Synovitis

What is synovitis?

Synovitis is inflammation of the synovium — the thin tissue that lines the inside of the knee joint. When this lining becomes inflamed, it produces extra fluid and the joint becomes swollen, stiff and painful.

Synovitis is a response rather than a primary disease. It can be triggered by many things — mechanical irritation from a meniscal or cartilage problem, osteoarthritis, an inflammatory condition such as rheumatoid arthritis, infection, or in some cases conditions specific to the knee lining itself.

Like a knee effusion, synovitis is an important clinical sign. The work to be done is identifying what's behind it.

What does it feel like?

The picture is similar to that of an effusion but with more emphasis on inflammatory features:

• Swelling and a feeling of warmth in the knee

• Aching, persistent pain that may be worse at night or at rest

• Stiffness, particularly first thing in the morning

• Reduced range of movement

• A sense that the joint feels 'angry' rather than just sore

Symptoms can fluctuate. In some inflammatory conditions there are clear flares, while mechanical synovitis may be more constant or activity-related.

How is it diagnosed?

Diagnosis combines examination, history and investigations. Ultrasound and MRI can demonstrate synovial thickening and fluid; blood tests may help identify inflammatory or autoimmune causes; analysis of joint fluid is sometimes essential to exclude infection or other specific diagnoses.

The pattern of symptoms — which joints are involved, the rhythm of the symptoms, associated features — guides the assessment. Sometimes the cause is straightforward; sometimes it requires more careful working up over time.

What are the treatment options?

Treatment depends on the cause. Mechanical synovitis driven by an internal knee problem usually settles when the underlying cause is addressed. Inflammatory synovitis may need disease-specific medical management. Infection requires urgent treatment.

Symptomatic measures — rest, anti-inflammatories, sometimes injections — can play a useful role alongside addressing the underlying driver. Nev will work through the right approach for your specific situation at your consultation.

When should you get it checked?

Seek a specialist assessment if:

• The knee is persistently swollen and warm

• Stiffness is significant first thing in the morning

• There are systemic features — fever, feeling unwell, multiple joints involved

• Symptoms keep returning despite simple measures

• You want clarity on what's happening and a plan to address it

Synovitis is treatable — but the right treatment depends on identifying what's driving it. Getting that picture right is the most important part of the assessment.