Synovitis

Synovitis is swelling in the synovial membrane, the thin lining inside some of your joints. When that lining becomes damaged or irritated it thickens and swells, which causes pain and stiffness in the joint.

What are the symptoms of synovitis?

Symptoms are felt in the affected joint rather than around it because the swelling is happening inside the joint itself.

• pain in the joint
• visible swelling
• warmth, or a hot feeling around the joint
• stiffness
• difficulty moving the joint as far as you normally can

Left untreated, the inflammation can permanently damage the tissue inside your joint. That risk is higher if you get synovitis repeatedly over time, and the damage can permanently reduce how far you're able to move the joint.

What causes synovitis and who is at risk?

Arthritis and joint injuries are the two most common causes. Synovitis is very common in people who already have arthritis, and experts estimate that as many as two-thirds of people with certain types of arthritis will get it at some point.

Forms of arthritis linked to synovitis include rheumatoid arthritis, psoriatic arthritis and gout.

Beyond arthritis, anything that puts heavy or repeated stress on a joint can bring it on:

• overuse, or repetitive strain from the same movement done again and again
• sports injuries
• trauma such as a fall or a road traffic accident
• infections
• autoimmune conditions affecting the joints, such as lupus
• allergic reactions

Anyone can develop synovitis. You're more likely to if you have arthritis or an autoimmune condition, or if you're an athlete or do manual work.

Are there different types of synovitis?

Any joint with a synovial membrane can be affected. The joints where it happens most are the knees, hips, shoulders, elbows and ankles.

The main distinction drawn in the sources is between synovitis that happens once and settles, and chronic synovitis, which keeps coming back over time. Chronic synovitis carries the greater risk of lasting joint damage.

Two other conditions are often confused with synovitis.

• Joint effusion is a build-up of extra fluid in or around a joint, making it look larger and puffier. Some fluid inside your joints is normal and necessary. An effusion is more fluid than there should be, whereas synovitis is swelling of the lining itself.
• Tendinitis, sometimes spelled tendonitis, affects a tendon rather than the joint lining. Tendons are the rope-like bands that join muscle to bone.

How is synovitis diagnosed?

Diagnosis usually starts with a physical examination. Your clinician will ask about your symptoms and check how far you can move the affected joint.

It helps to tell them when you first noticed the pain and whether particular activities make it worse.

You may then need one or more of the following:

• an X-ray
• an MRI scan
• an ultrasound scan
• blood tests, if an infection is thought to be causing your symptoms.

How is synovitis treated?

Treatment depends on what's causing the synovitis. Most of it is aimed at easing your symptoms and reducing the effect on your day-to-day life.

Rest and physical treatment

• resting the joint, and stopping the activity that brought the synovitis on
• wearing a brace or splint to take stress off the joint
• physiotherapy to strengthen the muscles around the affected joint.

Medicines

Non-steroidal anti-inflammatory drugs, usually shortened to NSAIDs, reduce both pain and inflammation. Some are available over the counter without a prescription.

Your doctor may also offer an injection of corticosteroids directly into the joint to bring the inflammation down.

Where synovitis is caused by an inflammatory type of arthritis, disease-modifying antirheumatic drugs, known as DMARDs, are sometimes used and initiated by a specialist. These treat the underlying arthritis and ease the synovitis with it.

Surgery

Where the inflammation keeps going despite medication, an operation called a synovectomy may be considered. It removes much of the joint lining.

The reasoning behind it is worth understanding. A healthy synovial membrane is only one or two cells thick. When it becomes inflamed and overgrown it produces too much synovial fluid, and that fluid contains an enzyme which, in large amounts, wears away the smooth cartilage on the surfaces of the joint. Removing the overgrown lining takes that process away.

In inflammatory arthritis, the overgrowth is part of an abnormal immune response, where the body treats its own cartilage as something foreign to attack.

Recovery is active rather than restful. For larger joints such as the knee, exercises to move the joint start straight after surgery to stop it stiffening up, and physiotherapy usually begins after one or two days. Working with a rehabilitation therapist matters here, because regaining flexibility is the point of the exercise.

You'll normally need to keep taking your medication afterwards, both to delay the inflammation returning in the treated joint and to protect your other joints. In some cases the dose can be reduced once the surgery has worked and your doctor will advise accordingly.

How long it takes

Synovitis should gradually improve as you rest the joint and treat the symptoms. Depending on the cause, that can take anywhere from a few days to a few weeks.

If your synovitis followed an injury, it should settle as the injury heals. Ask your clinician how long to expect based on your symptoms and which joint is involved and check with them before going back to physical activity.

When should I see a doctor?

See a doctor if you notice new pain or other symptoms in a joint, particularly if they haven't improved within a few days or weeks.

Get seen as soon as possible if you have a fever alongside swelling or warmth around a joint. This can mean an infection, which needs treating quickly.

Go to your nearest emergency department if you've had a significant injury, or if you have:

• severe pain
• reason to think you've broken a bone
• no ability to move or use part of your body

It's worth acting on mild symptoms too. Inflammation inside a joint can lead to more serious problems if it's left alone.