Published: 18 Jun 2025

ICD9: 711.00      ICD10: M00.9      ICD11: FA10.Z

Septic arthritis, also known as infectious arthritis, is a painful infection in a joint.
It's a serious condition that can rapidly damage the cartilage and bone within the joint, leading to chronic pain, deformity, and even disability if not treated quickly.

Here's a breakdown of what you need to know:

What is it?

Infection: Septic arthritis occurs when bacteria, viruses, or fungi infect a joint. Bacteria are the most common culprit.
Inflammation: The infection triggers inflammation within the joint, causing pain, swelling, redness, and warmth.
Damage: If left untreated, the infection and inflammation can destroy the cartilage and bone within the joint, leading to permanent damage.

Causes:

Bacterial infection: The most common cause, often Staphylococcus aureus (staph). Other bacteria include streptococcus, pneumococcus, and gram-negative bacteria.
Viral infection: Less common, but can be caused by viruses like parvovirus B19, hepatitis B, and HIV.
Fungal infection: Rare, typically seen in people with weakened immune systems.

How does the infection get into the joint?

Through the bloodstream: Bacteria or other infectious agents can travel from an infection elsewhere in the body (e.g., skin infection, pneumonia) to the joint. This is the most common route.
Directly: The joint can be infected directly through:
Penetrating injury (e.g., a cut, puncture wound).
Surgery.
Injection into the joint (e.g., corticosteroid injection) if sterile technique isn't followed.
Spread from nearby tissue: Infection can spread from an adjacent bone infection (osteomyelitis) or soft tissue infection.

Risk factors:

Existing joint problems: Osteoarthritis, rheumatoid arthritis, gout, previous joint injury.
Compromised immune system: HIV/AIDS, diabetes, cancer, chronic kidney disease, immunosuppressant medications (e.g., corticosteroids, chemotherapy).
Intravenous drug use: Increases the risk of blood-borne infections.
Prosthetic joint: Artificial joints are more susceptible to infection.
Skin infections: Provide a pathway for bacteria to enter the bloodstream.
Recent joint surgery or injection: Creates a risk of introducing infection.
Age: Infants and older adults are more vulnerable.

Symptoms:

Severe joint pain: Often intense and sudden onset.
Swelling: Significant swelling around the affected joint.
Redness: The skin over the joint may appear red or discolored.
Warmth: The joint feels warm to the touch.
Limited range of motion: Difficulty moving the joint due to pain and swelling.
Fever: Often present, but not always.
Chills: May accompany the fever.
General malaise: Feeling unwell, tired, and weak.

Which joints are most commonly affected?

Knee: The most common.
Hip: Also frequently affected, especially in children.
Ankle, shoulder, wrist, elbow: Can also be affected.
More than one joint: Possible, especially in people with weakened immune systems or certain types of infections.

Diagnosis:

Physical exam: The doctor will examine the affected joint.
Joint aspiration (arthrocentesis): A sample of fluid is drawn from the joint using a needle and syringe. This fluid is sent to the lab for:
Cell count and differential: To look for increased white blood cells, indicating infection.
Gram stain and culture: To identify the specific bacteria, virus, or fungus causing the infection.
Crystal analysis: To rule out gout or pseudogout.
Blood tests:
Complete blood count (CBC): To check for elevated white blood cell count.
Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP): Markers of inflammation.
Blood cultures: To see if the infection is also present in the bloodstream.
Imaging studies:
X-rays: To look for signs of joint damage.
MRI: More sensitive than X-rays and can detect early signs of infection.
Ultrasound: Can help guide joint aspiration and detect fluid collections.

Treatment:

Antibiotics (or antifungals/antivirals): The cornerstone of treatment. Antibiotics are usually administered intravenously (IV) initially and then may be switched to oral antibiotics. The specific antibiotic used depends on the organism identified in the joint fluid culture.
Joint drainage: Essential to remove the infected fluid and debris. This can be done through:
Repeated needle aspiration: Removing fluid with a needle and syringe.
Arthroscopic surgery: Using a small incision and a camera to visualize the joint and remove infected tissue.
Open surgery: May be necessary in some cases.
Pain management: Pain relievers, such as NSAIDs or opioids, may be prescribed.
Rest and immobilization: Protecting the joint can help reduce pain and inflammation.
Physical therapy: To regain strength and range of motion after the infection has cleared.

Complications:

Permanent joint damage: Cartilage and bone destruction leading to chronic pain, stiffness, and disability.
Osteomyelitis: Infection of the bone.
Sepsis: A life-threatening bloodstream infection.
Death: Rare, but possible, especially in people with weakened immune systems or delayed treatment.

Importance of early diagnosis and treatment:

Septic arthritis is a medical emergency. Prompt diagnosis and treatment are crucial to prevent permanent joint damage and other serious complications. If you suspect you have septic arthritis, seek immediate medical attention.

Disclaimer: This information is for general knowledge only and should not be considered medical advice. Always consult with a qualified healthcare professional for diagnosis and treatment of any medical condition.