Septic Arthritis

Septic arthritis is a germ (bacterial) infection of a joint. The most common germ that causes this problem is Staphylococcus aureus. Other common germs include Haemophilus influenzae and Group B streptococcus (common in toddlers). In septic arthritis, joint damage results from enzymes produced by the germs and white blood cells (leukocytes). White blood cells are the blood cells that work to fight infection. Blood vessel (secondary vascular) damage may occur from clots in the vessels (thrombosis) or direct compression of vessels.

Septic arthritis usually occurs suddenly with rapid onset of joint pain progressing to a fever and an illness that affects the whole body. On examination, the infected joint is:

  • Swollen.

  • Tender.

  • Painful.

  • Has a limited range of movement.

Your caregiver may use blood tests to help make the diagnosis. The results of these tests will show higher than normal:

  • White blood count (WBC).

  • C-reactive protein (CRP).

  • Erythrocyte sedimentation rate (ESR).

An infected joint in a newborn is often hard to detect. The newborn may show loss of movement of an arm or leg or hold the joint in one position. Often newborns do not appear as sick as an older child or adult might. Fever may be absent and laboratory work may be normal. There may be a history of mild injury to the extremity, a history of illness, or an infection. Septic arthritis may follow chickenpox. Dislocation of the hip joint (the hip comes out of joint) may occur along with fluid buildup (effusion) in the joint and infection that may result in permanent damage to the hip.

  • Early X-rays are often normal except for some swelling of soft tissue around the joint.

  • Widening of the joint space may develop over time.

  • With time, X-rays may demonstrate bone loss or thinning of the bones due to non-use or increased blood supply in the area.

  • X-rays may show a joint effusion.

  • Bone scintigraphy is a specialized x-ray that measures the uptake of an injected radioactive material in an area of inflammation (soreness). This test allows earlier diagnosis, showing localized increased uptake of radioactivity around the infected joint.

  • Ultrasound shows the joint effusion.

  • Blood testing (culture) may be helpful, but removing fluid from the joint (aspiration) confirms the diagnosis of septic arthritis. The joint fluid will be cloudy (usually joint fluid is clear) with a high white blood cell count and bacteria in the fluid. Blood testing may identify the bacteria causing the infection, but it is not uncommon for blood tests to show up negative even when there is an infection.


Treatment includes medications that kill germs (antibiotics) given through the vein (intravenously) and draining of the infected joint.


  • Because of the seriousness of an infected joint, this problem is often cared for in the hospital.

  • Take all medications as prescribed by your caregiver.If circumstances have forced care at home or your caregiver feels home care will be safe, take all medications as ordered. Do not stop taking medications if the problem seems better after a couple of days.

  • Take you or your child's temperature 2 times per day and record. Bring this information with you to your caregiver.

  • You must keep all of your follow-up appointments. Not keeping the appointment could result in a chronic or permanent injury, pain, disability, or even death. If there is any problem keeping the appointment, you must call back to this facility for assistance.

An infected joint is a serious problem. Even with the best of care, it can result in life-long disability. Follow all directions!