Septic Arthritis Following an Ear Infection....

A 25-year-old man presents in the casualty department with a two-day history of a painful and swollen left knee. He is pyrexial with a temperature of 38.5 °C. Examination of his cardiovascular and respiratory system is normal. An abdominal examination is normal. He also mentions that he developed a painful right ear and saw his doctor five days ago who told him he had an infected ear and prescribed antibiotics. His left knee is swollen, red, tender and slightly flexed. A diagnosis of septic arthritis is made.

What is the most likely causative organism?
A. Streptococcus viridans
B. Staphylococcus epidermidis
C. Staphylococcus aureus
D. Escherichia coli
E. Neisseria meningitides

Answer:
C--Staphylococcus aureus

Septic arthritis results from infection of the joints with pyogenic organisms, of which Staphylococcus aureus is the commonest.
Other organisms responsible are streptococci, Neisseria spp. and Gram-negative bacilli.
The organisms reach the joint via the bloodstream, sometimes from known sites of infection such as boils or otitis media. Less commonly, it may spread from osteomyelitis adjacent to the joint or it may be introduced into the joint as a result of trauma. The patient complains of a single painful joint, which appears red, warm and swollen.
Aspirating the joint and examining and culturing the fluid should establish diagnosis.
Treatment should be started immediately with appropriate antibiotics as delays can result in destruction of the cartilage. The joint should be immobilised. The joint should be drained by needle aspiration. Inaccessible joints such as the hip may require surgical drainage.