Bone and Joint Infections

Patients with bone and joint infections can present with native joint septic arthritis, osteomyelitis, or implant-associated bone and joint infections. Patients often present with an acute onset of hot, swollen, painful joint with restricted function in one or more joints over a couple of weeks. On examination the affected joint is painful with a limited range of movement, and fever is present. Risk factors for septic arthritis include an abnormal joint architecture due to pre-existing joint disease, e.g. patients with rheumatoid arthritis, or patients on haemodialysis, with diabetes mellitus, or older than 80 years of age. The differential diagnosis includes reactive arthritis, pre-patellar bursitis, gout, Lyme disease, brucellosis, and Whipples disease. Staphylococcus aureus is the most common cause of septic arthritis, followed by Group A streptococcus and other haemolytic streptococci including B, C and G. Gram-negative rods such as Escherichia coli are implicated in the elderly, immunosuppressed, or patients with comorbidities. Pseudomonas aeruginosa is implicated in intravenous (IV) drug users and patients post-surgery or intra-articular injections. Kingella kingae causes septic arthritis in children younger than four years of age. Neisseria gonorrhoeae, Neisseria meningitidis, and Salmonella species can also cause septic arthritis as part of a disseminated infection. Septic monoarthritis commonly occurs in patients with disseminated gonococcal infection. Blood cultures, white blood cell count, C reactive protein (CRP), electrolytes, and liver function tests are indicated. Serial CRP is useful in monitoring response to treatment. If there is a history of unprotected sexual intercourse, gonococcal testing is recommended. Brucella serology and Tropheryma whippei serology may be considered based on the clinical history. Joint fluid aspiration should be performed by a specialist within the hospital. Joint fluid aspirate is processed in the laboratory for microscopy, culture, and sensitivity. Gram stain can show an increase in neutrophils and presence of bacteria. The guidelines provided by the British Society for Rheumatology on the management of hot swollen joints in adults has provided advice for empirical treatment for suspected septic arthritis, but the local antibiotic policy should also be considered. Initial treatment is with intravenous flucloxacillin 2g four times daily, or 450– 600mg four times daily of intravenous clindamycin to cover S. aureus.