What is Septic Arthritis?
Septic arthritis is a condition that causes inflammation in your joints due to an infection. This is typically caused by bacteria, but it can also be caused by fungi, certain types of bacteria like mycobacteria, viruses, and other less common germs. Sepic arthritis usually occurs in one big joint, like your hip or knee. However, it can also affect multiple or smaller joints at the same time.
While it is not very common, septic arthritis is considered an emergency situation in the field of orthopedics — this is the branch of medicine dealing with the muscles and bones. If not treated promptly, it can cause significant damage to the joint that can lead to more serious health problems. It’s very important to identify and treat septic arthritis early to keep the joint working as it should.
A study involving healthcare costs of septic arthritis in the United States between 2009 and 2012 found a 26% increase in total expenses and a 24% increase in hospital fees for this condition. However, the study didn’t find any changes in how long hospital stays were or in the outcomes of these hospital stays during this time period.
In older individuals, septic arthritis results in a higher risk of death due to an increase in simultaneous health conditions that make the condition worse.
What Causes Septic Arthritis?
Arthritis, or joint inflammation, can occur for many reasons in kids. Staphylococcus aureus, a type of bacteria, is the most common cause overall. However, different bacteria can cause joint inflammation in specific age groups or medical conditions. For example, in children less than 2 to 3 years old, Kingella kingae, another type of bacteria, is often at fault.
Newborns often get joint inflammation from bacteria like Group B Streptococcus, Staphylococcus aureus, Neisseria gonorrhea, and some types of Bacilli. Sexually active teenagers need to be cautious of Neisseria gonorrhea. If a child has sickle cell disease, Salmonella infections can be a likely cause. Children who have been on antibiotics for a long time may be more prone to fungal infections. Also, if a child has been injured by a sharp object or uses injectable drugs, they might get a joint infection from Pseudomonas aeruginosa, another type of bacteria. In children, the hip joint is typically the one that gets infected the most.
Staphylococcus aureus is the most common infection-causing bacteria in adults too. Streptococcus pneumonia is less common but still a significant concern. Additional circumstances include Salmonella in patients with sickle cell disease, and Pseudomonas in case of injury or puncture wounds. If a sexually active person gets nontraumatic acute monoarthritis, it is typically caused by Neisseria gonorrhea. It is also important to test for Neisseria gonorrhea from other body parts as it is hard to grow from joint fluid. Fungal and mycobacterial infections, on the other hand, start slowly and may be harder to identify. Usually, a biopsy of the joint tissue can provide a diagnosis.
Around 5% of patients can have infections caused by multiple types of microbes due to injuries or abdominal infections. Those who abuse intravenous drugs can often get sternoclavicular and sacroiliac joint infections, typically from serratia and pseudomonas bacteria. In people with leukemia, they are quite susceptible to Aeromonas infections.
Patients with previously damaged joints, especially those with rheumatoid arthritis, are very susceptible to infections. The infectious organisms can damage the joint lining, often causing joint swelling and pain. In adults, the knee is most often affected, followed by the hip.
Risk Factors and Frequency for Septic Arthritis
Septic arthritis, an infection in a joint, occurs in about 2 to 6 out of every 100,000 people. The actual number can be greater if the individual has certain risk factors. Septic arthritis is more prevalent in children, particularly in those aged between 2 and 3 years. Boys are more likely to have it than girls, with a ratio of 2:1. Certain categories of children have a higher risk. They include newborn babies, children with continuous bleeding into the joints (hemophiliacs with hemarthroses), children with weakened immune systems (for example, those with sickle cell anemia, HIV infection), and those undergoing chemotherapy.
When it comes to adults, those over 80 years old, individuals with diabetes, rheumatoid arthritis, recent joint surgery, artificial joint implants, a history of joint injections, skin infections and skin ulcers, HIV, osteoarthritis, sexual activity (especially in regards to suspected gonococcal septic arthritis, a sexually transmitted bacteria that causes arthritis), or any other sources of sepsis are at higher risk of getting septic arthritis.
Signs and Symptoms of Septic Arthritis
Septic arthritis is a condition that typically starts suddenly with pain in a single joint. This might also be accompanied by a fever, swelling, and a reluctance or refusal to use the affected joint. However, a fever isn’t a reliable symptom as it’s present in only 40% to 60% of cases. Joints in the lower body, like the hips, knees, and ankles, are usually the ones affected, with the knee being the most common in adults. About 20% of cases affect more than one joint, particularly if the individual has severe sepsis, weakened immunity, rheumatoid arthritis, or multiple underlying health conditions. Joints that are not commonly affected, such as the sacroiliac or sternoclavicular joint, may be involved in people who inject drugs.
Young, healthy, and sexually active adults with septic arthritis may show signs of skin inflammation, tendon sheath inflammation, non-destructive arthritis, and a shifting pattern of arthritis.
Children with septic arthritis may only show symptoms in the affected area, or they could also display signs of being unwell systemically, including appearing unwell, fever, fast heart rate, fussiness, and loss of appetite.
- Local symptoms: Pain, swelling, warmth in the joint, limited movement, limp, avoiding using or moving the affected joint
- Systemic symptoms: appearing unwell, fever, fast heart rate, fussiness, loss of appetite
The knee is most frequently affected by septic arthritis, followed by the hip, shoulder, and ankle. Joint effusions, where fluid builds up in the joint, are common and range of motion is often limited. Touching the joint may cause pain. Different types of bacteria can lead to different patterns of joint involvement. Most staphylococcal infections are associated with monoarticular involvement but Neisseria often involves multiple joints. Group B streptococci often affects the sternoclavicular and sacroiliac joints. Most prosthetic joint infections will have a discharging sinus.
Testing for Septic Arthritis
If your doctor suspects you have septic arthritis, they’ll conduct a few tests to confirm this. Septic arthritis means there is an infection in your joint, and it needs to be appropriately examined and diagnosed.
Critical lab tests used for this purpose involve taking synovial fluid from the affected joint for analysis. Synovial fluid is the fluid that helps lubricate your joints. The lab will conduct a white blood cell count, search for bacteria, and analyze for any crystals in this fluid. If there are over 50,000 white blood cells and 90% neutrophils (a type of white blood cell) in the synovial fluid, this generally indicates a bacterial infection.
Your doctor will also request a complete blood count, testing for C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and blood cultures. The peripheral white blood cell count will usually be high in septic arthritis, and a raised ESR and CRP indicate inflammation in the body, supporting the diagnosis of septic arthritis.
Why are these tests important? Well, a high white blood cell count and neutrophils in the synovial fluid can sometimes confirm a diagnosis of septic arthritis, but it’s not absolute. Sometimes, certain conditions, like early infection, can cause a low white blood cell count. Also, if you have a joint prosthesis, the white blood cell count may be low.
Pictures of the affected joint can also help in evaluating your condition. Regular X-rays may show changes in the joint spaces and bone, or bulging of the soft tissues. But an X-ray can’t definitively rule out septic arthritis. An ultrasound can help doctor visually inspect the amount of fluid in your joints and guide them in pulling out fluid for examination. Magnetic resonance imaging (MRI) is useful for early detection of joint fluid, showing abnormalities in the surrounding soft tissue and bone, and determining the involvement of the cartilage.
Lastly, your doctor may order a bone scan. While this type of scan isn’t specific to infections, it can be helpful when examining the hip or sacroiliac (the joint between the sacrum and the ilium bones of the pelvis) joints for a localized infection.
Treatment Options for Septic Arthritis
Treatment for septic arthritis usually involves a two-step approach: antibiotics to fight the infection and draining fluid from the joint affected. This fluid drainage can be done in one of a few ways, such as open surgery (arthrotomy), a minimally invasive procedure using a camera (arthroscopy), or by aspirating (drawing out) fluid with a needle daily.
Immediately after fluid has been drawn from the joint for testing and the samples have been sent for culture, patients are started on antibiotics. These are given through a vein (intravenously). The initial choice of antibiotics usually includes drugs active against staphylococcus bacteria, which are a common cause of septic arthritis.
If the patient’s immune system is compromised or they use intravenous drugs, a broader-spectrum antibiotic, such as the third-generation cephalosporins ceftriaxone, ceftazidime or cefotaxime, may be given. These are designed to cover a wider variety of bacteria and are included if the initial stain of the joint fluid reveals no bacteria, indicating that more uncommon types of bacteria may be at play.
Results of cultures from the patient’s blood and joint fluid will eventually guide any changes needed in the antibiotics used for treatment. An orthopedic surgeon should be involved from an early stage, as they’ll help determine the best approach for draining the joint fluid.
For nongonococcal septic arthritis, treatment with intravenous antibiotics typically lasts for about 2 weeks. After that, a further 1 to 2 weeks of antibiotics taken by mouth completes the treatment, hence totaling 3 to 4 weeks of treatment. If a bacterium called Pseudomonas aeruginosa is identified, it might be necessary to treat for a longer period, of 4 to 6 weeks. Gonococcal arthritis, caused by bacteria that also cause gonorrhea, is usually successfully treated with intravenous ceftriaxone. After 24 to 48 hours of improvements in symptoms, oral treatment can be used for the rest of the treatment period.
If the patient’s condition hasn’t improved within 5-6 days, the doctor will need to take more samples of the joint fluid and also consider other possible causes of the symptoms, such as Lyme disease, fungal infections, or reactive arthritis. In such situations, imaging tests might be needed to rule out bone infection (osteomyelitis).
Unlike the olden days, it’s no longer considered necessary to avoid moving the affected joint after the first 2 or 3 days. In fact, physical therapy is actually recommended to help restore as much normal use of the joint as possible and to prevent muscle wasting.
An infected artificial joint might need to be removed and then replaced, with antibiotics incorporated into the cement used to secure the new joint in place.
What else can Septic Arthritis be?
When a doctor needs to diagnose acute monoarticular arthritis, they could consider a range of different health conditions, which include:
- Infections: These can be caused by bacteria, fungi, viruses, spirochetes, or mycoplasma.
- Crystal-induced arthropathies: These can include conditions like acute gout, pseudogout, or the presence of certain kinds of crystals, like calcium oxalate, cholesterol, or hydroxyapatite crystals.
- Osteoarthritis: This is a type of arthritis that occurs when flexible tissue at the ends of bones wears down.
- Intra-articular injury: This could be a fracture, a meniscal tear, osteonecrosis, foreign body, or plant thorn synovitis.
- Inflammatory arthritis: This could be rheumatoid arthritis, Bechet syndrome, seronegative spondyloarthropathies such like ankylosing spondylitis, psoriatic arthritis, reactive arthritis, inflammatory bowel disease-related arthritis, sarcoid, systemic lupus erythematosus, or Still disease.
- Systemic infection: This could be bacterial endocarditis, human immunodeficiency virus, or Lyme arthritis.
- Tumor: This could be a metastasis or pigmented villonodular synovitis.
- Other: This could be hemarthrosis, clotting disorders or anticoagulant therapy, neuropathic arthropathy, dialysis-related amyloidosis, or avascular necrosis
To accurately diagnose the condition, the doctor must carefully consider these multiple possibilities and conduct appropriate tests.
What to expect with Septic Arthritis
Even with the use of antibiotics, approximately 7% to 15% of people treated in the hospital for septic arthritis, or joint infection, unfortunately do not survive. It is also important to note that about one-third of patients experience ongoing health problems due to this condition.
The risk of both not surviving and having long-term health problems increases with age and other existing health conditions, particularly those affecting the joints. If a patient has artificial material in their joints, this can also increase the risk. That’s why early detection and immediate treatment for septic arthritis are critical, particularly those who already have health conditions or risk factors that can make the infection worse.
It’s also relevant to mention that infection caused by a specific type of bacteria known as Neisseria is infrequently associated with death. However, infections caused by another type known as staphylococcus can potentially lead to a mortality rate higher than 50%. So, treating and managing septic arthritis is not a one-size-fits-all approach, as different bacteria can cause very different outcomes.
Possible Complications When Diagnosed with Septic Arthritis
Septic arthritis can lead to several complications, such as:
- Bone infection, also known as osteomyelitis
- Constant aches or discomfort
- Death of bone tissue due to lack of blood supply, a condition called osteonecrosis
- Differences in the length of the legs
- General infection in the bloodstream, a condition referred to as sepsis
- Life-threatening situations leading to death
Preventing Septic Arthritis
Patients and their caregivers need to be informed about how serious this condition can be. They should also understand that the person may still face health risks even after successful treatment with antibiotics.
