Septic arthritis

Septic arthritis is a painful infection in a joint. It can come from germs that travel through the bloodstream from another part of the body. Septic arthritis also can happen when an injury that goes through the skin, such as an animal bite or trauma, sends germs into the joint.

There are many risk factors for septic arthritis. These include having other joint conditions and having artificial joints, called prosthetic joints.

Knees are most often affected. But septic arthritis also can affect hips, shoulders and other joints. The infection can quickly damage the bone and the tissue that connects the bone to the joint, called cartilage. So the infection needs fast treatment.

Treatment involves draining the joint with a needle or during surgery. Septic arthritis most often also needs treatment with antibiotics.

Septic arthritis often causes bad pain that comes on fast. The pain makes it hard to use the affected joint. The joint may be swollen and warm, and the skin over the joint area may have a change of color. And you might have a fever.

If septic arthritis happens in an artificial joint, it is called prosthetic joint infection. Pain and swelling may start months or years after surgery to replace a joint. Also, the joint may loosen. That causes pain when you move the joint or put weight on it.

See your healthcare professional if bad pain in a joint comes on quickly. Fast treatment can help lessen joint damage.

If you have had a joint replaced, see your healthcare professional if you have pain while using the joint.

Bacterial, viral or fungal infections can cause septic arthritis. Bacterial infection with Staphylococcus aureus (staph) is the most common cause. Staph lives on the skin and in the noses of many people.

You also can get septic arthritis when an infection, such as a skin infection or urinary tract infection, spreads through your bloodstream to a joint. Less often, a puncture wound, a shot of medicine or drugs, or surgery in or near a joint — including joint replacement surgery — can let the germs into the joint space.

Risk factors for septic arthritis include older age and:

• Having joint issues. Long-term conditions, called chronic conditions, that affect your joints can raise your risk of septic arthritis. These include osteoarthritis, gout, rheumatoid arthritis and lupus. Having had joint surgery or a joint injury also may raise the risk.
• Having an artificial joint, called a prosthetic joint. Germs can enter the joint area during joint replacement surgery. Also, germs can infect the joint by traveling through the bloodstream to the joint from another area of the body.
• Taking medicines for rheumatoid arthritis. Some medicines for rheumatoid arthritis lower the body's immune system response, making infections more likely. Diagnosing septic arthritis in people with rheumatoid arthritis may be hard. Many of the symptoms of septic arthritis are like those of rheumatoid arthritis.
• Having fragile skin. Skin that breaks easily and heals poorly can let germs into the body. Skin conditions such as psoriasis and eczema raise the risk of septic arthritis. So do skin sores that become infected.

  People who take drugs with a needle also have a higher risk of infection where the needle goes in.

• Having a weak immune system. People with weak immune systems are at higher risk of septic arthritis. This includes people with diabetes, kidney and liver issues, and those taking medicines that lower their immune system response.
• Having a joint injury. Animal bites, puncture wounds or cuts over a joint can raise the risk of septic arthritis.

Having a mix of risk factors puts you at greater risk than having just one risk factor does.

Delayed treatment for septic arthritis can lead to joint breakdown and long-term damage. In an artificial joint, septic arthritis may cause the joint to loosen or move.