Septic Arthritis (Joint Infection)

What is septic arthritis?

Septic arthritis is a bacterial infection inside a joint. It's a genuine emergency — the bacteria can rapidly damage the joint cartilage and have serious systemic consequences if not treated quickly.

In children, the hip and knee are the most commonly affected joints. The infection usually arrives via the bloodstream from another source, sometimes one that's been mild or unnoticed.

Septic arthritis can be confused with less serious conditions — particularly transient synovitis, which is much more common. Distinguishing the two reliably is one of the most important parts of assessing a child with a painful, limping joint.

What does it feel like?

The classic picture is a child who is significantly unwell as well as having joint symptoms. Common features include:

• Severe pain in the affected joint

• Refusal to weight-bear or move the joint

• Fever, often high

• Looking unwell or lethargic

• Heat, swelling and tenderness over the joint

Pain at rest, severe pain with any movement, and systemic illness all point towards a more serious diagnosis than a simple irritable hip.

How is it diagnosed?

Diagnosis combines clinical assessment with investigations. Blood tests showing significantly raised inflammatory markers, ultrasound demonstrating fluid in the joint, and analysis of joint fluid are all part of the workup.

Joint aspiration — drawing fluid from the joint with a needle — is often diagnostic. The fluid is examined for bacteria and white cells, and cultured to identify the responsible organism.

There are validated criteria that help distinguish septic arthritis from transient synovitis when the picture is uncertain. In practice, when there's real doubt, urgent imaging and assessment are the right path.

What are the treatment options?

Septic arthritis almost always requires urgent surgical washout of the joint, alongside intravenous antibiotics. Removing the infected fluid is essential — antibiotics alone often aren't enough.

Antibiotic treatment continues for several weeks and is tailored to the specific organism once it's identified. Recovery is gradual but most children do well, particularly when treatment has been timely. Nev will work through the specifics for your child at your consultation.

When should you seek urgent help?

Seek urgent assessment if your child has:

• Severe pain in a joint, particularly with refusal to move it

• A high fever alongside joint symptoms

• Looks unwell, lethargic or unusually tired

• A joint that is hot, swollen and very tender

• Symptoms developing rapidly over hours

This is a condition where time matters. If you're uncertain whether your child's symptoms might be septic arthritis, it's better to seek urgent assessment than to wait and see.