Septic arthritis

This is likely to be septic arthritis. Obviously, examination of the synovial fluid will help to exclude differentials such as gout and pseudogout. The most likely organisms are beta-haemolytic streptococci (20%) and staphlococci (70%). Antibiotics should be started empirically to cover these if the clinical suspicion is high. Ideally these should be intravenous for 2 weeks and then oral for 4 weeks. Arthroscopy is a risk factor for septic arthritis, but is rare. Fifty percent of cases will have an associated bacteraemia. Early x-rays are almost always normal.