child typically undergoes for a definitive diagnosis of septic arthritis:

Laboratory tests

WBC count: WBC is usually elevated, but normal range in an infant does not rule out septic arthritis.
ESR value: ESR is elevated and returns to normal after the infection clears.
C-reactive protein (CRP): CRP is elevated and returns to normal after the infection clears. CRP level is more sensitive than ESR and is a good indicator for response to treatment.
Blood culture: Blood culture tests are done to identify the microorganism.
Lyme titers: Lyme titers are performed to rule out Lyme arthritis in regions where Lyme disease is endemic.

In adolescents, if gonococcal arthritis is suspected, swabs from cervix/vagina in girls or urethral discharge in boys are tested. If sexual abuse is suspected, samples from rectum and pharynx are tested, in addition. The clinicians are obliged to report to the authorities and preserve all records as possible legal evidence.

Needle aspiration

Needle aspiration is the most important diagnostic test for septic arthritis. A needle aspiration test involves the insertion of a hollow needle directly into the joint to extract synovial fluid for testing.

Peripheral joints may be aspirated with local anesthesia, but deep joints such as hips are aspirated with the child under sedation or general anesthesia, using ultrasound guidance.

Imaging tests

Radiographs: Radiographs are not greatly useful in diagnosing septic arthritis but obtained to rule out other conditions.
Radionuclide scan: A type of bone scan using a radioactive chemical.
Ultrasonography: To detect abnormal fluid collection in the joint.
Magnetic resonance imaging (MRI): Used only if needle aspiration of the joint does not provide a diagnosis.
Computed tomography (CT): Obtained in patients with suspected abscess in the psoas muscle with negative joint aspiration culture.

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How do you treat septic arthritis?

Antibiotics

Immediately after the diagnosis of septic arthritis, the doctor starts the child on a course of antibiotics, typically a first- generation cephalosporin or clindamycin. In regions where clindamycin-resistant MRSA strains are prevalent, vancomycin is the first option, failing which linezolid may be administered.

The length of antibiotic treatment usually depends on the severity of the septic arthritis. All patients with septic arthritis are first treated with intravenous antibiotics for a period that may vary from two days to a week. Antibiotics will be continued till the ESR and CPR levels become normal.

Periods for oral continuation of the antibiotic course typically are as follows:

Two weeks for uncomplicated septic arthritis
Three weeks for septic arthritis with osteomyelitis
Four weeks for septic arthritis from MRSA

The doctor may also administer dexamethasone to reduce inflammation and nonsteroidal anti-inflammatory drugs (NSAIDs) for pain relief. Resistance to antibiotics is a potential complication with antibiotic treatment.

Surgical drainage

In addition to antibiotic treatment, septic arthritis also requires a drainage procedure to remove the infected material from the joint. Drainage may be performed by three methods:

Needle aspiration: Drainage may be performed with a hollow needle, if the infection is minimal and improving with treatment, and the joint is easily accessible for repeated aspirations, if necessary.
Open drainage: Open drainage involves cutting the joint open (arthrotomy) under anesthesia in the operating room, to clean and remove the infected tissue and fluid. Open drainage may be the option for treating septic arthritis with extensive infection and osteomyelitis.
Arthroscopy: Arthroscopy is a safe and effective alternative to arthrotomy. Arthroscopy is minimally invasive with tiny incisions through which the joint is irrigated and drained.

Post-procedure

After surgery the doctor immobilizes the joint with a splint, or sling in the case of shoulder joint, till it heals. The child has follow-up tests and X-rays for one to two years to make sure that:

The joint is stable and functions normally.
The joint space has not narrowed.
There is no bone tissue death (avascular necrosis).
Bone growth is normal.

How long does it take to recover from septic arthritis?

Symptoms of septic arthritis start improving within a day or two after starting treatment, though the infection may take a few weeks to clear completely. Recovery from a surgical procedure may take several weeks and require physical therapy to improve muscle strength.

What are the complications of septic arthritis?

Timely diagnosis and treatment is are the keys to complete recovery from septic arthritis. Complications from septic arthritis include the following:

Adverse effects on joint mobility.
Growth plate damage in the bone can result in uneven lengths of limb or uneven gait.
Permanent damage to the joint and nearby bones heightens risk for dislocation and fracture.