What is septic arthritis?
It is the infection of a joint. It affects the lining membrane of a joint called the synovium. In very young children it breaks into the joint from the bone. It occurs when inflammation and pus of the bone break into the joint. Osteomyelitis is infection of the bone.

Figure 1 Septic arthiritis of the right hip joint

How does it occur?
In newborns, due to weak immune system and a weak body resistance, infection spreads from other sites like boils, respiratory system, ear etc.

Hospital acquired infection occurs due to invasive procedures which involve tampering with the normal body linings e.g. when blood is drawn from the femoral vein it may cause hip joint infection. A heel puncture may cause infection of the heel bone. Infection can then spread from the bone to the adjacent joint.