What is Septic Arthritis of the Pediatric Hip?
Septic arthritis in a child’s hip is a serious condition that requires immediate surgery. If not treated quickly, it can rapidly damage the hip, cause severe body-wide infection (sepsis), and even lead to death. It’s important to tell the difference between septic arthritis and another condition known as transient synovitis of the hip. Unlike septic arthritis, transient synovitis isn’t an emergency and doesn’t need surgery. It can get better with pain relief and monitoring.
A mistake in diagnosing these conditions could lead to serious health problems. A crucial part of the correct diagnosis is identifying the infecting organism, which basically means finding out what type of germ is causing the infection. The type of germ can be different depending on the child’s age and other existing health conditions they may have.
What Causes Septic Arthritis of the Pediatric Hip?
Pediatric septic arthritis, a type of bacterial infection in the hip joint of children, often happens when bacteria spread through the bloodstream. In fact, about 80% of these infections follow an upper respiratory infection, such as the common cold.
The majority of these cases, around 70%, are caused by a specific type of bacteria known as Kingella kingae. This is a gram-negative coccobacillus, a term that describes the bacteria’s shape and cell wall characteristics. Another type of bacteria called Staphylococcus is responsible for about 10% of the cases. In the past, a different bacteria called Haemophilus was commonly seen causing this hip infection in children under two years old.
These bacteria can find their way into the hip joint through a process linked to the unique blood flow of long bones in children. Blood tends to pool in certain areas of these bones, creating a place where bacteria can start to multiply, or “seed”. From there, bacteria can spread through the natural channels made by blood vessels running through the bone, eventually reaching the hip joint and starting an infection.
Risk Factors and Frequency for Septic Arthritis of the Pediatric Hip
Septic arthritis of the hip is a condition often seen in children, especially those under two years old, making up half of all cases. This condition is two times more common in boys than girls. However, children with a weakened immune system, those with sickle cell disease or hemophilia, have a higher risk. In places where Lyme disease is common, septic arthritis of the hip could sometimes be related. This is particularly true when other signs of Lyme disease, such as joint pain, a unique ‘bull’s eye’ rash, heart palpitations, and irregular heartbeats, are present. Testing for Lyme disease can potentially confirm its presence.
- About half of kids with septic arthritis of the hip are under two years old.
- This condition is twice as frequent in boys as in girls.
- Kids with weak immune systems, sickle cell disease, or hemophilia are more likely to get it.
- In areas where Lyme disease is common, it can sometimes be related to septic arthritis of the hip.
- It’s particularly likely to be linked to Lyme disease if there are other signs like joint pain, a ‘bull’s eye’ rash, or heart issues.
- Testing can help confirm if Lyme disease is present.
Signs and Symptoms of Septic Arthritis of the Pediatric Hip
Kids suffering from a hip infection, known as septic arthritis, often show a sudden onset of hip pain. Those who can walk may limp and avoid putting weight on the affected leg. Those who are unable to walk often lay in bed, holding their hip in a position that is most comfortable for them – usually bent and moved sideways. This position helps to ease the hip joint, reducing the discomfort caused by any fluid build-up inside the joint. They often have a fever and might have had a recent throat infection.
While resting in bed, any movement or rotation of the child can lead to severe pain in the hip. Even the smallest motion of the hip joint can be painful.
Testing for Septic Arthritis of the Pediatric Hip
If you’re experiencing acute hip pain, it could be due to either septic arthritis or transient synovitis, both conditions that affect the hip. Septic arthritis is a potentially serious condition caused by a bacterial or fungal infection in the hip joint, and transient synovitis is an inflammation of the tissues around the hip joint, most common in children.
It can be challenging for doctors to determine which condition is causing the pain. The most accurate way to tell the difference is through hip aspiration, a procedure where a small amount of fluid is removed from the hip joint using a needle and tested in a lab.
Another tool doctors use is called the ‘Kocher Criteria’; these criteria help doctors decide if they need to start an aggressive treatment plan for septic arthritis. The Kocher Criteria looks at four factors in this order of importance:
- Having a fever higher than 38.5 C (101.3 F)
- Having an erythrocyte sedimentation rate (ESR) more than 40 (ESR is a type of blood test that can indicate inflammation in the body.)
- Being unable to bear weight on the affected hip
- Having a white blood cell count more than 12,000 (As white blood cells help your body fight infections, a higher count can be a sign of infection).
The percentage chance of septic arthritis increases based on meeting more of these criteria. For instance, children who meet just one of the four criteria have a 3% chance of having septic arthritis, but if they meet all four criteria, their chance increases to 99%.
Children and teenagers should also have an X-ray examination of the hip, as this can help rule out other conditions, like Perthes disease or slipped capital femoral epiphysis, which also cause hip pain.
Treatment Options for Septic Arthritis of the Pediatric Hip
If children experience hip pain but only meet one of the four Kocher criteria, they should be closely monitored for any changes in their condition. The Kocher criteria are a set of four signs that doctors use to diagnose a certain type of hip infection called septic arthritis. However, if a child meets at least two of these criteria, the child may need to have a procedure called an aspiration, where a sample of fluid is collected from their hip for tests.
This fluid can be tested for bacteria and the number of white blood cells (WBC). A high number of white blood cells can indicate infection. If bacteria are found or if the cell count shows a WBC count over 50,000 per cubic millimeter with 75% or more being PMN cells, or if the level of sugar in the fluid is more than 50 milligrams per deciliter lower than the sugar level in the blood, then the child’s hip may need to opened up and cleaned with a medicine that kills bacteria. PMN cells are a specific type of white blood cell that increases in number during infection.
Examining the percentage of PMN cells within the white blood cells in the fluid can be a more sensitive way to diagnose septic arthritis compared to just evaluating the total WBC count. A result showing 85% PMNs is associated with a high probability (88% sensitivity) of septic arthritis.
After diagnosing septic arthritis, the child will typically be treated with antibiotics. Some doctors recommend that the patient initially receives antibiotics using an IV (a tube placed in a vein), then switches to oral antibiotics after a certain period. The duration of IV and oral antibiotic treatment can vary, and the choice of antibiotics may be specialized depending on the detected bacteria. One particular bacterium called Kingella kingae often doesn’t respond to certain types of antibiotics called vancomycin and clindamycin, so it needs to be treated with a different group of antibiotics known as beta-lactamase antibiotics. The sooner septic arthritis is treated, the better the outcome and the fewer long-term complications the child will experience.
Depending on the patient’s conditions, doctors may decide to either perform an open drainage or an arthroscopic drainage. Arthroscopic drainage involves a smaller incision and the use of a camera called an arthroscope. Reports suggest that both procedures have similar outcomes.
Even after successful treatment, long-term monitoring is necessary to check for potential complications like avascular necrosis (the death of bone tissue due to a lack of blood), growth issues with the hip, and arthritis (joint inflammation) resulting from an earlier infection.
What else can Septic Arthritis of the Pediatric Hip be?
The following conditions can cause arthritis or symptoms similar to arthritis:
- Arthritis due to intrinsic bowel disease
- Crystalline Arthritides
- Drug-Induced Arthritis
- Postinfectious Diarrhea
- Postmeningococcal condition
- Postmeningococcal Arthritis
- Vasculitis